Biomedical subjects

M Verhelpen

Publications and source records attributed to M Verhelpen.

5 recordsLinked to original sources

PubMed1998

Digital image analysis of bone allograft union in sheep.

We compared the reliability of computer-assisted radiographic analysis (CARA) and visual evaluation of radiographs to assess host-graft junctions. 68 host bone/allograft junctions were obtained from an ongoing study on bone allografting in sheep. At 6 months, the grafted tibias were explanted and healing of the host-graft junctions were macroscopically determined. 49 junctions were macroscopically healed, whereas 19 had not united. 51 (0.8) of the junctions were correctly classified by radiographs, while 63 (0.9) of the junctions were correctly classified by CARA (p = 0.03). These findings warrant further evaluation in a clinical setting.

Animals↗

PubMed1995

Fixation and effect on bone strain pattern of a stemless hip prosthesis.

Given the relatively short survival time of total hip replacement in young patients, a different concept of femoral implant was designed and evaluated biomechanically prior to clinical application. The femoral component has no intramedullary stem and fits into an angular resection of the femoral neck. A trans-trochanteric screw provides immediate strong fixation. A comparative biomechanical study with cadaver femora and a dynamic hip simulator was performed. The study had three objectives. (1) The strains generated under loading in the intact proximal femur were compared to those generated in the presence of the experimental implant and a classic cemented implant. (2) The short-term stability of the experimental prosthesis under loading conditions encountered during fast walking was evaluated. (3) Most importantly, the implant design was improved in the light of the experimental observations prior to any clinical trial. Indeed, the prototype underwent several important modifications in the course of the study. With the modified design, later used in a clinical trial, it was demonstrated that if accurate fit and position of the prosthesis were provided, fixation remained sound for over one million loading cycles with peak loads of three times the body weight. The measured interface micromotion was compatible with direct bone apposition and ingrowth. No statistical difference was found between the strain measurements obtained before and after implantation of the experimental prosthesis whereas significant stress shielding was observed with a stemmed, cemented prosthesis.

Biomechanical Phenomena↗

PubMed1993

Mechanical simulator for the upper femur.

This paper describes a simulator designed to evaluate the mechanical behaviour of the proximal femur and the influence of a prosthesis on this behaviour. Cyclic dynamic loads, corresponding to those generated by walking or several other activities, are applied to the proximal end of a fresh cadaveric femur before and after implantation of different types of hip prosthesis. Three musculoaponeurotic groups are modelled (abductor group, fascia lata and vastus lateralis). Load cells and strain gauges coupled to a data acquisition system are used to measure and record the forces on the femoral head and in the different muscle groups, as well as the strain variations occurring in the bone. Displacement transducers monitor the displacements occurring about the bone/implant interface.

Activities of Daily Living↗

PubMed1992

Morphometric and physical investigations of segmental cortical bone autografts and allografts in canine ulnar defects.

Cortical bone grafts were implanted for six months in mature dogs using an osteoperiosteal 3-cm defect in the ulna to evaluate their respective morphometric and physical values compared with autografts. The bone-grafting material included fresh auto- and allografts, frozen and thimerosal preserved allografts, and partially demineralized bone allografts. The grafts were evaluated by roentgenograms, microradiograms, photon absorptiometry, porosity, fluorescence labeling measurements, and torsional loading at failure. Autografts achieved a better union score than the allografts, but intracortical bone porosity, percentage of cumulative new bone, and mineral apposition rate were not variables with statistical significance. Lamellar bone was found earlier and in greater quantity in autografts. Within the graft, new bone was deposited at a slower rate than in the recipient bone. Autografts showed less peripheral resorption and a greater torsional resistance than allografts. Photon absorptiometry demonstrated that nondemineralized allografts underwent a substantial loss of peripheral bone. This marked reduction in the outer diameter of the graft had more influence on torsional resistance than did the intracortical porosity of the graft. Demineralized allografts were osteoinductive in only 28% of the cases and appeared to respond in an all-or-nothing pattern. Frozen and thimerosal preserved allografts were the most acceptable substitutes to autografts.

Absorptiometry, Photon↗

PubMed1991

[Application and electric insulation of strain gauges used on fresh bone. Preliminary study].

This report describes the optimal use of strain gauges placed on fresh wet bones. Two principal stages in gauge installation were studied: surface preparation and gauge insulation. Different surface preparation procedures were tested on bovine bone specimens loaded in traction. The preparation efficiency was evaluated by comparing strains measured from gauges and from an extensometer with sharp edges. Results show the necessity of sufficient rubbing: a minimum of 5 rubbing cycles with n. 320 emery paper. Scanning electron microscopy was used to examine the effect of the preparation procedures. Different coatings were also tested with special attention given to the influence of these coatings on the measured strains. An optimal polyurethane coating is proposed.

Animals↗