Quantitative Analysis of the Limp in Coxarthrosis

Abstract

To establish quantitative analysis of the limp in patients with coxarthrosis, the rotation of the pelvis during walking was measured in three dimensions. Fifty-two normal subjects and 46 patients with coxarthrosis were studied. Eight patients were measured again after total hip replacement and we compared the findings before and after surgery. The rotation of the pelvis during walking was measured in the frontal, sagittal, and horizontal planes during free walking, using three gas rate-sensors fixed to the pelvis. Then we drew waveforms, using a microcomputer with an analogdigital converter. In the normal subjects, the waveforms were regular, symmetrical, and highly reproducible on repeated gait cycles in the frontal plane. In contrast, compared with those of the normal subjects, the waveforms of the patients with coxarthrosis were irregular, asymmetrical, and poorly reproducible. These characteristics of the patients’ waveforms were confirmed objectively when we calculated the symmetry, reproduction, and abnormality indices for the waveforms of the frontal plane, using the Fourier transform technique. In the sagittal plane, the pelvis was in anteversion at heel strike in each normal subject, while in most of the patients the pelvis inclined backward at heel strike of the affected side. In the horizontal plane, the waveforms were flat around the heel strike of the affected side in the majority of patients. The mean rotational angle of the patients was less than that of the normal subjects in the frontal plane, and larger in the sagittal plane. In all normal subjects, the rotational angle in the frontal plane was larger than that in the sagittal plane, while in 44 patients, the rotational angle in the frontal plane was less than that in the sagittal plane. We were therefore able to distinguish a patient from a normal subject by observation of the three indices of the frontal plane and by the ratio of the rotational angle in the sagittal plane to that in the frontal plane. The three indices, obtained by using the Fourier transform technique, and the ratio of the rotational angle, were useful for quantitative analysis of the limp in patients with coxarthrosis.