OBJECTIVE: To determine if a one-year change in walking speed is associated with receiving an incident knee replacement during the following year in adults with and at risk for knee osteoarthritis (OA). METHODS: Using data from the Osteoarthritis Initiative, we determined a one-year change in 20- meter walk speed from three observation periods (i.e., 0-12, 12-24, and 24-36 month). We operationally defined one-year change in walking speed as either: 1) decline: < -0.1 m/s change, 2) no change: between -0.1 and 0.1 m/s change, 3) increase: > 0.1 m/s change. Incident knee replacement was defined using each subsequent one-year period (i.e., 12-24, 24- 36, and 36-48 month). Combining data from the three observation periods, we performed a Poisson regression with robust error variance to determine the relative risk between a change in walking speed (exposure) and incident knee replacement over the following year (outcome). RESULTS: Of the 4,264 participants included within this analysis (11,311 total person visits), 115 (3%) adults received a knee replacement. Decline in walking speed was associated with a 104% increase in risk [adjusted relative risk (RR)=2.04; 95% confidence interval (CI)= 1.40-2.98], while an increase in walking speed associated with a 55% decrease in risk (RR=0.45; 95% CI=0.22-0.93) of incident knee replacement in the following year compared to a person with no change in walking speed. CONCLUSION: A one-year decline in walking speed is associated with an increased risk, while one-year increase in walking speed is associated with a decreased risk of future incident knee replacement.

The International Society of Arthroplasty Registries (ISAR) Patient-Reported Outcome Measures (PROMs) Working Group have evaluated and recommended best practices in the selection, administration, and interpretation of PROMs for hip and knee arthroplasty registries. The 2 generic PROMs in common use are the Short Form health surveys (SF-36 or SF-12) and EuroQol 5-dimension (EQ-5D). The Working Group recommends that registries should choose specific PROMs that have been appropriately developed with good measurement properties for arthroplasty patients. The Working Group recommend the use of a 1-item pain question ("During the past 4 weeks, how would you describe the pain you usually have in your [right/left] [hip/knee]?"; response: none, very mild, mild, moderate, or severe) and a single-item satisfaction outcome ("How satisfied are you with your [right/left] [hip/knee] replacement?"; response: very unsatisfied, dissatisfied, neutral, satisfied, or very satisfied). Survey logistics include patient instructions, paper- and electronic-based data collection, reminders for follow-up, centralized as opposed to hospital-based follow-up, sample size, patient- or joint-specific evaluation, collection intervals, frequency of response, missing values, and factors in establishing a PROMs registry program. The Working Group recommends including age, sex, diagnosis at joint, general health status preoperatively, and joint pain and function score in case-mix adjustment models. Interpretation and statistical analysis should consider the absolute level of pain, function, and general health status as well as improvement, missing data, approaches to analysis and case-mix adjustment, minimal clinically important difference, and minimal detectable change. The Working Group recommends data collection immediately before and 1 year after surgery, a threshold of 60% for acceptable frequency of response, documentation of non-responders, and documentation of incomplete or missing data.