Detailed Anatomical Mapping of Medial Collateral Ligaments

The insertion sites of the sMCL and dMCL were identified from their bony insertions of the femur and tibia (Fig. 1A). Three anatomic landmarks on the femur (ME = medial epicondyle, MGT = medial gastronomies tubercle, MAT = medial adductor tubercle) were specified as references for later measurements (Fig. 1B)[11 (link)]. The sMCL and dMCL were separated by a bursa in all cadaveric knees. The sMCL was carefully separated from the dMCL without damaging the dMCL during the dissection. The anterior part of the sMCL was vertically aligned but the posterior part was oblique (Fig. 2A). Unlike the anterior part, the posterior part of the sMCL was found firmly attached to the medial meniscus (Fig. 3)[13 ]. The dMCL, which consisted of a proximal portion (meniscofemoral ligament - MFL) and distal portion (meniscotibial ligament - MTL), was relative thinner compared to the sMCL (Fig. 4A). The pes anserinus tendons (sartorius, gracilis, and semitendinosus tendon) were detached from their tibial attachments during dissection. A fine-point marker was used to outline the location of the medial structures of the knee.
The outlines of the insertion sites of each ligament were then digitized using a 3D digitizing system which has a reported accuracy of 0.3 mm (MicroScribe G2LX; Immersion Technologies, San Jose, CA, USA). The digitized points were imported into solid modelling software (Rhinoceros; Robert McNeel and Associates, Seattle, WA, USA) to calculate the areas of the insertion sites and the centroids of the insertion areas. These values were calculated by using the inbuilt functions ("Area" and "AreaCentroid") of the Rhinoceros software.
In this study, we first determined the insertion areas of the sMCL and dMCL on the femur and tibia (Fig. 1A). We then measured the distances between the centroids of the insertion areas to determine the length of the ligament [11 (link)]. Joint line was determined according to the previous definitions of Laprade et al. [11 (link)], where the edge of the articular cartilage surface of the medial femoral condyle was defined as the femoral joint line and the medial tibial plateau as the tibial joint line. All measurements were performed according to a sequence of eight steps (Fig. 5).