Die messung von anzugsdrehmoment und vorspannkraft bei schenkelhalsverschraubung im experiment

Abstract

An experimental study was undertaken to evaluate the torque and axial force of the 6.5 mm ASIF lag screw implanted in the femoral neck after a subcapital osteotomy. The experiments were carried out on autopsied bones of more than 60 years of age. The average torque was 204 cmN, the screws in the upper half of the femoral head showing a higher torque than those in the lower half. The axial tension was measured by strain gauge transducer. Depending on the length of the thread of the screw (16 or 32 mm) the average tension reaches 1162 N or 1960 N. By tightening the screw until the impression of optimum fit is obtained, 70% of the maximum axial force is reached. It can therefore be estimated that at the beginning an interfragmentary pressure of 4000 to 8000 N is exerted on a medial femoral neck fracture fixed by four ASIF lag screws.

Holding power of different screws in the femoral head: A study in human cadaver hips

“…However, the holding power of cancellous bone screws observed here was less than half of that reported by Schwarz & Newald (1981), who in a similar set-up used ASIF cancellous bone screws with 16 mm and 32 mm length of thread. Such discrepancies, in what should be comparable results, could better be explained by variations in methodology than by differences in the autopsied bones.…”

“…Although different cancellous bone screws have been recommended for internal fixation of femoral neck fractures (Charnley 1960, Schwarz 1979, few researchers have studied the holding power of screws in the femoral head (Schwarz & Newald 1981, Frandsen & Madsen 1983.…”

Holding power impaired in rheumatoid femoral heads: Cadaveric study of fracture fixation devices

“…For screws, measurement of the maximum holding strength alone might be adequate, because further displacement is followed by a rapid decline in holding strength (Schwarz and Newald 1981, Fransen and Madsen 1983, Frandsen et al 1984, Hertz et al 1985, Iversen et al 1988. For implants that exhibit extended load/displacement profiles, as does the hook-pin in the present study, it is obvious that a combination of maximum holding strength and total extraction energy is a better measure of ability to resist extraction.…”

“…An adequate holding strength is therefore important also in these implants. If, in the experimental model, the pullout load is increased intermittently (Schwarz and Newald 1981, Frandsen and Madsen 1983, Hertz et al 1985 a similar timing of the load increase in all the specimens is essential, otherwise the result become unpredictably influenced by the viscoelastic properties of bone (Larsson et al 1987). By using a constant pullout rate that was repeated in all the specimens that possible methodologic error was neutralized.…”

“…The holding strength is determined by bone quality and by implant design, and the maximum holding strength in cadaveric femoral heads has previously been studied for hip compression screws and cancellous screws. A decrease in holding strength in elderly subjects is attributed to reduced bone strength (Schwarz and Newald 1981, Frandsen and Madsen 1983, Frandsen et al 1984, Hertz et al 1985. Clinical studies have revealed that internal fixation of femoral neck fractures in patients with rheumatoid arthritis are associated with a higher Biomechanical Laboratory', Wrightington Hospital, Wigan, England, and Department of Orthopedics2, University Hospital, S-901 85 Umel, Sweden.…”