Superior articular process-endplate angle is associated with postoperative contralateral symptoms after unilateral transforaminal lumbar interbody fusion
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Surgical Approach and Complications of Stand-alone Lateral Trans-Psoas Interbody Fusion
Published on: February 14, 2025
Yiting Tu1, Sunlong Li1, Shuqing Jin1
1Department of Orthopaedics, The Second Affiliated Hospital and Yuying Children's Hospital of Wenzhou Medical University, Wenzhou, Zhejiang Province, China; Zhejiang-Hong Kong Joint Laboratory for Precision Diagnosis and Treatment of Spinal Disorders, Wenzhou, Zhejiang Province, China; Zhejiang Engineering Research Center for Innovation and Application of Intelligent Prevention and Treatment of Scoliosis in Children and Adolescents, Wenzhou, Zhejiang Province, China.
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<.001). L5 SAP-E angle was smaller in DLS patients than in controls (109.45±16.05° vs 118.43±7.28°, p<.001). Symptomatic DLS patients had markedly smaller L5 SAP-E angles than asymptomatic patients (77.21±7.80° vs 111.06±14.72°, p<.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<.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.
