Instability and synovitis of the lesser MTP joints is a common cause of forefoot pain. Peck et al's (2006) series of 164 patients represented 26% of the patients presenting to their clinic with metatarsalgia.
The condition is commonest in middle-aged women. 82% of Peck et al's patients were women and the median age was 56.5 years. Most other (much smaller series support these demographics. Coughlin (1993) felt there was a distinct group of mainly male athletes, with a lower average age.
Pain in the second MTP with synovitis and vertical instability was first described in 1985 by Mann et al, who considered that the instability was due to synovitis of uncertain origin, perhaps associated with impingement from hallux valgus.
Early studies focused on synovitis stretching the capsule and the collateral ligaments. The collateral ligaments are important stabilisers of the MTP joint (Deland 1992). Bhatia (1994) found that division of the plantar plate reduced MTP stability by 30% and division of the collateral ligaments by 46%.
Attention became more concentrated on the plantar plate in the mid-1990s. Initially the plate was thought to be detached at its thin proximal margin (Johnston 1994, Fortin and Myerson 1995), but Yao (1994) showed that plantar plate tears usually occur close to the insertion into the proximal phalanx. Gazdag and Cracchiolo (1998) found plantar plate tears in all 13 patients examined by plain arthrography or MRI. Powless and Elze (2001) carried out plain arthrograms on 58 feet and found plantar plate tears in 24 (41%), collateral tears in 19 (33%) and combined lesions in 15 (26%). However, Gregg (2006) found MR or ultrasoound evidence of plantar plate tears in 35% of normal feet, becoming commoner in older age groups.