Histopathological changes due to osteoarthritis in articular cartilages of the knee

Introduction: The bony ends of a synovial joint are lined by a specialised hyaline cartilage termed the articular cartilage. Articular cartilage can be affected with degenerative diseases such as osteoarthritis. Knee being one of the larger joints built for weight bearing is the commonest site for osteoarthritis. The aim of this study was to describe the macroscopic and microscopic features of articular cartilages of the knee joint in patients diagnosed with primary osteoarthritis.Methods: Seventy-two articular cartilages removed during total knee replacement surgery were observed for macroscopic damage and graded according to the direct visual assessment score. Thirty specimens randomly selected were processed for histology and stained with Safranin-O-fast green-iron hematoxylin and observed and scored using the Mankins histological and histochemical grading system.Results: majority of specimens showed severe damage in the medial compartment and much less damage in the lateral compartment. In the tibia the damage was greatest on the medial most edge where the articular cartilage was absent leaving the bone exposed. Anteromedial area was relatively spared. In the femur the middle part of the medial condyle was seen to be more severely damaged. A similar pattern was observed in 19 (63.3%) of the specimens and showed exposure of bone. In the lateral compartment worst damage was observed in the middle of the lateral femoral condyle, with the rest of the lateral compartment being well persevered. This pattern was observed in 26 (86.6%) of the knee specimens.Conclusion: OA of the medial compartment causes the two cartilage surfaces to grind together, mechanically denuding the cartilage layers, while the lateral compartment which receives much less mechanical stress is well preserved.