Associations Between Physical Therapy Visits and Pain and Physical Function After Knee Arthroplasty: A Cross-Lagged Panel Analysis of People Who Catastrophize About Pain Prior to Surgery

Abstract

Objective: Physical therapy visit number and timing following knee arthroplasty (KA) are variable in daily practice. The extent to which the number and timing of physical therapy visits are associated with current and future pain and function-and, alternatively, whether pain and function are associated with the number of future physical therapy visits following KA-are unknown. The purpose of this study was to determine temporal and reciprocal associations between the number of physical therapy visits and future pain and function in people with KA.

Methods: A cross-lagged panel design was applied to a secondary analysis of data from a randomized clinical trial of patients with pain catastrophizing. The 326 participants underwent KA and completed at least 7 of 9 health care diaries over the year following surgery. The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain and physical function subscales were completed preoperatively and multiple times during follow-up. Separate cross-lagged panel analyses were conducted for WOMAC pain and physical function.

Results: From surgery to 2 months postsurgery, reciprocal associations were generally not found between physical therapy visit number and future pain or function. From 2 to 6 months postsurgery, a greater number of physical therapy weekly visits were associated with higher (worse) 6-month pain and function. Higher (worse) WOMAC pain at 2 and 6 months led to more visits from 2 to 6 and 6 to 12 months, respectively.

Conclusions: Higher pain scores 2 months postsurgery were associated with higher physical therapy use in the 2 to 6 months following surgery. However, patients with increased physical therapy use from 2 to 6 months had significantly higher pain scores 6 months postsurgery. Those patients with persistent pain 6 months postsurgery were higher users of physical therapy 6 to 12 months postsurgery. This reciprocal positive association between pain and physical therapy during this time period suggests minimal benefit of physical therapy despite an increased physical therapy use for patients with higher pain.

Impact: This is the first study to determine the association between the number and timing of physical therapy visits and current and future pain and function. Based on the results, physical therapy might not be a cost-effective strategy to treat patients with persistent pain following KA.

Trial registration: ClinicalTrials.gov NCT01620983.

Keywords: Knee Arthroplasty; Outcome Assessment (Health Care); Pain.