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Biomedical subjects

S M Perren

Publications and source records attributed to S M Perren.

189 records · Page 11Linked to original sources
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Intramedullary pressure increase for different commercial and experimental reaming systems: an experimental investigation.

OBJECTIVE: To measure the differences in intramedullary (IM) pressure for commercial reamer systems. DESIGN: IM pressure values for the following systems were measured: AO, Biomet, Howmedica grey reamer, Richards, and Zimmer. To investigate the influence of shaft diameter, the AO reamer head was additionally connected to a small shaft (A6/A7). The pressures were measured in plexiglass tubes filled with a mixture of petroleum jelly and paraffin oil with flow properties at 20 degrees C equivalent to those of bovine medullary fat at 36 degrees C. The reaming assemblies were inserted into the tubes using a materials testing machine at a constant speed. In addition, pressure measurements were made using five pairs of human femora to compare Biomet reamers with the AO reamer with thin, flexible drives (A6/A7). RESULTS: The following pressure distributions were obtained (millimeters of mercury; mean value +/- standard deviation): 9.5-millimeter reamer: low for Biomet (272+/-39); moderate for Richards (810+/-101); and high for Howmedica (990+/-132), AO conventional (1,000+/-97), and Zimmer (1,140+/-183); 13.0-millimeter reamer: low for Biomet (132+/-21), Howmedica (204+/-45), and Zimmer (226+/-33); moderate for AO conventional (474+/-42); and very high for Richards (1,734+/-127). The second worst system (AO conventional: 1,000+/-97) became the second best system by simple reduction of the shaft diameter (A6/A7: 378+/-33). CONCLUSION: A comparison of shaft diameters and pressure increase clearly showed that the system with the thinnest shaft produced the lowest pressure values and vice versa.

Equipment Design↗
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Influence of the design for fixation implants on local infection: experimental study of dynamic compression plates versus point contact fixators in rabbits.

OBJECTIVES: Comparison of infection resistance after local bacterial challenge associated with two different designs for fixation implants: the conventional dynamic compression plate (DCP) and the point contact fixator (PC-Fix). DESIGN: Randomized, prospective study in experimental animals. Grouped sequential experimental procedure. Observation time was twenty-eight days, with twenty animals per group. SETTING: Following surgery, animals were kept without restrictions in individual hutches. ANIMALS: Forty White New Zealand rabbits. Thirty-eight animals, nineteen per group, were included in the final evaluation. INTERVENTION: Under sterile conditions, specially manufactured titanium DCP or PC-Fix of identical dimensions were fixed to rabbit tibiae. After wound closure, different concentrations of Staphylococcus aureus, between 2 x 10(4) and 2 x 10(8) colony-forming units (CFU), were inoculated percutaneously at the implant site. MAIN OUTCOME MEASUREMENTS: Implants, underlying bone, and surrounding soft tissues were removed under sterile conditions and quantitatively evaluated for bacterial growth. Infection was defined as positive bacterial growth at the bone-implant interface. RESULTS: The overall infection rate was 45 percent. The infection dose of 50 percent (ID50) was 7.08 x 10(5) CFU for the DCP group and 8.51 x 10(6) CFU for the PC-Fix group. The infection rate was 63 percent (twelve of nineteen animals) for the DCP group and 26 percent (five of nineteen animals) for the PC-Fix group. This difference was statistically significant (p = 0.022). CONCLUSIONS: After local bacterial challenge, we found a statistically significant difference in the infection rates depending on the implant design. The higher infection resistance associated with the PC-Fix design seems to be related to the reduced contact area at the bone-implant interface.

Animals↗
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Physical and biological aspects of fracture healing with special reference to internal fixation.

Fracture healing is a repair process of a mechanical discontinuity loss of force transmission, and pathological mobility of bone. Through a sequence of changes of tissue development and geometry, the original structural integrity is restored. The recovery of rigidity and strength is related to tissue differentiation. In unified theory of non-operative and operative stabilized fractures, the mechanics of primary bone healing involves a complex interplay of physical and biological factors. The different patterns of bone repair respond to physical influences including strain tolerance.

Animals↗
PubMedDate not supplied

A radiological and histological analysis of fracture healing using prebending of compression plates.

The use of an exactly contoured compression plate to the surface of a bone will lead to asymmetrical loading of that fracture line with possible gapping of bone opposite the plate. The stability of fixation can be increased through the use of compression combined with prebending. The present study in 19 sheep demonstrates the biological effects of 3 modes of plating fixation: (1) no compression; (2) compression; and (3) compression after prebending using 2 types of compression plates with different stiffness evaluated radiographically and histologically. Compression together with prebending, especially when using plates of adequate stiffness, can prevent bone resorption at the fragment surfaces even under immediate weight-bearing conditions in the sheep tibia. Prevention of interfragmentary bone resorption lowers the risk of non-union and/or implant failure secondary to motion at the fracture site.

Animals↗
PubMedDate not supplied

Electrical stimulation of experimental nonunions.

Hypertrophic and oligotrophic nonunions were prepared by resection of a portion of the proximal ulna in dogs. In the hypertrophic nonunions, 20 muamps of direct current for eight weeks produced an increase in bone formation compared to the opposite control limb by radiography, photometry, point counting of new bone, and growth rate by sequential fluorochrome labeling and the dynamic uptake of 99mTc-labeled methylene disphosphonate. Oligotrophic nonunions were treated by plating and aspiration grafting in addition to direct-current stimulation. Ony the point counting of new bone showed a significant increase in bone formation with stimulation. Sequential fluorochrome labeling demonstrated that the new bone was laid down on existing bone and not primarily adjacent to the cathode within the fibrous nonunion. This finding supports the cell-mediated rather than physicochemical effect of electrostimulation.

Animals↗
PubMedDate not supplied

Treatment of nonuniting osteotomies with pulsating electromagnetic fields. A controlled animal experiment.

To evaluate treatment of nonunions or pseudarthrosis in humans by pulsating electromagnetic fields (PEMF), the authors tested the method in four- to six-year-old beagle dogs with midshaft osteotomies of both ulnae. This type of osteotomy in dogs leads to nonunion. After surgery one foreleg of each dog was stimulated for an average of 25 days; the second foreleg served as a control. Subsequently all ulnae were harvested, radiographs were obtained, and the stiffness of the callus was mechanically tested. Thus, the reputed efficiency is not confirmed by controlled experiments on dogs. The stimulated bones were neither radiologically nor mechanically superior to the controls.

Animals↗