One of the objectives of total hip arthroplasty is to restore femoral and acetabular combined anteversion. It is desirable to reproduce both femoral and acetabular antevesions to maximize the acetabular cup fixation coverage and hip joint stability. Studies investigated the resultant of implanted femoral stem anteversion in western populations showed that the implanted femoral stems had only a small portion can meet the desirable femoral anteversion angle1, and anteversion angle increases after the implantation of an anatomical femoral stem with anteverted stem neck comparing to anatomical femoral neck2. The purpose of this study was to anatomically measure the anteversion angular difference between metaphyseal long axis and femoral neck in normal Chinese population. The metaphyseal long axis represents the coronal fixation plane of modern cementless medial-lateral cortical fitting taper stem. This angular difference or torsion Δ angle provides the estimation of how much the neck antevertion angle of femoral stem would be needed to match for desirable anatomical femoral neck version. 140 (77 male and 63 female) anonymous normal adult Chinese CT data with average age of 54.6 (male 54.6, female 54.5, P=0.95) were segmented and reconstructed to 3D models in Trauson Orthopeadic Modeling and Analytics (TOMA) program. Femoral head center, femoral neck axis and center point of diaphyseal canal 100mm bellow calcar formed the femoral neck plane. The metaphyseal stem implantation plane was determined by the center point of medial calcar, proximal canal central axis formed by femoral neck plane and the center point of diaphyseal canal 100mm bellow calcar. [Fig. 1] The angle between two planes was the torsion Δ angle between femoral placement plane and anatomical femoral neck. [Fig. 2] The torsion Δ angles were measured for all 140 cases. The traditional anteversion angle for anatomical femoral neck was also measured by Murphy's method. Student T test was perform to compare the angles for male and female. The 98% confidence level was assumed.Introduction
Methods
Mechanical properties of irradiated Ultra High Molecular Weight Polyethylene (UHMWPE) after aging have been well documented. However there was no sufficient data for the dimensional change due to irradiation and aging. This change may have adverse effects to the implant modular locking mechanism. The purpose of this study was to characterize the dimensional change of UHMWPE after irradiation and aging. Total (30) ø15mm × 50mm virgin GUR 1050 UHMWPE rods were cleaned, dried, inspected, vacuum packaged and stored in 20°C environment for 2 days. Among them, (20) samples were measured along the 50mm length at 20°C +/-2°C before and after two conditions: 1, (10) were submerged in 40°C DI water for 2 hours and dried in 40°C to simulate the cleaning process and 2, (10) were soaked in 37°C saline for 14 days to simulate initial in-vivo environment. Remaining (10) samples were measured in the same way after irradiation of 30KGy dosage and then measured again after soaking in 37°C saline for 14 days to simulate the actual radiation sterilization and in-vivo soaking conditions. Same samples were measured once more after accelerated aging per ASTM-1980-07 for 80 days to simulate the 3 year in vivo life. The differences in measurements between virgin and end conditions were documented as the percentage dimensional change. After the measurements, in the groups of DI water, saline soaking and radiation + aging, (3) samples were randomly selected for DSC measurements. The results were compared with dimensional measurements. Statistical analysis was performed by the student t test to compare virgin condition and the conditions after each treatment. 95% significance level was assumed.Introduction
Materials and Method
