Three-dimensional measurement of intervertebral kinematics in vitro using optical motion analysis

Prospective quantitative assessment of spinal range of motion before and after minimally invasive surgical treatment of vertebral body fractures

INTRODUCTION

Randomized clinical trials have generated doubts regarding the therapeutic effectiveness of spinal kyphoplasty to reduce pain and improve quality of life in patients with vertebral fractures. There is a paucity of data on the influence of kyphoplasty on spinal range of motion. To quantify early postoperative changes following kyphoplasty in spinal motion, a noninvasive, radiation-free measurement method was used and results related to clinical and radiological parameters.

METHODS

The study group included 30 patients with an overall number of 54 symptomatic pathological vertebral compression fractures. All patients were treated with balloon kyphoplasty. Clinical results were recorded using the visual analog scale, SF 36, Roland Morris Score and the Oswestry Disability Index, at three time points; preoperative, 2 days postoperative, and at 12 weeks postoperative. The kyphosis angle/sagittal index were determined with biplanar X-rays. Amplitude/velocity of motion in extension/flexion was measured at each time point by use of the EpionicsSPINE(©) system (Epionics Medical GmbH; Potsdam, Germany) using two external sensor strips.

RESULTS

Preoperative magnetic resonance imaging scans showed bone marrow edema in all vertebral bodies indicative of a recent, non-consolidated fracture. Pain and quality of life was significantly improved by kyphoplasty, both for the immediate postoperative period, as well as at 12 weeks postoperative. Radiological parameters also showed significant improvement following surgery. Total ROM did not significantly change 2 days after kyphoplasty, but amplitude and velocity were found to be increased 12 weeks postoperatively. Significant positive correlations were observed between increased range of motion and improved clinical/radiological scores.

CONCLUSION

Significant clinical and radiological improvement following kyphoplasty supports the rational for cement augmentation in patients with pathological vertebral body fractures. To the knowledge of the authors, no prior study has assessed the influence of preservation and improvement of spinal range of motion on clinical outcome following kyphoplasty.

Evaluation of a robot-assisted testing system for multisegmental spine specimens

Mono- and multi-segmental testing methods are required to identify segmental motion patterns and evaluate the biomechanical behaviour of the spine. This study aimed to evaluate a new testing system for multisegmental specimens using a robot combined with an optical motion analysis system. After validation of the robotic system for accuracy, two groups of calf specimens (six monosegmental vs. six multisegmental) were mounted and the functional unit L3-4 was observed. Using rigid body markers, range of motion (ROM), elastic zone (EZ) and neutral zone (NZ), as well as stiffness properties of each functional spine unit (FSU) was acquired by an optical motion capture system. Finite helical axes (FHA) were calculated to analyse segmental movements. Both groups were tested in flexion and extension. A pure torque of 7.5 Nm was applied. Statistical analyses were performed using the Mann-Whitney U-test. Repeatability of robot positioning was -0.001±0.018 mm and -0.025±0.023° for translations and rotations, respectively. The accuracy of the optical system for the proposed set-up was 0.001±0.034 mm for translations and 0.075±0.12° for rotations. No significant differences in mean values and standard deviations of ROM for L3-4 compared to literature data were found. A robot-based facility for testing multisegmental spine units combined with a motion analysis system was proposed and the reliability and reproducibility of all system components were evaluated and validated. The proposed set-up delivered ROM results for mono- and multi-segmental testing that agreed with those reported in the literature. Representing the FHA via piercing points determined from ROM was the first attempt showing a relationship between ROM and FHA, which could facilitate the interpretation of spine motion patterns in the future.

Biomechanical characteristics of different regions of the human spine: an in vitro study on multilevel spinal segments

STUDY DESIGN.: An in vitro study on human multilevel spinal segments. OBJECTIVE.: To determine the differences in biomechanical characteristics between 4 separate regions of the human spine and to provide quantitative information is derived on the range of motion (ROM), neutral zone (NZ), neutral zone stiffness (NZstiff), and flexibility (FLEX). SUMMARY OF BACKGROUND DATA.: Limited literature is available about the biomechanical behavior of different regions of the human spine, in particular with multilevel segments. Test setup en protocols were different between studies and therefore outcomes of separate regions are hardly comparable. METHODS.: A total of 24 spinal segments of 6 human cadaveric spines were prepared for biomechanical testing. Each specimen contained 4 vertebrae and 3 intervertebral discs: T1-T4, T5-T8, T9-T12, and L1-L4. Pure moments were applied to a maximum of 4 Nm in flexion/extension, lateral bending, and axial rotation. Displacement of individual motion segments was measured using a 3-dimensional movement registration system. ROM, NZ, NZstiff, and FLEX of the spinal regions were calculated from the acquired load-displacement data. RESULTS.: In axial direction, ROM and NZ decreased and NZ stiffness increased from high to low vertebral levels. For flexion/extension and lateral flexion highest ROM and NZ and lowest NZ stiffness values were found at the T1-T4 and L1-L4 regions. NZ magnitudes and NZ stiffnesses were negatively correlated (P < 0.05). Flexibility of the spinal regions was variable; no significant differences were found between the 4 spinal regions. CONCLUSION.: This study showed the differences in ROM, NZ, and NZ stiffness between thoracolumbar regions of the human spine in axial rotation, flexion/extension, and lateral bending. Separate multilevel spinal segments were tested in 1 study, and therefore characteristics of different regions are truly comparable.