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Biomedical subjects

L Claes

Publications and source records attributed to L Claes.

At least 109 records · Page 6Linked to original sources
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↗
PubMed1997

[Dynamic pedography for assessing functional ankle joint instability].

Chronic functional instability of the lateral ankle may be difficult to distinguish from mechanical instability when radiological stress test reveal only small ligamentous defects. When a decision for or against surgical reconstruction of the ligaments has to be made it can be helpful to use additional information on joint function. Therefore, a prospective study of 65 patients (mean age 24.1 +/- 4.6 years) with long-standing chronic ankle instability was conducted to demonstrate that the dynamic measurement of plantar pressure distribution can identify patients with functional ankle instability. Plantar pressure patterns were measured during gait by means of a capacitive platform, the EMED-SF system. The impulses at eight points of the foot were calculated intraindividually and compared with those in a group of 100 healthy subjects. On the basis of clinical criteria alone, the two groups of patients were distinguished, 35 with functional instability and 30 with mechanical instability. The patients with functional instability showed significantly increased lateral loading of the unstable foot (P = 0.01), whereas the group with mechanical instability tended to walk more on the medial side of the unstable foot. This finding is explained by a deficit or peroneal strength during the stance phase, based on a proprioceptive deficit after trauma. The new technique provides additional information, which is relevant and sufficiently important to help in making decisions about the individual patient with chronic instability.

Adult↗
PubMed1997

[Resorbable bone cements].

Bone cements are used to treat compression fractures, fill bone defects and improve implant fixation in osteoporotic patients through reinforcement of weak bone. When the fracture repair is complete the bone cement ideally should degrade. In general, calcium-phosphate bone cements are biodegradable and can fulfill this temporary function. Several research groups have developed calcium-phosphate bone cements in the last years which have a chemical structure similar to that of the apatite of bone. However the conditions for processing the cement intraoperatively, as well as the mechanical properties and degradation characteristic of the various products show great variations. Clinical long-term studies have not yet been reported so far. Whether these new types of bone cements fulfill all the requirements for clinical application is still not certain and remains to be determined in future studies.

Absorption↗
PubMed1997

Quantitative assessment of experimental fracture repair by peripheral computed tomography.

An experimental fracture model was used to assess bone mineral density at the fracture site by peripheral computed tomography and to compare the model with biomechanical, histological, and radiographic methods for the quantification of the fracture repair process. Transverse osteotomies in the mid-diaphysis of 28 tibia of sheep were externally fixed and mineral densities, cross-sectional areas, flexural rigidities, tissue composition, and projected callus area were calculated after 9 weeks of healing time. BMD measured by pQCT was strongly correlated with histologically determined percentages of mineralized tissue in the osteotomy gap (R = 0.71) and in the periosteal callus (R2 = 0.62). The percentage of mineralized tissue in the osteotomy gap was the best predictor of the flexural rigidity of the tibiae (R2 = 0.74). Because of high correlations with the histological findings, the volumetric BMD at the level of the osteotomy gap was also strongly correlated with the biomechanical findings (R2 = 0.70). Neither the cross-sectional area in pQCT nor the projected callus area in plane film radiography were positively correlated to the flexural rigidity of the tibiae. Quantitative computed tomography proved to be a successful estimator for the prediction of the mechanical stability of healing bones. The noninvasive procedure is a reliable tool for the quantification of the fracture repair process in experimental studies and may be useful for treatment decisions in particular clinical situations.

Animals↗
PubMed1997

Patella position and biomechanical properties of the patellar tendon 1 year after removal of its central third.

OBJECTIVE: The aim of this study was to investigate how the removal of a patellar tendon graft for cruciate ligament reconstruction influences the mechanical properties of the remaining patellar tendon and the position of the patella at the knee joint. DESIGN: The experimental model of this in vivo study was the anterior cruciate ligament reconstruction in sheep. BACKGROUND: While the efficacy of a patellar tendon third as a ligament replacement has been extensively investigated, the consequences for the function of the remaining tendon and patella position remain unclear. METHODS: The central third of the patellar tendon from the right knees of 10 animals was removed for cruciate ligament replacement. One year postoperatively, the position of the patella within the joint and the stiffness and modulus of elasticity of the remaining tendon were compared with the non-operated contralateral controls. RESULTS: The patella position did not change in the operated knee joints in comparison with the controls. The cross-sectional area of the operated patellar tendon increased significantly by scar tissue formation at the defect site. CONCLUSION: Although the inferior mechanical properties of the scar tissue reduced the modulus of, elasticity of the tendon, the increase in cross-sectional area allowed it to develop a structural stiffness similar to the control tendons. RELEVANCE: The central third of the patellar tendon is often used for ligament replacement. Resulting biomechanical and structural changes in the remaining patellar tendon have not been previously reported using an in vivo animal model. The recovery of the biomechanical properties of the partially resected tendons allows for continued function.

Journal Article↗
PubMed1997

Measurement of plantar pressure distribution during gait for diagnosis of functional lateral ankle instability.

INTRODUCTION:: Chronic functional instability of the lateral ankle may be difficult to distinguish from mechanical instability when radiological stress tests reveal only small ligamentous defects. For decision making whether to surgically reconstruct the ligaments or not, it can be helpful to use additional information on joint and foot function. Therefore, the aim of a prospective study of patients with longstanding chronic ankle instability was to demonstrate that the dynamic measurement of plantar pressure distribution can identify patients with functional ankle instability. [Table: see text] MATERIALS AND METHODS:: Sixty five patients (mean age 24 (4.6 years)) were included. After clinical examination and radiological stress views, plantar pressure patterns were measured during gait using a capacitive platform, the EMED-SF 2-system. Five trials of each foot were documented and the maximum impulses in eight points of the foot (central heel, lateral and medial heel, midfoot, 1st, 2nd, 5th metatarsal head and hallux) were calculated intraindividually and compared with a group of 100 healthy subjects. The medio-lateral loading factor (MLF) as the quotient of the medial and lateral relative impulses indicated the tendency to walk on the lateral edge of the foot. RESULTS:: Based on clinical criteria alone, two comparable groups of patients were separated, 35 with functional instability and 30 with mechanical instability. After collective analyses of the results, the patients with functional instability showed a significantly increased lateral loading of the unstable foot (p=0 0 1), whereas the mechanically unstable group tended to walk more on the medial side of the unstable foot (Table 1). DISCUSSION:: Dynamic measurement of plantar pressure can identify a group of patients walking on the lateral side of the unstable foot when compared with the stable foot. This finding is explained by a deficit of peroneal strength during stance phase based on a proprioceptive defect after trauma. The new application of the EMED-system provides additional information which helps to make decisions about the individual patient with chronic instability.

Journal Article↗
PubMed1997

A new composite made of polyurethane and glass ceramic in a loaded implant model: a biomechanical and histological analysis.

The biocompatibility and osseous integration of a new composite material made of polyurethane and a calcium silicophosphate ceramic was investigated in a loaded implant model in sheep and compared to that of commercially pure titanium. Six months after implantation, interfacial shear strength was higher between the titanium and bone than between the composite and bone. After 2 years, however, the shear strength was significantly higher in the composite group. Histologically, both implants were surrounded by bone and fibrous tissue and there were no signs of inflammation. Direct contact of bone on the composite surface increased significantly with time, whereas there was no time-dependent increase of bone contact on titanium. It can be concluded that the biocompatibility and osseous integration of the composite was very good in the loaded implant model used. It is therefore suggested that the new composite is a promising biomaterial for orthopaedic implants.

Journal Article↗