Morphological Variation of PSOAS Minor Muscle

Introduction: The psoas muscle group is part of the posterior abdominal wall and is comprised of long muscles - major, minor. Out of those, only the psoas major muscle is an obligatory muscle present in all individuals. Psoas minor is a slender muscle of posterior abdominal wall, having short fleshy belly and long tendon, lying medial to Psoas major muscle. The psoas minor muscle (PMM) originates as vertical fascicles from the bodies of the last thoracic and first lumbar vertebrae and inserting into the iliopectineal eminence, pectineal line and iliac fascia. It is innervated by ventral ramus of L1 spinal nerve. The muscle provide weak flexion of the lumbar spine. The psoas muscle group, however, is extremely variable and the muscles have differences not only in their structure and morphology but also in their innervation. The psoas minor is an extremely variable inconstant, degenerative muscle. MATERIALS& METHODS: 22embalmed cadavers were used for the present study. Posterior abdominal wall muscles were exposed after removal of abdominal viscera. Presence of Psoas minor muscle was noted. The muscle was cleaned from its origin to insertion. Length and maximum width of its fleshy belly and tendon were measured with the help of digital vernier caliper, thread and scale. Results: The psoas minor muscle was present in one out of twenty two cadavers. During a standard posterior abdominal wall dissection of an adult male cadaver a unilateral left-sided psoas minor muscle was established, with a complete absence of the same muscle on the contralateral side. The unilateral left-sided psoas minor muscle was located superficially and medial to the psoas major muscle. CONCLUSION: The psoas muscle group is one of the most variable muscle groups in the human body. Psoas minor could be bilateral located on both sides of the vertebral column on medial to psoas major muscle. Our case is representation of one of the rare presentation variations of the psoas minor muscle with muscle morphology extremely representative of this type of unilateral variation.