Incidental Asymptomatic Fibular Stress Fractures Presenting as Varus Knee Osteoarthritis: A Case Report

The proximal fibula is a rare site for stress fractures, with most of these fractures occurring in military recruits.¹ To the authors’ knowledge, there has been only 1 documented case of a proximal fibular stress fracture in patients with severe osteoarthritis (OA) and fixed varus deformity, which mimicked L5 radiculopathy.² We are not aware of any reports of asymptomatic tension-side fibular stress fractures in varus knees. In our 2 cases, the patients were indicated for total knee arthroplasty (TKA) for varus degenerative joint disease after failing nonoperative treatment; however, further work-up was justified to rule out neoplasm after plain films revealed expansile deformities of the proximal fibular shaft. Each patient subsequently underwent magnetic resonance imaging (MRI) with and without gadolinium contrast, which demonstrated a healed and healing proximal fibular stress fracture. Magnetic resonance imaging is rarely indicated in the evaluation of degenerative joint disease, and stress fractures about a varus knee generally occur on the compression side of the tibia and are symptomatic.^3-7 The patients provided informed written consent for print and electronic publication of this case report.

CASE REPORT

The first patient was a 77-year-old male who presented with longstanding knee pain, left greater than right, exacerbated by weight-bearing activities. The patient had no improvement with physical therapy or anti-inflammatory medication. He denied any history of trauma, weakness, paresthesias, or a recent increase in activity. The patient also denied any fevers, chills, night sweats, or other constitutional symptoms. On physical examination, the patient had an antalgic gait and limited range of motion bilaterally. Examination of his right lower extremity demonstrated a fixed 5° varus deformity. No distinct point tenderness was noted.

Radiographs of the right knee demonstrated varus deformity and tricompartmental degenerative changes with severe medial joint space narrowing. An expansile deformity of the proximal right fibular shaft was also noted (Figure 1), which was not present on the films 2 years earlier (Figure 2). The absence of this deformity on previous imaging raised the suspicion of a tumor. An MRI with and without gadolinium, which was obtained to rule out a neoplastic process, showed an old, healed proximal fibular shaft fracture with chronic periosteal reaction (Figure 3). There was no marrow edema to suggest acute injury and no neoplastic lesion. He was reassured regarding the benign findings and was scheduled for a left TKA, as his pain was more severe on the left knee. The patient’s stress fracture healed without complications, and he underwent a successful left TKA. He returned approximately 6 months after his procedure with worsening right knee pain and underwent a successful TKA on the right knee as well.

The second patient was a 67-year-old male with longstanding bilateral knee pain, right greater than left, with no antecedent trauma. He denied a history of increased activity, or weakness or paresthesias. He denied any fevers, chills, night sweats, or other constitutional symptoms. One year prior to presentation at our clinic, he had received corticosteroid injections and hyaluronic acid, without relief. The patient also had a history with another surgeon of arthroscopy 1 year earlier and subchondroplasty 3 years before presentation to our clinic. On physical examination, the patient’s right knee displayed a fixed 7° varus deformity with decreased range of motion, effusion, and diffuse crepitus. Further examination revealed tenderness to palpation of the proximal fibula.

Radiographs of the right knee showed degenerative joint disease with varus deformity and medial compartment joint space narrowing. They also demonstrated an expansile deformity of mixed lucency and sclerosis involving the proximal right fibular shaft (Figure 4). Although these findings appeared to be consistent with a stress fracture, their appearance was also suspicious for a neoplasm. To rule out malignancy, an MRI with and without gadolinium was obtained that revealed a healing stress fracture of the proximal fibula (Figure 5). The patient was reassured, and plans were made to proceed with a TKA. The patient’s stress fracture healed without complications, and he underwent successful right TKA. Radiographs from the patient’s 8-week follow-up showed a healed fibular stress fracture (Figure 6).

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