Sacropelvic Parameters and L5 Spondylolysis: Computed Tomography Analysis

A radiological parametric comparison of low-grade lytic spondylolisthesis to degenerative spondylolisthesis - A retrospective approach to establish its dysplastic origin

Objectives

This study aims to compare low-grade lytic spondylolisthesis (LS) and degenerative spondylolisthesis (DS) radiologically. In addition, it seeks to identify underlying similarities between LS and DS.

Methods

This study included patients with low-grade single-level spondylolisthesis at L4-L5 or L5-S1. They were categorized into LS and DS. Radiological features, including pedicle height, width, transverse, and sagittal angle, as well as anterior vertebral heights (AVH) and posterior vertebral heights (PVH), were measured using T1-weighted magnetic resonance imaging.

Results

The study involved 88 patients: 46 in the DS group and 42 in the LS group. In the LS group, the AVH was significantly higher than the posterior height at L4 and L5 (L4 PVH/AVH ratio 0.93 in LS vs. 0.96 in DS; L5 PVH/AVH ratio 0.84 in LS vs. 0.92 in DS), and pedicles were more medially oriented (L4: 19.62° in LS vs. 17.7° in DS; L5: 28.92° in LS vs. 26.47° in DS). In addition, at L5, the pedicle height (10.67 mm in LS vs. 11.48 mm in DS) and width (13.56 mm in LS vs. 14.37 mm in DS) were smaller compared to the DS group.

Conclusions

Low-grade LS shows distinct radiological vertebral and pedicle anatomy compared to DS. Short and thin pedicles and wedge-shaped vertebrae in LS resemble DS, indicating its dysplastic origin.

Cost-Utility Analysis of Sacroiliac Joint Fusion in High-Risk Patients Undergoing Multi-Level Lumbar Fusion to the Sacrum

Purpose

Multi-level lumbar fusion to the sacrum (MLF) can lead to increased stress and angular motion across the sacroiliac joint (SIJ), with an incidence of post-operative SIJ pain estimated at 26–32%. SIJ fusion (SIJF) can help obviate the need for revisions by reducing range of motion and screw stresses. We aimed to evaluate the cost-utility of MLF + SIJF compared to MLF alone among high-risk patients from a payer perspective, where high risk is defined as high body mass index and high pelvic incidence.

Methods

A Markov process decision-analysis model was developed to evaluate cumulative 5-year costs, quality-adjusted life years (QALYs), and incremental cost-effectiveness ratio (ICER) of MLF + SIJF compared to MLF alone using published data; costs from Medicare claims data analyses and health state utility values (derived from EQ-5D) informed by three prospective, multicenter, clinical trials. The base case assumed a reduction in post-operative SIJ pain from 30% to 10% (relative risk reduction [RRR] of 67%). Costs and utilities were discounted 3% annually. The ICER is reported in 2020 US dollars. One-way, multi-way, and probabilistic sensitivity analyses were performed.

Results

With an assumed 30% incidence of SIJ pain after MLF alone, stabilizing with SIJF was associated with an additional 5-year cost of $2421 and a gain of 0.14 QALYs, resulting in an ICER of $17,293 per QALY gained (similar to total knee arthroplasty and more favorable than open discectomy). ICERs were most sensitive to the RRR of post-operative SIJ pain conferred by SIJF, time horizon, and probability of successful treatment with MLF alone. At a willingness-to-pay threshold of $50,000/QALY gained, MLF + SIJF has a 97.7% probability of being cost-effective in the target patient population.

Conclusion

Fusing the SIJ in high-risk patients undergoing MLF was cost-effective when the incidence of post-operative SIJ pain after MLF alone exceeds approximately 25%, providing value-based healthcare from a payer perspective.

Comparison of L5 pedicle morphology in patients with and without L5 spondylolysis

Only a small number of studies have reported on L5 pedicle morphology in the presence of spondylolisthesis let alone isolated spondylolysis and findings are therefore variable. The aim of this radiographic study was to analyze L5 pedicle morphology in the presence and absence of L5 spondylolysis. The was a retrospective cross-sectional analysis of computed tomographic (CT) imaging. Assessment of the L5 pedicle morphology (height, width, length, transverse angle and screw length) were measured in patients with and without L5 spondylolysis. Pelvic measures including pelvic incidence, sacral anatomic orientation and sacral table angle were recorded. Patients were matched for age and gender. Twenty-three patients with spondylolysis were matched to 46 patients without. The presence of spondylolysis alone did not have a significant influence on either pelvic or pedicle morphologic parameters. Only with the presence of associated spondylolisthesis was there a difference noted with an increase in pedicle length observed. Correlation analysis suggested further morphologic changes may result with increased remodeling. Isolated spondylolysis at L5 appears to have little influence on pedicle morphology in this CT-based analysis. Morphologic changes appear likely to become significant only with associated spondylolisthesis and associated remodeling.