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Background: Patellofemoral pain syndrome is not really a diagnosis but rather describes the symptoms of this non-traumatic knee joint disease. Decreased movement control of the entire leg is discussed as a reason for the developing pain. Assessments of movement control include functional performance tests. A test to assess postural control and movement control of the foot, knee, hip and lumbar spine is the "Single Leg Pick-Up Test". The aim of the present study is to evaluate the interrater reliability of this test. Subjects/Material and Methods: 56 healthy subjects and three experienced raters participated in the study to assess the interrater reliability. Live rating and video rating were assessed and compared by pairs., Results: Intraclass correlations of the reached scores ranged from good to excellent (ICCunjust 0.72/0.63/0.85). Kappa and PABAK calculations of the observation criteria reached moderate to good values. The Ø PABAK for all observation criteria was 0.70/0.69/0.80 for the paired comparison of the raters. The agreement of six of seven observation criteria based on PABAK calculations were good to very good for the pairs of raters., Conclusions: All motor control deficits present in patellofemoral pain syndrome can be observed by the "Single Leg Pick-Up Test" with substantial reliability. Future studies should confirm reliability and further evaluate discriminative validity of the test. The "Single Leg Pick-Up" can be carried out easily and has the potential to assess patients with patellofemoral pain syndrome and healthy athletes for movement control deficits., (© Georg Thieme Verlag KG Stuttgart · New York.)

Background: If lumbar interbody fusion is indicated, there are several options for instrumentation of the affected motion segment. Intervertebral cages are implanted in the disc to restore disc height and to stabilize the motion segment by tensioning the ligamentous structures., Methods: Based on a selective literature search with the focus on biomechanical aspects of intervertebral cages, experimental and clinical studies are shown, interpreted, and discussed., Results: In the literature, biomechanical flexibility tests of "stand alone" cages without supplemental instrumentation showed a limited stabilizing effect, particularly in extension and axial rotation, as well as an increased load transfer through the ventral column. Applying supplemental dorsal instrumentation can return the ventral/dorsal load sharing to the range of an intact motion segment and causes a marked increase of stability in all motion planes. Compared to bilateral dorsal instrumentation, unilateral dorsal instrumentation showed a reduced primary stability and leads to an asymmetrical loading of the cage which can cause unilateral loss of reduction. Nonmetallic cages with a stiffness adapted to bone allow better radiological evaluation of the bony fusion of the motion segment and theoretically have a reduced tendency to migrate., Conclusion: In combination with bilateral dorsal instrumentation, cage geometry and material have only a minor influence on primary stability and the main stability is provided by the internal fixator.

Aim: The goal of this study was to analyse the muscle strength of the cervical and lumbar spine in ironman triathletes. The values were compared to the results obtained from a reference group. The test of the triathletes was carried out in an attempt to define a specific strength profile for these athletes., Method: In this study, 20 long-distance triathletes (∅ 37.3 ± 7.6 years of age, ∅ 1.80 ± 0.1 m, ∅ 73.7 ± 6.0 kg) were evaluated with regard to their individual and sport-specific strengths of the cervical spine in 2 planes and of the trunk strengths in all 3 planes of motion. The trunk strength profile of the triathletes revealed good average results in the trunk extensors and the lateral flexors of the left trunk. The reference group is the data base of the company Proxomed®, Alzenau. It is based on results of 1045 untrained, symptom-free subjects of different ages., Results: Lumbar extension: The extension of the force values shows no significant difference from the reference group. Lumbar flexion: The flexion tests show highly significantly lower force values (5.025 ± 0.81 N/kg vs. 6.67 ± 0.6 N/kg) than the reference group. Flexion/extension: In the sagittal plane values for the triathletes demonstrate an imbalance in muscle strength ratios. The abdominal muscles turn in relation to the back extensor muscles too weakly to be very significant. Lumbar rotation: The force values of the athletes in both directions (right: 6.185 ± 1.46 N/kg, left: 7.1 ± 1.57 N/kg vs. 10.05 ± 0.34 N/kg) are highly significantly (p ≤ 0.001) lower than the reference values. Ratio of rotation left/right: The ratio of left/right rotation in the reference group is set at 1 and thus shows an equally strong force level between the two sides. Lumbar lateral flexion: The triathletes do not show any significant differences between the force values. Compared to the reference group there is no significant difference to the left side flexion. In the lateral bending the athletes have significantly better values than the reference group. Ratio of lateral left/right: In the reference group the ratio is set at 1. For triathletes, it shows an average value of 0.93. This difference is not significant. Cervical extension: The extension of the force values (1.96 ± 0.59 N/kg vs. 3.03 ± 0.24 N/kg) shows a highly significant difference from the reference group. Cervical flexion: In flexion (1.3 ± 0.42 N/kg vs. 2.17 ± 0.22 N/kg) triathletes have highly significantly lower strength values than the reference group. Flexion/extension: The triathletes did not differ significantly from the reference values (0.69 ± 0.23 and 0.72 ± 0.08). Lateral cervical spine: In comparison to the reference group (left: 1.67 ± 0.48 N/kg, right: 1.55 ± 0.46 N/kg vs. 2.36 ± 0.15 N/kg) in which there is left/right lateral flexion, there is a highly significant difference. Right lateral flexion is weaker than the left. Ratio of lateral left/right: The triathletes have a significant imbalance in the lateral flexion of the cervical spine compared to the reference group (1.07 ± 0.15 to 1)., Conclusion: In conclusion, in the triathlon there is a specific stress that is obviously not an adequate stimulus for the muscles of the cervical spine in order to achieve a balanced musculature and the athletes should be advised to practice a preventive approach with regard to these areas., (© Georg Thieme Verlag KG Stuttgart · New York.)

Aim of the Study: Maintaining segmental motion is one of the most reported theoretical advantages of total disc replacement (TDR). Several inlay sizes are available for reconstruction of the physiological disc height. The influence of the implant height on the range of motion (ROM) was investigated in a biomechanical study., Methods: A total of 10 human lumbar cadaver spines were subjected to biomechanical testing. Flexion/extension and side-bending moments were applied from 2.5-7.5 Nm on a spine load simulator allowing for all 6 degrees of freedom. Motion under different loads was monitored by the Zebris system in 3 dimensions. Initially intact specimens were tested in 3 load cycles. Then a total disc prothesis was implanted with an 8.5 mm inlay and the cycles were repeated. Finally in 5 cases a 1-mm larger inlay was inserted while in the remaining 5 cases the inlay was exchanged with a 2-mm larger implant. Neutral zone (NZ) and ROM were recorded under the different loads., Results: The average motion for the various loads showed no significant difference when the intact motion segment was compared to the specimen containing the 8.5-mm inlay. After the larger inlay had been mounted the average reduction of the ROM in flexion/extension was 25% under the load of 7.5 Nm, 26% under a torque of 5.0 Nm and 30% when 2.5 Nm were applied. The NZ was reduced by 37%. For side-bending the ROM was reduced by 21% under a load of 7.5 Nm, by 26% under 5.0 Nm and by 35% under a torque of 2.5 Nm. The NZ was decreased by 27%. The reduction of the ROM was significant (p=0.0057)., Conclusion: Segmental lumbar motion is maintained after TDR. The size of the inlay can significantly change the ROM in lumbar spine segments treated by TDR.

Background and Objective: Accelerated bone loss is a well recognized complication after cardiac transplantation (HTx). The role of an immunosuppressive-induced hypogonadism, a well-known cause of osteoporosis in men and its prevention are less defined after HTx. The aim of this study was first, to evaluate the incidence of hypogonadism after HTx and its influence on bone mineral metabolism and second, to assess the effect of a testosterone replacement therapy in hypogonadal transplants., Patients and Methods: Due to hormonal status, 88 male cardiac transplants were randomised to a normogonadal or hypogonadal group. At baseline as well as after 1 and 2 years bone mineral density (BMD g/cm (2), T-score) was measured at the lumbar spine with DEXA. All patients received a basic therapy of calcium and vitamin D. The hypogonadal patients received additional testosterone., Results: 21 patients (24 %) showed an age-independent hypogonadism. Hypogonadal transplants showed a significant lower BMD (p < 0.001) (BMD = 0.8070 g/cm (2), T-value = -2.6514) than normogonadal patients (BMD = 0.9882 g/cm (2), T-value = -1.0568). Despite testosterone replacement hypogonadal patients showed no significant additional increase in BMD over 1 - 2 years compared with the normogonadal., Conclusion: Male cardiac transplants in all age groups show an high prevalence of hypogonadism (approximately 25 %) which contributes to a significant bone loss. An additional testosterone substitution did not significantly increase BMD.

Aim: The primary stability of ventral fixation systems has been improved over the past years and special implants supporting minimally invasive procedures have been developed. The aim of this study was to analyze the primary stability of several of these implants., Methods: Thirty (30) lumbar segments from 5 to 7-month-old calves were harvested and tested on a pure moment apparatus (PMA) as well as a modified materials testing machine (MTS) according to the European standard recommendations of Wilke et al. Three different implant systems (MACS, Centaur and Z-plate) were included. ROM, neutral zone and stiffness were tested on the PMA up to 10 Nm, stiffness at an eccentric axial load of up to 1500 N was tested on the MTS. Bone density was investigated for all specimens. Statistical analysis was performed by ANOVA and LSD tests., Results: Primary stability was improved by all fixation devices compared to the physiological specimen. The MACS implant was more stable than the Centaur and Z-plate with the exception of in lateral bending [where the Z-plate was stiffer]. Bone density was comparable in the three different experimental groups., Conclusion: Minimal invasive ventral fixation devices are becoming popular. The primary stability of the minimal invasive MACS was comparable to those of other well-known ventral fixation devices of the lumbar spine.

The study quantified the stress levels in treated and untreated vertebral bodies following kyphoplasty. Three-dimensional FE models of treated and untreated T11, T12, L1, and L2 vertebral bodies were evaluated to examine the stress levels within the bone and bone cement. A validated T12-L1 model was used to investigate the effect of kyphoplasty treatment on adjacent vertebral stresses and strains. Using the single vertebral models, bone cement modulus changes had minimal effect on the stresses in the bone or the cement. The presence of bone cement had a minimal effect on the stress magnitudes or distribution in the adjacent T12 vertebra. This study provides quantification of the stress levels in bone cement and bone in vertebral bodies treated with kyphoplasty under in vivo-like loading conditions. The presence of bone cement immediately following kyphoplasty has only a slight effect on the stress magnitudes or distributions in adjacent vertebrae.

Multisegmental biomechanical studies on the lumbar spine are steadily increasing in importance. Only in this way can we acquire knowledge about the physiological behaviour of the entire lumbar spine. Furthermore, these studies allow us to analyse in vitro the biomechanics of manipulated lumbar spines after various surgical operations on the spine. A load simulator was developed to investigate multisegmental lumbar spine mobility, and its function was investigated in an initial study on 19 fresh--frozen specimens of human lumbar spine. After x-ray examination and determination of the bone mineral density, the specimens were loaded up to 10 Nm in the automatic electromechanical loading system under flexion/extension, lateral bending and axial rotation. An ultrasound-based motion analysis system was used to measure the displacements of the vertebrae involved.

Aim: Flexible lumbar corsets should contribute to an improved active and passive stabilisation of the lumbar spine. In the present study, the effects of flexible corsets on sensory-motor abilities have been investigated., Methods: 24 healthy subjects (m = 10, f = 14, 26.7 years) performed angle- and force-reproduction tasks with and without wearing a flexible corset. The subjects tried to reproduce trunk flexion angles of 20 degrees und 40 degrees as well as forces of 33% and 66% of the maximum strength of the back extensor muscles. Additionally, muscular reactions were measured during destabilizing stimuli., Results: No significant differences were found for the reproduction tasks. When wearing the corset, the left erector spinae muscles showed a delayed onset (+15 ms, p < 0.05), and the obliquus abdominis reached maximal activity more rapidly (-18 ms, p < 0.05). In the preinnervation phase the obliquus abdominis (-33%, p < 0.01), in the eccentric phase the erector spinae (-27%, p < 0.05) and the right obliquus abdominis (-46%, p < 0.05) and in the concentric phase the right obliquus abdominis (-35%, p < 0.01) and the rectus abdominis (-32%, p < 0.05) showed lower activities., Conclusion: The reduced muscle activities with destabilizing stimuli can be interpreted as the result of an improved passive stabilisation of the lumbar region by wearing a flexible corset.

The objective measurement of functional lumbopelvical movements enables the evaluation of the quantity and quality of movements referring to functional disorders in dynamic test-situations. The goal of the present study is the determination of the reproducibility of time-continuous movement analysis of the pelvic region during walking and the determination of possible errors. The movements of the thoracic (Th12), lumbar and sacrum-region (S1) of 17 healthy subjects (age: 32.1 +/- 2.3 years) during walking on a treadmill (4.5 km/h) were investigated twice in an interval of 24 hours by means of a 3D ultrasonic movement analysis system. The ensemble averages of the low-pass filtered and time-normalized angle-time sequences of all anatomical planes and regions showed high test-retest correlations (r > or = 0.92, p < 0.01) except fo the lumbar movement in the sagittal plane (r = 0.79, p < 0.01). A paired t-test showed no significant differences for the amplitudes of test and retest measurements except for the thoracolumbar movement in the sagittal plane (p < .05). The results show that the evaluation of lumbar movement patterns can be regarded as admissible and desirable for clinical movement analysis. The data can be used as a diagnostic tool for the planning and control of therapeutic interventions.

Objectives: The purpose of the present investigation was to determine the influence of nucleotomy for the biomechanical properties of the lumbar motion segment., Methods: From 11 human cadavers the lumbar-vertebral segment L3/4 was taken. The segment was tested by an 3D testing device. Measurements were taken under physiological loads up to 7 Nm. Load application was performed in flexion/extension, lateral bending and rotation direction. For each step translation and rotation were measured in three axis of space. Next measurement was performed after a nucleotomy simulated by rectangular excision of the anulus and total nucleotomy on an average of 6 g tissue., Results: There was a significant relation (p < 0.05) between removed disc material and flexibility of the lumbar motion segment., Conclusion: The nucleotomy plays a crucial role in the segmental mobility.

The vertebral bodies and vertebral arches show a characteristic distribution of cortical and cancellous bone. The pedicles are loaded by uniplanar bending that is reflected by the arrangement of the Corticalis. The ligaments of the vertebral column consist of longitudinal and (with exception of the lig. longitudinal anterius) horizontal/oblique segmental ligament bundles. In combination with the anulus fibrosus, the ligaments work as a kind of gear system. They regulate the process of movements of adjacent vertebral bodies in a very precise manner and control the final phase of motion. Besides maintaining the necessary amount of pretension the intervertebral disc distributes the loads uniformly onto the adjacent vertebral bodies. The intervertebral joints are important for guided motion, by restricting the extent in specific planes and directions. Because of their position, they are able to take up the shear forces and to simultaneously restrict them in different planes. The integrity of the fascia thoracolumbalis warrants the protective function of the autochthonuos muscles.

Background and Objective: The direct connections between a reduction in bone density and an increase in the incidence of fractures with increasing age is well known. When interpreting bone density measurements the attending physician is confronted with an overlap of false-positive and false-negative parameters, as is also the case with biochemical data. Aim of this study was to determine, in addition to bone density, a fracture threshold, i.e. a value for bone density with maximal sensitivity and specificity, in a representative cohort of women., Patients and Methods: 534 healthy women (mean age 60.9 +/- 8.07, range 40-83 years), seen in an out-patient osteological clinic between 1993 and 1996 were included. After full biochemical investigation to exclude a metabolic bone disease, bone density (LBD) of the lumbar vertebrae 1-5 and the number of vertebral body fractures were documented, together with age and menopausal status. LBD was measured by quantitative computed tomography (qCT), results being analysed with the Wilcoxon 2-sample test and logistic regression and assessed by receiver operating characteristics (ROC) analysis., Results: None of the women with a qCT value over 111 mg/cc had evidence of vertebral fractures. Those with values under 60 mg/cc had at least one vertebral fracture (defined as at least 15% reduction in vertebral body height). There was a highly significant negative correlation between age and LBD (r = -0.56; P < 0.0001), as well as between LBD and the number of fractured vertebrae (r = -0.58, P < 0.0001). But there was no longer any correlation between age and number of vertebral body fractures once allowance was made for LBD (r = 0.001, not significant). The least overlap of false-positive and false-negative values was at an LBD with qCT values of 102 mg/cc., Conclusions: LBD is the determining variable for fracture risk independent of age. Despite an overlap of false-positive and false-negative LBD values, the probability of fractures can be predicted from bone mineral content.

Unlabelled: The DXA-technique is a well established method to study bone mineral density (BMD). Until now there are no reliable reference data based on the male population of Germany., Question: Are the data base, given by the manufacturer transferable to the male population in Germany?, Methods: So a cross sectional study based on 715 healthy males with German ethnic background (age 20-89) was carried out. Comparison was made to the ap spine reference data of northern Europe., Results: The peak bone mass was 1,26 +/- 0,17 g/cm2 at the age of 20-24 years. After that the BMD decreases to the sixth decade (1,09 +/- 0,18 g/cm2), further on there is an increase to 1,18 +/- 0,21 g/cm2 in the ninth decade., Conclusion: Looking at a comparable Swedish study there are no significant differences, looking at a Finnish study there are statistically significant differences in the sixth decade (t = 3,246) and seventh decade (t = 2,413). The results of our study complete the data base until now, but one should be careful to transfer the data base provided by the manufacturer.

Problem: The interdependencies between movements of the thighs and the lumbar vertebral shape are of high practical interest. Which are the normals of this phenomenon?, Method: In an experiment on 107 volunteers without before known spinal disorders and complaints of back pain (47 f, 60 m, 17 a-30 a), the interdependencies between movements of the thighs in the sagittal and the lumbar back profile were analysed. Hip joint movements were provoked by a lift jack, elevating the feet to the volunteers, which sat on a bicycle chair. The hip joint flexion was measured by a Zebris CMS 50. The sagittal profile of the lower back was sensed by a comb of steel needles with low friction support., Results: At 30 degrees of hip flexion, 68% of the volunteers demonstrated a kyphotic, 17% a straight and 15% a lordotic lumbar shape. Starting at 90 degrees of hip flexion, "definitively kyphosating movements" of the lumbar motion segments occur. At the end of the motion, 89% of the volunteers had a kyphotic, 3% a straight and 8% a lordotic lumbar configuration. Each 2 degrees of additional hip joint flexion caudo-cranially one more lumbar motion segment is recruited for the definitive kyphosation of the lumbar spine., Conclusions: Instead of a "physiological shape of the lumbar spine" its "physiological function" or its "physiological interaction between shape und function" should be in the focus of future discussions. In the sitting, hip joint flexion leads to a coupled motion of the thighs, the pelvic girdle and the lumbar vertebral column with the consequence of a kyphosation of the lumbar back shape.

Unlabelled: Theoretical considerations help define the requirements for an apparatus that is to localize the instantaneous helical axes (IHA) of axial rotations of lumbar segments., Result: Since the range of axial rotation of an L3/4 segment is in only approximately +/- 1.5 degrees the rotational angle intervals have to be smaller than 0.3 degree with an resolution less than 0.03 degree in order to be able to determine the loci of the IHAs. For the first time in vitro measurements are presented that satisfy this requirement. The data prove that the guidance by the artt. zygapophysiales critically influence the possible positions of the IHA. Comparatively, ligaments and intervertebral disk play a marginally role. During axial torques Tz the IHAs lie dorsal to the intervertebral disk and migrate from one joint to the other depending on axial rotation (length of migration: approximately 3-4 cm). The IHAs lie almost parallel to the axial torque vector. When the joints are removed the IHA is stationary and almost perpendicular to the intervertebral disk and intersects the disk's central region. The screw inclination (pitch) of the instantaneous screw movement is proportional to the rotational angle. Therefore, depending on the direction of rotation, one obtains left or right handed screw movements. This means: axial torsional load leads to an increase in thickness of the intervertebral disk. During preloads that produces extensions the fixed centrodes (paths of axis migration) of intact segments are dorsally beaten out, whereas during flexional loads they are ventrally beaten out. Then, the IHAs migrate through the canalis vertebralis. By the concept "dimeric link chain" the different shapes of the fixed centrode are traced back to the morphology of curvature of the articulating surfaces. The measurements suggest the hypothesis that the distinct nonlinearity of the load displacement curves (s-shape of alpha = alpha (Tz) funktion is an affection of IHA migration. Comparatively, the influence of ligaments can be neglected. The measurements suggest the hypothesis that the hysteresis of the load displacement curves (neutral zone) is an artefact that does not appear in vivo. Altogether, the experiments prove that the loci of the IHAs are determined by the interplay of preload, structure of the applied force system and morphology of curvature of the articulating surfaces. By that the possibility is clinically given to calculate the multitude of possible movements as function of muscle activity when in the individual the shape and the position of the articulating surfaces are measured in vivo (by NMR-methods e.g.). A physically based classification of pathological cases seems to be possible.

The stability provided by three anterior spinal fixation devices (VDS, TSRH, CDH) designed for multisegmental instrumentation have been studied in an in-vitro model using L1-L5 sections of six human cadaveric spines for each instrumentation. Three-dimensional measurement of rotation and translation for the intact and instrumented spine under physiological loads in flexion/extension, lateral bending, and axial rotation were determined. After measuring the intact spine the destabilization was performed by complete intersection of the intervertebral disc, all spines were instrumented for 3 segments. TSRH was found to be significantly (p < 0.05) higher in stiffness in flexion/extension and torsion than VDS. In bending there was no statistical difference. In all tests CDH was significantly more stable than VDS. In flexion/extension it proved higher in stiffness than TSRH, no statistical difference was observed in bending and rotation.

Biomechanical models of the human body play an important role in the analysis of the mechanical loading of the musculo-skeletal system. The whole-body model presented in this paper is based on a CAE (Computer Aided Engineering) program that permits the dynamic simulation of complex systems of rigid bodies. The model we developed on this basis consisted of 19 segments and 18 joints. The experimental data are derived from the 3D motion analysis system VICON, which is provided with 5 cameras, a force-plate and a 10-channel EMG recorder. The kinematic data are fed into the simulator after first being processed in a special manner to generate drivers for joint angles. The model was first used to calculate the compression forces generated within the lumbar spine during the asymmetric lifting and putting down of a 15 kg stone. The quasistatic calculation shows a dynamic contribution to the compression forces generated during the lifting of 11%. Increasing or decreasing the inertial moments of the segments by the factor 2 had an effect of less than 1% with the identical movement.

Only little is known about the loads acting on internal spinal fixation devices. The forces and moments for different external loads were now measured using instrumented implants. Measurements were performed on intact cadaver spines and after a corpectomy. Additionally the influence of the mounting accuracy on the distribution of the loads in the fixators was investigated. It could be shown that the implants are not loaded symmetrically. After a corpectomy the loads on the implants are significantly higher than for an intact spine.

Three different internal fixateurs ("Dick", "Kluger", "SOCON") were investigated in an in-vitro setting. The systems showed nearly identical deformation under physiological loads. A new definition for the stabilizing capacity indicated a distinct weakness under compressive and torsional loading. In order to avoid early failure of the implant and/or the vertebra-implant interface bracing and a restricted mobilisation is recommended until healing of the fracture/fusion has taken place.

The implantation of fixation devices increases the primary stability after surgery significantly. Little is known about the comparison of flexibility of instrumented and posterolateral fusions or the lumbosacral distractions spondylodesis (LSDS). The purpose of the study was to compare the flexibility of instrumented and posterolateral fusions or LSDS after simulation with polymethylmethacrylate (PMMA). Dynamic testing from 0-16 Nm in flexion/compression and 0-900 N in compression was performed on 14 lumbosacral spines. The spines were tested intact, after laminectomy, instrumentation with an internal fixateur L5-S1, and simulation of posterolateral fusion L4-S1 or LSDS and thereafter a pseudoarthrosis was simulated. The laminectomy resulted in a significant increase of flexibility and posterior distraction in flexion and compression. The stabilization with an internal fixateur or PMMA simulation for posterolateral fusion or LSDS resulted in a significant decrease of the flexibility. Creation of a unilateral pseudoarthrosis did not effect the flexibility. The instrumented fusion as well as the PMMA simulated bony posterolateral fusion and LSDS resulted in this model in a significant stabilization of the laminectomy. After unilateral fusion the flexibility was not significantly increased.

APLD is considered as the last step of conservative treatment for lumbar disc herniation assuming that a negative biomechanical effect of APLD is not expected. Biomechanical effects of APLD were investigated in comparison to open discectomy. APLD decreased disc height less than open discectomy and increased instability and flexibility less. The position of the center of rotation was not significantly altered.

The range and type of ventrodorsal motion between two adjacent vertebra (L3-S1) was analyzed on isolated vertebral columns of 13 German Shepherd Dogs. All except one were neurologically normal dogs. The movement from maximal flexion to maximal extension was divided into 5 degree steps. For each step, the center of motion was determined on laterolateral radiographs. It could be shown that mobility between two adjacent vertebra within the lumbar spine increases towards the lumbosacral region with the highest mobility in this joint. In the cranial portion of the lumbar spine, rotation and ventrodorsal (parallel) displacement between two adjacent vertebra was seen. Rotation dominated in the lumbosacral joint in 11 dogs, whereas parallel displacement was mainly seen in 2 dogs. Further studies on pathologic and surgically modified vertebral columns are necessary to clarify the significance of these findings in the pathogenesis of lumbosacral instability and cauda equina compression in the German Shepherd Dog.

In the dog congenital or acquired stenosis of the lumbosacral region is commonly encountered. In humans the lumbosacral junction is the most often affected part of the vertebral column. Lumbosacral instability, one possible etiology for stenosis of the vertebral canal plays an important role in man. This study summarizes the functional anatomy and some important geometric and kinematic considerations necessary for the understanding of the motion (flexion-extension) between two adjacent vertebra.

In this study the derivation of a two-dimensional mathematical model of the human lumbar spine and its approximate solution using the method of finite elements is described. The computer model LUSP (Lumbar Spine) serves as a basis for studying the kinematic and load-bearing behaviour of the lumbar spine. The underlying working hypothesis is that the smallest spinal unit, the so called functional spinal unit (Junghanns, reflects the basic characteristic behaviour of the musclefree spine. On the basis of Lagrange's virtual work principle the nonlinear static and dynamic equations of motion for a sagitally symmetrical spine model of comprising rigid bodies, springs, beams and dampers are derived. The finite element method is used as an appropriate approximation scheme. Intensive research was conducted to provide the necessary geometrical and material input data. Special attention was paid to achieving a realistic description of the nonlinear stress-strain relationships for the soft tissue involved. A database-type preprocessor and a graphics-oriented postprocessor are made for convenient handling of the input and output data. The efficiency of the present computer model is demonstrated by means of an orthopaedic-biomechanical study on degenerative phenomena in so-called juxta-fused lumbosacral motion segments.

The physiological fate of every organism and its organ systems is aging which--as general opinion has it--after the age of 50 leads to a measurable mass of bone loss in the human skeletal system. This so-called physiological osteoporosis, however, affects the individual bones differently: Thus, the volumetric density in the neck of the femur and in the lower three lumbar vertebral bodies (LVB) decreases by 30%, but not in the lower three cervical vertebral bodies (CVB), while in the thyroid cartilage it increases constantly from the age of 15/20 years onwards. From the functional point of view, the so-called osteoporosis of old age is thus an expression of an aging bone adapting to the physical activity of the body, which, as such--just like the bone of the younger adult--merely reflects the current stressing of the cancellous bone by the locomotor system. Osteoporosis proper, in contrast, is a manifestation of disease of the bone causing clinical symptoms, in which underlying osteopenia results in fractures and spontaneous deformations.

To analyze mechanical properties of a lumbar functional unit a mathematical simulation model was developed. Using this model in different lumbar fusions immediate postoperative and secondary stability was analysed. Stability of different interbody and posterior fusions was compared looking at different techniques of operation an instrumentation. The calculation showed best results in the combination of posterolateral fusion with interspinal distraction or transpedicular screw instrumentation. These showed well-balanced load carrying properties primarily and high secondary stability.

The estimation of the centre of rotation of a spine segment can be shown as a transient pole, which follows the polar curve of the movement of the upper segment of the spine, relative to the lower one. With the help of X-ray, it is possible to evaluate two separate positions of the pole, from the normal position to the medium flexion and from the medium to the extreme flexion of the lumbal segment. Based on these expected values, as well as their intervals, pathological cases can be recognized, which is also shown in an example.

In 240 autopsy cases of both sexes, aged between 19 and 88 years and with no evidence of clinically manifest bone disease, the structure of the spongy bone and the external form of the 3rd and 5th lumbar vertebrae were investigated quantitatively and morphometrically on the basis of high-contrast X-ray images of 100 mu-thick polished bone sections, using the Leitz texture analysis system. The structure of the spongy bone was analysed on the basis of the parameters volumetric density, surface density and specific surface in horizontal "fifths", the form being determined by measuring the greatest and smallest heights and widths. In the individual "fifths", the structural parameters manifest a "stepped" distribution, the highest values being in the outer, the lowest values in the middle "fifths". With increasing age, this distribution pattern flattens to differing degrees so that, in old age, only the outer"fifths"differ from the middle and inner"fifths". The form parameters of the vertebrae reveal an age-independent constant heigh and an age-dependent increase in maximum width. The vertebral bodies are subjected mainly to compressive forces and represent a compound construction of spongy bone and fluid-filled medullary cells. The inhomogeneity of the vertebral structure is the constructional equivalent of the intravertebrally regionally differing mechanical forces. Also the structure of the residual spongy bone resulting from the age-dependent remodelling process, is oriented to these mechanical forces. Despite the considerable intravertebral remodelling of structure, the form of the vertebral bodies remains largely constant. The increase in maximum width is based on an increase in the tensile forces acting upon the outer edges of the vertebral bodies consequent upon degenerative intervertebral disc changes.

The loading of the lumbar spine in the working process can be judged by the loads to be raised or carried and the bending of the body, a biomechanical model serving as the basis of calculation. Up to now our knowledge on the length of work loading the body in the working process in insufficient, that's why statements on the amount of heavy labour causing harm to the body can scarcely be given. The results of detailed time studies done with welders and mechanics in the field of heavy mechanical engineering and the building of installations were: postures loading the lumbar spine were taken for less than 1 minute on average, in most cases up to 20 seconds, and altogether they had a share in the shift of 16% on average.

Using macerated and nonmacerated lumbar vertebrae and/or whole lumbar vertebral columns as well as x-rays, the attempt was made to contribute to the knowledge of the mechanics of the small joint in the lumbar section of the spinal column on the basis of the shape of the joint surfaces. The joint surfaces of the lumbar vertebral column deviate from the usual demonstration of primarily angular surfaces. Right and left joint surfaces of a locomotor segment do not lie on the same geometrical plane, i.e., there is nothing like a common right and left curvature center. As a result, conclusions can be drawn in regard to the role played by the small joint of the lumbar vertebral column under the various types of strain during movement, particularly during rotation. The relation of the small joint in rotation positions was demonstrated radiographically in isolated preparations of individual locomotor segments.

In 114 autopsy cases of both sexes, aged between 31 and 97 years and without bone disease, the influence of mechanical forces on the age-dependent remodelling of the spongy bone was determined in the 3rd and 5th lumbar vertebrae and the neck of the femur. For this purpose contrasty X-ray images of 100 mu thick polished bone sections were analysed using the LEITZ texture analysis system. The volumetric density and the surface density are highest in the neck of the femur, lowest in the 3rd lumbar vertebra, and almost as low in the 5th lumbar vertebra. The volumetric density decreases with increasing age by about one-third in all three bones. Correspondingly, the surface density also decreases in the lumbar vertebrae by one-third, but only by 18% in the neck of the femur. The specific surface reveals no age differences in the lumbar vertebrae, but increases by 19% in the neck of the femur. The constancy of the specific surface in the lumbar vertebrae can be explained by the fact that compensatory hypertrophy of the remaining trabeculae takes place. This compensatory growth of bone does not occur in the neck of the femur. The age-dependent decrease in spongy bone manifests itself in a residual spongiosa structure that depends on compressive forces in the case of the lumbar vertebrae and bending forces in the neck of the femur.