The iliopsoas muscle is formed by the psoas major and iliacus muscles, which mainly arise from the lumbar vertebrae and ilium. They fuse to insert on the lesser trochanter of the femur. This muscle functions as a hip flexor. In sporting and working dogs, acute traumatic strain injury can occur during periods of high activity. A larger percentage of dogs likely have chronic repetitive microtraumatic injury. This type of injury is often correlated with underlying pre-existing neurologic or orthopedic conditions such as lower back pain, hip pain, or stifle disease. Many of these patients have slipped into a splay leg position and have acutely exacerbated a chronic injury.

Diagnosis
Iliopsoas myositis generally results in significant lameness and can be unilateral or bilateral depending on the underlying reason for injury. Direct palpation of the tendinous insertion point of the iliopsoas typically will result in marked discomfort and will confirm this diagnosis. Hip extension and concurrent internal rotation can also cause discomfort, as it increases the pressure on the musculature. Often, the asymmetry of response in a unilaterally affected case is impressive, as dogs with a normal iliopsoas muscle won’t respond to compression at the lesser trochanter. Watch video below to learn more about palpating for an iliopsoas strain.

Physical examination findings are generally diagnostic, but additional characterization can be completed with imaging modalities such as radiography, ultrasound, or MRI. A well-positioned ventrodorsal extended hip radiograph may show a lesser trochanter avulsion fracture or dystrophic mineralization at insertion site. Ultrasound may show evidence of hemorrhage, edema, or fibrosis. MRI is by far the most sensitive modality for detecting musculotendinous injuries.

Treatment
It has been demonstrated that early detection and institution of early treatment will generally result in resolution of an acute injury. These injuries need at least 4-6 weeks of strict rest to prevent repeated trauma. This is absolutely critical to success, and failure of resolution of an acute athletic injury is often the result of poor owner compliance. Physical therapy with stretching and massage can also be pursued during this period of strict rest. Following this period of strict rest, low impact activities, such as leash walks or controlled swimming, should slowly be introduced over a few weeks before concussive activities, like jumping and rough housing, are allowed. Other modalities, such as therapeutic ultrasound with concurrent stretching, may provide benefit. Local injection of platelet-enriched plasma products may be applicable to help repair damaged muscle fibers. This is under investigation in human medicine.

Adjunctive medications can be used. Nonsteroidal anti-inflammatory medications (NSAID) are usually prescribed. Some anecdotally recommend a short course of 7-10 days, but I will often extend this course to 3 weeks if appropriate for the patient. Muscle relaxants, such as methocarbamol, may also provide benefit. Femoral nerve compression can play a role in nerve pain, so gabapentin can also be considered. Occasionally if NSAIDs are ineffective, and after an adequate wash out period, I have had some success with a tapering course of steroids.

Surgical options have been reported in a few canine case studies. If MRI indicates significant fibrosis, tenectomy at the insertion site can successfully relieve the chronic source of pain.

Conclusion
In conclusion, iliopsoas strain is a source of pelvic limb lameness. Palpation and a complete orthopedic evaluation will often result in diagnosis. If discovered in a timely fashion, medical management, adequate rest, and physical therapy are often successful; however, if pain persists, underlying disease must be suspected. An MRI would be of great benefit to assess the musculotendinous and nerve structures in that region if no orthopedic injury can be found to account for the chronic pain. Tenectomy at the insertion site is a viable option to relieve pain if medical management fails.

If you have a patient that you suspect may have an iliopsoas strain, please do not hesitate to contact our surgery team for a consultation. We are always happy to help!