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Biomedical subjects

L Claes

Publications and source records attributed to L Claes.

At least 73 records · Page 4Linked to original sources
PubMed1999

Biomechanical evaluation of a newly developed monocortical expansion screw for use in anterior internal fixation of the cervical spine. In vitro comparison with two established internal fixation systems.

STUDY DESIGN: The primary biomechanical stability of anterior internal fixation of the cervical spine obtained with a new monocortical expansion screw in vitro was evaluated. OBJECTIVES: To determine whether the anterior internal fixation of the spine obtained with the new monocortical expansion screw provides biomechanical stability comparable with that obtained with bicortical fixation. SUMMARY OF BACKGROUND DATA: The anterior plate instrumentation used with bicortical screw fixation in the cervical spine provides a primary stability superior to that associated with monocortical screw fixation. However, bicortical screws have the potential to perforate the posterior cortex. Therefore, monocortical instrumentation systems were developed, but without the biomechanical stability associated with bicortical systems. A new expansion screw for monocortical fixation was developed to improve biomechanical stability of monocortical systems. METHODS: Three different internal fixation systems were compared in this study: 1) H-plate with AO 3.5-mm bicortical screws, 2) cervical spine locking plate with monocortical screws, and 3) H-plate with the new monocortical expansion screws. Eight fresh human cadaver spine segments from C4 to C7 were tested in flexion-extension, axial rotation, and lateral bending using pure moments of +/- 2.5 Nm without axial preload. Five conditions were investigated consecutively: 1) intact spine; 2) uninstrumented spine with the segment C5-C6 destabilized; 3-5) instrumentation of the segment C5-C6 with the three implants mentioned above after removal of the disc and insertion of an interbody spacer. RESULTS: Between bicortical and monocortical expansion screw H-plate fixation, no significant differences were observed in all load cases concerning range of motion and neutral zone. The neutral zone and range of motion were significantly larger for the cervical spine locking plate than for bicortical and monocortical expansion screw fixation in all load cases, except neutral zone for axial rotation versus bicortical screw fixation. The instrumented cases only had a significantly lower range of motion and neutral zone than the intact cases in extension-flexion, whereas for lateral bending and axial rotation no significant differences could be observed. Because the experimental design precluded any cyclic testing, the data represent only the primary stability of the implants. CONCLUSIONS: In anterior instrumentation of the cervical spine using a H-plate, the new monocortical expansion screw provides the same biomechanical stability as the bicortical 3.5-mm AO screw and a significantly better biomechanical stability than the cervical spine locking plate. Therefore, the expansion screw may be an alternative to the bicortical fixation and does not involve the risk of penetration of the posterior vertebral body cortex.

Aged↗
PubMed1999

A new radiolucent system for vertebral body replacement: its stability in comparison to other systems.

Anterior intervention of metastatic lesions of the spine can accomplish relief of pain, spinal decompression, and restoration of spinal stability. Ventral vertebral body replacements have been developed to provide these conditions but there have been problems with loosening at the implant-bone interface, mechanical failure, and X-ray artifacts from the metal. Intraoperative stability of the vertebral body replacement is especially critical to avoid loosening of the implant and to achieve long-term bony incorporation. This study compared the biomechanical performance in vitro of a new radiolucent system for vertebral body replacement to three currently marketed systems. The new system features a composite bioglass-polyurethane body and a new configuration of polymeric fastening hardware. Range of motion, neutral zone, and several interfacial motion parameters were measured under pure moments of 3.75 Nm in the three anatomical directions. The new system provided the significantly highest restraint of motion for all parameters. Mechanically, the new system is preferable at least initially to a sampling of systems representative of those currently used.

Artifacts↗
PubMed1999

Cell orientation induced by extracellular signals.

Cells like fibroblasts and osteoblasts are oriented by different extracellular guiding signals like an electric field, a bent surface, and a periodically stretched surface. An automatic controller is responsible for the cell alignment. The controller contains both a deterministic and a stochastic signal. The following machine properties were determined: (1) The angle dependence of the cellular signal transformer is cos 2(psi 0 - psi). (2) The set point of the automatic controller is psi 0 = +/- 90 degrees. The cells like to orient their long axis perpendicular to the direction of the applied guiding signal. (3) The signal transformer measures the extracellular signal in a quadratic fashion. The cells cannot register the sign of the guiding field. (4) The stochastic signal in the automatic controller can be quantified by a characteristic time (approximately 130 min for fibroblasts). (5) The extracellular signal is registered in cell-made standards (ratio of the deterministic and stochastic signal equals one): 0.3 +/- 0.05 V/mm for human fibroblasts (electric field) and 85 +/- 3 microns for human fibroblasts and osteoblasts (cyclindrically bent surface). (6) The lag-time in the signal transduction system of fibroblasts is approximately 4 min.

Cell Polarity↗
PubMed1999

[Preparing a manuscript for publication in a scientific journal].

Nowadays scientific publishing in peer reviewed international accepted journals is not easy. Rejection rates up to 75% occur. The aim of this paper is to provide guidance in the preparation of journal papers for the inexperienced scientific writer. The traditional paragraphs Abstract, Introduction, Material and Methods, Results, and Discussion are described with respect to its contents and basic message and how these sections are designed to build a logical flow. Approved suggestions for the structural outline of each paragraph are made. The significance of reference list, figures, and tables is also explained. The review of a manuscript is discussed and the criterias for acceptance of a journal paper are indicated.

Authorship↗
PubMed1999

[Sonographic imaging of leg geometry].

Posttraumatic malalignments are a frequent sequlae of IM nailing of lower extremity fractures. Conventional US has proven to be inferior to CT determinations of tibial or femural length and torsion. A new 3-D US method is presented that allows for accurate single step determination of lower extremity length and torsion without ionizing radiation. A regular US machine with a 5 Mhz linear probe is combined with an US localizer. Reference markers affixed to the lower extremity eliminate errors associated with patient position or motion. The 3-D US method was compared against CT (Ulm's method) in the measurement of torsion and length of the tibia and femur in 50 adults and 50 children. In both methods, the maximum difference of the intraindividual torsional angles and length measurements was 7 degrees and 7 mm. The maximum standard deviation for reproducibility in length measurement was 1.6 mm and 1.5 degrees for angular torsion. The new 3-D US technique was superior to CT in terms of reliability and reproducibility. Clinical advantages of the 3-D US technique include rapidity, independence from patient motion or positioning and the avoidance of ionizing radiation. Indications for 3-D torsional and length determinations include follow-up evaluation of adult and pediatric tibial and femoral fractures, pediatric limb and gait evaluations, and osteotomy planning.

Adolescent↗
PubMed1999

Characteristics of an extended internal fixation system for polysegmental transpedicular reduction and stabilization of the thoracic, lumbar, and lumbosacral spine.

The Kluger internal fixator, with its artificial fulcrum outside the operative site, had to be extended for multisegmental use. Three different prototypes, called Central Bar (CB), Double Bar I (DB I) and Double Bar II (DB II) were designed, which were fully compatible with the existing reduction system. To evaluate the ability of these newly developed systems to provide primary stability in a destabilized spine, their stiffness characteristics and stabilizing effects were investigated in multidirectional biomechanical stability tests and compared with those of the clinically well-known Cotrel-Dubousset (CD) system. The investigations were performed on a spine tester using freshly prepared calf spines. The model tested was that of an intact straight spine followed by a defined three-column lesion simulating the most destabilizing type of injury. Pure moments of up to 7.5 Nm were continuously applied to the top of each specimen in flexion/extension, left/right axial rotation, and left/right lateral bending. Segmental motion was measured using a three-dimensional goniometric linkage system. Range of motion and stiffness within the neutral zone were calculated from obtained load-displacement curves. The DB II attained 112.5% (P = 0.26) of the absolute stiffness of the CD system in flexion and enhanced its stability in extension by up to 144.3% (P = 0.004). In axial rotation of the completely destabilized spine, this system achieved 183.3% of the stiffness of the CD system (P < 0.001), and in lateral bending no motion was measured in the most injured specimens stabilized by the DB II. The DB I, which was the first to be designed and was considered to provide high biomechanical stability, did not attain the stiffness standard set by the CD system in either flexion/extension or axial rotation of the most injured spine. The study confirms that it is worthwhile to evaluate in vitro the biomechanical properties of a newly developed implant before its use in patients, in order to refine weak construction points and help to reduce device-related complications and to better evaluate its efficacy in stabilizing the spine.

Animals↗
PubMed1999

Evaluation of a new monocortical screw for anterior cervical fusion and plating by a combined biomechanical and clinical study.

The purpose of this combined study was to evaluate the stability and safety of a new monocortical screw-plate system for anterior cervical fusion and plating (ACFP) according to Caspar in comparison with classical bicortical fixation. In the biomechanical part of the study two groups, each comprising six fresh human cadaveric spines (C4-C7), matched for bone mineral density, additionally resulting in almost the same mean age, were used. Range of motion and neutral zone were analyzed in flexion-extension, rotation (left, right) and lateral bending (left, right) using pure moments of +/- 2.5 Nm for each specimen in the intact state, after discectomy at C5/6 and after discectomy at C 5/6 followed by bone grafting plus plating (Caspar plates), with either monocortical or bicortical screws. For all three motion planes, no significant difference could be found between the new monocortical and the bicortical fixation techniques. The clinical part of the study was performed as a prospective study on 30 patients suffering from symptomatic degenerative cervical disc disease in one segment. At the latest follow-up, no hardware- or graft-related complications were seen in any of the patients. Following these findings monocortical screw fixation can be recommended for the majority of anterior cervical fusion and plating procedures in degenerative disease, making the procedure quicker, easier, and safer. Bicortical screw fixation still has specific indications for multilevel stabilization, poor bone quality (osteoporosis, rheumatoid disease - as bicortical oversized rescue screw), unstable spines (trauma, tumour) and in particular for the realignment of kyphotic deformities (restoration of the normal lordotic curve). Due to the design of the study the results apply only to surgical treatment of monosegmental degenerative disc disease at the time.

Adult↗
PubMed1999

Fixation technique influences osteogenesis of comminuted fractures.

Comminuted fractures most often are associated with compromised soft tissue conditions and diminished vascularization leading to a reduced osteogenesis. In contrast to stable fixation by compression plating with lag screws, the less stable but also less invasive techniques of external fixation, unreamed nailing, or bridging plates have become increasingly popular. The aim of this study was to compare the bone healing and osteogenesis of these fixation techniques. A triple wedge osteotomy of the sheep tibia was used as a bone healing model. Internal compression plate fixation of all fragments with lag screws was used in one group. In the other three groups, only the main proximal and distal fragments were fixed by external fixation, unreamed interlocking nail, or bridging plate. The sheep with compression plate fixation and lag screws showed the worst results after 12 weeks. The periosteal and endosteal osteogenesis and the apparent density of the newly formed bone in the fracture gaps were significantly lower than those seen in the sheep in the other three technique groups. The best results were found for the bridging plate and external fixator. From these results, it can be concluded that compression plate fixation should be avoided for treatment of comminuted fractures.

Animals↗
PubMed1999

Clinical and functional outcome after anatomic and nonanatomic ankle ligament reconstruction: Evans tenodesis versus periosteal flap.

The present study investigated the effects of two different surgical procedures for the treatment of chronic ankle instability. Ten patients treated with an anatomic reconstruction using a periosteal flap were compared with a second group that received an Evans tenodesis. All patients were evaluated before and after surgery with clinical and radiographic examinations as well as dynamic pedobarography. Patient satisfaction and radiographic and functional results were comparable in both groups and revealed a good restoration of joint stability and gait symmetry. Our results indicate that both methods of ankle ligament reconstruction achieve a comparable clinical and functional outcome within 1 year after surgery.

Adult↗
PubMed1998

Local tissue properties in bone healing: influence of size and stability of the osteotomy gap.

To characterize the site-specific mechanical and histological properties in fracture repair and to relate these properties to the initial mechanical situation, an experimental fracture model was used in the metatarsus of 42 sheep. The mechanical situation of a transverse osteotomy was described by three gap sizes (1, 2, or 6 mm) and two amounts of strain (7 or 31%). An external fixator that allowed a defined axial movement provided control of these settings. Nine weeks following surgery, the healing area was dissected and tensile and compressive properties were measured in subregions of the fracture gap and the periosteal callus. The central, sagittal section was used for quantitative histology. We found the quality of the tissue along the osteotomy line to be most important for regaining mechanical stability. Increasing the size of osteotomy gaps resulted in poorer mechanical and histological qualities, and the repair process was less complete. Interfragmentary strain did not significantly influence the repair process. The smaller strain levels had already stimulated the secondary repair process, and this stimulatory effect could not be further enhanced by increasing the amount of strain. Our finding that large gaps between bone segments were not as well healed as were smaller gaps suggests that it is advantageous to avoid large gaps in fracture treatment.

Animals↗
PubMed1998

[Possibilities for static and dynamic stabilization of the spine in lesions of the anterior and posterior ligament complex].

Defects of the dorsal and ventral ligament complexes of the lumbar spine results to an instability of the functional spinal unit. For the prognosis of secondary instability due to disko-ligamentous injuries the functional insufficiency of the lasting scars is a larger problem than the primary loss of osseous stability with fast healing tendency. The main goal of the present biomechanical study in vitro was to demonstrate the different grades of instability in the correlation to progressive disko-ligamentous defects as well as stabilisation through dynamic and static procedures. With a transpedicular screw-ringband-system the segmental function was preserved and instability was abolished. After rigid instrumentation with a fixateur intern remained a residual range of motion due to which can result refuse to bending moments without spondylodesis in an implant failure.

Adult↗
PubMed1998

Testing criteria for spinal implants: recommendations for the standardization of in vitro stability testing of spinal implants.

New implants and new surgical approaches should be tested in vitro for primary stability in standardized laboratory tests in order to decide the most appropriate approach before being accepted for clinical use. Due to the complex and still unknown loading of the spine in vivo a variety of different test loading conditions have been used, making comparison of the results from different groups almost impossible. This recommendation was developed in a series of workshops with research scientists, orthopedic and trauma surgeons, and research and development executives from spinal implant companies. The purpose was to agree on in vitro testing conditions that would allow results from various research groups to be compared. This paper describes the recommended loading methods, specimen conditions, and analysis parameters resulting from these workshops.

Biomechanical Phenomena↗
PubMed1998

Laminectomy and functional impairment of the lumbar spine: the importance of muscle forces in flexible and rigid instrumented stabilization--a biomechanical study in vitro.

Laminectomy is the accepted treatment for spinal canal stenosis in cases where conservative treatment has failed. Opinions diverge on the resulting clinical instability and the necessity of instrumented stabilization. The present biomechanical study was performed to determine the functional impairment following laminectomy and the stabilizing effect of flexible and rigid devices. This was the first time that the effects of agonist and antagonist intersegmental lumbar muscle forces acting on intact, unstable and instrumentally stabilized functional spinal units have been investigated. Six human cadaveric lumbar spines were tested in a spine tester. The coactivation of agonist and antagonist muscle forces resulted in increased stability under the load conditions of bending and rotation; a slight increase in the range of motion was noted during flexion. The functional impairment following laminectomy was corrected by ligamentoplasty and by means of muscle forces. Ligamentoplasty appears to be an alternative to decompression with spondylodesis, especially in patients with well-developed muscles.

Biomechanical Phenomena↗
PubMed1998

A method to determine the 3-D stiffness of fracture fixation devices and its application to predict inter-fragmentary movement.

Inter-fragmentary movement considerably influences the fracture healing process. Large shear movement delays while moderate axial movement stimulates the healing process. To be able to control the mechanical situation at a fracture site and to achieve optimal bony healing it is essential to understand the relationship between inter-fragmentary movement, bony loading and fixation stiffness. A 6 x 6 stiffness matrix is introduced which completely describes the linear relationship between the 6 inter-fragmentary movements and the resulting bony loading (3 forces and 3 moments). Further, it is illustrated that even in relatively stiff external fixateur constructs simple axial loading of the bony fragments leads to complex inter-fragmentary movement. When the 3-D stiffness description is multiplied by the load state in sheep tibiae, movements similar to those measured in vivo are calculated. The relationship between axial compression and medio-lateral or dorso-ventral shear varies depending on the mounting plane of the external fixateur. The authors conclude that a single value is not sufficient to describe the mechanical relationship between inter-fragmentary movement and bony loading. Only a complete description of fixation stiffness allows prediction of inter-fragmentary movement and differentiation between various configurations of fixation devices and their potential for mechanically promoting bony healing.

Animals↗
PubMed1998

Analysis of inter-fragmentary movement as a function of musculoskeletal loading conditions in sheep.

It is well accepted that inter-fragmentary movement influences the fracture healing process. Small axial movement can stimulate callus formation whereas larger shear movement delays the healing process. It is, therefore, essential for optimal fracture healing to minimize shear and to control axial movement. Unfortunately, the complex gap movements are mostly unknown under the large variety of clinical as well as experimental conditions of fracture fixation. To further understand the complex interactions of musculoskeletal loading and inter-fragmentary movements in bones and to reduce the need for animal experiments, a three-dimensional (3D) musculoskeletal model of the left hind limb of a sheep was developed. From 3D ground reaction forces and inverse dynamics, resultant joint loading was determined over a gait cycle. Muscle and joint contact forces were derived from an optimization routine and internal loads in the tibia and metatarsus from beam theory. Finally, inter-fragmentary movements were calculated from the bony loading condition and experimentally determined stiffness matrices of monolateral AISF external fixator constructs. Both the joint contact forces at the hip and gap movement of a mid-shaft tibial fracture agree with in vivo data reported in the literature. The bones proved to be mainly axially loaded with slightly increasing shear forces toward their ends. The results suggest that inter-fragmentary movement of metatarsal fractures is fairly independent of the fracture location whereas the movement increases in proximal tibial fractures compared to those in the distal and diaphyseal tibia. Considerable shear movement was found for all locations and external fixator mountings. However, shear movement could be minimized with a cranio-lateral rather than a cranio-medial shift from the cranial fixator plane.

Animals↗
PubMed1998

Influence of muscle forces on femoral strain distribution.

Musculoskeletal loading influences the stresses and strains within the human femur and thereby affects the processes of bone modeling and remodeling. It is essential for implant design and simulations of bone modeling processes to identify locally high or low strain values which may lead to bone resorption and thereby affect the clinical outcome. Using a finite element model the stresses and strains of a femur with all thigh muscle and joint contact forces were calculated for four phases of a gait cycle. Reduced load sets with only a few major muscles were analyzed alternatively. In a completely balanced femur with all thigh muscles the stress and strain patterns are characterized by combined bending and torsion throughout the bone. Similar to in vivo recordings, the model with all thigh muscles showed peak surface strains below 2000 mu epsilon (45% gait cycle). Under simplified load regimes surface strains reached values close to 3000 mu epsilon. Within the proximal femur, the simplified load regimes produced differences in strain as high as 26% in comparison to those with all thigh muscles included. This difference is reduced to 5% if the adductors are added to a loading consisting of hip contact, abductors and ilio-tibial band. This study demonstrates the importance of an ensemble of muscle forces to reproduce a physiological strain distribution in the femur. Analytical attempts to simulate bone modeling, remodeling or bone density distributions should therefore rely on fully balanced external load regimes which account for the role of the various soft tissue forces.

Biomechanical Phenomena↗
PubMed1997

Influence of size and stability of the osteotomy gap on the success of fracture healing.

Flexible fixation of fractures with minimally invasive surgical techniques has become increasingly popular. Such techniques can lead to relatively large fracture gaps (larger than 5 mm) and considerable interfragmentary movements (0.2-5 mm). We investigated the influence of the size of the fracture gap, interfragmentary movement, and interfragmentary strain on the quality of fracture healing. A simple diaphyseal long-bone fracture was modeled by means of a transverse osteotomy of the right metatarsus in sheep. In 42 sheep, the metatarsus was stabilized with a custom-made external ring fixator that was adjustable for gap size and axial interfragmentary movement. The sheep were randomly divided into six groups with three different gap sizes (1, 2, or 6 mm) and small or large interfragmentary strain (approximately 7 or 31%). The movement of the fracture gap was monitored telemetrically by a displacement transducer attached to the fixator. After 9 weeks of healing, the explanted metatarsus was evaluated mechanically in a three-point bending test to determine bending stiffness and was radiographed to measure the amount of periosteal callus formation. Increased size of the gap (from 1 to 6 mm) resulted in a significant reduction in the bending stiffness of the healed bones. Larger interfragmentary movements and strains (31 compared with 7%) stimulated larger callus formation for small gaps (1-2 mm) but not for larger gaps (approximately 6 mm). The treatment of simple diaphyseal fractures with flexible fixation can be improved by careful reduction of the fracture; this prevents large interfragmentary gaps. The experimental fracture model for the metatarsus showed that the healing process was inferior when the gap was larger than 2 mm.

Animals↗