Gregg Schmidig

The Effects of Acetabular Shell Deformation and Liner Thickness on Frictional Torque in Ultrahigh-Molecular-Weight Polyethylene Acetabular Bearings

The purposes of this study were to determine if there were differences in the frictional torque generated between spherical acetabular shells and acetabular shells deformed as a result of implantation and to evaluate how changes in polyethylene insert thickness and head diameter affected these frictional torque data. An established bench top model was used for mechanical testing. A total of 70 samples were tested. Acetabular shells were impacted into polyurethane foam that was designed to create spherical or deformed shell models. We found that deformed acetabular shells produced higher frictional torque than spherical shells. Also, larger femoral head sizes produced greater frictional torque than smaller femoral head sizes. For the deformed models, the thicker polyethylene inserts produced greater frictional torque than the thinner polyethylene inserts.

Evaluation of surgical impaction technique and how it affects locking strength of the head–stem taper junction

Cases of fretting and corrosion at the taper junction have been reported in large metal-on-metal bearing combinations, and more recently, this concern has included metal-on-polyethylene bearing combinations. Many of these patients have been revised due to adverse local tissue reaction secondary to taper corrosion. This taper corrosion–related adverse local tissue reaction seems to be a multifactorial issue and difficult to assess. The aim of this study was to look at one potential variable, the impaction behavior (impaction force, number of blows, etc.) of orthopedic surgeons, and understand how this can affect the locking strength of tapers. A group of experienced orthopedic surgeons were asked to use their typical surgical approach to impact a femoral head onto a hip femoral stem using an Operating Room (OR)-simulated test setup. Impaction parameters such as impaction force, velocity, and energy, as well as the number of impacts, were characterized and applied in a bench-top study used to evaluate the effect of these parameters on the initial stability of the taper junction. High variation was found in the surgical impaction parameters, but overall it was determined that increased impaction force correlated to superior stability of the taper junction.

Method Development for Determination of Initial Stability of Cementless Femoral Stems

For press-fit (cementless) total hip arthroplasty, area of non-contact (gaps) between the bone and the implant may reduce the mechanical stability of the implant. Stability is essential for osteointegration and ultimately the long-term success of the implant. Therefore, it is necessary to assess the micromotion that occurs at the bone/implant interface and identify whether this micromotion is within an appropriate range to allow for successful osteointegration between the implant and host bone [1].Copyright