OPTOELECTRONIC GAIT ANALYSIS AFTER METARSOPHALANGEAL HALLUX ARTHRODESIS

Abstract

Purpose: Two questions arise after metatarsophalangeal hallux arthrodesis: what are the 3D changes observed when walking on flat ground ? and is the arthrodesis compensation essentially at the talocrural or interphalangeal level ?

Material and methods: Our series included twelve patients (ten women and two men) mean age 60.7 years. Nine patients had unilateral arthrodesis and three bilateral arthrodesis. The optoelectronic exploration was conducted barefoot. The patients wore underclothes and 27 reflectors. A miniaturised reflector was placed on the distal end of each hallux. Three valid recordings were made.

Results: General gait parameters and kinematic and kinetic values were unchanged (excepting nonsignificant maximal ankle dorsiflexion). On the arthrodesis side we observed: significant decline in propulsion force in the anteroposterior and vertical planes; significantly later heel lift-off; systematic anterior displacement of the ground reaction force of the metatarsophalangeal joint (not seen on the healthy side).

Discussion: We propose a coherent explanation of these observations. The kinetics of balance movement under the head of the first metatarsal head is changed. When the foot is flat on the ground, as the ankle balance movement occurs, the weight of the body is transferred earlier and massively to the forefoot. While in the healthy foot this occurs under the metatarsophalangeal joint of the great toe, in arthrodesis patients body weight is transferred under the interphalangeal joint of the great toe. The balance movement of the interphalangeal joint of the great toe occurs when the ankle balance movement is terminated. The centre of the balance movement is more distal and heel lift-off tends to occur later. During the propulsion phase, the greater lever arm limits the propulsion force, explaining the lesser peak force observed on the arthrodesis side. Use of reflectors on the distal end of the hallux demonstrated that the arthrodesis compensation occurs essentially at the interphalangeal level, exposing this joint to greater risk of degeneration.