The iliopsoas muscle is the combination of the iliacus muscle and the psoas major muscle. The iliacus muscle originates from the ventral surface of the ileum and the psoas major muscle originates from the transverse processes of L2 and L3 (second and third lumbar vertebrae), and the bodies of L4, L5, L6 and L7. Both the iliacus muscle and psoas major muscle insert on the lesser trochanter of the femur. The iliopsoas muscle moves the hindlimb forward through hip flexion.
An iliopsoas strain is the most common muscle related injury in dogs. Iliopsoas strain injuries are caused by excessive stretching of the muscles or stretching of the muscles during muscle activation leading to tears in the fibers. These injuries are commonly seen with high athletic performance such as agility competitors, dogs that play fetch frequently, or those that go hiking a lot. This can occur during rough housing, jumping out of a car, or if the dog slips into a splayed leg position. Iliopsoas strains can also been seen secondary to an orthopedic issue. Rather than it being a primary injury from a quick movement it can be secondary to compensation where the dog is holding it’s leg up more not giving the iliopsoas muscle a break.
Dogs with an iliopsoas strain can present with anywhere from a subtle intermittent hindlimb lameness to severe hindlimb lameness. Agility dogs may slow down through weave poles or knock down poles over jumps with their hindlimbs. When watching the dogs gait we often see external rotation of the hind limb and a reduced stance phase since they do not want to extend their leg back.
We often diagnose iliopsoas strains by exam. These are very painful injuries so we try to catch them by palpating spasming or tension in the muscle belly or at the tendon insertion rather than getting reaction from the dog. The pet will often have a hunch lower back, trigger points in the lumbar paraspinals, reduced hip extension with internal rotation.
Sometimes we can catch signs of an iliopsoas strain on ultrasound. Severe iliopsoas strains may develop into mineralization at the tendon insertion and may be seen on radiographs.
When healing a muscle strain we first focus on pain management through massage, heat therapy, acupuncture, laser therapy, electrotherapy, and PEMF therapy. Sometimes we may start medications in the acute phase such as a muscle relaxer and pain medication. Then we progress into bringing in lots of blood flow to the muscle belly and breaking up mineralization of the muscular-tendon junction. This can be done with laser, ultrasound therapy, or even shockwave therapy.
Once the muscle belly is more relaxed and pain is well managed we progress into light strength building. First we start with isometric exercises where we are asking the muscle belly to contract without shortening or lengthening. After that we progress into concentric exercises where we are asking the muscle belly to shorten and the hip goes into flexion. Following is eccentric exercises where we are stretching the muscle belly while contracting it. These are mostly lunging exercises. Lastly we focus on reintroducing sport activities such as running, jumping, fast turns, quick starts, and stops.
For iliopsoas strain we try to avoid heavy resistance exercises such as hiking or swimming as these may worsen the strain. Activity is well controlled so during the rehab process we do not recommend running, jumping, or playing fetch. Iliopsoas strains need to be treated conservatively and slowly as re-injury can occur.