Computer navigation systems enable precise measurement and intra- operative knee range of movement analysis. We present a series of five knees that demonstrated unusual kinematics.

Five of 80 computer navigated knee replacements that were part of a prospective randomised trial were found to have unusual joint lines. Range of motion assessment was performed with computer assisted navigation after exposure and registration of bony landmarks and before bony resection was commenced. This revealed valgus alignment in extension that drifted into varus with knee flexion. We referred to these unusual patterns as ‘oblique joint lines’.

The data from the navigation log files of these five knees was analysed in detail. Average age of patients in this series was 68years and all were female. The average pre- operative angle between femoral axis and distal femoral articular surface was 101 degrees. All five knees had a tibial varus with average angle between the tibial axis and articular surface being 85 degrees. In two knees, more bone was resected from the medial posterior femoral condyle using 4 degrees external rotation. These two knees showed improved kinematics and horizontal joint line post- operatively.

Computer assisted navigation provides a precise understanding of the pre- operative knee kinematics. Bony cuts can be tailored to suit the pre- operative deformity. Increased external rotation of the femur with adequate medial soft tissue release is an alternate approach for difficult knees with ‘oblique joint lines’.

Introduction: The use of uncemented arthroplasty in joint replacement surgery requires osseointegration of the prosthesis to maximise function and longevity. It has been demonstrated that osteoblast-like cells will preferentially proliferate, differentiate and produce mineralised matrix in pits and grooves on non-biological surfaces, of similar dimensions to those of Howslip’s lacunae produced by osteoclasts in vitro. The hypotheses of this study were that a photochemically etched titanium alloy surface would 1) induce proliferation and differentiation in osteoblast-like cells; 2) induce osteoblastic differentiation of human mesenchymal stem cells and 3) induce greater bone to implant contact in a caprine model.

Methods: Three microgrooved titanium alloy surfaces (fine, medium & coarse) were created by photochemical etching, with dimensions of 200 to 515 microns. Human Mesenchymal stem cells (MSC) and Human Osteosarcoma (HOS) cells (TE-85) were seeded onto these surfaces and cultured in standard media; in the case of MSC, with and without the addition of osteogenic supplements. At intervals of time each surface and cell type were assessed for proliferation by Alamar blue assay and osteoblastic differentiation by Alkaline Phosphatase expression. A polished titanium surface was used as a control. A plate of each surface dimension was placed into a femoral condyle of ten adult male goats. The animals were euthanased at 6 and 12 weeks post-implantation. The specimens were histologically processed and examined under light and backscattered electron microscopy to establish the percentage of bone to implant contact and the presence of new bone within the grooves.

Results: In vitro, all cells showed an increase in proliferation with time, the greatest occurring on the coarse surface. Alkaline phosphatase expression showed a rise with time on all surfaces, the greatest being on the coarse surface seeded with HOS cells (p< 0.05). MSC could not be induced to differentiate to an osteogenic lineage by these surface textures alone. On addition of osteogenic supplements their results followed the trends of HOS cells. In vivo, histomorphometric analysis showed significantly greater bone implant contact on the coarse surface at both 6 and 12 weeks (p< 0.05). In a number of cases there were signs of osteogenesis occurring deep within the pits and grooves.

Discussion: This study confirms that a photochemically etched surface topography mimicking that created by osteoclasts will increase the proliferation and differentiation of osteoblastic cells in vitro. The rate of differentiation of these cells increased significantly in relation to the size of the grooves. When implanted in vivo these same surfaces were shown to support osseointegration. This surface has the potential to improve the function of uncemented arthroplasties in the future.