Disclosures: Mani Singh, MD: No financial relationships or conflicts of interest

Case Diagnosis: 68-year-old-female with history of prior right total knee arthroplasty (TKA) and recent TKA revision presenting with 2 months of right foot drop.

Case Description or Program Description: She reported weakness of right foot dorsiflexion, eversion, and toe extension associated with dorsal foot pain. She required single point cane and ankle-foot orthosis for ambulation. Review of systems was otherwise negative. Initial physical examination of the right leg illustrated 0/5 strength in the tibialis anterior, extensor hallucis longus, and extensor digitorum longus. Sensation was decreased to light touch in the lateral lower leg. Examination was negative for vascular abnormalities or upper motor neuron signs.

Setting: Outpatient clinic

Assessment/Results: X-ray of right knee was unremarkable. High-resolution ultrasound evaluation of the common fibular nerve illustrated compression and flatting proximal to the fibular head at the level of the fabella without other sites of entrapment, focal thickening, or fascicle changes. Evaluation of the deep fibular nerve, superficial fibular nerve, sciatic nerve, tibial nerve, and cutaneous nerves was unremarkable. She received physical therapy and electrical stimulation with improvement in her gait/strength over subsequent 3-months.

Discussion (relevance): Foot drop may be a clinical manifestation of common fibular mononeuropathy, generally secondary to compression at the fibular neck or injury following TKA. The fabella, an infrequently occurring anatomic variation, is a sesamoid bone that may be located in the head of the lateral gastrocnemius in close proximity to the common fibular nerve. We present a rare case of common fibular compression secondary to the fabella following revision TKA, diagnosed by physical examination and high-resolution ultrasound. Treatment should consist of physical therapy with evaluation for assistive devices or orthotics. Nerve hydro-dissection or surgical repair may be required in refractory cases.

Conclusions: Common fibular nerve compression by the fabella following revision TKA is a rare etiology of foot drop. High-resolution diagnostic ultrasound may aid in the evaluation and diagnosis of this injury.

Level of Evidence: Level V

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PM&R Meeting Abstracts - https://pmrjabstracts.org/abstract/foot-drop-secondary-to-fibular-nerve-compression-at-the-fabella-a-case-report/