Hind limb sprains and strains (Proceedings)

The most common hind limb orthopedic/sports medicine conditions afflicting active dogs are iliopsoas strains, cranial cruciate ligament (CCL) insuffiency and gracilis and semitendinosus contracture. Of the hind limb muscular injuries iliopsoas strain is, by a considerable margin, seen more frequently than gracilis and semitendinosus contracture. Because contracture of the gracilis and/or semitendinosus is less common, it is often undiagnosed until significant pathology is established. Diagnosis and treatment in early stages of the disease process can significantly inhibit progression. For these reasons, it is included in this presentation.

Iliopsoas strains

Acute, stretching-induced muscle injuries are estimated to account for over 30% of injuries seen in a typical human sports medicine practice and have been reported to be the most common injury seen in human general practices. Acute muscle injuries have rarely been reported in the small animal veterinary literature, and discussion of chronic muscle disorders in dogs is limited to a handful of classical syndromes or inflammatory conditions. Given the similarities between the human and canine musculoskeletal system, it seems unlikely that such common injuries in human athletes would not also be common in the canine athlete. It is probable that the low reported prevalence of muscle injury in dogs is due to a failure to diagnose the condition.

Anatomy

The iliopsoas muscle represents the fusion of the psoas major and the iliacus muscles as seen inthe anatomy illustration. The psoas major muscle arises from the transverse processes of the lumbar vertebrae of the lower spinal column at L2 and L3 and the bodies of L4-7, and the iliacus arises from the ventral or lower surface of the ilium. The two muscles combine and have a common insertion on the lesser trochanter of the femur. The action of this muscle is to move the pelvic hind limb relative to the trunk via hip flexion, primarily moving the pelvic hind limb forward.

Cause

Iliopsoas strains occur as the result of excessive force acting on this muscle, and are commonly associated with highly athletic activities such as agility. These injuries often occur at or near the muscle-tendon junction, which is the weakest part of the myotendinous unit. Eccentric contraction, in which the muscle is activated during stretch, is known to be an important factor in the development of these acute strain injuries. Traumatic incidents that result in active eccentric muscle contraction, such as slipping into a splay-legged position, jumping out of a vehicle, aggressive agility training, or roughhousing with other dogs are often suspected in precipitating acute lameness. It is not uncommon to find dogs with iliopsoas strains that have other concurrent orthopedic problems, or that have recently undergone surgical treatment for another orthopedic condition, such as cranial cruciate ligament rupture.

Diagnosis

Dogs with iliopsoas strains commonly present with a history ranging from a subtle intermittent offloading of the hind limb to significant unilateral hind limb lameness that is exacerbated with activity. These dogs commonly demonstrate performance issues such as knocking bars with the hind limbs and slowing in the weave poles.

On direct palpation, discomfort and spasm of the myotendinous unit may be noted. Pain and spasm will also be noted when stretching the myotendinous unit by either placing the hip in extension with abduction, or by simultaneous extension of the hip with internal rotation of that pelvic hind limb.

Radiographs are of little value in the early phase, but may reveal mineralization just cranial to the lesser trochanter in chronic cases. The use of advanced imaging modalities to demonstrate lesions of the affected muscle and/or tendon can increase confidence in the diagnosis. Ultrasonography is a relatively inexpensive noninvasive imaging modality for canine musculoskeletal evaluation with the additional advantage that general anesthesia is not required. This imaging modality is particularly dependent on the expertise of the operator, which may limit its practical application in some settings. Advanced diagnostics such as CT (computerized tomography) scan and MRI (magnetic resonance imaging) may be used to identify iliopsoas strains and are both widely used in diagnosing acute, stretch-induced muscle injury in human patients. Although CT is valuable for imaging soft tissue lesions, the use of MRI has greatly increased the ability to detect submacroscopic lesions.

Treatment

Acute iliopsoas strains should be treated conservatively. Skeletal muscle relaxants may be administered in severe cases to reduce pain and muscle spasms. Medical management may also include NSAIDs, cryotherapy and controlled activity. Rehabilitation can be very effective in treating iliopsoas strains. Treatments may include laser therapy to increase circulation, remove waste products, and promote healing. Pain-free PROM (passive range of motion) and high-repetition exercise also are recommended. Acute strain injuries should not be stretched as microtears may occur. Core strengthening is essential in the return of the athletic dog to competition and a pain free lifestyle. Activities such as theraball work needs to be performed to work on the dog's core control – the lower back and abdominals. Since the origin of the iliopsoas is the lumbar spine, the lumbar spine and lumbosacral area may need to be treated in acute cases. PROM, interferential e-stimulation, stabilization exercises, and gradual increases in weight bearing of the involved limb are recommended. Active ROM and strengthening exercises are added next. Strengthening exercises might include stepping over cavaletti poles, para standing (lifting both front and hind limbs on one side of the dog's body while he balances on the remaining limbs), paws on the counter, and use of the wobble board. Hill walking should be added to increase the strength of the caudal musculature. A steep hill, approximately 20 to 40 degrees in incline and the dog should be slowly walked up the hill. It is important that the dog walks and not bunny hops or trots up the hill. Slow walking will promote an equal balance of each hindlimb and focus on the caudal musculature, the hamstrings and the gluteals. The dog should be walked up approximately 100 feet and then slowly walked down. The downward motion will work the iliopsoas in an eccentric fashion. This can be repeated three to five times, and repeated a few times during the week. Acupuncture may be helpful to assist with pain control and to promote healing, including the lumbar and lumbosacral region. Joint mobilization and other manual therapy may also be needed to assist with the lumbar range of motion and motion of the coxofemoral joint.

In chronic iliopsoas strains, it is important to re-initiate the inflammatory process to assist in the remodeling of the tendon fibers. NSAIDs should be avoided with chronic iliopsoas strains as they impair the inflammatory response. Rehabilitation therapy is recommended with chronic iliopsoas strains. Modalities might include heat, ultrasound, and laser, followed by massage therapy. Be sure to check movement in the sacroiliac joint (SI joint) and lumbar region (lower spine). Chronic iliopsaos strains may come from a problem with mechanics, therefore, working on correcting the mechanics of movement, will help to take the strain off the iliopsoas and contribute to its healing. If you miss correcting movement mechanics, it may not get better. The exercise progression is similar to that for acute iliopsoas strains, but initiating stretching (hip extensors with abduction) after modalities and massage is advised as are longer walks. In chronic muscle strain injuries it usually takes longer to recover and progress through the stages of healing and exercise because of the chronic nature of the changes in the myotendinous unit. Education of owners/trainers is extremely important since they should be instructed to move the dog ahead slowly. Core strengthening and activities focusing on the strength of the gluteals and hamstrings, as well as the eccentric strength of the iliopsoas should be focused on. The underwater treadmill, hiking and hill work are all appropriate. With regard to aquatic therapy, swimming may aggravate the iliopsoas injury as it forces the body to maintain the hip in a shortened or flexed position.

When returning to agility training, weave poles and tight turns at full jump heights should be avoided during the early stages of retraining. The risk of reinjury to a previously strained muscle is well established in human patients when a previous minor injury often predates a major strain injury. The risk of more significant strain is increased when pre-existing strain injury has not completely healed. This also appears to be the case in canine patients, in whom pain from iliopsoas strain injuries may recur. Appropriate warm-ups, stretching, and retraining are extremely important in preventing injury and in returning your dog to a competitive performance level. Examples of retraining techniques for iliopsoas strains include starting with low, straight-line jumps, and later incorporating very wide sweeping turns that progress over time to higher jumps with tighter angles. Do not include higher jumps and weave poles until late in the retraining period. It has been well-reported that stretching without an appropriate warm up is detrimental to both the dog's tissues and his performance. In fact, it is much more important to do an appropriate warm-up than stretching if time does not permit both. Following training and performance, make sure to implement iliopsoas stretching techniques (hip extension with abduction) and use an appropriate cool down with ice therapy (5 minutes on, 5 minutes off, 5 minutes on).

Surgical treatment is warranted for those that do not respond to conservative medical management and rehabilitation therapy. In these cases, where there are irreversible changes to the myotendinous unit, such as fibrosis (forming excess fibrous tissue while healing) of the muscle-tendon junction, surgical treatment by tenotomy/tenectomy (releasing the tendon) or reattachment may be indicated. Surgical intervention should be considered when the strain injury recurs at regular intervals or does not respond to medical treatment or rehabilitation therapy, although the lesion should be first confirmed with ultrasonography, CT, or MRI imaging. Good to excellent results have been reported with dogs returning to function although performance dogs may work at a lower level.

Cranial cruciate ligament insufficiency

Although the knee joint in dogs is similar to ours, the forces applied to the joint during weight bearing are vastly different. Our hip, knee and ankle joints are perpendicular to our weight bearing surface, our feet. When we stand, there is minimal stress to the ligaments in our knee. Dogs, however, stand on their toes with the ankle elevated and the knee forward. The top of the dog's tibia (tibial plateau) is sloped and weight bearing creates a force that pushes the femur down the slope of the tibia. This force is called "tibial thrust" and it is the job of the CCL is prevent this motion. Each time the dog bears weight, the CCL is called to work. If you think of the tibial plateau as a hill and the femur as a car parked on the hill, the CCL is the break. If the ligament ruptures, it allows the femur to slide down the slope or, in our example, the break releases and the car rolls down the hill. When the ligament is ruptured, each time the dog bears weight this motion occurs and causes discomfort. Within the joint, there will be inflammation and swelling, referred to as synovitis and effusion.

Cause of injury

Rupture of the CCL can occur in several different ways. There may be a single incident which causes a sudden complete rupture of the ligament. When this occurs the dog is typically painful and non-weight bearing. The rupture can also occur over time. Dogs with a high tibial plateau angle (greater slope) have greater stress to the CCL and the ligament can tear incrementally. Dogs can also partially tear the ligament due to an incident. With a partial rupture, the dog typically experiences an intermittent lameness. The majority of partial ruptures will progress to a complete rupture within weeks to months. Common causes of partial and/or complete ruptures include hyperextension and internal rotation of knee from sudden turns or stepping into a hole; jumping if force of cranial tibial thrust exceeds breaking strength of CCL; repetitive normal activities; and degeneration with aging. Obesity can increase the risk of a rupture as can the "weekend warrior" routine, in which the pet is relatively inactive during the week but very active on weekends. Dogs that have ruptured their CCL in one knee have a 50% - 70% chance of rupturing the CCL in their other knee. Therefore, surgical correction is recommended as soon as possible to decrease the stress placed on the uninjured CCL, thereby, decreasing the risk of CCL rupture to that knee.

Clinical signs

If the CCL rupture is complete and acute, often the pet will be non-weight bearing lame. However, in the case of a partial or gradual rupture, the pet will be weight-bearing lame or have an intermittent lameness. Lameness will often worsen with activity. Stiffness upon rising and/or a stiff gait is another common complaint. You may note that the dog sits with the affected leg out to the side. He or she may have difficulty rising and be less active. Physically, you may note a swelling or thickening of the knee and muscle atrophy (wasting) in the affected limb. Dogs which have ruptured the CCL in both knees do not routinely carry or off-load a particular limb since they do not have a good limb to stand on.

Diagnosis

Diagnosis of CCL injury can be determined on palpation (cranial drawer test and/or cranial tibial thrust test). Partial CCL ruptures can be identified by thrust or drawer while the stifle is in flexion. In addition, the McMurray test may be performed to assess for meniscal injury. Radiographs are typically obtained and will reveal effusion and peri-articular osteophytosis (depending on the chronicity). If these tests alone are not completely diagnostic, arthroscopic evaluation of the joint and structures may be recommended. If arthroscopic evaluation reveals the ligament is injured, a stabilizing procedure can then be performed.

What are the non-surgical options for a ruptured CCL?

Treatment for Grade 1 sprains of the CCL may include rehabilitation therapy, a hinged functional stifle brace and in some cases regenerative medicine (stem cell therapy). Dogs with complete CCL ruptures who are not surgical candidates due to financial constraints, concurrent medical issues, etc may also benefit greatly from rehabilitation therapy and a functional stifle brace. These devices are covered in greater detail in the notes and lecture for Orthopedic Devices.

What are the surgical options for a ruptured CCL?

There currently is no "best" CCL repair technique. There is however, a "best" technique for each individual patient based on certain variables. These variables include the patient's age, breed, size/weight, tibial plateau slope, activity level and desire for return to work/sport.

Current surgical options include the lateral suture technique (extracapsular stabilization); TightRope stabilization (TR); Tibial tuberosity advancement (TTA); and the tibial plateau leveling osteotomy (TPLO). Each of these procedures has its "advantages" and "disadvantages" and will be discussed during the presentation.

There are numerous studies indicating the positive benefits of rehabilitation therapy following CCL surgery. In summary, rehabilitation therapy has been shown to improve muscle mass and attenuate muscle atrophy that occurs in the post-operative period, increase stifle joint ROM, especially extension, improve weight-bearing as measured by force plate analysis, and reduce the progression of osteoarthritis.

Rehabilitation guidelines following stifle surgery are structured to direct the clinician in returning dogs to pre-injury activity levels as quickly and safely as possible. Criterion-based protocols eliminate subjective progression through rehabilitation by dictating the milestones that must be reached in order to progress to the next phase. The rate of progression can differ between dogs and is dependent on the individual rate of healing and the demands of the dog's activity level. Also, clinicians should prescribe therapeutic interventions within each phase that are tailored to the patient's needs. Prescribing therapeutic interventions in a 'cookbook' fashion for each particular diagnosis is committing a disservice to the patient.

Gracilis and semitendinosus myopathy/contracture

Muscle contracture is defined as, 'The abnormal shortening of muscle tissue, rendering the muscle highly resistant to stretching. A contracture can lead to permanent disability. There is a significant difference between muscle contraction and muscle contracture. Contraction refers to the normal physiological process of muscle shortening, resulting in work. Contracture refers to the abnormal pathologic process resulting in fibrosis and permanent damage to a muscle. It is important to remember that a muscle can have a significant amount of scar tissue from prior injury and still not be considered a contracture based on its ability to function. The pathological process of muscle contracture is characterized by replacement of most or all of the entire muscle and/or associated tendon with fibrous connective tissue. This process can take weeks to months and leads to shortening of the affected muscle or muscle group. A muscle contracture can also severely affect the associated joints by fixing them in flexion or extension. In general, muscle contractures of the forelimb respond better to treatment and carry a better prognosis than muscle contractures of the hind limb.

Canine muscle contracture is reported to affect several different muscles, is associated with a number of predisposing factors, and a varying prognosis depending upon which muscle is affected. Most patients suffer some form of trauma weeks to months before the contracture is present. The clinical signs include: lameness, pain, weakness, decreased range of motion, a firmness noted throughout the entire muscle, and usually a characteristic gait. Pre-disposing factors for muscle contracture include: compartment syndrome, infection, trauma, repetitive strains, fractures, infectious diseases, immune-mediated diseases, neoplasia, and ischemia. Contractures of the gracilis and semitendinosus may be concurrent or found individually. History associated with a contracture of the gracilis and/or semitendinosus typically consists of a single or repeated strain injury with a gait abnormality developing afterwards. Gait abnormalities usually start abruptly and progress over a period of six weeks to months, at which time it becomes static. With gracilis contracture, during locomotion, the affected leg is raised in a jerky fashion with the hock hyperflexed and rotated laterally, the metatarsus is rotated medially, and the overall stride is shortened. A shortened stride with a rapid medial rotation of the paw, external rotation of the hock and internal rotation of the stifle mid stride is noted with contracture of the semitendinosus. There does appear to be some breed and age predilection, however, the sex of the animal does not have an appreciable influence. Gracilis muscle and semitendinosus contracture most often affect highly active German Shepherd Dogs and Shepherd related breeds between the ages of three and seven years. The suspected cause in the working and performing German shepherd is repetitive strain injury leading to secondary contracture.

Anatomy

The gracilis in the dog forms an extensive broad muscular sheet that is found in the superficial layer of the caudal portion of the inner surface of the thigh. The muscle arises from the pelvic symphysis and ends along the entire length of the cranial border of the tibia. An aponeurosis also spreads out into the crural fascia and from its caudal border sends a well developed reinforcing band to the calcanean tendon and attach to the tuber calcanei. The gracilis is responsible for adduction of the thigh, extension of the hip and extension of the hock.

The semitendinosus arises from the tuber ischiadicum and inserts distally on the medial surface of the tibia; it also inserts by means of a fascial attachment on the tuber calcanei. It is responsible for extension of the hip and tarsal joints and flexion of the stifle joint in the free non-weight bearing limb.

Cause

Skeletal muscle tissue cells have a very limited ability for regeneration, and differ somewhat from cardiac muscle cells which are classified as nondividing cells that cannot undergo further mitotic division in the postnatal life, and differing greatly from smooth muscle cells which are classified as quiescent cells that have a moderate capacity for regeneration and can be driven into the G1 mitotic phase of regeneration after damage. Repair to damaged muscle tissue begins early in the inflammatory cascade and involves two processes: regeneration of injured tissue by parenchymal cells of the same type, and replacement by connective tissue (fibroplasia). The balance of the two dictates how well new skeletal muscle tissue is produced and how much scar tissue is formed. It appears to be this limitation for skeletal muscle cell regeneration that drives the formation of scar tissue and inevitable fibrosis after skeletal muscle trauma instead of regenerating new cells and replacing the damaged.

Fibrotic myopathy or muscular contracture is a chronic, progressive disorder of severe muscle contracture and fibrosis. The exact cause is usually unknown. The fibrotic myopathy may result from acute trauma, chronic repetitive trauma, autoimmune disease, drugs reactions, infections, neurogenic disorders and vascular abnormalities. Ischemia secondary to indirect trauma may also lead to fibrosis and contracture. Histologically, muscle is replaced by dense, collagenous connective tissue. In humans, indirect muscle injuries occur subsequent to rapid acceleration during athletic activities. Muscle strains are caused by excessive force or stress on the muscle that induces tearing of muscle fibers or, most often, tearing of the musculotendinous junction. The type and severity of injury determines whether the muscle heals predominately by regeneration of functional myofibrils or by scar formation. Severe damage to a muscle is followed by fibrosis and contracture, with minimal regeneration. Although fibrous scar tissue provides tensile strength and plays a part in normal muscle healing, excessive scar tissue impedes muscle fiber regeneration and interferes with muscle contraction and relaxation, resulting in varying degrees of mechanical lameness.

Muscle injuries in dogs may be underestimated because of the failure to establish a definitive diagnosis, poor recognition of muscular damage when accompanied by concurrent, more severe trauma, and problems with the classification of muscular trauma. Muscle injuries are said to account for only 5% of reported musculoskeletal disease. Lameness is usually more intense in the acute phase and improves with time. When injured muscle undergoes fibrous contraction, a mechanical lameness may remain.

Diagnosis

Presentation of gracilis and/or semitendinosus contracture is very unique and consistent and diagnosis can be effectively made with a thorough history, observation of gait and physical examination.

Most contractures have a history of acute injury or lameness weeks to months before the onset of contracture. The lameness and initial swelling usually subsides with supportive treatment, however, clinical signs of the contracture present a few weeks later. Dogs typically have a hind-limb gait abnormality characterized by a shortened stride with a rapid, elastic medial rotation of the paw, internal rotation of the hock and external rotation of the calcaneus [corrected] and internal rotation of the stifle during the mid-to-late swing phase of the stride.

Physical exam may be normal, except for a firm mass within the gracilis and/or semitendinosus muscle(s). Typically, a taut, firm band is palpable in the caudo-medial aspect of the thigh.

A complete chemistry panel and CBC are usually within normal limits, however, creatinine phosphokinase (CK) may be elevated. Radiographs of the hind limb are typically normal, however an increased radiopacity may be observed between muscle and the lower tendon junction in some cases. Ultrasound may be a useful diagnostic tool and may reveal a slightly echogenic muscle. MRI may also be useful for diagnosing this condition in both the acute and chronic phases. Histopathology of the contracted muscle typically shows replacement of degenerating myofibers with connective tissue. The findings are consistent with primary myopathy due to polyphasic muscular damage (degeneration, segmental necrosis, phagocitosis, and fibrosis).

Treatment

Medical management prior to or in lieu of surgery was attempted in a previous report with no apparent response. Fifteen dogs had one or multiple surgical procedures. Although transection, partial excision, or complete resection of the affected muscle resulted in resolution of lameness following surgery, lameness recurred six weeks to five months (mean, 2.5 months; median, two months) following surgery. Adjunctive medical treatment did not prevent recurrence. Variable replacement of the affected muscle with fibrous connective tissue (predominantly along the caudolateral border of the muscle) was evident grossly, and replacement of myofibers with fibrous connective tissue was confirmed histologically. A definitive etiology could not be established. Myectomy of the entire gracilis muscle still has a poor prognosis because the gait abnormality will still return within three to five months due to semitendinosus involvement.

Rehabilitation therapy is currently the treatment of choice. Rehabilitation therapy may consist of continuous ultrasound therapy, manual therapy and a home therapeutic exercise program including massage and stretching. While rehabilitation therapy may significantly improve the gait abnormality and function of the hind limb in chronic cases it rarely leads to complete resolution of clinical signs. Working Shepherds with this condition may continue to remain on active duty, however a continued rehabilitation and home maintenance program is crucial.

Education for all German Shepherd and Shepherd related breed owners and handlers is an important component to prevention. Appropriate warm-ups, active stretching followed by cool-downs and passive stretching and massage should be performed whenever possible before working and events.

Conclusion

Performance dogs can have a wide range of sport-related conditions and injuries. A sound knowledge base of structure and biomechanics and of the sport involved aids in successful rehabilitative management. In addition, rehabilitative needs may change as the patient progresses through therapy and returns to activity, therefore, appropriate and successful rehabilitative management requires constant reevaluation of the patient and modification of the rehabilitation therapy program to address those changing needs.