Ananth Swaminathan Siddarth, Taheri Nima, Becker Luis, Pumberger Matthias, Schmidt Hendrik, Checa Sara
Julius Wolff Institute Berlin Institute of Health, Charité - Universitätsmedizin Berlin Berlin Germany.
Center for Musculoskeletal Surgery Charité- Universitätsmedizin Berlin Berlin Germany.
JOR Spine. 2025 Jul 14;8(3):e70075. doi: 10.1002/jsp2.70075. eCollection 2025 Sep.
Lumbar spinal fusion is currently regarded as one of the most effective surgical treatments for patients with spinal deformities, degenerative disc disease, and degenerative spondylolisthesis. However, the procedure still faces a high incidence of non-unions. A key factor contributing to non-union is stress shielding effects related to unfavorable mechanical signals at the fusion site. Mechanical conditions at the fusion site are determined by the loading conditions that result from daily activities. Recent studies have reported that humans spend most of the day with their spine in a flexed position. The role of flexion loading in the progression of bone fusion remains poorly understood. This study explores the influence of habitual flexion loading on the spinal fusion process using a computational modeling framework that integrates finite element analysis with bone healing algorithms to simulate bone regeneration following fusion surgery.
A finite element model of the lumbar spine based on a healthy subject was developed and validated with in vitro experimental data. Thereafter, a virtual posterior lumbar interbody fusion was performed where 2 intervertebral cages were inserted at the L4-L5 level together with posterior fixation. The influence of two loading conditions on the predicted fusion process were investigated: (1) A compression load (2) A hybrid (compression + flexion) loading protocol simulating habitual flexion encountered during daily living.
Bone bridging was predicted to occur 14 weeks after surgery. At week 14, for the hybrid loading, the model predicted a bone volume of 70%, whereas for compression load, the bone volume prediction was 59%. Computer model predictions showed that habitual flexion loading can promote bone formation in the anterior and peripheral regions by inducing a mechanical environment favorable for bone formation.
Flexion loading may enhance bone healing by promoting mechanically advantageous conditions. The computational framework could guide the development of optimized rehabilitation protocols to improve fusion outcomes.
腰椎融合术目前被认为是治疗脊柱畸形、椎间盘退变疾病和退变性椎体滑脱患者最有效的外科手术方法之一。然而，该手术仍面临较高的不融合发生率。导致不融合的一个关键因素是与融合部位不利机械信号相关的应力屏蔽效应。融合部位的力学条件由日常活动产生的负荷条件决定。最近的研究报告称，人类一天中的大部分时间脊柱处于屈曲位置。屈曲负荷在骨融合进展中的作用仍知之甚少。本研究使用一个计算建模框架来探索习惯性屈曲负荷对脊柱融合过程的影响，该框架将有限元分析与骨愈合算法相结合，以模拟融合手术后的骨再生。
基于一名健康受试者建立了腰椎的有限元模型，并用体外实验数据进行了验证。此后，进行了虚拟后路腰椎椎间融合术，在L4-L5水平植入2个椎间融合器并进行后路固定。研究了两种负荷条件对预测融合过程的影响：（1）压缩负荷；（2）模拟日常生活中遇到的习惯性屈曲的混合（压缩+屈曲）负荷方案。
预计术后14周会出现骨桥形成。在第14周，对于混合负荷，模型预测骨体积为70%，而对于压缩负荷，骨体积预测为59%。计算机模型预测表明，习惯性屈曲负荷可通过诱导有利于骨形成的力学环境，促进前部和周边区域的骨形成。
屈曲负荷可能通过促进力学上有利的条件来增强骨愈合。该计算框架可指导制定优化的康复方案，以改善融合效果。
