Background/Purpose: For patients undergoing total knee replacement (TKR) for osteoarthritis (OA), preoperative musculoskeletal (MSK) complaints in areas beyond the index knee are common; however, the risk for new MSK comorbidities after TKR is not well studied.

Methods: We used data from the Adding Value in Knee Arthroplasty (AViKA) prospective cohort study on patients undergoing elective TKR for OA at a tertiary academic center. Preoperative questionnaires included demographics, data for Charlson Comorbidity Index, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) Pain and Function Scales, Mental Health Inventory-5 (MHI-5), Pain Catastrophizing Scale (PCS), and presence of MSK symptomatic areas by region (neck, hands/wrists/arms/shoulders, back, hips, non-index knee, and ankles/feet). Follow-up questionnaires including data on incident symptomatic areas were distributed at 3, 6, 12, 24, 36, and 48 months post-TKR. Cumulative incidence (number of new cases per number of subjects at risk) and incidence rates (number of new cases per person time) were calculated for each symptomatic area.  We used Poisson regression models to identify factors associated with incident MSK symptomatic areas.  Covariates with two-sided p-values < 0.05, or incidence rate ratio (RR) < 0.8, or RR >1.25 in univariate analyses were incorporated in the final parsimonious models.

Results: Among 308 patients undergoing elective TKR for OA, 87% were younger than 75 years and 60% were female.  One-quarter of subjects had at least one symptomatic area at baseline, and of those, non-index knee was the most common presurgical symptomatic area (10%). The cumulative incidence of any new MSK symptomatic area over 4 years was 45%, while the incidence rate was 192 per 1000 person-years (95% CI 153-242 per 1000 person-years). Cumulative incidence was highest for non-index knee (23%) and back (15%); incidence rates for non-index knee and back were 69 per 1000 person-years (95% CI 52-92 per 1000 person-years) and 53 per 1000 person-years (95% CI 38-74 per 1000 person-years) respectively. Based on the final Poisson model (Table), variables associated with developing an incident MSK symptomatic area after TKR included female sex (RR 1.51, 95% CI 1.13-2.04), body mass index ≥35 (RR 1.34, 95% CI 1.03-1.74), baseline index knee WOMAC function score ≥41 (RR 1.49, 95% CI 1.12-1.97), and symptoms consistent with anxiety/depression (MHI-5 <68) (RR 1.41, 95% CI 1.10-1.82). 

Conclusion: Incident MSK comorbidities, particularly in the non-index knee and back, will occur in roughly half of elective TKR recipients in the four years following TKR.  Factors associated with incident MSK comorbidities include female sex, obesity, worse baseline index knee function scores, and anxiety/depression.  Further study is needed to examine the long-term impact of these incident comorbidities on postoperative rehabilitation and quality of life.