Analyses of proximal adjacent segment degeneration and prognostic factors after lumbar fusion surgery: study based on proximal facet joint angle

Abstract

Objective: Lumbar fusion surgery is a common procedure for treating various degenerative spinal conditions. However, the incidence of proximal adjacent segment degeneration (PASD) remains a concern. This study aimed to investigate the effect of proximal facet joint angle (FJA) on PASD and then identify factors that influence prognosis after lumbar fusion surgery.

Methods: In this retrospective study, the cases of 192 patients who underwent lumbar fusion surgery between January 2020 and June 2022 were analysed. Patients were classified in accordance with their baseline proximal FJA into the high (≥ 40°) and low (< 40°) FJA groups. Prognosis was evaluated during the last follow-up by using clinical, imaging and functional recovery criteria. PASD was assessed using Weishaupt criteria, and imaging parameters were measured on postoperative computed tomography (CT) reconstructions. Statistical analyses, including univariate and multivariate logistic regression, were performed to identify prognostic factors. Receiver operating characteristic (ROC) curves were used to assess predictive value.

Results: The high FJA group exhibited significantly higher rates of PASD compared with the low FJA group (P < 0.001). No significant differences were observed in sex, age, body mass index (BMI) or follow-up duration between the two groups. Poor prognosis was associated with higher BMI, larger FJA and wider facet joint diameter. Logistic regression analysis identified BMI (odds ratio [OR] = 1.801, P = 0.001), FJA (OR = 6.320, P < 0.001) and facet joint sagittal (OR = 1.888, P < 0.001) and coronal (OR = 1.462, P < 0.001) diameters as independent predictors of poor prognosis. A smaller screw inclination angle was associated with better outcomes (OR = 0.907, P = 0.017). Joint ROC analysis underscored the significant predictive power of these factors (area under the curve = 0.881).

Conclusion: This study demonstrates that a larger proximal FJA is associated with increased PASD. It also identifies several prognostic factors that influence outcomes after lumbar fusion surgery. Patients with higher BMI, larger FJA and wider sagittal and coronal diameters are at increased risk for poor prognosis. These findings highlight the importance of comprehensive preoperative assessments to optimise surgical planning and improve outcomes in lumbar fusion surgery.

Keywords: Influencing factors; Lumbar fusion surgery; Patient prognosis; Proximal adjacent facet degeneration; Proximal facet joint angle.

Fig. 1

Assessment of proximal adjacent segment degeneration (PASD). A shows from top to bottom: mild subchondral bone erosion, joint space narrowing, and subchondral cyst formation. B arrows indicate from top to bottom: severe subchondral erosion, joint space narrowing, and large osteophyte formation. C arrows show facet joint fusion. D shows the air sign in the facet joint

Fig. 2

Weishaupt criteria for classification of facet joint degeneration. A: Grade 0, normal facet joint. B: Grade 1, slightly narrowed joint space, small osteophytes formation, and mild hypertrophy of the small joints. C: Grade 2, visible joint space narrowing, moderate osteophyte formation, moderate hypertrophy of the small joints, and subchondral bone erosion. D: Grade 3, severe joint space narrowing, severe osteophyte formation, and severe subchondral bone erosion

Fig. 3

Method for measuring facet joint diameters: In thin-slice CT 3D reconstructions, the most clearly visible bone window layer was selected for observing and measuring facet joint axial diameter (A), sagittal diameter (B) and coronal diameter (C)

Fig. 4

Joint ROC analysis of factors that influence prognosis after lumbar fusion surgery. A: Calibration curve, B: decision curve, C: nomogram, D: combined ROC curve