Higher screw-to-cage length ratios in standalone lateral interbody fusion using integrated, expandable implants provide more predictable outcomes with less variability: A 2-year follow-up study

IF 3.2 Q3 Medicine

North American Spine Society Journal Pub Date : 2025-12-01 Epub Date: 2025-10-27 DOI:10.1016/j.xnsj.2025.100817

Dean T. Biddau BBiomedSci , Dean P. McKenzie BA (Hons) PhD , Nigel R. Munday MBBS, MBA , Gregory M. Malham BSc, MBChB, DMed, FRACS

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Abstract

Background Context

Lateral Lumbar Interbody Fusion (LLIF) is widely used for degenerative spinal disorders. Standalone LLIF with expandable cages integrating plate-screw fixation (eLLIFp) has emerged to address disc degeneration and adjacent segment disease while reducing the need for posterior fixation. Biomechanical data suggest greater stability with longer screws, but the clinical impact of screw-to-cage length ratios remains unclear. This study evaluates outcomes following eLLIFp and investigates whether screw-to-cage ratios influence results.

Methods

Eighty-one patients (87 levels) underwent eLLIFp, mean age 63.8±10.8 years (49.4% female), BMI 27.7±4.9 kg/m². Common levels treated were L2/3 (35%) and L3/4 (29%). Mean retractor time was 30.2±5.5 min. Retrospective analysis of prospectively collected data examined integrated screw length (30–60 mm) and cage length (50–65 mm). Screw-to-cage ratios were grouped into tertiles: Low (0.46–0.75, n=36), Medium (0.76–0.82, n=18), and High (0.83–1.0, n=27). Outcomes included pain (VAS), disability (ODI), quality of life (SF-12), and fusion status on 12-month CT. Minimum follow-up was 2 years.

Results

At 12 months, all patients showed significant improvement (p<0.0001) [VAS back: 7.6→0.9; VAS leg: 6.3→0.7; ODI: 25.7→5.1; SF-12 PCS: 29.9→49.2; MCS: 37.3→55.6]. Improvements were comparable across tertiles, though the high-ratio group exhibited less variability in leg pain outcomes. Fusion was achieved in 79/81 (97.5%) patients. Complications occurred in 5 (6.2%): 3 neurological (motor radiculopathy, radicular pain, transient thigh numbness) and 2 symptomatic nonunions requiring posterior fixation, both with lower screw-to-cage ratios (0.7).

Conclusions

Higher screw-to-cage ratios (0.83–1.0) in standalone eLLIFp constructs may enhance consistency in leg pain relief without increasing complications. Maximizing screw length relative to cage dimensions may optimize outcomes and reduce variability in standalone LLIF.

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一项为期2年的随访研究表明，采用一体化、可扩展植入物进行独立侧体间融合时，更高的螺钉-保持器长度比可提供更可预测的结果，变异性更小

背景背景侧位腰椎椎体间融合术（LLIF）广泛用于退行性脊柱疾病。独立llifp与可扩展的固定架结合钢板螺钉固定（eLLIFp）已经出现，用于治疗椎间盘退变和邻近节段疾病，同时减少后路固定的需要。生物力学数据表明，较长的螺钉更稳定，但螺钉与保持器长度比的临床影响尚不清楚。本研究评估eLLIFp后的结果，并调查螺钉-笼比是否影响结果。方法87个级别81例患者行eLLIFp手术，平均年龄63.8±10.8岁（女性49.4%），BMI 27.7±4.9 kg/m²。常见的治疗水平为L2/3（35%）和L3/4（29%）。平均牵开时间为30.2±5.5 min。回顾性分析前瞻性收集的数据，检查综合螺钉长度（30 - 60mm）和保持器长度（50 - 65mm）。螺钉-笼比分为低（0.46-0.75,n=36）、中（0.76-0.82,n=18）和高（0.83-1.0,n=27）。结果包括疼痛（VAS）、残疾（ODI）、生活质量（SF-12）和12个月CT上的融合状况。最小随访时间为2年。结果12个月后，所有患者均有显著改善（p<0.0001） [VAS back: 7.6→0.9；VAS腿：6.3→0.7；海外:25.7→5.1;Sf-12件：29.9→49.2；MCS: 37.3→55.6]。尽管高比例组在腿痛结果上表现出较少的可变性，但改善在各组间是可比性的。81例患者中有79例（97.5%）实现融合。5例（6.2%）出现并发症：3例神经系统（运动神经根病、神经根痛、一过性大腿麻木）和2例需要后路固定的症状性骨不连，均采用较低的螺钉-笼比（0.7）。结论独立eLLIFp结构较高的螺钉-笼比（0.83-1.0）可以增强腿部疼痛缓解的一致性，而不会增加并发症。最大化相对于保持器尺寸的螺钉长度可以优化结果并减少独立LLIF的变异性。

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