STUDY DESIGN: A retrospective review. OBJECTIVE: The purpose of this study is to trend PROMIS PF scores following lumbar fusion surgery and to investigate how the presence of functional comorbidities affects PROMIS PF scores. In addition, we compare trends in PROMIS PF scores to the Oswestry Disability Index (ODI) and PROMIS Pain Interference (PI) scores. SUMMARY OF BACKGROUND DATA: National Institute of Health's (NIH) Patient-reported Outcomes Measurement Information System (PROMIS) Physical Function (PF) domain has been validated in spine surgery. However, little is known about how PROMIS-PF scores are affected by functional comorbidities and how these scores change in patients recovering from lumbar fusion surgery over time. In this study, we hypothesize that functional comorbidities negatively affect recovery. MATERIALS AND METHODS: We retrospectively identified 1893 patients who underwent thoracolumbar, lumbar, or lumbosacral fusion for degenerative conditions between January 2, 2014, and January 7, 2022. We summarized PF at three-month intervals for 2 years following surgery between those with and without functional comorbidity, defined as the presence of congestive heart failure (HF), chronic obstructive pulmonary disease (COPD), cerebrovascular disease (CVD), or paraplegia. Mixed effects multivariable regressions were used to model between group trends in PF through 2 years postoperatively controlling for age, gender, indication, and surgical invasiveness. The minimally clinically important difference (MCID) was defined as 5+ point improvement from baseline in PF. RESULTS: The cohort includes 1224 (65%) patients without functional comorbidity and 669 (35%) with functional comorbidity. The mean age was 65.0, and the Charlson index was 1.0 in the cohort without functional comorbidity compared with 65.4 and 3.8 in the cohort with functional comorbidity ( P =0.552 and <
0.001, respectively). The groups were otherwise similar with respect to surgical invasiveness index, vertebral levels, and spine diagnosis (all P >
0.05). At 24 months postoperatively, the functional comorbidity group had a 2.5-point lower absolute PF score and a 1.3-point less improvement from baseline ( P =0.012 and 0.190, respectively). 19.3% of patients in the functional comorbidity group achieved the MCID compared with 80.9% in patients without functional comorbidity ( P <
0.001). CONCLUSIONS: Based on PROMIS PF scores, patients with functional comorbidities do not recover to the same extent and are less likely to achieve an MCID compared with patients without baseline functional comorbidities. PROMIS-PF can help benchmark patients along their recovery, and other metrics may be needed to better understand the recovery of patients with functional comorbidities.