Distal semimembranosus muscle-tendon-unit review: morphology, accurate terminology, and clinical relevance

Abstract

Background: Our knowledge of the stability of the posteromedial knee is evolving. The distal semimembranosus is an important posteromedial stabilizer of the knee. Current anatomical texts and atlases do not accurately detail the distal insertion. Journal literature commonly mentions multiple distal insertions, one of which contributes to the oblique popliteal ligament. The purpose of this study was to review the literature, current morphology, terminology and clinical relevance of the distal semimembranosus muscle-tendon-unit (SMTU), and suggest alternative nomenclature.

Methods: Literature search was conducted on anatomical and clinical texts, atlases, journals and websites to analyze the distal morphology of the semimembranosus muscle. Deep dissections were performed on 31 embalmed cadavers, 56 knees in total (27Rt and 29L), identifying the distal semimembranosus tendon morphology.

Results: Literature search revealed significantly inconsistent morphology of the distal semimembranosus muscle-tendon-unit. Cadaver dissection revealed a consistent trifurcation with three dominant expansions. Cadaver dissection also revealed an oblique popliteal tendon/expansion, indigenous to SMTU, not a ligament.

Conclusion: This study provides evidence of a consistent morphology and suggests a more precise nomenclature of the distal SMTU, which includes renaming the oblique popliteal ligament as the oblique popliteal tendon/expansion.