Closed Reduction and Stabilization

The anesthesia protocol of patients with elbow joint luxation should take into consideration the need for analgesia and muscle relaxation of the forelimb. Neuromuscular blockade and regional analgesia may be considered in these cases. Alternating a hanging limb preparation with elbow joint hyperflexion may facilitate reduction. The technique for closed reduction is influenced by the position of the anconeal process, with the goal being to lock the anconeal process into the olecranon fossa and use it as a fulcrum to facilitate reduction. In most cases, the anconeal process lays lateral to the fossa. First, the limb should be flexed beyond 90 degrees and the antebrachium internally rotated (pronated) and abducted to slide the anconeal process over the lateral epicondylar crest and into the olecranon fossa. Placement of a towel clamp or a Lewin bone clamp through the skin and into the olecranon provides a means by which caudal distraction can be applied to the proximal ulna, and aids in positioning of the anconeal process in the olecranon fossa. Once the anconeal process has been reduced, the limb is slightly extended and the antebrachium is adducted and internally rotated. Pressure is applied to the radial head to force it medially while continuing to extend the limb. In cases in which the anconeal process remains within the fossa, reduction starts directly with adduction and internal rotation of the antebrachium with the elbow joint slightly extended, as described previously. Once reduced, the joint is taken through a range of motion multiple times to eliminate hematoma and remnants of the joint capsule from the articulation.

After reduction, the joint is assessed both radiographically and physically for instability (Figure 53-5). Radiographic evidence of mild radial head subluxation is interpreted carefully. Mild signs of laxity could be attributed to muscle relaxation under anesthesia, as documented in human beings.⁷⁴ Stress radiographs with the limb extended and placed in varus and valgus may help to fully document the degree of elbow joint instability. Collateral ligament integrity can be determined by manipulating the extended elbow joint in a varus or valgus direction, or by flexing the carpus and elbow joint to 90 degrees and rotating the antebrachium, as was first proposed by Campbell in 1969 and validated by Farrell in 2007.^18,40 Campbell’s test is performed with the elbow joint and carpus at 90 degrees of flexion to position the anconeal process caudal to the olecranon fossa, so that rotational stability of the elbow joint relies primarily on the collateral ligaments. The anconeal process has been found to act as the primary rotational stabilizer in pronation if the elbow joint is extended to a standing angle of 135 degrees.¹⁵² In flexion, pronation of normal cadaver canine elbow joints approached a mean of 30 degrees (range, 17 to 40 degrees), and supination averages 46 degrees (range, 31 to 67 degrees).⁴⁰ Transection of the medial collateral ligament increases pronation to 60 to 100 degrees, whereas transection of the lateral collateral ligament increases supination to 70 to 140 degrees.^18,40 Angles of pronation and supination appear to vary widely between individuals, with the range of motion correlating inversely with the weight of the animal.⁴⁰ The degree of laxity of the reduced elbow joint should therefore be compared with that of the normal contralateral elbow joint when the integrity of the collateral ligaments is assessed.

The incidence of collateral ligament injury associated with elbow joint luxation varies between studies. Some authors report collateral ligament injury in 18% to 50% of luxations.18,108,135 It is interesting to note that normal elbow joints could not be luxated unless at least the lateral collateral ligament was transected in a cadaver experiment.⁴⁰ However, traumatic elbow joint luxation may be associated with elongation rather than disruption of the collateral ligaments. This would explain why a successful outcome can be obtained even when mild to moderate instability is present after closed reduction of the elbow joint. In normal feline cadaver elbow joints, the mean angle of pronation increased from about 50 degrees (30 to 70 degrees) to 99 degrees after transection of the medial collateral ligament. Supination increased from nearly 130 degrees (108 to 150 degrees) to 167 degrees after sectioning of the lateral collateral ligament.⁴⁰ In this experiment, luxation of feline elbow joints was not possible unless both collateral ligaments were transected. If marked physical or radiographic evidence of varus or valgus instability is found, an open approach with reconstruction of the collateral ligament is indicated. Otherwise, conservative management and immobilization of the joint in extension can be attempted.

Open Reduction and Stabilization

Open reduction is indicated in cases of avulsion fracture of the humerus at the site of collateral ligament attachment, articular fracture, intra-articular interposition of soft tissues, marked instability or reluxation after closed reduction, and chronic luxation (Figure 53-6). Chronic luxations are often associated with marked fibrosis and contracture that prevent closed reduction. Although elbow joint luxation is rare in cats, open reduction and reconstruction of soft tissues is usually indicated. This recommendation is based on experimental evidence indicating that elbow joint luxation in this species requires transection of both collateral ligaments, as well as on a case report and the author’s personal clinical impressions.^7,40 The goals of open reduction are to reduce the luxation, to assess articular surfaces, and to reconstruct the collateral support structures. Salvage procedures may be considered as an alternative treatment for severely degenerative elbow joints or chronic luxation.

The elbow joint is treated via a caudolateral approach.¹¹⁷ The skin incision extends from the distal third of the humerus to the proximal third of the ulna, cranial to the olecranon. The lateral epicondyle of the humerus usually is difficult to palpate as a landmark because of the lateral displacement of the ulna and radius. If the anconeus muscle has not been lacerated in the injury, a myotomy may be used to further approach and enter the joint. Hemorrhage is minimized if the muscle can be elevated from the olecranon by subperiosteal dissection. The articular surfaces are inspected and the antebrachium manipulated to lever the anconeal process over the lateral epicondylar crest to engage the olecranon fossa. Muscle relaxation and placement of a clamp to allow caudal traction on the olecranon facilitate reduction. A blunt or Freer periosteal elevator can be used to lever the radius and ulna medially, with caution taken to avoid damage to the articular surface. The use of a fracture distractor anchored in the distal humerus and proximal ulna has been proposed to displace the ulna distally in difficult cases.³² After reduction, the joint is thoroughly lavaged and elbow joint stability assessed using Campbell’s test, as was previously described for closed reduction. Reconstruction of supporting soft tissues (joint capsule, muscles, and collateral ligament) is indicated if there is any doubt as to the stability of the joint.

Collateral ligaments can be reconstructed by primary repair with augmentation or ligament replacement with synthetic materials.7,18,108 The lateral collateral ligament can be approached through a caudolateral incision, but access to the medial collateral ligament requires a separate medial approach to the elbow joint. Midsubstance tears tend to be sutured primarily with nonabsorbable suture material in a locking loop or similar pattern, with or without augmentation with synthetic materials or autogenous tissue.¹⁸ Avulsions of humeral attachments of the collateral ligaments can be reattached through transverse bone tunnels in the humeral epicondyle. Alternatively, they may be anchored using screws and spiked washers. Avulsions of the distal attachment of the collateral ligaments are sutured to the annular ligament and surrounding fibrous tissues. Avulsion fractures at the proximal or distal ligament attachment may allow placement of a small lag screw or a tension band device if the fragment is of sufficient size.³²

Damaged ligaments tend to be friable and offer poor holding properties for suture repair. Therefore, ligament replacement is often indicated as an adjunct to primary repair of collateral ligaments, or as a sole repair technique, if the ligaments cannot be sutured. Prosthetic replacement of collateral ligaments requires placement of screws and washers, or bone anchors, at the sites of attachment in the humeral epicondyle and radial neck (Figure 53-7). Heavy nonabsorbable suture is looped over each screw in a figure of eight pattern. Nylon, polypropylene, or a braided polyblend suture (FiberWire, Arthrex Inc., Naples, FL) may be used. Following repair, stability is reassessed and surrounding soft tissues inspected. The flexor or extensor muscle groups are occasionally avulsed from their origin on the humeral epicondyle. If this occurs, they are reattached to the surrounding periosteum and fibrous tissues prior to routine closure of the fascia and subcutaneous and cutaneous tissues. Cases with medial and lateral collateral ligament rupture may be managed by a technique that relies on transcondylar tunnels and biaxial suture repair.⁴⁰ A humeral transcondylar bone tunnel is drilled, starting at the humeral attachment of the lateral collateral ligament, immediately craniodistal to the lateral epicondyle of the humerus, and directed to a point immediately craniodistal to the medial epicondyle. A guide wire may be used to ensure adequate placement before the tunnel is drilled with a cannulated drill bit. A transradial tunnel is created in a lateral-to-medial direction at the attachment of the lateral collateral ligament on the radial head. A transulnar tunnel is created at the level of the midportion of the ulnar trochlear notch, midway between the articular surface and the caudal ulnar cortex. A double loop of braided polyblend suture (FiberWire) is threaded through the humeral tunnel and cut so that one end is passed through each of the distal tunnels. Sutures are tied with half-hitch knots, with the elbow joint maintained in a standing position.

After surgical reduction and stabilization, the joint is evaluated for stability and radiographs obtained to assess alignment and implant positioning. A soft-padded bandage is applied for 24 to 48 hours to improve the patient’s comfort and to minimize soft tissue swelling.

Joint Immobilization and Aftercare

Postoperative management depends on the severity of the injury, the method of repair, and the client’s compliance. External coaptation is indicated after closed reduction to maintain the limb in extension, thereby relying on locking of the olecranon into the olecranon fossa to prevent recurrence. Adjunct fixation is also indicated following open reduction and repair of collateral ligament(s) to allow fibrosis and healing of supporting structures. This recommendation is supported by a nondestructive biomechanical study in which cadaver elbow joints were approached medially with transection of the medial collateral ligament. Operated elbow joints retained only 19% of their original stiffness, and all medial collateral ligament repairs failed from suture pull-out.¹⁴¹ These findings support the need for adjunct fixation after repair of torn collateral ligaments. Although transarticular pinning has been described,^108,124 the standard of care currently consists of providing external support in the form of a splint or a modified external skeletal fixator. In patients with acute luxation and mild residual instability, the application of a well-padded bandage or splint (spica) for 2 to 3 weeks is recommended.^108,135,139 After removal of the bandage or splint, clients are encouraged to initiate rehabilitation measures. Strict exercise restriction is enforced for the first 4 to 6 weeks, but nonforceful passive range of motion exercises and controlled limb use are promoted. The benefits of early mobility of the joint include decreased adhesions between periarticular structures, stimulation of the synthesis of glycosaminoglycans and hyaluronate, encouragement of more orderly collagen deposition and normal cross-linkage, improved joint nutrition, and improved clearance of the joint hematoma.^32,89 Prolonged immobilization (≥3 weeks) decreases synovial fluid production, as well as cartilage stiffness and thickness, and leads to degenerative joint disease and loss of muscle mass and bone mineral content.^14,105 To avoid these limitations, flexible external skeletal fixation has been proposed to maintain the reduction of elbow joints with mediolateral instability.¹³⁹ This technique requires placement of two centrally threaded pins of appropriate diameter parallel to the articular surface of the elbow joint. One full pin is placed in the distal humerus, proximal to the supratrochlear foramen, and the other is placed through the center of the olecranon (Figure 53-8; see also Figure 53-7). The elbow joint is held at approximately 140 degrees of extension while the two pins are fixed to connective bars on the medial and lateral aspects of the joint. Rubber plugs (such as blood sampling tube stoppers) are driven over the pins before and after placement of the elastic bands to prevent migration of the bands, friction against the skin, and other injuries. This rigid frame is maintained until postoperative swelling has decreased, or longer in cases of chronic elbow joint luxation. The connective bars can then be replaced by tight elastic bands on the medial and lateral aspects of the elbow to allow range of motion (see Figure 53-8). A soft-padded bandage should be applied to the limb and changed once daily until soft tissue swelling has resolved. The pin tracts should be cleaned daily initially and as needed after removal of the bandage, and the frame should be checked twice daily after the elastic bands have been placed. Owners should be instructed to watch for migration of the bands or signs of wear and tear. At this point, physical therapy should include warm compresses, passive range of motion exercises, and cold packing. Only short leash walks are allowed, followed by massage of the limb. The flexible external skeletal fixator is usually removed within 3 to 4 weeks after surgery.

Prognosis and Complications

The outcome following treatment of elbow joint luxation has not been assessed objectively, most likely because this condition is uncommon. The prognosis is typically considered as good to excellent when the luxation is treated early, stability is achieved after closed reduction, and physical rehabilitation is started early. One retrospective study reported good to excellent results in about 89% of 35 dogs treated with closed reduction.¹⁰⁸ In another study, a good to excellent outcome was attained in only 8 of 19 dogs (47%) with closed reduction, largely because of residual instability in 7 of these 19 joints.¹³⁵ Therefore, the prognosis is affected by the severity of cartilage and soft tissue damage, duration before repair, degree of persistent instability, and compliance of the client. The most common major complication after a closed reduction is reluxation, warranting open reduction and repair of the collateral ligaments. The most common complication likely consists of degenerative joint disease, observed in all cases in a small retrospective study with long-term follow-up.⁷ Owners therefore should be informed of the likelihood of decreased range of motion and advised about preventive measures against osteoarthritis.⁷

The most common complication specific to flexible fixation of the elbow joint is excessive drainage and infection around the pin tracts.¹³⁹ This complication seems more likely to occur when flexible fixation is applied within 2 to 3 days after surgery, before postoperative swelling has resolved. Other complications include fracture of the olecranon (Figure 53-9), premature pin loosening, pin breakage, and deterioration of the bands.

Treatment

Conservative treatment is an option in dogs with mild clinical signs. Patients should be closely monitored until maturity (see Figure 53-11). Monthly orthopedic examinations are indicated to monitor limb conformation and lameness; serial radiographs are obtained to evaluate joint congruence and continued growth, particularly at the distal ulnar physis. Delaying treatment until skeletal maturity may be advantageous to limit the risk of limb-length discrepancies caused by damage to growth plates. However, delaying surgery increases the risk of irreversible changes such as remodeling of the articular surfaces and degenerative joint disease. Therefore, surgical treatment is recommended based on severity of pain, progressive subluxation of the elbow joint, and remodeling of the radial head.¹⁴⁷ Surgical options include open reduction and stabilization, radial head ostectomy, and arthrodesis.

Open reduction is performed through a lateral approach to the proximal radius.¹¹⁸ An oblique osteotomy or ostectomy distal to the radial physis may be indicated to facilitate reduction. Care is taken to avoid detachment of the proximal radial epiphysis during reduction in younger patients. The joint is stabilized by reconstruction of the lateral collateral ligament and joint capsule in younger patients with mild disease. More severe conditions may necessitate another means of fixation, such as application of bone plates or an external skeletal fixator (see section on traumatic elbow joint luxation) or placement of a screw or pin between the proximal radius and ulna. Surgical synostosis between the ulna and the radius is contraindicated in young and rapidly growing dogs, as this will lead to joint incongruity and potential limb angulation. Resolution of muscle atrophy and normal function were reported in a 4-month-old Dalmatian puppy with type I chronic elbow joint luxation treated with a modified Bell-Tawse procedure.¹⁵⁰ This surgical intervention included four steps: (1) dissection of the soft tissues surrounding the radial head and humeral condyle through a lateral approach radial, (2) wedge ostectomy and counterclockwise rotation of the proximal radius, followed by plate fixation to align load transmission along the axis of the radius, (3) reconstruction of the annular ligament with a muscular fascial strip obtained from the extensor carpi ulnaris muscle (modified Bell-Tawse procedure), and (4) temporary (20 days) humeroradial fixation with a transarticular Kirschner wire. Although further evaluation of this technique is indicated, the approach may be superior to radial head ostectomy, which usually results in poor outcome.³² Arthrodesis of the elbow joint generally is successful in relieving pain but induces a marked gait abnormality. It is considered a superior alternative to amputation and is reserved for chronic dislocations and joints with severe degeneration. Joint replacement has not been reported as a treatment option. Congenital elbow joint luxation is currently considered a contraindication to joint replacement (Loic Dejardin, personal communication).

Aftercare

Radiographs obtained immediately following surgery are evaluated to assess joint alignment and implant positioning. Depending on the method of fixation, a well-padded bandage or spica splint may be applied for 7 to 10 days. If weight bearing is not desired, a carpal flexion bandage may be used to allow passive range of motion of the elbow joint and rehabilitation. Transarticular pins and external skeletal fixators are usually removed after 2 to 3 weeks. If an external skeletal fixator (see section on traumatic luxations) is used, frequent evaluations of the pins and apparatus are necessary to correct possible complications quickly. Physical therapy is encouraged as soon as possible after the elbow joint is stable. Judicious use of swimming, stair climbing, and frequent nonforceful passive manipulation helps restore flexion and extension. Exercise should be limited to leash walks for 4 to 6 weeks.

Complications include reluxation, infection, decreased range of motion, progressive osteoarthritis, physeal arrest, and implant failure or migration. In general, the later the timing of the repair and the more severe the condition, the more guarded is the prognosis.

Diagnosis

Lateral rotation/luxation of the ulna affects predominantly small purebred dogs such as Yorkshire Terrier, Boston Terrier, Shetland Sheepdog, Miniature Poodle, Pekingese, Miniature Pinscher, Pomeranian, Pug, Cocker Spaniel, English Bulldog, and Chihuahua.8,17,97,98 The thoracic limb deformity is typically noted at birth or shortly thereafter, along with variable degrees of lameness. Partial joint flexion and internal rotation of the antebrachium characterize the posture. Bilaterally affected dogs may almost cross their thoracic limbs and be forced to bear weight on the caudal or caudomedial aspects of the elbows and antebrachium. The olecranon can be palpated lateral to the distal humerus, limiting extension of the joint with little to no pain response.

Radiographic findings include craniolateral rotation of the proximal ulna with a relatively normal humeroradial articulation and a narrowed radial neck (see Figure 53-10). The anconeal process and the medial portion of the coronoid process are variably present, and more severe manifestations include lateral displacement of the radial head. In chronic cases, other changes include muscle atrophy and remodeling of the humeral epicondyles, trochlear notch, and olecranon fossa.⁷⁸

Treatment

Conservative treatment may be considered in cases with good function and no pain. However, early reduction and stabilization of the joint are generally indicated, before secondary degenerative and remodeling changes become severe. The principle of treatment relies on closed or open reduction, combined with stabilization of the joint. Technique selection depends on the severity and chronicity of the pathologic process. Both approaches are considered palliative but have a fair to good long-term functional outcome if reduction can be maintained.

Epidemiology

Breeds predisposed to ununited anconeal process consist of large to giant dogs, such as the Bernese Mountain Dog, German Shepherd Dog, Golden Retriever, Labrador Retriever, Mastiff, Newfoundland, Rottweiler, and Saint Bernard Dog.⁸⁴ In a study of breed susceptibility to developmental orthopedic diseases based on data retrieved from 10 hospitals, odds ratios for ununited anconeal process were greatest in Bernese Mountain Dogs and Mastiffs.⁸⁴ Other breeds affected by ununited anconeal process include Great Danes, French Bulldogs, Dachshunds, and Weimaraners.¹⁴⁴ Ununited anconeal process is bilateral in 20% to 35% of affected dogs, and male dogs are affected twice as frequently as female dogs.^61,144 Most dogs present with lameness between 5 and 12 months of age; however, with bilateral disease, owners may not initially identify affected dogs. A subpopulation of mature animals with ununited anconeal process was reported as an incidental finding.

Fragmentation of the medial portion of the coronoid process has been reported in 13% of elbow joints with ununited anconeal process, based on arthrotomy or arthroscopy.⁹⁴ Seventy-two percent of dogs in this study were German Shepherd Dogs, with an overall male-to-female ratio of 2 : 1. Seventy-seven German Shepherd Dogs were diagnosed with ununited anconeal process. Additionally, radioulnar incongruence was diagnosed in 50% of cases, with a radioulnar step greater than 5 mm in five elbow joints.⁹⁴

Pathogenesis and Pathophysiology

The anconeal process articulates with the humerus by engaging the supratrochlear foramen from the olecranon fossa. This process provides stability to the elbow joint by limiting mediolateral movement when engaging the humerus. The anconeal process in small-breed dogs does not have a separate center of ossification.²⁹ In large-breed dogs, especially German Shepherd Dogs, Mastiffs, Basset Hounds, Bloodhounds, and Greyhounds, the anconeal process develops as a single separate center or as several small centers of ossification within the process.¹⁴⁴ In a longitudinal study examining the radiographic appearance of canine elbows, this fusion normally occurred at 14 to 15 weeks in Greyhounds. Fusion occurred later in German Shepherd Dogs, at between 16 and 20 weeks of age.⁵⁵ In this study, postmortem evaluation of dogs with ununited anconeal process documented the presence of an easily movable anconeal process surrounded by osteophytes. Osteophytosis appeared more frequent and more pronounced on the ulna than on the radius or humerus. Compared with other conditions associated with elbow dysplasia, the ununited anconeal process led to formation of the greatest number of osteophytes, and the severity of changes correlated with the age of the dog.

The pathogenesis behind lack of fusion of the anconeal process remains unclear. Nutritional deficiencies, genetic disturbance of growth-stimulating hormones, growth rate, and trauma to the physis have all been advocated as potential causes.¹⁵⁸ In a study of elbow dysplasia in German Shepherd Dogs, three dominant genes were proposed in the transmission of these traits in that breed.²⁹ Ununited anconeal process has also been described as a manifestation of osteochondritis dissecans, with a disturbance in endochondral ossification leading to epiphyseal lysis and ununited anconeal process.^30,144 The microcirculation may become disrupted during ossification, leading to subsequent separation in the weakened cartilage, thus preventing bony union.¹¹¹ The most recent literature describes elbow joint incongruity, radioulnar (short radius syndrome) incongruence, or an abnormally shaped trochlear notch as a likely cause of ununited anconeal process.^{144,158,171,172}

Damage to the distal ulnar physis is the most common cause of asynchronous growth of the radius and ulna. In this instance, the ulna becomes shorter than the radius, thereby decreasing the distance between the anconeal process and the radial head compared with normal joints.¹⁴³ If the radial head is located proximal to the medial portion of the coronoid process, the humeral condyle shifts proximally, leading to excessive force on the developing anconeal process. Repeated microtrauma would damage the center of ossification, leading to failure of union.¹⁴³ This hypothesis is supported by clinical reports of fusion of the anconeal process in young dogs with ununited anconeal process treated by proximal ulnar osteotomy.¹⁴³ A second theory proposing elbow joint incongruity as a cause of ununited anconeal process proposes that a reduction in shortening of the vertical distance between the anconeal process and the radial incisure (decreasing the radius of the trochlear notch) leads to poor articulation between the ulna and the humeral condyle. The disparity between the size of the trochlear notch and that of the humeral condyle was found to increase the loading of the anconeal process, thus preventing its bony union.¹⁴³ Wind hypothesized in 1986 that if the proximal ulna does not grow faster than the humeral condyle, elbow joint incongruence secondary to an elliptically shaped notch can occur.¹⁷¹

Diagnosis

A diagnosis of ununited anconeal process is made easily based on physical examination findings and radiographic changes (Figure 53-12). Dogs with ununited anconeal process present with gradual onset of weight-bearing unilateral or bilateral forelimb lameness that is generally chronic and worse after exercise. Joint effusion tends to be more profuse than with medial compartment disease and can be detected by palpating over the caudolateral aspect of the joint. Pain is elicited during palpation of this region and during extension of the joint.

Radiographic views should include mediolateral, craniocaudal, and hyperflexed lateral projections. The maximally flexed lateral radiograph helps diminish the superimposition of the humeral epicondyles over the anconeal process and the distal humeral physis.27,158 An area of lucency is apparent between the anconeal process and the proximal ulna in elbows in which a ununited anconeal process is present. Other radiographic changes may include periarticular osteophyte production, joint distention, muscle atrophy, and irregular subchondral sclerosis.¹³⁸ Osteophyte production tends to be faster and more pronounced with ununited anconeal process than with fragmentation of the medial portion of the coronoid process or osteochondritis dissecans, and most osteophytes are located in the proximal region of the ulna.⁵⁵ Radiographs of both elbows should be obtained because of the incidence of bilateral disease. Radiographic diagnosis should not be made until after the dog is 22 to 24 weeks of age. Advanced imaging or arthroscopy is recommended to assess the presence of concurrent lesions in the medial compartment of elbow joints with ununited anconeal process. It should also be noted that use of the lateral radiographic projection, which is ideal for identifying ununited anconeal process, causes superimposition of the coronoid processes.⁹⁴ Advanced imaging such as computed tomography or arthroscopy may be considered for diagnosis of concurrent elements of elbow dysplasia.

Treatment and Outcome

The traditional surgical treatment for ununited anconeal process consists of excising the affected process through a caudolateral approach, with a midbelly incision through the anconeus muscle. The fragment is grasped with pointed bone forceps or a towel clamp, and surrounding soft tissue attachments are excised. Early intervention is recommended to optimize functional outcome and minimize the postoperative progression of degenerative joint disease. A retrospective study of dogs with ununited anconeal process treated by surgical excision reported that 90% of owners were satisfied with their dogs’ level of activity after surgery and rated the outcome as good to excellent.¹³⁰ Another study of 16 dogs with a mean follow-up of 19.5 months after surgery reported a normal degree of elbow joint flexion in 58% and normal extension in 84% of operated dogs.¹⁴⁴ Although owners appeared satisfied with the surgical outcome, only 50% of dogs were free of lameness. The postoperative prognosis seems to vary with the measures of outcome tested, and owners should be warned of the progression of degenerative joint disease (50% of dogs were free of lameness).¹⁴⁴ An objective evaluation of function following excision is warranted. Use of force plate analysis to quantitatively measure function in the operated limb compared with unoperated or disease-free limbs would provide a better measure of outcome.

Surgical reattachment of the anconeal process has been proposed as an alternative treatment for ununited anconeal process in dogs younger than 24 weeks of age with a normally formed ulnar notch.¹⁵⁸ The procedure is performed via a lateral approach to the elbow, and the fragment bed is debrided prior to implant placement. The anconeal process is fixed to the proximal ulna by placement of lag screws or Kirschner wires. The implants can be driven from the articular surface or from the caudal aspect of the ulna into the anconeal process. Exact positioning is important, as deviation from the normal position can induce contact between the anconeal process and the olecranon fossa, thus increasing the risk of implant failure.^144,158 Union between the anconeal process and the proximal ulna was obtained 2 to 6 months after surgery in six of ten dogs evaluated retrospectively.⁴⁷ These results are encouraging, but the value of the study is limited by its small sample size.

Another therapeutic strategy for ununited anconeal process addresses elbow joint incongruity as the underlying cause of ununited anconeal process and involves an ulnar osteotomy performed alone or in combination with reattachment of the anconeal process (Figure 53-13). The rationale behind this procedure relies on contraction of the triceps brachii muscle to pull the ulna proximally during weight bearing. This proximal migration of the ulna is expected to restore the natural alignment of joint surfaces, thereby alleviating the biomechanical loads applied on the anconeal process. Restoration of congruity by ulnar osteotomy can encourage union between the anconeal process and the ulna.¹⁴³ The osteotomy is traditionally located 30 to 60 mm distal to the radial head joint surface and is created through a limited caudal approach to the ulna. This proximal location has been recommended to facilitate the proximal migration of the ulna but may be associated with higher morbidity.^119,158 Indeed, a distal osteotomy did not restore the radioulnar contact patterns in an experimental model of incongruity, presumably because the interosseous ligament prevents migration of the proximal ulna relative to the radius.¹¹⁹ The postoperative tendencies for caudal tipping of the proximal ulna and varus deformation can be minimized by orienting the osteotomy in an oblique plane: The osteotomy starts at a proximal, caudal, and lateral point and aims for a distal, cranial, and medial position, about 40 to 50 degrees to the long axis. Alternatively, an intramedullary pin may be placed in the medullary canal of the ulna to maintain the axis of the ulnar displacement.¹⁰⁶ The most common complication associated with this approach is pin migration.

In a study of 21 dogs treated with ulnar osteotomy, the anconeal process healed to the ulna in 15 cases, but a radiolucent line persisted in 6 cases.¹⁴³ Seventeen dogs had a good to excellent clinical outcome. Only one dog had severe osteophytosis on radiographs, and most osteophytes were present before surgery. Results were less favorable in another study of 17 dogs, in which lameness was improved in 21 of 23 elbows, but only 5 of 23 anconeal processes achieved postoperative union.¹⁵⁹ Ulnar osteotomy has been combined with internal fixation of the anconeal process, but additional studies are warranted to evaluate the benefits of this procedure. Only one study reported on long-term outcome in 4 dogs, all with excellent clinical results.⁸³