gms | German Medical Science

Objectives: Surgeons often face difficulties predicting the stability of cervical lesions, for ligamentous and non-ligamentous structures, during treatment planning for the cervical spine. To accurately assess the impact on a patient’s well-being, it is crucial to understand the biomechanical changes caused by lesions. To achieve this, a stepwise resection of cervical ligaments is performed to evaluate the effect of spinal structures on the Range of Motion (ROM) in the cervical vertebral segments. Altogether, this human specimen biomechanical study aims to help spine surgeons to estimate whether a given cervical lesion is stable or unstable and needs to be surgically addressed. Additionally, a secondary objective is to obtain experimental data to be the basis for a nonlinear material calibration of numerical models of the cervical spine, namely a patient-specific Finite Element (FE) model.

Methods: The soft tissue of 18 fresh frozen cervical segments of C2-C3, C4-C5, and C6-C7 was removed, keeping ligaments, intervertebral discs, and facet joints intact. The endpoint of each functional segment was embedded with Technovit^® 4004 to subsequently be attached to a custom spine test machine (Dyna-Mess^®). Testing in the three directions (flexion-extension, lateral bending, axial rotation) was done with pure moment load, displacement constant rotation of ±1°/s, until the reach of ±0.5 Nm, while the ROM was recorded. The resection order for sequential testing was: Supraspinous- (SSL); Interspinous- (ISL); Intertransverse- (ITL); Flavum- (FVL); Capsular- (CCL) Ligaments; Vertebral arches (VTA); Posterior- (PLL) and Anterior longitudinal ligament (ALL). The experimental data were analyzed with a custom script. Statistical nonparametric Wilcoxon signed-rank test was used.

Results: The posterior ligaments had a significant impact on the ROM in the direction of flexion. Noteworthy, the structure with the most influence on the ROM was the VTA. Furthermore, each spinal structure has its effect on the constrain of the motion of the spine evaluated in the three anatomical planes and at intermediate load levels. The findings also account for coupled motion measurements. Additionally, the neutral zone of the specimens had increased following the range of motion pattern.

Figure 1 [Fig. 1], Table 1 [Tab. 1]

Conclusions: In Summary, our experimental data provides additional evidence to assist surgeons define patient specific conditions and developing personalized operations plans.Additionally, it provides the reference for multi-step-load calibration of nonlinear material parameters in FE to predicts more precisely the patient specific spine kinematics with present injury.