The RM Pressfit Vitamys: 5-Year Swiss Experience of the First 100 Cups

Abstract

ORIGINAL ReseARch ARTIcLemonoblock designs may be cheaper than their modular counterparts. Despite this, monoblock cups are not used as commonly as modular designs possibly because of concerns over adequate seating and positioning (2). Regardless of modularity, the overall survival of uncemented cups, however, depends on primary and secondary stability plus wear resistance.The RM Pressfit vitamys cup (Mathys Ltd.) is a titaniumcoated, vitamin E stabilised, highly cross-linked polyethylene monoblock cup. It achieves primary stability by equatorial press-fit and secondary stability by bony on-growth to the titanium coating (Fig. 1). This coating in itself conveys no structural stiffness which allows the cup to remain isoelastic compared to bone. The cup can accept supplemental screw fixation which potentially improves initial stabilisation in unexpectedly osteopaenic bone or acetabulae with wall deficiencies. The RM Pressfit vitamys (Fig. 2) is the evolution of the RM classic cup which has shown survivorship of 94% at 20 years for aseptic loosening (3). Osteolysis is seldom encountered if the annual wear rate is less than 0.1 mm/year (4). Secondary benefits of this design are the use of larger femoral head sizes to diminish instability -the commonest cause of early revision (1).

The concept of a cementless isoelastic monoblock cup made of highly cross-linked polyethylene infused with vitamin E: Clinical outcome and radiological analyses of migration and wear using EBRA at mid-term follow-up

“…They found a mean migration of 1.5 mm at 5 years, which can be confirmed by the present study. The majority of migration occurred within the first 12 weeks after surgery, thus, the authors concluded it can be explained just by the initial cup seating and all components can be considered stable thereafter [5]. The present study also shows that migration stagnates at 1-2 years postoperatively and subsequently in most cases secondary stabilization occurs.…”

“…Early migration is considered a predictor of aseptic loosening [5,35], as a mean cup migration of more than 2 mm in the first 2 years has previously been shown to correlate significantly with aseptic loosening in the long-term [21][22][23][24][25]33]. The present investigation resulted in a mean total migration of 1.34 mm at 5 years.…”

“…To date, only few previous publications can be found regarding the newest generation of the investigated cup. Wyatt et al [5] also analyzed cup migration, however, only few EBRA measurements (n = 13) could be included. They found a mean migration of 1.5 mm at 5 years, which can be confirmed by the present study.…”

“…1c). The body of the cup is made of highly-crosslinked UHMW-PE (HXLPE) stabilized with vitamin E [5,11,18].…”

“…Aseptic loosening of the components is one of the most prevalent causes for revision surgery [2,3]. In the last decades, a substantial effort has been made to avoid or prolong aseptic loosening and mechanical failure of the implants, and this will remain a major challenge in the future [4][5][6][7].…”