Disclosures: George R. Malik, MD: No financial relationships or conflicts of interest

Case Diagnosis: Tibialis anterior muscle herniation with irritation of a superficial peroneal nerve (SPN) branch

Case Description or Program Description: A 28-year-old female with 6 months of insidious right anterolateral shin pain. She describes it as a sharp and tight sensation. The pain is non-radiating and provoked with walking and stretching; partially improved with anti-inflammatories, compression, and rest. She had an extensive negative work-up, including MRI, angiography studies (popliteal artery entrapment syndrome), and electromyography. She underwent lower leg compartment pressure testing twice; first test positive for chronic exertional compartment syndrome (anterior compartment increased from 5 mmHg to 30 mmHg with exercise) and second test negative. She completed physical therapy without improvement. The patient was tender to palpation over the anterolateral right shin, with increased pain during single-leg hop. She was neurologically intact, but noted pain with right ankle dorsiflexion.

Setting: Orthopedic specialty hospital outpatient clinic

Assessment/Results: A musculoskeletal ultrasound of the anterior compartment demonstrated a small facial defect with muscle herniation at the crural fascia abutting a branch of the SPN. A lidocaine injection at the site of herniation resulted in 70% improvement in pain for 4 hours. Based on her positive response to the diagnostic injection, she was referred for a surgical consultation and is scheduled to undergo partial fasciotomy of the anterior compartment.

Discussion (relevance): Compartment pressure testing of the extremities has ambiguous results among different providers and with different measurement protocols. In these cases, ultrasound can be helpful in detecting contributing dynamic muscle herniations (83% vs MRI 17%). While nonoperative management is first-line for muscle herniations, recalcitrant cases should undergo fasciotomy to further expand the fascial opening. This aims to relieve pain from a focal herniation and limit impingement of nearby nerves.

Conclusions: Exertional lower leg pain has a broad differential. When traditional work-up is equivocal, dynamic musculoskeletal ultrasound can identify muscle herniations and nerve entrapment as a source of pain.

Level of Evidence: Level IV

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PM&R Meeting Abstracts - https://pmrjabstracts.org/abstract/face-the-fascia-a-case-report-of-a-tibialis-anterior-muscle-herniation/