Prophylactic Tibial Stem Fixation in the Obese: Comparative Early Results in Primary Total Knee Arthroplasty.

Purpose: Obesity is a risk factor for aseptic loosening after total knee arthroplasty (TKA). Prophylactic use of tibial stems may enhance tibial fixation in obese patients. The aim of this study was to determine whether a tibial stem extension decreases rates of early failure in obese patients.

Monotonic and fatigue behavior of five clinically relevant conventional and highly crosslinked UHMWPEs in the presence of stress concentrations.

Five formulations of clinically relevant UHMWPE (conventional, moderately crosslinked annealed and remelted, and highly crosslinked annealed and remelted) were investigated in a physiologically relevant environment. Their monotonic stress-strain behavior in the presence of notches of two different severities and at two different displacement rates was examined using a custom developed video based system. It was found that both an elevation of yield stress and a truncation of orientation hardening took place under monotonic loading and that these changes were found to be material and elastic stress concentration factor dependent.

Notch sensitivity of PEEK in monotonic tension.

Poly(ether-ether-ketone) (PEEK) has been used as a load bearing orthopaedic implant material with clinical success. All of the orthopaedic applications contain stress concentrations (notches) in their design; however, little work has been done to examine the stress-strain behavior of PEEK in the presence of a notch. This work examines both the stress-strain behavior and the fracture behavior of neat PEEK in a uniaxial loaded condition, and in circumferentially grooved round bar specimens with different elastic stress concentration factors.

Notched stress-strain behavior of a conventional and a sequentially annealed highly crosslinked UHMWPE.

Contemporary total joint replacement designs contain stress-risers such as fillets, grooves, and undercuts; therefore, it is of interest to analyze the behavior of UHMWPEs in the presence of such design-related stress-risers. This study examined the engineering and true axial stress-strain behavior of smooth cylindrical and notched cylindrical test specimens, under applied axial tensile loading (2 displacement rates, 37 degrees C) for a conventional and a highly crosslinked second generation UHMWPE. Both materials were prepared from ram extruded GUR 1050.

Large deformation compression induced crystallinity degradation of conventional and highly crosslinked UHMWPEs.

The effect of a large compressive plastic deformation on the melt temperature (Tm), lamellar thickness, crystallinity, and density of four UHMWPEs (two conventional and two highly crosslinked) was examined. The materials were prepared from a single batch of medical grade GUR 1050 resin (Ticona, Bayport, TX, USA). The two conventional UHMWPEs were as-received (virgin) and gamma radiation sterilized at 30 kGy in a nitrogen atmosphere (radiation sterilized).