Frailty index, accelerometer-measured physical activity, and delayed physical functional recovery after spinal fusion surgery in older adults.

Abstract

Despite the growing implementation of preoperative physical exercise in frail individuals, no research has explored whether low physical activity mediates the relationship between frailty and delayed physical functional recovery (PFR) after spinal fusion surgery. This study aimed to investigate whether, and to what extent, low physical activity mediates the association between frailty and delayed PFR in older adults undergoing lumbar fusion surgery. The authors enrolled 419 patients aged ≥ 65 years scheduled for elective lumbar fusion. Frailty was assessed using the modified 5-item frailty index. Physical activity was measured both subjectively (International Physical Activity Questionnaire-Short Form) and objectively (ActiGraph accelerometers). The primary outcome was delayed PFR, defined as delayed ambulation (> 48 hours) plus either prolonged length of hospital stay or nonhome discharge. Multivariate regression and mediation analyses with bootstrap resampling were applied. Of 419 patients, 146 (34.8%) were frail. Frail patients had higher rates of low physical activity and delayed PFR (31.5% vs 15.1%, p < 0.001). Frailty was associated with delayed PFR (β 0.84, 95% CI 0.43-1.26), attenuated after adjusting for low physical activity (β 0.79, 95% CI 0.44-1.26). Mediation analysis showed low physical activity partially mediated the frailty-PFR relationship (average causal mediation effect 0.012, 95% CI 0.001-0.03). Results were consistent using accelerometer-based moderate to vigorous physical activity classification. Low physical activity partly mediates the effect of frailty on delayed functional recovery after lumbar fusion surgery. These findings highlight the importance of incorporating physical activity assessment and optimization into perioperative care pathways for frail patients.