Abstract
OBJECTIVE OF THE STUDY
The objective of this study is to establish the medium-term clinical and radiological results with the cementless three-dimensional Vektor-Titan stem compared with conventional cementless stem, such as PerFix stem. The latter stem has a double-wedge design with a rounded distal portion for canal filling (Fig. 1).
MATERIALS AND METHODS
From July, 2004, to May, 2010, fifty seven Vektor-Titan stems and 150 PerFix stems were implanted for the patients with osteoarthritis, avascular necrosis, femoral neck fracture, and rheumatoid arthritis in our hospital. The results were evaluated clinically using Japanese Orthopedic Association (JOA) scores and the Merle d’Aubigne and Postel (M&P) scores. Radiographs were analyzed retrospectively. The criteria used for determining loosening were migration or a total radiolucent zone between the prosthesis/bone cement and host bone, wherein the width increased progressively or change of position, i.e., migration or subsidence of the prosthesis. Migration of the socket seen on the radiograph was defined as either the presence of a ≥2-mm position change or rotation. Position changes of the stem seen on the radiograph were defined as the presence of a progressive subsidence of ≥2 mm or change of position, e.g., varus or valgus. The follow-up period was 9.2 ± 2.6 (range, 5.0–14.0) years.
RESULTS
One patient had intraoperative femoral shaft fracture and healed by conservative treatment. The mean JOA and M&P scores improved from preoperative 39.3 and 6.8 points to postoperative 90.9 and 17.2 points, respectively. Thigh pain was less frequent for Vektor-Titan stems (Table 1). Radiolucent lines was far less likely to appear for Vektor-Titan stems evaluated by Gruen's zonal analyses (Table 2). On the other hand, there were radiolucent zones of more than 90% in zone 4 with cementless PerFix stems (Table 2). There was no cases of loosening or postoperative infection. Although signs of bone atrophy were found in the proximal femur and the trochanters in 66.7 % of all cases, bone structure was radiologically normal without stress shielding in most cases (Table 2). On the contrary, there was evidence of an even denser bone structure, such as trabeculae, at the tip of the stem and the lateral implant fixation within the greater trochanter in Vektor-Titan stem cases. These findings remained unchanged over observation periods.
DISCUSSION AND CONCLUSIONS
The cementless Vektor-Titan stem is made of Ti6AI7Nb, has got the shape of a straight three-dimensional cone. 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. Radiologically, newly formed trabeculae toward to the stem were indicative of direct biological fixation at the bone-implant interface. Medium-term results with the cementless Vektor-Titan stem show no implant loosening with stable metaphyseal fixation and preservation of bone structure in the proximal femur and the absence of radiolucent zones around the stem compared with conventional cementless stem.
