Chapter 11 Surgery of the Bovine Musculoskeletal System

11.1 Musculoskeletal Examination in Cattle

Musculoskeletal examination of cattle lacks uniformity, and many techniques for lameness examination have been described. Veterinarians most often subjectively evaluate the animal to determine which limb or region is affected and then rely on physical examination to determine the diagnosis. This system is useful in identifying lameness sites in most cases because the temperament and lack of training of cattle prevents a thorough lameness exam and necessitates consideration of other information, such as most commonly affected sites, diseases more common to a given age group, and historical data. In horses, flexion and extension tests, selective perineural anesthesia, and intraarticular anesthesia are used to isolate a focal area of pain. These techniques can be adapted to use in cattle, but they have not become commonplace because cattle are infrequently halter trained, often do not tolerate limb handling followed by controlled walking and trotting, and commonly are housed on surfaces that have a higher risk of falling (e.g., wet concrete). Further, cattle are less commonly presented to the veterinarian for examination of subtle diseases that cause mild lameness (e.g., osteochondrosis, bowed tendons, stress fracture). Thorough history, observation of stance and stride, and physical examination is critical to the diagnosis of lameness in cattle. The clinician should remember that 80% to 90% of lameness in cattle originates distal to the fetlock. For this particular reason, unless there is an obvious lesion on the limb, such as a swollen joint or fracture, examination of the claws should always be performed.

History

Historical data for the affected individual and of the farm are important to refining differential diagnosis of lameness. The veterinarian should obtain a detailed knowledge of production levels, nutrition programs, vaccination regimens, origin of the animal and length of residence at the facility, any changes in management, and occurrence of other diseases on the farm. Questions more specific to the affected animals should be posed to determine the duration of lameness, when the first clinical signs were observed, what the initial signs were, how the animal’s condition has progressed, what medications have been administered—at what dose, by what route, and for how long—and what response was noted after giving medications.

Lameness Examination

OBSERVATION

Significant information can be gained by taking a few minutes to look at the animal quietly in its stall or in its normal environment. Lameness most easily can be assessed when the cow is observed in motion. Certain types of walking surfaces may exacerbate some lameness (e.g., grass vs. dirt vs. gravel vs. concrete). A cow with a sole lesion may experience more pain to walk on concrete or gravel rather than grass because concussion is more pronounced.

Many lamenesses are obvious by observing the cow’s stance. Attention should be paid to the posture of the cow—including the back, shoulders, pelvis, and major limb joints. Back posture was a primary factor in a lameness scoring system proposed by Sprecher et al. (Table 11.1-1). With the animal standing, observe the general stance first and more specifically of each limb and digit. Compare one region to the opposite side and determine whether obvious swelling, wounds, shifting of weight, and foot posture such as toe touching or displacement of weight-bearing onto the medial or lateral claw are present. A cow with heel lesions (Figure 11.1-1) will have a tendency to relieve its pain by standing on the toes. A cow with laminitis will tend to place the feet such that weight is shifted to the heels. Cows with sole lesions of the medial digits of the front limbs tend to place their feet such that weight is shifted to the lateral digit. Cows in which bilateral sole lesions are present may cross their forelimbs (Figure 11.1-5).

TABLE 11.1-1 Lameness-Scoring Systems Described for Cattle

Figure 11.1-1 Cow with sole ulcer in medial claw.

(Courtesy Norm G. Ducharme; Cornell University.)

Figure 11.1-5 Bull with bilateral medial sole abscesses; note crossing of limbs to avoid medial weight-bearing.

(Courtesy Thomas J. Divers; Cornell University.)

If only one of the digits is affected and the disease is not severe, the animal will bear weight on the sound digit of the same foot. Examination of the foot reveals excess wear of the wall and sole of the healthy digit. In long-standing diseases with severe lameness, the heels are taller and the wall longer on the affected digit in comparison to that of the healthy claw. A dropped fetlock (e.g., hyperextension of the fetlock joint) may be noticed on the sound limb because of excessive load on the flexor tendons and suspensory ligament (Figure 11.1-2). In young animals, angular limb deformities secondary to uneven weight-bearing occur rapidly with chronic lameness. When chronic lameness occurs in a hind limb, the contralateral tarsus typically will develop varus deformity (the limb is bowed outward so the convex surface occurs in the lateral aspect of the limb; see Figure 15.3-3). When chronic lameness occurs in a forelimb, the carpus typically develops a valgus deformity (the limb is bowed inward so the lateral aspect of the limb has a concave appearance, Figure 11.1-3).

Figure 11.1-2 Dropped fetlock as a result of excessive weight-bearing.

(Courtesy Michael Wildenstein; Cornell University.)

Figure 11.1-3 Calf with bilateral valgus deformity of the carpi.

(Courtesy Norm G. Ducharme; Cornell University.)

Cows with laminitis often stand with the back arched and the feet placed under the body (Figure 11.1-4A and B). They are reluctant to walk. Draining tracts above a swollen coronary band associated with a severe lameness is typical of septic arthritis of the distal or proximal interphalangeal joint (see Figure 11.4-12). Cattle affected with heel erosion or inderdigital dermatitis will tend to keep their heels just on the border of the gutter in a tie stall barn to relieve the pain. They shift weight constantly because of the discomfort. On certain occasions, the animal will relieve the pain on the affected claw by bearing weight on the sound claw only. If both front medial claws are affected, they may cross their legs (Figure 11.1-5).

Figure 11.1-4 A, Guernsey with laminitis in the hind limbs. Laminitis results in underrun heels with the characteristic stance on the toes. B, Underrun heels of same cow.

(Courtesy Thomas J. Divers; Cornell University.)

Figure 11.4-12 Contaminated laceration at the pastern area.

Differential diagnoses for non–weight-bearing lameness should always include the following: sole abscess, fracture, joint luxation, weight-bearing ligament or tendon injury, nerve injury (e.g., radial nerve, femoral nerve, sciatic nerve), septic arthritis, and septic tenosynovitis. An abnormal deviation of the limb is usually related to a fracture, collateral ligament rupture or joint luxation. The stance and position of the limb is abnormal with nerve damage, tendon rupture, or a severe ligament injury. Cattle affected with a radial nerve paralysis will have a dropped elbow, but this must be differentiated from a humerus fracture, radius/ulna fracture, or septic arthritis of the elbow joint. A rupture of the muscular or tendinous portion of the gastrocnemius muscles is shown by hyperflexion of the hock and a dropped calcaneus (e.g., hock is horizontal rather than vertical during weight-bearing; see Figure 11.4-29), but this must be differentiated from a fractured calcaneus or sciatic nerve paralysis (Figure 11.4-31). Careful attention should be paid to muscle atrophy because this may be caused by nerve injury or disuse atrophy. Neurogenic muscle atrophy occurs rapidly and is severe. Muscle atrophy caused by disuse occurs over a longer period of time. Chronic lameness of the front limb will usually bring atrophy of the triceps, biceps, and scapular muscles. The consequence of this atrophy is a more apparent shoulder with joint instability and the animal may be falsely diagnosed with shoulder joint diseases. Similarly, atrophy of the muscles of the rear limb causes pronounced greater trochanter of the femur that may be misdiagnosed as a coxofemoral joint luxation.

Figure 11.4-29 Jersey calf with acute avulsion of the gastrocnemius muscles after a misdirected intramuscular injection was made near the sciatic nerve. The calf’s weight is partially supported by an assistant to prevent complete plantigrade stance, as seen in Figure 11.4-30.

Figure 11.4-31 Same calf as in Figure 11.4-29. Note peroneal nerve deficit resulting in knuckling of the metatarsophalangeal joints.

EXAMINATION IN MOTION

In certain cases, lameness is subtle, and other procedures are necessary to localize the lesion. The characteristics of the lameness can more easily be assessed with the animal walking. The observer should attempt to describe the severity of the lameness and assess the individual components of the gait including the arc of flight, position of the digit when it touches or leaves the ground, and the relative time spent in each phase of the stride. An example is a sole ulcer of the left front medial digit (see Figure 11.1-1). This disease may cause a shortened weight-bearing phase of stride and a prolonged non–weight-bearing phase of stride in the affected limb because the cow is reluctant to place the foot down and quick to relieve pressure by picking the foot up off the ground. This animal may place the foot with the limb carried further under the body in an attempt to transfer weight to the lateral digit and may place the foot closer to the body, rather than extending the limb in an attempt to spare the pressure on the heel.

When diseases of the proximal limb, such as the hip, stifle, or shoulder, are suspected, the individual structures should be palpated as the animal walks. Bone-on-bone crepitation may be felt if a luxation or fracture is present. Soft tissue crepitation may be felt if tendon or ligament injury is present. Gas crepitation may be felt if emphysema of the tissues is present (e.g., sucking wound, clostridial myositis). It is sometimes difficult to pinpoint the location of the crepitation because it can be felt some distance from the lesion. Marked bone-on-bone crepitation that originates from the stifle often feels similar to the coxofemoral joint; they can be difficult to distinguish. Identification of swelling over the greater trochanter and rectal palpation of the hemipelvis and region of the coxofemoral joint during ambulation may help localize the lesion to the coxofemoral joint. Alternatively, auscultation of the suspected regions with a stethoscope during walking or manipulation of the limb may help localize the point of maximum intensity of the crepitus.

Conformation is involved in certain types of lameness. Cattle that have a post-legged conformation (e.g., hyperextended joints during weight-bearing, usually tarsus and stifle) are more subject to degenerative changes in the joints. The animal does not have the same capacity of shock absorption because hyperextension causes weight-bearing on cartilage that is not designed for weight-bearing and insufficient flexion of those joints exacerbates the cartilage insult. Sickle-hocked (e.g., hyperflexion of the hock during weight-bearing) cows endure excessive stress in flexor tendons that may result in a drop in the fetlock and rapid wearing of the heels.

GRADING OF LAMENESS

Assessment of the severity of the lameness is helpful to classify lameness and monitor responses to treatment. For this reason, lameness-scoring systems have been created. Equine lameness-scoring systems have been well standardized. However, these systems are difficult to extrapolate for use in cattle because of the need to control the gait (e.g., walk, trot) and perform various tests (e.g., circling, flexion tests). These tests may be performed in show cattle, but no standardization has been established for cattle. Various scoring systems have been described for use in lameness examination of cattle, and these scoring systems are based more on locomotion rather than responses to specific tests. Greenough and Wells, Sprecher et al, and Anderson (see Table 11.1-1) have described lameness-scoring systems that use grades of 1-to-5 or 0-to-4, but none has been universally accepted in practice. Multiple variations of lameness scoring have been published. Whatever the system used, veterinarians should be consistent and coherent to evaluate with precision. All associates in the same practice should agree on a grading system to facilitate communication within the practice and with the clients.

LIMB EXAMINATION

At this point, the clinician should have an idea of which leg is affected and an estimation of the affected region of the limb. Now, the affected limb must be examined carefully. Unless an obvious lesion is apparent, the authors start by a palpation of the limb. The clinician should watch for pain reaction and determine whether swelling, deformation, crepitation, warmth, and wounds are present. A hoof tester may be used to evaluate pain of the claw. The hoof tester should be applied where the common lesions of the sole surface are usually situated, including the apical region of the sole, the white line zone, and the prebulbar region. The hoof tester may be used to impact the dorsal and abaxial hoof wall to evaluate for a pain response that suggests laminitis, submural infection, and fracture of the distal phalanx. These manipulations can be performed with the animal standing and by picking up the affected limb for a short time. Alternatively, these procedures may be done with the animal free-standing and rope restraints used on the limb, restrained in a head gate or chute (see Figure 4.4-29), restrained in a standing hoof-trimming chute, restrained in lateral recumbency on the ground after a casting rope is used, or restrained in lateral recumbency on a tilt table. Sedatives and tranquilizers should be avoided whenever observations of pain responses are desired. After localization of the lesion, local anesthesia or sedation may be required to complete the examination.

Examination of long bones is performed by applying firm pressure in regions of minimal soft tissue presence (e.g., medial aspect of tibia and radius, greater trochanter of femur, greater tubercle of humerus, etc). If the animal has an adverse response—as evidenced by withdrawal, avoidance, attempts to kick the evaluator, or muscular flinching—the opposite leg should be palpated for comparison. Most fractures are obvious, but incomplete nondisplaced fractures can be suspected if deep palpation of the limb elicits a pained reaction. Each joint should be palpated separately, and complete flexion, extension, abduction, and adduction of the limb should be done. Isolation of the shoulder and elbow or of the stifle and tarsus is difficult when flexion or extension movements are performed because muscle tendon units unite these joints.

Special techniques are employed when injuries to the coxofemoral joint or cruciate ligaments are suspected.

Examination of the coxofemoral joint requires manipulation of the rear limb. These tests can be performed with the animal standing, but they are easier to perform with the animal in lateral recumbency with the affected limb uppermost. The relative position of the greater trochanter to that of the tuber coxae and the tuber ischii should be determined before than animal is laid down. The normal position of the greater trochanter is ventral to both of these bony prominences and imaginary lines drawn between them will create a “triangle” (Figure 11.1-6). Failure to palpate the greater trochanter may suggest a ventral luxation of the coxofemoral joint. Positioning of the greater trochanter in-line with the tuber coxae and tuber ischii suggests dorsal luxation of the coxofemoral joint. After the animal is laid down with the affected leg uppermost, the foot or the metatarsus III/IV is grasped and the entire limb rotated while performing repeated abduction and adduction motions. Fracture of the physis of the head of the femur (i.e. capital physeal fracture) should elicit crepitation of the hip that can be felt and occasionally heard. Coxofemoral joint luxation should elicit more crepitation, excessive movement of the greater trochanter, and ease of abduction if the luxation is ventral.

Figure 11.1-6 Lateral view of a cow with white tape on the greater trochanter, tuber coxae, and tuber ischia. Note the relative position of the greater trochanter is ventral to the tuber coxae and tuber ischia.

(Courtesy Norm G. Ducharme; Cornell University.)

Cranial cruciate ligament (CCL) rupture is more difficult to diagnose. Typically, the stifle is swollen and painful to palpation. A “drawer” test can be performed with the animal standing and is easier to perform when the injured limb is weight-bearing. The examiner should stand immediately behind the affected leg and place both hands on the tibial crest by encircling the limb. Then, the examiner’s knee is placed on the back of the calcaneus (see Figure 11.4-20). A drawer test is positive if displacement or crepitation can be felt after firm caudal traction on the tibial crest followed by a sudden release. The anatomy and function of the rear limb of cattle is such that the tibia is already displaced cranial to the femur when the CCL is ruptured. Thus caudal movement of the tibia is a sign of “positive drawer.” The examiner must be careful when performing this test to avoid being kicked. An alternative technique is for the examiner to stand cranial and lateral to the affected limb and place both hands on the tibial crest. Then, a firm, rapid thrust is applied to the proximal tibia, and the limb is observed for displacement and felt for crepitus. Although this test is safer to perform, we have found this technique to be less sensitive for detecting injury to the CCL.

Figure 11.4-20 Drawer test in cattle. The examiner’s knee is placed on the caudal aspect of the hock while the tibia is retracted caudally by placing both hands over the tibial crest. Increased laxity and crepitus can be detected with this test.

USE OF SELECTIVE ANESTHESIA

Selective perineural anesthesia with lidocaine HCl 2% solution is common practice in equines for lameness diagnosis but is uncommon in cattle. Nonetheless, selective perineural anesthesia can be used to isolate regions of lameness. The clinician must be familiar with the anatomy of the nerves of cattle because these are quite different from those of the horse. The authors often employ regional anesthesia by placing intravenous lidocaine distal to a tourniquet (intravenous regional anesthesia, IVRA). The tourniquet is left in place for 10 to 20 minutes, released, and the lameness reevaluated. IVRA induces anesthesia for a significantly shorter period of time in comparison to that of selective perineural anesthesia. Therefore lameness evaluation must be expedited. This technique is useful when the clinician wants to rule out the digits as a source of pain that has failed to be localized by previously mentioned diagnostic tests. With selective perineural anesthesia, each digit can be anesthetized individually, and this procedure aids in more specific isolation of lameness. Occasionally, intraarticular anesthesia is desired to isolate subtle lameness to a specific joint. We have found this to be most useful for diseases that affect the coxofemoral joint, scapulohumeral joint, femoropatellar and femorotibial joints, and the elbow. In complex joints, the examiner should pay special attention to the frequency of joint communication, depending upon which joint is injected (Table 11.1-2).

TABLE 11.1-2 Joint Communications in Cattle

JOINT	COMMUNICATION	FREQUENCY (%)
Fetlock	Medial to lateral digit	99%
Stifle	Femoropatellar to medial femorotibial	100%
	Lateral femorotibial to medial femorotibial and femoropatellar	65%
	All three together	57%
Carpus	Antebrachiocarpal—no communications	96%
	Middle carpal to carpometacarpal joint	86%
	Middle carpal joint to antebrachiocarpal and carpometacarpal joints	14%
	Carpometacarpal joint to middle carpal joint	86%
	Carpometacarpal joint to middle carpal and antebrachiocarpal joints	22%
Tarsus	Tibiotarsal to proximal intertarsal	100%
	Proximal intertarsal to distal intertarsal	0%
	Distal intertarsal to tarsometatarsal	21%
	Tarsometatarsal joint to distal intertarsal joint	43%

Frequency of communication is based on communication when the first joint listed is injected. The phrase all three together indicates that communication did not depend upon which joint was injected.

Adapted from Desrochers A: Characterization of the anatomic communications of the carpus, fetlock, stifle, and tarsus in cattle using intraarticular latex and positive contrast arthrography. Master’s Thesis. Kansas State University, Manhattan, Kan, 1995.

EXAMINATION OF THE FOOT

Adequate restraint is critical to performing a thorough examination of the claw. Fortunately, claw-trimming chutes have become commonplace and facilitate the ease, safety, and efficiency of examination (see Figure 4.4-29). If a chute is not available, different techniques have been described for restraining the animal. Certain animals require sedation either for restraint or to complete the examination. Xylazine HCl is commonly used because of its rapid onset of action, short duration, and the availability of reversal drugs. It is preferable to withhold feed from these animals for 12 to 24 hours before sedation to avoid bloating and reduce the risk of regurgitation while in lateral or dorsal recumbency. However, we routinely place cattle in lateral recumbency for short periods of time (e.g., <30 to 45 minutes) without restricting feed. Close monitoring of the patient is required to prevent respiratory compromise or regurgitation. Immediately after application of restraint, the foot is thoroughly cleansed. Thorough examination is difficult to perform when mud, manure, and debris contaminate the foot. The total time the animal is maintained in lateral recumbency should be minimized to reduce the likelihood of development of muscle or nerve injury. Heavily muscled and obese cattle are at increased risk of developing myopathy or neuropathy after prolonged periods of lateral recumbency. Excessively thin animals are at increased risk of developing nerve injury. These conditions are caused by direct compression injury and by indirect injury resulting from compression of vessels that causes hypoxia to the tissues.

A hoof tester is applied to the different areas of the claw. Firm pressure should be applied, but the examiner must be cautious to apply similar degrees of pressure to each point and—most importantly—on each claw. Without consistency of application, response to hoof pressure tests can misinterpreted. When hoof testers are applied with consistent pressure, they can be reliable. Corrective trimming may be performed first, followed by detailed inspection of the lesions. Each blackened area (e.g., cavity filled with manure, dirt, debris or necrotic tissue) should be explored. This is particularly important along the white line or the apical region of the sole. A pinpoint lesion is often similar to the “tip of an iceberg,” and further trimming may reveal large defects or an abscess. The interdigital space is inspected for redness, abnormal proliferation, or necrotic tissue. The heel bulbs are closely inspected for the presence of erosions, separation, digital dermatitis, or other lesions. Any draining tract should be inspected with a malleable probe or a teat cannula.

Selected Diagnostic Tests

Ancillary diagnostic tests for lameness evaluation in cattle include radiography, arthrocentesis, ultrasonography, CT scan, scintigraphy, histopathology, microbial culture, and thermography. Each test has specific indications to be performed, but we most commonly perform radiography, ultrasonography, microbial cultures, and arthrocentesis. If a joint or tendon sheath is suspected to be involved, sterile saline may be injected into the joint, after aseptic preparation of the skin. The lesion is observed for drainage as evidence that a communication with the wound exists. This must be done aseptically to prevent iatrogenic infection of the joint or tendon sheath. In many areas, nuclear scintigraphy is banned in all food-producing species. This has greatly limited use of scintigraphic bone scans as diagnostic tools to discover bone inflammation or bacterial infection.

11.2—Internal Fixation

Steven S. Trostle

In the past, simple forms of orthopedic treatment have been used to treat long bone fractures in farm animals. In the last decade, three major factors have advanced ruminant orthopedics. As veterinarians, we have developed a better understanding of bone physiology and biomechanics related to fracture repair. Implants and equipment available to treat animals have increased in size and dimension; therefore mechanical support can be provided to large animals by internal fixation devices in appropriate situations. As the economic value and potential of selected ruminants have increased via advances in assisted reproductive technology, clients have demanded that conditions once thought irreparable be treated.

Selection of Cases for Internal Fixation

Guidelines have not been defined to help determine when internal fixation should be selected to repair orthopedic conditions in ruminants. Internal fixation’s major advantages are that it provides rigid stabilization of the fracture and immediate, functional use of the limb. This point cannot be overemphasized; ruminant orthopedic patients are generally weight-bearing and ambulatory early, if not immediately, in the postoperative period. The disadvantages of internal fixation are the associated costs of general anesthesia, the implants, and equipment required to apply internal fixation devices. Aside from economic issues, internal fixation requires a basic understanding of orthopedic fixation principles and first-hand knowledge of the implants and equipment, which generally requires advanced training or extensive experience to be proficient.

Internal fixation should be considered for ruminant long bone fractures proximal to the carpus and tarsus, because these bones are more difficult to stabilize with other forms of fixation. Highly comminuted fractures distal to the carpus and tarsus may also benefit from the rigid stability offered by internal fixation.

SPECIAL CONSIDERATIONS FOR CALVES

Ruminant neonatal bones have a low bone density and thin bony cortices; and their ability to support and sustain implants such as intramedullary pins and screws is a primary concern (Fessler and Adams, 1996). The bone/implant interface is very weak (Figure 11.2-1A-C). Recent studies have evaluated various screws’ holding power in neonatal bones (Kirpenstein et al, 1992; Kirpenstein et al, 1993). No difference between the holding power of 4.5-mm cortical, 5.5-mm cortical, and 6.5-mm fully threaded cancellous screws in neonatal femurs was found, but a direct correlation between the screws’ holding power and bone cortical thickness was found. The 6.5-mm fully threaded cancellous screws had greater holding power than either 5.5-mm or 4.5-mm cortical screws in neonatal metacarpal and metatarsal bones, particularly the metaphysis. No difference between the holding power of 4.5-mm and 5.5-mm cortical screws in the diaphysis or metaphysis was found. In a recent study, the force required for screw pullout seemed to be more directly related to bone mineral density than cortical bone thickness (Shettko et al, 2001). Washers and bolts have been used with screws for calf internal fixation to overcome pullout problems and prevent bony failure at the screw-to-bone-to-implant interfaces in neonatal bone (Ferguson, 1985). Regardless of whether bone mineral density, cortical bone thickness, or both are responsible for a screw’s holding power, it remains a concern in calf internal fixation.

Figure 11.2-1 A, Lateral radiograph of 3-day-old calf with a Salter-Harris type II fracture of the distal radius. B, Lateral radiograph of same fracture treated with a dorsally placed bone plate and screws. C, Lateral radiograph of previously described repair 14 days postoperatively. The distal two screws are backing out, and there was loss of contact between the distal radius and bone plate.

(Courtesy of Dr. Ryland B. Edwards III, University of Wisconsin.)

Many fractures that occur in young farm animals involve the physis (growth plate). It has been proposed that younger animals are predisposed to physeal-type fractures because the physis cartilaginous makeup is weaker than bone and the surrounding support structures. The Salter-Harris classification (Figure 11.2-2) is used to describe fractures that involve the physis and adjacent metaphysis. In clinical practice, Salter-Harris type I and II fracture in farm animals makes up a large majority (>95%) of physeal fractures. Type I fractures, which are not as common, involve complete separation of the epiphysis from the metaphysis through the physis. A typical type I physeal fracture is the slipped capital femoral physis, which occurs through the femur prox-imal growth plate (Figure 11.2-3A). Other, even less common Salter-Harris type I fractures occur in the tuber calcaneus and olecranon. These latter two fractures occur through traction growth plates (i.e., where muscles or tendons insert or originate). In Salter-Harris Type II fractures (the most common farm animal physeal fracture), the epiphysis separates from the metaphysis through the physis with a small corner of the metaphysis fractured as well. These most commonly occur in the distal metatarsus and metacarpus, distal femur and radius, or proximal tibia (Figure 11.2-4A).

Figure 11.2-2 Schematic of Salter Harris fracture classification system.

Figure 11.2-3 A, Ventrodorsal radiograph of a slipped capital femoral physeal fracture in a 14-month-old bull. B, Previously described fracture repaired with 7-mm cannulated screws.

(Courtesy of Dr. Ryland B. Edwards III; University of Wisconsin.)

Figure 11.2-4 A, Craniocaudal radiograph of a 16-month-old, 490-kg bull with a Salter-Harris type II fracture of the proximal tibia. B, Previously described fracture repaired with two T-plates placed medially across the physis.

(Courtesy of Dr. Ryland Edwards III; University of Wisconsin.)

Salter-Harris type I and II physis fractures in farm animals generally have a favorable prognosis, but concern about how healing may impact long bone growth and an angular limb deformity developing always remains. Salter-Harris type III (through the physis and metaphysis) and Salter-Harris type IV (through the physis, epiphysis and metaphysis) fractures are very rare in ruminants because they involve a joint surface, and have a more guarded prognosis. Type V physeal fracture, the least common, is seen as a crushing injury to the physis.

Clinicians dealing with younger animals must be careful not to forget the rest of the body while concentrating on the fracture. It is important to assess the immunological status of newborn calves and be assured passive transfer has occurred before attempting any form of surgical intervention. Lack of a competent immune status will predispose the calf to postoperative infection. Other common calf diseases, such as pneumonia, omphalophlebitis, or septic polyarthritis, should also be evaluated before giving owners a prognosis.

SPECIAL CONSIDERATIONS FOR ADULTS

The primary concern for internal fixation in adult cattle is implants, unlike calves, in which the bone may be a limiting factor for successful internal fixation. Much progress has been made in implant design and material properties, but most are still adaptations from human surgery. Because early ambulation in adult ruminants is generally necessary, implants bending or failing during the postoperative period is not uncommon. The clinician who attempts internal fixation in adults must have substantial knowledge and pay attention to details. Because a lot of force is required to cause an adult long bone fracture, disruption of soft tissue and skin integrity is a concern. Open fractures are more difficult to treat successfully. Bone grafting should be strongly considered in all adult cattle fractures.

Evaluation of a Fracture for Internal Fixation Repair

RADIOGRAPHY

Preoperative radiographs provide the definitive diagnosis of fractures in most farm animals. In selected cases, other imaging modalities—such as nuclear medicine, computed tomography, and magnetic resonance imaging—increased diagnostic accuracy over radiography. Radiographs should be of high quality and carefully evaluated for fissure fractures. Multiple views of the affected area should be taken to provide a complete study and minimize the risk of missing a lesion(s).

Intraoperative radiography should also be considered when one is using any form of fixation—but particularly internal fixation. Intraoperative radiography can assess the positioning and placement of implants as well as the reduction of the fracture. Intraoperative radiographs should be completed in more than one view whenever possible to ensure that the repair is appropriate.

GENERAL

All ruminants should be held off feed for at least 24 hours and ideally 48 hours to minimize regurgitation and decrease the likelihood of aspiration pneumonia. If this cannot be completed, ruminal decompression should be attempted before general anesthesia by oral passage of a Kingman tube. Internal fixation is a time-consuming process, and complications associated with ruminal distension during anesthesia should be minimized. The surgical team should consider alternative plans in case the primary surgical plan cannot be completed. All equipment and supplies potentially needed in surgery should be readily available at the start of the operation.

EVALUATION OF THE PATIENT

The veterinarian must give as complete and accurate an assessment of the fracture and potential outcome of the repair to the client as possible. Both veterinarian and client must consider a “risk-benefit” ratio. The size, weight, age and disposition of the animal should always be considered. In general, a successful outcome for internal fixation repair is inversely related to age, weight and size. The fracture must be evaluated to give an accurate prognosis. The more highly comminuted fractures generally have a less favorable prognosis. However, not all simple fractures are candidates for internal fixation; and not all comminuted fractures are hopeless because of farm animals’ ability to rapidly produce significant periosteal bone and their more passive demeanor protecting the repair. Generally, transverse fractures are more amenable to repair than comminuted fractures. Although most fractures in adult cattle can be treated successfully, they are always more difficult to repair than identical fractures in calves.

The condition of the surrounding soft tissues should be considered in evaluation of a fracture. The surrounding soft tissues are responsible for extramural blood supply to the fracture site. Open or closed fractures with severely traumatized soft tissues often become infected, which significantly complicates the repair. Infection as a complication is discussed later in this chapter. However, it is paramount to remember that infection and instability are intolerable together. If contamination of the fracture site occurs and persistent infection develops, instability and failure of the repair are highly probable. This is the primary reason open fractures have a much less favorable prognosis than closed fractures. Broad spectrum, preoperative antibiotics are always recommended before fracture repair with internal fixation. Antimicrobials’ duration and withdrawal time needed to achieve proper care must be carefully considered during the selection process because of human public health concerns. The duration and frequency of antimicrobial coverage is controversial among surgeons but should be directly correlated to the type of fracture (open vs. closed) and extent of soft tissue damage.

ANESTHESIA

Chapter 6 discusses anesthesia.

POSITIONING

Positioning is a more relevant issue for adult cattle because they are prone to radial nerve paralysis and torn adductor musculotendinous structures. The down forelimb should always be extended as much forward as possible with adequate padding. Likewise, the hind limbs should be properly supported and padded as myopathy in the hind limbs may predispose the animal to slip and tear the adductor musculature. When possible, place the animal in right lateral recumbency, which allows needle decompression of the rumen if necessary. During positioning, cautiously pull on the tail; it is relatively easy to create coccygeal fractures by using manual traction. Finally, marked tension is required to reduce certain long bone fractures. A rope should be placed around the front and rear quarters to prevent the animal from changing position while traction is applied. Be careful to properly pad the areas where traction or countertraction will be applied.

SURGICAL APPROACH

The optimal surgical approach should minimize soft tissue trauma while allowing direct visualization of the fractured bone and site. In general, the greater the trauma is to soft tissues and surrounding area, the longer the surgical approach necessary to gain adequate exposure. After the fracture is exposed, debride the clotted blood and devitalized tissue. A culture of the deep surrounding soft tissues is recommended for open fractures to define potential pathogens and select appropriate antimicrobials. The fracture site should be continuously lavaged during the surgical procedure with a solution containing an antibiotic such as cephalosporin to reduce contamination. Aseptic techniques should be maintained throughout the surgical procedure. The surgery team should plan and use a time-efficient procedure to decrease the risk of anesthetic and surgical complications.

FRACTURE REDUCTION

The goal of a successful internal fixation is accurate, rigid anatomic reduction. Anatomic reduction allows the bone to share the load transfer and restore function to the leg. Nonanatomical and/or inaccurate reduction predisposes the implant to migration and/or failure. Reduction should be performed by gradually fatiguing the inverse myotactic reflex. Reduction may be achieved by tenting the bone ends out of the incision and toggling them against one another until they align anatomically. However, mechanical devices such as a large animal fracture distractor,* a calf jack, or other pulley system may be needed to provide consistent tension and resultant muscle fatigue in cases in which reduction cannot be performed manually (Ames, 1995). Reduction can be maintained by using bone reduction forceps, placing a lag screw across the fracture gap, or using cerclage wire. The efficacy of neuromuscular blocking agents used is not always predictable, and they do require positive pressure ventilation to overcome respiratory depression.

General Principles of Internal Fixation

BONE PLATES

Several basic principles regarding use of bone plates in fracture fixation are important (Trostle and Markel, 1996). These include bone properties, plate material and geometry, screw-bone interface, number of screws, screw material and tension, plate-bone interface, placement of the plate relative to loading, and compression between fragments. A bone plate’s bending stiffness is related to the third power of the plate’s thickness. Therefore changing the plate thickness does more to change plate rigidity. The mechanical properties of bone also affect the behavior of the plate-bone system. For example, less stiff bone will increase the load-sharing contribution of the plate. Loads can be transmitted between the plate and bone through bone screws and friction-type forces between the plate surface and bone.

In large animal orthopedics, a bone plate is a device that shares the load by passing some of the load from the plate to bone fragments. Subjected to bending loads, a plated bone can take on a bending open (compressive surface) or bending closed (tensile surface) configuration (Figure 11.2-5). The plate’s placement relative to the loading direction determines the load proportion supported by the plate. The plate/bone composite is far stiffer in the bending closed position than in the bending open position. This makes it important to anatomically reconstruct the bone cortex opposite the bone plate placement.

Figure 11.2-5 Illustration of the principle of placing a bone plate on the tension surface of a bone, so the bone receives compressive forces. For example, the long bone (A) can be compared to a bent column (B). A plate applied to the convex or tension side of the bone when it is loaded counteracts the tension forces and provides rigid internal fixation in the bending closed position. If the plate is applied on the concave surface (D), it does not give as rigid fixation, and the plate is subjected to excessive bending forces that predispose it to failure.

(Modified with permission from Brinker WO, Piermattei DL, Flo GL, editors: Handbook of small animal orthopedics and fracture treatment, ed 1, Philadelphia, 1983, WB Saunders.)

Plating provides the most rigid form of internal fixation used in ruminant orthopedics. Application of bone plates should be performed on the tension surface whenever possible because of the biomechanical advantages previously noted. In younger, lighter-weight animals, one plate may be used to achieve stabilization. Oftentimes, two plates are used in larger animals in an effort to obtain adequate stabilization of the fracture. The surgeon should contour the plate(s) to ensure that the entire surface of the plate is in contact with the bone (bone-plate interface). Every effort should be made to optimize the bone-plate interface because this provides a more rigid and stable fracture repair and enhances the likelihood of a positive outcome. Plate(s) should span from the proximal to distal metaphysis to enhance the bone-plate interface and minimize stress concentrated at the bone ends. When two plates are used, they should be placed at 90 degrees to one another and end in a staggered fashion to prevent stress concentration at the bone end and facilitate easier screw placement.

The standard plates used for repair fractures of the long bones are the 4.5-mm narrow and 4.5-mm broad dynamic compression plates; however, other specialty plates are available (Table 11.2-1). The oval shape of the holes in dynamic compression plates allows them to be used to compress fracture fragments. Narrow plates have holes aligned in a straight line, whereas the holes in broad plates are staggered. Narrow plates have a smaller width (12 mm vs. 16 mm) and thickness (3.6 mm vs. 4.5 mm) in comparison to broad plates. Recent reports cite successful use of dynamic condylar screw (DCS) and dynamic hip screw (DHS) plates in long bone fracture repair (Auer et al, 1993) (Figure 11.2-6). The DCS and DHS plates are identical in width to the 4.5-mm broad plates but thicker at 5.6 mm and 5.8 mm, respectively. Other plates—such as the angled, Cobra head, T-, and semitubular plates—have been used in special circumstances.

TABLE 11.2-1 Standard and Special Plates Used in Farm Animal Surgery

Figure 11.2-6 A, Lateral and B, craniocaudal radiographs of an adult bull weighing 900 kg with a comminuted distal radius fracture. C, Lateral and (D) craniocaudal radio-graphs of the previous fracture repaired with a dynamic condylar screw and plate system.

(Courtesy of Dr. Ryland B. Edwards III; University of Wisconsin.)

The use of bone plate luting has been recommended to augment fracture repair in large animal surgery (Nunamaker et al, 1991). Bone plate luting involves placing bone cement (polymethylmethacrylate) between the plate and bone as well as the screw head and plate. To lute a bone plate, one must loosen all the screws in the plate and lift the plate off the bone. The bone cement is then placed between the plate and bone, and the screws are immediately retightened. Bone cement should be kept out of the fracture site as it may delay or prevent healing. After the screws are retightened, the bone cement redistributes into the unoccupied space in the plate screw holes. The two proposed mechanisms behind plate luting are the following: 1) plate luting enhances the bone-plate interface; and 2) decreases shear stress at the screw head in the plate. Bone plate luting does not compensate for poor contouring of plates. The additional use of antimicrobials (with consideration for public health standards) in the bone cement may provide sustained local antimicrobial activity.

Comminuted fractures should be converted to two-part fractures by attaching the fragments to the parent bone with lag screws. Screws (3.5 mm) are recommended for this procedure because the head can be sufficiently countersunk to prevent interference with bone plate application. Ideally, if one plate is used, it should be placed on the tension surface of the bone and loaded in compression. Plates placed on a tension surface should be prestressed before they are applied to ensure transcortical compression and stability. Plates are prestressed by slightly overbending the plate to leave a gap between the fracture line and plate at the level of the fracture line. When screws are applied, prestressing brings the bone to the plate, creating compression up to the far cortex and along the entire fracture line. If a second plate is used, it may be loaded in compression or neutralization. Screws should be placed in every hole of a bone plate to maximize the bone-implant interface. Lag screw principles may be used within the bone plate and should be performed with large comminuted fragments.

SCREWS

Two basic types of screws (cancellous and cortical) are used in ruminant orthopedic surgery (Table 11.2-2). The parts of a screw include head, shaft, core, thread, pitch, shaft length, thread length, and total screw length, which vary among the different screw sizes. Cortical screws are completely threaded and have a relatively thin thread width. Cancellous screws are available in various thread lengths and have a wider thread diameter and pitch than cortical screws.

TABLE 11.2-2 Screw, Drill Bit, Tap Chart

Screws are also commonly classified by their diameter. In general, 4.5-mm and 5.5-mm cortical and 6.5-mm cancellous screws are used in ruminant orthopedics. The 5.5-mm cortical screws have demonstrated superior strength characteristics in comparison to the 4.5-mm cortical and 6.5-mm cancellous screws. The 6.5-mm cancellous screws are available in three different thread lengths (16-mm, 32-mm, and fully threaded). The 3.5-mm cortical screw also has been used to achieve interfragmentary compression, since the head is small enough that it may be completely countersunk in the adult bovine cortex and covered by a bone plate.

A 7-mm cannulated screw system has been advocated to repair slipped capital femoral physeal fractures in adult bulls (Wilson et al, 1990). A study biomechanically compared 7-mm cannulated screws to 5.5-mm cortical and 6.5-mm cancellous screws in a femoral head fracture model. Results of this study demonstrated that 7-mm cannulated screws had greater holding power than 6.5-mm cancellous screws but their holding power was similar to 5.5-mm cortical screws. The study also noted that the cannulated screw systems (4.5-, 7-, and 7.3-mm) offer added flexibility when screw placement is critical. This is because smaller-diameter guide wires (1.5- to 2.8-mm) are used to place the cannulated screws, and these small guide wires can be replaced easily if they are not in the optimal position.

Screws should be placed so the near (cis) and far (trans) cortices are engaged to achieve optimal stability. Interfragmentary compression may be achieved by using screws within and outside the bone plate. Ideally, three screws each should be placed proximal and distal to the fracture fragments to achieve security. The use of power assistance in tapping and placing the screws does not alter the pullout strength when proper technique is utilized (Gillis et al, 1992). Power assistance can greatly reduce surgical and anesthetic times with their subsequent risk of complications.

INTRAMEDULLARY PINS AND INTERLOCKING NAILS

Intramedullary devices have several advantages in fracture treatment, including restoration of bony alignment and early recovery of weight-bearing in young, lightweight animals. These devices are intended to stabilize a fracture by acting as an internal splint, thus forming a composite structure of bone and rod in which both contribute to fracture stability. This load-sharing property is fundamental to the rods’ design and should be recognized when they are used for fracture treatment (Figure 11.2-7).

Figure 11.2-7 A, Lateral radiograph of a 2-day-old calf with a middiaphyseal femoral fracture. B, Previously described fracture repaired by using intramedullary pins (stack pinning) and cerclage wire.

(Courtesy of Dr. Ryland B. Edwards III; University of Wisconsin.)

Several material and structural properties of intramedullary rods alter their axial, bending, and torsional rigidities. These include cross-sectional geometry, rod length, the presence of a longitudinal slot, and the elastic modulus of the material. The cross-sectional geometry of the rod significantly affects all rigidities. In general, the overall rigidity of intramedullary rods increases with rod diameter, because the “moment of inertia” is approximately proportional to the fourth power of the rod’s radius. The contact distance between an implant and bone at the proximal and distal segments of bone is the unsupported length of intramedullary fixation. This distance shortens as the fracture heals. The unsupported length of the rods is important in the initial stages of fracture healing. The interfragmentary motion is proportional to the square of the unsupported length in bending; therefore a small increase in unsupported bent length can lead to a larger increase in interfragmentary motion.

With torsional loading, the unsupported length is determined by the points at which sufficient mechanical interlocking occurs between bone and implant to support torsional loads. The concept of unsupported length is not applicable to simple rod designs without proximal or distal locking mechanisms, since there may be little resistance to torsion. Clinically, placing multiple pins (stack pinning) is recommended to increase intramedullary contact and enhance torsional and bending stability when one uses simple rod designs.

The most commonly used intramedullary pins are Steinmann pins, which range in size from 3.2 mm up to 6.35 mm. Intramedullary pins are available with trocar, chisel, or trocar-threaded tips. Threaded pins are recommended to repair neonatal bone, which is less dense and more prone to migration. Intramedullary pins can be applied by using a hand-driven or power-assisted device. Single or multiple stack pins may be used and placed in normograde or retrograde fashion, depending on the nature of the fracture. Stack pins increase frictional forces between the pins and the cortical surface, thus decreasing rotational instability. Intramedullary pins should be secured in the subchondral epiphysis, and care should be taken not to introduce or maintain intramedullary pins through the articular surface because of ensuing risk of degenerative joint disease.

In general, intramedullary pins should be used for diaphyseal fractures of relatively straight bones. Intramedullary pins are contraindicated for the repair of long oblique, spiral, or comminuted fractures without the use of devices that augment the primary repair and prevent overriding or rotation of the fracture fragments. Commonly used devices include cerclage wire and screws. Intramedullary pins have also been “tied in” with external skeletal fixators to provide additional stability (St-Jean et al, 1992b).

Interlocking nails have been used in human surgery to repair fractures of the humerus, tibia, and femur (Figure 11.2-8). Similar to intramedullary pins, interlocking nails provide stiffness in bending. The use of both proximal and distal locking with screws can prevent axial displacement of the bone along the rod and provide enhanced torsional rigidity. For interlocking nails, the distance between the proximal and distal locking points typically determines the unsupported length. Interlocking nail systems for large animal surgery are commercially available.* Interlocking nails have a single trocar point, are 13 mm in diameter, and vary in length. The interlocking nails have 5.7-mm diameter screw holes placed 16.5 mm apart over their entire length. An open surgical technique is recommended with interlocking nails because of their large diameter. A 6.35-mm diameter intramedullary pin placed in normograde fashion from the proximal location into the medullary cavity and seated distally in the subchondral bone of the distal epiphysis creates a pathway for interlocking nail insertion. The intramedullary pin is then removed. The interlocking nail replaces the intramedullary pin in the same pathway, which decreases the likelihood of the bone fracturing during interlocking nail placement. A slightly smaller-diameter (11 or 12 mm) reaming device is an alternative. The interlocking nail is inserted as described above with a large hand chuck. The aiming device is then attached to the proximally exposed portion of the interlocking nail. The aiming device ensures that drilling and tapping the bone is achieved within the screw holes of the interlocking nail. Longer-shanked drills and taps may need to be used to accomplish this task. Generally two screws each are placed in the distal and proximal primary fracture fragments. Interlocking nails have been used to repair humeral and femoral fractures in calves. The quality of the surrounding bone in neonates may determine the strength of repairs that use interlocking nails. Distal placement of intramedullary devices should be checked by intraoperative radiography or stifle arthrot-omy. Intramedullary pins should be cut proximally at the level of the skin to allow for pin removal and prevent impingement of the sciatic nerve. Intramedullary pin removal can be difficult to perform in rapidly growing animals that have achieved clinical union but poses no problem to the animal if they remain in situ. Removal should be considered if the intramedullary pins have migrated or are associated with an infective process. Interlocking nail length should be selected so soft tissues and skin can cover the proximal end. Interlocking nails cannot be removed without a second surgical procedure.

Figure 11.2-8 A, Lateral radiograph of a 1-day-old calf with a diaphyseal femoral fracture. B, Previously described fracture repaired using an interlocking nail.

(Courtesy of Dr. Ryland B. Edwards III; University of Wisconsin.)

Fractures of the Femur

CLINICAL PRESENTATION

Fractures of the femur are the second most common fracture that occurs in cattle—particularly in neonatal calves. Femur fractures result in extensive swelling, hematoma formation, and crepitus of the proximal hind limb (Trostle and Markel, 1996b). Cattle are lame on the injured leg, and the degree of lameness depends on the age and weight of the animal as well as displacement of the fracture fragments. Cattle often toe-touch with the affected leg and may appear to have a shortened leg if the pull from the quadriceps muscles causes marked overriding of fracture fragments. A differential list of other considerations for cattle with proximal hind limb lameness should include coxofemoral luxation, cranial cruciate rupture, and septic arthritis of the coxofemoral or stifle joints.

The definitive diagnosis of a femoral fracture is made by radiography (see Figures 11.2-7 and 11.2-8). At least two standard radiographic views should be performed to assess the fracture. This is most easily accomplished if the animal is tranquilized and placed in lateral recumbency to obtain both mediolateral and craniocaudal views. The most commonly reported femur fractures are an oblique-to-spiral fracture of the mid-to-distal diaphysis or a short transverse-to-oblique fracture of the distal metaphysis, although proximal diaphyseal fractures have been reported (Ferguson, 1994). Comminution is usually present, and high-quality radiographs should be obtained to accurately evaluate the degree of comminution. Spiral and oblique fractures are generally thought to be caused by torsional and bending forces acting upon the bone. Reasons for the high prevalence of distal metaphyseal/physeal region fractures are not completely understood but may be related to the high torsional forces placed on the distal femur.

SURGICAL APPROACH

To facilitate the surgical approach, cattle should be positioned in lateral recumbency, with the affected limb upward. A lateral approach is employed, and a liberal superficial dissection should be performed because the large muscle masses of the proximal hind limb limit femur exposure. A linear incision is made starting slightly caudal to the greater trochanter and extending to the lateral epicondyle of the femur. The plane of dissection parallels the cranial border of the biceps femoris through the tensor fascia lata muscle. Exposure to the diaphysis is gained by incising through the vastus lateralis muscle parallel to its muscle fibers.

METHODS OF INTERNAL FIXATION REPAIR

Dynamic compression, Cobra head, angled blade, and condylar bone plates and screws have had limited success in repairing femoral fractures. The tension surface of the femur is generally considered to be the lateral to craniolateral aspect of the bone from the middiaphysis proximally. Torsion is the predominant distal force on the femur. For maximum stabilization, applying bone plates to the femur at these sites is recommended. In calves, generally one laterally placed plate may be used. In older animals, two plates placed at ninety degrees to one another on the lateral and cranial surfaces are recommended.

Retrograde, intramedullary stack pinning has been used to repair neonatal bovine femoral fractures with success (St-Jean et al, 1992a). In a recent report, 83% of the fractures treated in this manner were considered to have healed satisfactorily. However, complications such as pin migration occurred in 50% of the cases, and osteomyelitis developed in one case. The authors suggested the use of partially threaded pins to aid in preventing pin migration. All calves in this study had considerable callus formation present, thus suggesting instability. Although intramedullary pins are noted for their strength and stiffness in bending, fracture fragments tend to rotate or displace axially along single intramedullary pins. Stack pinning, external fixators, and cerclage wires have been used to help stabilize the torsional and compressive instability of single intramedullary pin fixation repair; but the results have been variable (Figure 11.2-9).

Figure 11.2-9 A, Lateral radiograph demonstrating a middiaphyseal fracture of the humerus in a 2-day-old calf. B, Previously described fracture 30 days after being repaired with a single intramedullary pin, lag screws and cerclage wire.

(Courtesy of Dr. Ryland B. Edwards III; University of Wisconsin.)

Intramedullary pins may be placed in either a normograde or retrograde fashion. A closed surgical technique can be used to place intramedullary pins in normograde fashion in minimally displaced fractures, but ensuring proper placement in the distal fragment requires care. Both normograde and retrograde placement of intramedullary pins can be performed with open surgical techniques.

Interlocking nails have been proposed as a possible alternative repair method for diaphyseal fractures of the femur (Trostle et al, 1994). Interlocking, intramedullary nails provide rigid fixation in bending similar to intramedullary pins. The addition of screws helps lock fracture fragments and provides enhanced compressive and torsional stability. The bone-plating problems associated with bone quality, as seen in neonatal calves, may persist. The author has had several successful clinical outcomes after using interlocking nails as a fixation technique for neonatal femoral fractures.

Fractures of the Femoral Head

CLINICAL PRESENTATION

Fractures of the femoral head or slipped capital physeal (Salter-Harris type I) fractures occur in two primary populations. One is young calves after forced fetal extraction associated with hip lock and shear forces placed across the coxofemoral region. The second population is young (1 to 2 years old) bulls in group housing. Blunt trauma in a lateromedial direction to the coxofemoral region results in shear force across the physis and ultimately failure. Cattle with slipped capital femoral physis have lameness but generally bear weight on the affected leg. In chronic cases, marked muscle atrophy may appear, but visually it is difficult to distinguish between it and other abnormalities. Palpation of the right coxofemoral joint while the left is being placed through a full range of motion typically elicits crepitus. If an assistant is not available, one can often detect a noticeable clicking and crepitus by placing one hand over the coxofemoral joint while pulling the animal’s tail towards the affected side with the other hand. Ventrodorsal or lateral positioned radiographs with the affected leg up, flexed, and abducted (frog-legged) provide a definitive radiographic diagnosis (see Figure 11.2-3, A).

SURGICAL APPROACH

The animal is placed in lateral recumbency with the affected leg uppermost. A dorsolateral approach just cranial to the greater trochanter is used to expose the coxofemoral joint. The incision is extended distally to the distal aspect of the femur. A plane of dissection is created through the fascia lata and cranial border of the biceps femoris. A partial tenotomy of the origin of the vastus lateralis and sometimes middle gluteal and gluteus accessorius is required to provide exposure of the joint capsule (Figure 11.2-10).

Figure 11.2-10 Schematic of surgical approach to coxofemoral joint.

METHODS OF INTERNAL REPAIR

The leg is internally rotated to facilitate reduction of the fracture. The fracture can then either be stabilized with 5- to 6.32-mm Steinman pins or 7- or 7.3-mm cannulated screws (Wilson et al, 1994; Hull, 1996) (see Figure 11.2-3, B). The implants are inserted retrograde from the insertion of the accessory gluteal through the femoral neck and into the fragment. Care should be taken not to invade or leave implants in the joint. Radiographic guidance (including fluoroscopy) at surgery is extremely helpful when one is placing implants. Devascularization of the femoral head may occur as a result of fracture or surgical dissection. This is because the blood supply to the femoral head flows through the round ligament of the head of the femur, joint capsule, and femoral neck. The latter two are disrupted by a fracture. During a surgical procedure, every effort should be made to preserve the blood supply to prevent femoral head necrosis from occurring. This is followed by revascularization, bone resorption, flattening of the femoral head, and osteoarthritis (Figure 11.2-11).

Figure 11.2-11 Femoral head necrosis as viewed on a ventrodorsal radiograph.

(Courtesy of Dr. Ryland B. Edwards III; University of Wisconsin.)

In case of irreversible damage to the articular cartilage of the acetabulum and/or femoral head, femoral head excision should be considered (Squire et al, 1991). In this case an osteotomy of the greater trochanter is performed. Before the osteotomy, the greater trochanter is drilled and tapped, and two or three 6.5 mm cancellous screws are inserted into the intended proximal fragment before the osteotomy. A Gigli wire is used to perform the osteotomy. The femoral neck is transected with an oscillating saw or Gigli wire. The greater trochanter is put back in place with a 1.2-mm wire in a tension band fashion (see Figure 11.4-35). Closure is done by reapposition of the various anatomical planes.

Figure 11.4-35 Lateral oblique (A) and ventrodorsal (B) radiographs of a 3-year-old 630-kg adult cow’s pelvis, which shows a luxated coxofemoral joint (in the adductor foramen). Note how the acetabulum is free of the femoral head in comparison to the contralateral side. In addition to the luxation, there is a greater trochanter fracture (black arrow) and a slipped capital femoral physeal fracture (white arrow). C, Postoperative ventrodorsal radiograph after the fractures and luxation are reduced and stabilized with internal fixation.

Fractures of the Humerus

CLINICAL PRESENTATION

Fractures of the humerus are relatively uncommon, but they do occur, most often secondarily to trauma (Rakestraw, 1996). Cattle with fractures of the humerus typically have a “dropped elbow” appearance and drag the effected limb in the flexed position. Other differentials for cattle with a dropped elbow appearance include olecranon fracture, triceps myopathy, and radial nerve paralysis. Palpation of the limb demonstrates extensive soft tissue swelling around the fracture site with associated crepitation when the limb is passively adducted and abducted. Concurrent damage to the radial nerve is often present because the radial nerve runs adjacent to the musculospiral groove off the humerus. The integrity of the radial nerve is critical for a positive outcome. It is difficult to clinically assess the function of the radial nerve with electrodiagnostics such as electromyography and nerve conduction velocity. Transient functional interruption is common because of the inflammation surrounding the nerve (neuropraxia). Clinical signs generally provide strong support for the diagnosis of a humeral fracture, and the diagnosis is confirmed by radiography. Radiographs of the humerus are difficult to obtain in healthy standing animals and can be even more difficult to obtain with extensive soft tissue swelling and pain. Short-acting anesthesia may be required to obtain quality images.

The most common types of fractures of the humerus include diaphyseal fractures that typically have a spiral-to-long oblique configuration. Fractures of the humerus are seldom open because of the extensive soft tissue surrounding the bone. Fractures can also occur through the distal physis and usually are a Salter-Harris type II configuration. Fractures of the deltoid tuberosity and greater tubercle can occur but are extremely rare in ruminants.

SURGICAL APPROACHES

The two described surgical approaches to the humerus include a lateral and cranial approach. The radial nerve is the most important vital structure that must be identified and preserved when either surgical approach is performed. The lateral approach provides exposure to the irregular lateral surface of the humerus and is not a desirable surface for plating the humerus. However, this approach is useful for assisting in placement of intramedullary pins or interlocking nails. The cranial approach provides access to the straighter and more regular surface of the humerus.

For the cranial approach, the animal is placed in lateral position with the affected leg uppermost (Figure 11.2-12). The skin and subcutaneous tissue is incised from the cranial aspect of the greater tubercle of the humerus distally over the cranial aspect of the extensor carpi radialis muscle. The plane of dissection is established by proximally splitting the brachiocephalicus muscle cranial to the deltoid tuberosity. At the distal half of the incision, the caudal border of the brachiocephalicus is separated from its attachment to the brachial fascia. The cephalic vein is identified, double-ligated, and transected. The insertions of the brachiocephalicus muscle on the crest of the humerus distal to the deltoid tuberosity are transected. The underlying deltoid muscle is elevated from the deltoid tuberosity, thus exposing the brachialis muscle along the lateral aspect of the humerus in the musculospiral grove. The belly of the biceps muscle is elevated from the humerus. To gain further access to the distal part of the humerus, a portion of the origin of the extensor carpi radialis muscle is elevated from its attachment to the lateral humeral condyle. The radial nerve is identified along the caudal border of the brachialis muscle and distally between the brachialis and extensor carpi radialis muscle. Retraction of the brachialis muscle caudally and the biceps brachii muscle medially provides sufficient exposure to the cranial cortex. Retraction of the brachialis muscle cranially allows exposure to the lateral aspect of the humerus.

Figure 11.2-12 Schematic of surgical approach to humerus.

In the lateral approach, the animal is positioned in lateral recumbency with the affected leg uppermost. The skin and subcutaneous tissues are incised from the greater tubercle to the lateral epicondyle of the humerus. The incision lies cranial to the cranial border of the triceps brachii muscle. To gain exposure to the proximal humerus, a plane of dissection is created under the caudal border of the brachiocephalicus muscle. The brachiocephalicus muscle is reflected cranially to reveal the cranial border of the brachialis muscle. The cranial border of the brachialis muscle is retracted caudally and the brachiocephalicus muscle cranially to expose the proximal third of the humerus. The close approximation of the brachialis muscle to the musculospiral groove of the humerus makes exposure of the middle third of the humerus difficult. To expose the distal third of the humerus, the brachialis muscle must be retracted cranially, the triceps brachii muscle caudally, and the extensor carpi radialis muscle caudoventrally. The radial nerve runs craniodistally in close approximation to the musculospiral groove of the humerus and deep to the triceps brachii and extensor carpi radialis muscles.

METHODS OF INTERNAL FIXATION REPAIR

Intramedullary pins or interlocking nails may be used to treat diaphyseal fractures of the humerus. Intramedullary pins can be placed in either normograde fashion starting proximally from the greater tubercle passing distally to the medial side of the humeral condyle. Care should be taken to avoid driving pins into the olecranon fossa of the humerus. A single intramedullary pin can be used, or multiple stack pins can be used to increase rotational stability and decrease the likelihood of longitudinal collapse of the fragments. Cerclage wire or interfragmentary compression with lag screws is also com-monly performed when utilizing intramedullary pins (see Figure 11.2-8B). Interlocking nails can also be used to repair diaphyseal and distal fractures of the humerus. Interlocking nails insertion and placement landmarks are similar to those of intramedullary pins.

Bone plate fixation and screws can be used to treat humeral fractures. In younger calves, single-plate application to the cranial aspect of the humerus usually provides enough support for healing. In animals above 200 kg, double-plating techniques that use both the cranial and lateral surfaces should be attempted. If possible, 4.5-mm broad DCP plates should be used because of their strength. Contouring the plate on the lateral side is extremely difficult because of the deltoid tuberosity, and for that reason, use of a lateral plate as the sole means of repair is not recommended.

Fractures of the Radius/Ulna

CLINICAL PRESENTATION

Fractures of the radius are not very common in cattle. Fractures of a cow’s radius usually occur because a leg in a fixed position is struck, typically either in a lateral-to-medial or cranial-to-caudal direction. Fractures of the radius commonly occur in the mid diaphysis or distally through the growth plate as a Salter-Harris type II fracture (see Figure 11.2-1). In adults, fractures of the radius are commonly highly comminuted. Because of the large amount of soft tissue covering the radius, most radial fractures are typically closed. Cattle with fractures of the radius have an appreciable lameness with associated soft tissue swelling of the antebrachium. They tend to rest with the leg pointed and are minimally weight-bearing. On occasion, marked angulation is visible at the fracture site; it is best viewed with a cranial-to-caudal leg position. Radiographs provide the definitive diagnosis. Olecranon fractures are extremely rare (Hague et al, 1997) and present as severe forelimb lameness and an inability to bear weight. The elbow is dropped because of the lack of functional triceps activity. Palpation of the olecranon reveals pain and swelling. The diagnosis is confirmed by radiography (Figure 11.2-13).

Figure 11.2-13 A, Lateral radiograph of the olecranon of a 3-year-old 500-kg Hereford cow with an acute olecranon fracture. B, After repair with a narrow DCP plate. C, Implant failed and D, was repaired by removing the broken plate and replacing it with 2 DCP plates using the same screw holes. In addition, bone grafting was performed.

(Courtesy of Dr. Ned Dykes; Cornell University.)

SURGICAL APPROACH TO RADIUS

The animal is positioned in lateral recumbency with the affected leg uppermost. A curvilinear incision through the skin and subcutaneous tissue is started at the lateral epicondyle of the humerus and extended distally to the lateral tuberosity of the radius where the collateral ligament of the carpal joints originates (Figure 11.2-14). The apex of the curvilinear incision is directed cranially to help gain exposure to the dorsal aspect of the radius. The skin is reflected, and the plane of dissection is established between the common digital extensor muscle and extensor carpi radialis muscle. Care must be exercised not to damage the radial nerve as it courses the most proximal aspect of the radius. The cranial and lateral surfaces of the radius are readily exposed by this surgical approach. The abductor digiti I longus closely adheres to the lateral aspect of the distal radius and may need to be bluntly reflected.