Diagnosing and treating strains and sprains (Proceedings)

Musculotendinous injuries occur infrequently in dogs and cats, but the consequence of such an event can lead to marked dysfunction due to disruption of the muscle-tendon unit (MTU). The MTU is composed of the muscle origin, muscle belly, tendon and tendon insertion. Clinically, MTU disruption causes inability to properly flex or extend the joint served by the affected muscle. Pain, swelling and lameness also are present. Injuries may be acute or chronic. Strain injury is not the result of muscle contraction alone, rather, strains are the result of excessive stretch or stretch while the muscle is being activated. When the muscle tears, the damage is localized very near the muscle-tendon junction. After injury, the muscle is weaker and at risk for further injury. The force output of the muscle returns over the following days as the muscle undertakes a predictable progression toward tissue healing. Current imaging studies have been used clinically to document the site of injury to the muscle-tendon junction. Strains are categorized in a similar manner to sprains: Grade I Strain: This is a mild strain and only some muscle fibers have been damaged. Healing occurs within two to three weeks. Grade II Strain: This is a moderate strain with more extensive damage to muscle fibers, but the muscle is not completely ruptured. Healing occurs within three to six weeks. Grade III Strain: This is a severe injury with a complete rupture of a muscle. This typically requires a surgical repair of the muscle; the healing period can be up to three months. Tendon injuries of the biceps brachii, triceps, patellar tendon, long digital extensor, superficial digital flexor, gastrocnemius, supraspinatis and infraspinatus are most commonly seen. Avulsion of tendons from their bony insertion require reattachment using bone tunnels, screw and washer, bone staple or suture anchors. Muscle belly tears may be treated conservatively or surgically. Conservative therapy may be used with mild injury using cold therapy, laser therapy, and rest initially, followed by heat therapy and rehabilitation exercises. Surgical therapy usually requires debridement of necrotic tissue and primary repair of muscle tissues. Fibrotic contracture of muscle tissues occur secondary to trauma. Fibrotic contractures are generally treated by muscle tendon transaction, Muscle belly resection or tendon elongation.

Tendon injury

Tendon injury usually results from substantial trauma. An important factor to consider in treatment of tendon injuries is the ability to maintain not only structural strength, but also gliding function. Structural strength will be greatest if the structure can be returned to as near as normal as possible; the tensile strength of scar tissue is inferior to that of normal tendinous tissue. Prompt repair of tendinous injuries increases the chance of optimal healing and decreases the amount of scar tissue formation. Scar tissue formation between the tendinous and surrounding soft tissues also leads to adhesion formation and loss of gliding function. Factors to limit adhesion formation include early surgical intervention, meticulous handling of tissues, anatomical apposition of tendinous tissues, adjunctive postoperative bandaging, passive range of motion exercise, and appropriate postoperative restriction of activity. Early healing of tendons occurs with formation of immature collagen during the initial four postoperative weeks. Tensile strength of the repair tissue increases as remodeling of the collagen occurs until about 20 weeks postoperatively.1 Tendon repair is accomplished using a variety of suture materials and suture patterns, depending on the preference of the surgeon. A variety of locking-loop and three-loop suture patterns have been used effectively.1,2 Nonabsorbable suture material such as monofilament nylon, polypropylene and braided polyester is preferable to absorbable material due to the long period of time until adequate tensile strength is reached in the repair tissue. After the tendon is repaired, the paratenon or synovial sheath should also be primarily repaired with appositional sutures if possible. Reestablishment of these structures decreases the chance of adhesions and preserves gliding function.

Repair guidelines for tendons

A tendon surrounded by a sheath will usually not heal spontaneously. The tendon ends will heal in a rounded fashion and function is lost because of loss of continuity of a tendon. A tendon not surrounded by a sheath is thought to regenerate by proliferation and extending a pseudopodial mass to attach to the opposite end that also extends tissue. Regeneration is thought to be a result of haematoma organisation or paratenon proliferation. Paratenon covered tendons are more vascular than synovial sheathed.

     1. After the paratenon and tendon have been completely incised the wound fills with inflammatory products (blood cells, nuclear debris, fibrin). During the first week the fibrin is invaded by fibroblasts (from the paratenon) that combine with invading capillary buds to form the granulation tissue that fills the space between the tendon ends. Fibroblasts begin to synthesise collagen by the 3rd day after trauma

     2. During the 2nd wk a dramatic fibroblastic proliferation and collagen production continues. The growth and migration of fibroblasts and the collagen fibres between the stumps are orientated perpendicular to the long axis of the tendon and the vascular reaction reaches its peak.

     3. During the 3rd and 4th wk the fibroblasts and collagen fibres near the tendon begin to orient themselves // to the long axis of tendon. This orientation is due to directional stress on scar - the more distant or central scar remains unorganised. The difference in orientation of collagen fibres in the newly synthesised scar tissue is defined as secondary remodelling. Two important factors in secondary remodelling are increase in tensile strength and reduction in mass of scar tissue. It continues for many months. Increase in tensile strength suggests orientation along stress lines. Collagenisation continues until 20 weeks. In animals tensile strength is more important than gliding motion

Healing of tendons within a tendon sheath should feasibly occur due to intrinsic repair but in clinical practice is usually a combination of intrinsic and extrinsic.

Suture anchors

Soft tissue fixation to bone is a basic technique of orthopedic surgery for which many procedures and devices have been developed. Early techniques used bone tunnels, screws and washers and bone staples. These techniques are relatively simple, but can have disadvantages including increased surgical exposure, damage to suture material, interference with joint structures and non-isometric placement. Suture anchors, also known as bone anchors, were developed in the late 1980s and present distinct advantages over the above methods. Suture anchors have the advantage of a lower profile than screws and washers, which help avoid interference and abrasion of articular surfaces and adjacent soft tissues during joint movement. They also can be more precisely placed to allow improved reattachment of ligamentous structures to their isometric origin or insertion. Suture anchors can be used effectively for reattaching avulsed soft tissues to bone, thus reestablishing integrity to tendons and ligaments.3 Tendons repaired primarily can also be augmented by placing adjunctive sutures from the injured tendon to tissue anchors placed in bone near the disrupted structure. Lastly, suture anchors can be used to secure luxating tendons in their proper location (Figure 1).

Figure 1: A luxating long digital extensor tendon is secured using suture anchors to create a prosthetic retinaculum.

Biceps tendon injury

Biceps tendon abnormalities are more commonly diagnosed today due to the availability of arthroscopy. The normal biceps tendon has a smooth white surface with a small amount of vascularity at its origin (Figure 2). Bicipital tenosynovitis was once the most common injury to the biceps diagnosed, but this diagnosis was often made based on history, clinical signs and arthrography. Definitive diagnosis was usually not made based on direct visualization or histopathology. This diagnosis is made much less frequently now because many of these patients have been found to have partial or complete tears of the biceps tendon.

Figure 2 Arthroscopic appearance of the normal biceps tendon

Partial biceps tendon tears, complete biceps tendon tears, supraglenoid tuberosity fractures and labral injury (Figure 3). Treatment of the biceps tendon can also be accomplished in some cases under arthroscopic-assistance. Biceps tendon release is easily performed procedure accomplished using a radiofrequency probe or scalpel blade (Figure 4). Arthroscopic-assisted biceps tenodesis is also possible, but is technically more demanding. The surgeon must be cautious not to over-interpret changes seen as generalized inflammation within the joint, such as occurs with OCD, may lead to hypervascularity and synovial proliferation at the origin of the biceps tendon. Removal of the OCD flap leads to resolution of these changes in the tendon (Figure 5).

Supraspinatus tendon

Dogs with injury to the supraspinatus tendon present with a chronic foreleg lameness; some dogs will exhibit periods of non-weight bearing lameness. Lameness is usually minimally responsive to anti-inflammatory medication. Any age or breed of dog can be afflicted; however, the condition is more common in large breeds of dogs. Gait analysis generally shows a visible lameness; occasionally dogs are only lame after exercise. Manipulation of the shoulder (flexion, extension, rotation) will elicit discomfort in most dogs. The differential diagnosis includes OCD, bicipital tenosynovitis and shoulder instability. Radiographic views should include standard lateral projections of both shoulders. Mineralization is seen adjacent to the greater tubercle of the humerus. (Fig. 6) Histologic patterns of mineralization are irregular, non-homogeneous or well-circumscribed and are found in dense foci. A "skyline" view of the bicipital groove is helpful to delineate the location of dystrophic mineralization. Arthrography can be used to outline the bicipital groove to determine if irregularities or filling defects suggestive of bicipital tenosynovitis are present. Computerized tomography (CT) of the shoulder is an excellent resource to delineate the position of dystrophic mineralization. Resection of the mineralized tissue and reattachment of the supraspinatus tendon to a position that is under less tension is performed if physical therapy, anti-inflammatory therapy and restricted activity do not resolve the clinical signs. It is important to note that many dogs with mineralization of the supraspinatus tendon do not show clinical signs of pain or lameness. Dogs having clinical supraspinatus mineralization on one foreleg may have non-clinical supraspinatus mineralization of the opposite foreleg.

Displacement of tendon of the sdf

Displacement of the superficial digital flexor (SDF) tendon is most commonly seen in the hind leg of the Shetland sheepdog, but is also seen in other breeds including the Greyhound, Mastiff, and Weimaraner. Clinical signs include acute or chronic lameness with swelling (bursitis) and pain over the calcaneus. Palpable lateral (in most cases) displacement or motion of tendon is found. The condition can be unilateral or bilateral. Tearing of the medial retinaculum of the tendon occurs, allowing lateral luxaiton of the tendon. The flexor groove of the proximal aspect of the calcaneus may be shallow. Treatment involves stabilizing the SDF in its proper anatomic position by imbrication of the medial retinaculum and placement of an interference post (using a bone anchor) or deepening of the flexor groove of the calcaneus (similar to a trochlear block recession for treatment of patellar luxation). The tarsus should be immobilized for 2-4 weeks and rest enforced for 6 weeks. The prognosis is good following treatment.

Contracture of the infraspinatus

Contracture of the infraspinatus muscle is most common in working or active dogs. It may be bilateral. The condition occursw as a result of traumatic disease leading to incomplete rupture and fibrotic contracture of the muscle. Histology shows hemmorhage, degeneration, atrophy and fibrosis. The patient may have a history of as acute onset of lameness at exercise. Use of the limb improves initially, but an abnormal limb action persists characterized by lateral circumduction of the forelimb with a rapid flip-like extension of the paw when the foot is advanced. The elbow is held adducted and the foot abducted. The dogs are unable to pronate the shoulder and the shoulder range of motion is reduced. The treatment is release of the infraspinatus tendon insertion. The distal part of the tendon is resected. Fibrous adhesions are broken down and the range of motion of the shoulder is restored while the patient is anesthetized. Treatment of this condition has a good prognosis with an immediate improvement in gait in most dogs.

Contracture or fibrotic myopathy of the gracilis

Contracture of the gracilis, semitendinosus and semimembranosus is uncommon, but is primarily seen as a unilateral problem in German shepherd dogs. The condition has also been report in a Boxer and Belgian shepherd. The clinical features include a typical movement or Goose-stepping. Short stride, rapid elastic medial rotation of paw external rotation of hock and internal rotation of stifle during the middle to late swing phase of the stride are also seen.

Palpation of the swollen muscle belly is taut, hard, cold, and non-painful. Passive movements of limb abduction may be reduced. Mineralizaiton may occasionally be seen on radiographic evaluation. Elevation of muscle enzymes is occasionally see. Recommended treatment with myotomy or myectomy has a guarded prognosis as contracture almost invariably recurs within 3-4 months. No response to medical management has been seen.

Avulsion of the insertion of the gastrocnemius (at the calcaneus)

Avulsion of the insertion of the tendon of the gastrocnemius at the calcaneus may be partial or complete. This condition most commonly occurs in Doberman pinschers and Shetland sheepdogs, but may occur in any breed. The SDF and DDF are intact. Clinical signs include hyperflexion of the tarsus and extension of the stifle. A gap may be palpable in the tendon in acute cases. The gap fills in with fibrous tissue & difficult to identify in chronic cases. An avulsion fragment and enlargement of the tendon insertion may be seen on radiographs.

Treatment requires reattachment of the tendon. Holes are drilled through the proximal calcaneus and the tendon is reattached with a locking pulley suture. The tarsus can be temporarily immobilized with a calccaneotibial positional screw. The screw can be removed in 6-8 weeks. The limb should be further immobilized with a splint or heavy bandage while the screw is in place and for 2 weeks following its removal. A transarticular external fixator may also be used. The prognosis is good.

Rupture of achilles tendon

Five tendons make up the Achilles tendon – the superficial digital flexor tendon, gastrocnemius, semitendinosus, gracilis and biceps femoris. The gastrocnemius is the most powerful extensor of the hock. It terminates on the proximal lateral surface of calcaneus, while the common tendon (BF, ST, gracilis) terminates on the medial side. Trauma can result in tearing of one or more components of the tendon. Clinical sings include lameness, hyperflexion of the tarsus, and swelling over the tendon. Surgical repair of the tendon is requires using a locking pulley suture and a immobilization of the tarsus using a temporary calcaneotibial screw, fiberglass splint or transarticular external fixator. The prognosis is good following proper repair.

Sprains are injuries which involve extra-articular or intra-articualr ligaments. The severity of the injury depends on the mode of trauma, age of the patient and general health. Sprains may be classified based upon fibril disruption.

     • Grade I Sprain: A grade I (mild) sprain causes overstretching or slight tearing of the ligaments with no joint instability. Adog/cat with a mild sprain usually experiences minimal pain, swelling, and little or no loss of functional ability. Bruising is absent or slight, and the person is usually able to put weight on the affected joint.

     • Grade II Sprain: A grade II (moderate) sprain causes partial tearing of the ligament and is characterized by bruising, moderate pain, and swelling. A dog/cat with a moderate sprain usually has some difficulty putting weight on the affected joint and experiences some loss of function.

     • Grade III Sprain: A grade III (severe) sprain results in a complete tear or rupture a ligament. Pain, swelling, and bruising are usually severe, and the patient is unable to put weight on the joint. An x-ray is usually taken to rule out a broken bone. This type of a muscle sprain often requires surgery.

The most common ligament sprain in the dog or cat is injury of the cranial cruciate ligament. Optimal outcome is best achieved with surgical intervention in bone the dog and cat. Medium, large, and giant breeds of dogs are usually afflicted with partial ongoing cranial cruciate ligament injuries. Small breeds of dogs and cats are generally afflicted with sudden onset complete tears.

Additional ligament sprains include shoulder luxation/subluxations, elbow luxations, carpal hyper-extension injuries, coxofemoral luxations and tarsal injuries.