[Anatomic reconstruction of hip joint biomechanics: conventional vs. short-stem prosthesis]

Currently, short cementless femoral stems are alternative implants to treat osteoarthritis in young patients with sufficient bone quality in order to get a more proximal load transfer. The purpose of the present study was to biomechanically compare joint reconstructions resulting from implantations of a short-stemmed and a conventional hip replacement.

100 patients (50 short-stemmed and 50 conventional) were retrospectively examined. For evaluation of biomechanical parameters standardised pre- and postoperative X-rays (pelvic AP views) were used and digitally analysed.

The horizontal femoral off-set increased within both groups (short: 2.0 mm and conventional: 3.3 mm), with a significant increase in the conventional group. The hip centre of rotation was significantly medialised after both procedures (short: 6.0 mm and conventional: 4.2 mm). Limb length was shorter preoperatively at the arthroplasty side, but increased thereafter (short: 2.1 mm and conventional: 2.6 mm). Compared to the native contralateral side the limb length was almost equal after THA (short: 0.7 mm and conventional: 0.8 mm).

Our study shows that an almost anatomic reconstruction of hip joint biomechanics is possible with a short-stemmed prosthesis compared to a conventional stem, regarding limb length, centre of rotation and offset.