Management of Muscle and Tendon Injury or Disease

General Principles and Techniques

Muscle Contusion and Strains

A contusion is a bruise of the muscle with varying degrees of hemorrhage and fiber disruption. A strain is a longitudinal stretching or tearing of muscle fibers or groups of fibers. Muscle strains tend to occur near a musculotendinous junction. Muscle strains are categorized as grades 1 through 4; grade 1 strains are disruptions of a limited number of muscle fibers; grade 4 strains are complete ruptures. Contusions and strains result in disruption of the normal architecture of the muscle-tendon unit secondary to interstitial edema, hemorrhage, or overstretching. Compartment syndrome is an increase in pressure of a compartmentalized muscle usually due to trauma.

Surgical Treatment

When a severe contusion is recognized during surgical stabilization of a fracture, decompression of the muscle compartment can be achieved through incision of the epimysium (see p. 1377). Surgical treatment is necessary only if interstitial fluid accumulation causes sufficient pressure to compromise blood flow (i.e., compartment syndrome). Compartment syndrome has been diagnosed rarely in dogs and has not been reported in cats. Fibrotic contracture of the infraspinatus muscle may be a sequela of osteofascial compartment syndrome in dogs (Devor et al, 2006).

Preoperative Management

Surgical intervention should occur as soon as possible. The animal should be confined before surgery to prevent further damage to the muscle.

Anesthesia

Anesthetic considerations for animals with orthopedic disease are given on p. 1046.

Skeletal muscle is made of long, cylindrical fibers encased within connective tissue sheaths (Fig. 35-2). Each individual fiber is enclosed within a sheath called the endomysium. Each fiber bundle is also enclosed within a sheath (perimysium), as is the entire muscle (epimysium). The connective tissue sheaths house blood vessels and nerve fibers that serve to integrate muscle contraction of individual fibers. Muscles are attached to bone by cordlike tendons or flat aponeuroses. The fascial compartment overlying the muscle group appears tight and congested with contusions, and the underlying muscle appears severely bruised and often protrudes from the incision through the fascial compartment.

FIG 35-2 Normal muscle anatomy. Note how the individual muscle fibrils combine to form muscle fibers. Groups of muscle fibers form fascicles, which are surrounded by the perimysium. Groups of fascicles form the muscle, which is covered by a thin fascial layer (epimysium).

Positioning

The animal should be positioned so that the affected muscle group can be exposed. A generous area should be clipped and prepared for aseptic surgery to allow the incision to be extended beyond the boundaries of the affected muscle if necessary.

Surgical Technique

Make an incision through the skin and subcutaneous tissue overlying the muscle to be exposed. Once the muscle group is identified, make an incision through the fascia to decompress the muscle compartment. Suture subcutaneous tissue and skin using standard methods.

Suture Materials and Special Instruments

Self-retaining retractors are useful for retracting soft tissue from the area of interest.

Postoperative Care and Assessment

The wound should be monitored for swelling and/or drainage for 7 to 10 days after surgery. Suture removal can be performed when the skin incision has healed.

Prognosis

Return to normal function should be expected with most contusions and muscle strains; however, repeat injury is likely if adequate rest is not provided.

References

Bar-Am, Y, Anug, AM, Shahar, R. Femoral compartment syndrome due to haemangiosarcoma in the semimembranosus muscle in a dog. J Small Anim Pract. 2006;47:286.

Devor, M, Sørby, R. Fibrotic contracture of the canine infraspinatus muscle: pathophysiology and prevention by early surgical intervention. Vet Comp Orthop Traumatol. 2006;19:117.

Radke, H, Spreng, D, Sigrist, N, et al. Acute compartment syndrome complicating an intramuscular haemangiosarcoma in a dog. J Small Anim Pract. 2006;47:281.

Ragetly, GR, Griffon, DJ, Johnson, AL, et al. Bilateral iliopsoas muscle contracture and spinous process impingement in a German Shepherd dog. Vet Surg. 2009;38:946.

Stahl, C, Wacker, C, Weber, U, et al. MRI features of gastrocnemius musculotendinopathy in herding dogs. Vet Radiol Ultrasound. 2010;51:380.

Definition

Lacerations are tears within the muscle-tendon unit.

General Considerations and Clinically Relevant Pathophysiology

Lacerations are usually due to penetration of the muscle-tendon unit by a sharp object. These injuries most commonly involve tendons near the carpometacarpal and tarsometatarsal joints but may involve muscle units elsewhere.

Diagnosis

Clinical Presentation

Signalment.

Any age, breed, or sex of dog or cat may be affected.

History.

The animal usually has an open wound and a non–weight-bearing lameness.

Physical Examination Findings

Non–weight-bearing lameness is typical after acute penetration of a muscle-tendon unit by a foreign object. The extent of internal damage can be assessed only by visualizing the wound. The wound should be explored after the patient has been stabilized, and this usually requires general anesthesia. Failure to explore the wound can result in lacerations remaining undiagnosed until the patient attempts to bear weight. The greater the time span from injury to repair, the more difficult it will be to appose severed tendon ends.

Dogs with chronic tendon lacerations have lameness exacerbated by exercise. Those with isolated deep digital flexor tendon lacerations have characteristic hyperextension of one digit.

Diagnostic Imaging

Standard craniocaudal and medial-to-lateral radiographs should be taken to determine whether foreign bodies or concurrent fractures are present. Mild swelling may occur in the area of chronic tendon lacerations. Ultrasonography helps localize the site of tendon injury and may differentiate partial from complete tendon rupture. Tendon injuries have a variable sonographic appearance depending on the severity of the trauma and the stage of healing. The normal ultrasound appearance of tendons depends on the incidence of the ultrasound beam. In a sagittal plane, the tendon or ligament will have a parallel, linear fiber alignment pattern that is hyperechoic. Damaged or torn tendons or ligaments will have disruption of the fiber alignment and edema, which appears as hypoechogenicity between fibers. In acute injury, the tendon is often enlarged because of the presence of edema, whereas with chronic injury, thickening of the tendon with focal areas of mineralization may be seen. A complete disruption may be identified by the presence of a hypoechoic band bordered by the retracted hyperechoic tendon ends.

Laboratory Findings

Consistent laboratory abnormalities are not present.

Differential Diagnosis

Muscle-tendon lacerations must be differentiated from superficial lacerations and muscle strain (see p. 1375).

Medical Management

Lacerations that involve a tendon should be managed with surgery; medical management is not indicated. Minor lacerations of muscle may be treated conservatively.

Physical Rehabilitation

Physical rehabilitation may include cryotherapy and pulsed therapeutic ultrasound. Major lacerations of muscle should be treated with a combination of surgical repair and postoperative physical rehabilitation (see Chapter 11).

Surgical Treatment

Muscular lacerations require appositional sutures supported with deeper stent sutures. If the laceration goes through the tendon, delicate manipulation and apposition with small-diameter suture are recommended.

Preoperative Management

The wound should be cleaned and a sterile bandage applied until definitive treatment is performed. Exercise should be restricted before surgery.

Anesthesia

Anesthetic management of animals with orthopedic disease is described on p. 1046.

Surgical Anatomy

Tendons are longitudinally oriented bundles of collagen fibers that are surrounded by loose connective tissue sheaths. Blood vessels and nerves also reside within tendon sheaths. The entire tendon is surrounded by the epitenon, which is enveloped by an outer connective tissue sheath called the paratenon. Tendons crossing joint surfaces are often encased in a tendon sheath to facilitate movement during joint motion.

Positioning

The animal should be positioned so that the tendon and the muscle can be fully exposed. A generous area should be clipped and prepared for aseptic surgery to allow the incision to be extended above and below the injury if necessary.

Surgical Technique

Muscle Laceration

Thoroughly débride the wound edges to fresh, bleeding muscle (Fig. 35-3). Débride carefully to prevent excess removal of tissue, which makes apposition of the severed ends difficult. Place interrupted sutures in the outer muscle sheath around the circumference of the muscle. Support the appositional sutures with heavy stent sutures placed in a cruciate pattern.

FIG 35-3 Repair of muscle laceration with appositional sutures supported by tension stent sutures.

Tendon Laceration

Delicately manipulate and débride the tendon ends. With small, flat tendons, use small-diameter, nonabsorbable material placed in a series as interrupted vertical mattress or cruciate sutures. For larger tendons, select the largest suture diameter that will readily pass through the tendon atraumatically. A locking-loop suture pattern is recommended (Fig. 35-4). Place each loop of the pattern in a slightly different plane (i.e., near-far, middle-middle, and far-near pattern). Alternatively, use a three-loop pulley or a Bunnell-Mayer, far-near, or near-far suture pattern. Use adjoining fascia to support the tendon appositional sutures.

FIG 35-4 Suture patterns used to appose tendon ends.

Suture Materials and Special Instruments

Nonabsorbable or absorbable suture material may be used to repair muscle, provided the material maintains its mechanical strength for 3 to 4 weeks. Nonabsorbable suture material is recommended for tendon repair. Swaged-on needles are helpful in limiting tissue trauma during suturing. Self-retaining retractors are useful for holding surrounding tissue away from the working area.

Healing of Tendons and Muscles

Healing of tendons follows a pattern similar to that of other connective tissue. The inflammatory phase is characterized initially by neutrophils and later by mononuclear cells. Tendon injury is rarely isolated but exists in a zone with other wounded tissue. Unsuccessful attempts to isolate tendon healing from surrounding tissue have led to the concept of one wound, one scar. This implies that successful healing is dependent on activation of undifferentiated mesenchymal cells, which migrate into the wound. Mesenchymal cells produce the collagen and matrix that lend strength to the entire wound. The resultant scar unites the tendon ends, which remodel with collagen fibers oriented parallel to lines of stress. Strength is regained through the one-wound, one-scar principle, but function is regained through active and passive postoperative use of the limb.

Postoperative Care

After tendon repair, the limb should be immobilized for 3 weeks with the use of rigid external coaptation or external fixation with the joint positioned to release stress on the repaired tendon (see p. 1067). However, placement of an external fixator has not been demonstrated to significantly decrease strain in the Achilles tendon (Lister et al, 2009). When the splint is removed, the limb should be semi-rigidly immobilized for an additional 3 weeks with a heavy padded bandage or a half cast (i.e., one side of a split cast applied cranially or caudally to the limb). If an external fixator was used, it may be dynamized by the use of hinges or resistance bands. Hinges placed at the center of rotation of the joint can be adjusted to increase the range of motion and subsequently the tendon load. Elastic bands placed between the pins above and below the joint to replace the side bars allow partial loading of the tendon. After muscle repair, the limb should be immobilized for 5 days, followed by 4 to 6 weeks of protected activity. The use of platelet-rich plasma is under investigation as an aid in the healing of muscle and tendon in dogs (see Chapter 14).