# Anatomical relationship between the anterior arm of the semimembranosus tendon and the medial collateral ligament: A cadaveric study

## TL;DR

This study examines the anatomical relationship between the semimembranosus tendon's anterior arm and the medial collateral ligament in cadaveric knees to help prevent damage during knee surgery.

## Contribution

The study provides quantitative anatomical data on the anterior arm of the semimembranosus tendon and its relationship with the medial collateral ligament.

## Key findings

- The vertical distances from the joint line to the anterior arm's margins are 8.9 ± 1.5 mm and 16.8 ± 1.5 mm.
- The anterior arm shares a common attachment area with the deep medial collateral ligament and connects to the superficial ligament via loose connective tissue.

## Abstract

Despite its close anatomical relationship with the superficial medial collateral ligament (sMCL) and deep medial collateral ligament (dMCL), the primary stabilisers of the medial knee, the anterior arm of the semimembranosus (SM) tendon has been scarcely studied anatomically. In addition, there is concern about potential damage to the anterior arm during the tibial cut in total knee arthroplasty (TKA). This study aimed to quantitatively evaluate the anatomical location of the SM's anterior arm and clarify the anatomical relationship with the MCL using gross and histological evaluation.

Twenty‐two formalin‐fixed cadaveric knees were used. The distance from the joint line to the anterior arm, the anterior arm′s length, and the entry ratio of the anterior arm underneath the sMCL were measured. Four equal‐thickness sections were harvested from the medial tibial condyle, including the anterior arm and MCL, and stained with Masson's trichrome, hematoxylin, and eosin. The anatomical relationship between the anterior arm, sMCL, and dMCL was evaluated.

The vertical distances from the joint line to the proximal and distal margin of the anterior arm are 8.9 ± 1.5 mm and 16.8 ± 1.5 mm, respectively. The entry ratio of the anterior arm underneath the sMCL was 0.53 ± 0.21. The anterior arm fibres intersected with distally extending dMCL fibres. The loose connective tissue was located at the junction of the sMCL, anterior arm, and dMCL.

Anterior arm of the SM tendon shares a common attachment area with the dMCL tibial attachment and is connected to the sMCL via loose connective tissue. The measurements obtained in the present study may serve as useful indicators for avoiding damage to the anterior arm during tibial cut in TKA.

Level Ⅳ.