Injuries in the adolescent porcine spine exposed to mechanical compression

Porcine Functional Spine Unit in orthopedic research, a systematic scoping review of the methodology

Purpose

The aim of this study was to conduct a systematic scoping review of previous in vitro spine studies that used pig functional spinal units (FSU) as a model to gain an understanding of how different experimental methods are presented in the literature. Research guidelines are often used to achieve high quality in methods, results, and reports, but no research guidelines are available regarding in vitro biomechanical spinal studies.

Methods

A systematic scoping review approach and protocol was used for the study with a systematic search in several data bases combined with an extra author search. The articles were examined in multiple stages by two different authors in a blinded manner. Data was extracted from the included articles and inserted into a previously crafted matrix with multiple variables. The data was analyzed to evaluate study methods and quality and included 70 studies.

Results

The results display that there is a lack of consensus regarding how the material, methods and results are presented. Load type, duration and magnitude were heterogeneous among the studies, but sixty-seven studies (96%) did include compressive load or tension in the testing protocol.

Conclusions

This study concludes that an improvement of reported data in the present field of research is needed. A protocol, modified from the ARRIVE guidelines, regarding enhanced report-structure, that would enable comparison between studies and improve the method quality is presented in the current study. There is also a clear need for a validated quality-assessment template for experimental animal studies.

Relationship between degree of separation of endplate cartilage and severity of intervertebral disc herniation

Degeneration of intervertebral disc and fissures in the anulus was caused by compression and distraction, which lead to nucleus pulposus herniation. However, controversy remains regarding the exact mechanism behind disc herniation. The aim of this study is to analyze histologically the differences between the three types of disc herniations in an attempt to infer the underlying mechanism. Disc samples extracted from 49 patients who underwent discectomy of the lumbar region were studied by histological analysis. The severity of disc herniation was classified as bulging, protrusion, extrusion, or sequestration based on preoperative magnetic resonance imaging measurements. For comparative analysis of sequestration characteristics, 49 patients were classified into either the sequestration or the non-sequestration group (i.e., protrusion and extrusion) according to disc herniation type. Forty of the 49 patients had cartilage present in their disc samples upon histological analysis. The endplate cartilage-containing samples included two of four (50%) protruded disc patients, 22 of 29 (75.9%) extruded disc patients, and 16 of 16 (100%) sequestrated disc patients and had statistical significance (p = 0.019). There were no significant differences in age, sex, body mass index, length of hospital stays, injection history, surgical methods, and Visual Analog Scale between the sequestration and non-sequestration group (all p > 0.05). Separation of endplate cartilage increased with the severity of disc herniation. Therefore, the mechanism of disc herniation should consider the connection with endplate cartilage as an initiating link in the mechanical failure of intervertebral discs.

A biomechanical study on the effect of lengthening magnitude on spine off-loading in magnetically controlled growing rod surgery: Implications on lengthening frequency

Purpose: To assess whether the magnitude of lengthening in magnetically controlled growing rod (MCGR) surgeries has an immediate or delayed effect on spinal off-loading. Methods: 9 whole porcine spines were instrumented using two standard MCGRs from T9 to L5. Static compression testing using a mechanical testing system (MTS) was performed at three MCGR lengthening stages (0 mm, 2 mm, and 6 mm) in each spine. At each stage, five cycles of compression at 175N with 25 min of relaxation was carried out. Off-loading was derived by comparing the load sustained by the spine with force applied by the MTS to the spine. Micro-CT imaging was subsequently performed. Results: The mean load sustained by the vertebral body before lengthening was 39.69N, and immediately after lengthening was 25.12N and 19.91N at 2 mm and 6 mm lengthening, respectively; decreasing to 10.07N, 8.31N, and 8.17N after 25 minutes of relaxation, at 0 mm, 2 mm, and 6 mm lengthening stages, respectively. There was no significant difference in off-loading between 2 mm and 6 mm lengthening stages, either instantaneously (p = 0.395) or after viscoelastic relaxation (p = 0.958). CT images showed fractures/separations at the level of pedicle screws in six spines and in the vertebral body's growth zone in five spines after 6 mm MCGR lengthening. Conclusion: This study demonstrated MCGRs cause significant off-loading of the spine leading to stress shielding. 6 mm of lengthening caused tissue damage and microfractures in some spines. There was no significant difference in spine off-loading between 2 mm and 6 mm MCGR lengthening, either immediately after lengthening or after viscoelastic relaxation.

The Influence of Axial Compression on the Cellular and Mechanical Function of Spinal Tissues; Emphasis on the Nucleus Pulposus and Annulus Fibrosus: A Review

In light of the correlation between chronic back pain and intervertebral disc (IVD) degeneration, this literature review seeks to illustrate the importance of the hydraulic response across the nucleus pulposus (NP)-annulus fibrosus (AF) interface, by synthesizing current information regarding injurious biomechanics of the spine, stemming from axial compression. Damage to vertebrae, endplates (EPs), the NP, and the AF, can all arise from axial compression, depending on the segment's posture, the manner in which it is loaded, and the physiological state of tissue. Therefore, this movement pattern was selected to illustrate the importance of the bracing effect of a pressurized NP on the AF, and how injuries interrupting support to the AF may contribute to IVD degeneration.

Sagittal Alignment With Downward Slope of the Lower Lumbar Motion Segment Influences Its Modes of Failure in Direct Compression: A Mechanical and Microstructural Investigation

STUDY DESIGN

Microstructural investigation of compression-induced herniation of ovine lumbar discs with and without added component of anterior-inferior slope.

OBJECTIVE

Does increased shear arising from a simulated component of motion segment slope imitating sacral slope weaken the lateral annulus and increase risk of overt herniation at this same region.

SUMMARY OF BACKGROUND DATA

An increase in sacral slope secondary to lordosis and pelvic incidence increases shear stresses at the lumbosacral junction and has been associated with an increase in spondylolisthetic disorders and back injury. The small component of forward shear induced when a segment is compressed in flexion is suggested to cause differential recruitment of the lateral annular fibers leading to its early disruption followed by intra-annular nuclear tracking to the posterolateral/posterior regions. However, the influence of even greater forward shear arising from the added component of slope seen where pelvic incidence and lumbar lordosis are increased in the lower lumbar spine is less understood.

METHODS

Ovine motion segments were compressed at 40 mm/min up to failure; 9 with a horizontal disc alignment and 26 with a segment slope of 15° and then analyzed structurally.

RESULTS

All the horizontal discs failed (11.8 ± 2.4 kN) via vertebral fracture without any evidence of soft tissue failure even in the lateral aspects of the discs. The increased forward shear resulting from the slope decreased the failure load (6.4 ± 1.6 kN). The sloping discs mostly suffered mid-span, noncontinuous disruption of the lateral annulus with some extruding nuclear material directly from these same lateral regions.

CONCLUSION

The increased level of forward shear generated in moderately sloping lumbar segments when compressed was abnormally damaging to the lateral regions of the disc annulus. This is consistent with the view that shear differentially loads the oblique-counter oblique fiber sets in the lateral annulus, increasing its vulnerability to early disruption and overt herniation.

LEVEL OF EVIDENCE

N/A.

Experimental Model of Proximal Junctional Fracture after Multilevel Posterior Spinal Instrumentation

There is a high risk of proximal junctional fractures (PJF) with multilevel spinal instrumentation, especially in the osteoporotic spine. This problem is associated with significant morbidity and possibly the need for reoperation. Various techniques have been proposed in an attempt to decrease the risk of PJF but there is no experimental model described for in vitro production of PJF after multilevel instrumentation. The objective of this study is to develop an experimental model of PJF after multilevel posterior instrumentation. Initially, four porcine specimens including 4 vertebrae and instrumented at the 3 caudal vertebrae using a pedicle screw construct were subjected to different loading conditions. Loading conditions on porcine specimens involving cyclic loading along the axis of the center vertebral body line, with constrained flexion between 0° and 15° proximally, and fully constraining the specimen distally resulted in a fracture pattern most representative of a PJF seen clinically in humans, so to undergo human cadaveric testing with similar loading conditions was decided. Clinically relevant PJF were produced in all 3 human specimens. The experimental model described in this study will allow the evaluation of different parameters influencing the incidence and prevention of PJF after multilevel posterior spinal instrumentation.

How maturity influences annulus-endplate integration in the ovine intervertebral disc: a micro- and ultra-structural study

The annulus-endplate anchorage system plays a vital role in structurally linking the compliant disc to its adjacent much more rigid vertebrae. Past literature has identified the endplate as a region of weakness, not just in the mature spine but also in the immature spine. The aim of this structural study was to investigate in detail the morphological changes associated with annulus-endplate integration through different stages of maturity. Ovine lumbar motion segments were collected from two immature age groups: (i) newborn and (ii) spring lamb (roughly 3 months old); these were compared with a third group of previously analysed mature ewe samples (3-5 years). Sections from the posterior region of each motion segment were obtained for microstructural analysis and imaged in their fully hydrated state via differential interference contrast (DIC) optical microscopy. Selected slices were further prepared and imaged via scanning electron microscopy (SEM) to analyse fibril-level modes of integration. Despite significant changes in endplate morphology, the annular fibre bundles in all three age groups displayed a similar branching mechanism, with the main bundle splitting into several sub-bundles on entering the cartilaginous endplate. This morphology, previously described in the mature ovine disc, is thought to strengthen significantly annulus-endplate integration. Its prevalence from an age as young as birth emphasizes the critical role that it plays in the anchorage system. The structure of the branched sub-bundles and their integration with the surrounding matrix were found to vary with age due to changes in the cartilaginous and vertebral components of the endplate. Microscopically, the sub-bundles in both immature age groups appeared to fade into the surrounding tissue due to their fibril-level integration with the cartilaginous endplate tissue, this mechanism being particularly complex in the spring lamb disc. However, in the fully mature disc, the sub-bundles remained as separate entities throughout the full depth of their anchorage into the cartilaginous endplate. Cell morphology was also found to vary with maturity within the cartilaginous matrix and it is proposed that this relates to endplate development and ossification.

Ring apophysis fractures induced by low-load low-angle repetitive flexion in an ex-vivo cervine model

Ring apophysis fractures of the spine occur in physically-active adolescents causing low back pain and the potential for chronic pain. Many of these fractures occur without memorable trauma, suggesting that the fractures occur during everyday movements and activities. The benign nature of this poorly understood potential mechanism of injury hampers appropriate diagnosis and early treatment. The purpose of this study was to establish an ex-vivo model of ring apophysis fracture and demonstrate that these fractures can be initiated by repetitive non-traumatic loading. Six 5-vertebra cervine lumbar (L1-L5) motion segments were cyclically loaded in low-angle low-load flexion (to 15° flexion, with peak load of 230±50N), a representative movement component of daily activities for both human and deer lumbar spines. Pinned end conditions replicated physiologically realistic loading. Ring apophysis fractures were created under low-load low-angle conditions in healthy vertebrae of similar bone mineral density and a similar degree of skeletal maturity to adolescent humans. All specimens developed ring apophysis fractures, some as early as 1400 cycles. The load-displacement data, and hysteresis loops during the cyclic loading, suggest that the fractures occurred gradually, i.e., without trauma. The ease at which these fractures were created suggests that ring apophysis fractures may be more prevalent than current diagnosis rates. Therefore, clinically, healthcare providers should include the potential for ring apophysis fracture in the differential diagnosis of all physically-active adolescents who present with back pain.

Approach to the pediatric athlete with back pain: more than just the pars

Back pain in a pediatric patient can present a worrisome and challenging diagnostic dilemma for any physician. Although most back pain can be attributed to muscle strains and poor mechanics, it is necessary to appreciate the full differential of etiologies causing back pain in the pediatric population. The physician must recognize areas of mechanical weakness in the skeletally immature spine and the sport specific forces that can predispose a patient to injury. A comprehensive history involves determining the onset, chronicity, and location of the pain. A focused physical exam includes a neurological exam as well as provocative testing. The combination of a thorough history and focused physical exam should guide appropriate imaging. Radiographic tests are instrumental in narrowing the differential, making a diagnosis, and uncovering associated pathology. Treatment modalities such as activity modification, heat/cold compresses, and NSAIDs can provide pain relief and allow for effective physical therapy. In most cases nonoperative methods are successful in providing a safe and quick return to activities. Failure of conservative measures requires referral to an orthopedic surgeon, as surgical intervention may be warranted.

"Surprise" Loading in Flexion Increases the Risk of Disc Herniation Due to Annulus-Endplate Junction Failure: A Mechanical and Microstructural Investigation

STUDY DESIGN

Microstructural investigation of compression-induced herniation of the flexed lumbar disc.

OBJECTIVE

To provide a microstructural analysis of the mechanisms of annular wall failure in healthy discs subjected to flexion and a rate of compression comparable with the maximum rate at which the muscles of the spinal column can generate a force.

SUMMARY OF BACKGROUND DATA

Clinical evidence indicates the involvement of the endplate in herniation. It is known that both an elevated rate of compression and a flexed posture are necessary to cause disc failure either within the midspan of the annulus or at the annular-endplate interface. However, the question of what effect a sudden or "surprise" loading might have on the mode of failure is, as yet, unanswered.

METHODS

Twenty-four healthy mature ovine lumbar motion segments were compressed to failure in high physiological flexion (10º). This occurred over approximately 5 mm of crosshead displacement in 0.75 seconds that resulted in a displacement rate of 400 mm/min (defined as a "surprise" rate) and was intended to simulate the maximum rate at which the muscles of the spinal column can generate a force. The damaged discs were then analyzed microstructurally.

RESULTS

Fifty-eight percent of discs suffered annular-endplate junction rupture, 25% suffered midspan annular rupture, and the balance of 17% endplate fracture. Microstructural analysis indicated that annular rupture initiated at the endplate apical ridge in the mid-to-outer region of the annulus in both annular-endplate and midspan annulus rupture.

CONCLUSION

Motion segments subjected to a "surprise" loading rate are likely to fail via some form of annular rupture. Failure under such sudden loading occurs mostly via rupture of the annular-endplate junction and is thought to arise from a rate-induced mechanostructural imbalance between the annulus and the endplate.

LEVEL OF EVIDENCE

N/A.

How healthy discs herniate: a biomechanical and microstructural study investigating the combined effects of compression rate and flexion

STUDY DESIGN

Microstructural investigation of compression-induced disruption of the flexed lumbar disc.

OBJECTIVE

To provide a microstructural analysis of the mechanisms of annular wall failure in healthy discs subjected to flexion and an elevated rate of compression.

SUMMARY OF BACKGROUND DATA

At the level of the motion segment failure of the disc in compression has been extensively studied. However, at the microstructural level the exact mechanisms of disc failure are still poorly understood, especially in relation to loading posture and rate.

METHODS

Seventy-two healthy mature ovine lumbar motion segments were compressed to failure in either a neutral posture or in high physiological flexion (10°) at a displacement rate of either 2 mm/min (low) or 40 mm/min (high). Testing at the high rate was terminated at stages ranging from initial wall tearing through to facet fracture so as to capture the evolution of failure up to full herniation. The damaged discs were then analyzed microstructurally.

RESULTS

Approximately, 50% of the motion segments compressed in flexion at the high rate experienced annulus or annulus-endplate junction failure, the remainder failed via endplate fracture with no detectable wall damage. The average load to induce disc failure in flexion was 18% lower (P < 0.05) than that required to induce endplate fracture. Microstructural analysis indicated that wall rupture occurred first in the posterior mid-then-outer annulus.

CONCLUSION

Disc wall failure in healthy motion segments requires both flexion and an elevated rate of compression. Damage is initiated in the mid-then-outer annular fibers, this a likely consequence of the higher strain burden in these same fibers arising from endplate curvature. Given the similarity in geometry between ovine and human endplates, it is proposed that comparable mechanisms of damage initiation and herniation occur in human lumbar discs.

LEVEL OF EVIDENCE

N/A.

ISSLS Prize winner: The anatomy of failure in lumbar disc herniation: an in vivo, multimodal, prospective study of 181 subjects

STUDY DESIGN

A prospective multimodal study including clinical, radiological, serial postcontrast magnetic resonance imaging, intraoperative findings, and histopathological study.

OBJECTIVE

To document in vivo, the site of anatomical failure in lumbar disc herniation (LDH).

SUMMARY OF BACKGROUND DATA

Although in vitro mechanical disruption studies have implicated both the endplate junction (EPJ) and the annulus fibrosus (AF) as the site of failure in LDH, there are no in vivo human studies to document the exact anatomy of failure.

METHODS

One hundred eighty-one consecutive patients requiring microdiscectomy at a single level formed the study group. The status of the endplate and AF in the operated level (study discs) and the other discs (control) were evaluated by plain radiograph, thin slice computed tomographic scan, plain and contrast magnetic resonance imaging, intraoperative examination, and histopathological analysis.

RESULTS

LDH due to EPJ failure (EPJF- type I herniation) was more common (117; 65%) than annulus fibrosis rupture. Herniated discs had a significantly higher incidence of EPJF than control discs (P < 0.0001). The EPJF was evident radiologically as vertebral corner defect in 30 patients, rim avulsion in 46, frank bony avulsions in 24, and avulsion at both upper and lower EP in 4. Thirteen discs with normal EP radiologically had cartilage or bone avulsion intraoperatively. Sixty-four discs (35%) had intact EP of which annular high intensity zone was found in 21 (11%), suggesting a disruption of AF (type II herniation). Postcontrast magnetic resonance image of 20 patients showed dye leak at the EPJ proving EPJF as main cause of LDH.

CONCLUSION

Our study provides the first in vivo evidence that LDH in humans is more commonly the result of EPJF than AF rupture and offers clinical validation of previous in vitro mechanical disruption studies. Future research must focus on the EPJ as a primary area of interest in LDH.

LEVEL OF EVIDENCE

N/A.

Percutaneous disc decompression with nucleoplasty-volumetry of the nucleus pulposus using ultrahigh-field MRI

PURPOSE

To evaluate changes in nucleus pulposus volume as a potential parameter for the effects of disc decompression.

METHODS

Fifty-two discs (T8 to L1) were extracted from 26 pigs and separated into thoracic (T8 to T11) and thoracolumbar discs (T12 to L1). The discs were imaged using 7.1 Tesla ultrahigh-field magnetic resonance imaging (MRI) with acquisition of axial T2-weighted turbo spin-echo sequences for determination of baseline and postinterventional nucleus pulposus volumes. Volumes were calculated using OsiriX® (http://www.osirix-viewer.com). After randomization, one group was treated with nucleoplasty, while the placebo group was treated with an identical procedure but without coblation current. The readers analyzing the MR images were blinded to the kind of procedure performed. Baseline and postinterventional volumes were compared between the nucleoplasty and placebo group.

RESULTS

Average preinterventional nucleus volume was 0.799 (SD: 0.212) ml. Postinterventional volume reduction in the nucleoplasty group was significant at 0.052 (SD: 0.035) ml or 6.30% (p<0.0001) (thoracic discs) and 0.082 (SD: 0.042) ml or 7.25% (p = 0.0078) (thoracolumbar discs). Nucleoplasty achieved volume reductions of 0.114 (SD: 0.054) ml or 14.72% (thoracic) and 0.093 (SD: 0.081) ml or 11.61% (thoracolumbar) compared with the placebo group.

CONCLUSIONS

Nucleoplasty significantly reduces thoracic and thoracolumbar nucleus pulposus volumes in porcine discs.

Biomechanical in vitro evaluation of the complete porcine spine in comparison with data of the human spine

The purpose of this study was to provide quantitative biomechanical properties of the whole porcine spine and compare them with data from the literature on the human spine. Complete spines were sectioned into single joint segments and tested in a spine tester with pure moments in the three main anatomical planes. Range of motion, neutral zone and stiffness parameters of the spine were determined in flexion/extension, right/left lateral bending and left/right axial rotation. Comparison with data of the human spine reported in the literature showed that certain regions of the porcine spine exhibit greater similarities than others. The cervical area of C1-C2 and the upper and middle thoracic sections exhibited the most similarities. The lower thoracic and the lumbar area are qualitatively similar to the human spine. The remaining cervical section from C3 to C7 appears to be less suitable as a model. Based on the biomechanical similarities of certain regions of the porcine and human spines demonstrated by this study results, it appears that the use of the porcine spine could be an alternative to human specimens in the field of in vitro research. However, it has to be emphasized that the porcine spine is not a suitable biomechanics surrogate for all regions of the human spinal column, and it should be carefully considered whether other specimens, for example from the calf or sheep spine, represent a better alternative for a specific scientific question. It should be noted that compared with human specimens each animal model always only represents a compromise.

Estudo biomecânico da fixação pedicular curta na fratura-explosão toracolombar

OBJETIVO: Comparar a rigidez biomecânica entre a coluna toracolombar intacta, a coluna com fratura explosão e a coluna com fratura explosão associada à fixação pedicular curta em suínos. MÉTODOS: 30 amostras de coluna toracolombar (T11-L3) de suínos foram divididas em três grupos com 10 amostras cada. O Grupo 1 representava a coluna intacta, o Grupo 2 representava a coluna com fratura explosão e o Grupo 3 a fratura explosão associada à fixação pedicular curta. Foi realizado o corte ósseo em "V" do terço médio do corpo vertebral comprometendo a coluna anterior e média de L1 para simular a fratura explosão. No Grupo 3 foi realizada a fixação pedicular com Pinos de Schanz. Os grupos foram submetidos ao teste biomecânico em compressão axial controlada. Os parâmetros de carga (N) e deslocamento (mm) eram gerados em um gráfico instantâneo e a rigidez (N/mm) foi determinada. O teste era interrompido quando ocorria uma queda súbita na curva no gráfico indicando falência da amostra. RESULTADOS: A rigidez das colunas fraturadas foi 53% menor do que a rigidez das colunas intactas, sendo essa diferença estatisticamente significativa (p < 0,05). A fixação pedicular curta apresentou uma rigidez 50% maior do que a coluna fraturada. Esse aumento foi estatisticamente significativo (p < 0,05). A rigidez da fixação pedicular curta foi 30% menor do que a rigidez das colunas intactas. Essas diferenças foram estatisticamente significativas (p < 0,05). CONCLUSÃO: A fixação pedicular curta não é suficiente para restabelecer a rigidez da coluna intacta nos testes biomecânicos in vitro de compressão axial pura em modelos de fratura toracolombar de suínos.

ISSLS prize winner: how loading rate influences disc failure mechanics: a microstructural assessment of internal disruption

STUDY DESIGN

Mechanically induced disruption and subsequent microscopic investigation of lumbar intervertebral discs following a previously published testing protocol, but using a much higher rate of loading.

OBJECTIVE

To explore if loading rate affects the internal disruption mechanics of lumbar intervertebral discs.

SUMMARY OF BACKGROUND DATA

The failure mechanics of some bone-ligament-bone constructs vary with the rate of tensile load application. Like many ligaments, recent reports indicate that the mechanical response of the disc wall varies with strain-rate. It is possible that the internal failure mechanics of the disc wall also varies with strain-rate.

METHODS

Nuclear pressurization was used to deliver sudden pressure impulses directly to the nucleus of ovine lumbar motion segments. Pressure impulses were delivered to 12 neutrally positioned motion segments, and 15 motion segments held at 7° flexion. Aside from loading rate, testing was conducted in the same manner as 2 previously published studies that employed a gradual nuclear pressurization regime. Following testing, the internal damage resulting to each disc was analyzed using micro-CT and serial microscopy in tandem.

RESULTS

Radial tears of the medioposterior disc wall were the most frequent cause of disc failure. In most cases, radial tears involved a combination of annular and endplate disruption: Neutrally positioned discs frequently suffered tears within the superior cartilaginous endplate adjacent to the transition zone and/or inner anulus. Flexed discs frequently suffered tears adjacent to the outer anulus at the cartilaginous/vertebral endplate junction, or within the vertebral endplate. Both groups frequently suffered endplate tears adjacent to the mid anulus at the inferior cartilaginous/vertebral endplate junction.

CONCLUSION

The internal morphologies of the disc disruptions created in this study using high strain-rate impulse pressurization differed significantly from those documented previously for both neutrally positioned and flexed discs subjected to gradual low strain-rate pressurization. These morphologic differences show that the internal failure mechanics of lumbar intervertebral discs vary with the rate of internal radial load application.

An Examination of the Influence of Strain Rate on Subfailure Mechanical Properties of the Annulus Fibrosus

Disk herniation is often considered a cumulative injury in that repetitive stress on the posterior annulus can result in the nucleus pulposus penetrating the annulus fibrosus and eventually extruding posteriorly. Further, it has been documented that the nucleus pulposus works its way through the annulus through clefts, which form as a result of repetitive tensile strain. The annulus fibrosus is viscoelastic in nature and therefore could express different mechanical responses to applied strain at varying rates. Other viscoelastic tissues, including tendons and ligaments, have shown altered mechanical responses to different rates of applied strain, but the response of the annulus to varying rates of strain is largely unknown. The present study examined the mechanical properties of 20 two-layered samples of porcine annulus fibrosus tissue at three distinct rates of applied 20% biaxial strain (20% strain over 20 s (slow), over 10 s (medium), and over 5 s (fast)); these three rates are considered applicable to nontraumatic loading. No differences in the stiffness or maximum stress in each of the two directions of applied strain were observed between the three strain rates. Specifically, the average (standard deviation) moduli calculated at the fast, medium, and slow rates, respectively, in the axial direction were 7.42 MPa (6.06), 7.77 MPa (6.61), and 7.63 MPa (6.67) and 8.22 MPa (8.4), 8.63 MPa (9.00), and 8.49 MPa (8.69) in the circumferential direction. The maximum stress values reached during the fast, medium, and slow rates, respectively, in the axial direction were 0.40 (0.36) MPa, 0.40 (0.36) MPa, and 0.39 (0.35) MPa and 0.45 (0.47) MPa, 0.44 (0.46) MPa, and 0.43 (0.46) MPa in the circumferential direction. At submaximal strain magnitudes over a range of nontraumatic rates likely to result in clefts in the annulus and potentially leading to disk herniation, any strain rate dependence is not significant.

All-terrain vehicle use in agriculture: exposure to whole body vibration and mechanical shock

Whole body vibration (WBV) and mechanical shock were measured in 12 New Zealand farmers during their daily use of all-terrain vehicles (ATVs). As per the International Organization for Standardization (ISO) guidelines for WBV exposure, frequencies between 0 and 100Hz were recorded via a seat-pad tri-axial accelerometer during 20min of ATV use. The farmers were also surveyed to estimate seasonal variation in daily ATV usage as well as 7-day and 12-month prevalence of spinal pain. Frequency-weighted vibration exposure and total riding time were calculated to determine the daily vibration dose value (VDV). The daily VDV of 16.6m/s(1.75) was in excess of the 9.1m/s(1.75) action limit set by ISO guidelines suggesting an increased risk of low back injury from such exposure. However, the mean shock factor R, representing cumulative adverse health effects, was 0.31 indicating that these farmers were not exposed to excessive doses of mechanical shock. Extrapolation of daily VDV data to estimated seasonal variations of farmers in ATV riding time demonstrated that all participants would exceed the ISO recommended maximum permissible limits during the spring lambing season, as compared to lower exposures calculated for summer, autumn and winter. Low back pain was the most commonly reported complaint for both 7 day (50%) and 12 month prevalence (67%), followed by the neck (17% and 42%) and the upper back (17% and 25%) respectively. The results demonstrate high levels of vibration exposure within New Zealand farmers and practical recommendations are needed to reduce their exposure to WBV.

The immediate effect of repeated loading on the compressive strength of young porcine lumbar spine

The human spine is exposed to repeated loading during daily activities and more extremely during sports. Despite this, there remains a lack of knowledge regarding the immediate effects on the spine due to this mode of loading. Age-specific spinal injury patterns has been demonstrated and this implies differences in reaction to load mode and load history The purpose of the present study was to investigate the impact of cyclic pre-loading on the biomechanical properties and fracture patterns of the adolescent spine in an experimental model. Eight functional spinal units from four young porcine spines were harvested. The functional spinal units were cyclic loaded with 20,000 cycles and then axially compressed to failure. The compression load at failure, ultimate stress and viscoelastic parameters were calculated. The functional spinal units were examined with plain radiography, computer tomography and MRI before and after the loading, and finally macroscopically and histologically. The median compression load at failure in this study was 8.3 kN (range 5.6-8.7 kN). The median deformation for all cases was 2.24 mm (range 2.30-2.7 mm) and stiffness was 3.45 N/mm (range 3.5-4.5 N/mm). A fracture was seen on radiograph in one case, on CT and macroscopically in seven, and on MRI and histologically in all eight cases. The cyclic loaded functional spinal units in the present study were not more sensitive to axial compression than non-cyclic loaded functional spinal units from young porcine. The endplate and the growth zone were the weakest part in the cyclic loaded functional spinal units. Disc signal reduction and disc height reduction was found on MRI. The E-modulus value found in this study was of the same order of magnitude as found by others using a porcine animal model.

Acute injury of an intervertebral disc in an elite tennis player: a case report

STUDY DESIGN

A case report.

OBJECTIVE

To present a previously not described rare case of intradiscal hematoma due to acute trauma in an elite tennis player.

SUMMARY OF BACKGROUND DATA

Several studies have demonstrated a high frequency of radiological changes in the spine of athletes, especially in sports with high loads on the back. Signs of disc degeneration without disc herniation have frequently been found in magnetic resonance imaging (MRI) studies of the spine of athletes. It has also been shown that radiological abnormalities of the spine in young athletes are correlated to back pain.

METHODS

An elite male tennis player experienced pain in the right buttock after a backhand stroke. He was successfully treated for hip problems and started to play competitive tennis, 2 weeks later. After few games, a backhand stroke again resulted in intense pain projected in the os coccyx region. At examination, there were no neurologic disturbances. At palpation over the spinal processes (Springing test) of L1-L2, the patient experienced intense pain projected to the os coccyx region.

RESULTS

MRI examination showed an injured L1-L2 disc with fluid inside the disc with a signal similar to blood. Four additional MRI examinations were performed 2 weeks and 2 years after the injury until disc degeneration is formed. Radiograph examination before and 2 years after the injury is available.

CONCLUSION

In conclusion, trauma in athletes can cause intradiscal hematoma, which probably is a new etiology for disc degeneration. Also that sudden onset of pain in the hip or the gluteal region may be caused by referred pain due to a disc lesion. Intradiscal hematoma can be visualized using MRI.

Micro-computed tomography evaluation of vertebral end-plate trabecular bone changes in a porcine asymmetric vertebral tether

We conducted a micro-CT analysis of subchondral bone of the vertebral end-plates after application of compressive stress. Thoracic and lumbar vertebral units were instrumented by carrying out left asymmetric tether in eleven 4-week-old pigs. After 3 months of growth, instrumented units and control units were harvested. Micro-CT study of subchondral bone was performed on one central and two lateral specimens (fixated side and non-fixated side). In control units, bone volume fraction (BV/TV), number of trabeculae (Tb.N), trabecular thickness (Tb.Th), and degree of anisotropy (DA) were significantly higher, whereas intertrabecular space (Tb.Sp) was significantly lower in center than in periphery. No significant difference between the fixated and non-fixated sides was found. In instrumented units, BV/TV, Tb.N, Tb.Th, and DA were significantly higher in center than in periphery. BV/TV, Tb.N, and Conn.D were significantly higher in fixated than in non-fixated side, while Tb.Sp was significantly lower. We noted BV/TV, Tb.N, and Tb.Th significantly lower, and Tb.Sp significantly higher, in the instrumented levels. This study showed, in instrumented units, two opposing processes generating a reorganization of the trabecular network. First, an osteolytic process (decrease in BV/TV, Tb.N, Tb.Th) by stress-shielding, greater in center and on non-fixated side. Second, an osteogenic process (higher BV/TV, Tb.N, Conn.D, and lower Tb.Sp) due to the compressive loading induced by growth on the fixated side. This study demonstrates the densification of the trabecular bone tissue of the vertebral end-plates after compressive loading, and illustrates the potential risks of excessively rigid spinal instrumentation which may induce premature osteopenia.

Intervertebral disc cell death in the porcine and human injured cervical spine after trauma: a histological and ultrastructural study

STUDY DESIGN

Histologic and ultrastructural study of disc cell death after traumatic injury to the human cervical spine and postmortem (p-m) in the porcine cervical spine.

OBJECTIVE

To determine the changes in disc cell morphology, viability, and manner of cell death after trauma in human discs and p-m in porcine discs.

SUMMARY OF BACKGROUND DATA

Similarities in the morphology of human and porcine spine have been shown in many histologic and biomechanical investigations. It is known that compressive or traumatic injuries to cartilage and intervertebral discs can result in cell death by necrosis or apoptosis. An additional form of apoptosis, chondroptosis, has been reported in articular cartilage, but not to date in the disc.

METHODS

The anterior portion of intervertebral discs and endplates of 30 patients with traumatic injuries to the cervical spine were studied histologically (including trypan blue exclusion and TUNEL staining) and ultrastructurally. Fractures were classified according to Magerl and degeneration of the intervertebral disc according to Thompson and Benneker. Similar studies of disc and endplate were undertaken on porcine cervical spine 0 to 24 hours p-m.

RESULTS

Electron and light microscopy showed up to 75% of human disc cells die within the first 24 hours of trauma, mainly by necrosis, similar to that seen in pig discs p-m. This study reports on 2 morphologies, chondroptosis and balloon cells, previously not described in the disc. Chondroptosis had been significantly higher and ballooned cells were exclusively seen in discs from fractures with compression, where apoptosis was also most common. Porcine samples revealed comparable rates of apoptosis and chondroptosis as fractures with less compression. Glycogen was commonly found in disc cells after trauma.

CONCLUSION

Traumatic injuries of the human cervical spine lead to rapid changes in disc cell morphology and cell death, particularly via necrosis. The type of fracture and load seems to influence cell death.

Clinical significance of ring apophysis fracture in adolescent lumbar disc herniation

STUDY DESIGN

Retrospective review and post-test-only control group design.

OBJECTIVE

To study the incidence and associated factors of ring apophysis fracture in adolescent lumbar disc herniation and to evaluate the long-term morbidity of untreated apophyseal fracture.

SUMMARY OF BACKGROUND DATA

Ring apophysis fracture is a feature in adolescent disc herniation, but the incidence and prognosis are unknown. It is still controversial whether to remove the apophyseal fragment at time of discectomy.

METHODS

We studied 96 adolescents (mean age, 14.7 years) with clinical diagnosis of disc herniation proved by computerized tomography (CT). In CT scan ring, apophyseal fracture is classified by the size (large/small) and the location (central/lateral). We used modified Oswestry classification in the nonoperative patients for pain and functional evaluation. Patients with and without apophyseal fracture were compared to define the significance of the lesion.

RESULTS

Twenty-seven of the 96 CT studies (28%) demonstrated apophyseal fractures. All but 2 were at the level of the herniated disc. Large-central fragments were the most common in 16 patients (48%), large-lateral fragments in 2, small-central fragments in 6, and small-lateral fragment in 6. Rate of surgery was significantly higher in the disc herniation patients with apophyseal fractures. Sixty-four nonoperative patients were evaluated 6.6 years (range, 2.3-14.3) after the CT study and questionnaires were completed in 54 patients (84%). Patients with large apophyseal fragments had more chance of chronic back pain and limitation of daily activities than the patients with small fragments and patients without apophyseal fracture.

CONCLUSION

Apophyseal fracture is not uncommon in adolescent lumbar disc herniation. The surgical decision must depend on clinical symptoms instead of radiologic findings, but disc herniation with apophyseal fracture may exhibit more severe symptoms. Patients with large apophyseal fragments must be informed of a greater chance of chronic back pain later on. Small apophyseal fragments had no clinical significance.

Relationship between disc injury and manual lifting: a poroelastic finite element model study

Understanding how failure originates in a lumbar motion segment subjected to loading conditions that are representative of manual lifting is important because it will pave the way for a better formulation of the exposure-injury relationship. The aim of the current investigation was to use a poroelastic finite element model of a human lumbar disc to determine its biomechanical characteristics under loading conditions that corresponded to three different, commonly occurring lifting activities and to identify the most hazardous type of loading with regard to damage to the disc. The current study showed that asymmetric lifting may increase the risk of back injury and pain. Lifting that involved lateral bending (asymmetric lifting) of the trunk was found to produce stresses at a localized area in the annulus, annuluar fibres, end plates, and facet joints that were higher than their respective tissue failure strength. Thus asymmetric lifting, if performed over a large number of cycles, might help to propagate this localized failure of the disc tissue to a larger area, owing to fatigue. The analyses also showed that largest fluid exchange between the nucleus and the end plates occurred during asymmetric lifting. If the fluid exchange is restricted owing to end plate calcification or sclerosis of the subchondral bone, high intradiscal pressure might develop, leading to higher disc bulge causing back pain.

Vertebral end-plate fractures as a result of high rate pressure loading in the nucleus of the young adult porcine spine

In a healthy spine, end-plate fractures occur from excessive pressurization of the intervening nucleus. Younger spines are most susceptible to such type of injury due to the highly hydraulic nature of their intervertebral discs. The purpose of this paper was to confirm this fracture mechanism of the healthy spine through the pressurization of the nucleus in the absence of external compressive loading. Sixteen functional porcine spine units were dissected and both injection and pressure transducer needles were inserted into the nucleus of the intervertebral disc. Hydraulic fluid was rapidly injected into the nucleus until failure occurred. Peak pressure and rate of pressure development were monitored. Spine units were dissected to determine the type and location of fracture. Fifteen of the 16 spine units fractured (the remaining unit had a degenerated disc). Of the 15 fractures, 13 occurred at the posterior margin of the end-plate along the lines of the growth plates. A slightly exponential relationship was found between peak pressure and its rate of development (R(2) = 0.544). Also, in each of the growth-plate fractured specimens, nuclear material was forcefully emitted, during fracture, from the intervertebral disc into the vertebral foramen. The posterior end-plate fractures produced here are similar to those often seen in young adult humans. This provides insight into a mechanism of fracture development through pressurization of the nucleus that might be seen in older adolescents and younger adults during athletic events or mild trauma.

A vertebral fracture in childhood is not a risk factor for disc degeneration but for Schmorl's nodes: a mean 40-year observational study

STUDY DESIGN

Observational cohort study.

OBJECTIVE

To evaluate by MRI whether a vertebral fracture during childhood is a risk factor for degeneration of adjacent discs.

SUMMARY OF BACKGROUND DATA

Several studies infer that trauma is a major cause of disc degeneration. Only 1 study has by magnetic resonance imaging (MRI) evaluated disc degeneration in children with a former thoracic or lumbar vertebral fracture. That study reported a 50% prevalence of degenerative disc changes 4 years after the fracture. However, due to the sparse literature, it is still unclear whether a vertebral fracture in childhood represents a risk factor for disc degeneration in a long-term perspective.

METHOD

Nine boys and 11 girls with a mean age of 12 years (range, 7-16 years) when sustaining a lumbar or thoracic vertebral fracture without neurologic deficits were examined at a mean of 40 years (range, 33-53 years) after the injury. Eighteen of the subjects had 1-column compression fractures, and 2 had Denis Type B burst fractures. All were mobilized without brace or surgery directly after being injured. A favorable long-term clinical and plain radiographic outcome has previously been reported for this cohort. In the present study, the intervertebral discs were evaluated with MRI by applying the Oner classification scheme. Degenerative disc changes were defined as loss of signal intensity on T2-weighted images with or without disc height reduction.

RESULTS

Degenerative changes were not more prevalent in discs adjacent to the previously fractured vertebrae than in discs at a distance from those segments. However, there were more Schmorl's nodes at the disc levels adjacent to the earlier fractures.

CONCLUSION

Stable vertebral fractures in childhood with no neurologic deficits at injury do not render more degenerative changes than can be expected according to age, but they are associated with more Schmorl's nodes at adjacent disc levels.

A pelvic fracture model for the assessment of treatment options in a laboratory environment

BACKGROUND

Optimal prehospital and clinical management of patients with severe pelvic trauma is controversial. Prospective evaluations of different treatment strategies have not been performed and treatment is currently not evidence-based. The purpose of the present study was to develop a porcine model of reproducible severe pelvic trauma for subsequent laboratory trials.

METHODS

The study was performed on 13 juvenile porcine cadavers. Pelvic fractures were created by applying a pure anterior-posterior compression load to the pelvic ring using a servohydraulic material testing machine. Fracture patterns were classified according to the Young-Burgess classification and the Tile classification using postfracture CT scans including 3D-reconstructions.

RESULTS

Disruptions of the posterior pelvic ring segment were unilateral in 12 cases and bilateral in one case transforaminal vertical sacrum fractures. Injuries of the anterior ring segment were obturator ring fractures bilateral, ipsilateral or contralateral to the injury of the posterior ring segment. According to the Tile classification this resulted in 12 type C1 and 1 type C3 fractures. In the Young classification all injuries were classified as type APC III. In six cases transverse process fractures were found ipsilateral to the posterior ring disruption. Initial force drops indicating bony or ligamentous injuries occurred at mean forces of 4030 +/- 269N (range, 3617-4374N).

CONCLUSION

The present model was able to create reproducible unstable pelvic fractures and can be used for controlled laboratory trials to study the management of patients with pelvic fractures.

Are animal models useful for studying human disc disorders/degeneration?

Intervertebral disc (IVD) degeneration is an often investigated pathophysiological condition because of its implication in causing low back pain. As human material for such studies is difficult to obtain because of ethical and government regulatory restriction, animal tissue, organs and in vivo models have often been used for this purpose. However, there are many differences in cell population, tissue composition, disc and spine anatomy, development, physiology and mechanical properties, between animal species and human. Both naturally occurring and induced degenerative changes may differ significantly from those seen in humans. This paper reviews the many animal models developed for the study of IVD degeneration aetiopathogenesis and treatments thereof. In particular, the limitations and relevance of these models to the human condition are examined, and some general consensus guidelines are presented. Although animal models are invaluable to increase our understanding of disc biology, because of the differences between species, care must be taken when used to study human disc degeneration and much more effort is needed to facilitate research on human disc material.

Three-dimensional motion analysis of the lumbar spine during "free squat" weight lift training

BACKGROUND

Heavy weight lifting using a squat bar is a commonly used athletic training exercise. Previous in vivo motion studies have concentrated on lifting of everyday objects and not on the vastly increased loads that athletes subject themselves to when performing this exercise.

HYPOTHESIS

Athletes significantly alter their lumbar spinal motion when performing squat lifting at heavy weights.

STUDY DESIGN

Controlled laboratory study.

METHODS

Forty-eight athletes (28 men, 20 women) performed 6 lifts at 40% maximum, 4 lifts at 60% maximum, and 2 lifts at 80% maximum. The Zebris 3D motion analysis system was used to measure lumbar spine motion. Exercise was performed as a "free" squat and repeated with a weight lifting support belt. Data obtained were analyzed using SAS.

RESULTS

A significant decrease (P < .05) was seen in flexion in all groups studied when lifting at 40% maximum compared with lifting at 60% and 80% of maximum lift. Flexion from calibrated 0 point ranged from 24.7 degrees (40% group) to 6.8 degrees (80% group). A significant increase (P < .05) was seen in extension when lifting at 40% maximum was compared with lifting at 60% and 80% maximum lift. Extension from calibrated 0 point ranged from -1.5 degrees (40% group) to -20.3 degrees (80% group). No statistically significant difference was found between motion seen when exercise was performed as a free squat or when lifting using a support belt in any of the groups studied.

CONCLUSION

Weight lifting using a squat bar causes athletes to significantly hyperextend their lumbar spines at heavier weights. The use of a weight lifting support belt does not significantly alter spinal motion during lifting.

The vertebral endplate: disc degeneration, disc regeneration

The vertebral endplates are critical for maintaining disc function yet like other components of the disc are vulnerable to degeneration. This paper provides an overview of the development and normal function of the endplates as well as an impression of what happens when they undergo progressive degeneration. Recent research suggests that the degenerative process can be retarded or reversed.

Vertebral fractures and separations of endplates after traumatic loading of adolescent porcine spines with experimentally-induced disc degeneration

BACKGROUND

Abnormalities of the intervertebral discs have been found in a high frequency among young elite athletes. Several studies have also reported that the adolescent spine, especially the vertebral growth zones, is vulnerable to trauma. However, there is incomplete knowledge regarding the injury mechanism of the growing spine. In this study, the injury patterns of the adolescent porcine spine with disc degeneration were examined.

METHODS

Twenty-four male pigs were used. A degenerative disc was created by drilling a hole through the cranial endplate of a lumbar vertebra into the disc. Two months later the animals were sacrificed and the degenerative functional spinal units (segments) were harvested. The segments were divided into three groups and exposed to axial compression, flexion compression or extension compression to failure. The load and angle at failure were measured for each group. The segments were examined with magnetic resonance imaging and plain radiography before and after the loading and finally examined macroscopically and histologically.

FINDINGS

The degenerated segments required considerably more compressive load to failure than non-degenerated segments. Creating a flexion injury required significantly more load than an extension injury. Fractures and/or separations of the endplates from the vertebral bodies were seen at the margins of the endplates and in the growth zone. Only severe separations and fractures could be seen on plain radiography and magnetic resonance imaging.

INTERPRETATION

The weakest part of the adolescent porcine lumbar spine with experimentally-induced degeneration, when loaded in axial compression, flexion compression or extension compression, was the growth zone, and, to a lesser extent, the endplate. Degenerated discs seem to withstand higher mechanical loads than non-degenerated discs, probably due to altered stress distribution.

A fibronectin fragment alters the metabolism by rabbit intervertebral disc cells in vitro

STUDY DESIGN

A biochemical and gene expression study was conducted to determine the effects of the 30-kDa N-terminal fibronectin fragment (Fn-f) on the glycosaminoglycan content of nucleus pulposus (NP) explant cultures, and on the gene expression profile of NP cells in alginate culture.

OBJECTIVE

To determine the effects of Fn-f on NP cells in alginate culture and disc explant cultures.

SUMMARY OF BACKGROUND DATA

The macroscopic and histologic features of disc degeneration have been well described, but the molecular biology of disc degeneration remains poorly understood. Although fibronectin and fibronectin fragments are known to accumulate in degenerative discs, the role of fibronectin fragments on the degenerative process has not been elucidated. This study sought to define the effects of Fn-f on the expression of key matrix and degradative genes and on disc matrix proteins.

METHODS

New Zealand white rabbits discs were harvested. NP cells were either isolated and grown in alginate culture or cultured as explanted tissue. The cultured cells were exposed to 10 nmol/L, 100 nmol/L, and 1 micromol/L concentrations of 30-kDa N-terminal Fn-f or a control substance and then analyzed histologically, biochemically, and with gene expression studies.

RESULTS

Alginate-cultured NP cells maintained a histologic appearance and phenotypic expression pattern similar to disc cells in vivo. Exposure of these cells to Fn-f led to the up-regulation of the MMP-9, MMP-13, and Fas genes and the down-regulation of the Type II collagen and aggrecan genes. In explant culture, Fn-f exposure led to a 60% reduction in glycosaminoglycan content compared with controls.

CONCLUSION

Treatment of NP cells in vitro with Fn-f led to changes in matrix proteins and gene expression similar to those seen during disc degeneration in vivo. This supports a possible detrimental role of the N-terminal fibronectin fragment in degenerative disc disease.

Fracture patterns of the adolescent porcine spine: an experimental loading study in bending-compression

STUDY DESIGN

To expose functional spinal units from adolescent porcine to mechanical flexion-compression and extension-compression to failure. The biomechanical, radiologic, magnetic resonance imaging, and histologic characteristics are described.

OBJECTIVES

The aim of the present study was to investigate the fracture pattern of functional spinal units from adolescent porcine lumbar spines in in vitro compression loading and bending.

SUMMARY OF BACKGROUND DATA

In several studies, it has been shown that the adolescent spine, especially the vertebral growth zones, is vulnerable to trauma. A high frequency of abnormalities affecting the spine has been found among athletes participating in sports with high demands on the back. The etiology of these abnormalities is still a controversial issue.

METHODS

Sixteen functional spinal units obtained from eight adolescent male pigs were used. Eight functional spinal units were exposed to flexion-compression and eight functional spinal units to extension-compression loading to failure. They were examined with plain radiography and magnetic resonance imaging before and after the loading. The functional spinal units were finally examined macroscopically and histologically.

RESULTS

Fractures/separations were seen in the growth zone anteriorly and more frequently, posteriorly in functional spinal units exposed to flexion-compression. In the extension-compression group, such injuries occurred only anteriorly. Only large fractures could be seen on plain radiographs and on magnetic resonance imaging. Macroscopically, a fracture/separation could be seen in 15 cases and histologically in all 16 cases. The median angle at failure for the flexion group was 17 degrees (range, 12-19) and for the extension group 17 degrees (range, 13-19 degrees). The median ultimate compression load in the flexion-compression group was 1894 N (range, 1607-3138 N) and in the extension-compression group 1801 N (range, 1158-2368 N).

CONCLUSIONS

The weakest part of the growing porcine lumbar spine, when compressed into flexion- or extension-compression, was the growth zone. The injury was more extensive in extension loading than during flexion loading. Growth zone injuries of the adolescent spine may go undetected on plain radiographs and magnetic resonance imaging.

Experimental disc degeneration due to endplate injury

The aim of this study was to create an experimental model of disc degeneration that closely mimicked human disc degeneration. In six domestic pigs, an L4 cranial endplate perforation into the nucleus pulposus was made. Three months postoperatively, compressive testing was performed on the L2-L4 motion segments, and intradiscal pressure was measured in the intervening discs. Histochemical and morphologic examinations were made on the excised degenerated and adjacent discs. A significant reduction in water content was observed in the outer anterior annulus of the degenerated disc. In the nucleus, the proteoglycan content was significantly reduced, as well as the cellularity, although not significantly. The nucleus lost its gel-like structure and was discolored, and there was delamination of annular layers. Intradiscal pressure in the nucleus was significantly lower in the degenerated disc. In conclusion, experimental degeneration of the intervertebral disc induced by endplate penetration resembled human disc degeneration, as exemplified by biochemical and structural changes.

Flexion-distraction injuries in the thoracolumbar spine: an in vitro study of the relation between flexion angle and the motion axis of fracture

A new concept, the motion axis of fracture (MAF), which is defined as the transitional point from anterior compressive to posterior splitting failure on a lateral radiograph, has provided a true understanding of the mechanisms of flexion-distraction injuries in clinical cases. This study was designed to produce in vitro injuries that have MAFs and to clarify the relation between the flexion angle and the MAF location. Adolescent porcine thoracolumbar spines were exposed to a vertical compressive load to failure at three different flexion angles and then examined radiographically. The MAF location was recorded as the distance from the anterior border to the MAF expressed as a percentage of the anteroposterior diameter of the vertebral body. All specimens showed similar injuries, with MAFs consisting of anterior compression fractures in the vertebral bodies and posterior disruptions. A significant negative correlation emerged between the flexion angle and the MAF location (r = -0.890; p < 0.0001). These results suggest that even a vertical compressive load contributes to the production of a flexion-distraction injury with an MAF in the thoracolumbar spine. They also indicate that the flexion angle of the spine at which the vertical compressive load is applied is an important factor in determining the MAF location; that is, the larger the flexion angle, the more anterior the MAF.

Back pain in the young athlete

Back pain in the pediatric athlete is rare compared to the adult population. However, the diagnosis should be accurate as most have specific etiologies and treatment. Nearly 50% of the time, the cause of the pain is an injury to the pars interarticularis. A thorough history and careful physical examination should guide the physician to a working differential diagnosis. Based on this, appropriate laboratory and imaging work-up is pursued to arrive at a timely diagnosis and subsequent treatment regimen.

Radiologic abnormalities and low back pain in elite skiers

Lumbar radiographs of 120 adolescent elite skiers were evaluated for radiologic abnormalities by two independent observers. All athletes had no symptoms before the study. Radiographs were taken before enrollment of the students in elite level training. To determine the clinical significance of these abnormalities, all athletes were observed prospectively during the subsequent 2-year period for development of low back pain under high performance training. Anterior end plate lesions, Schmorl's nodes, posterior end plate lesions, spondylolysis, scoliosis, and spina bifida occulta were found. The depth of anterior end plate lesions showed a two-peak distribution, with peaks at 11% and 22% and a valley at 18% vertebral body height. The overall low back pain incidence was 12.5%. Students with severe anterior lesions (greater than 18% vertebral body height, n = 25) had significantly more low back pain (incidence, 32%) than did students without severe anterior lesions (incidence, 7.4%). Accordingly, students with severe anterior lesions had a significantly higher risk of having low back pain develop. Moderate end plate lesions and other abnormalities were not related to an increased incidence of low back pain. Adolescent students of elite sports with severe lumbar anterior end plate lesions have an increased risk of having low back pain develop under high performance training.

Back injuries in the young athlete

The diagnosis of back pain in the young athlete should be specific and not attributed to nonspecific, mechanical causes. Risk factor identification and intervention are required. Treatment is then initiated in a specific pattern, addressing flexibility and muscular imbalances. Bracing is often used to allow healing of growth tissue. The lumbosacral orthosis may be molded in a lordotic posture to unload the disc or antilordotic posture to relieve the posterior column; however, customizing the lordosis to the individual biomechanics may be required. Spinal stabilization is initiated with therapy for strengthening isolated weaknesses and progressing to coactivation and proprioceptive techniques, such as the balance ball. Returning to competition is preceded with sport-specific training.