Total hip arthroplasty (THA) is the treatment of choice for advanced hip osteoarthritis (OA). THA effectively reduces hip pain^1,2, improves self-reported function and quality of life compared to pre-operative levels^1–8 and most patients are highly satisfied with the outcome⁹. Despite these positive outcomes, patients continue to have physical impairments, functional limitations and altered movement patterns when compared to healthy-aged matched samples. Patients after THA demonstrate functional limitations on both self-reported and performance-based measures, when compared to healthy controls^5,8,10. Those patients also move with altered movement patterns during dynamic tasks such as the sit to stand task. Patients rise from the chair with a strategy that increases the loads on the non-operated limb and decreases the reliance on the operated limb^11,12. These asymmetrical movement patterns are concerning because the pattern of overloading of the non-operated joints after THA coincides with the non-random progression of OA in which the contralateral lower extremity joints are most likely to show degenerative changes¹³. In addition, after knee replacement, asymmetrical movement patterns have been linked to worse functional performance¹⁴.

The underlying impairments that may contribute to functional limitations and abnormal movement strategies in THA population are not known;​ however, muscle weakness of the lower extremity is likely a contributor. Residual muscle weakness of the operated lower extremity is still detectable even years after THA, when compared to the non-operated side^15–18, and to a healthy matched group^8,19. It is also possible that movement asymmetries presented after THA might result as learned behaviors that developed before or after surgery in the presence of pain or soon after surgery in the presence of instability or weakness.

The overall goal of this dissertation was two-fold. First, we intended to identify the primary physical impairments that contribute to functional limitations and abnormal movement patterns before and after THA. Second, we evaluated the utility of using the real-time visual feedback for reducing asymmetrical movements in patients after THA. The results from this work will allow to design targeted rehabilitation programs that may maximize functional and biomechanical recovery after THA.

In this dissertation, we conducted four studies. In the first study, we evaluated self-reported and performance-based functional recovery at 3 months after THA and we determined the contributions of physical impairments to functional limitations at 3 months post-surgery. The results of this study show that despite the improvements in self-reported and performance-based function, patients after surgery have lower level of function and strength compared to healthy controls, and that pain and strength measures differently contributed to self-reported and performance-based function. In the second study, we evaluated sit to stand biomechanics in patients before and after THA, and determined the relationships between physical impairments and altered performance during STS. The results of this study indicate that patients before and after surgery move with asymmetrical movement patterns that unload the operated limb and shift the load to the non-operated limb. We also determined that weakness in the operated limb was related to greater asymmetries in which the load on the operated limb was lower than the non-operated limb. In the third study, we evaluated the acute effect of real-time visual feedback of weight distribution on movement symmetry during STS in before and after THA, and examined whether strength of the operated limb influenced the response to the feedback. The results of this study indicate that subjects moved with more inter-limb symmetry in the sagittal and frontal planes when they were given the feedback, but this single instance of feedback did not eliminate all asymmetries. Subjects before and after THA showed similar response to visual feedback, and muscle strength measures were not related to the feedback response. In the final study, we examined whether the Wii balance board (WBB) can be used as a clinical tool to accurately assess weight bearing asymmetry during standing from and sitting to a chair, in comparison to laboratory-grade force plates as “gold-standard”. The results of this study indicate that the WBB and laboratory force plates have agreement for measuring peak VGRF and the inter-limb symmetry ratio. Although the WBB may serve as a low-cost alternative to expensive, laboratory force plates for measuring weight bearing asymmetry in a clinical or home-based setting, the results did show a systematic bias in which the WBB recorded more symmetrical force distribution.

Overall, this dissertation provides evidence for the post-operative improvements in functional abilities and movement symmetry for patients undergoing THA. However persistent physical impairments, functional limitations and asymmetrical movement strategies were found in patients 3 months after THA. This dissertation lays down the foundation of using the real time visual feedback to reduce interlimb asymmetries. Albeit feedback did not perfectly normalize symmetrical patterns, it could be that developing structured program that utilizes higher intensity and longer duration of visual feedback, combined with addressing underlying physical impairments may have beneficial effects on mitigating movement asymmetries and subsequently improving functional abilities.