Poster 127: The Posteromedial Knee: An Anatomic, Biomechanical, and Radiographic Analysis of the Posterior Oblique Ligament

OBJECTIVES: The structures of the posteromedial knee are important for coronal and rotational stability. These can be injured along with the medial collateral ligament (MCL) during traumatic or sporting activities. The posterior oblique ligament (POL) is largest and best-known structure at the posteromedial knee at risk of injury. When surgical reconstruction is needed, the location and positioning of this reconstruction is often grouped together with the medial collateral ligament, despite the specific biomechanical role of and the much larger anatomic area covered by the various structures of the posteromedial knee. The POL provides a complex load sharing interplay with the MCL, such that these ligaments both contribute to resist the combination of valgus and rotational strains. As such, the POL is an important structure that contributes to the stability of the medial knee, and severe injuries may benefit from a separate procedure to directly address the ligament. The purpose of this study was to evaluate the anatomy of the posteromedial knee as well as the radiographic locations and biomechanical strengths of the POL. METHODS: 10 nonpaired fresh cadaveric knees were dissected and the medial structures were elevated off bone, except for the POL. The anatomic locations were noted and recorded with a robotic coordinate measuring device to establish structure location, distances, and attachment areas for the superficial MCL, adductor tubercle, medial epicondyle, meniscofemoral ligament, tibiofemoral ligament, semimembranosus and the POL. For the radiographic analysis, radiopaque T-pins were placed in the POL attachment sites, as well as other clinically relevant and bony landmarks. True anteroposterior (AP) and lateral radiographs were taken with fluoroscopy. Digital software was utilized to measure the distances from these anatomic points to the center of the attachment of the POL. Biomechanically, the specimens were loaded onto a computerized actuator, and all soft tissues connecting the tibia and the femur were resected except for the POL. A pull-to-failure test was completed and the ultimate tensile strength and location of the failure was recorded. RESULTS: On average, the POL attachment on the femur is 15.4mm posterior and 6.6mm superior to the medial epicondyle. On the tibia, the POL attachment center is 21.4mm posterior and 2.2mm inferior to the center of the meniscotibial ligament, and 28.6mm posterior and 41.9mm superior to the center of the superficial MCL tibial attachment. On radiographic exam, the femoral POL was 17.6mm distal to the adductor tubercle, and 17.3mm posterosuperior to the medial epicondyle on the lateral radiograph. On the tibial side, the center of the POL attachment is 5.0mm distal to the joint line on the AP radiograph and 6.3mm distal to the tibial joint line on the lateral, at the far posterior aspect of the tibia. The biomechanical pull-to-failure demonstrated an average ultimate tensile strength of 225.2N ± 71.0N. CONCLUSIONS: This study successfully localized the medial and posteromedial knee structures, establishing their anatomic location, the radiographic location of the POL relative to clinically relevant structures, and established the pull-to-failure ultimate tensile strength. This provides good clinical information for location and type of graft that can help anatomically reconstruct the central arm of the POL.