3. DISCUSSION
OC is a benign tumor of bone tissue that occurs mainly during endochondral ossification of growth plates of long bones. OC is often caused by hereditary multiple exostoses in the areas of the tibiofemoral and patellofemoral joints (6). Of course, this lesion is rarely observed in the patellar ligament and usually causes stiffness of the knee joint (joint locking), dysfunction of the anatomic function of the quadriceps femoris muscle tendon and loss of knee joint extension, edema, chronic pain, ossification of the ligament, formation of fibro- fatty tissue, degenerative arthritis and finally neurovascular compression (7).
In the present case, the patient presented with common symptoms of OC, including edema, chronic pain and stiffness in the knee joint and palpation of solid masses in the patellar ligament. These symptoms could be due to the inflammatory processes involved in the degeneration of dense connective tissue around the mass of exostoses in the lacunae of the patellar ligament. Studies show that OC is associated with good prognosis and low risk of metastasis, but due to the disturbance in the anatomical alignment of the knee joint, the masses are removed by radical resection and the patellar ligament is fixed and stabilized at the connection to the tibial tuberosity (5). In the report of Pandian et al. (2016), in a 22-year-old man, bilateral OC masses in the patella and patellar ligament caused severe arthritis, chronic pain, edema, and impaired flexion-extension knee movements (8). In 15% of cases, the mass is surrounded by a calcified cartilage cap around the bony lacuna, and its thickness even reaches >15 mm (4). Studies show that the incidence ranges of OC are 0.9 - 1.4% per 100,000, which is rare in the patellar ligament. If there is no intervention, valgus deformity in the ankle, knee and pelvic joints is expected in the third decade of life. However, vascular compression and/or nerve compression along with acute pain, extensive edema and tissue degeneration are observed in OC of the hip (sacroiliac-iliofemoral) and shoulder (glenohumerus) joints (9 and 10).