Impact of Concomitant Spine Comorbidities on Patient-Reported Outcomes After Total Knee Arthroplasty.

Background: The impact of clinically symptomatic spine comorbidities on patient-reported outcomes after total knee arthroplasty (TKA) remains unclear. We hypothesized that patients with pre-TKA spine comorbidities would demonstrate inferior outcomes compared with those without spine comorbidities. Methods: We retrospectively reviewed 492 patients who underwent primary TKA performed between 2020 and 2022. Spine comorbidities were defined as a history of lumbar injection, spine surgery, low back pain, or radiating pain. Three propensity score-matched analyses were performed: (1) primary analysis comparing patients with pre-TKA spine comorbidities vs. controls (141 pairs; 1:1 matching), (2) secondary analysis excluding patients who developed post-TKA spine comorbidities to isolate the effect of preexisting spine conditions (127 pairs; 1:1 matching), and (3) subgroup analysis comparing patients with prior spine surgery vs. those without (47 vs. 138; 1:3 matching). The Knee injury and Osteoarthritis Outcome Score (KOOS) was assessed preoperatively and at 1 and 2 years postoperatively. Results: There were 282 patients (141 pairs) in the primary analysis cohort (mean age, 72 years; 85% female). KOOS Sport showed the most consistent between-group differences across analyses. In the primary analysis, KOOS Sport was significantly lower in the spine comorbidity group at 2 years after false discovery rate (FDR) correction (mean, 43.4 vs. 53.9; mean difference, -10.5; Cohen's d = -0.45). KOOS Total showed nominally lower scores, although this did not remain significant after multiplicity adjustment. In the secondary analysis, KOOS Symptoms (71.2 vs. 78.0), Sport (44.1 vs. 56.5), and Total scores (66.4 vs. 72.9) were significantly lower at 2 years after FDR correction. In the subgroup analysis, patients with prior spine surgery showed lower KOOS scores in unadjusted comparisons at 2 years, although none of these differences remained significant after FDR correction. Conclusions: Pre-TKA spine comorbidities are associated with inferior KOOS outcomes, most consistently in high-demand activities. Awareness of these coexisting conditions may be helpful when counseling patients undergoing TKA about realistic expectations for postoperative functional recovery. Level of Evidence: Level III, Therapeutic Study. See Instructions for Authors for a complete description of levels of evidence.