Bilateral Spontaneous Osteonecrosis of Knee with Concomitant Medial Femoral and Tibial Condyle Involvement – A Rare Presentation and Short Review

INTRODUCTION: Osteonecrosis of knee is classified as primary spontaneous osteonecrosis of knee (SPONK) and secondary osteonecrosis of knee. Primary SPONK usually involves medial femoral condyle (MFC). Incidence of medial tibial plateau (MTP) is only 2% among the patients with SPONK and simultaneous involvement of MFC and MTP is very rare. CASE REPORT: We report a very rare case of 45-year-old female with SPONK affecting both MFC and MTP simultaneously with subchondral insufficiency fractures. She presented with pain in both the knees and difficulty in walking since 1 year. Physical examination revealed decreased range of motion and local tenderness over MFC and medial tibial condyle. Subchondral fracture with articular surface collapse of MFC with joint space narrowing and varus deformity was seen on X-ray in both the knees. Sclerosis was seen in the medial tibial condyle bilaterally. Magnetic resonance imaging showed characteristic focal hyperintense areas surrounded by band like hypointense areas in both MFC and MTP which was suggestive of subchondral collapse with ill-defined bone marrow changes. X-ray of both knees revealed SPONK in Koshino’s Stage IV and Carpintero’s Stage IV. Bilateral total knee replacement (TKR) was planned. First left knee was operated. A cruciate retaining type of TKR was done. Two weeks, later right side TKR was operated. MFC of right side also had a large osteochondral fragment which was excised to leave defect with depth more than 2 cm. Defect was reconstructed with bone graft obtained from posterior condylar cuts. Posterior stabilized type of knee replacement component was used along with femoral extender stem. Histopathological examination revealed necrotic bone surrounded by an area of fibrovascular granulation tissue on both the femoral and tibial sides. Patient has good functional outcome at 2 years follow-up. CONCLUSION: Concomitant SPONK of MFC and MTP in bilateral knee is very rare and in advanced stages TKR can provide good radiological and functional outcome. Furthermore, pre-operative assessment of bone defects is necessary and appropriate use of augments (extender stem or metal wedges) is crucial.