Design of patient-specific gait modifications for knee osteoarthritis rehabilitation

Abstract

Abstract-Gait modification is a nonsurgical approach for reducing the external knee adduction torque in patients with knee osteoarthritis (OA). The magnitude of the first adduction torque peak in particular is strongly associated with knee OA progression. While toeing out has been shown to reduce the second peak, no clinically realistic gait modifications have been identified that effectively reduce both peaks simultaneously. This study predicts novel patient-specific gait modifications that achieve this goal without changing the foot path. The modified gait motion was designed for a single patient with knee OA using dynamic optimization of a patient-specific, full-body gait model. The cost function minimized the knee adduction torque subject to constraints limiting how much the new gait motion could deviate from the patient's normal gait motion. The optimizations predicted a "medial-thrust" gait pattern that reduced the first adduction torque peak between 32% and 54% and the second peak between 34% and 56%. The new motion involved three synergistic kinematic changes: slightly decreased pelvis obliquity, slightly increased leg flexion, and slightly increased pelvis axial rotation. After gait retraining, the patient achieved adduction torque reductions of 39% to 50% in the first peak and 37% to 55% in the second one. These reductions are comparable to those reported after high tibial osteotomy surgery. The associated kinematic changes were consistent with the predictions except for pelvis obliquity, which showed little change. This study demonstrates that it is feasible to design novel patient-specific gait modifications with potential clinical benefit using dynamic optimization of patient-specific, full-body gait models. Further investigation is needed to assess the extent to which similar gait modifications may be effective for other patients with knee OA.

Fig. 1

Schematic of the 27 degree-of-freedom (DOF) full-body gait model used to predict novel gait motions that reduce the peak knee adduction torque. All joints are traditional engineering joints (gimbal, universal, pin) with the exception of the ground to pelvis joint which possesses 6 DOFs. Parameters defining the positions and orientations of joints in the body segments and the masses, mass centers, and moments of inertia of the body segments were calibrated to gait data collected from a single patient with knee osteoarthritis.

Fig. 2

Visualization of the moment arm of the ground reaction force vector about the knee center for experimental and optimized gait motions. (a) Nominal experimental gait motion. (b) Gait motion predicted using tighter tracking of leg control torques and center of pressure locations. (c) Gait motion measured posttraining when the patient tried to walk using his old gait pattern. (d) Gait motion predicted using looser tracking of leg control torques and center of pressure locations. (e) Gait motion measured posttraining when the patient tried to walk using an exaggerated version of the predicted gait motions. The selected time frame is the location of the first peak in the knee adduction torque curve.

Fig. 3

Left knee adduction torque curves measured experimentally for the nominal gait motion (solid lines), predicted by the optimizations (dashed lines), and measured experimentally after gait retraining (dotted lines). (a) Results corresponding to tighter tracking of nominal experimental data. (b) Results corresponding to looser tracking of nominal experimental data.

Fig. 4

Pelvis obliquity and axial rotation curves measured experimentally for the nominal gait motion (solid lines), predicted by the optimizations (dashed lines), and measured experimentally after gait retraining (dotted lines). (a) Results corresponding to tighter tracking of nominal experimental data. (b) Results corresponding to looser tracking of nominal experimental data.

Fig. 5

Left hip, knee, and ankle flexion curves measured experimentally for the nominal gait motion (solid lines), predicted by the optimizations (dashed lines), and measured experimentally after gait retraining (dotted lines). (a) Results corresponding to tighter tracking of nominal experimental data. (b) Results corresponding to looser tracking of nominal experimental data.

Fig. 6

Left hip abduction, knee extension, and ankle inversion torque curves measured experimentally for the nominal gait motion (solid lines), predicted by the optimizations (dashed lines), and measured experimentally after gait retraining (dotted lines). (a) Results corresponding to tighter tracking of nominal experimental data. (b) Results corresponding to looser tracking of nominal experimental data.

Fig. 7

Left foot center of pressure locations on the bottom of the foot measured experimentally for the nominal gait motion (solid lines), predicted by the optimizations (dashed lines), and measured experimentally after gait retraining (dotted lines). (a) Results corresponding to tighter tracking of nominal experimental data. (b) Results corresponding to looser tracking of nominal experimental data.

Fig. 8

Left foot ground reaction forces measured experimentally for the nominal gait motion (solid lines), predicted by the optimizations (dashed lines), and measured experimentally after gait retraining (dotted lines). (a) Results corresponding to tighter tracking of nominal experimental data. (b) Results corresponding to looser tracking of nominal experimental data.