[Effect of shaft shape on the stress distribution of hip endoprostheses in the femoral cortical layer. A technical and clinical study]

The primary stability of intertrochanteric osteotomies. An experimental comparison of techniques

We have compared the quality of intertrochanteric functional pre-bending with other techniques for varus and flexion intertrochanteric osteotomies by measuring interfragmentary compression, the tension in the angled blade-plates used and the stability of the different procedures. Intertrochanteric osteotomies with any kind of plate pre-bending gave the best results in our experimental studies. Impacting techniques gave poor primary stability and the Schneider method produced only moderate stability in flexion osteotomies. Using intertrochanteric functional prebending, varus and flexion osteotomies produced the best primary stability and the most equitable interfragmentary compression. This could be achieved with the highest precision by using a sawing gauge system at operation.

[Dynamic force measurement in implantation of total endoprostheses of the hip joint]

The forces within the femoral shaft have been studied in preparation for the total hip replacement. The experimental device consisted of a personal computer connected with a digital enhanced measurement system which converted the data, that was received from the strain gauges, mounted on the femur. The bitochanter hip replacement designed by Ecke was used as an example of a press fit endoprosthesis which is anchored cementless. It was implanted in femora of cadavers. The results showed an extension of the femur at first within the intertrochanteric region, and as the rasp was further implanted, it showed at the distal end of the rasp a medial extension and a lateral traction with a delay of 3 ms, proving that it was a result of a medullary extension. The maximum forces applied with the metal hammer were 3500 N. Fractures and fissures were provoked and the result showed that they were mostly due to a misplacement of the rasp.

[Experimental evaluation of a newly developed 90 degree angle plate (MC angle plate) for intertrochanteric derotation osteotomy]

A newly developed 90 degrees angled blade plate that permits high interfragmentary compression with a potential sliding way of 9 mm, is described. In the majority of intertrochanteric osteotomies, and especially when applying "functional pre-bending", the use of an external compression device is not necessary with this plate. The plate consists of 2 modules which permit a temporary thickening of the plate up to 10 mm, and the principle of dynamic compression can be performed with a 45 degree screw hole for the sliding way of 9 mm. The results of testing showed that a compression force of up to 1200 N was possible. The resulting interfragmentary compression could not be increased even with the aid of an external compression device or by idealized experimental conditions. Whenever dynamic compression is necessary for fixation, the modular compression principle described here can be used with any other plate system.

[The Giessen model of a cement-free implantable total endoprosthesis for the hip joint]

Complete endoprostheses of the bitrochanteric type were implanted in Giessen in 111 patients the average age of whom was 74 years. Computer-assisted evaluation showed that more than 70% of these patients developed autonomous mobility. The rest had not been able to walk before surgery, but could be nursed or became able to sit after the operation or were still followed up. At the end of follow-up treatment, a rate of 90% of mobile patients with or without stick is to be expected. Initially, the implantation technique is certainly more difficult to learn with this model than with other allo-endoprostheses of the hip joint. This is due to the fact that the implants are an exact replica of the pertrochanteric region, thus permitting a broad contact face to the cortical substance instead of the punctiform contact of some other models. Once learned, the technique can be applied without considerable problems. At our Department it has proved to be successful.