Case Report: A giant gouty tophus of the lateral knee involving the lateral collateral ligament and adjacent to the common peroneal nerve

Background Periarticular gouty tophi of the knee can cause pain, mechanically restrict joint motion, and damage adjacent bone and soft tissues. However, giant gouty tophi involving the lateral collateral ligament (LCL) and closely related to the course of the common peroneal nerve are rare. Medical therapy alone may be insufficient to reverse established structural changes, whereas surgical treatment requires careful balancing of lesion excision, nerve protection, and preservation of joint stability. Case presentation A 41-year-old man presented with a giant gouty tophus on the lateral aspect of the left knee, progressive pain, and restricted range of motion (ROM). Radiography, computed tomography (CT), and magnetic resonance imaging (MRI) demonstrated a large space-occupying lesion at the lateral aspect of the knee, involving the LCL and extending close to the anatomical course of the common peroneal nerve. Open surgical excision was performed. The common peroneal nerve was first identified, carefully dissected, and protected, after which the main lesion and visible scattered chalky deposits were excised. Histopathological examination confirmed the diagnosis of gouty tophus. At the 3-month postoperative follow-up, the patient experienced marked pain relief and improved ROM, with no palpable mass suggestive of local recurrence on clinical examination. Conclusion This case suggests that open excision may be a reasonable treatment option for giant periarticular gouty tophi of the knee associated with a substantial mechanical mass effect, functional impairment, and involvement of critical lateral structures, provided that careful preoperative imaging assessment and perioperative management are undertaken. In particular, early identification and meticulous protection of the common peroneal nerve are essential when the lesion is closely related to its anatomical course.