An increasing demand for less traumatic THA combined with a faster recovery time has led to minimal invasive surgical approaches and to bone and soft tissue preserving short stem prostheses. Short stem prosthesis should have metaphyseal fixation, primary stability and lesser changes in femoral elasticity which would lead to less stress shielding. The need for a good joint stability and a higher mobility after THA has led to navigated hip surgery together with the use of modular necks to restore the biomechanics. From November 2004 to July 2008 we implanted 154 Metha prostheses by a modified less invasive Watson-Jones approach. 104 THA were navigated. The indication was primary (32%) or dysplastic coxarthritis (50%) or femoral head necrosis (18%) without affection of the femoral neck, patients age under 50 years and above with good bone density. Evaluation was done with regard to primary stability, ease of minimal invasive implantation and restoration of the biomechanics. The cup position was aimed at 45° of inclination and 15° of anteversion. The most used modular neck adapter in the non navigated group was standard (135°CCD, 0° antetorsion). In the navigated group more often different variations of neck adapters were used (mainly 135°CCD, 7.5° retrotorsion). Reliable length (+7mm overall) and offset (−3.5mm) measurements could be achieved in the navigated group. The average antetorsion of the stem was 20°. Bone loss is low with short stem and it is suitable for minimal invasive procedures. A good primary stability seems to be achievable. Modularity leads to a better restoration of the hip biomechanics. In the navigation of the short stem prosthesis the placement of the stem is separated from the restoration of the biomechanics of the hip. The criteria offset, leg length antetorsion, and center of rotation of the head and implant range of motion can be controlled for restoration by navigation. No dislocation was seen in the intraoperative test and in the postoperative follow up. The short term results show good functional result and a low complication rate without any dislocation. The use of a lesser invasive approach without detaching muscle led to a subjectively faster recovery. The navigation system helps to be precise in cup positioning and to restore biomechanics in term of center of rotation, leg length and offset by advising the best fitting modular neck and reliably predicting the safe range of motion. In our experience the navigated short stem prosthesis offered a good intraoperative handling and good preliminary results.
Malposition of cups and stems in THA leads to a higher rate of dislocation and wear, to leg length discrepancies and to a higher revision rate. Surgical navigation of the implant components should lead to a more accurate position of THA. 1481 consecutive THA were evaluated from November 2001 to June 2006. In a first series until December 2002 127 THA with navigated cups were compared with 110 manually implanted THA. In a second series all following 766 THA with navigated cups were compared to 384 THA with both navigated cup and stem. Navigated surgery was done as a routine procedure by all surgeons, from residents to consultants. Evaluation was done for radiographs, clinical results, the navigation system data for cup anteversion and inclination, centre of rotation, leg lengthening, offset and antetorsion of the stem, technical exclusions and intra- and postoperative complications as dislocation, seroma, thrombosis and duration of surgery. The results showed a better alignment in inclination and anteversion of navigated cups compared to non navigated cups and additional improvement when cup and stem were navigated. In stem navigation a good control of the leg lengthening and a reliable prediction of the safe range of motion could be seen. The overall dislocation rate was 0.3% in the navigated groups after December 2002. Thrombosis, seroma and infection were seen in a very low rate in all groups.
