Iliac Attachment of the Psoas Major Muscle: Anatomical Study of a Novel Muscle Attachment

The iliopsoas muscle is important functionally and is often encountered during various surgical procedures. During routine cadaveric dissection, a previously undescribed muscular structure was located deep to the iliacus muscle and coursed inferomedially to merge with the posterior aspect of the psoas major, running over the iliopectineal bursa. A cadaveric study was performed to better understand this muscle attachment. Two hundred embalmed adult human cadaver donor sides were dissected. The iliacus and psoas major muscles were carefully detached from their origins and reflected anteriorly to expose the iliac fossa. Particular attention was directed toward identifying accessory muscular slips, distinct structures from the medial aspect of the iliac fossa. When present, the accessory muscles were documented according to presence and anatomy. Selected measurements were made of the muscle and its distance to surrounding structures. Histological analysis of the muscle was performed. An accessory attachment of the psoas major was identified in 28% of sides. This structure was located deep to the iliacus and distinct from the more laterally placed iliocapsularis muscle, although the two muscles traveled in the same plane. This muscle's vertically oriented fibers were lateral to the anterior inferior iliac spine, the lumbosacral trunk, and the obturator nerve. The iliopectineal arch gave rise to this muscle's medial attachment. Its origin was from the medial aspect of the ilium near the arcuate line. The muscle had a variable length, but distally, always attached to the deep surface of the psoas major, usually near the level of the inguinal ligament. Its mean length and width were 83.4 mm (52-100.4 mm, SD 10.4) and 11.3 mm (9.6-15.4 mm, SD 3.1), respectively. Histologically, the iliac attachment of the psoas major was composed of typical skeletal muscle fibers that had an intimate relationship to the underlying iliopectineal bursa. An accessory muscular structure located along the arcuate line of the ilium was identified in 28% of hemipelves examined. We have termed this muscle the iliac attachment of the psoas major. It demonstrated a consistent fascial separation from the overlying iliacus and merged with the psoas major inferiorly. Its anatomical position suggests a potential role in stabilizing the psoas major muscle and is related to the anterior hip joint. Further investigation using imaging correlation and biomechanical modeling is necessary to clarify its functional significance. Recognition of this variation may be relevant for surgeons treating hip pathology and for anatomists describing muscular variations of the iliac fossa. To our knowledge, this is the first report of an iliac attachment of the psoas major in humans.