Preoperative health-related quality of life across four degenerative lumbar conditions in a multi-ethnic Southeast Asian surgical cohort: a cross-sectional SF-36 analysis

Purpose The evidence base for preoperative health-related quality of life (HRQoL) in degenerative lumbar conditions derives predominantly from Western populations. This study characterised HRQoL across four degenerative lumbar conditions in a multi-ethnic Southeast Asian surgical cohort and identified factors associated with physical and mental health at composite and domain levels. Methods Cross-sectional analysis of 1173 preoperative patients from a Singaporean spine surgery registry (2017–2022). SF-36 norm-based T-scores were computed for eight domains and two component summaries. Diagnosis-stratified stepwise multiple regression identified factors associated with the Physical Component Summary (PCS), Mental Component Summary (MCS), and domain scores. LASSO regression served as a sensitivity analysis. Results Mean PCS was 35.6 (SD 8.9), 1.4 SD below the US normative mean, whereas MCS was 50.3 (SD 9.7), near normative levels. Physical functioning and role-physical were the most impaired domains. Scores differed across the four diagnoses on six of the ten SF-36 outcomes (one-way ANOVA, all p < 0.05; corroborated by Kruskal–Wallis tests), although effect sizes were small (eta-squared ≤ 0.02). Functional disability showed the strongest association with PCS across all four conditions (β range: − 0.32 to − 0.28; adjusted R 2 = 0.48–0.52). MCS models explained limited variance (adjusted R 2 = 0.09–0.22). At the domain level, physical functioning had the highest adjusted R 2 (0.57–0.67), exceeding even PCS. Indian ethnicity was independently associated with lower MCS in two conditions. LASSO sensitivity analyses corroborated the stepwise findings. Conclusion Functional disability was most strongly associated with physical HRQoL, channelled through physical functioning limitations. Conventional variables explained limited mental HRQoL variance, suggesting unmeasured psychological and cultural factors play a substantial role. While functional disability’s primacy was consistent with Western evidence, secondary patterns diverged from Western cohorts. These findings underscore the need to incorporate psychological and culturally adapted measures into preoperative assessment.