Clin. Biomech. 1993; 8: 135- 141 Assessment of foot disorders using biomechanical analysis of foot loads during locomotion H Lanshammar PhD’, I Turan MD~, U Lindgren MD* ‘Department of Technology, Uppsala University, Uppsala, Sweden; *Department of Orthopaedic Surgery, Karolinska Institutet, Huddinge University Hospital, Huddinga, Sweden Summary The aim of this study was to investigate techniques for assessment of surgical procedures for foot disorders. An optoelectronic system was used to obtain position data during walking for the knee joint, ankle joint and the second metatarsal joint. The ground reaction forces were simultaneously measured and the moment of force at the mentioned joints were analysed. Pressure transducers in the shoe were used to measure the local pressure at the great toe, first and fifth metatarsal heads, and heel pad. Among studied procedures were Keller’s operation for hallux rigidus and distal oblique osteotomy for hallux valgus. The study indicated that both methods can be used to assess mediolateral shifts of the centre of pressure on the foot due to the operation. A difference between operation results were that the moment arm of the ground reaction force with respect to the knee joint increased after distal oblique osteotomy, while it decreased after the Keller type operation. From a clinical point of view this can have the effect that the loads at the knee joint and especially at the medial condyle increases after the distal oblique osteotomy. Relevance The study showed that the described techniques have a potential for assessment of surgery for first metatarsophalangeal joint. Of special relevance is the possibility of studying the effect of foot pathologies on the loads at the knee joint. Key words: Hallux valgus, hallux rigidus, moment, force, pressure, knee Introduction A malfunction in the foot not only causes a disturbance in other parts of the foot, but also affects the loading conditions in the more proximal parts of the musculo- skeletal system. If for instance the point of application of the ground reaction force (GRF) is shifted medially due to pain in the lateral parts of the foot, the loads on different parts of the foot will be affected. In addition loads in the knee will also change, since the moment arm of the GRF vector with respect to the centre of the knee joint will change (Figure 1). This applies both to standing and walking conditions, although the direc- Received: 19 May 1990 Accepted: 12 June 1992 Correspondence and reprint requests to: HBkan Lanshammar, Department of Technology, Uppsala University, Box 27, S-751 03 Uppsala, Sweden 0 1993 Butterworth-Heinemann Ltd 0268~0033/93/030135-07 tion of the force vector will usually also change during walking. In practice the resulting change in moment arms when the GRF vector point of application is moved cannot be computed by a mere translation, since the point of application and the direction of the GRF vector may change simultaneously due to compen- satory behaviour in other parts of the body. Therefore, to assess the biomechanical consequences of a defect in the foot, and particularly of a surgical procedure on the foot, it is necessary to measure the time history of the ground reaction force vector together with kinematic data for the joint of the involved leg. All data must be collected during locomotion. The overall aim of the present study was to evaluate objectively the results of surgical treatment for foot disorders by biomechanical methods. Since this type of analysis has been rarely used for this application the specific purpose was to investigate the usefulness of techniques for assessment of foot disorders.