DEVELOPING A VALID METHOD OF PREDICTING RETURNING TO WORK FOLLOWING PRIMARY TOTAL KNEE ARTHROPLASTY

Purpose: The aim of this study was to design and validate a patient-completed questionnaire capable of accurately predicting whether a primary total knee arthroplasty (TKA) patient will or will not have returned to work by a given post-operative time point.

Method: A prospective cohort study was conducted involving primary TKA patients who were currently employed, aged 18-69 years and planned on returning to work post-operatively.  The patients completed a questionnaire pre-operatively that assessed patient characteristics, motivation to work, physical demands of their job, workplace characteristics, knee functionality, and global health. The questionnaire was comprised of both novel and previously validated items including the Knee injury and Osteoarthritis Outcome Score (KOOS) and 12-item Short-Form Health Survey (SF-12 version 2) measure of global health. The participants were assessed at 4-6 weeks, 3 months, and 6 months post-operatively to identify when they returned to work.  Questionnaire items were evaluated using factor analysis and reliability testing to develop subscales. Survival analysis identified which items and subscales were significant predictors of the patient’s return to work. A composite score was calculated based on the results of the survival analysis to predict whether a patient would return to work by the three time points: 6 weeks, 3 months, and 6 months post-operatively. This composite score became the Cleveland Occupational Knee (CLOCK) Index and by using set cut-points in the index score, its ability to accurately predict returning to work by a given time point was calculated.

Result: The Cleveland Occupational Knee (CLOCK) Index is completely patient-derived and can be completed within five to ten minutes.  Participants in the study (N=162) were predominantly white (84.6%) and female (68.5%) with a median age of 57 years. Based on the 162 patients enrolled, the CLOCK Index has a negative predictive value of 84.7% when predicting if the patient will have returned to work within 6 weeks post-operatively.  At the three and six month endpoints, the index can accurately predict if the patient will have returned to work with positive predictive values of 75.4% and 92.4% respectively.

Conclusion: The CLOCK Index can aid in the pre-operative counseling of patients considering a primary TKA by accurately predicting if and when the patient might anticipate returning to work post-operatively.