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.

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.