Iris Busscher

Comparative anatomical dimensions of the complete human and porcine spine

New spinal implants and surgical procedures are often tested pre-clinically on human cadaver spines. However, the availability of fresh frozen human cadaver material is very limited and alternative animal spines are more easily available in all desired age groups, and have more uniform geometrical and biomechanical properties. The porcine spine is said to be the most representative model for the human spine but a complete anatomical comparison is lacking. The goal of this descriptive study was to compare the anatomical dimensions of the cervical, thoracic, and lumbar vertebrae of the human and porcine spine in order to determine whether the porcine spine can be a representative model for the human spine. CT scans were made of 6 human and 6 porcine spines, and 16 anatomical dimensions were measured per individual vertebrae. Comparisons were made for the absolute values of the dimensions, for the patterns of the dimensions within four spinal regions, and normalised values of the dimensions within each individual vertebra. Similarities were found in vertebral body height, shape of the end-plates, shape of the spinal canal, and pedicle size. Furthermore, regional trends were comparable for all dimensions, except for spinal canal depth and spinous processus angle. The size of the end-plates increased more caudally in the human spine. Relating the dimensions to the size of the vertebral body, similarities were found in the size of the spinal canal, the transverse processus length, and size of the pedicles. Taking scaling differences into account, it is believed that the porcine spine can be a representative anatomical model for the human spine in specific research questions.

In vitro biomechanical characteristics of the spine: a comparison between human and porcine spinal segments.

Study Design. An in vitro study on human and porcine multilevel spinal segments. Objective. To compare human and porcine thoracolumbar spinal segments with respect to their biomechanical characteristics and the effects of creep, recovery, and removal of ligaments and posterior parts on the biomechanical characteristics. Summary of Background Data. Availability of human cadaver spines for in vitro testing of new spinal implants and surgical procedures is limited. Therefore, it is important to search for animal models with representative biomechanical characteristics. Methods. A total of 6 human and 6 porcine cadaver spines were dissected in multilevel spinal segments. Pure moments were applied to each segment in flexion/extension, lateral bending, and axial rotation. Creep tests were performed for 30 minutes in 4 creep directions, followed by cyclic tests, a recovery period of 30 minutes, and a series of cyclic tests after removal of ligaments and posterior parts. The range of motion, neutral zone (NZ), and neutral zone stiffness (NZStiff) were calculated from the acquired load-displacement data and results were compared between human and porcine segments. Results. The porcine segments generally had significantly higher absolute values for range of motion and NZ and significantly lower absolute values for NZStiff than the human segments in all directions. The effects of creep and recovery were quite similar in the higher and midthoracic regions of the spine. The influence of removal of ligaments was the same in human and porcine segments. After removal of posterior parts, the lower thoracic porcine spine behaved quite similar to the lumbar human spine. Conclusion. This study showed that the porcine spine can be a good biomechanical model for the human spine in specific situations. The question if the porcine spine can be used to predict the behavior of a human spine depends mainly on the application and the research question.

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.

Predicting growth and curve progression in the individual patient with adolescent idiopathic scoliosis: design of a prospective longitudinal cohort study.

BackgroundScoliosis is present in 3-5% of the children in the adolescent age group, with a higher incidence in females. Treatment of adolescent idiopathic scoliosis is mainly dependent on the progression of the scoliotic curve. There is a close relationship between curve progression and rapid (spinal) growth of the patient during puberty. However, until present time no conclusive method was found for predicting the timing and magnitude of the pubertal growth spurt in total body height, or the curve progression of the idiopathic scoliosis.The goal of this study is to determine the predictive value of several maturity indicators that reflect growth or remaining growth potential, in order to predict timing of the peak growth velocity of total body height in the individual patient with adolescent idiopathic scoliosis. Furthermore, different parameters are evaluated for their correlation with curve progression in the individual scoliosis patient.Methods/designThis prospective, longitudinal cohort study will be incorporated in the usual care of patients with adolescent idiopathic scoliosis. All new patients between 8 and 17 years with adolescent idiopathic scoliosis (Cobb angle >10 degrees) visiting the outpatient clinic of the University Medical Center Groningen are included in this study. Follow up will take place every 6 months. The present study will use a new ultra-low dose X-ray system which can make total body X-rays. Several maturity indicators are evaluated like different body length dimensions, secondary sexual characteristics, skeletal age in hand and wrist, skeletal age in the elbow, the Risser sign, the status of the triradiate cartilage, and EMG ratios of the paraspinal muscle activity.Correlations of all dimensions will be calculated in relationship to the timing of the pubertal growth spurt, and to the progression of the scoliotic curve. An algorithm will be made for the optimal treatment strategy in the individual patient with adolescent idiopathic scoliosis.DiscussionThis study will determine the value of many maturity indicators and will be useful as well for other clinicians treating children with disorders of growth. Since not all clinicians have access to the presented new 3D X-ray system or have the time to make EMGs, for example, all indicators will be correlated to the timing of the peak growth velocity of total body height and curve progression in idiopathic scoliosis. Therefore each clinician can chose which indicators can be used best in their practice.Trial registration numberNTR2048

The effects of creep and recovery on the in vitro biomechanical characteristics of human multi-level thoracolumbar spinal segments

BACKGROUND Several physiological and pathological conditions in daily life cause sustained static bending or torsion loads on the spine resulting in creep of spinal segments. The objective of this study was to determine the effects of creep and recovery on the range of motion, neutral zone, and neutral zone stiffness of thoracolumbar multi-level spinal segments in flexion, extension, lateral bending and axial rotation. METHODS Six human cadaveric spines (age at time of death 55-84 years) were sectioned in T1-T4, T5-T8, T9-T12, and L1-L4 segments and prepared for testing. Moments were applied of +4 to -4 N m in flexion-extension, lateral bending, and axial rotation. This was repeated after 30 min of creep loading at 2 N m in the tested direction and after 30 min of recovery. Displacement of individual motion segments was measured using a 3D optical movement registration system. The range of motion, neutral zone, and neutral zone stiffness of the middle motion segments were calculated from the moment-angular displacement data. FINDINGS The range of motion increased significantly after creep in extension, lateral bending and axial rotation (P<0.05). The range of motion after flexion creep showed an increasing trend as well, and the neutral zone after flexion creep increased by on average 36% (P<0.01). The neutral zone stiffness was significantly lower after creep in axial rotation (P<0.05). INTERPRETATION The overall flexibility of the spinal segments was in general larger after 30 min of creep loading. This higher flexibility of the spinal segments may be a risk factor for potential spinal instability or injury.

Coupled motions in human and porcine thoracic and lumbar spines

Coupled motions, i.e., motions along axes other than the loaded axis, have been reported to occur in the human spine, and are likely to be influenced by inclined local axes due to the sagittal plane spine curvature. Furthermore, the role of facet joints in such motions is as yet unclear. Therefore, this study aimed at assessing coupled motions in multiple spine sections in vitro, before and after removal of posterior elements. Six elderly human and 6 young porcine spines were sectioned in four segments (high thoracic, mid thoracic, low thoracic and lumbar), each consisting of four vertebrae and three intervertebral discs. Segments were loaded along each of the three axes, and three-dimensional rotations of the middle segment were quantified. Subsequently, posterior elements were removed and the protocol was repeated. To avoid mixed loading between Axial Rotation (AR) and Lateral Bending (LB), in contrast to other studies, local axes at the vertebrae were defined as aligned with the loading device prior to each load application. Expressed as a percentage of motion in the loaded direction, coupled motions were on average larger in human (22.7%, SD = 2.2%) than in porcine (11.9%, SD = 1.2%) spines (p < .001). Largest coupled motions were obtained in AR loading of the lumbar spine segments, with mean magnitudes averaged over coupling axes for human L2-L3 joints of 48.9% (SD = 13.2%), including somewhat more LB (56.4%, SD = 18.6) than FE (41.4%, SD = 14.1%) coupling. For porcine L3-L4 joints average coupling in AR loading was 29.3% (SD = 8.2%). In human segments removal of posterior elements only had substantial effects in the lumbar spine segments, where posterior element removal decreased coupled motion during AR loading, averaged over LB and FE coupling, from 48.9% (SD = 13.2%) to 27.7% (SD = 6.1%), mainly through increased motion in the loaded direction. The present results indicate that coupled motions were largest in the lumbar spine. In human spines, posterior elements only contributed to coupled motions in lumbar axial rotation loading.