Validation of a Novel Device for the Knee Monitoring of Orthopaedic Patients.

Fast-track surgery is becoming increasingly popular, whereas the monitoring of postoperative rehabilitation remains a matter of considerable debate. The aim of this study was to validate a newly developed wearable system intended to monitor knee function and mobility. A sensor system with a nine-degree-of-freedom (DOF) inertial measurement unit (IMU) was developed. Thirteen healthy volunteers performed five 10-meter walking trials with simultaneous sensor and motion capture data collection. The obtained kinematic waveforms were analysed using root mean square error (RMSE) and correlation coefficient (CC) calculations. The Bland-Altman method was used for the agreement of discrete parameters consisting of peak knee angles between systems. To test the reliability, 10 other subjects with sensors walked a track of 10 metres on two consecutive days. The Pearson CC was excellent for the walking data set between both systems (r = 0.96) and very good (r = 0.95) within the sensor system. The RMSE during walking was 5.17° between systems and 6.82° within sensor measurements. No significant differences were detected between the mean values observed, except for the extension angle during the stance phase (E1). Similar results were obtained for the repeatability test. Intra-class correlation coefficients (ICCs) between systems were excellent for the flexion angle during the swing phase (F1); good for the flexion angle during the stance phase (F2) and the re-extension angle, which was calculated by subtracting the extension angle at swing phase (E2) from F2; and moderate for the extension angle during the stance phase (E1), E2 and the range of motion (ROM). ICCs within the sensor measurements were good for the ROM, F2 and re-extension, and moderate for F1, E1 and E2. The study shows that the novel sensor system can record sagittal knee kinematics during walking in healthy subjects comparable to those of a motion capture system.

Application of a novel spinal posture and motion measurement system in active and static sitting.

The quantification of work-related musculoskeletal risk factors is of great importance; however, only a few tools allow objective, unrestricted measurements of spinal posture and motion in workplaces. This study was performed to evaluate the applicability of the Epionics system in a sedentary workplace. The system is mobile and wireless and assesses lumbar lordosis, pelvic orientation and spinal motion, without restricting subjects in their movements. In total, 10 males were monitored while sitting for 2 h on static and dynamic office chairs and on an exercise ball, to evaluate the effect of dynamic sitting. The volunteers were able to perform their work unhampered. No differences among the tested furniture could be detected with respect to either the lordosis or the number of spinal movements after habituation to the furniture; however, differences in pelvic orientation were statistically significant. The results of the present study indicate that Epionics may be useful for the quantitative assessment of work-related risk factors. Practitioner Summary: Only a few tools allow objective, unrestricted measurements of spinal posture and motion in the workplace. Epionics SPINE measures lumbar lordosis, pelvic orientation and spinal motion under nearly unrestricted conditions and can be used to quantify work-related musculoskeletal risk factors. We demonstrated the use of this tool in the workplace-analysis.

Measurement of the number of lumbar spinal movements in the sagittal plane in a 24-hour period.

PURPOSE: Little is known about the number of spinal movements in the sagittal plane in daily life, mainly due to the lack of adequate techniques to assess these movements. Our aim was to measure these movements in asymptomatic volunteers. METHODS: Two sensor strips based on strain gauge technology (Epionics SPINE system) were fixed on the skin surface of the back parallel to the spine on a total of 208 volunteers without back pain. First, the lordosis angle was determined during relaxed standing. The volunteers were then released to daily life. The increases and decreases in the back lumbar lordosis angle over a period of 24 h were determined and classified into 5° increments. Changes in the lordosis angle greater than 5° were considered. RESULTS: The median number of spinal movements performed within 24 h was approximately 4,400. Of these movements, 66 % were between 5° and 10°. The proportions of higher-magnitude lordosis angle changes were much lower (e.g., 3 % for the 20-25° movement bin). Surprisingly, the median total number of movements was significantly higher (29 %) in women than in men. Large inter-individual differences were observed in the number of movements performed. The volunteers spent a median of 4.9 h with the lumbar spine flexed between 20° and 30° and only 24 min with the spine extended relative to the reference standing position. A median of 50 movements reached or exceeded full-flexion angle and zero movements full-extension angle. CONCLUSIONS: These data illustrate the predominantly small range of movement of the spine during daily activities and the small amount of time spent in extension. These unique data strongly contribute to the understanding of patients' everyday behavior, which might affect the development and testing of spinal implants and the evaluation of surgical and nonsurgical treatments.

Optimal assessment of upper body motion - Which and how many landmarks need to be captured for representing rigid body orientation?

In biomechanical studies, the thorax is often considered rigid. Since it's a well-known simplification, usually more than three markers are used to describe its movement in motion analyses. However, there is uncertainty about how many markers are advisable and which landmarks should be used. The results of the present study describe the expected error depending on the number of markers used. Furthermore, a recommendation is given for the landmarks with the least errors. This recommendation is valid for men and women as well as for different movements. The recommendations roughly reduce the error to about 50% and are beneficial especially in case only a small number of markers were used. For general motion capture, we recommend to use at least six thoracic markers.

The Effect of Fat Distribution on the Inflammatory Response of Multiple Trauma Patients-A Retrospective Study.

Objectives In recent years; increasing evidence pointed out the clinical importance of adipose tissue (AT) distribution in various patient populations. In particular, visceral adipose tissue (VAT), when compared to subcutaneous adipose tissue (SAT), was found to play a pivotal role in the development of inflammatory reaction. The aim of the present study was to examine whether body fat distribution has an impact on the development of systemic inflammatory response syndrome (SIRS) in patients with polytrauma. Methods In our retrospective study; we filtered our institution records of the German Trauma Registry (Trauma Register DGU) from November 2018 to April 2021 and included 132 adult polytrauma patients with injury severity score (ISS) >16. Subsequently; we measured the visceral and subcutaneous adipose tissue area based on whole-body CT scan and calculated the ratio of VAT to SAT (VSr). Thereafter, the patient population was evenly divided into three groups; respectively VSr value less than 0.4 for the first group (low ratio), 0.4-0.84 for the second group (intermediate ratio), and greater than 0.84 for the third group (high ratio). Considering the other influencing factors; the groups were further divided into subgroups in the respective analysis according to gender (male/female), BMI (<25 or ≥25), and ISS (<26 or ≥26). Result VSr was an independent factor from body mass index (BMI) (r2 = 0.003; p = 0.553). VSr in male patients was significantly higher (p < 0.001). Patients with low VSr had higher ISS scores (p = 0.028). Polytrauma patients with higher VSr tended to have lower SIRS scores and significant differences of SIRS score were found on multiple days during the whole hospitalization period. In the low VAT/SAT group, male patients, and patients with BMI greater than 25, both exhibited higher SIRS scores during hospital stay (day 16: p = 0.01; day 22: p = 0.048 and p = 0.011; respectively). During hospitalization, patients with higher ISS score (≥26) in the low VSr group was found to have higher SIRS score (day 16; p = 0.007). Over the hospital stay; serum markers of CRP; CK; and leukocyte in patients with low VSr were higher than those in patients in the intermediate and high VSr groups; with significant difference discovered on multiple days (day 16: 0.014; day 22: p = 0.048). Conclusion Lower VSr is associated with increased inflammatory response and worse clinical outcome in patients with polytrauma. Furthermore; VSr is an independent factor providing additional information to BMI.

Relationship between intervertebral disc and facet joint degeneration: A probabilistic finite element model study.

Both intervertebral disc (IVD) and facet joint (FJ) degeneration are frequently associated with chronic low back pain. While genetic factors are considered the most relevant in the onset of degeneration, the mechanics play an important role in its progression. Degenerative changes in one of these two structures are believed to induce degeneration in the other. However, despite decades of research, there is no consensus on the mechanical interplay between the two structures. On the basis of a parametric finite element model of a human L4-L5 spinal motion segment, one thousand individual segments were probabilistically generated covering all grades of degeneration in both structures. The segments were subjected to combined compression and flexion/extension loads. Correlation matrices were created to identify the effect of individual degeneration parameters of each structure on the mechanical stresses in the corresponding counterpart. In the non-degenerated group, a strong positive and a moderate negative correlation was found between the strain of the capsular ligament and the disc height and the nucleus compressibility, respectively. With increasing degeneration, the correlation between IVD morphologies and the FJ loads gradually decreased, whereas the correlation between FJ morphologies and disc load gradually increased. The results suggest that early mechanical changes associated with IVD degeneration have the greatest effect on the FJ loading. With progression of degeneration, this effect is diminished, whereas the appearance of FJ degeneration increasingly influences the disc loading, which might indicate an increasing support of the disc degeneration.

Is the sheep a suitable model to study the mechanical alterations of disc degeneration in humans? A probabilistic finite element model study.

Intervertebral disc degeneration is one major source of low back pain, which because of its complex multifactorial nature renders the treatment challenging and thus necessitates extensive research. Experimental animal models have proven valuable in improving our understanding of degenerative processes and potentially promising therapies. Currently, the sheep is the most frequently used large animal in vivo model in intervertebral disc research. However, despite its undoubted value for investigations of the complex biological and cellular aspects, to date, it is unclear whether the sheep is also suited to study the mechanical aspects of disc degeneration in humans. A parametric finite element (FE) model of the L4-5 spinal motion segment was developed. Using this model, the geometry and the material properties of both the human and the ovine spinal segment as well as different appearances of disc degeneration can be depicted. Under pure and combined loads, it was investigated whether degenerative changes to both the human and the ovine model equivalent caused the same mechanical response. Different patterns of degeneration resulted in large variations in the ranges of motion, intradiscal pressure, ligament and facet loads. In the human, but not in the ovine model, all these results differed significantly between different degrees of degeneration. This FE model study highlighted possible differences in the mechanical response to disc degeneration between human and ovine intervertebral discs and indicates the necessity of further, more detailed, investigations.

How reproducible do we stand and sit? Indications for a reliable sagittal spinal assessment.

BACKGROUND: Currently, an upright standing posture is normally adopted for evaluations of spinal alignment, which is however sensitive to posture variations. Thus, finding a reproducible reference is essential. This study aimed to evaluate the reproducibility of standing and sitting postures at different arm positions in five consecutive repetitions. METHODS: 22 asymptomatic subjects (11 males; 11 females) aged 20-35 years were included. Subjects were repeatedly asked to adopt different arm positions in standing and sitting. The absolute reposition errors of lumbar lordosis and sacral orientation between two consecutive repetitions were assessed with a non-radiological back measurement system. FINDINGS: During standing at the relaxed arm position, the median absolute reposition errors of lumbar lordosis and sacral orientation were 1.14° (range 0.23°-3.80°) and 0.92° (range 0.17°-3.27°), respectively, which increased to 1.75° (range 0.21-4.97°) and 1.36° (range 0.35°-4.08°) during sitting (P < 0.01). The absolute reposition error of lumbar lordosis was non-significantly lower at the relaxed and clasped arm positions than at other arm positions. Between the first two repetitions, the absolute reposition errors of both, lumbar lordosis and sacral orientation, were greater than between the remaining two consecutive repetitions (P < 0.01). Both during standing and sitting, lumbar lordosis was smallest when hands holding two bars (P < 0.05). INTERPRETATION: Sitting showed a worse reproducibility than standing. When assessing sagittal spinal balance, the clasped arm position during standing is recommended and an initial trial can help to reduce inception irreproducibility.

Numerical simulations of bone remodelling and formation following nucleotomy.

Nucleotomy is the gold standard treatment for disc herniation and has proven ability to restore stability by creating a bony bridge without any additional fixation. However, the evolution of mineral density in the extant and new bone after nucleotomy and fixation techniques has to date not been investigated in detail. The main goal of this study is to determine possible mechanisms that may trigger the bone remodelling and formation processes. With that purpose, a finite element model of the L4-L5 spinal segment was used. Bone mineral density (BMD), new tissue composition, and endplate deflection were determined as indicators of lumbar fusion. A bone-remodelling algorithm and a tissue-healing algorithm, both mechanically driven, were implemented to predict vertebral bone alterations and fusion patterns after nucleotomy, internal fixation, and anterior plate placement. When considering an intact disc height, neither nucleotomy nor internal fixation were able to provide the necessary stability to promote bony fusion. However, when 75% of the disc height was considered, bone fusion was predicted for both techniques. By contrast, an anterior plate allowed bone fusion at all disc heights. A 50% disc-height reduction led to osteophyte formation in all cases. Changes in the intervertebral disc tissue caused BMD alterations in the endplates. From this observations it can be drawn that fusion may be self-induced by controlling the mechanical stabilisation without the need of additional fixation. The amount of tissue to be removed to achieve this stabilisation remains to be determined.

Are there characteristic motion patterns in the lumbar spine during flexion?

Flexion is the main motion of the lumbar spine. While in vitro tests with pure moments suggest larger intra-segmental rotations for the more caudal segments, in vivo results show diverging motion distributions. The present study analysed the motion distribution in vivo of 320 asymptomatic subjects. The change of the back curvature between standing and upper body flexion was determined using a non-invasive measurement device. Linear, bilinear, trilinear, quadratic, and cubic regression models were fitted to the segmental motion distribution over the lengths of the lordosis to categorise characteristic motion patterns. Simplicity and approximation quality were used to assign the motion distributions to the regression models. Seventy-seven percent of the motion distributions could be explained by a bilinear model. A further 12% and 11% could be represented by a trilinear and linear model, respectively. Less than 1% of the distributions could not satisfactorily be represented by the models. All of the bilinear models displayed maximum flexion in approximately the middle of lordosis. All linear models showed a decreasing rotation from caudal to cranial. Most of the trilinear models displayed a distribution similar to the bilinear. Age, sex, body height, and weight did not significantly affect these distributions. This in vivo study identified characteristic motion patterns in the lumbar spine during flexion. The quantitative results provide a clear description of the healthy condition and may serve to identify spinal motion abnormalities.

Effect of disc degeneration on the mechanical behavior of the human lumbar spine: a probabilistic finite element study.

BACKGROUND CONTEXT: Intervertebral disc degeneration has been subject to numerous in vivo and in vitro investigations and numerical studies during recent decades, reporting partially contradictory findings. However, most of the previous studies were limited in the number of specimens investigated and, therefore, could not consider the vast variety of the specimen geometries, which are likely to strongly influence the mechanical behavior of the spine. PURPOSE: To complement the understanding of the mechanical consequences of disc degeneration, whereas considering natural variations in the major spinal geometrical parameters. DESIGN/SETTING: A probabilistic finite element study. METHODS: A parametric finite element model of a human L4-L5 motion segment considering 40 geometrical parameters was developed. One thousand individual geometries comprising four degeneration grades were generated in a probabilistic manner, and the influence of the severity of disc degeneration on the mechanical response of the motion segment to different loading conditions was statistically evaluated. RESULTS: Variations in the individual structural parameters resulted in marked variations in all evaluated parameters within each degeneration grade. Nevertheless, the effect of degeneration in almost all evaluated response values was statistically significant. With degeneration, the intradiscal pressure progressively decreased. At the same time, the facet loads increased and the ligament tension was reduced. The initially nonlinear load-deformation relationships became linear whereas the segment stiffness increased. CONCLUSIONS: Results indicate significant stiffening of the motion segment with progressing degeneration and gradually increasing loading of the facets from nondegenerated to moderately degenerated conditions along with a significant reduction of the ligament tension in flexion.

Computational study of the role of fluid content and flow on the lumbar disc response in cyclic compression: Replication of in vitro and in vivo conditions.

The intervertebral disc viscoelastic response is governed primarily by its fluid content and flow. Invivo measurements demonstrate that the disc volume, fluid content, height and nucleus pressure completely recover during resting even after diurnal loading with twice longer duration (16 vs. 8 h). In view of much longer periods required for the recovery of disc height and pressure in vitro, concerns have been raised on the fluid inflow through the endplates that might be hampered by clogged blood vessels post mortem. This in silico study aimed to identify fluid-flow dependent response of discs and conditions essential to replicate in vitro and in vivo observations. An osmo-poroelastic finite element model of the human lumbar L4-L5 disc-bone unit was used. Simulating earlier in vitro experiments on bovine discs, the loading protocol started with 8 h preload at 0.06 MPa followed by 30 high/low compression loading cycles each lasting 7.5min at 0.5/0.06 MPa, respectively. Three different endplate configurations were investigated: free in- and outflow, no inflow and closed endplates with no flow. Additionally, the preload magnitude was increased from 0.06 MPa to 0.28 MPa and 0.50 MPa, or the initial nucleus hydration was reduced from 83% to 50%. For 0.06 MPa preload, the model with no inflow best matched in vitro trends. The model with free inflow increased segment height and nucleus pressure while the model with no fluid inflow resulted in a relatively small recovery in segment height and a rather constant nucleus pressure during unloading periods. Results highlight an excessive mobile fluid content as well as a restricted fluid inflow through endplates as likely causes of the discrepancies between in vivo and in vitro studies. To replicate in vivo conditions in vitro and in silico, disc hydration level should be controlled by adequate selection of preload magnitude/period and/or mobile fluid porosity.

Differences in 3D vs. 2D analysis in lumbar spinal fusion simulations.

Lumbar interbody fusion is currently the gold standard in treating patients with disc degeneration or segmental instability. Despite it having been used for several decades, the non-union rate remains high. A failed fusion is frequently attributed to an inadequate mechanical environment after instrumentation. Finite element (FE) models can provide insights into the mechanics of the fusion process. Previous fusion simulations using FE models showed that the geometries and material of the cage can greatly influence the fusion outcome. However, these studies used axisymmetric models which lacked realistic spinal geometries. Therefore, different modeling approaches were evaluated to understand the bone-formation process. Three FE models of the lumbar motion segment (L4-L5) were developed: 2D, Sym-3D and Nonsym-3D. The fusion process based on existing mechano-regulation algorithms using the FE simulations to evaluate the mechanical environment was then integrated into these models. In addition, the influence of different lordotic angles (5, 10 and 15°) was investigated. The volume of newly formed bone, the axial stiffness of the whole segment and bone distribution inside and surrounding the cage were evaluated. In contrast to the Nonsym-3D, the 2D and Sym-3D models predicted excessive bone formation prior to bridging (peak values with 36 and 9% higher than in equilibrium, respectively). The 3D models predicted a more uniform bone distribution compared to the 2D model. The current results demonstrate the crucial role of the realistic 3D geometry of the lumbar motion segment in predicting bone formation after lumbar spinal fusion.

What does the shape of our back tell us? Correlation between sacrum orientation and lumbar lordosis.

BACKGROUND CONTEXT: Sacral slope and lumbar lordosis (LL) have been studied extensively in recent years via X-ray examinations and strongly correlate with each other. This raises, first, the question of the reproducibility of this correlation in multiple standing phases and, second, if this correlation can be achieved using non-radiological measurement tools. PURPOSE: This study aimed (1) to determine the extent to which the back-shape measurements correspond to the correlations between the sacral slope and LL found in previous radiological investigations, (2) to identify a possible effect of age and gender on this correlation, and (3) to evaluate the extent to which this correlation is affected by repeated standing phases. STUDY DESIGN/SAMPLE: This is an observational cohort study. PATIENT SAMPLE: A total of 410 asymptomatic subjects (non-athletes), 21 asymptomatic soccer players (athletes), and 176 patients with low back pain (LBP) were included. OUTCOME MEASURES: The correlation between sacrum orientation (SO) and LL was determined in six repetitive upright standing postures. MATERIALS AND METHODS: A non-invasive strain-gauge based measuring system was used. RESULTS: Back-shape measurements yielded a similar correlation to that measured in previous X-ray examinations. The coefficient of determination (R2) between SO and LL ranged between 0.76 and 0.79 for the asymptomatic cohort. Athletes showed the strongest correlation (0.76≤R2≤0.84). For patients with LBP, the correlation substantially decreased (0.18≤R2≤0.39). R2 was not strongly affected by repeated standing phases. CONCLUSIONS: The correlation between SO and LL can be assessed by surface measurements of the back shape and is not influenced by natural variations in the standing posture.

How do we stand? Variations during repeated standing phases of asymptomatic subjects and low back pain patients.

An irreproducible standing posture can lead to mis-interpretation of radiological measurements, wrong diagnoses and possibly unnecessary treatment. This study aimed to evaluate the differences in lumbar lordosis and sacrum orientation in six repetitive upright standing postures of 353 asymptomatic subjects (including 332 non-athletes and 21 athletes - soccer players) and 83 low back pain (LBP) patients using a non-invasive back-shape measurement device. In the standing position, all investigated cohorts displayed a large inter-subject variability in sacrum orientation (∼40°) and lumbar lordosis (∼53°). In the asymptomatic cohort (non-athletes), 51% of the subjects showed variations in lumbar lordosis of 10-20% in six repeated standing phases and 29% showed variations of even more than 20%. In the sacrum orientation, 53% of all asymptomatic subjects revealed variations of >20% and 31% of even more than 30%. It can be concluded that standing is highly individual and poorly reproducible. The reproducibility was independent of age, gender, body height and weight. LBP patients and athletes showed a similar variability as the asymptomatic cohort. The number of standing phases performed showed no positive effect on the reproducibility. Therefore, the variability in standing is not predictable but random, and thus does not reflect an individual specific behavioral pattern which can be reduced, for example, by repeated standing phases.

Influence of spinal disc translational stiffness on the lumbar spinal loads, ligament forces and trunk muscle forces during upper body inclination.

Inverse dynamic musculoskeletal human body models are commonly used to predict the spinal loads and trunk muscle forces. These models include rigid body segments, mechanical joints, active and passive structural components such as muscles, tendons and ligaments. Several studies used simple definition of lumbar spinal discs idealized as spherical joints with infinite translational stiffness. The aim of the current sensitivity study was to investigate the influence of disc translational stiffness (shear and compressive stiffness) on the joint kinematics and forces in intervertebral discs (L1-L5), trunk muscles and ligaments for an intermediately flexed position (55°). Based on in vitro data, a range of disc shear stiffness (100-200N/mm) and compressive stiffness (1900-2700N/mm) was considered in the model using the technique of force dependent kinematics (FDK). Range of variation in spinal loads, trunk muscle forces and ligaments forces were calculated (with & without load in hands) and compared with the results of reference model (RM) having infinite translational stiffness. The discs' centers of rotation (CoR) were computed for L3-L4 and L4-L5 motion segments. Between RM and FDK models, maximum differences in compressive forces were 7% (L1-L2 & L2-L3), 8% (L3-L4) and 6% (L4-L5) whereas in shear forces 35% (L1-L2), 47% (L2-L3), 45% (L3-L4) and more than 100% in L4-L5. Maximum differences in the sum of global and local muscle forces were approximately 10%, whereas in ligament forces were 27% (supraspinous), 40% (interspinous), 56% (intertransverse), 58% (lig. flavum) and 100% (lig. posterior). The CoRs were predicted posteriorly, below (L3-L4) and in the disc (L4-L5). FDK model predicted lower spinal loads, ligament forces and varied distribution of global and local muscle forces. Consideration of translational stiffnesses influenced the model results and showed increased differences with lower stiffness values.

Differences between clinical "snap-shot" and "real-life" assessments of lumbar spine alignment and motion - What is the "real" lumbar lordosis of a human being?

The individual lumbar lordosis and lumbar motion have been identified to play an important role in pathogenesis of low back pain and are essential references for preoperative planning and postoperative evaluation. The clinical "gold-standard" for measuring lumbar lordosis and its motion are radiological "snap-shots" taken while standing and during upper-body flexion and extension. The extent to which these clinically assessed values characterise lumbar alignment and its motion in daily life merits discussion. A non-invasive measurement-system was employed to measure lumbar lordosis and lumbar motion in 208 volunteers (age: 20-74yrs; ♀/♂: 115/93). For an initial short-term measurement, comparable with the clinical "snap-shot", lumbar lordosis and its motion were assessed while standing and during flexion and extension. Subsequently, volunteers were released to their daily lives while wearing the device, and measurements were performed during the following 24h. The average lumbar lordosis during 24h (8.0°) differed significantly from the standardised measurement while standing (33.3°). Ranges of motion were significantly different throughout the day compared to standing measurements. The influence of the factors age and gender on lordosis and its motion resulted in conflicting results between long- and short-term-measurements. In conclusion, results of short-term examinations differ considerably from the average values during real-life. These findings might be important for surgical planning and increase the awareness of the biomechanical challenges that spinal structures and implants face in real-life. Furthermore, long-term assessments of spinal alignment and motion during daily life can provide valid data on spinal function and can reveal the importance of influential factors.

Intradiscal pressure measurements: A challenge or a routine?

Intradiscal pressure (IDP) is an essential biomechanical parameter and has been the subject of numerous in vivo and in vitro investigations. Although currently available sensors differ in size and measurement principles, no data exist regarding inter-sensor reliability in measuring IDP. Moreover, although discs of various species vary significantly in size and mechanics, the possible effects of sensor insertion on the IDP have never been investigated. The present in vitro study aimed to address these issues. The synchronized signals of two differently sized pressure transducers (Ø1.33 and Ø0.36 mm) obtained during the measurements in two species (bovine and caprine) and their influence on the measured pressure were compared. First, the discs were subjected to three loading periods, and the pressure was measured simultaneously to assess the inter-sensor reliability. In the second test, the effect of the sensor size was evaluated by alternatingly inserting one transducer into the disc while recording the resulting pressure change with the second transducer. Although both sensors yielded similar pressure values (ICC: consistency: 0.964-0.999; absolute agreement: 0.845-0.996) when used simultaneously, the sensor size was determined to influence the measured pressure during the insertion tests. The magnitude of the effect differed between species; it was insignificant in the bovine specimens but significant in the caprine specimens, with a pressure increase of 0.31-0.64 MPa (median: 0.43 MPa) obtained when the larger sensor was inserted. The results suggest that sensor selection for IDP measurements requires special attention and can be crucial for species with smaller disc sizes.

The effects of age and gender on the lumbopelvic rhythm in the sagittal plane in 309 subjects.

Frequent upper body bending is associated with low back pain (LBP). The complex flexion movement, combining lumbar and pelvic motion, is known as "lumbopelvic rhythm" and can be quantified by dividing the change in the lumbar spine curvature by the change in pelvic orientation during flexion movement (L/P ratio). This parameter is clinically essential for LBP prevention, for diagnostic procedures and therapy; however, the effects of age and gender, in detail, are unknown. The Epionics SPINE system, utilizing strain-gauge technology and acceleration sensors, was used to assess lumbar lordosis and sacrum orientation during standing and lumbar angle and sacrum orientation during maximal upper body flexion in 309 asymptomatic subjects (age: 20-75 yrs; ♂: 134; ♀: 175). The effects of age and gender on these characteristics as well as on the resultant range of flexion (RoF) and lumbopelvic rhythm were investigated. Aging significantly reduced lumbar lordosis by 8.2° and sacrum orientation by 6.6° during standing in all subjects. With aging, the lumbar RoF decreased by 7.7°, whereas the pelvic RoF compensated for this effect and increased by 7.0°. The L/P ratio decreased from 0.80 to 0.65 with age; however, this decrease was only significant in men. Gender affected sacrum orientation in standing and in flexion as well as the L/P ratio. This study demonstrated the effects of age and gender on lordosis, sacrum orientation and lumbopelvic rhythm. These findings are of importance for the individual prevention of LBP, and provide a baseline for differentiating symptomatic from asymptomatic age- and gender-matched subjects.

Computational analyses of different intervertebral cages for lumbar spinal fusion.

Lumbar spinal fusion is the most common approach for treating spinal disorders such as degeneration or instability. Although this procedure has been performed for many years, there are still important challenges that must be overcome and questions that need to be addressed regarding the high rates of non-union. The present finite element model study aimed to investigate the influence of different cage designs on the fusion process. An axisymmetric finite element model of a spinal segment with an interbody fusion cage was used. The fusion process was based on an existing mechano-regulation algorithm for tissue formation. With this model, the following principal concepts of cage design were investigated: (1) different cage geometries with constant compressive stiffness and (2) cage designs optimized to provide the ideal mechanical stimulus for bone formation, first at the beginning of fusion and then throughout the entire fusion process. The cage geometry substantially influenced the fusion outcome. A cage that created an optimized initial mechanical stimulus did not necessarily lead to accelerated fusion, but rather resulted in delayed fusion or non-union. In contrast, a cage made of a degradable material produced a significantly higher amount of bone and resulted in higher segmental stiffness. However, different compressive loads (250, 500 and 1000 N) substantially affected the amount of newly formed bone tissue. The results of the present study suggest that aiming for an optimal initial mechanical stimulus may be misleading because the initial mechanical environment is not preserved throughout the bone modeling process.