Long-term loss of intervertebral disc height after posterior cervical surgery for ossification of the posterior longitudinal ligament: a retrospective study with more than 3 years of follow-up

Abstract

Background: Posterior decompression is a common treatment for cervical OPLL but may accelerate intervertebral disc degeneration by disrupting posterior tension-band structures. The long-term behavior of intervertebral disc height (IDH) after surgery remains poorly understood.

Purpose: To evaluate the prevalence and radiographic predictors of long-term IDH loss following posterior cervical surgery for OPLL.

Methods: This single-center retrospective study included 108 patients who underwent posterior decompression for cervical OPLL between 2007 and 2020, with ≥ 3 years of follow-up. Total C3-C7 IDH was measured on midsagittal CT preoperatively and at final follow-up. Patients were grouped by IDH loss (> 1 mm vs. ≤ 1 mm). Radiographic and clinical parameters were compared. Multivariate logistic regression with AIC-based stepwise selection identified independent predictors. Model performance was assessed by AUC and F1 score.

Results: At a median follow-up of 61 months, 24.1% of patients exhibited IDH loss > 1 mm. The IDH group had a larger preoperative C0-2 Cobb angle (27.4° vs. 22.9°, P = 0.008), higher C2 slope (17.9° vs. 13.2°, P = 0.014), and greater total disc height (11.8 mm vs. 10.7 mm, P = 0.040). Multivariate analysis identified preoperative OALL at C5/6 (OR = 3.02, 95% CI 1.08-8.49, P = 0.036) and larger C0-2 Cobb angle (OR = 1.10, 95% CI 1.02-1.17, P = 0.009) as independent risk factors, whereas OPLL at C6 was protective (OR = 0.26, 95% CI 0.09-0.77, P = 0.015). The final model yielded an AUC of 0.74 and F1 score of 0.52.

Conclusions: Approximately one-quarter of patients developed significant IDH loss after posterior cervical surgery for OPLL. Larger cranio-cervical extension (C0-2 Cobb), OALL at C5/6, and absence of OPLL at C6 were associated with greater risk. Preoperative sagittal alignment and ossification patterns may help identify patients at risk for postoperative disc degeneration.

Keywords: CT-based measurement; Cranio-cervical alignment; Intervertebral disc height; OALL; OPLL; Posterior decompression.

Fig. 1

Flowchart of patient enrollment and group classification

Fig. 2

Representative sagittal reconstructed CT images demonstrating the measurement of intervertebral disc height (IDH) from C3 to C7. a Preoperative image showing clearly demarcated disc spaces with a total C3–7 IDH of 12.30 mm. b Postoperative image showing decreased intervertebral spaces with a total C3–7 IDH of 10.20 mm. The postoperative reduction exceeded 1 mm, meeting the criteria for the IDH group

Fig. 3

Segmental distribution of ossification lesions at each cervical level before and after surgery. a Distribution of ossification of the posterior longitudinal ligament (OPLL) across cervical vertebral levels (C2–C7). The OPLL lesions were most frequently located at the C4, C5, and C6 vertebral levels both preoperatively and postoperatively. b Distribution of ossification of the anterior longitudinal ligament (OALL) across intervertebral disc levels. OALL was predominantly observed at the C4/5, C5/6, and C6/7 disc levels

Fig. 4

a Forest plot of independent predictors for postoperative disc height loss > 1 mm at C3–7. b ROC curve of the final logistic regression model. a Forest plot shows odds ratios (ORs) and 95% confidence intervals (CIs) for variables selected by AIC-based stepwise logistic regression. Red markers indicate risk factors (OR > 1); blue markers indicate protective factors (OR < 1). Asterisks denote significance levels (* p < 0.05, ** p < 0.01, *** p < 0.001). b Receiver operating characteristic (ROC) curve for the final model (AUC = 0.74), indicating moderate discrimination. The optimal cutoff was determined using the Youden index