Rahm Mark D, Brooks Daina M, Harris Jonathan A, Hart Robert A, Hughes Jessica L, Ferrick Bryan J, Bucklen Brandon S
Department of Orthopaedic Surgery, Baylor Scott and White Health/Texas A&M University College of Medicine, 2401 S 31(st) Street, Temple, Texas, 76508, USA.
Musculoskeletal Education and Research Center, Globus Medical, Inc., 2560 General Armistead Avenue, Audubon, PA 19403, USA.
Clin Biomech (Bristol). 2019 Dec;70:217-222. doi: 10.1016/j.clinbiomech.2019.10.008. Epub 2019 Oct 19.
Although the rib cage provides substantial stability to the thoracic spine, few biomechanical studies have incorporated it into their testing model, and no studies have determined the influence of the rib cage on adjacent segment motion of long fusion constructs. The present biomechanical study aimed to determine the mechanical contribution of the intact rib cage during the testing of instrumented specimens.
A cyclic loading (CL) protocol with instrumentation (T4-L2 pedicle screw-rod fixation) was conducted on five thoracic spines (C7-L2) with intact rib cages. Range of motion (±5 Nm pure moment) in flexion-extension, lateral bending, and axial rotation was captured for intact ribs, partial ribs, and no ribs conditions. Comparisons at the supra-adjacent (T2-T3), adjacent (T3-T4), first instrumented (T4-T5), and second instrumented (T5-T6) levels were made between conditions (P ≤ 0.05).
A trend of increased motion at the adjacent level was seen for partial ribs and no ribs in all 3 bending modes. This trend was also observed at the supra-adjacent level for both conditions. No significant changes in motion compared to the intact ribs condition were seen at the first and second instrumented levels (P > 0.05).
The segment adjacent to long fusion constructs, which may appear more grossly unstable when tested in the disarticulated spine, is reinforced by the rib cage. In order to avoid overestimating adjacent level motion, when testing the effectiveness of surgical techniques of the thoracic spine, inclusion of the rib cage may be warranted to better reflect clinical circumstances.
尽管胸廓为胸椎提供了相当大的稳定性，但很少有生物力学研究将其纳入测试模型，且尚无研究确定胸廓对长节段融合结构相邻节段运动的影响。本生物力学研究旨在确定完整胸廓在器械固定标本测试过程中的力学贡献。
对5个具有完整胸廓的胸椎（C7-L2）实施带器械（T4-L2椎弓根螺钉-棒固定）的循环加载（CL）方案。记录完整肋骨、部分肋骨和无肋骨情况下屈伸、侧弯和轴向旋转的运动范围（±5 Nm纯力矩）。对相邻上位（T2-T3）、相邻（T3-T4）、首个固定节段（T4-T5）和第二个固定节段（T5-T6）水平在不同条件下进行比较（P≤0.05）。
在所有3种弯曲模式下，部分肋骨和无肋骨情况时相邻节段运动均有增加趋势。在相邻上位水平，两种情况均观察到这一趋势。在首个和第二个固定节段水平，与完整肋骨情况相比，运动无显著变化（P>0.05）。
长节段融合结构相邻节段在分离脊柱测试时可能显得更不稳定，但胸廓可增强其稳定性。为避免高估相邻节段运动，在测试胸椎手术技术有效性时，可能有必要纳入胸廓以更好地反映临床情况。
