Intra-articular Knee Neurofibroma in a Patient with Neurofibromatosis: A Case Report and Review of Literature.

Introduction: Neurofibromatosis type I (NF1) is an autosomal dominant disorder that typically results in Café-au-lait macules and peripheral nerve sheath tumors (i. e, neurofibromas). While peripheral neurofibromas are common, intra-articular knee neurofibromas are rarely described in the literature. To date, there only have been two other case reports noting intra-articular knee neurofibromas. The authors present the case of a patient with NF1 who was found to have an intra-articular knee neurofibroma incidentally discovered during the surgical approach to a retrograde femoral nail. Case Report: The patient is a 65-year-old female who presented to the emergency room after a fall from standing height with left distal thigh pain. X-rays were obtained and demonstrated a left supracondylar, extra-articular distal femur fracture. The patient had known NF1 with widespread cutaneous neurofibromas and was noted to have a large palpable soft-tissue mass over the anterior aspect of the knee on pre-operative examination. After an incision was made for a retrograde femoral intramedullary nail, the large soft-tissue mass prevented adequate surgical visualization. The mass was noted to track laterally around the patellar tendon, into the knee joint, communicating with Hoffa's fat pad. The mass was resected and sent for pathology. The case proceeded uneventfully. The mass sent for pathology was positive for a neurofibroma. Clinical features alongside radiographic, computed tomography, and histopathological findings are presented. Conclusion: Intra-articular knee neurofibromas are rare and there is a paucity of literature on the topic. While found incidentally in our patient, the discovery of an intra-articular neurofibroma underscores the need for further investigation into its potential association with neuropathic arthropathy and other associated joint disorders.