Recent advances in lumbar spinal mechanics and their clinical significance

The acute effects of kinesio-taping on movement kinematics and muscle co-activation in rowing athletes

BACKGROUND

Rowing-related low back disorders may occur from inconsistent technique, high trunk flexion and training volumes, overactivation of paraspinal muscles, and fatigue.

OBJECTIVE

To examine if kinesiology tape (KT) affixed to the trunk dorsum affects muscular co-activation and neuromuscular control to limit dangerous rowing movements and associated injuries.

METHODS

Participants (n= 18) completed two 2000 m rowing trials under BASELINE and KT conditions. KT was applied to the skin superficial to the paraspinals bilaterally with 60% pre-strain. Participants were instructed to minimize any sensation of tension. Whole body kinematics were obtained using inertial measurement units (IMUs), and surface electromyograms (EMGs) were recorded from trunk and lower extremity. Changes in joint range-of-motion (ROM) and co-activation indices (CAIs) were analyzed for shoulder, lumbar, hip, and knee.

RESULTS

Responding participants (n= 5) were identified by reduced maximum lumbar flexion during the KT condition. As expected, significant differences occurred in maximum and minimum lumbar flexion/extension between responders and non-responders to KT. Additionally, there was significant reduction in mean trunk muscle co-activation in both those who did and did not respond to KT through reductions in maximum lumbar flexion.

CONCLUSION

KT can be an effective at reducing mean trunk co-activation during a rowing trial in the flexed catch position. Variable responses suggest that further work is necessary to optimize the efficacy of sensory cues derived from KT during rowing movements.

Identification of preoperative radiological risk factors for reoperation following percutaneous endoscopic lumbar decompression to treat degenerative lumbar spinal stenosis

Background

This study aimed to identify radiological risk factors associated with reoperation after percutaneous transforaminal endoscopic decompression (PTED) for degenerative lumbar spinal stenosis (DLSS).

Methods

The preoperative clinical data of 527 consecutive patients with DLSS who underwent PTED were retrospectively reviewed. Overall, 44 patients who underwent reoperation were matched for age, sex, body mass index, and surgical segment to 132 control patients with excellent or good clinical outcomes. Radiological characteristics were compared between the groups using independent sample t-tests and Pearson's chi-square tests. A predictive model was established based on multivariate logistic regression analysis.

Results

The analyses revealed significant differences in the presence of lumbosacral transitional vertebra (LSTV, 43.2% vs. 17.4%, p = 0.001), the number of levels with senior-grade disc degeneration (2.57 vs. 1.96, p = 0.018) and facet degeneration (1.91 vs. 1.25 p = 0.002), and the skeletal muscle index (SMI, 849.7 mm²/m² vs. 1008.7 mm²/m², p < 0.001) between patients in the reoperation and control groups. The results of the logistic analysis demonstrated that LSTV (odds ratio [OR] = 2.734, 95% confidence interval [CI]:1.222-6.117, p < 0.014), number of levels with senior-grade facet degeneration (OR = 1.622, 95% CI:1.137-2.315, p = 0.008), and SMI (OR = 0.997, 95% CI:0.995-0.999, p = 0.001) were associated with reoperation after PTED. The application of the nomogram based on these three factors showed good discrimination (area under the receiver operating characteristic curve 0.754, 95% CI 0.670-0.837) and good calibration.

Conclusion

LSTV, more levels with senior-grade facet degeneration, and severe paraspinal muscle atrophy are independent risk factors for reoperation after PTED. These factors can thus be used to predict reoperation risk and to help tailor treatment plans for patients with DLSS.

Risk factor analysis of disc and facet joint degeneration after intersegmental pedicle screw fixation for lumbar spondylolysis

Background

Patients who do not respond to conservative treatment of the isthmus are often treated with surgery. We used direct repair plus intersegment pedicle screw fixation for the treatment of lumbar spondylolysis. The aim of this observational study was to assess the effects of this technique and evaluate various risk factors potentially predicting the probability of disc and facet joint degeneration after instrumentation.

Methods

The study included 54 male L5 spondylolysis patients who underwent pars repair and intersegment fixation using pedicle screws. Bony union was evaluated using reconstruction images of computed tomography. Radiographic changes, including disc height, vertebral slip, facet joint and disc degeneration in the grade of adjacent and fixed segments, were determined from before to final follow-up. Logistic regression analysis was performed to identify factors associated with the incidence of disc and facet joint degeneration.

Results

Bony union was achieved in all cases. Logistic regression analysis revealed that instrumentation durations of greater than 15.5 months and 21.0 months were significant risk factors for the incidence of L4/5 and L5S1 facet degeneration, respectively.

Conclusions

Intersegmental pedicle screw fixation provides good surgical outcomes and good isthmic bony union rates in patients with lumbar spondylolysis. The duration of fixation was confirmed as a risk factor for facet joint degeneration. Once bony union is achieved, instrument removal should be recommended.

Computed tomography osteoabsorptiometry for imaging of degenerative disc disease

Background

Lower back pain is a common condition with significant morbidity and economic impact. The pathophysiology is poorly understood but is in part attributable to degenerative disc disease (DDD). The healthy intervertebral disc ensures spine functionality by transferring the perceived load to the caudally adjacent vertebrae. The exposure to recurring mechanical load is mirrored in the mineralization pattern of the subchondral bone plate (SBP), where increased bone density is a sign of repetitive localized high stress. Computed tomography -osteoabsorptiometry (CT-OAM) is a technique based on conventional CT scans that displays the mineral density distribution in the SBP as a surface-color map. The objective of this study was to measure and analyze the SBP mineral density patterns of healthy lumbar intervertebral disc (IVDs) and those suffering DDD using CT-OAM densitograms. These findings should provide in vitro insight into the long-term morphological properties of the IVD and how these differ in the state of disc degeneration.

Methods

The CT-data sets of spines from 17 healthy individuals and 18 patients displaying DDD in the lumbar spine were acquired. Individual vertebrae of both cohorts were 3D reconstructed, processed using image analysis software, and compared to one another. Maximum intensity projection of the subchondral mineralization provided surface densitograms of the SBP. The relative calcium concentration, the local maxima of mineralization, and a mean surface projection of level-defined SBPs were calculated from the densitogram and statistically compared.

Results

The inferior SBP, adjacent to degenerating disc, display an 18-41 % higher relative calcium concentration than their healthy counterparts. In the opposing superior SBPs the relative calcium content is significantly increased. Whereas it is reasonably consistent for L1-L3 (L1: 132 %, L2: 127 %, L3: 120 %), the increase grows in caudal direction (L4: 131 %, L5: 148 %, S1: 152 %). Furthermore, a change in the areal distribution of excessive mineralization can be differentiated between healthy and diseased motion segments.

Conclusions

The acquired data provide in vitro proof of the mechanical and anatomical properties of the SBP in relation to the state of disc degeneration. In conjunction with the diagnostic use of CT-osteoabsorptiometry, our data provide a basis for a non-invasive and sensitive technique that correlates with disc functionality. This could be promising in various cases, from early identification of early stages of DDD, tracking disease progression, and assessing the repercussions of surgical procedures or experimental therapies.

Early Detection of Cartilage Degradation Among Heavy Manual Workers Using Serum Level of Collagen Type II Metabolite

BACKGROUND

Work-related musculoskeletal disorders are common health problems in brick manufacturers, where mechanical load leads to degenerative joint diseases. Collagen type II metabolite (C2C) is a small peptide excreted in urine, and its serum concentration can directly reflect articular cartilage decomposition.

OBJECTIVE

Early detection of musculoskeletal disorders among brick workers, using serum C2C as a biomarker of cartilage damage.

METHODS

This study involved 88 male brick workers in Arab Abu Saed matched to 88 age- and sex-matched controls. Full history taking, pain assessment using the Standardized Nordic Questionnaire, and complete clinical examination were done for both groups. Serum C2C was measured using a competitive immunoassay method.

RESULTS

Brick workers involved in the study were of a mean age 30.66 ± 7.90 years and mean work duration 14.80 ± 7.89 years, matched to 88 controls. The majority of the participants (77.3%) were of normal body mass index. An increase in pain/discomfort was found among the exposed group. Serum C2C had an increased mean among the exposed group compared with the control. Pearson correlation between serum C2C level, body mass index, age, and years of employment showed no correlation.

CONCLUSIONS

Musculoskeletal disorders are prevalent among brick workers who adopt specific awkward postures, unhealthy working conditions, and nonexistent safety procedures, for prolonged periods. Detection of serum C2C level can be used as a predictive biomarker for the early detection of musculoskeletal disorders among brick workers.

Computational modeling of lumbar disc degeneration before and after spinal fusion

BACKGROUND

Advancing age and degeneration frequently lead to low back pain, which is the most prevalent musculoskeletal disorder worldwide. Degenerative changes in intervertebral discs and musculo-ligamentous incapacity to compensate sagittal imbalance are typically amongst the sources of instability, with spinal fusion techniques being the main treatment options to relieve pain. The aims of this work were to: (i) assess the link between ligament degeneration and spinal instability by determining the role of each ligament per movement, (ii) evaluate the impact of disc height reduction in degenerative changes, and (iii) unveil the most advantageous type of posterior fixation in Oblique Lumbar Interbody Fusion to prevent adjacent disc degeneration.

METHODS

Two L3-L5 finite element models were developed, being the first in healthy condition and the second having reduced L4-L5 height. Different degrees of degeneration were tested, combined with different fixation configurations for Oblique Lumbar Interbody Fusion.

FINDINGS

Facet capsular ligament and anterior longitudinal ligament were the most influential ligaments for spinal stability, particularly with increasing degeneration and disc height reduction. Pre-existent degeneration had lower influence than the fusion procedure for the risk of adjacent disc degeneration, being the highest stability and minimal degeneration achieved with bilateral fixation. Right unilateral fixation was more suited to reduce disc stress than left unilateral fixation.

INTERPRETATION

Bilateral fixation is the best option to stabilize the spinal segment, but unilateral right fixation may suffice. This has direct implications for clinical practice, and the extension to a population-based study will allow for more efficient fusion surgeries.

Patient-Related Risk Factors for the Development of Lumbar Spine Adjacent Segment Pathology

Objectives

Individual risk factors for the development of adjacent segment pathology (ASP) need to be investigated and identified to address possible modifiable factors in advance and improve outcomes and reduce medical costs. This study aimed to review the literature regarding patient-related risk factors and sagittal alignment parameters associated with ASP development.

Methods

The authors performed an extensive review of the literature addressing the objectives mentioned earlier.

Results

Certain patient factors such as age, gender, obesity, preexisting degeneration, osteoporosis, postmenopausal state, rheumatoid arthritis, and facet tropism may contribute to adjacent segment degeneration. Genetic influences, such as polymorphisms of the vitamin D receptor and collagen IX genes, can also be a potential cause for disc degeneration with consequent deterioration of the motion segment.The influence of sagittal imbalances, particularly after lumbar fusion, is a significant parameter to be taken into account as an independent risk factor for ASP development.

Conclusions

Patient-specific risk factors, such as age, gender, obesity, preexisting degeneration, and genetic features increase the likelihood of developing ASP. On the other hand, sagittal alignment plays a significant role in the development of this condition.

Influence of an on-body lifting aid (HAL® for Care Support) on kinematics during repetitive lifting in healthy men

Work-related lower back pain (LBP) leads to socio-economic burden and demands solutions. The hybrid assistive limb (HAL) for Care Support (Cyberdyne Inc., Ibaraki, Japan) is an active on-body lifting aid to assist joint motion according to the wearer's voluntary motor drive to reduce the lumbar load. A few studies investigated HAL and stated efficacy in terms of enhanced performance and reduced fatigue, yet the question remained if the use of HAL may result in a different execution of movement, for example by influencing the kinematics of the lower extremities. The aim of this study was to determine the influence of HAL on kinematics of the lower limbs and the spinal column during repetitive freestyle symmetrical lifting. Kinematic data was recorded by an inertial measurement unit sensor system in 11 healthy men lifting and lowering a 19.5 kg barbell under three conditions (no HAL, HAL Level 3/5, HAL Level 5/5). Outcome parameters were maximum and minimum angles as well as range of motion (ROM) of thoracic spine, lumbar spine, hip- and knee joint in sagittal plane. We found a significantly decreased ROM of the lumbar spine as well as a significantly reduced maximum and minimum thorax extension when starting lifting and in upright position after lifting, respectively, while using HAL. Influence of HAL on the kinematics of the lower limbs was not significant. Differences between both evaluated HAL conditions were not significant. This study proved limited lumbar spine ROM and reduced thorax extension without alterations of lower limbs kinematics when using HAL. This might potentially decrease the risk of work-related LBP.

Demographic, Surgical, and Radiographic Risk Factors for Symptomatic Adjacent Segment Disease After Lumbar Fusion: A Systematic Review and Meta-Analysis

BACKGROUND

Although multiple studies have investigated risk factors for symptomatic adjacent segment disease (ASD) after lumbar fusion, their findings were diverse and inconsistent. This review aimed to summarize risk factors for ASD in order to guide the management of ASD and future research.

METHODS

Six electronic databases were systematically searched from inception to December 2019. Two reviewers independently screened titles, abstracts, and full-text articles to identify studies investigating risk factors for ASD after lumbar fusion in humans. The methodological quality of the included studies and the strength of evidence regarding risk factors were evaluated.

RESULTS

Sixteen studies involving 3,553 patients were included. Meta-analyses revealed that high body mass index, facet joint violation, anterior shift of the preoperative and postoperative lumbosacral sagittal plumb line, decreased preoperative and postoperative lumbar lordosis, preoperative adjacent disc degeneration, decreased preoperative adjacent disc height, increased postoperative lumbopelvic mismatch, postoperative pelvic incidence, and postoperative pelvic tilt were significantly related to ASD.

CONCLUSIONS

This meta-analysis addressed the limitations of prior reviews and summarized evidence with regard to risk factors for ASD following lumbar fusion. Future prospective studies should investigate whether modification of these risk factors can reduce the ASD development.

LEVEL OF EVIDENCE

Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Development of a finite element biomechanical whole spine model for analyzing lumbar spine loads under caudocephalad acceleration

Background:Spine injury risk due to military conflict is an ongoing concern among defense organizations throughout the world. A better understanding of spine biomechanics could assist in developing protection devices to reduce injuries caused by caudocephalad acceleration (+Gz) in under-body blasts (UBB). Although some finite element (FE) human models have demonstrated reasonable lumbar spine biofidelity, they were either partial spine models or not validated for UBB-type loading modes at the lumbar functional spinal unit (FSU) level, thus limiting their ability to analyze UBB-associated occupant kinematics.Methods:An FE functional representation of the human spine with simplified geometry was developed to study the lumbar spine responses under +Gz loading. Fifty-seven load curves obtained from post mortem human subject experiments were used to optimize the model.Results:The model was cumulatively validated for compression, flexion, extension, and anterior-, posterior-, and lateral-shears of the lumbar spine and flexion and extension of the cervical spine. The thoracic spine was optimized for flexion and compression. The cumulative CORrelation and Analysis (CORA) rating for the lumbar spine was 0.766 and the cervical spine was 0.818; both surpassed the 0.7 objective goal. The model's element size was confirmed as converged.Conclusions:An FE functional representation of the human spine was developed for +Gz lumbar load analysis. The lumbar and cervical spines were demonstrated to be quantitatively biofidelic to the FSU level for multi-directional loading and bending typically experienced in +Gz loading, filling the capability gap in current models.

Simulation of L-4 lumbar spine model of motorist exposed to vibration from speed hump

BACKGROUND

The motorcycle is often used in recurring travel between locations, dense traffic, poor conditioned roads and thus the repetitive loading on the musculoskeletal system of the rider leads to risk factors associated with musculoskeletal disorders. This study was aimed to examine the biomechanical response of the L-4 lumbar spine while riding the motorcycle on the speed hump at 20 km/h.

METHODS

Three-dimensional (3D) model of the L-4 lumbar spine was reconstructed based on the CT scan data obtained from the subjects. Material properties of the L-4 lumbar spine were assumed to be isotropic and homogenous. Mesh convergence and sensitivity analyses were performed and validated before simulation. Static and dynamic analyses were accomplished using quasi-static and steady-state dynamic analyses.

RESULTS

Static analysis results show that the highest stress concentrations were found around the pedicle and spinal canal. It is an expected commonplace for injuries because of loading. The dynamic simulation results showed the major resonance of the L-4 lumbar spine model is about 8-40 Hz. The stress, displacement, velocity, and acceleration value declines beyond 40 Hz as the frequency increases.

CONCLUSIONS

The simulation specifies the symmetric and unsymmetrical distributions of vibration magnitude regions of the lumbar spine. This study provides the modelling of the lumbar spine (L-4) and validated the effect of overloading failure as well as identified the biomechanical behaviour.

Biomechanics of Back Pain

This paper offers a mechanistic account of back pain which attempts to incorporate all of the most important recent advances in spinal research. Anatomical and pain-provocation studies show that severe and chronic back pain most often originates in the lumbar intervertebral discs, the apophyseal joints, and the sacroiliac joints. Psychosocial factors influence many aspects of back pain behaviour but they are not important determinants of who will experience back pain in the first place. Back pain is closely (but not invariably) associated with structural pathology such as intervertebral disc prolapse and endplate fractures, although age-related biochemical changes such as those revealed by a ‘dark disc’ on MRI have little clinical relevance. All features of structural pathology (including disc prolapse) can be re-created in cadaveric specimens by severe or repetitive mechanical loading, with a combination of bending and compression being particularly harmful to the spine. Structural disruption alters the mechanical environment of disc cells in a manner that leads to cell-mediated degenerative changes, and animal experiments confirm that surgical disruption of a disc is followed by widespread disc degeneration. Some people are more vulnerable to spinal degeneration than others, largely because of their genetic inheritance. Age-related biochemical changes and loading history can also affect tissue vulnerability. Finally the concept of ‘functional pathology’ is introduced, according to which, back pain can arise because postural habits generate painful stress concentrations within innervated tissues, even though the stresses are not high enough to cause physical disruption.

Changes of lumbar posture and tissue loading during static trunk bending

Static trunk bending is an occupational risk factor for lower back pain (LBP). When assessing relative short duration trunk bending tasks, existing studies mostly assumed unchanged spine biomechanical responses during task performance. The purpose of the current study was to assess the biomechanical changes of lumbar spine during the performance of relatively short duration, sustained trunk bending tasks. Fifteen participants performed 40-s static trunk bending tasks in two different trunk angles (30° or 60°) with two different hand load levels (0 or 6.8 kg). Results of the current study revealed significantly increased lumbar flexion and lumbar passive moment during the 40 s of trunk bending. Significantly reduced lumbar and abdominal muscle activities were also observed in most conditions. These findings suggest that, during the performance of short duration, static trunk bending tasks, a shift of loading from lumbar active tissues to passive tissues occurs naturally. This mechanism is beneficial in reducing the accumulation of lumbar muscle fatigue; however, lumbar passive tissue creep could be introduced due to prolonged or repetitive exposure.

Paraspinal muscle, facet joint, and disc problems: risk factors for adjacent segment degeneration after lumbar fusion

BACKGROUND CONTEXT

Adjacent segment degeneration (ASD) is one of the major complications after lumbar fusion. Several studies have evaluated the risk factors of ASD. Although the paraspinal muscles play an important role in spine stability, no study has assessed the relationship between paraspinal muscle atrophy and the incidence of ASD after lumbar fusion.

PURPOSE

In the present study, we aimed to verify the known risk factors of ASD, such as body mass index (BMI), preoperative adjacent facet joint degeneration, and disc degeneration, and to assess the relationship between paraspinal muscle atrophy and ASD.

STUDY DESIGN

This is a retrospective 1:1 pair analysis matched by age, sex, fusion level, and follow-up period.

PATIENT SAMPLE

To calculate the appropriate sample size for the study, we performed a pre-study analysis of the paraspinal muscle cross-sectional area (CSA), and estimated that at least 35 cases would be needed for each group. Among the 510 patients who underwent posterior lumbar fusion for degenerative lumbar disease between January 2009 and October 2009, a total of 50 patients with ASD after surgery were selected. Another group of 50 matched patients with degenerative lumbar disease without ASD after spinal fusion were selected as the control group. Each patient in the ASD group was matched with a control patient according to age, sex, fusion level, and follow-up period.

OUTCOME MEASURES

Radiographic measurements and demographic data were reviewed.

METHODS

The risk factors considered were higher BMI, preoperative adjacent segment disc and facet degeneration, and preoperative paraspinal muscle atrophy and fatty degeneration. The radiographic data were compared between the ASD and control groups to determine the predictive factors of ASD after posterior lumbar fusion by using logistic regression analysis. The study was not externally funded. The authors have no conflict of interest to declare.

RESULTS

Multivariate logistic regression analysis indicated that higher BMI (odds ratio [OR]: 1.353, p=.008), preoperative facet degeneration on computed tomography examination (OR: 3.075, p=.011), disc degeneration on magnetic resonance imaging (MRI) (OR: 2.783, p=.003), fatty degeneration (OR: 1.080, p=.044), and a smaller relative CSA of the paraspinal muscle preoperatively (OR: 0.083, p=.003) were significant factors for predicting the development of ASD.

CONCLUSIONS

The occurrence of radiological ASD is most likely multifactorial, and is associated with a higher BMI, preexisting facet and disc degeneration on preoperative examination, and a smaller preoperative relative CSA of the paraspinal muscle on MRI.

Impact of body mass index on adjacent segment disease after lumbar fusion for degenerative spine disease

BACKGROUND

Adjacent segment disease is an important complication after fusion of degenerative lumbar spines. However, the role of body mass index (BMI) in adjacent segment disease has been addressed less.

OBJECTIVE

To examine the relationship between BMI and adjacent segment disease after lumbar fusion for degenerative spine diseases.

METHODS

For this retrospective study, we enrolled 190 patients undergoing lumbar fusion surgery for degeneration. BMI at admission was documented. Adjacent segment disease was defined by integration of the clinical presentations and radiographic criteria based on the morphology of the dural sac on magnetic resonance images.

RESULTS

Adjacent segment disease was identified in 13 of the 190 patients, accounting for 6.8%. The interval between surgery and diagnosis as adjacent segment disease ranged from 21 to 66 months. Five of the 13 patients required subsequent surgical intervention for clinically relevant adjacent segment disease. In the logistic regression model, BMI was a risk factor for adjacent segment disease after lumbar fusion for degenerative spine diseases (odds ratio, 1.68; 95% confidence interval, 1.27-2.21; P < .001). Any increase of 1 mean value in BMI would increase the adjacent segment disease rate by 67.6%. The patients were subdivided into 2 groups based on BMI, and up to 11.9% of patients with BMI ≥ 25 kg/m were diagnosed as having adjacent segment disease at the last follow-up.

CONCLUSION

BMI is a risk factor for adjacent segment disease in patients undergoing lumbar fusion for degenerative spine diseases. Because BMI is clinically objective and modifiable, controlling body weight before or after surgery may provide opportunities to reduce the rate of adjacent segment disease and to improve the outcome of fusion surgery.

Does mechanical stimulation really protect the architecture of trabecular bone? A simulation study

Although it is beyond doubt that mechanical stimulation is crucial to maintain bone mass, its role in preserving bone architecture is much less clear. Commonly, it is assumed that mechanics helps to conserve the trabecular network since an "accidental" thinning of a trabecula due to a resorption event would result in a local increase of load, thereby activating bone deposition there. However, considering that the thin trabecula is part of a network, it is not evident that load concentration happens locally on the weakened trabecula. The aim of this work was to clarify whether mechanical load has a protective role for preserving the trabecular network during remodeling. Trabecular bone is made dynamic by a remodeling algorithm, which results in a thickening/thinning of trabeculae with high/low strain energy density. Our simulations show that larger deviations from a regular cubic lattice result in a greater loss of trabeculae. Around lost trabeculae, the remaining trabeculae are on average thinner. More generally, thin trabeculae are more likely to have thin trabeculae in their neighborhood. The plausible consideration that a thin trabecula concentrates a higher amount of strain energy within itself is therefore only true when considering a single isolated trabecula. Mechano-regulated remodeling within a network-like architecture leads to local concentrations of thin trabeculae.

Axial rotation mechanics in a cadaveric lumbar spine model: a biomechanical analysis

BACKGROUND CONTEXT

Postoperative patient motions are difficult to directly control. Very slow quasistatic motions are intuitively believed to be safer for patients, compared with fast dynamic motions, because the torque on the spine is reduced. Therefore, the outcomes of varying axial rotation (AR) angular loading rate during in vitro testing could expand the understanding of the dynamic behavior and spine response.

PURPOSE

To observe the effects of the loading rate in AR mechanics of lumbar cadaveric spines via in vitro biomechanical testing.

STUDY DESIGN

An in vitro biomechanical study in lumbar cadaveric spines.

METHODS

Fifteen lumbar cadaveric segments (L1-S1) were tested with varying loading frequencies of AR. Five different frequencies were normalized with the base line frequency (0.125 Hz n=15) in this analysis: 0.05 Hz (n=6), 0.166 Hz (n=6), 0.2 Hz (n=10), 0.25 Hz (n=10), and 0.4 Hz (n=8).

RESULTS

The lowest frequency (0.05 Hz) revealed significant differences (p<.05) for all parameters (torque, passive angular velocity, axial velocity [AV], axial reaction force [RF], and energy loss [EL]) with respect to all other frequencies. Significant differences (p<.05) were observed in the following: torque (0.4 Hz with respect to 0.2 Hz and 0.25 Hz), passive sagittal angular velocity (SAV) (0.4 Hz with respect to all other frequencies; 0.166 Hz with respect to 0.25 Hz), axial linear velocity (0.4 Hz with respect to all other frequencies), and RF (0.4 Hz with respect to 0.2 Hz and 0.25 Hz). Strong correlations (R2>0.75, p<.05) were observed between RF with intradiscal pressure (IDP) and AR angular displacement with IDP. Intradiscal pressure (p<.05) was significantly larger in 0.2 Hz in comparison with 0.125 Hz.

CONCLUSIONS

Evidences suggest that measurements at very small frequencies (0.05 Hz) of torque, SAV, AV, RF, and EL are significantly reduced when compared with higher frequencies (0.166 Hz, 0.2 Hz, 0.25 Hz, and 0.4 Hz). Higher frequencies increase torque, RF, passive SAV, and AV. Higher frequencies induce a greater IDP in comparison with lower frequencies.

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.

Human carrying simulation with symmetric and asymmetric loads using optimization

Human carrying is simulated in this work by using a skeletal digital human model with 55 degrees of freedom. An optimization-based approach is used to predict the carrying motion with symmetric and asymmetric loads. In this process, the model predicts joint dynamics using optimization schemes and task-based physical constraints. The results indicate that the model can predict different carrying strategies during symmetric and asymmetric load-carrying tasks. The model can also indicate the risk factors for extreme loading situations. With such robust prediction capability, the model could be used for biomedical and ergonomic studies.

Lumbopelvic motion during seated hip flexion in subjects with low-back pain accompanying limited hip flexion

PURPOSE

Limited hip flexion may lead to a poor lumbopelvic motion during seated active hip flexion in people with low-back pain (LBP). The purpose of this study was to compare lumbopelvic motion during seated hip flexion between subjects with and without LBP accompanying limited hip flexion.

METHODS

Fifteen patients with LBP accompanying limited hip flexion and 16 healthy subjects were recruited. The subjects performed seated hip flexion with the dominant leg three times. A three-dimensional motion-analysis system was used to measure lumbopelvic motion during seated hip flexion.

RESULTS

During seated active hip flexion, the angle of hip flexion was significantly lower in patients with LBP accompanying limited hip flexion (17.4 ± 4.4 in the LBP group, 20.8 ± 2.6 in the healthy group; t = 2.63, p = 0.014). The angle of the lumbar flexion (4.8 ± 2.2 in the LBP group, 2.6 ± 2.0 in the healthy group; t = -2.96, p = 0.006) and posterior pelvic tilting (5.0 ± 2.6 in the LBP group, 2.9 ± 2.0 in the healthy group; t = 2.48 p = 0.019), however, were significantly greater in patients with this condition.

CONCLUSIONS

The results of this study suggest that limited hip flexion in LBP can contribute to excessive lumbar flexion and posterior pelvic tilting during hip flexion in the sitting position. Further studies are required to confirm whether improving the hip flexion range of motion can reduce excessive lumbar flexion in patients with LBP accompanying limited hip flexion.

Load-relaxation properties of the human trunk in response to prolonged flexion: measuring and modeling the effect of flexion angle

Experimental studies suggest that prolonged trunk flexion reduces passive support of the spine. To understand alterations of the synergy between active and passive tissues following such loadings, several studies have assessed the time-dependent behavior of passive tissues including those within spinal motion segments and muscles. Yet, there remain limitations regarding load-relaxation of the lumbar spine in response to flexion exposures and the influence of different flexion angles. Ten healthy participants were exposed for 16 min to each of five magnitudes of lumbar flexion specified relative to individual flexion-relaxation angles (i.e., 30, 40, 60, 80, and 100%), during which lumbar flexion angle and trunk moment were recorded. Outcome measures were initial trunk moment, moment drop, parameters of four viscoelastic models (i.e., Standard Linear Solid model, the Prony Series, Schapery's Theory, and the Modified Superposition Method), and changes in neutral zone and viscoelastic state following exposure. There were significant effects of flexion angle on initial moment, moment drop, changes in normalized neutral zone, and some parameters of the Standard Linear Solid model. Initial moment, moment drop, and changes in normalized neutral zone increased exponentially with flexion angle. Kelvin-solid models produced better predictions of temporal behaviors. Observed responses to trunk flexion suggest nonlinearity in viscoelastic properties, and which likely reflected viscoelastic behaviors of spinal (lumbar) motion segments. Flexion-induced changes in viscous properties and neutral zone imply an increase in internal loads and perhaps increased risk of low back disorders. Kelvin-solid models, especially the Prony Series model appeared to be more effective at modeling load-relaxation of the trunk.

Rowing injuries

Context:

Rowing is one of the original modern Olympic sports and was one of the most popular spectator sports in the United States. Its popularity has been increasing since the enactment of Title IX. The injury patterns in this sport are unique because of the stress applied during the rowing stroke.

Evidence Acquisition:

This review summarizes the existing literature describing the biomechanics of the rowing stroke and rowing-related injury patterns. Data were obtained from previously published peer-reviewed literature through a search of the entire PubMed database (up to December, 2011) as well as from textbook chapters and rowing coaching manuals.

Results:

Rowing injuries are primarily overuse related. The knee, lumbar spine, and ribs are most commonly affected. The injury incidence is directly related to the volume of training and technique.

Conclusion:

Familiarity of the injury patterns and the biomechanical forces affecting the rowing athlete will aid in prompt diagnosis and appropriate management.

Lumbar bone mass predicts low back pain in males

STUDY DESIGN

Longitudinal study of lumbar bone mass as predictor of low back pain (LBP).

OBJECTIVE

To investigate whether low bone mineral content (BMC) and bone mineral density (BMD) values at the age of 36 years are associated with the prevalence of LBP at the age of 42 years among the study population of the Amsterdam Growth and Health Longitudinal Study.

SUMMARY OF BACKGROUND DATA

Results of epidemiological, clinical, and in vitro studies indicate that spinal injuries, caused by mechanical loading, might be a cause of LBP. BMC and BMD are determinants of spinal strength. We therefore hypothesized that BMC and BMD are associated with LBP.

METHODS

At the age of 36 years, the lumbar BMC and BMD were determined by dual-energy x-ray absorptiometry in 140 men and 152 women. At the age of 42 years, the participants were asked whether they had experienced LBP in the previous 12 months. Logistic regression analyses were performed to determine odds ratios (ORs)-adjusted for stature, body weight, physical activity, and smoking-for the relationship of BMC and BMD with LBP.

RESULTS

BMC and BMD at the age of 36 years were significantly associated with the reported 12-month prevalence of LBP at the age of 42 years. This association, however, was observed only for men and not for women. Men within the quartile with the lowest BMC or BMD values had higher odds for LBP with ORs of 4.78 (95% confidence interval, 1.52-15.00) and 3.48 (95% confidence interval, 1.23-9.85), respectively.

CONCLUSION

For a male population that is not characterized by osteoporosis or old age, lower lumbar BMC and BMD values at the age of 36 years are associated with an increased risk of reporting to have had LBP in the previous 12 months at the age of 42 years.

The effects of upper limb loading on spinal shrinkage during treadmill walking

INTRODUCTION

Everyday activities such as walking may elicit spinal shrinkage in an order of magnitude that has been related to lower back pain. The present study aims to compare the effects of unloaded treadmill walking with walking carrying loads representing everyday shopping tasks.

MATERIALS AND METHODS

Walking tasks were performed on seven healthy males and motion analysis was used to track four reflective markers at 100 Hz, dividing the spine into three segments. Static data was collected in 5-min intervals over a 30-min period.

RESULTS

Total spinal length and lumbar segment decreased with respect to time (p < 0.001). Load affected the percentage length change at each spinal segment (p < 0.005), with the lumbar segment showing greatest height loss at the highest load. The upper and lower thoracic segments showed greater anterior lean with the heavier loads (p = 0.000) and the lumbar segment showed the opposite trend (p = 0.000).

CONCLUSION

Results suggest that the body adopts less anterior lean with an immediate load-bearing demand, to decrease the necessary extension moment generated by the spinal extensors for spinal stability. Further postural alteration in the same direction is observed with prolonged loading. In combination with lumbar spinal shrinkage, such postural changes are likely to increase the loading on the facet joints and subsequently unload the discs which may be beneficial for those with low back pain.

Comparing lower lumbar kinematics in cyclists with low back pain (flexion pattern) versus asymptomatic controls--field study using a wireless posture monitoring system

The aim of this study was to examine lower lumbar kinematics in cyclists with and without non-specific chronic low back pain (NS-CLBP) during a cross-sectional cycling field study. Although LBP is a common problem among cyclists, studies investigating the causes of LBP during cycling are scarce and are mainly focussed on geometric bike-related variables. Until now no cycling field studies have investigated the relationship between maladaptive lumbar kinematics and LBP during cycling. Eight cyclists with NS-CLBP classified as having a 'Flexion Pattern' (FP) disorder and nine age- and gender-matched asymptomatic cyclists were tested. Subjects performed a 2 h outdoor cycling task on their personal race bike. Lower lumbar kinematics was measured with the BodyGuard™ monitoring system. Pain intensity during and after cycling was measured using a numerical pain rating scale. The NS-CLBP (FP) subjects were significantly more flexed at the lower lumbar spine during cycling compared to healthy controls (p = 0.018), and reported a significant increase in pain over the 2 h of cycling (p < 0.001). One-way repeated measures ANOVA revealed a significant main effect for group (p = 0.035, F = 5.546) which remained just significant when adding saddle angle as a covariate (p = 0.05, F = 4.747). The difference in posture between groups did not change over time. These findings suggest that a subgroup of cyclists with NS-CLBP (FP) demonstrate an underlying maladaptive motor control pattern resulting in greater lower lumbar flexion during cycling which is related to a significant increase in pain.

Predicting the lumbosacral joint centre location from palpable anatomical landmarks

The kinematics of the lumbar spine have previously been described by considering the bearing of the pelvis and lower back. However earlier studies have not described an intersegmental angle measured about a single point; which is necessary for investigation into movement, posture and balance, and lower back pain and injury. This study used computed tomography (CT) scans of 16 pelves to determine the location of palpable bony landmarks, and the junction of the fifth lumbar and first sacral vertebrae within a pelvis axis system. Data were used to derive equations which express the three-dimensional location of the lumbosacral joint centre as an offset from palpable surface landmarks. The magnitude of X, Y, Z offsets was controlled using individual pelvic geometry, and robustness and repeatability of the method was assessed. Regression equations provided the location of the lumbosacral junction to within 8.2mm (+/- 3.4mm) of its true coordinate. Leave-one-out analyses calculated equation coefficients using 15 of the original pelves, with the 16th acting as a control; average errors increased by 6.7 per cent (+/- 0.1 percent). To the authors' knowledge the current method is the most accurate non-invasive means of locating the lumbosacral junction and may be useful for constructing biomechanical models.

Spine abnormalities depicted by magnetic resonance imaging in adolescent rowers

BACKGROUND

Most lesions of the spine of athletes, which often are detected incidentally, do not cause important symptoms or make the athletes discontinue their physical activities. To better understand the significance of these lesions, new imaging studies have been conducted with asymptomatic athletes in several sports, aiming to detect potentially deleterious and disabling abnormalities.

PURPOSE

To compare the magnetic resonance imaging (MRI) lumbar spine findings in a group of asymptomatic adolescent rowers and in a control group of adolescents matched according to age and sex who do not practice any regular physical activity.

STUDY DESIGN

Cohort study (prevalence); Level of evidence, 3.

METHODS

Our study evaluated 44 asymptomatic adolescent boys distributed in 2 groups of 22 rowers and 22 control subjects. All the examinations were performed using a 0.35-T open-field MRI unit and evaluated by 2 experienced radiologists blinded to the study groups. Each MRI scan was analyzed for the presence of disc degeneration/desiccation, herniated or bulging disc, pars interarticularis stress reaction, and spondylolysis. The Student t test and the Fisher exact test were used for statistical analyses.

RESULTS

Nine rowers (40.9%) had at least 1 abnormality detected by MRI in the lumbar spine, whereas only 2 participants (9.1%) in the control group had at least 1 MRI abnormality (P = .03). Seven disc changes (31.8%) and 6 pars abnormalities (27.3%) were found in the group of elite rowers. In the control group, 3 disc changes (13.6%) and no pars abnormalities were found in the MR scans. The comparison between groups showed statistically significant differences in stress reaction of the pars articularis.

CONCLUSION

Disc disease and pars interarticularis stress reaction are prevalent abnormalities of the lumbar spine of high-performance rowers.

Back pain is associated with changes in loading pattern throughout forward and backward bending

STUDY DESIGN

Experimental study to determine the kinetics of the lumbar spine (LS) and hips during forward and backward bending.

OBJECTIVE

To investigate the effects of back pain, with and without a positive straight leg raise (SLR) sign, on the loading patterns in the LS and hip during forward and backward bending.

SUMMARY OF BACKGROUND DATA

Forward and backward bending are important components of many functional activities and are part of routine clinical examination. However, there is a little information about the loading patterns during forward and backward bending in people with back pain with or without a positive SLR sign.

METHODS

Twenty asymptomatic participants, 20 back pain participants, and 20 participants with back pain and a positive SLR sign performed 3 continuous cycles of forward and backward bending. Electromagnetic sensors were attached to body segments to measure their kinematics while 2 nonconductive force plates gathered ground reaction force data. A biomechanical model was used to determine the loading pattern in LS and hips.

RESULTS

Although the loading on the LS at the end of the range decreased significantly, the loading at the early and middle ranges of forward bending actually increased significantly in people with back pain, especially in those with positive SLR sign. This suggests that resistance to movement is significantly increased in people with back pain during this movement.

CONCLUSION

This study suggested that it is not sufficient to study the spine at the end of range only, but a complete description of the loading patterns throughout the range is required. Although the maximum range of motion of the spine is reduced in people with back pain, there is a significant increase in the moment acting through the range, particularly in those with a positive SLR sign.

Características biomecânicas, ergonômicas e clínicas da postura sentada: uma revisão

A posição sentada é a mais adotada nos ambientes de trabalho, na escola e nas atividades de lazer. Porém, a manutenção prolongada dessa posição ocasiona a adoção de posturas inadequadas e sobrecarrega as estruturas do sistema musculoesquelético, o que pode acarretar dor e lesão na coluna lombar. A presente revisão teve como objetivo identificar os fatores biomecânicos, ergonômicos e clínicos envolvidos na sustentação da postura sentada. Para isso, foram consultadas as bases de dados ISI Web of Knowledge, Medline, Pubmed e EBSCO Host, sendo selecionados 72 artigos publicados entre 1965 e 2010. Foi possível identificar que na posição sentada não existe uma postura ideal a ser sustentada, mas algumas posturas são mais recomendadas do que outras, tal como a postura sentada ereta e a postura lordótica. As cadeiras influenciam o padrão da posição sentada: conforme seu design, pode permitir maior variedade de posturas. Modificações na cadeira e a utilização de exercícios para o aumento da resistência muscular e da propriocepção, bem como a reeducação postural, são intervenções úteis para reduzir o impacto causado pela posição sentada prolongada no sistema musculoesquelético.

Viscoelastic properties of the ovine posterior spinal ligaments are strain dependent

BACKGROUND

The biomechanical role of the posterior spinal ligaments for spinal stability has been stated in previous studies. The investigation of the viscoelastic properties of human lumbar spinal ligaments is essential for the understanding of physiological differences between healthy and degenerated tissues. The stress-relaxation behavior of biological tissues is commonly described with the quasi-linear viscoelastic model of Fung, which assumes that the stress-relaxation response is independent of the applied strain. The goal of this study was to investigate the stress-relaxation response of ovine posterior spinal ligaments at different elongations to verify the above-mentioned hypothesis.

METHODS

Twenty-four ovine lumbar spinal segments, consisting of only the supraspinous and interspinous ligaments and adjoining spinous processes, were elongated uniaxially to different strain levels within the physiological elastic region (5-20%). The experimental data were described with a non-linear viscoelastic model: the modified superposition method of Findley.

FINDINGS

A linear dependency of the relaxation rate to the applied strains was observed on intact segments, when both ligaments were considered, as well as on each individual ligament. This result can be applied to the human spinal ligaments, due to similarities observed between the sheep and human spinal segment under physiological loading.

INTERPRETATION

The non-linear viscoelastic modified superposition method of Findley is an appropriate model for describing the viscoelastic properties of lumbar spinal ligaments in vitro due to its ability to address variation in applied strain during the force relaxation measurements.

New suggestions for the mechanical control of bone remodeling

Bone is constantly renewed over our lifetime through the process of bone (re)modeling. This process is important for bone to allow it to adapt to its mechanical environment and to repair damage from everyday life. Adaptation is thought to occur through the mechanosensitive response controlling the bone-forming and -resorbing cells. This report shows a way to extract quantitative information about the way remodeling is controlled using computer simulations. Bone resorption and deposition are described as two separate stochastic processes, during which a discrete bone packet is removed or deposited from the bone surface. The responses of the bone-forming and -resorbing cells to local mechanical stimuli are described by phenomenological remodeling rules. Our strategy was to test different remodeling rules and to evaluate the time evolution of the trabecular architecture in comparison to what is known from micro-CT measurements of real bone. In particular, we tested the reaction of virtual bone to standard therapeutic strategies for the prevention of bone deterioration, i.e., physical activity and medications to reduce bone resorption. Insensitivity of the bone volume fraction to reductions in bone resorption was observed in the simulations only for a remodeling rule including an activation barrier for the mechanical stimulus above which bone deposition is switched on. This is in disagreement with the commonly used rules having a so-called lazy zone.

Biomechanical effects of transverse partial sacrectomy on the sacroiliac joints: an in vitro human cadaveric investigation of the borderline of sacroiliac joint instability

STUDY DESIGN

In vitro laboratory study.

OBJECTIVE

To measure the effects of transverse partial sacrectomies on the compressive and torsional stiffness of the sacroiliac joints.

SUMMARY OF BACKGROUND DATA

Surgical treatment for sacral tumor of different location and nature includes partial or complete sacrectomy. Though the biomechanical investigations about the local destructive force of residual sacrum after partial sacrectomy have been reported, biomechanical properties of the residual sacroiliac joints after different transverse partial sacrectomies remain unknown.

METHODS

Seven fresh human cadaveric L5-pelves with normal bone mineral density were used in this study. Each specimen was tested in intact condition first, followed by a series of segmental transverse partial sacrectomies: under S2 partial sacrectomy (U-S2); U-(1/2)S2; U-S1; U-(1/2)S1; and right side sacroiliac joint resection (one-side). A material testing machine was used to apply 800 N compression and 7 Nm torsion loads through the L5/S1 joint. The resected dimensional area of sacroiliac joints and structural stiffness of the residual sacroiliac joints were analyzed.

RESULTS

Average percentages of the resected area of sacroiliac joints were 8.4% in U-S2, 15.1% in U-(1/2)S2, 24.8% in U-S1, and 72.3% in U-(1/2)S1, respectively. In compression U-S2 approximately one-side preserved 98.7%, 97.1%, 94.4%, 82.9%, and 55.2% of the initial stiffness of the sacroiliac joint, respectively. No significant differences were detected among intact, U-S2, U-(1/2)S2, and U-S1 (P > 0.05). However, compressive stiffness of U-(1/2)S1 and one-side was markedly less than that of intact, U-S2, and U-(1/2)S2 (P < 0.05). In Torsion U-S2 approximately one-side preserved 90.7%, 88.5%, 81.9%, 71.9%, and 44.5% of the initial sacroiliac joint stiffness, respectively. No significant differences were demonstrated among intact, U-S2, and U-(1/2)S2 (P > 0.05); However, U-S1, U-(1/2)S1 and one-side exhibited significantly less torsional stiffness than intact and U-S2 (P < 0.05).

CONCLUSION

In surgical treatment of distal sacral tumor, transverse partial sacrectomy involving S1 could result in rotational instability, and the resection level beyond (1/2)S1 further led to compressive instability. When the sacrectomy was at or above the S1/2 level, local reconstruction should be considered.

Different ways to balance the spine: subtle changes in sagittal spinal curves affect regional muscle activity

STUDY DESIGN

Exploratory study of regional muscle activity in different postures.

OBJECTIVE

To detail the relationship between spinal curves and regional muscle activity.

SUMMARY OF BACKGROUND DATA

Sagittal balanced spinal posture (C7 above S1 in the sagittal plane) is a goal for spinal surgery and conservative ergonomics. Three combinations of thoracolumbar and lumbar spinal curves can be considered sagittal balanced postures: (i) flat-at both regions, (ii) long lordosis-lordotic at both regions, and (iii) short lordosis-thoracic kyphosis and lumbar lordosis. This study compares regional muscle activity between these 3 sagittal balanced postures in sitting, as well as a slump posture.

METHODS

Fine-wire electromyography (EMG) electrodes were inserted into the lumbar multifidus (deep and superficial), iliocostalis (lateral and medial), longissimus thoracis, and transversus abdominis in 14 healthy male volunteers. Fine-wire or surface EMG electrodes were also used to record activity of the obliquus internus, obliquus externus, and rectus abdominis muscles. Root mean square EMG amplitude in the flat, long lordosis, short lordosis, and slump sitting postures were normalized to maximal voluntary contraction, and also to the peak activity across the sitting postures. Muscle activity was compared between postures with a linear mixed model analysis.

RESULTS

Of the extensor muscles, it was most notable that activity of the deep and superficial fibers of lumbar multifidus increased incrementally in the 3 sagittal balanced postures; flat, long lordosis, and short lordosis (P < 0.05). Of the abdominal muscles, obliquus internus was more active in short lordosis than the other postures (P < 0.05). Comparing the sagittal balanced postures, the flat posture showed the least muscle activity (similar to the slump posture at most muscles examined).

CONCLUSION

Discrete combinations of muscle activity supported the 3 different sagittal balanced postures in sitting, providing new detail for surgeons, researchers, and therapists to distinguish between different sagittal balanced postures.

Using "spinal shrinkage" as a trigger for motivating students to learn about obesity and adopt a healthy lifestyle

Obesity is a global problem; however, relatively little attention is directed toward preparing and inspiring students of medicine and allied medical sciences to address this serious matter. Students are not routinely exposed to the assessment methods for obesity, its overall prevalence, causative factors, short- and long-term consequences, and its management by lifestyle modification. This physiology laboratory exercise involving students of medicine (n = 106) was developed to 1) introduce medical students to methods of obesity assessment and to differentiate between general and abdominal obesity, 2) generate an interest and sensitivity about obesity, and 3) stimulate thinking about modification of their lifestyle in relation to eating habits, weight control, and physical activity. Spinal shrinkage (the difference between the standing height of a person and his/her recumbent length) was used as an immediate observable parameter to demonstrate the effect of adiposity. Spinal shrinkage is recognized as an index of the compressive forces acting on the spine and is related to body mass index. A positive correlation (r = 0.365, P < 0.05) was observed between body mass index and spinal shrinkage. A questionnaire was used to assess student responses to this exercise. Students were motivated to engage in more physical activity (74%), adopt healthier eating (63%), and enhance their knowledge about obesity (67%). They expressed keen interest in the laboratory exercise and found the sessions enjoyable (91%). The laboratory exercise proved to be a success in motivating the students to actively learn and inquire about obesity and to adopt a healthier lifestyle.

Sitting versus standing: Does the intradiscal pressure cause disc degeneration or low back pain?

Studies of lumbar intradiscal pressure (IDP) in standing and upright sitting have mostly reported higher pressures in sitting. It was assumed clinically that flexion of the lumbar spine in sitting relative to standing, caused higher IDP, disc degeneration or rupture, and low back pain. IDP indicates axial compressive load upon a non-degenerate disc, but provides little or no indication of shear, axial rotation or bending. This review is presented in two main parts. First, in vivo IDP data in standing and upright sitting for non-degenerate discs are comprehensively reviewed. As methodology, results and interpretations varied between IDP studies, in vivo studies measuring spinal shrinkage and spinal internal-fixator loads to infer axial compressive load to the discs are also reviewed. When data are considered together, it is clear that IDP is often similar in standing and sitting. Secondly, clinical assumptions related to IDP in sitting are considered in light of basic and epidemiologic studies. Current studies indicate that IDP in sitting is unlikely to pose a threat to non-degenerate discs, and sitting is no worse than standing for disc degeneration or low back pain incidence. If sitting is a greater threat for development of low back pain than standing, the mechanism is unlikely to be raised IDP.