Stemmed TKA in a femur with a total hip arthroplasty: is there a safe distance between the stem tips?

When a stemmed TKA is needed in a femur in which a THA is already present, choosing an appropriate length for the TKA stem is crucial. Many surgeons intuitively fear that the distance between the stem tips correlates with the femur risk for fracture (RF). However, to date, no biomechanical data to support this intuition are available. Therefore, in this study, the RF in such a configuration was determined and compared for several activities, using a finite element modeling technique. During gait and sideways falling no difference in RF among different stem lengths was shown. However, a clear threshold appears during four-point bending. Stem tip distances shorter than 110 mm dramatically increased RF and, in osteoporotic bone, will certainly lead to fracture (RF>1) and thus should be avoided.

Pulsed plasma deposition of zirconia thin films on UHMWPE: proof of concept of a novel approach for joint prosthetic implants.

Wear of ultra-high molecular weight polyethylene (UHMWPE) has been recognized as the main cause for long-term revision in joint arthroplasty. A new approach to overcome this detrimental issue is here presented: zirconia (ZrO2) thin films were directly deposited onto the surface of UHMWPE by Pulsed Plasma Deposition (PPD) technique. The obtained films were structurally, morphologically and mechanically characterized by X-ray diffraction, scanning electron microscopy and nanoindentation tests, respectively. The critical fracture load was estimated by the analysis of the indenter footprints, while the adhesion degree was evaluated by a cross-cut tape test. Zirconia films exhibited a fully cubic structure, with densely packed grains, whereas mechanical tests showed that hard, tough and well-adherent films were deposited. These preliminary results suggested the feasibility of pursuing this alternative route to improve UHMPWE performances while preserving its well-established mechanical properties.