Which functional assessments predict long-term wear after total hip arthroplasty?

BACKGROUND: There is a paucity of literature concerning functional assessment at long-term followup of THAs in general and in young patients specifically. Functional data may be useful in determining differences in the performance of various implants and surgical techniques in THA. QUESTIONS/PURPOSES: The purposes of this study were to evaluate a group of young patients who were still active 10 years after THA to determine (1) which functional tests and (2) which patient-reported outcome assessments predicted long-term THA function, as measured by acetabular UHMWPE wear, and (3) whether medical comorbidities influenced patient performance on activity tests and patient outcome questionnaires.
METHODS: Fifty patients (58 hips) 50 years and younger at the time of THA were followed clinically and radiographically for a minimum of 10 years. All patients wore step activity monitors for up to 21 days, performed 6-minute walk (6-MW) tests, and every patient had minimum 10-year radiographs and sequential radiographs evaluated for wear using edge detection techniques. Mean age and BMI at surgery were 39 years and 29 kg/m(2), respectively.
RESULTS: Patients who walked more as determined by step activity monitor (average daily steps) had more linear acetabular UHMWPE wear per year and more volumetric wear per year. The 6-MW, University of California Los Angeles (UCLA), and Tegner Lysholm scores did not correlate with acetabular wear. Mean 6-MW distance was 335 m and pedometer data averaged 1.56 million steps per year. Average UCLA and Tegner Lysholm scores were 6 and 3, respectively. Mean linear wear rate was 0.266 mm/year; mean volumetric wear rate was 82.6 mm(3)/year. The number of comorbid medical conditions had a detrimental effect on our activity parameters and outcomes questionnaires, but the relationships were not statistically significant.
CONCLUSIONS: Of functional tools measured, only pedometer data correlated with THA polyethylene wear. Obtaining pedometer data should be considered when trying to distinguish differences in various hip arthroplasty designs and techniques over the long term.