Comparison of conventional and highly crosslinked UHMWPE patellae evaluated by a new in vitro patellofemoral joint simulator

Abstract

A series of in vitro patella damage tests were developed using a knee simulator to investigate electron-beam-irradiated and -melted ultra-high molecular weight polyethylene and conventional ultra-high molecular weight polyethylene at the patellofemoral articulation. Three different simulations were created: (i) normal gait with optimal component alignment, (ii) stair climbing with optimal component alignment, and (iii) stair climbing with 4 degrees of femoral component internal rotation to simulate a component malalignment condition. In the last two simulations, all patellae were artificially aged. In normal gait, the unaged conventional and highly crosslinked patellae demonstrated similar behavior. In both stair climbing tests, unlike the aged highly crosslinked components, the aged conventional patellae developed cracks by 2 million cycles. These results demonstrate the potential advantage of highly crosslinked polyethylene for the patella.

In vitro simulation and quantification of wear within the patellofemoral joint replacement

“…8B;Hood et al, 1983;Schwartz et al, 2002) to previously reports of in vivo wear scars. A similar finding was reported by Burroughs et al (2006) in an in vitro experiment using a simplified non-physiological simulator. The wear scar area was seen to be constant at all measurement points.…”

“…The wear scar area was seen to be constant at all measurement points. This is in contrast to previous testing of sombrero style patellar buttons where the scar area was reported to increase with test duration (Burroughs et al, 2006). It is important to note the wear reflects extent of wear, creep and the translation of the contact area.…”

Patellofemoral interactions in walking, stair ascent, and stair descent using a virtual patella model

“…8). This difference is likely due to the peak compressive PFJRF used in the two studies; here, the peak load was set at 606 N, whereas Burroughs et al (2006) used a peak load of 1750 N. The contact patterns seen here in deep flexion, when the patella engages with the two femoral condyles, are also similar to those measured experimentally using pressure-sensitive film during other deep flexion activities (Wilkens et al, 2007).…”

“…Additionally, whereas contact pressure and contact area of the polyethylene can be effectively measured at a single flexion angle, measurement of these quantities throughout articulation is more challenging. Nevertheless, patterns of contact pressure and plastic strain presented here compare favorably with the wear and deformation patterns from physical testing on components subjected to simulated stair ascent (Burroughs et al, 2006). Patterns from this experimental study obtained from simulated walking extended to the medial and lateral edges of the patella (Burroughs et al, 2006), unlike results here which demonstrate only a small button of contact under walking conditions (Fig.…”

Ultra high molecular weight polyethylene/organoclay hybrid nanocomposites

“…[1][2][3] Consequently, it has been used in a number of specific areas including bearing components, gears, sporting goods, guide rails, and medical materials in total joint replacement. [4][5][6][7] Nanocomposites are promising materials for applications where improved mechanical properties, thermal stability, and chemical resistance are desired. 8 Because nanofillers such as carbon nanotubes, nanoclays, and nanofibres can be used at lower concentrations than conventional fillers, processability is facilitated in nanocomposites.…”