A Massive Proximal Tibia Geode – Can we Afford to Miss it?

INTRODUCTION: Osteoarthritis is now understood to be an aberrant remodeling of the joint organ caused by wear-and-tear mechanism and by a variety of inflammatory mediators. Subchondral cysts have been one of the important radiological features of knee osteoarthritis that is not well understood. We report a case of large subchondral lytic lesion which was initially thought to be a giant cell tumor and later was identified as subchondral cyst. CASE REPORT: A 50-year-old man presented to the outpatient department with complaints of intermittent pain and swelling over the left knee associated with difficulty in performing his daily activities Patient had undergone cerclage wiring for fracture left patella fracture 8 years back following which pain started. Radiographs showed extensive degenerative change at the knee with a large, multilocular lytic lesion in the proximal tibia. Magnetic resonance imaging showed similar features with an additional lesion in the distal femur. Core needle biopsy and histopathological examination of both lesions showed fibrocollageous tissue with bone fragments and lymphocytes. Patient was treated conservatively with analgesics and physiotherapy. He had good relief of pain and is on regular follow-up till date. DISCUSSION: Osteoarthritis knee is the most prevalent and leading cause of pain and disability worldwide. Subchondral cysts are strongly associated with osteoarthritis. Articular cartilage damage in osteoarthritis exposes the subarticular bone to injury, particularly in the weight-bearing joints. Large cysts are a well-recognized feature of other disorders such as simple bone cyst, aneurysmal bone cyst, giant cell tumor, and osteomyelitis. As these cases are rarely reported the treatment options are not standardized. Studies had shown similar cases treated both conservatively and surgically. The occurrence of the pathological fracture in these cases is high so prophylactic surgical fixation of massive geodes is advised. We decided to treat our case conservatively with analgesics and physiotherapy. The patient has good relief of pain at present and is on regular follow-up. He has been counseled that he may need a total knee replacement in the future if pain increases in severity. CONCLUSION: In the presence of osteolytic lesion showing very large cyst with cortical expansion and septations in radiographs with adjacent joint arthritis, the diagnosis of subchondral cyst/Geode should be strongly considered.