Dual Mobility Cup: A New THA Revolution

Introduction: In 1946-1948, JUDET brothers performed the first series of THA. Only 16 years later in 1962, date of the first moderne THA by Sir John CHARNLEY long-term FU demonstrates very good functional results, with an 85% survivorship at 25y and 65% at 40y FU. But dislocation still remains an unsolved and major risk.Dislocation may occur throughout patients' and implants' lives and was termed «cumulative risk» by J CATON and D BERRY in 2004. The risk of CHARNLEY's THA increases by 1% every 5y according to D BERRY and by 1.39% every 5y according to J CATON. According to national implant registries in SWEDEN, AUSTRALIA, ENGLAND and WALES, dislocations also become the prime reason for revisions in the first 2y after THA.Biomechanics show that a wider diameter of the head prosthesis increases the «jump distance» (the head displacement required to escape the socket) and hence reduces the dislocation risk. Large femoral heads are being increasingly used in routine THA; however there are limitations associated with a larger femoral head component, such as the risk of increased wear, and with a head diameter superior to 36mm, an increased risk of head/ neck taper fretting and corrosion (with the risk of an adverse reaction to metal debris) and also for ceramic on ceramic bearings, an increased risk of noises and squeaking.Dual mobility liners represent an alternative to large femoral heads and were developed in FRANCE in the early seventies (1974-1977) by Gilles BOUSQUET from SAINT ETIENNE and his engineer Andre RAMBERT.Biomechanical principles: The concept is a large head free of the adverse effects of the over-36mm diameter head.The biomechanical principles are very simple: a small (22.2 or 28mm) metallic or ceramic head, which is snap-fit within a large PE cup or «head» (smaller joint), and which nowadays hinges on a metal chrome-cobalt cup with a highly polished inner surface (larger joint).This DMC improves the movement capacity range of motion by a two-step recruitment mobility phenomenon: first with the inner (smaller) articulation and then the outer (larger) one, thus increasing the jump distance and enhancing the stability of the hip.In 2003 Daniel NOYER (France) described a «third articulation» in this system, between the stem neck and the chamfer of the PE cup, true metal/ PE bearing. In 1977 the first DM cup, named NOVAETM, was manufactured by SERF.Since 1977 many modifications have taken place, though based on the same principle: a metallic shell (stainless steel, or in our case, chrome cobalt in QUATTROTM from the LEPINE group), either cemented or cementless (with a double-layer titanium plasma spray and HA), on the PE insert (standard or HXLPE, lower or high inducing more resistance to plastic deformation), a true chamfer to optimize the neck contact (by making it thinner, and a real retentive rim to avoid the dislocation of the metallic head).Today the DMC are used routinely in FRANCE, in some European countries, but also in the USA, particularly for high-risk patients.The technique for performing a THA using a DMC is similar to a standard THA (approach, cup positioning...)