1538 - The Tightest Branch: A Femoral Neuropathy with Isolated Rectus Femoris Involvement

A 60-year-old male presented with subacute-on-chronic right quadriceps weakness, visible rectus femoris atrophy, and intermittent paresthesias after a near-slip incident involving sudden hip extension and rotation. Initial L4-distribution radicular pain resolved, but quadriceps weakness persisted. Three months after the incident, nerve conduction studies demonstrated reduced femoral nerve motor amplitude to the rectus femoris (right 2.5 mV vs left 4.8 mV). Needle electromyography showed mild active denervation with increased motor unit amplitude, prolonged duration and reduced recruitment isolated to the rectus femoris. Diagnostic ultrasound showed chronic myotendinous scarring at the proximal rectus femoris central tendon, intact direct/indirect heads and quadriceps tendon, and a normal femoral nerve. With rehabilitation, the patient achieved significant improvement in hip flexion and quadriceps atrophy.

Discussions:

Femoral neuropathy is a rare mononeuropathy, often linked to surgical, compressive, or traumatic causes. This case was related to a stretch injury and demonstrates evidence of neurapraxia (conduction block, overall intact nerve on US) and axonotmesis (spontaneous activity and neuropathic motor unit changes on needle EMG) isolated to the rectus femoris. Ultrasound confirmed additional myotendinous injury. Literature highlights that multimodal evaluation - electrodiagnostics to assess functional integrity of the nerve and ultrasound to exclude compressive or structural pathology - optimizes diagnosis and management. Axonotmesis is characterized by axonal disruption with intact connective tissue, enabling regeneration at a rate of approximately 1–2 mm per day under optimal conditions and with a generally favorable prognosis—but even then, ongoing denervation and target muscle changes often limit full functional recovery.

Conclusions: Femoral neuropathy should be considered in patients with isolated quadriceps weakness after stretch injuries including the individual nerve branches to the different quadriceps muscles. Combined electrodiagnostic and ultrasound evaluation ensures accurate localization, prevents unnecessary interventions, and supports patient reassurance.