Modular short-stem prosthesis in total hip arthroplasty: implant positioning and the influence of navigation.

Successful total hip arthroplasty with the Metha short-stem prosthesis (B. Braun Aesculap; Tuttlingen, Germany) depends on the correct indication and an accurate preoperative measurement of the femoral bone shape. Intraoperatively, bone quality, osteotomy, and implant position are of particular importance. Navigation assists with the selection of modular neck adapters for optimal free range of motion. The selection of adapters differs significantly depending on whether navigation is used during surgery. The positioning of the osteotomy depends on the surgeon's experience and judgment as well as the local anatomical circumstances. The osteotomy can be checked intraoperatively by the positioning of the rasp. Correct positioning of the osteotomy and correct dorsolateral contact of the short stem determine the optimal implant position. Implant depth should be adjusted in relation to the lateral circumference of the femoral neck rather than in relation to the calcar osteotomy. Valgus positioning with loss of the lateral support must be avoided. Use of a double osteotomy and routine radiographic controls make it easy to implant the short-stem prosthesis in this less invasive manner. The use of navigation influences the choice of neck position toward reduced anteversion compared with non-navigated selection.