Spine Journal - 2026-09-14 - Journal Article
Superior Articular Process-Endplate Angle Is Associated With Postoperative Contralateral Symptoms After Unilateral Transforaminal Lumbar Interbody Fusion.
Tu Y, Li S, Jin S, Wu Z, Yang S, Jones MEB, Kwan KYH, Jin H, Wang X
Topics
Key Takeaway
A preoperative L5 SAP-E angle <92.13° predicted postoperative contralateral symptoms after unilateral open L4/5 TLIF with 100% sensitivity and 89.3% specificity (AUC 0.961) in a cohort of 296 DLS patients.
Summary Depth
Choose how much analysis to show on this article page.
Summary
This study evaluated whether the preoperative L5 superior articular process-endplate (SAP-E) angle predicts new-onset contralateral symptoms after unilateral open L4/5 TLIF for degenerative lumbar spondylolisthesis. Among 296 surgical patients, 15 developed contralateral symptoms; their mean L5 SAP-E angle was 77.21° vs. 111.06° in asymptomatic patients (P<0.001). Firth logistic regression confirmed independent association (OR 0.89 per 1° increase), and a 92.13° cutoff achieved 100% sensitivity and 89.3% specificity on ROC analysis.
Key Limitation
Only 15 contralateral-symptom events in 296 patients produces an event-per-variable ratio insufficient to support a reliable predictive model, and the absence of reported follow-up duration prevents assessment of symptom timing or resolution.
Original Abstract
BACKGROUND CONTEXT
New-onset contralateral symptoms after unilateral transforaminal lumbar interbody fusion (TLIF) are clinically important, but simple preoperative predictors are limited.
PURPOSE
To characterize sagittal superior articular process-endplate (SAP-E) angle distribution and evaluate its association with postoperative contralateral symptoms after unilateral open L4/5 TLIF in L4 degenerative lumbar spondylolisthesis (DLS).
STUDY DESIGN/SETTING
Retrospective observational imaging and clinical cohort study.
PATIENT SAMPLE
The study included 111 normal individuals and 296 patients with L4 DLS who underwent unilateral open L4/5 TLIF. Among the DLS patients, 15 developed postoperative contralateral symptoms.
OUTCOME MEASURES
Radiographic measures included SAP-E angles at L3-L5 in normal individuals and the preoperative L5 SAP-E angle in patients with DLS. The primary clinical outcome was new-onset contralateral symptoms after unilateral open L4/5 TLIF.
METHODS
SAP-E angles at L3-L5 were measured in normal individuals to evaluate lower lumbar distribution. In patients with DLS, the preoperative L5 SAP-E angle was compared between symptomatic and asymptomatic groups. Measurement reliability was assessed using intraclass correlation coefficients. Repeated-measures analysis of variance, Welch t tests, Fisher exact tests, Firth logistic regression, receiver operating characteristic analyses, and bootstrap internal validation were performed. This study was supported by the Zhejiang Provincial Health Science and Technology Program (financial support amount, USD 100,001-500,000; paid to the institution). The funder had no role in the conduct or reporting of the study. The authors report no study-specific conflicts of interest or associated sources of bias.
RESULTS
In normal individuals, the SAP-E angle decreased from L3 to L5 (125.58±8.62°, 123.13±7.39°, and 118.43±7.28°; P<0.001). L5 SAP-E angle was smaller in DLS patients than in controls (109.45±16.05° vs. 118.43±7.28°, P<0.001). Symptomatic DLS patients had markedly smaller L5 SAP-E angles than asymptomatic patients (77.21±7.80° vs. 111.06±14.72°, P<0.001). In Firth logistic regression, a smaller L5 SAP-E angle was significantly associated with postoperative contralateral symptoms (odds ratio per 1° increase, 0.89; 95% CI, 0.848-0.924; P<0.001). Receiver operating characteristic analysis showed apparent discrimination (area under the curve, 0.961); an exploratory 92.13° cutoff yielded 100.0% sensitivity, 89.3% specificity, 33.3% positive predictive value, and 100.0% negative predictive value.
CONCLUSIONS
The SAP-E angle shows a level-dependent decrease in normal lower lumbar spines and is reduced in DLS patients. A smaller preoperative L5 SAP-E angle was associated with contralateral symptoms after unilateral open L4/5 TLIF. Its potential role as an adjunctive marker for preoperative risk assessment requires further evaluation and external validation.