Iliopsoas (pronounced: ilio-so-as) or hip flexor strains are common injuries both in professional (human) athletes and in dogs. The iliopsoas muscle is the major hip flexor muscle of the dog’s body, bringing the knee up towards his abdomen. We find that dogs have iliopsoas strains for two main reasons.

• First, when a dog has a knee injury, we find that he first withdrawals due to pain, similar to how we would pull our hand away from a hot stove.  He then maintains a posture with hip flexion and his paw non-weight bearing or off of the ground.  This chronic hip flexion results in the shortening of the muscle and creates uncomfortable tension in the muscle, with resistance to stretch.

• The second theorized manner of injury to the iliopsoas is by “doing the splits” whether while running and abruptly changing direction or slipping on ice or ceramic, tile, or hardwood floors.  This injury usually occurs during eccentric muscle activity in which the muscle contracts and is stretched at the same time.

The iliopsoas muscle attaches at the transverse processes (L2-L3) and bodies (L4-L7) of the lumbar spine, the ilium, and the lesser trochanter of the femur. As a result of the initial pain of injury and chronic misuse of the injured limb, on physical therapy evaluation, we find that the iliopsoas muscle might be “adaptively shortened,” tight, and painfully resistant to stretch.

Strains are tears within the muscle or tendon and may be graded dependent upon their severity. A grade I muscle strain might be evidenced by microtears within the muscle belly while a grade III muscle strain is a full-thickness tear or rupture of part of the muscle.  Regardless of the severity of the strain, muscle heals with scar tissue, which is less organized and less flexible than the original muscle tissue. This makes the muscle that is strained more at risk to be strained again in the future. Most other tissues in our body (bone, ligament, skin) repair themselves with tissue more similar to the original, allowing nearly a full recovery.

A dog with an iliopsoas or hip flexor strain might “use” his leg with a subtle or obvious limp at a walk or trot. He might “carry” his leg in a non-weight-bearing manner or skip or hop when trotting, galloping, or running. He might sit in a “lazy” way, not aligning his legs symmetrically.  He might tuck his pelvis or tail more than prior to his injury. Most obvious and almost-diagnostic is the reluctance to allow hip extension with internal rotation. With a belly rub, many of these dogs will stretch their hips backwards, but also turn their knees and paws upwards or outwards (into external rotation). Only when we turn the hip inward do we stress the iliopsoas muscle.

What should I do if I suspect that my pet has had an iliopsoas strain?

First, contact your veterinarian so that other injuries can be ruled out (for example, cruciate ligament tears, osteoarthritis due to hip dysplasia, etc). Your veterinarian might also refer you and your pet to a board-certified veterinary surgeon for further diagnostics. If your veterinarian or veterinary surgeon confirms an iliopsoas strain (through palpation, selective tissue tension testing, CT, MRI, or diagnostic ultrasound), a visit to your pet’s physical therapist should be your next step. Depending upon the stage of healing or the level of discomfort that your pet has as a result of the strain, medications might be prescribed (at least initially) to make him more comfortable. In the meantime, activity restriction (on-leash activity only with no running, jumping, stair, or furniture climbing) should begin.

Here’s hoping your pet never experiences an iliopsoas or other muscle strain and stays off of the DL!