From the Guidelines
The etiology of weakness in the tibialis anterior and peroneus muscles, sparing the tibialis posterior, is most likely due to a common peroneal nerve injury or neuropathy. This pattern occurs because the common peroneal nerve innervates both the tibialis anterior (deep peroneal branch) and peroneus muscles (superficial peroneal branch), while the tibialis posterior is innervated by the tibial nerve, which is a separate division of the sciatic nerve. Some key points to consider in this condition include:
- Common causes of common peroneal nerve injury include compression at the fibular head, direct trauma, prolonged external pressure, diabetes mellitus, vasculitis, or mass lesions, as noted in the context of surgical procedures like microphlebectomy 1.
- Patients typically present with foot drop, difficulty with dorsiflexion and eversion, and sensory changes over the lateral calf and dorsum of the foot, while ankle inversion and plantar flexion remain intact due to preserved tibialis posterior function.
- Management depends on the underlying cause but may include removing sources of compression, physical therapy, ankle-foot orthoses for foot drop, and in some cases, surgical decompression.
- Recovery can take weeks to months depending on the severity of nerve damage, with axonal injuries requiring longer healing times than demyelinating injuries.
- It's crucial to avoid or exercise care around the common peroneal nerve during surgical procedures, given its location near the fibular head, to prevent iatrogenic injury 1.
From the Research
Etiology of Weakness in Tibialis Anterior and Peroneus Muscles
The etiology of weakness in the tibialis anterior and peroneus muscles, while sparing the tibialis posterior, can be attributed to various factors, including:
- Peroneal nerve injury or lesions, which can result in foot drop and weakness in the affected muscles 2
- Trauma or knee injuries, which can damage the peroneal nerve and lead to muscle weakness 3
- Common peroneal nerve palsy, which can cause supinated equinovarus foot deformity and foot drop 4
Peroneal Nerve Injury
Peroneal nerve injury can occur due to various reasons, including:
- Traction injuries, which can result in significant morbidity due to tibialis anterior muscle paralysis and loss of ankle dorsiflexion 5
- Penetrating trauma, which can cause peroneal nerve damage and lead to foot drop 6
Muscle Strength and Recovery
The strength of the affected muscles can vary after injury or treatment, with some patients regaining significant strength and others experiencing limited recovery:
- Ankle dorsiflexion strength can be measured using the British Medical Research Council grading system, with some patients regaining Grade 3 or 4 strength after treatment 3
- Factors influencing functional success of surgery include the mechanism of peroneal nerve injury, delays in surgery, and the presence of donor deficits 3