Anatomic variation of the iliacus and psoas major muscles

Routine dissection has identified a previously unrecorded unilateral variation of the iliacus and psoas muscles in a 91-year-old female cadaver. A variant iliacus muscle belly originated from the superior lateral aspect of the iliac fossa and after traversing the iliac fossa in a nearly horizontal plane, inserted into the psoas major muscle forming a blended iliacus-psoas muscle. The femoral nerve coursed laterally behind the muscle variant to the superior edge of the blended iliacus-psoas. The femoral nerve then coursed over the anterior aspect of the muscle variant and continued inferiorly in a typical course toward the inguinal ring. The current findings and clinical significance are discussed.