Background: Measures of long-term success of total hip arthroplasty (THA) over the past 50 years have focused primarily on implant survival, with less evidence on long-term functional outcomes. Questions/Purposes: We aimed to study 20-to-40-year functional outcomes after primary THA. We investigated the extent to which (1) functional outcomes after THA are maintained long term; (2) patient characteristics such as age, hip disease diagnosis, and comorbidities affect recovery of function and survivorship after THA; and (3) patients’ overall function after THA is affected by the need for revision, the aging process, and associated comorbidities. Methods: We retrospectively reviewed outcomes of the senior author’s patients between 1968 and 1993. Of 1207 patients, we identified 167 patients (99 female, 68 male; 276 primary THAs) who were at least 65 years old at follow-up and had at least 20 years of follow-up. Mean age at surgery was 55 years; mean follow-up time was 27 years. Bilateral THAs were performed in 109 patients (65%), and revisions in 81 patients (48.5%). Clinical outcomes including pain level, walking ability, range of motion, and overall function were determined by the Hospital for Special Surgery (HSS) hip scoring system. Contralateral and revision surgery, as well as patient age, sex, and body mass index, were included as covariates. To account for unequally spaced follow-up time points and competing causes of functional decline (e.g., age, contralateral hip disease, and need for revision THA), a latent class mixed model approach was used to identify unobserved classes of patients who had similar outcomes. Linear, quadratic, and piecewise-polynomial growth models were considered for class identification. The best fitting model was determined based on Bayesian information criterion. Results: A four-class model of this patient population was identified: (1) the Elderly Class, who had a mean age of 62 years at the time of primary THA; (2) the Bilateral Class, who underwent simultaneous or staged bilateral THA; (3) the Revision Class, who required at least one revision; and (4) the Youngest Class, who had a mean age of 49 years. After an initial period of improvement in all groups, the functional trajectory diverged according to classifications. Age was the strongest determinant of long-term outcome, with HSS hip scores in the Elderly Class declining after about 20 years. The Youngest Class maintained good-to-excellent hip function for over 30 years. Revision THA and contralateral THA accounted for a temporary decline in function, after which overall good function was regained for the long term. Conclusions: All classes in the study population enjoyed good-to-excellent outcomes after THA for about 20 years. Thereafter, functional decline was attributed more to aging than to the need for revision. One or more revision THA did not negatively influence long-term clinical outcomes, suggesting that, even for younger patients, symptoms, rather than the avoidance of possible revision, should be the primary determining factor when indicating THA.
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