The Effects of Hip Abductor Muscle Strengthening on Long Term Outcomes Following Total Knee Arthroplasty

Submission note: A thesis submitted in fulfillment of the requirements for the degree of Doctor of Philosophy to the School of Allied Health, Human Services and Sport, College of Science, Health and Engineering, La Trobe University, Victoria, Australia.

Total knee arthroplasty (TKA) is a successful treatment option for relieving the symptoms associated with endQstage knee osteoarthritis. Restoration of strength as well as physical function has been shown within six months after surgery. However, these outcomes still represent a moderate level of impairment compared to healthy individuals. It is important that rehabilitation programs for people following TKA achieve outcomes beyond preoperative status that are more comparative to normal function. Rehabilitation programs to date have typically focused primarily on restoring quadriceps strength, with moderate improvements in outcome. Preliminary evidence indicates that hip abductor strength is also related to improved physical function in people post TKA, and intervention that improves hip abductor strength may also improve outcome from surgery. This thesis therefore investigated the effectiveness of targeted hip abductor strength training in people post TKA to improve outcome from surgery. The overall aim was to determine whether the incorporation of targeted hip abductor strength training into rehabilitation resulted in improved hip abductor muscle strength, functional performance and patient reported outcomes in people following TKA. A systematic review and metaQanalysis of available evidence was completed to evaluate the impairments in lower limb muscle strength following TKA. Evidence was found for the presence of quadriceps muscle weakness in people post TKA relative to a nonQTKA population, which persists well beyond three years after TKA. Evidence was also found for the presence of hamstring weakness in people who were one to three years post TKA. No study had specifically compared hip abductor strength between people post TKA and a nonQTKA population, although several studies reported a relationship between hip abductor strength and physical function in people post TKA. In order to proceed with the proposed research, a reliable method of recording hip abductor strength that was applicable for use in the clinical setting with people post TKA needed to be developed and formally tested. IntraQrater reliability was found to be excellent when measuring hip abductor strength using a handQheld dynamometer either when combined with externalQresistance (i.e. belt fixation) (ICC3,1 equal 0.82) or with therapistQresistance (ICC3,1 equal 0.80). Individual hip abductor strength changes of greater than 33N (72 percent) for belt resisted and 57N (79 percent) for therapist resisted measurements exceeded the 95 percent confidence interval (95 percent CI) and may represent real change when an individual patient is tested at two timepoints. For groups of patients, hip abductor strength changes of greater than 8N (14 percent) (belt resisted) and 14N (17 percent) (therapist resisted) could be interpreted as real change. The magnitude of hip abductor strength obtained when measured against therapist resistance was found to be significantly higher than when measured using belt resistance. The belt resistance approach was therefore applied in the main study. The main study in this thesis was a prospective randomised controlled trial that was conducted on 105 people. Participants were recruited into the study at a mean 8 days (SD equal2) post TKA. This study sought to determine whether the incorporation of targeted hip abductor strength training into a standard care rehabilitation program xiv following TKA resulted in greater improvements in hip abductor muscle strength, functional performance and patient reported outcomes relative to a control group that completed the standard care rehabilitation program alone. Participants attended inpatient rehabilitation for approximately 12 days followed by weekly outpatient rehabilitation for approximately six weeks. Participants were reassessed at six weeks and at six months after the commencement of rehabilitation. The incorporation of targeted hip abductor strengthening in this study did not result in significantly greater improvements in any of the primary or secondary outcome measures, and both rehabilitation protocols were found to be equally effective. This result was most likely because the functional exercises that formed a large component of the standard care rehabilitation program provided enough stimulus to strengthen the hip abductor muscles and generate significant improvement in all outcome measures. Given the similar response for both groups, it would appear that hip abductor strength in people post TKA can be improved through a variety of means. Clinicians therefore have some flexibility regarding exercise prescription, which allows for rehabilitation programs to be tailored specifically to the patients’ abilities and preferences. Further research is recommended to determine whether targeted hip abductor strengthening may be worthwhile if optimal dosage, type of exercise, and compliance by patients and therapists are evaluated and potentially improved.