Abstract
INTRODUCTION AND IMPORTANCE: Patellar bone tumors are very rare, and most are benign or of intermediate type. In this report, we describe our experience of a metastatic patellar bone tumor caused by gastric cancer, which resembled a very rare primary or secondary aneurysmal bone cyst and review the literature. CASE PRESENTATION: A 65-year-old man presented with severe pain in the patellar region and marked limitation of the knee joint range of motion. He had a history of gastric cancer; however, epidemiological, clinical, and imaging findings led us to strongly suspect an aneurysm-like bone cyst. Thus, we performed bone tumor curettage and autologous artificial bone grafting without biopsy because of the severe pain. Pathology results showed gastric cancer metastasis; hence, patellectomy and patellar tendon augmentation with femoral fascia were performed. The Musculoskeletal Tumor Society (MSTS) score was taken postoperatively to assess pain and function. CLINICAL DISCUSSION: We experienced a very rare gastric cancer-related metastatic patellar bone tumor, which resembled a primary or secondary aneurysmal bone cyst in frequency and imaging findings. Patellectomy was ultimately performed, and the patient's MSTS score improved markedly. CONCLUSION: Despite its very low frequency, patellar metastatic bone tumors must be taken into account without being misled by the frequency or imaging findings and a biopsy should necessarily be performed.