Baxter’s nerve, formally known as the inferior calcaneal nerve, is a small but significant structure in the foot that is frequently a source of chronic discomfort. It is a potential cause of persistent heel pain, often misdiagnosed as the more common plantar fasciitis. When compressed or irritated, this nerve leads to a specific type of foot pain that can be debilitating and unresponsive to standard treatments. Understanding its role and location is important for anyone experiencing long-lasting heel discomfort.
The Anatomy of Baxter’s Nerve
Baxter’s nerve is the first branch of the lateral plantar nerve, a division of the posterior tibial nerve. It is referred to as the inferior calcaneal nerve due to its position near the heel bone (calcaneus). The nerve begins beneath the deep fascia of the abductor hallucis muscle on the inner side of the foot.
The nerve follows a distinct path, running vertically between the abductor hallucis muscle and the quadratus plantae muscle before turning sharply outward around the heel bone. Its small size and tight anatomical pathway make it vulnerable to external pressure.
The nerve is subject to compression at two primary locations, known as entrapment zones. The most common site is where the nerve passes between the deep fascia of the abductor hallucis muscle and the medial plantar margin of the quadratus plantae muscle. A second site occurs more distally as the nerve runs along the medial calcaneal tuberosity.
Primary Function and Role
Baxter’s nerve is a mixed nerve, carrying both motor and sensory fibers. It primarily provides motor innervation to the abductor digiti minimi muscle, which moves the small toe away from the others.
The nerve also supplies the quadratus plantae muscle and sometimes the flexor digitorum brevis muscle. These intrinsic foot muscles stabilize the foot’s arch and maintain structural integrity during walking and standing. The nerve also carries sensory fibers that provide feeling to the periosteum of the heel bone and surrounding ligaments.
Understanding Baxter’s Nerve Entrapment
Entrapment of this nerve, known as Baxter’s neuropathy, occurs when pressure or stretching damages the nerve fibers. This condition can account for up to 20% of chronic heel pain cases and is often mistaken for plantar fasciitis due to the overlapping location of discomfort. The characteristic symptom is a chronic, deep, and sometimes burning pain located on the inner and bottom side of the heel.
Unlike plantar fasciitis pain, which often improves after the first few steps in the morning, the discomfort from nerve entrapment is persistent and intensifies with activity. The pain may also be accompanied by tingling, numbness, or a pins-and-needles sensation in the arch or outer heel area.
Common causes include repetitive microtrauma from activities like running, which can cause surrounding muscles to swell. Structural issues, such as flat feet or excessive overpronation, alter foot mechanics and place increased tension on the nerve. Bony growths like heel spurs near the calcaneal tuberosity can also mechanically compress the nerve against the bone.
Diagnostic and Treatment Approaches
Diagnosing Baxter’s nerve entrapment requires clinical suspicion because its symptoms mimic other foot conditions. A physical examination involves palpation to locate specific tenderness near the nerve’s course, often at the origin of the abductor hallucis muscle. Clinicians may also perform a Tinel’s sign test, gently tapping the nerve to see if it reproduces the patient’s burning or tingling sensation.
Imaging techniques like magnetic resonance imaging (MRI) or ultrasound are used to rule out other causes of heel pain and visualize surrounding structures. MRI can reveal changes in the abductor digiti minimi muscle, such as atrophy, indicative of chronic nerve compression. The most definitive diagnostic tool is a targeted nerve block: an injection of local anesthetic near the nerve. If the injection provides significant, temporary pain relief, it confirms Baxter’s nerve as the source of discomfort.
Initial treatment focuses on conservative, non-surgical methods aimed at reducing inflammation and relieving pressure. This includes physical therapy to stretch and strengthen foot muscles and the use of custom orthotics to correct faulty foot biomechanics like overpronation. Anti-inflammatory medications may also be prescribed to manage pain and swelling.
If conservative measures fail, interventional treatments address the underlying compression. Ultrasound-guided injections, combining a corticosteroid with a local anesthetic, can provide therapeutic relief by reducing inflammation. For chronic cases that do not respond to non-surgical treatment, surgical decompression (neurolysis) may be an option. This procedure involves surgically releasing the entrapped nerve by cutting the confining fascia or removing compressive elements, such as a heel spur.