Correlates of the Lumbar–Femoral T-Score Difference in Older Adults: Sex Outweighs the Triglyceride–Glucose Index

Background/Objectives: We examined correlates of lumbar–femoral T-score differences (ΔT), retaining the triglyceride–glucose (TyG) index as the prespecified primary exposure. Methods: This retrospective cross-sectional analysis of routine records included 528 geriatric outpatients assessed in Ankara, Türkiye, in 2023; primary regression used 506 complete cases. ΔT was lumbar minus femoral-neck T-score. Device L1–L4 composites were used without vertebra-level exclusions because scan images were unavailable. Firth models and an exploratory post hoc arithmetic decomposition were secondary. Results: Male sex was associated with higher ΔT (B = +0.984; p < 0.001), uniquely explaining 9.87% of variance versus 0.88% for TyG. TyG estimates (95% CI) were +0.243 (+0.033 to +0.453; p = 0.023) in the primary analysis, +0.214 (−0.010 to +0.438; p = 0.061) retaining two records excluded by plausibility limits, and +0.070 (−0.115 to +0.255; p = 0.458) excluding influential observations. The male lumbar-worse OR was 0.12 (95% CI 0.03–0.31), based on 3/165 male events. Among patients with femoral-neck osteoporosis, lumbar T-scores exceeded −2.5 in 22/30 men versus 43/89 women (post hoc, unadjusted). Conclusions: Sex explained more unique ΔT variance than TyG. The TyG association was small and sensitive to analytic decisions. Unmeasured degeneration and selection bias limit interpretation.