Muscle Injuries of the Hindlimb (insertion gastronemius, iliopsoas, ...)

Iliopsoas muscle
As its name implies, the iliopsoas muscle comprises of 2 muscles: the iliacus and the psoas.

Origin:

1. iliacus: originates on the ventral surface of the ilium
2. psoas major: originates on the transverse processes of the vertebral bodies of L2 and 3, attached at its mid body to the ventral surfaces of the vertebral bodies of L4 to L7.

Insertion: The two muscle bellies join together at the level of the ilium and insert as a common tendon on the lesser trochanter of the femur.

Function: to flex the hip and stabilise the lumbar spine. Innervation is by the lumbar and femoral nerves.

Injuries are usually the result of chronic repetitive sprains although acute injuries do occur. Laceration or blunt trauma are unlikely injuries as the muscle is so deep. Fibrosis secondary to migrating grass seed and haemangiosarcoma have been reported.

Diagnosis: Injury to the iliopsoas muscle is uncommon and is associated with lameness. Considering the anatomy of the muscle, manual extension of the hip with internal rotation of the hip would be expected to be painful. This is not specific to iliopsoas muscle injury and pain on direct palpation of the muscle as it runs ventral to the ilial wing to insert of the femur is a much more reliable finding. Pain may also be evident on palpation of the epaxial musculature lateral to the midline on the affected side of the lumbar region.

An interesting feature of iliopsoas muscle injuries is that they can be associated with femoral neuropathy (reduced ability to hold the stifle in extension, decreased patellar reflex, reduced flexor withdrawal, quadriceps atrophy and reduced sensation to the medial thigh and distal limb) (Stepnik et al 2006). The femoral nerve courses through the iliopsoas muscle and its function can be affected by the swelling associated with myositis. Compression of the femoral nerve may be very painful.  [...]