[Proximal osseous integration in THR using the cementless Vektor-Titan stem: medium- and long-term results]

The objective of this study is to establish the medium-term and long-term clinical and radiological results with the cementless Vektor-Titan stem. Special consideration has been given to evaluate the extent to which the implant design achieves proximal stress transfer, thus avoiding stress shielding in the proximal femur.

From October 10, 1996, to May 18, 2000, 432 Vektor-Titan stems were implanted in 348 patients in the Wichernhaus Orthopaedic Clinic at Rummelsberg Hospital. The results were evaluated clinically and radiologically within the scope of a retrospective cohort study. The Vektor stem is a titanium straight stem designed for cementless fixation. It has a high proximal volume in the form of a three-dimensional taper with longitudinal ribs. This design achieves strong primary fixation in the proximal metaphysis.

The survival probability of the stem was 99.08 % after a mean time of 7.5 years after surgery. One implant had to be replaced due to a traumatic periprosthetic fracture. Another had to be replaced after 9 months due to septic loosening, and a third after 14 months due to a suspected low-grade infection which, however, was not confirmed intraoperatively. The fourth stem required replacement after 75 months, again due to a periprosthetic fracture. Based on the Merle d'Aubigné score , surgery led to very good clinical results in 254 cases (58.8 %) and to good improvement in 130 cases (30.1 %). In 33 cases (7.6 %) there was a moderate improvement in the score, and in 15 cases (3.5 %) there was no improvement. Bone structure was radiologically normal in 421 cases (97.5 % of all cases). No signs of atrophy were found in the proximal femur and the trochanters. On the contrary, there was evidence of an even denser bone structure at the level of the osteotomy and the lateral implant fixation within the greater trochanter. There the trabeculae were visibly aligned towards the surface of the implant, indicative of direct biological fixation at the bone-implant interface. These findings remained unchanged over long observation periods. There were no changes along the diaphyseal stem.

Medium-term and long-term results with the cementless Vektor-Titan stem show a low rate of implant loosening with stable metaphyseal fixation and preservation of bone structure in the proximal femur and the absence of changes along the diaphyseal stem.