Baxter’s nerve entrapment is an often-overlooked source of chronic heel pain that frequently leads to an incorrect diagnosis of plantar fasciitis. This condition involves the compression, or “pinching,” of a small nerve in the heel known as the first branch of the lateral plantar nerve (FBLPN). This nerve is also sometimes referred to as the inferior calcaneal nerve or Baxter’s nerve. When entrapped, it causes neuropathic pain and may be responsible for up to 20% of all chronic heel pain cases.
The Location and Vulnerability of Baxter’s Nerve
Baxter’s nerve takes a path through the foot that makes it particularly susceptible to pressure and compression. It originates from the lateral plantar nerve and runs along the inside of the heel. The nerve is a mixed sensory and motor nerve, providing sensation to the calcaneal periosteum (the membrane covering the heel bone) and supplying motor control to the abductor digiti minimi muscle, which moves the little toe.
The nerve courses vertically between two layers of muscle, the abductor hallucis and the quadratus plantae, before making a sharp turn. This sharp, ninety-degree angle as it turns to run horizontally is the first of two primary points where it can become pinched against surrounding structures. This turn is located near the medial calcaneal tuberosity, a bony prominence on the underside of the heel bone.
Direct Structural Causes of Entrapment
The most common structural cause is the enlargement, or hypertrophy, of the abductor hallucis muscle. As this muscle becomes overdeveloped, its increased bulk and the tightening of its deep fascia reduce the space available for the nerve. Another frequent physical cause is the presence of a heel spur, or osteophyte, on the calcaneus (heel bone).
If a bone spur develops along the medial calcaneal tuberosity, the nerve can be compressed against the hard bone, especially where the nerve makes its sharp turn. The nerve can also be trapped by the tension of fibrous bands or a thickened plantar fascia. Space-occupying lesions like masses or cysts in the heel area are less common. Chronic inflammation from conditions like arthritis or scar tissue from previous injury or surgery can also contribute to the restriction and compression of the nerve.
Biomechanical and Activity Risk Factors
Excessive or repetitive high-impact activities, such as long-distance running or prolonged standing, place considerable strain on the muscles and fascia of the foot. This repeated trauma can lead to the muscular enlargement and inflammation that subsequently compresses the nerve.
Improper foot biomechanics are a significant predisposing factor for nerve entrapment. Individuals with a flat foot or excessive pronation—where the arch collapses inward—experience increased tension on the plantar fascia and the abductor hallucis muscle. This altered foot posture stretches the soft tissues and forces the medial calcaneal tuberosity to compress the nerve.
Obesity and weight gain increase the overall load on the foot, which contributes to the hypertrophy of the foot muscles and greater pressure on the heel structures. Wearing unsupportive or poorly fitting footwear, particularly shoes that lack adequate arch support, can exacerbate poor foot mechanics.
How Symptoms Differ from Common Heel Pain
The pain from Baxter’s nerve entrapment differs from common heel pain in several key ways. The pain is typically felt more toward the inside and bottom of the heel and may radiate forward into the arch of the foot. In contrast, the pain of classic plantar fasciitis is usually centered directly under the heel bone where the fascia attaches.
A major distinguishing factor is the pattern of pain throughout the day. While plantar fasciitis is characterized by severe “first-step” pain in the morning that often improves with walking, the pain from Baxter’s nerve entrapment commonly worsens as the day progresses and with increased activity.
Because it is a nerve issue, Baxter’s entrapment often includes specific neuropathic symptoms. Patients may report a sharp, burning sensation, as well as numbness or tingling (pins and needles) along the inner side of the heel or arch. These neurological signs, which are less typical of an inflamed ligament, suggest nerve involvement. The pain may also be elicited by direct pressure on the inside of the heel, where the nerve is compressed.