Load cell analysis following silastic arthroplasty of the hallux

The first metatarsophalangeal joint was replaced by a flexible silastic hinge prosthesis in 33 joints of 25 patients. Most patients were pleased with the operation but one third had some discomfort under the second and third metatarsal heads. We used a computer linked load cell matrix to analyse the forces under these feet during normal walking. After silastic arthroplasty there was a rise of 65% in peak load under the second and third metatarsal heads compared with that found in the opposite feet which had not undergone operation (P less than 0.001). This was associated with a fall in peak load under the hallux of 43% (P less than 0.03) compared to normal and a less significant fall averaging 23% in the peak pressure experienced under the first metatarsal head. There was a rise in peak heel loading and a reduction in the normal pronation which occurs during the stance phase of walking.