Identifying Hidden Zones of the Far Posterior Cartilage of the Femoral Condyles Not Visible During Knee Arthroscopy

OBJECTIVE. The purpose of this study was to compare standard knee arthroscopic and MRI findings and measurements for visualization of the femoral condyle articular cartilage. The hypothesis was that certain posterior cartilage defects identified with MRI may not be accessible with routine arthroscopy. MATERIALS AND METHODS. Six cadaveric knees were examined by routine arthroscopy through standard inferomedial and inferolateral portals. Suture anchors were inserted into the femoral condyles at 30 degrees, 60 degrees, 90 degrees, and 120 degrees of flexion as markers of the cartilage surface at the most posterior aspect of the condyle that could be accessed at each degree of flexion. Each specimen was then examined with 3-T MRI and gross dissection. Measurements were obtained and compared. RESULTS. During arthroscopy at 90 degrees of knee flexion, only 5.83 mm of the medial femoral condyle and 6.83 mm of the lateral femoral condyle were visualized posterior to the anchor placed at 90 degrees of flexion. These arthroscopic measurements were statistically significant underestimates of the actual amount of cartilage identified posterior to the 90 degrees anchor at gross dissection (medial condyle, 44.20 mm; lateral condyle, 37.50 mm) and MRI (medial, 41.33 mm; lateral, 38.87 mm). This indicates that 85.9% of the medial and 81.8% of the lateral posterior articular cartilage of the femoral condyle seen at MRI were not visualized during arthroscopy. CONCLUSION. More than 80% of the articular cartilage proximal to the menisci seen at MRI is not visible during routine arthroscopy. This far posterior articular cartilage should be called the hidden zone.