Nearly 60% of patient’s with chronic forefoot pain presenting to a podiatry practice have surgical intervention, yet only 50-60% of them get relief of foot pain long-term and 20% get significantly worse, requiring multiple surgeries. Accurate diagnosis is critical to appropriate treatment, common areas where foot pain is misdiagnosed include:
The metatarsophalangeal joint plantar plates are major stabilizers and form part of the plantar capsule. The plantar plates provide strength and support during ambulation. Disruption can lead to toe deformities. The normal plantar plate is a slightly hyper echoic broad-curved band, which protects the metatarsal head and inserts onto the proximal phalanx. Plantar plate tears typically appear as hypo echoic defects. The torn plantar plate is often swollen and hyper vascular in the acute phase of degeneration.
Adventitial bursitis is acquired bursitis in the metatarsal fat pad as a result of trauma. Sonographically these areas may either be ill-defined or focal collections. These are generally compressible and hypo echoic, although complex collections may appear heterogeneous.
Joint effusions are compressible anechoic collections best seen on the dorsal aspect of metatarsophalangeal joints. Synovial proliferation appears on ultrasound as a thickening of the synovial layer. Hyper vascularity and bone erosions may also be present.
A Morton’s neuroma is caused by mechanical damage to the interdigital nerve, resulting in perineural fibrosis. On ultrasound it commonly appears as an ovoid hypo echoic mass, although the shape and echogenicity may vary. Intermetatarsal bursitis appears as a hypo echoic or anechoic zone in a normally echogenic webspace, generally dorsal to the interdigital nerve, although sometimes enveloping it. This soft tissue collection may become complex and heterogeneous with time. Dynamic assessment of a webspace will show poor compressibility of a neuroma and high compressibility of a bursitis (note: complex bursa may mimic a neuroma). Treatment options include ultrasound guided cortisone or alcohol injection.
Common causes of forefoot pain include joint inflammation (arthritis, capsulitis & synovitis), plantar plate tears, tendinosis (“tendinitis”), bursitis and Morton’s neuroma.
A Morton’s neuroma occurs when scar tissue builds upon a nerve in between the toes known as the interdigital nerve (nerve between the digits, or toes). In Morton’s entrapment, the common plantar digital nerve, also referred to as the intermetatarsal nerve, gets compressed from forefoot plantar pressure in the late midstance and propulsive phases of gait against the distal margin of the transverse intermetatarsal ligament This is most frequently seen in women and is and is attributed to high heeled shoes. The pain is often severe and has an electric shock character to it. Common symptom descriptions include some or all of the following: “It feels like my sock is wadded up under my foot,” “cramping,” “numbness,” “burning,” “radiating sensations into the adjacent toes,” “the inability to walk barefoot on a hard floor,” and “tingling.” Others describe a feeling like having a pebble in their shoe or walking on razor blades.
Symptoms include: pain on weight bearing, frequently after only a short time. The nature of the pain varies widely among individuals. Some people experience shooting pain affecting the contiguous halves of two toes. Burning, numbness, and paresthesia may also be experienced. Usually, patients with Morton’s entrapment demonstrate pain with plantar palpation of the interspace between the metatarsal heads.
As a true nerve entrapment no different in pathology from carpal tunnel syndrome, Morton’s entrapment treatment should be oriented toward decompression. Indeed, the treatment success rate of peripheral nerve decompression in Morton’s entrapment is higher than with surgical resection, has a much lower complication rate, and precludes serious complications associated with nerve excision.
Diagnostic lidocaine blocks are extremely beneficial in assisting in making an accurate diagnosis and can help the practitioner decide on a course of treatment, specifically when two adjacent interspaces are symptomatic. It has generally been recommended that prior to surgical treatment for Morton’s entrapment, all methods of “conservative” care should be exhausted, including corticosteroid injections, application of offloading pads, sclerosing injections with alcohol or phenol, or radiofrequency ablation.
Radiofrequency nerve treatment is a technique, which has been used for over 10 years for the treatment of longstanding pain. Using local anesthesia, an electrode is placed into the tissue at the painful site and an electric current is delivered, generating heat that destroys the sensory nerve fiber.