[Impact of the apex position of lumbar lordosis on adjacent segment disease following short-segment lumbar fusion surgery].

To investigate the impact of the apex position of lumbar lordosis on the occurrence of adjacent segment disease (ASD) following short-segment lumbar fusion surgery. A retrospective analysis was conducted on 234 patients [102 males and 132 females with a mean age of (60.1±10.0) years] who underwent posterior lumbar interbody fusion for lumbar degenerative diseases from January 2009 to January 2019 at the Third Affiliated Hospital of Nanjing Medical University, Changzhou Second People's Hospital and Affiliated Drum Tower Hospital, Medical School of Nanjing University. The patients were divided into an ASD group and a non-ASD group based on whether ASD occurred postoperatively. The actual postoperative apex position of lumbar lordosis was compared with the theoretical position, and the patients were categorized into "matched" (actual apex position congruent with theoretical position) or "mismatched" groups according to the comparing results. General patient data were compared between the two groups, and multivariate logistic regression analysis was performed to identify factors associated with risk of ASD. Furthermore, patients were stratified into three subgroups based on apex position: ideal position group, superior-to-ideal group, and inferior-to-ideal group. Stratified analyses were subsequently conducted to compare ASD incidence and perioperative parameter variations among the subgroups. All patients successfully underwent surgery and completed follow-up with a mean duration of (70.6±11.9) months. Among the 234 patients, 68 (29.1%) developed ASD postoperatively. The ASD group exhibited a significantly higher proportion of postoperative lumbar lordosis apex position mismatch (64.7%, 44/68) compared to the non-ASD group (41.0%, 68/166) (=0.001). Pelvic incidence (PI) demonstrated significant correlations with the proximal lordosis (PL) and lordosis distribution index (LDI) (0.447, =-0.300, both <0.01), but demonstrated no correlation with the distal lordosis (DL) (=0.098, =0.133). Multivariate logistic regression identified the following risk factors for ASD: old age (=1.057, 95%: 1.014-1.103), two-level fusion (=3.195, 95%: 1.494-6.832), smaller postoperative DL (=0.950, 95%: 0.912-0.990), and apex position mismatch (=3.165, 95%: 1.625-6.163). Stratified analysis demonstrated that the three groups exhibited statistically significant differences in postoperative DL, PL, and LDI (all <0.001). Patients in the superior-to-ideal group and inferior-to-ideal group position groups adjusted sagittal balance through pelvic retroversion compensation and persistent upper lumbar opening compensation, respectively; however, both compensatory mechanisms may increase the risk of ASD due to stress concentration at adjacent segments. The apex position of lumbar lordosis significantly impacts the occurrence of ASD, to restore the physiological apex position intraoperatively, strategic adjustment of the DL is imperative.