Symptom patterns in Peck et al (2006)
The typical patient is a middle-aged woman. Most patients have no history of trauma or inflammatory arthritis. There is a strong association with hallux valgus.
Peck et al identified three main patterns of symptoms:
- generalised forefoot pain - like many patients with metatarsalgia, there are often multiple factors such as reduced ankle dorsiflexion, first ray insufficiency and toe deformities
- pain related to the index MTP joint which may then decrease and be partly replaced by a feeling of walking on a pebble and toe deformity
- toe deformity with predominantly pressure symptoms, but where MTP instability influenced treatment
Examination may show:
- Puffiness around one or more MTP joints (usually the second), sometimes with divergence of the toes
- Tenderness around the joint, especially under the plantar plate
- Hammertoe and/or crossover toe deformity
- Instability, subluxation or dislocation of the MTP joint – probably about 10-20% present with fixed dislocation
- Hallux valgus
The Thompson draw test demonstrates instability with the MTP joint flexed slightly and the proximal phalanx drawn up and down.
- Grade 1 - <50% vertical translocation
- Grade 2 – 50-100% translocation
- Grade 3 – dislocatable
It may be difficult to distinguish the pain of MTP instability from that of an interdigital neuroma. Indeed, Coughlin's series of neuromas had about 5% of patients who also had instability, and about the same proportion of Peck's MTP instability patients also had neuromas. Diagnostic injections are the simplest method of differentiating the two pathologies (Miller 2001). Ultrasound and MR will show both.
Differential local anaesthetic injections can help differentiate MTP instability from a neuroma
Distinguish between tenderness under the metatarsal head and under the MTP joint and plantar plate
The Thompson-Hamilton draw test. The MTP joint is in neutral. Dorsal and plantar leverage on the proximal phalanx subluxes and reduces the joint.