Biomedical subjects

Lutz Claes

Publications and source records attributed to Lutz Claes.

At least 55 records · Page 3Linked to original sources

PubMed2004

Establishment of a knee-joint coordinate system from helical axes analysis--a kinematic approach without anatomical referencing.

This study establishes a functional knee-joint coordinate system (FCS) derived from active motion. The scale invariant properties of helical axes were used in order to avoid inter-observer errors associated with the traditional anatomical referencing techniques. The algorithm was tested with six cadaveric specimens in a knee-joint motion and loading apparatus. To determine the FCS sensitivity to variable loading, rotational moments were applied to the tibia while extending and flexing the knee. Each derived FCS was compared with the clinically derived anatomical coordinate system (ACS). The FCS was reproducible when the loading condition was the same. Changing the rotational moments from internal to external affected the orientations and the positions of the FCS. The largest displacement of 20.8 mm in average occurred in the medio/lateral direction. The FCS corresponded with the ACS for all specimens and loading conditions. The origin was always located within the femur along the transepicondylar line. The orientations differed less than 16.6 degrees in average, thus allowing the use of clinical terminology. These findings suggest that the FCS might improve the ability to clinically assess kinematic alterations provided that the reference motion is reproducible.

Adult↗

PubMed2003

Influence of haemorrhagic shock on fracture healing.

BACKGROUND: The purpose of the study was to evaluate the effect of haemorrhagic shock on the outcome of fracture healing. MATERIAL AND METHODS: Forty-two male Wistar rats were randomly divided into a control group and a shock group. After producing a tibia fracture we induced shock by creating a blood loss of 12 ml/kg body weight. The rats were isovolumetrically resuscitated with a colloid volume solution. Blood flow was measured by laser Doppler flowmetry. Mechanical properties were tested by three-point bending after 4 weeks. RESULTS: The blood flow of the shock group was characterised by no reduction in the distal region and in the soft tissue in the first 24 h, while the flow in the control group was reduced to 39% of the pre-fracture level. Biomechanical testing showed a better fracture healing outcome for the shock group than for the control group in failure load (31/11 N; P=0.06) and flexural rigidity (22,7/4,7 Nmm2; P=0.07). CONCLUSIONS: In the shock group the restoration of vascularity in the distal region and in the soft tissue in the early healing stages, provoked by the isovolumic resuscitation, led to enhanced fracture healing. In addition, the results indicate that a fast blood supply may generate an improved initial healing process that results in an increased mechanical outcome of bone healing. In general, our findings underline the close interrelation between blood supply and successful fracture healing.

Animals↗

PubMed2003

The fracture gap size influences the local vascularization and tissue differentiation in callus healing.

BACKGROUND: Revascularization of a fracture depends on fracture stability and fracture gap conditions. The aim of the study was to determine quantitatively the revascularization and tissue differentiation in an animal model with different fracture gaps and controlled biomechanical conditions. MATERIALS AND METHOD: The study was performed on ten sheep with an osteotomy on the right metatarsal. The fracture was stabilized by an external fixator that allowed adjustable axial interfragmentary movement. Two groups of five sheep each were adjusted to a medium sized gap (M, 2.1 mm) and a large gap (L, 5.7 mm) under comparable interfragmentary strain (30-32%). The animals were killed after 9 weeks, and the metatarsals were prepared for undecalcified histology and analysis of tissue differentiation and vessel distribution. RESULTS: Group M showed significantly more revascularization (M=1.62, L=0.85 vessels/mm2), more bone formation (M=37.2%, L=13.9%) and less fibrocartilage tissue (M=18.1%, L=39.1%) than group L. Larger vessels (>40 microm) were found mainly in the medullary channel, and smaller vessels (<20 microm) mainly in the peripheral callus. Histologically, group M showed partial bony bridging of the osteotomy gap, and the group L had delayed healing. CONCLUSION: A good reduction of a fracture with small interfragmentary gaps is important for its revascularization and healing.

Animals↗

PubMed2003

Glucocorticoid-treated sheep as a model for osteopenic trabecular bone in biomaterials research.

The purpose of this study was to determine the alterations in ovine trabecular bone induced by a combination of ovariectomy and steroid treatment. Twenty-four female skeletally mature Merino sheep were randomly assigned to ovariectomy alone (OVX), ovariectomy combined with glucocorticoid treatment for 6 months (OVX + GC), or no treatment (control). Biopsies of trabecular bone were harvested 6 and 12 months after the beginning of the study from the proximal tibia. The biopsies were scanned for apparent bone mineral density by quantitative computed tomography and were mechanically tested. Three-dimensional bone reconstructions were obtained by micro-computed tomography. Trabecular bone from the OVX + GC animals had a markedly reduced apparent bone mineral density (27% less than control), bone volume (34%), and elastic modulus (36%) at 6 months. At 12 months, the reductions in apparent bone mineral density (33%), bone volume (37%), and elastic modulus (62%) appeared to be even more pronounced. Ovariectomy alone did not result in a perceptible reduction in any parameter. The combination of ovariectomy and glucocorticoid treatment in sheep resulted in a successful induction of substantial loss of trabecular bone and thus may serve as a large-animal model for osteopenic trabecular bone for the development and testing of orthopedic implants and techniques under osteoporotic conditions.

Animals↗

PubMed2003

Pedicle screws enhance primary stability in multilevel cervical corpectomies: biomechanical in vitro comparison of different implants including constrained and nonconstrained posterior instumentations.

STUDY DESIGN: 6 human cervical spines were tested in vitro in a biomechanical nondestructive set-up to compare different anterior, posterior and combined instrumentations after a corpectomy C4-C6. OBJECTIVES: To evaluate the primary three-dimensional stability of the different instrumentations. SUMMARY OF BACKGROUND DATA: The clinical results after stabilization of multilevel corpectomies are often disappointing. Higher biomechanical stability could enhance the rate of successful outcomes. The best instrumentation for these high-grade instabilities has yet to be found. METHODS: Six human cervical specimens were loaded nondestructively with pure moments and unconstrained motion at C3/7 was measured. The six specimens were instrumented with each of the following fixation techniques: 1. Cage 2. Nonconstrained posterior screw and rod system with lateral mass (NC-LM) 3. and pedicle screws (NC-P) 4. Constrained posterior screw and rod system with lateral mass (C-LM) and 5. pedicle screws (C-P) 6. Circumferential (C-P and anterior plate) 7. Anterior plate (OAP). RESULTS: For flexion/extension and axial rotation the circumferential instrumentation showed lowest ROM values, followed by C-P. The use of pedicle screws showed only a lower ROM when using the constrained system. No difference was found between the two screw types in the nonconstrained system. The anterior plating had the lowest stabilizing effect of all instrumentations, except for the cage alone. CONCLUSIONS: Usage of pedicle screws enhances primary stability only when using an constrained screw and rod system. In axial rotation the nonconstrained system showed no distinct difference compared to the intact state, independent of the screw type.

Aged↗

PubMed2003

Minimally invasive ventral spondylodesis for thoracolumbar fracture treatment: surgical technique and first clinical outcome.

A new instrumentation system for ventral stabilization of the spine that can be used for an endoscopic and minimally invasive approach was developed. We describe the implantation technique and report on the first clinical results. This prospective study covers the first 45 patients to undergo this new technique since it was introduced in 1999. In all patients the operation was successfully performed in a completely minimally invasive procedure. Mono- and bisegmental stabilization was performed mainly at the thoracolumbar junction after initial posterior instrumentation in most cases. Lesions varied from fresh/old fractures to metastases (T5-L3). Pre- and postoperative follow-up included clinical examination and radiological visualization via X-ray and computed tomographic scan. Our experience with this minimally invasive procedure demonstrated the feasibility of the method.

Adolescent↗

PubMed2003

Influence of K-Cl cotransporter activity on activation of volume-sensitive Cl- channels in human osteoblasts.

The whole cell recording mode of the patch-clamp technique was used to study the effect of hypotonic NaCl or isotonic high-KCl solution on membrane currents in a human osteoblast-like cell line, C1. Both hypotonic NaCl or isotonic high-KCl solution activated Cl- channels expressed in these cells as described previously. The reversal potential of the induced Cl- current is more negative when activated through hypotonic NaCl solution (-47 +/- 5 mV; n = 6) compared with activation through isotonic high-KCl solution (-35 +/- 3 mV; n = 8). This difference can be explained by an increase in intracellular [Cl-] through the activity of a K-Cl cotransporter. Potassium aspartate was unable to activate the current, and furosemide or DIOA suppressed the increase in Cl- current induced by isotonic high-KCl solution. In addition, we used the polymerase chain reaction to demonstrate the presence of KCC1-KCC4 mRNA in the osteoblast-like cell line. From these results, we conclude that human osteoblasts express functional K-Cl cotransporters in their cell membrane that seem to be able to induce the indirect activation of volume-sensitive Cl- channels by KCl through an increase in the intracellular ion concentration followed by water influx and cell swelling.

Aspartic Acid↗

PubMed2003

Axial compression force measurement acting across the strut graft in thoracolumbar instrumentation testing.

OBJECTIVE: Current recommendations for spinal implant testing do not consider the determination of axial compression forces of the overbridging implant on the strut graft. No direct data exist on the influence of load transfer through the strut graft and of the kind of instrumentation, especially in thoracolumbar corpectomy models. DESIGN: Therefore in this biomechanical in vitro study a method for measurement of the axial compression force acting across the strut graft in different thoracolumbar instrumentations was developed. METHODS: In this in vitro study, a corpectomy model was simulated and anterior, posterior and combined short fixation devices currently available were tested under pure moments to evaluate their biomechanical stabilizing characteristics. Range of motion, neutral zone and the axial compressive force acting on the strut graft were measured continuously in the three primary directions. RESULTS: Without loads, the combined stabilization and followed by anterior instrumentation created a higher axial compression force than the dorsal instrumentation on the strut graft. Especially during maximal extension there was no axial compression of the dorsal instrumentation on the strut graft, which resulted in an increase of the range of motion. CONCLUSION: The feasibility of the new method was demonstrated in this study. For the purpose of standardization and comparison it should be considered in spinal implant testing.

Aged↗

PubMed2003

Mitogens are increased in the systemic circulation during bone callus healing.

UNLABELLED: The influence of mechanical tissue strain caused by flexible fracture fixation on the systemic occurrence of systemic mitogens during callus healing was investigated. For this purpose the mitogenic capacity and growth factor concentration of sera from patients undergoing fracture treatment were determined. Sera from 9 patients whose fractures had been stabilized by external fixation were collected before and during fracture treatment. The sera were added to cell culture media of the osteoblastic cell line SaOS-2. After 5-6 days cell proliferation was measured. Transforming growth factor-beta1 (TGF-beta1) and insulin-like growth factor-I (IGF-I) concentrations were analyzed in serum samples from different healing stages. STATISTICS: paired Wilcoxon-test. Sera from fracture patients decreased SaOS-2 proliferation in the first week after surgery (p<0.05) compared to sera obtained prior to surgery. In the fourth or fifth week proliferation increased significantly (p<0.03). The increased proliferation of the SaOS-2 cells was associated with elevated levels of TGF-beta and IGF-I (p<0.05). The higher mitogenic activity of sera suggests an increased level of circulating mitogens. In a previous study this increase had also been observed in patients during distraction osteogenesis treatment but not in patients with primary bone healing by a stable fixated plate. It is therefore assumed that their release from the fracture site is a consequence of mechanical stimulation by interfragmentary movement of fracture ends.

Adult↗

PubMed2003

Shear movement at the fracture site delays healing in a diaphyseal fracture model.

This study tested the hypothesis that interfragmentary axial movement of transverse diaphyseal osteotomies would result in improved fracture healing compared to interfragmentary shear movement. Ten skeletally mature merino sheep underwent a middiaphyseal osteotomy of the right tibia, stabilized by external fixation with an interfragmentary gap of 3 mm. A custom made external fixator allowed either pure axial (n=5) or pure shear movement (n=5) of 1.5 mm amplitude during locomotion by the animals. The movement of the osteotomy gap was monitored weekly in two sheep by an extensometer temporarily attached to the fixator. After 8 weeks the sheep were killed, and healing of the osteotomies was evaluated by radiography, biomechanical testing, and undecalcified histology. Shear movement considerably delayed the healing of diaphyseal osteotomies. Bridging of the osteotomy fragments occurred in all osteotomies in the axial group (100%), while in the shear group only three osteotomies (60%) were partially bridged. Peripheral callus formation in the shear group was reduced by 36% compared to the axial group (p<0.05). In the axial group bone formation was considerably larger at the peripheral callus and in between the osteotomy gaps but not in the intramedullary area. The larger peripheral callus and excess in bone tissue at the level of the gap resulted in a more than three times larger mechanical rigidity for the axial than for the shear group (p<0.05). In summary, fixation that allows excessive shear movement significantly delayed the healing of diaphyseal osteotomies compared to healing under axial movement of the same magnitude.

Animals↗

PubMed2003

Glucocorticoid treatment of ovariectomized sheep affects mineral density, structure, and mechanical properties of cancellous bone.

UNLABELLED: Thus far, orthopedic research lacks a suitable animal model of osteoporosis. In OVX sheep, 6 months of steroid exposure reduced bone density and mechanical competence. Bone properties and bone formation did not recover for another 6 months. Therefore, steroid-treated OVX sheep may serve as a large animal model for osteopenic bone. INTRODUCTION: The purpose of this study was to explore the effects of glucocorticoid treatment on cancellous bone density, microarchitecture, biomechanics, and formation of new bone. MATERIALS AND METHODS: Sixteen ovariectomized merino sheep received either a 6-month glucocorticoid treatment (GLU; 0.45 mg/kg methylprednisolone) or were left untreated (control). Cancellous bone biopsy specimens from the tibia were harvested 6 months after ovariectomy. After 12 months, the animals were killed, and biopsy specimens were obtained from the contralateral tibia and the lumbar spine. All biopsy specimens were scanned for apparent bone mineral density by peripheral quantitative computed tomography (pQCT) and tested mechanically in uniaxial compression. Three-dimensional bone reconstructions were obtained by microcomputed tomography. Formation of new bone was analyzed using histologies of the femoral condyles. RESULTS: After 6 months, mineral density (-19%) and mechanical competence (-45%) were reduced by glucocorticoid treatment (p < 0.1). BV/TV (-21%; p < 0.01) and trabecular thickness (-20%; p = 0.01) declined, whereas BS/BV increased (24%; p = 0.01). After 12 months, mineral density (-33%) and mechanical properties (-55%) were reduced even more profoundly (p < 0.05). Also, the structural parameters (BS/BV and Tb.Th.) still seemed to be affected by glucocorticoid treatment (p < 0.05). New bone formation, assessed by measurement of osteoid surface, was markedly reduced (-63%, p < 0.1) by glucocorticoid treatment. The differences between groups were generally more pronounced at the tibia and the femur than at the spine. CONCLUSION: The effects of short-term high-dose steroid administration on bone mineral in this animal model were comparable with those observed in humans after long-term corticoid treatment. Reduction in bone quality and bone formation rate persisted after the cessation of steroid administration. Glucocorticoid treatment of ovariectomized sheep may therefore serve as a large animal model for steroid-induced osteopenia.

Animals↗

PubMed2003

Accurate determination of a joint rotation center based on the minimal amplitude point method.

In many computer-assisted surgery procedures in the field of joint replacement a joint rotation center must be located. To this end, joints such as the hip or the shoulder are approximated as spherical joints, and the most commonly used numerical method is the sphere-fitting algorithm. However, this method has a numerical instability where there is a limited range of motion caused by, for example, joint impingement. The aim of the present study was to develop an alternative kinematic method called the minimal amplitude point method. This method estimates the localization of the rotation center and can easily be integrated into program codes of computer-assisted surgery modules. It mainly consists of identifying the point of a mobile segment that moves least in the reference coordinate system of an immobile segment using an optimization procedure (genetic algorithm). The point determined can then be assumed to be the rotation center of the joint. To compare results of the two methods, an experimental set-up of two rigid solids linked by a spherical joint with known geometry was used to compute the rotation center. In contrast to the sphere-fitting method, the minimal amplitude point method permits the evaluation of the rotation center with an error of less than 4.1 mm, having a range of motion (ROM) of 5 degrees. An equivalent accuracy for the sphere-fitting method requires an ROM of 45 degrees.

Algorithms↗

PubMed2002

Posterior atlantoaxial fixation: biomechanical in vitro comparison of six different techniques.

STUDY DESIGN: Six different techniques for atlantoaxial fixation were biomechanically compared in vitro by nondestructive testing. OBJECTIVE: To evaluate the immediate three-dimensional stability of a new atlas claw combined with transarticular screws and alternative techniques for transarticular screw fixation in comparison with established techniques. SUMMARY OF BACKGROUND DATA: Posterior transarticular screw fixation in combination with wire-bone graft constructs is frequently used for C1-C2 fixation. Sublaminar wire passage carries the potential risk of neurologic complication. Transarticular screw fixation is technically demanding and, for anatomic reasons, not always feasible. METHODS: Six human cervical specimens were loaded nondestructively with pure moments, and unconstrained motion at C1-C2 was measured. The six specimens were instrumented with each of the following fixation techniques: Gallie fixation, transarticular screws and Gallie fixation, transarticular screws, transarticular screws and a new atlas claw, isthmic screws in the axis and the atlas claw, and lateral mass screws in the atlas and isthmic screws in the axis connected with rods. RESULTS: The transarticular screws restricted lateral bending and axial rotation best. The three-point fixations (transarticular + Gallie and transarticular + claw) additionally restricted flexion-extension, with lowest values for transarticular screws and the atlas claw. The alternative techniques were not as stable as the three-point fixations, but more stable than the Gallie fixation. CONCLUSIONS: Biomechanically, the three-point fixation with transarticular screws and the atlas claw provides a rigid internal fixation that is not dependent on bone graft and sublaminar wiring. In cases wherein transarticular screws are not feasible, the isthmic screws and claw or the lateral mass screws and isthmic screws are biomechanical alternatives with less immediate stability.

Aged↗

PubMed2002

Pullout test with three lumbar interbody fusion cages.

STUDY DESIGN: In vitro biomechanical testing was performed on 12 cadaveric human lumbar spines. OBJECTIVE: To determine the initial dislocation resistance, as quantified by the pullout force of three different cage designs. SUMMARY OF BACKGROUND DATA: Interbody cage devices frequently are used as stand-alone cages in the surgical treatment of degenerative conditions in the lumbar spine. In contrast to the wide clinical acceptance of interbody fusion cages, there are only a few biomechanical studies of posterior pullout trials. METHODS: Cylindrical threaded cages (Ray TFC Surgical Dynamics), bullet-shaped cages (Stryker), and newly designed rectangular titanium cages with an endplate anchorage device (Marquardt) were used for posterior interbody implants. For each device, the pullout test was performed in four specimens on both sides (L3-L4). RESULTS: In the pullout test, the Stryker cages required a median pullout force of 130 N (minimum, 100 N; maximum, 220 N), as compared with the higher pullout force of the Marquardt cages (median, 605 N; minimum, 450 N; maximum, 680 N), and the Ray cages (median, 945 N; minimum, 125 N; maximum, 2230 N). CONCLUSIONS: Differences in pullout resistance were noted depending on the cage design. A cage design with threads or a hook device provides superior stability, as compared with ridges. The initial pullout resistance was highest for the Ray cages and lowest for the Stryker cages.

Biomechanical Phenomena↗

PubMed2002

Proliferation of human-derived osteoblast-like cells depends on the cycle number and frequency of uniaxial strain.

We tested the hypothesis whether the number of applied load cycles and the frequency of uniaxial strain have an effect on proliferation of human bone derived osteoblast-like cells. A new approach was developed in order to differentiate between the effects of frequency and the effects of cycle number and strain duration. Monolayers of subconfluently grown cells were stretched in rectangular silicone dishes with cyclic predominantly uniaxial movement along there longitudinal axes. Strain was applied over 2 days varying the number of applied load cycles (4-3600) at a constant frequency (1Hz) or varying the frequency (0.1-30Hz) at a constant number of applied cycles (1800) or at a constant strain duration (5min). At a constant frequency, proliferative response increases (103%) with the number of applied cycles until a cycle number maximum (1800 cycles) was reached. 3600 cycles reduced cell number (43%) in contrast to the maximum. The variation of the frequency of applied strain tended to result in slight differences with regard to cell proliferation when cycle number was left constant. However, combined with an appropriate number of cycles there was an optimal frequency (1Hz) as stimulus for bone cell proliferation (84%). A higher frequency (30Hz) in combination with a high cycle number (9000) reduced cell number to control level (4%). This study demonstrates a frequency and cycle number dependent proliferative response of human osteoblast-like cells. It could be shown that effects of the frequency should not be considered separately from the effects of the cycle number.

Biomechanical Phenomena↗

PubMed2002

Primary stability in cementless femoral stems: custom-made versus conventional femoral prosthesis.

OBJECTIVE: To compare a custom-made femoral stem with a conventional cementless stem for initial stability in human femurs. DESIGN: The bone-femoral prosthesis interface motion was measured in vitro using displacement transducers. Combined axial and torsional loads simulating single-leg stance, loading were applied. BACKGROUND: The custom-made prosthesis is a cementless femoral stem fabricated from the patient's CT-reconstruction. To justify its clinical use its design has to be tested regarding his primary stability. METHODS: Seven pairs of human cadaveric femurs were used for testing the custom-made prosthesis versus a conventional cementless stem. Subsidence, rotation and interface motion were measured with load cycles up to 2000 N. RESULTS: The critical interface motion of 150 microm for the cementless prosthesis was not exceed for both types of prosthesis. The custom-made prosthesis enlarged in its metaphyseal part showed a decrease of dynamic micromotions and rotation behavior in the proximal region compared to the Alloclassic prosthesis stem. CONCLUSIONS: The initial stability of the custom-made femoral stem was comparable to that of a conventional femoral stem. RELEVANCE: The data set for initial stability justifies the clinical use of a custom-made femoral stem in primary hip replacement. An individualized stem fit into the endosteal cortical bone decrease micromotion.

Adult↗

PubMed2002

The traumatic spondylolisthesis of the axis. A biomechanical in vitro evaluation of an instability model and clinical relevant constructs for stabilization.

OBJECTIVE: Stepwise destabilization of the traumatic spondylolisthesis C2 with an increasing anterior defect of C2-C3 was investigated. The three-dimensional stabilizing capabilities of posterior transpedicle screw osteosynthesis and two anterior plate systems C2-C3, the H-plate and the titanium locking plate were tested. DESIGN: A biomechanical in vitro study was performed using a standardized experimental protocol in a spine tester. BACKGROUND: The extent of the instability of the traumatic spondylolisthesis of C2 within its different types remains unclear. Posterior and anterior approaches for stabilization exist for patients with isthmusfractures at C2, the stabilizing effect has not been demonstrated yet. METHODS: The motion levels from C2-C3 in six human specimen were tested in flexion, extension, right and left lateral bending and left and right axial rotation. The specimens were tested intact, after destabilization and after stabilization. RESULTS: In extension and axial rotation, each step of destabilization decreased the moment significantly, to achieve the range of motion of the intact specimen. In flexion a statistical significant destabilization after separation of the posterior longitudinal ligament was present. The flexibility tests showed an increasing range of motion of the posterior transpedicle screws, with increasing anterior instability markedly in flexion and extension. After H-plate and locking plate fixation, a significant decrease of the range of motion resulted in flexion. The stiffness in flexion and extension increased consecutively, while in lateral bending and axial rotation the transpedicle screw fixation showed the highest stiffness. CONCLUSIONS/RELEVANCE: The traumatic spondylolisthesis of C2 is a significantly unstable injury in case of additional segmental damage of C2-C3. Anterior stabilization in these injuries is mandatory.

Aged↗

PubMed2002

The effect of mechanical stability on local vascularization and tissue differentiation in callus healing.

To investigate the influence of the stability of an osteotomy fixation on the local vascularization and tissue differentiation in callus healing, a transverse osteotomy of the right metatarsal with a gap size of 2 mm was performed in 10 sheep and stabilized with an external fixator. This fixator permitted a defined axial movement. Two groups of 5 sheep were each operated upon to allow 0.2 mm (group A) or 1 mm (group B) of axial movement. Nine weeks after surgery, the callus was dissected and histological sections prepared. The type of tissue and the vessel distribution were determined. Larger interfragmentary movements led to significantly more fibrocartilage (small axial movement A: 6.2%, large axial movement B: 21.6%) and significantly less bone formation (A: 38.2%, B: 26.3%). On average, and particularly close to the periosteum the number of vessels in the callus healing area was greater in the group with smaller movements than in the group with larger movements. There was a significant difference between the distribution of small (< 20 microm) and large (> 40 microm) vessels across the whole healing area for both groups. Whereas the large vessels showed maximum density in the medullary cavity, the small vessels showed the highest frequency in the peripheral part of the periosteal callus.

Animals↗