Biomedical subjects

L Claes

Publications and source records attributed to L Claes.

At least 127 records · Page 7Linked to original sources

PubMed1997

Acutely repaired proximal anterior cruciate ligament ruptures in sheep - by augmentation improved stability and reduction of cartilage damage.

The aim of this study was to evaluate the healing capacity of proximal anterior cruciate ligament (ACL) ruptures following primary repair with and without a bioresorbable augmentation. The ACL was transected at the femoral origin in the right knee joint of 24 sheep. The ACL was repaired in eight sheep (group B) without, and in eight sheep (group C) with a bioresorbable augmentation. Eight sheep without repair served as a control (group A). No immobilization was performed in any group. The sheep were sacrificed 13 weeks post-operatively. Macroscopically, all repaired ACLs were healed. The augmentation device was broken in all cases, but not completely degraded. In group A, none of the transected ACLs had healed. The anterior drawer under a load of 50 N was significantly lower in group C than in group A (p<0.01). No significant difference was seen between groups B and A. The distribution and extent of chondromalacia (CM) in the operated knees depended on the type of operative treatment (p<0.01). Groups A and B showed significantly more CM in the operated knee than in the non-operated knee (each p<0.05). Proximal ACL ruptures can heal in sheep after both non-augmented and augmented ACL repair with free-functional rehabilitation. However, augmented repair leads to significantly better stability of the knee joint compared to transected controls and better limits the development of degenerative changes.

Journal Article↗

PubMed1997

Functional evaluation of the 10-year outcome after modified Evans repair for chronic ankle instability.

The Evans tenodesis is an operative treatment for chronic ankle instability with good short-term results. The disadvantage of impaired hind foot kinematics and restricted motion has been described, and only few reports of long-term results can be found. No techniques have been used to assess the outcome objectively. We wanted to determine whether a modified Evans procedure led to a satisfactory clinical and functional outcome. Nineteen patients were available at a 10-year follow-up. The clinical examination included a detailed questionnaire and stress radiographs. Foot function was evaluated with plantar pressure distribution measurements during walking and peroneal reaction time measurements elicited on a rapidly tilting platform (recorded with surface electromyography). High subjective patient satisfaction was contrasted with a high rate of residual instability, pain, and swelling. The radiographs showed an increased number of exostoses. The gait analysis revealed reduced peak pressures under the lateral heel and increased values under the longitudinal arch. The reaction times of the peroneal muscles were shorter on the operated side (significant: peroneus longus). The persistent clinical problems as well as the functional changes indicate that the disturbed ankle joint kinematics permanently alter foot function and may subsequently support the development of arthrosis. Therefore, the Evans procedure should only be applied if anatomical reconstruction of the lateral ankle ligaments is not feasible.

Adult↗

PubMed1997

A cell strain system for small homogeneous strain applications.

A cell culture system has been developed that enables application of well characterized, homogeneously distributed cyclic strains to monolayer cell cultures. Optically clear silicone culture dishes atop Plexiglas base plates are deformed by four-point bending of flexible silicone culture wells driven in user specified strain cycle patterns using computer controlled electromagnetic linear actuators. Cyclic mechano-transduction can be induced in amplitudes of 0 to 3000 mustrain, in frequencies of 0 to 30 Hz and in any specified strain cycle pattern. The cell culture system, which contains six simultaneously driven culture wells, has been mechanically characterized by holographic interferometry, laser displacement sensor recordings of the dish surfaces, strain gauge monitoring of the base plates, and finite element modeling of the dishes on the base plates. The standard deviation of the strain amplitudes among the six simultaneously stimulated culture wells is less than 5%. The cell culture system allows accurate generation of small magnitudes of well characterized, homogeneous strain, easy handling of the culture wells, flexible setting of cyclic strain pattern parameters, simultaneous stimulation of 6 culture wells, and light microscopic observation of the cell cultures.

Animals↗

PubMed1996

Biomechanical comparison of calf and human spines.

Given the limited availability of human cadaveric specimens and their potential risk of infection, calf spines have been used as substitutes for human spines in the evaluation of spinal implants. Few biomechanical data comparing calf and human spines are available, however. The purpose of this study was to determine the biomechanical properties of the calf spine and to compare them with properties previously reported for the human spine. We determined the range of motion neutral zone, and stiffness of thoracic and lumbar calf spines (T6 to L6) under pure moment loading in flexion-extension, axial rotation, and lateral bending. These properties were shown to be similar to those of the human spine. The results suggest that the calf spine can be used as a substitute for the human spine in some in vitro tests.

Animals↗

PubMed1996

Calcaneal fractures cause a lateral load shift in Chopart joint contact stress and plantar pressure pattern in vitro.

In order to evaluate the effects of the anatomical changes after calcaneal fractures on joint loading characteristics we investigated the effects of simulated calcaneal fractures on intra-articular loading in the Chopart joint and on plantar pressure patterns in vitro. Five fresh-frozen lower leg specimens were axially loaded with 500 N in three positions: neutral, 10 degrees plantarflexion and 10 degrees dorsiflexion. The loading characteristics were determined before and after creating a tongue-type fracture by osteotomy. Plantar loading patterns were measured with a capacitive pressure distribution platform. Intra-articular contact areas and pressures were recorded on pressure sensitive film introduced into the talonavicular and calcaneocuboid joint. Increased loading in the calcaneocuboid joint (+25%,p = 0.005) and decreased loading in the talonavicular joint (-16%,p = 0.01) corresponded to increased loading of the lateral aspects of the plantar surface. These findings were independent of the foot position. The results suggest that the effects of increased lateral foot loading which have been observed in calcaneal fracture patients (Rosenbaum et al., Clin. Biomech. 10, 345-351, 1995) are caused by changes in joint kinematics and do not appear to result from a protective gait pattern established after the injury.

Adult↗

PubMed1996

Comparative animal study of three ligament prostheses for the replacement of the anterior cruciate and medial collateral ligament.

Three different ligament prostheses (Leeds-Keio, Gore-Tex and a prototype of Aramid) were implanted in sheep knee joints replacing the anterior cruciate ligament and the medial collateral ligament. After 1 yr the knees were explanted and their biomechanical properties were assessed by a drawer test and tensile tests of the implants. Additionally the ligament replacements, the synovial membrane and the lymph nodes were inspected histologically. For each type of prosthesis partial or total ruptures occurred. None of the operated joints regained normal stability and stiffness. Anterior knee stability was best for the Gore-Tex treated group and worst for those joints that received a Leeds-Keio implant. The stiffness and rupture strength were highest for the Gore-Tex prostheses. Histologically the strongest intra-articular inflammatory response was observed in the Gore-Tex treated joints. Inside the drill tunnels the severest foreign body reaction was found for the Aramid prostheses. Gore-Tex fibres often showed good bony integration. Wear particles formed from all prostheses and caused small granulomas and mild synovities. The results suggest that none of the tested materials represent an ideal solution for ligament replacement. Relatively good stability does not guarantee good biocompatibility and vice versa. This suggests that ligament prostheses should be applied only in salvage cases.

Animals↗

PubMed1996

[Functional deficits of the foot after calcaneus fracture].

The present study investigated the clinical and functional outcome of calcaneal fractures. 14 patients were evaluated at a mean follow-up of 52 months. Two groups, group A with good and group B with poor calcaneal restoration were distinguished by Böhler's angle. Ten normal subjects were used for comparison. Clinical results were evaluated with a questionnaire, radiography and range of motion measurements. Plantar pressure patterns were recorded with a capacitive pressure distribution platform. A comparison of the injured and healthy foot of all patients revealed a load shift towards lateral foot regions. A comparison of the patient groups with the controls did not reveal more pronounced changes in the poorly restored group. The results demonstrate that a disturbance of foot function persists even after long healing.

Adult↗

PubMed1996

Tenodesis versus carbon fiber repair of ankle ligaments: a clinical comparison.

To compare the clinical and functional outcomes after using different reconstruction methods for chronic ankle instability, the authors followed 2 groups of patients after 69 and 72 months, respectively. Thirty patients (mean age, 28; range, 23-39 years) were treated with modified Evans tenodesis. Twenty-three patients (mean age, 32.2; range, 22-39 years) underwent total replacement of the lateral ankle ligaments by carbon fibers. The protocol of the retrospective study included a questionnaire, clinical examination, radiographic stress diagnostics, and gait analysis with use of the EMED-SF system. Dorsiflexion and inversion were significantly restricted after tenodesis in contrast to the carbon fiber replacement. Although radiographic stability was improved after surgery for both groups, progress of the arthrosis could not be stopped. After tenodesis, the measurement of plantar pressure distribution revealed a 20% increase of midfoot loading as compared with the opposite foot, whereas symmetrical loading of both feet was found after carbon fiber replacement. Additionally, the tenodesis feet had a significantly increased loading of the medial side of the foot. It was concluded that tenodesis and anatomic reconstruction of ankle ligaments lead to subjectively similar results. Foot function and range of motion, however, were less influenced after anatomic repair.

Adult↗

PubMed1996

Early, full weightbearing with flexible fixation delays fracture healing.

Secondary fracture healing is known to be accelerated by the process of periosteal callus formation that can be induced by flexible fracture fixation in connection with loading of the injured extremity. The purpose of this study was to compare the healing of experimental fractures of long bones in sheep under early weightbearing with that of fractures under delayed, steadily increasing weightbearing. Differences in the quality of fracture healing were described by biomechanical (rigidity of fracture, indentation stiffness of callus) and histologic methods. Prevention from early, full weightbearing resulted in a higher flexural rigidity of the fracture, an increased mechanical stiffness of the callus tissue, and an enhanced bone formation at the healing front. Although early loading of a fresh fracture initiated an enormous amount of periosteal callus, the healing of the osteotomy was significantly delayed, and the quality of the newly formed tissue was reduced as compared with fractures with a reduced loading situation. A reduction of load transfer by delaying full weightbearing is advantageous for the healing of fractures stabilized with flexible fixation systems.

Animals↗

PubMed1996

[Foot stress simulator for biomechanical in vitro studies of lower leg segments].

In this paper we describe a foot-loading simulator that permits in vitro studies on human lower leg and foot specimens. The specimens are fixed in a jig and loaded axially with the aid of a pneumatic cylinder. The resulting transfer of forces through the ankle joint complex and Chopart's articulation (line) can be demonstrated on a pressure-sensitive film. Plantar pressure measurements obtained in patients or normal subjects can be used to ensure the comparability of in vivo and in vitro measurements. The supporting platform can be tilted in such a manner as to provide a range of foot positions up to 20 degrees in plantar- or dorsiflexion, eversion or inversion. The system is used for investigating the effects on the intra-articular pressures and plantar pressure patterns of physiological muscle activity and pathological conditions following fracture of the calcaneum or damage to the lateral ligament. By way of an example, the effects of muscle forces on plantar pressure distribution are presented.

Ankle Joint↗

PubMed1996

Long-term results of the modified Evans repair for chronic ankle instability.

We treated 19 patients for chronic ankle instability with a modified Evans procedure. All patients were evaluated after an average follow up of 128 months with detailed questionnaire, clinical examination, and stress radiographs. Although the subjective results were reported as 8 excellent, 7 good, and 4 fair, residual pain was reported by 11 patients. There was a significantly increased number of osteophytes in the treated ankle joint. Stress radiographs demonstrated significantly improved stability in the operated ankle joint. Range of motion was significantly reduced in hindfoot inversion. The results showed that the modified Evans procedure achieved sufficient joint stability at the expense of inversion range of motion. This reconstruction method apparently did not prevent the development of arthrosis.

Adult↗

PubMed1995

Increase of stability in external fracture fixation by hydroxyapatite-coated bone screws.

A major problem in fracture treatment by external fixation is screw loosening, which often results in reduced stability and can lead to prolonged treatment. A load-carrying experiment was conducted to determine whether coating implants with bioactive hydroxyapatite (HA) increases screw stability. Twelve HA-coated ASIF screws with 3 different macroporosities were inserted in 12 sheep that had already been fitted with a 6-pin external fixator for the treatment of a tibial osteotomy. The same number of uncoated polished steel screws served as controls. Although initial stability was not different for HA-coated screws, average removal torque after a 9-week implantation period increased with increasing macroporosity of the HA coating (p < .002). Instability of some screws was accompanied by histologic findings of cartilagenous tissue and proliferation of periosteal callus. Near the threads in the tibial cortex and in the shaft area of the screw were seen large numbers of HA particles that had been sheared off during implantation as well as during screw removal because of high contact forces between the HA coating and bone. Particulate debris of HA particles as well as the release of small bone fragments during explanation is likely to be unavoidable since HA adherence to bone is greater than adherence to steel after several weeks of implantation.

Animals↗

PubMed1995

Ilizarov callus distraction produces systemic bone cell mitogens.

We tested the hypothesis that the application of strain during callus distraction induces systemic osteoblast stimulating factors that enhance osteoblast activity both locally and systemically. To study the systemic occurence of strain-induced osteoblast stimulating factor during callus distraction, we investigated the mitogenic capacity of sera from 12 patients who had undergone callus distraction on the osteoblastic cell line SaOS-2 (part I). Serum samples from six patients who had undergone rigidly fixed high tibial osteotomy (i.e., without distraction) served as controls. The sera were assayed for platelet-derived growth factor and transforming growth factor-beta. In part II of the study, the in vitro effects of mechanical strain were investigated in a simplified model by cyclic stimulation of osteoblast cultures isolated from cortical bone explants from the same patients; a specially developed apparatus was used for cell-stretching. Sera taken during the third to fourth week of callus distraction demonstrated a significant increase in proliferation of SaOS-2 cells (p < 0.005). In contrast, sera from patients who had had an osteotomy failed to induce or decreased the mitogenic capacity of SaOS-2 cells. The concentration of platelet-derived growth factor increased significantly (p < 0.01) in sera from both the patients who had undergone callus distraction and the controls who had had osteotomy. However, the level of transforming growth factor-beta was increased (p < 0.05) in the sera from the patients who had distraction (sera that stimulated proliferation of SaOS-2 cells), but the level was not increased in the sera from patients who had osteotomy.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1995

Human osteoblasts from younger normal and osteoporotic donors show differences in proliferation and TGF beta-release in response to cyclic strain.

Mechanical stimulation of bone tissue by physical activity stimulates bone formation in normal bone and may attenuate bone loss of osteoporotic patients. However, altered responsiveness of osteoblasts in osteoporotic bone to mechanical stimuli may contribute to osteoporotic bone involution. The purpose of the present study was to investigate whether osteoblasts from osteoporotic patients and normal donors show differences in proliferation and TGF beta production in responses to cyclic strain. Human osteoblasts isolated from collagenase-treated bone explants of 10 osteoporotic patients (average age 70 +/- 6 yr) and 8 normal donors (average age 54 +/- 10 yr) were plated into elastic rectangular silicone dishes. Subconfluent cultures were stimulated by cyclic strain (1%, 1 Hz) in electromechanical cell stretching apparatus at three consecutive days for each 30 min. The cultures were assayed for proliferation, alkaline phosphatase activity and TGF beta release in each three parallel cultures. In all experiments, osteoblasts grown in the same elastic dishes but without mechanical stimulation served as controls. Significant differences between stimulated cultures and unstimulated controls were determined by a paired two-tailed Wilcoxon test. In comparison to the unstimulated controls, osteoblasts from normal donors significantly increased proliferation (p = 0.025) and TGF beta secretion (p = 0.009) into the conditioned culture medium. In contrast, osteoblasts from osteoporotic donors failed to increase both proliferation (p > 0.05) and TGF beta release (p > 0.05) in response to cyclic strain. Alkaline phosphatase activity was not significantly affected (p > 0.05) in normal as well as osteoporotic bone derived osteoblasts. These findings suggest a different responsiveness to 1% cyclic strain of osteoblasts isolated from normal and osteoporotic bone that could be influenced by both the disease of osteoporosis and the higher average age of the osteoporotic patient group. While osteoblasts from osteoporotic donors failed to increase proliferation and TGF beta release under the chosen mechanical strain regimen that stimulated both parameters in normal osteoblasts, it is possible that some other strain regimen would provide more effective stimulation of osteoporotic cells.

Age Factors↗

PubMed1995

Long-term effects of hindfoot fractures evaluated by means of plantar pressure analyses.

The present study investigated the long-term effects of calcaneal fractures on the plantar pressure distribution during human gait. Fourteen patients participated in a follow-up study and were assigned to a group with good or poor calceneus restoration as indicated by normal or reduced Böhler's angle. Ten normal subjects with similar anthropometric characteristics were used for comparison. Gait analysis was performed by means of a capacitive pressure distribution platform. A comparison of the injured with the healthy foot of all patients revealed a statistically significant peak pressure decrease under medial areas of the foot (first metatarsal -24%) and an increase in lateral areas (midfoot +135%, fifth metatarsal +122%). This load shift towards a lateral loading indicates a persisting deviation of the gait pattern long after healing. Furthermore we investigated whether the success of the restoration of hindfoot geometry as reflected in Böhler's angle had an effect on the foot loading characteristics. Therefore we compared the gait patterns of the two patient groups with the normal subjects. However, the results did not reveal more abnormal pressure patterns in the poorly reduced group. RELEVANCE:--The restoration of the shape of the calcaneus with joint surface congruity and reconstruction of Böhler's angle appears generally accepted as a major aim in the treatment of calcaneal fractures. While this goal can usually be achieved by contemporary surgical techniques, the restoration of foot function under dynamic loading conditions is not guaranteed and should be assessed objectively. The investigation of the foot loading characteristics by means of plantar pressure measurements can be used to support the evaluation of the patient's recovery after trauma.

Journal Article↗

PubMed1995

In vivo effect of shock-waves on the healing of fractured bone.

In a controlled animal experiment we attempted to clarify the question of whether there is a stimulating effect of extracorporeal shock-waves on the repair process of fractured long bones. As a fracture model we used an osteotomy in the diaphysis of the ovine tibia and an external fixation device. Shock-wave treatment at two levels of intensity and with four different numbers of applied shocks was performed with an electromagnetic acoustic source. Healing of the osteotomized bone was evaluated by biomechanical and radiological investigations on the whole bone as well as on bone sections from areas of the fracture gap and the periosteal fracture callus. We found a non-significant tendency to deterioration of the fracture healing with increasing shock-wave intensities. The study of treatment parameters led neither to significantly different biomechanical outcomes nor to altered radiological results in comparison to the untreated control group. RELEVANCE:--While we cannot comment upon the effectiveness of extracorporeal shock-waves in the delayed treatment of fractures or pseudarthrosis, our results suggest that shock-waves have no beneficial effect in acute fracture repair.

Journal Article↗

PubMed1995

Influence of water temperature on pressure pulses generated by an electromagnetic type lithotripter.

The need to survey and compare in vitro investigations on the effect of extracorporeally generated pressure pulses demands precise description of experimental conditions. We determined the effect of water temperature on the pressure characteristics in and around the focus area of an electromagnetic type lithotripter. The peak pressure amplitude at the geometrical focus of the lens was reduced to 60% of the original peak pressure if water at room temperature was used instead of water with human body temperature. By decreasing the temperature of the lithotripter's internal water, we observed shifting of the focus point at a rate of 1.4 mm per degree. This dramatic reduction of the peak pressure and the shifting of the focus point resulting from changes in the acoustic and thermal parameters of the propagation medium and of the focusing device could lead to differences of up to 80% of peak pressure amplitude.

Acoustics↗

PubMed1995

Gait asymmetry following successful surgical treatment of ankle fractures in young adults.

Forty patients (mean age, 22.8 years) admitted for displaced ankle fracture were observed retrospectively to determine by clinical examination and measurement of plantar pressure distribution whether successful surgical treatment of ankle fractures led to gait symmetry, and whether intraindividual differences were related to fracture type and clinical outcome. The mean followup was 18.5 months (range, 12-36 months). The deviation of gait was quantified using a symmetry index of the total impulse. Using a clinical score, 6 patients had unsatisfactory results, and the remaining 34 had satisfactory results. The symmetry index of the good (-1.1%) and the poor results (-2.3%) decreased in the range of a healthy control group (-0.31%, n = 90), indicating that overall gait symmetry was achieved after trauma. The plantar pressure distribution showed significant load asymmetries. There was increased loading in the lateral forefoot of the injured leg in patients with good results and decreased pressure under the metatarsal heads of patients with bad results. Although those asymmetries were related neither to fracture type nor clinical outcome, the findings may illustrate compensation mechanisms that are used to regain gait symmetry after ankle alteration by trauma.

Adult↗