Ultrasound Evaluation and Surgical Excision of a Fabella Causing Peroneal Neuropathy in a Track Athlete

Abstract

Background: There are multiple causes of posterior knee pain and radicular symptoms. A symptomatic fabella is a rare cause but should be considered in the differential diagnosis.

Purpose: Physicians should consider a symptomatic fabella as a diagnosis when common treatments for posterior knee pain have not alleviated the symptoms.

Study design: Case report.

Methods: Review of clinical documentations of an orthopedist, physiatrist, physical therapist, 2 primary care sports medicine physicians, and the surgical report of an orthopedist.

Results: It took time and resources including several referrals and imaging modalities to make a final diagnosis.

Conclusion: Symptomatic fabellae are an uncommon finding but should be considered in the differential diagnosis with an athlete with posterior knee pain.

Clinical relevance: Considerable time and resources were used to ultimately diagnose and treat a NCAA Division 1 athlete. Surgical excision was required of a sesamoid bone that is present in 30% of individuals.

Figure 1

X-ray showing the fabella in a normal posterior location on the lateral X-ray.

Figure 2

Fabella located lateral out from behind the lateral femur on the AP X-ray.

Figure 3

Axial ultrasound of the posterior lateral knee (blue: femoral condyle, red: fabella causing acoustic shadowing, and gold: peroneal nerve).

Figure 4

Preoperative marking of the fabella with the patient.

Figure 5

Exposure of the fabella.

Figure 6

Fabella was removed as a single unit and measured 13 mm × 10 mm.