Abstract
Identification of gait deviations and compensations in patients with total hip arthroplasty (THA) is important for the management of their fall risks. To prevent collapse of the lower limbs while balancing and supporting the body, proper combinations of joint moments are necessary. However, hip muscles affected by THA may compromise the sharing of load and thus the whole body balance. The current study aimed to quantify the control of body support in patients with THA in terms of the total support moment (Ms) and contributions of individual joint moments to Ms during walking.
Six patients who underwent unilateral THA via an anterolateral approach for at least six months at the time of the gait experiment, and six age- and gender-matched healthy controls were recruited. Twenty-eight infrared retro-reflected markers were placed on specific landmarks of the pelvis-leg apparatus to track the motion of the segments during walking. Kinematic and kinetic data were measured using an 8-camera motion analysis system (Vicon, Oxford Metrics, U.K.) and two force plates (AMTI, U.S.A.). The Ms of a limb was calculated as the sum of the net extensor moments at the hip, knee and ankle during stance phase. The contributions of the hip, knee and ankle to the first and second peaks of Ms (Ms1 and Ms2) were calculated by dividing the joint moment value by the corresponding peak values of Ms. Independent t-tests were performed to compare between groups at a significance level set at α=0.05 using SAS version 9.2 (SAS Institute Inc., NC, USA).
No significant differences in Ms1 and Ms2 were found between the THA group and normal controls (P >0.05). However, compared to the healthy controls, significantly increased hip and ankle contributions but decreased knee contributions to Ms1, and significantly increased hip contributions but decreased ankle contributions to Ms2 were found in the THA group.
Similar Ms1 and Ms2 between groups indicates that the lower limbs in the THA group were able to provide normal body supports. However, this was achieved via an altered contributions of the hip, knee and ankle. Hip and knee extensors play important roles in supporting the body when the Ms1 occurs during early stance of walking. In the THA group, greater hip and ankle contributions but lesser knee contributions for the Ms1 indicates that the function of hip extensors were not affected but compensatory mechanisms of the knee and ankle were found. For the Ms2, hip flexor and ankle plantarflexors are important for supporting the body during late stance. Decreased hip flexor (i.e., greater hip extensor contributions) and ankle plantarflexor moments in the THA patients suggests that the hip flexors and ankle plantarflexor muscles were affected by THA surgery. Hip muscles affected by the THA may compromise the sharing of load at the hip and thus the whole body balance. Further postoperative rehabilitation is suggested for the patients following THA. Further studies on the effects of different surgical approaches on the support moments is needed for improving treatment plans.
