Loosening of the tibial component after total knee arthroplasty (TKA) is a common indication for revision. Increasing the strength of the initial tibial implant/cement interface is desirable. There is little information about the surgical techniques that lead to the highest strength. We investigated the effects of eight variables on the strength of the initial tibial baseplate/cement interface. A total of 48 tibial trays were cemented into acrylic holders using cement from two manufacturers, at three different times (early, normal, and late) using two techniques: cementing the tibial plateau or the plateau and the keel; and involving two conditions of contamination with marrow fat (at the metal/cement and cement/cement interfaces). Push-out tests were performed with load continuously recorded.Aims
Materials and Methods
The objective of this study was to compare the performance of the Explant Acetabular Cup Removal System (Zimmer), which has been the favored system for many surgeons during hip revision surgery, and the new EZ 54mm Stryker Trident® acetabular shells were inserted into the foam acetabula of 24 composite hemi-pelvises (Sawbones). The hemi-pelvises were mounted on a supporting apparatus enclosing three load cells. Strain gauges were placed on the hemipelvis, on the posterior and the anterior wall, and on the internal ischium in proximity to the acetabular fossa. A thermocouple was fixed onto the polar region of the acetabular component. One experienced orthopaedic surgeon and one resident performed mock revision surgery 6 times each per system.Introduction
Methods
What factors influence tibial tray-cement interface bond strength? We developed a laboratory model to investigate this issue with the goal of providing technical recommendations to mitigate the risk of tibial tray-cement loosening. Forty-eight size 4 Triathlon® tibial trays were cemented into an acrylic holder using two different cements: Simplex® and Palacos®; three different cementing times: early (low viscosity), per manufacturer (normal, medium viscosity), and late (high viscosity); two different cementation techniques: cementing tibial plateau only and cementing tibial plateau and keel; and two different fat (marrow) contamination conditions: metal/cement interface and cement/cement interface. A push-out test was applied at a velocity of 0.05 mm/s, and the load recorded continuously throughout the test at a rate of 10 Hz. The test was stopped when the plate debonded from the cement (i.e. the tray visibly separated from the acrylic support and the load dropped substantially). Statistical analysis was performed using Welch's t-tests and Cohen's d tests.Questions/purposes:
Methods:
TKR backside wear studies have concluded that, compared to rough trays, polished trays decrease total amount of backside wear by 80% to 87%. However, size and volumetric concentration of sub-micron-sized polyethylene particles are critical factors for macrophage-mediated osteolysis. We assessed the size and morphology of polyethylene wear debris from TKR backside wear simulations comparing polyethylene fretting against polished and blasted metal surfaces. A 3-station fretting wear simulator reproduced loads and motions typical of the backside of fixed-bearing inserts of TKRs. 5-million cyclic experiments combined low (50μm) or high (200μm) linear motion with +3o rotational motion. Load profile was double-peak Paul curve (peak 10MPa). Eight 3-station experiments measured polyethylene wear against blasted or polished metal surfaces of Ti6Al4V or CoCr. Polyethylene particles were isolated from serum following gradient separation and filtration on 0.01μm polycarbonate filters. Using SEM analysis, average 200 particles per sample were characterized with Meta-morph™ image analysis software. Concentration of submicron particles in the debris from rough surfaces was 31–32% under 50μm motion, 28–30% under 200μm. Surprisingly, this concentration from polished surfaces was substantially greater: 69–78% (50μm), and 57–63% (200μm). However, total poly wear against rough surfaces was 0.45–1.63mm3/ Mcycles, and 0–0.35mm3/Mcycles against polished. Taking this into account, the volume of submicron particles from polished surfaces is less than 0.1mm3/ Mcycles and from rough surfaces between 0.1 and 0.45mm3/Mcycles. In conclusion, although polished metal trays produce up to five times less wear than blasted surfaces, they may also lead to an increase in the osteolytic potential of the polyethylene debris.
