Baxter’s neuritis, also known as Baxter’s nerve entrapment or inferior calcaneal nerve compression, is a nerve impingement in the foot involving the compression of the first branch of the lateral plantar nerve (FBLPN). This nerve is a mixed sensory and motor nerve. It is estimated that this entrapment accounts for up to 20% of cases involving pain in the medial heel region. Because its symptoms closely mimic those of the more common plantar fasciitis, Baxter’s neuritis is often misdiagnosed.
The Anatomy and Mechanism of Nerve Entrapment
The first branch of the lateral plantar nerve, or Baxter’s nerve, originates from the lateral plantar nerve, a division of the posterior tibial nerve. This nerve provides sensation to the calcaneal periosteum and the long plantar ligament, and motor function to the abductor digiti minimi muscle. Its path runs along the inside of the heel, diving deep beneath the abductor hallucis muscle.
Two common sites of entrapment are recognized: where the nerve passes beneath the deep fascia of the abductor hallucis muscle, and more distally, where it courses between the quadratus plantae muscle and the medial calcaneal tuberosity. Mechanical stressors contribute significantly to this compression, often involving repetitive microtrauma or foot biomechanics such as excessive pronation.
Compression can also be caused by the enlargement (hypertrophy) of surrounding intrinsic foot muscles, such as the abductor hallucis, often due to overactivity or altered foot mechanics. Bony growths like calcaneal spurs near the medial calcaneal tuberosity can also directly press against the nerve, reducing the space it needs to pass through.
Recognizing the Signs and Symptoms
The characteristic pain of Baxter’s neuritis is typically described as a burning, sharp, or tingling sensation located deep in the heel, primarily along the inner (medial) side of the foot. This discomfort may radiate forward toward the arch or along the outer side of the foot. Numbness or paresthesia (pins and needles) in the heel area may also occur.
The timing of the pain differentiates it from plantar fasciitis, as symptoms often worsen as the day progresses and with increased weight-bearing activity. Unlike the classic “first steps in the morning” pain of plantar fasciitis, the discomfort tends to build up with prolonged standing or walking. In severe cases, motor involvement may lead to weakness and eventual atrophy of the abductor digiti minimi muscle.
Confirming the Diagnosis
The diagnostic process begins with a detailed physical examination and history, where a clinician will assess for localized tenderness over the course of the nerve path. Specific clinical maneuvers, such as tapping over the nerve (Tinel’s sign), may reproduce the patient’s tingling or pain, suggesting nerve irritation. However, because the nerve is small and deeply situated, a definitive clinical diagnosis can be challenging.
X-rays are typically used to exclude bony pathologies like stress fractures or to identify calcaneal spurs that might be contributing to the compression. Magnetic Resonance Imaging (MRI) is considered the imaging modality of choice, as it can indirectly confirm nerve entrapment by visualizing denervation-related changes. MRI can detect signs like swelling or fatty atrophy in the abductor digiti minimi muscle.
The most important confirmation method is a targeted diagnostic nerve block, where a local anesthetic is injected near the suspected entrapment site, often guided by ultrasound. A significant, temporary reduction in pain immediately following this injection strongly indicates that the Baxter’s nerve is the source of the chronic heel pain.
Treatment Pathways
Conservative, non-surgical approaches are the initial management focus, involving a period of rest and activity modification to avoid movements that exacerbate the compression. Non-steroidal anti-inflammatory drugs (NSAIDs) may be recommended to manage pain and reduce localized inflammation.
Custom-designed orthotics are frequently prescribed to correct underlying biomechanical issues like excessive foot pronation. Physical therapy, incorporating stretching and strengthening exercises for the foot and calf muscles, also helps improve foot mechanics and flexibility. If conservative measures do not provide sufficient relief, the next step may involve targeted injections.
Corticosteroid injections, often performed under ultrasound guidance, can deliver powerful anti-inflammatory medication directly to the area surrounding the entrapped nerve. If chronic pain fails to respond to these methods, surgical consultation may be necessary. The surgical procedure, known as nerve decompression or neurolysis, aims to physically release the entrapped nerve by cutting the tight fascia of the abductor hallucis muscle or removing other compressive structures.