Remy Van Audekercke

Mechanical properties, bone mineral content, and bone composition (collagen, osteocalcin, IGF-I) of the rat femur: Influence of ovariectomy and nandrolone decanoate (anabolic steroid) treatment

SummaryNandrolone decanoate (ND) is an anabolic steroid with a positive effect on bone mass in osteoporotic patients. The mechanism of action, (i.e., reduction of bone resorption and/or Stimulation of bone formation), the ultimate effect on mechanical properties, and the most effective dosage are not yet clear. To address these issues, dose-related effects of the long-term effect of ND on Serum and bone biochemistry, bone mineral content, and bone mechanical properties in ovariectomized (OVX) rats (12 weeks old at the Start of the experiment) were Studied for 6 months. The results were compared with those obtained in agematched, intact, and OVX rats. OVX caused in the femur a significant increase in net periosteal bone formation and net endosteal bone resorption of bone collagen content and torsional strength, and of Serum alkaline phosphatase, osteocalcin, and insulin-like growth factor-I (IGF-I) levels, whereas cortical bone density and calcium/creatinine and phosphorus/creatinine in 24-hour urine were Significantly reduced.Treatment of OVX rats with 1 mg ND/14 days resulted in a Significant increase in periosteal bone formation, femur length, cortical and trabecular bone mineral content and density, torsion stiffness and Strength, and bone IGF-I content, and a decrease in Serum osteocalcin, urinary calcium/creatinine levels, and bone collagen content compared with OVX controls. The higher ND dosage of 2.5 mg/14 days did not improve the results. ND treatment did not reverse all changes induced by OVX to the level of the intact controls.These results indicate that ND acts as an antiresorptive drug and as a bone formation Stimulating drug. Furthermore, the increased bone mass and bone mineral density is associated with improved bone Strength and stiffness and the presence of an increased amount of IGF-I. IGF-I is a growth factor considered to play a role in the maintenance of normal skeletal balance by a paracrine or autocrine mechanism.

Computer-aided craniofacial surgical planning implemented in CAD software

Accurate presurgical planning is imperative for successful cranial surgery. This article introduces a simulation program developed in a computer-aided design environment. The neurocranium is introduced as a mathematical surface, since this is the part on which the actual operation will be performed. The viscerocranium, which serves as reference, is visualized using small triangular surfaces. The development of the program commenced with a classification of the different surgical techniques mentioned in the literature into six basic actions. The use of mathematically described surfaces has the advantage that the program can simulate actions which change the shape of a surface and perform an on-line estimation of the fracture risk during bending. Three-point bending tests were carried out to provide the necessary data to perform the mathematical check, as these data are not available in the literature. A database with reference distances was introduced to guide the surgeon to obtain the best possible results. During one clinical trial, the computer was taken into the operating room so that the surgical plan developed with the simulation program could be applied to the actual operation.

A new technique for the three-dimensional study of the spine in vitro and in vivo by using a motion-analysis system

We introduce a new method with a motion-analysis system (MAS) to study the vertebral model in vitro. Compared with the currently most accurate technique, roentgen stereophotogrammetric analysis (RSA), the difference between the RSA and the MAS is 0.12 degree +/- 1.64 degrees. An accuracy with an error of 0.08 degree +/- 1.15 degrees is determined by means of an angle gauge. Although a significant difference between the MAS and the goniometer (p = 0.04) is found around the X-axis (theta; transverse plane), it is limited to < 1 degree. The MAS provides an in-depth insight into the mechanism of the three-dimensional rotation at each vertebra in vivo. The backward inclination of the apical vertebra (AV) and forward inclination of the upper-end vertebra (UEV) around the Y-axis (phi) results in a correction of the hypokyphosis shown by the Cobb angle in the sagittal plane. The clockwise rotation of the UEV in the Z-axis (psi) leads to a reduction of the Cobb angle in the frontal plane. Additionally, the MAS as an intraoperative alternative shows different results of the derotation maneuver by the Cotrel-Dubousset instrumentation (CDI) compared with the computed tomography (CT) scan. Our method gives more direct details of the derotation not influenced by patient posture, as observed in the CT scan.

Finite element analysis applied to bone remodelling in revision arthroplasty of the femur using morselized allograft and cement

Finite element models have extensively been developed and reported for primary cemented and uncemented total hip replacement, but not for revision arthroplasty of the hip. A two-dimensional equivalent thickness model was developed of the proximal femur with bone grafts, a thin but uniform cement layer and a standard femoral component. This model represents the reconstructed femoral revision setting described by Gie et al (1). The effects of surface texture, cement-stem friction, cement creep and stem malplacement were evaluated. Within the range of coefficients of friction which was investigated in this study (0.03, 0.136 and 0.3) it was observed that the influence of the value of the coefficient upon the stresses in the bone-implant structure are less than 5%. Also static cement creep and certain stem malalignments which were simulated showed a relatively small influence upon the stress distribution within this structure. An agreement between trabecular orientations in the remodeled bone allograft and the principal stress orientations in this structure was observed in the calcar region. It was concluded that the remodelling which occurs in the bone allografts follows Wolffs law of optimal material use in the trabecular structure.