Towards a better understanding of foot and ankle kinematics in rheumtoid arthritis, the effects of walking speed and structural impairments

From an early stage of the disease 40% to 60% of the Rheumatoid arthritis (RA) patients suffer from walking impairments such as pain, diminished mobility and problems with daily activities. With the recent development of optical recording technologies and detailed foot and ankle computer models, typical RA foot and ankle kinematic measures have been assessed and reported. However, the relationships between kinematics and walking impairments or pathological changes of foot and ankle structures are not yet fully understood. Such fundamental knowledge may support the development and evaluation of interventions, which aim to improve or restore normal foot and ankle kinematic function. The aim of this thesis was to improve our understanding of the causes of the alterations in foot and ankle kinematics of patients with RA compared to healthy subjects. Gait of 23 RA patients with various stages of disease severity and gait of 14 healthy age-matched subjects was recorded. Their foot and ankle kinematic measures were assessed by means of a foot and ankle model consisting of segments for the leg, hindfoot, midfoot, forefoot and hallux. In the healthy subjects, strong and consistent coupling of motion was observed between hindfoot inversion and hallux dorsi-flexion motion and also between leg rotation and medial-arch collapse. Such strong motion relationships may explain why a local pathology such as joint erosion has a global effect on segment motion elsewhere in the foot. The healthy subjects walked at comfortable and two lower walking speeds, which matched the walking speeds of the RA subjects. However, the factor walking speed alone was not able to explain all observed differences between RA and healthy subjects walking at comfortable speed. The hallux dorsiflexion, midfoot supination and hindfoot inversion motions were influenced by the factor disease, independent of the walking speed. These three segment motions could be related to clinical scores. Local joint erosion and synovitis influenced hallux motion. Hindfoot alignment as well as pathological changes to Achilles and peroneus tendons influenced midfoot and hindfoot motion, respectively. In conclusion, relationships between kinematics and pathological degeneration of foot and ankle structures were found and improve our understanding of RA gait impairments.