The Anatomy of the Oblique Popliteal Ligament

Abstract

Purpose: A major structure on the posterior aspect of the knee is the oblique popliteal ligament (OPL). Current literature on the morphology of the ligament is inconsistent and provides minimal quantitative data. The aim of this study was to reinvestigate the anatomy of the OPL, obtain quantitative data and determine its visibility on magnetic resonance imaging (MRI).

Methods: The region of the posterior knee was investigated using dissection, serial E12 plastinated slices, MRI and histology. For the dissection study, 13 lower limbs from 7 embalmed cadavers aged 64-87 years were used; 5 of these were randomly selected for histology. Serial E12 slices (2mm thick) of 4 knees from 2 additional male cadavers (aged 69 and 77 years) were prepared and examined. The knees of 10 healthy, physically active males aged 21-30 years were investigated using MRI. Some measurements from the dissection, E12 and MRI studies were repeated and the intraclass correlation coefficients were calculated to determine repeatability of the measurements.

Results: The OPL is a distinct expansion of the semimembranosus tendon and courses superolaterally to attach to the fabella (when present) or to the tendon of the lateral head of the gastrocnemius at the lateral femoral condyle. The OPL also inserts into the knee joint capsule at the medial border of the lateral femoral condyle. Ligamentous fibres from the medial joint form a secondary medial origin. The OPL splits into two bands where the middle genicular neurovascular bundle pierces the posterior joint capsule. The mean width of the OPL was 50.5mm (43-55.7mm) and its mean height at origin and lateral attachment was 11mm (range 6.3-16.8mm) and 9.7mm (range 6.5-12mm) respectively. Fibres from the medial and lateral knee joint capsule blended with the ligament. The OPL was composed of transverse layers of collagen; it was visible as a distinct entity in all proton density scans.

Conclusion: The OPL is a distinct ligament with distinct anatomical boundaries. It is clearly visible on MRI scans. A better understanding of the ligament may help define its involvement in posterior knee joint injuries and consequences of sectioning in posterior knee surgery.