The effect of total hip arthroplasty surgical approach on gait

Abstract

This study examined the effect of the surgical approach used in total hip arthroplasty (THA) on gait mechanics six months following surgery. Quantitative gait analysis was performed on 29 subjects: 10 anterolateral (A-L) and 10 posterolateral (P-L) THA patients and nine able-bodied, velocity-matched subjects. Discriminant function analysis was used to determine the distinction of the groups with respect to sagittal plane hip range of motion, index of symmetry, trunk inclination, pelvic drop, hip abduction, and foot progression angles. The A-L group had the largest trunk inclination (3.0 ± 2.4°) and the smallest hip range of motion (34.0 ± 7.4°). Both THA groups demonstrated greater asymmetry as expressed by the smaller symmetry index (0.97 ± 0.04 for A-L and 0.98 ± 0.05 for the P-L) than the able-bodied group (0.99 ± 0.01). The classification procedure correctly classified 89% of the control group cases, 90% of the A-L cases, and 50% of the P-L cases. These results support the conclusion that six months following surgery, the gait of the majority (85%) of THA patients has not returned to normal. The A-L patients displayed distinct gait patterns, while a small percentage (30%) of the P-L patients demonstrated normal gait. While these differences are statistically significant, the clinical significance is unknown and linked to the duration that they persist. Keywords Gait Joint replacement Biomechanics Asymmetries Introduction Total hip arthroplasty (THA) is now the most common adult reconstructive hip surgery in the United States, with approximately 168,000 surgeries performed in 1999 [15] . THA has had significant clinical success by providing patients with improved quality of life, physical function, and relief of pain [18] . Despite the success of the operation, the gait characteristics of the post-operative patients may not return to normal for several years [10] . Following hip replacement surgery, gait has been shown to improve significantly in several areas, including improved symmetry of stance time and load distribution between limbs, increased walking speed, and increased range of motion at the hip [10,13,20] . Despite these improvements, post-operative gait is not to a level that would be considered normal [10,12,13,16,17,20] . The effects of THA on the function of the muscles and static restraints surrounding the hip could be one of the factors that prevent the gait pattern from returning to normal and, thus, variation in the surgical approach could be a factor in post-operative gait. Previous studies used quantitative gait analysis to provide information about pre- and post-operative walking in the THA population, but did not study the effect of surgical approach on post-operative gait. Two common surgical approaches are used in THA. The anterolateral (A-L) approach used in this study was a modified Mallory approach where the abductor muscle fibers were spread along anatomic planes, salvaging the muscle fiber integrity [5] . The A-L approach could affect the function of the gluteus minimus, gluteus medius, tensor fasciae latae, and vastus lateralis muscles [2] . Anatomically, the gluteus medius and gluteus minimus are responsible for much of the torque needed for hip abduction and control of pelvic obliquity during gait. The posterolateral (P-L) approach affects the posterior joint capsule and external rotator muscle group, which is predominantly responsible for posterior and lateral stability of the hip joint [2] . The clinically observed opinion is that the A-L approach has a higher rate of post-operative limp, while the P-L approach has a higher risk of dislocation [19] . Studies have addressed how surgical approach affects the functioning of hip abductor muscles following THA [1,4,6,14,20,22–24] . The A-L approach has been shown to produce more positive results in static Trendelenburg tests, an indication of hip abductor dysfunction, than the P-L approach [24] . Post-operative isometric hip strength was examined by Gore et al. [6] , who found the P-L approach resulted in a higher and more normal level of measured strength than the A-L approach. In contrast, Downing et al. [4] demonstrated no difference in isometric hip strength following THA between the posterior and lateral approaches. Although Downing et al. compared the posterior approach to a direct lateral approach instead of the A-L approach, the muscle groups affected were very similar, since the direct lateral approach reflected the anterior fibers of the gluteus medius and minimus. Discrepancies about the effect of approach on hip abductor strength exist; however, the relation between isometric muscle strength and function remains unclear [23] . Previously, Ritter et al. we examined the post-operative limp after THA and found no difference between the A-L and P-L approaches [19] . However, the limp assessment was qualitative, gathered through physician observation and questionnaires about the patient’s perceptions. Although the studies examining clinical differences between the two surgical approaches are beneficial, they cannot detect the subtle effects distinguished through the use of gait analysis [7] . The outcome of both approaches is clinically sound [11,19] , but quantitative data documenting the possible differences in post-operative gait are lacking. The choice of surgical approach is based on the preference and experience of the surgeon, and patient specific information such as lifestyle and physical condition are given little weight in the decision. The purpose of this study was to examine the effects of the surgical procedure on the mechanics of gait six months post-operatively. Specifically, load and kinematic characteristics of post-operative A-L and P-L patients were compared at a self-selected velocity of progression. The characteristics of these groups were also compared to a velocity of progression matched able-bodied control group....