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Biomedical subjects

S M Perren

Publications and source records attributed to S M Perren.

At least 127 records · Page 7Linked to original sources
PubMed1984

Stress analysis of a partially slotted intramedullary nail.

A finite element analysis of the Arbeitsgemeinschaft für Osteosynthesefragen/Association for the Study of Internal Fixation (AO/ASIF) intramedullary femoral nail was performed to study the failure of the nail from circumferential cracking near the slot tip. These failures are evidently the result of a stress-concentrating effect owing to the partially slotted nail design. Several finite element models were created of the proximal one-fourth of the nail. One model of the nail incorporated the cloverleaf profile as it is presently manufactured, and one had a circular cross section. An additional three models were created with alternative slot-tip geometries: a narrowed slot, a tapered slot, and a widened slot. Antero-posterior (AP) and medio-lateral (ML) bending loads and torsion loads were applied in two fundamentally different loading modes: (1) loads that were applied on both sides of the slot tip (spanned); and (2) loads that were self-equilibrating distal to the slot tip (non-spanned). For the load cases studied, for all models, the stresses predicted from the finite element models were locally highest at the junction between the open and closed cross sections. Alternative slot-tip shapes had a marked effect on the predicted stresses, in one case reducing maximum stress by 40%. However, no alternative slot tip shape was uniformly superior for all load cases. Therefore, until the in vivo loading modes are known more precisely, an alternative slot-tip shape cannot be proposed.

Biomechanical Phenomena↗
PubMed1984

Three-dimensional finite element analysis of a simplified compression plate fixation system.

A three-dimensional, linear finite element model was generated for an intact plexiglass tube with an attached six-hole stainless steel compression plate. We examined external forces representing axial, off-center axial, and four-point bending, along with superimposed plate and screw pretension. Strain gage experiments were conducted to test model validity and the finite element results were contrasted to a composite beam theory solution. Excellent correspondence was observed between finite element and strain gage data for the most significant strain components. Composite beam theory tended to overestimate the neutral axis shift which results from plate application. The model also demonstrated fracture site distraction due to plate pretension, and the tendency for outer screw failure for the combination of bending-closed with a preload in the plate and screws.

Biomechanical Phenomena↗
PubMed1984

A locking hook spinal rod system for stabilization of fracture-dislocations and correction of deformities of the dorsolumbar spine. A biomechanic evaluation.

Existing internal fixation systems for the injured or deformed spine present problems with overdistraction and control of the contoured rod necessary for transverse forces. A locking hook spinal rod avoids these problems by using a locking cover to secure the lamina in the hook and meshing radial grooves to lock the contoured rod to both the upper and lower hooks in 6 degrees intervals of rotation. The 7-mm stainless-steel rod is 50% stronger than the 1/4-in Harrington rod and also avoids the weakening effect of the notches. Cadaver spine testing gives nearly a threefold increase in failure strength (125 +/- 17 Nm versus 44.1 +/- 2.1).

Adult↗
PubMed1983

Rigidity of pure lag-screw fixation as a function of screw inclination in an in vitro spiral osteotomy.

The rigidity of lag-screw fixation of experimental tibial fractures was tested in 27 anatomic specimens. Spiral osteotomies with a 60 degree angle of ascent were produced using a Gigli saw. Three screws with an axial force of 100 kp were inserted at 90 degree, 80 degree, or 70 degree of longitudinal inclination. The 70 degree group was stable in axial compression up to 88 kp and the 80 degree group up to 151 kp. Rigidity in bending was 50% in the 70 degree and 80 degree groups and 27% in the 90 degree group, while rigidity in torsion was 20% as compared with the intact bone. Screws tightened with 50 kp and 150 kp showed increased rigidity as axial screw force increased. There were only small gains in torsion and bending, whereas there was a 200% gain in compression. This confirms the view that in long spiral fractures of the tibia three lag screws alone can maintain sufficient stability to permit early limb mobility. If the screws are inserted perpendicular to the bone, the high resistance to axial compression may permit early partial weight-bearing.

Biomechanical Phenomena↗
PubMed1982

A method for making reproducible experimental fractures of the rabbit tibia.

A method for making reproducible fractures of the tibia of the rabbit is described. The fractures may be stabilized by plating with either metallic compression, or plastic plates. If a stainless steel dynamic compression plate is used, the rigid immobilization of the fragments leads to direct Haversian remodelling across the fracture, i.e. primary healing, whereas when a plastic plate is used, the fixation is unstable and this leads to secondary healing with the development of a cartilaginous callus. Thus the method of healing may be determined predictably.

Animals↗
PubMed1981

Effects of plates on cortical bone perfusion.

Using disulphine blue, sheep tibial cortex perfusion was decreased by subperiosteal stripping but not by extraperiosteal exposure. Semitubular plates applied with either low (20 kp) force, sufficient for extraosseous vascular occlusion, or high (200 kp) force, similar to that used clinically, both produced significant ischemia beneath the plate. In contrast, the dynamic compression plate produced significantly greater ischemia only with the higher force.

Animals↗
PubMed1980

[A method for morphometry of bone formation using fluorochromes (author's transl)].

A reliable morphometric determination of newly formed bone requires a continuous labeling of the tissue of interest. A technique is described which uses the fluorochromes Calcein and Xylenolo-range as bone labels. Image contrast in the fluorescence microscope can be increased by means of special filter combinations to permit data collection by computer-compatible video-systems. This technique offers a wide field of applications in experimental bone biology.

Animals↗
PubMed1980

[Area of contact between osteosynthesis plate and bone in internal fixation (author's transl)].

The bone can be protected against excessive stress if the plate is properly adapted to the surface of the contact area between plate and bone, thus ensuring good and longlasting repositioning of the fracture. The article describes an in-vitro method for the quantitative evaluation of the contact area between plate and bone in osteosynthesis. With four different bones and the requisite plates, six expert surgeons were able to obtain an area of contact between plate and bone which varied between 13 and 60%, the average being 32%. The available data allow us to conclude that the peak loads of pressure occurring with small contact areas may be so great that they exceed the maximum compressive strength of the bone.

Bone Plates↗
PubMed1980

Biomechanics of fracture healing.

Internal fixation of fractures alters the physical environment of living bone. The authors have studied the reaction of living bone to force and motion, mainly in sheep. Cortical bone does not undergo pressure necrosis when compression is applied in internal fixation. Compressing the fragments increases the stability of the reduction and leads to uneventful healing without resorption. Small areas of plastic bone deformation owing to mechanical overload are nor removed by surface resorption but by internal remodelling. Interfragmentary motion produces callus and resorption of the contact surfaces. The static compression applied to cortical bone does not induce a change in the rate of internal remodelling. The static forces must exceed the dynamic load to maintain close coaptation at the contact surface.

Animals↗