Distal Semimembranosus Muscle Tendon Unit and Oblique Popliteal Ligament: Morphology and Accurate Terminology Taylor Delamarter Western University of Health Sciences COMP-Northwest 2.22.14 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. Results: Cadaver Dissection • Embalmed cadaver dissection revealed a trifurcation of the distal SMTU at the posterior aspect of the medial femoral condyle in each of the 56 dissected knees. • The first identified expansion coursed in a superior oblique direction to attach into the lateral aspect of the joint capsule directly posterior to the lateral femoral condyle. • The second identified expansion of the trifurcation had an anterior course. It provided fibers into the medial meniscus and the medial collateral ligament, and terminated into the anteroinferior aspect of the medial tibial condyle. • The third and terminal identified expansion of the trifurcation took an inferior course to the posterior inferior aspect of the medial tibial condyle, and was consistently more inferior than the anterior limb. This limb also provided fibers to the fascia of the popliteus muscle. Fig. 2 Oblique Popliteal Tendon/Expansion Anterior OPT Expansion Inferior Expansion Discussion • This study reveals a consistent trifurcation of the distal SMTU; therefore, the authors propose that the expansions of the trifurcation be named the oblique popliteal expansion (oblique popliteal tendon, not ligament), the anterior expansion, and the inferior expansion. ABSTRACT • INTRODUCTION. The objective of this study was to investigate the ‘oblique popliteal ligament’ (OPL) and challenge its alleged ligament status. The posterior aspect of the knee has been increasingly studied because of its clinical relevance. Surgeons, biomechanists, physical therapists, all health care providers dealing with the musculoskeletal system and anatomists need to have a definitive and precise understanding of the structures of the posteromedial knee. The currently named OPL is indigenous to the distal semimembranosus (SMT); therefore, by definition is not a ligament inserting from bone to bone. This is clinically important because of the proprioception of a tendon versus a ligament. • METHODS. Literature search was conducted on texts, journals and websites regarding the formation of the OPL. Dissection of 70 knees included macro analysis, harvesting OPL, distal SMT and LCL samples and performing immunohistochemistry to 16 knees with antibody staining to the OPL, distal SMT and LCL. • RESULTS. All but one text claimed the OPL receives fibers from SMT. Macro dissection of 70 knees revealed the OPL forming from the distal SMT tendon trifurcation (100%). Microanalysis of OPL, distal SMT and LCL samples from 16 knees demonstrated expression of nervous tissue within selected samples. • DISCUSSION. Woodburne stated the OPL formed from the fibers of the distal SMT tendon; however, no journals or texts have hypothesized that this ligament is indigenous to the SMT thus, a tendon itself. Clinically it is important we know what type of tissue for purposes of maximizing rehabilitation and surgical techniques. • CONCLUSION. This study suggests the OPL be considered the oblique popliteal tendon as a result of the macro and micro evidence revealed. Fig. 1a Superior Fig. 1b L a OPL OPL M t e e d r i a a l l Inferior Deep dissections revealed that the alleged oblique popliteal ligament’s distal (medial) attachment originated from the SMTU in 100% of 70 knees. Its proximal (lateral) attachment inserted into the joint capsule in 39/70, bone in 11/70, and both joint capsule and bone in 20/70 knees Fig 3 SMTU OPL Fig 3a: SMTU Fig 3b: OPL Fig 3c: LCL Fig 4a: SMTU Fig 4b: OPL Fig 4c: LCL CONCLUSION • The macro analysis of the OPL revealed unequivocally it is indigenous to the distal SMTU. The microanalysis using an immunohistochemistry stain with PGP9.5 revealed a positive result for neuronal axons within both the SMT and OPL. Further microanalysis using an immunohistochemistry stain with β-Tubulin revealed a positive stain for neuronal axons in the SMT, OPL, and LCL. Though the latter result leads the authors to question the validity of differentiating tendon from ligament using this particular immunohistochemistry stain. The macro analysis results are overwhelming and the microanalysis reveals striking similarities in the histology of both the OPL and SMT. The authors strongly suggest that the oblique popliteal ligament be renamed the oblique popliteal tendon (OPT) due this macro and microanalysis study. Clinically, this study improves terminology accuracy and medical international language, allowing for better understanding of successful rehabilitation methods and rationale for current and future surgical procedures. THANK YOU .