Mechanical stability of the greater trochanter following osteotomy and reattachment by wiring.

Greater trochanters of fresh and formalin-perserved cadaver femora were osteotomized, rewired using techniques described by Amstutz, Charnley, Coventry and Harris, and then mechanically tested. Force simulating abductor muscle pull was applied to the trochanter in the plane of section while its displacement was measured continuously with an extensometer. Although many trochanters appeared rigidly fixed when stressed manually, all displaced visibly when 27 kg load was first applied. When released, permanent sets averaging 0.1 mm (Charnley and Harris) to 3--4 mm (Coventry) were measured. Subsequent repeated loadings (0--27 kg) from this new "rest" position produced recoverable cyclic "functional" displacements averaging 0.7 mm (Charnley and Harris) to 2.3 mm (Coventry). With the exception of the specimens wired by the Coventry technique, results for a simulated 45 degrees anterior pull were generally comparable to those for a neutral pull. Ultimate failure loads of the trochanteric fixation were on the order of 110 kg for selected fresh specimens.