Calcific tendinitis of popliteus tendon: arthroscopic excision and biopsy

Calcific tendinitis results from the deposition of calcium hydroxyapatite crystals in periarticular muscular attachments. It is a rare cause of knee pain commonly affecting patients aged 40 to 70 years. Although commonly seen in the shoulder, it should be kept in mind in nontraumatic cases, particularly when the pain is severe and localized to the lateral aspect of the knee. The exact mechanism of hydroxyapatite deposition is unclear, although genetic and metabolic factors have been suspected. A 45-year-old man presented with severe pain in the lateral aspect of his knee with local tenderness over the lateral epicondyle. Radiographs revealed multiple calcific deposits just below the lateral epicondyle of the femur. Magnetic resonance imaging showed multiple areas of low-signal present intra-articularly near the popliteus tendon that was suspected to be calcification. Erythrocyte sedimentation rate and C-reactive protein were slightly raised and other blood investigations including uric acid were within normal limits. Due to failure of conservative treatment, arthroscopy was performed through standard anteromedial and anterolateral portals. Arthroscopy revealed reddish synovial congestion in the lateral gutter. Partial synovectomy was performed with a shaver through a superolateral portal and the calcific deposit was found to lie between the popliteus tendon and the lateral collateral ligament. This was excised and sent for biopsy. Histopathological evaluation revealed the presence of hydroxyapatite crystals within degenerated tendon thereby confirming the diagnosis of calcific tendinitis. Immediate resolution of symptoms following excision allowed the patient to perform activities of daily living immediately postoperatively without pain.