Sheath of distal tendon of semimembranosus muscle and it's functional significance

Abstract

Introduction: Semimembranosus (SM) muscle is important in maintaining the stability of knee joint, and the distal end of it's tendon is not only complex but has been described differently in the available literature, which is quite perplexing. How a muscle with such divergent attachments can efficiently perform it's functions? Hence a detailed study of the distal semimembranosus tendon unit was undertaken. Material and Methods: One hundred lower limbs (Rt-50; lt.-50) were utilized for the present study. The posterior surface of SM was exposed and as the main tendon could not be traced to its insertion hence a vertical incision was made on the posterior surface of this tendon and this lead to the splitting of the tendon-sheath which exposed the thick shining distal tendon of SM. Results: Surprisingly, it was found that the main tendon of the SM (SMT) was surrounded by a fibrous sheath which was derived from the main muscle mass in the lower part of the thigh and in the majority of cases it was separated from it by a synovial space. Traced inferiorly it was observed that it is the sheath that spreads out to various divergent destinations described in the literature, whereas the main tendon gets attached to the groove on the posterior aspect of the medial condyle of tibia and a rough triangular area below the groove. Discussion and Conclusion: It is the nature's ingenuity that a single muscle with such divergent distal attachments can still efficiently perform its functions due to the formation of a sheath of distal tendon of SM.