Investigation of the effect of the modified surface geometric femoral head on lubrication and surface wear in total hip prosthesis

Polyethylene liner wear and the result debris material is the most important cause of osteolysis, in the practice of total hip arthroplasty. Osteolysis reduces the lifespan of the total hip replacement. The effect of the modification of the geometry of the femoral head used in THA, is not known. In this study, we aimed to investigate the effect of geometrically modified femoral head on polyethylene wear by biomechanical experiment. The geometry of the standard femoral head was changed with a groove, which has a radius of 5 mms, parallel to the center of the sphere and 2 grooves perpendicular to each other on the surface of the sphere. In this study standard femoral head and modified femoral head were used in two different groups. A total of 12 experiments were performed with six polyethylene liners in each experimental group. One polyethylene liner was evaluated for comparison without testing. The device simulated the hip joint movements by creating and applying a maximum load of 1000 N and a minimum load of 500 N. 10,000 cycles were performed. Saline solution was used as lubricant. The polyethylene acetabular liners used in the experiment were weighed before and after the experiment. After the experiment, polyethylene liner was removed and samples were obtained 8 mm from the loading area using a punch. Punched samples were examined by surface profilometer and scanning electron microscope. The absorbance values of different wavelengths were compared with the lubricating liquid spectrophotometer used in the experiment. The obtained data were compared statistically. There was no statistically significant difference between the experimental groups before and after the experiment (p = 0.229). There was no significant difference between the groups in Ra value on the profilometric examination (p = 0.062). Rq, Rt and Rz values were significantly different between the groups (p = 0.014, p = 0.013, p = 0.044). Spectrophotometric measurements showed that the light transmittance was lower in all four wavelengths in the OB group. There was no significant difference between the two groups in spectrophotometric measurements (p = 0.109, p = 0.259, p = 0.631, p = 0.337, respectively). It was observed that there was an increasing correlation between the weight differences and the spectrophotometric absorbance values before the polyethylene experiment as the wavelength increased. In this study, no significant difference was found in the post-test weight difference, Ra value and spectrophotometric absorbance values of the newly developed femoral head and standard femoral head. Rq, Rt, and Rz values showed that modified femoral head increases the wear rate of the implant. The correlation between weight difference before and after the experiment and spectrophotometric absorbance values at wavelength of 595nm and 650 nm shows that spectrophotometer can be used to determine the wear of the implant.