Abstract
Introduction
Revision Total Hip Arthroplasties (THA) have a significantly higher failure rate than primary THA's and the most common cause is aseptic loosening of the cup. To reduce this incidence of loosening various porous metal implants with a rough surface and a porous architecture have been developed which are said to increase early osteointegration. However, for successful osteointegration a minimal micromotion between the implant and the host bone (primary stability) is beneficial. It has not been previously determined if the primary stability for the new Gription® titanium cup differs from that of the old Porocoat® titanium cup.
Material and Methods
In 10 cadaveric pelvises, divided into 20 hemipelvises, bilateral THA's were performed by an experienced surgeon (RGB) following the implant manufacturer's instructions and with the original surgical instruments provided by the company. In randomized fashion the well established Porocoat® titanium implant was implanted on one side of each each hemipelvis whereas on the corresponding opposite side the modified implant with a Gription® coating was inserted. Radiographs were taken to confirm satisfactory operative results. Subsequently, the hemipelvis and cups were placed in a biomechanical testing machine and subjected to physiological cyclic loading.
Three-dimensonal loading corresponded to 30% of the load experienced in normal gait was imposed reflecting the limited weight bearing generally prescribed postoperatively. The dynamic testing took place in a multi-axial testing machine for 1000 cycles. Relative motion and micromotion were quantified using an optical measurement device (Pontos, GOM mbh, Braunschweig, Germany). Statistical evaluation was performed using the Wilcoxon signed-rank test.
Results and conclusion
The standard Porocoat® titanium cups showed a mean relative motion with respect to the host bone of 54.74µm (Range 26.04 – 127.06µm), while the porous Gription® titanium cup displayed a relative motion with respect to the host bone of 49.77µm (Range 24.69 – 128.37µm). The Wilcoxon test did not reveal a significant difference between the two surfaces.
The in-vitro biomechanical evaluation of both acetabular cups under a physiologic loading scenario showed no significant difference with regard to primary stability. Both the extensively tried and clinically successful Porocoat® titanium cup and the newer Gription® coated cup showed very little micromotion and both implants should therefore allow good osteointegration.
