Intervertebral Kinematics Research Articles

Three-Dimensional Measurement of Intervertebral Kinematics in Vitro Using Optical Motion Analysis

Measurement of the stiffness of spinal motion segments is widely used for evaluating the stability of spinal implant constructs. A three-dimensional motion analysis technique has been developed that allows accurate measurement of the relative movement of the vertebral bodies about a well-defined anatomical axis system. The position of marker clusters on each vertebra is tracked using digital infrared cameras (Qualisys AB, Gothenburg). Landmarks are identified using a marked pointer, and an anatomical coordinate system is defined for each vertebra. The transformation relating the upper and lower vertebrae is calculated, using the joint coordinate system approach of Grood and Suntay to find the rotations and translations in each anatomical plane. The stiffness of vertebrectomy constructs was investigated using a Synex vertebral body replacement and an anterior rod with one or two screws in each vertebral body, with or without damage to the posterior longitudinal ligament (PLL). A moment of 2 N m was applied about each anatomical axis, and the range of motion about each axis was calculated. The range of motion in flexion-extension and lateral bending was significantly greater with only one screw. When the PLL was cut, there was no significant increase in the range of motion.

Intervertebral stiffness of the spine is increased by evoked contraction of transversus abdominis and the diaphragm: in vivo porcine studies.

In vivo porcine study of intervertebral kinematics. This study investigated the effect of transversus abdominis and diaphragm activity, and increased intra-abdominal pressure on intervertebral kinematics in porcine lumbar spines. Studies of trunk muscle recruitment in humans suggest that diaphragm and transversus abdominis activity, and the associated intra-abdominal pressure contribute to the control of intervertebral motion. However, this has not been tested in vivo. Relative intervertebral motion of the L3 and L4 vertebrae and the stiffness at L4 were measured in response to displacements of the L4 vertebra imposed via a device fixed to the L4 vertebral body. In separate trials, diaphragm and transversus abdominis activity was evoked by stimulation of the phrenic nerves and via electrodes threaded through the abdominal wall. When intra-abdominal pressure was increased by diaphragm or transversus abdominis stimulation, the relative intervertebral displacement of the L3 and L4 vertebrae was reduced and the stiffness of L4 was increased for caudal displacements. There was no change in either parameter for rostral displacements. In separate trials, the diaphragm crurae and the fascial attachments of transversus abdominis were cut, but intra-abdominal pressure was increased. In these trials, the reduction in intervertebral motion was similar to trials with intact attachments for caudal motion, but was increased for rostral trials. The results of these studies indicate that elevated intra-abdominal pressure, and contraction of diaphragm and transversus abdominis provide a mechanical contribution to the control of spinal intervertebral stiffness. Furthermore, the effect is modified by the muscular attachments to the spine.

Biomechanical evaluation of total disc replacement arthroplasty: an in vitro human cadaveric model.

This in vitro biomechanical study was undertaken to quantify the multidirectional intervertebral kinematics following total disc replacement arthroplasty compared to conventional stabilization techniques. Using an in vitro human cadaveric model, the primary objective was to compare the multidirectional flexibility properties and map the center of intervertebral rotation of total disc arthroplasty versus conventional threaded fusion cages and cages augmented with transpedicular fixation for single-level spinal instrumentation. The utilization of motion-preserving implants versus instrumentation systems, which stabilize the operative segments, necessitates improved understanding of their comparative biomechanical properties. A total of eight human cadaveric lumbosacral spines (L2 to sacrum) were utilized in this investigation and biomechanically evaluated under the following L4-L5 reconstruction conditions: 1) intact spine; 2) SB Charitè disc prosthesis; 3) BAK cages; and 4) BAK cages + ISOLA pedicle screw/rod fixation (anteroposterior). The superior (L3-L4) and inferior (L5-S1) intervertebral levels remained uninstrumented to quantify adjacent level properties. Multidirectional flexibility included pure, unconstrained moments (+/-8 Nm) in axial rotation, flexion-extension, and lateral bending, with quantification of the operative and adjacent level range of motion and neutral zone, which were normalized to the intact spine condition. The SB Charitè prosthesis indicated an average percentage increase in axial rotation range of motion by 44% compared to the intact condition (P < 0.05), whereas the BAK and anteroposterior reconstructions decreased range of motion by 29% and 80%, respectively (P < 0.05). The SB Charitè was significantly different from BAK and combined anteroposterior reconstructions (P < 0.05). Flexion-extension indicated a minor increase in range of motion for the SB Charitè (3%) versus the intact disc (P > 0.05), whereas the BAK and anteroposterior stabilization groups resulted in significant decreases in range of motion (BAK = 57%, anteroposterior = 93%) (P < 0.05) when compared to the intact and SB Charitè conditions. Based on flexion-extension radiographs, the intervertebral centers of rotation were in the posterior one-third of the operative intervertebral disc only for the SB Charitè reconstruction and intact spine condition, with definitive evidence of physiologic intervertebral translation (intact 2.06 +/- 77 mm; SB III = 1.9 +/- 0.98 mm). Total disc arthroplasty serves as the next frontier in the surgical management of discogenic spinal pathology. The SB Charitè restored motion to the level of the intact segment in flexion-extension and lateral bending and increased motion in axial rotation. The anterior annular resection necessary for device implantation and unconstrained design of the prosthesis account for this change in rotation. The normal lumbar flexion-extension axis of rotation is an ellipse rather than a single point. Only disc replacement rather than pedicle instrumentation or BAK interbody instrumentation preserves the kinematic properties and normal mapping of segmental motion at the operative and adjacent intervertebral disc levels.

Gender dependent cervical spine segmental kinematics during whiplash

Clinical and epidemiological studies have frequently reported that female occupants sustain whiplash injuries more often than males. The current study was based on the hypothesis that segmental level-by-level cervical intervertebral motions in females are greater than in males during rear impact. The hypothesis was tested by subjecting 10 intact human cadaver head–neck complexes (five males, five females) to rear impact loading. Intervertebral kinematics were analyzed as a function of spinal level at the time of maximum cervical S-curve, which occurred during the loading phase. Segmental angles were significantly greater ( p<0.05) in female specimens at C2–C3, C4–C5, C5–C6, and C6–C7 levels. Because greater angulations are associated with stretch in the innervated components of the cervical spinal column, these findings may offer a biomechanical explanation for the higher incidence of whiplash-related complaints in female patients secondary to rear impact acceleration.

Is there a connection between the clinical response after an external fixation test or a subsequent lumbar fusion and the pre-test intervertebral kinematics?

Evaluation of a possible correlation of clinical symptoms of chronic low back pain (LBP) patients before and after application of external spinal fixation (ESF) with three-dimensional motion patterns. To determine whether the intervertebral kinematics in chronic LBP patients correlate with pain relief after stabilization of the suspected painful segments. Chronic LBP is a complex clinical entity with mechanical, biochemical, and psychosocial components. Although clinically controversial, ESF has been shown to reduce intervertebral motion, and thus, it provides a mechanism to investigate the mechanical aspect of LBP. Thirty-four chronic LBP patients were tested with ESF of the suspected painful segments. The subjective pain relief experienced by the patients during the test and 2 years after spinal fusion surgery was determined, along with the Oswestry Disability Index. Before removal of ESF, the three-dimensional intervertebral kinematics of the painful segments (specifically range of motion, coupling patterns, and motion asymmetries) were analyzed with a precision optoelectronic camera system during active trunk motions. A series of linear correlations were performed between the clinical measures and the motion parameters. The subjective pain relief during the ESF test was nominally, but not significantly, associated with lateral bending asymmetry ( = 0.22) and "abnormal" axial rotation-lateral bending coupling ( = 0.13). The improvement in the Oswestry Disability Index both post-test and at 2 years after lumbar fusion surgery was significantly correlated with the extension range of motion ( = 0.049 and = 0.036, respectively) and the extension-to-flexion range of motion ratio ( = 0.035 and = 0.044, respectively). The "abnormal" motion patterns of chronic LBP patients did not correlate with subjective pain relief after ESF of the suspected symptomatic levels or with the midterm outcome of subsequent lumbar fusion surgery. The results suggest that preserved motion of the symptomatic segments before surgery is positively correlated with the clinical result of the subsequent spinal fusion in case of a positive ESF test result.

The effect of nucleotomy on lumbar spine mechanics in compression and shear loading.

An in vitro biomechanical investigation on human cadaveric specimens was conducted before and after nucleotomy. Endplate and vertebral body deformation patterns were measured under compression and shear loading, in addition to kinematics and disc pressure. The working hypotheses of this study were that in compression, nucleotomy results in an altered deformation pattern of the endplate and that in shear, nucleotomy does not result in an altered endplate deformation pattern or disc pressure. The pressure distributions within the intervertebral disc have been studied in compression loading but not in shear loading. Severe degeneration and surgical nucleotomy result in small nuclear pressure and altered loading distribution in compression. The effect of these changes on the vertebral endplate and the response under shear loads are not well understood. Five L3-L4 and two L4-L5 functional spinal units were tested under compression and shear loading, intact and after nucleotomy. Vertebral body deformations, intradiscal pressure, and intervertebral kinematics were measured. A series of compression-type (maximum 1000 N) and shear-type (maximum 500 N) loads were applied. With nucleotomy, the disc pressure and the endplate strains decreased under compression, but the vertebral rim strains did not change. In shear, the vertebral rim and endplate strains did not change with nucleotomy. Disc pressure was lower in shear than in compression. Nucleotomy resulted in decreased disc pressure, decreased endplate deformation, and modified loading patterns onto the inferior vertebra in compression loading. However, nucleotomy did not appreciably affect the behavior of the disc in shear loading.

Automatic recognition of vertebral landmarks in fluoroscopic sequences for analysis of intervertebral kinematics.

Intervertebral kinematics closely relates to the functionality of the spinal segments. Direct measurement of the intervertebral kinematics in vivo is very problematic. The use of a fluoroscopic device can provide continuous screening of the lumbar tract during patient spontaneous motion, with an acceptable, low X-ray dose. The kinematic analysis is intended to be limited to planar motion. Kinematic parameters are computed from vertebral landmarks on each frame of the image sequence. Landmarks are normally selected manually in spite of the fact that this is subjective, tedious to perform and regarded as one of the major contributors to errors in the computed kinematic parameters. The aim of this work is to present an innovative method for the automatic recognition of vertebral landmarks throughout a fluoroscopic image sequence to provide an objective and more precise quantification of intervertebral kinematics. The recognition procedure is based upon comparing vertebral features in two adjacent frames by means of a cross-correlation index, which is also robust despite the low signal-to-noise ratio of the lumbar fluoroscopic images. To provide a quantitative assessment of this method a calibration model was used which consisted of two lumbar vertebrae linked by a universal joint. The reliability and accuracy of the kinematic measurements have been investigated. The errors are of the order of a millimetre for the localisation of the intervertebral centre of rotation and tenths of a degree for the intervertebral angle. Error analysis suggests that this method improves the accuracy of the intervertebral kinematic calculations and has the potential to automate the selection of anatomical landmarks.

Influence of muscle morphometry and moment arms on the moment-generating capacity of human neck muscles.

The function of neck muscles was quantified by incorporating experimentally measured morphometric parameters into a three-dimensional biomechanical model. To analyze how muscle morphometry and moment arms influence moment-generating capacity of human neck muscles in physiologic ranges of motion. Previous biomechanical analyses of the head-neck system have used simplified representations of the musculoskeletal anatomy. The force- and moment-generating properties of individual neck muscles have not been reported. A computer graphics model was developed that incorporates detailed neck muscle morphometric data into a model of cervical musculoskeletal anatomy and intervertebral kinematics. Moment arms and force-generating capacity of neck muscles were calculated for a range of head positions. With the head in the upright neutral position, the muscles with the largest moment arms and moment-generating capacities are sternocleidomastoid in flexion and lateral bending, semispinalis capitis and splenius capitis in extension, and trapezius in axial rotation. The moment arms of certain neck muscles (e.g., rectus capitis posterior major in axial rotation) change considerably in the physiologic range of motion. Most neck muscles maintain at least 80% of their peak force-generating capacity throughout the range of motion; however, the force-generating capacities of muscles with large moment arms and/or short fascicles (e.g., splenius capitis) vary substantially with head posture. These results quantify the contributions of individual neck muscles to moment-generating capacity and demonstrate that variations in force-generating capacity and moment arm throughout the range of motion can alter muscle moment-generating capacities.

Automatic location of vertebrae in digitized videofluoroscopic images of the lumbar spine

Back pain is a widespread problem, and the disability it engenders continues to grow, despite efforts to contain it. A major problem in the diagnosis and management of back pain is the assessment of the degree to which mechanical factors play a part. Of considerable importance in understanding these mechanical factors is being able to quantify how the human spine actually moves in vivo. Digitized videofluoroscopy is currently the only practical method available for studying spinal motion in vivo at the segmental level. Low-dose, planar motion X-rays of the spine are captured on videotape and subsequently digitized for analysis. Until now, vertebrae in the digitized images were identified and marked manually as a basis for calculating intervertebral kinematics. This paper describes a procedure for automatically identifying the vertebrae in the motion sequences. The process increases objectivity and repeatability, and significantly reduces the manual effort required in locating the vertebrae prior to calculating the kinematics. The technique has been applied to images of a calibrated model and the results are promising. In-plane rotations may be calculated to an accuracy of at least 1°. Repeated analysis reveals standard deviations of less than 0.5° for intervertebral rotations and less than 0.25 mm for translations.