Psoas Minor: Major Confusion

Abstract

Introduction & ObjectiveThe psoas minor muscle is found in the retroperitoneum with close association to the psoas major and iliacus muscles. Major anatomical textbooks fail to offer a clear consensus on psoas minor, providing conflicting information on the insertion site, function, and relationship to the iliopsoas complex. Reported prevalence of the psoas minor muscle ranges from 40‐65% in each individual hip, but available research is limited by sample size or is not representative of U.S. demographics. Accurate descriptions of the structure of the psoas minor muscle would allow for improved hypotheses regarding muscle function and repercussions of muscle dysfunction. This study aims to document the presence and insertion of the psoas minor muscle in a U.S. donor population, suggest an alternative source to lumbar back pain, and discuss ramifications of muscle dysfunction and applicable osteopathic intervention.Materials & MethodsAt this time, eleven donors were evaluated in the Sam Houston State University College of Osteopathic Medicine’s Human Anatomy Lab. The presence or absence of the psoas minor muscle was determined bilaterally. Muscles were manually traced from origin to the tendon and then the point of insertion. If needed, the inguinal ligament and anterior pelvic structures were dissected for better visualization. Findings were recorded in a secure database and photographed.ResultsThe psoas minor muscle was present bilaterally in seven donors, present unilaterally in one donor, and bilaterally absent in three donors. On all donors evaluated, the insertion site was the pectin pubis with distal blending of the tendon with iliac fascia.Significance & ConclusionAnatomical texts have a variety of descriptions for the documented insertion, such as the pectin pubis, iliopubic eminence, arcuate line, pectineal line or iliopubic ramus. In this study, donors with a psoas minor muscle were determined to have a common insertion site: the pectin pubis. Muscle origin (lateral surface of T12‐L1 vertebral bodies and discs) and bilateral presence (n=7/11; 63%) in the study aligned with current literature.Findings of this study support hypotheses of alternative sources of dysfunction that may contribute to lumbar back pain and hip snapping syndrome rather than more commonly reported sources, such as lumbar back musculature or the iliacus and psoas major muscles. Proximal dysfunction of a psoas minor muscle may contribute to lumbar back pain by abnormally rotating the originating vertebrae in the direction of the hypertrophic muscle. Distal dysfunction may contribute to hip snapping syndrome, in which the iliopsoas tendon “snaps” over the iliopectineal eminence when returning the leg from a position of flexion, abduction, or external rotation. From an osteopathic manipulative approach, the psoas minor may be treated with counterstrain techniques or muscle energy to the lumbar spine to restore normal tone and function. We will continue to collect data in an ongoing study in order to provide an evidence‐based recommendation for the reporting of psoas minor insertion and function, as well as the presentation and potential treatment of psoas minor dysfunction.