In the early 1970s, Professor Gilles Bousquet and engineer André Rambert laid the foundations of the principle of the Dual Mobility (DM) acetabular cup and also the necessary modularity of the components to contain the articular instability of the hip. The overall design of the DM cup is based on a very precise set of parameters, one of the most important safety factors is the retentive rim in a domain with several degrees of freedom with; a 1st and a 2nd mobility at the origin of 3 articulations characteristic of DM. Are discussed; the characteristics (design, diameters of inserts, materials, clearance, impaction / extraction of different diameter heads, different materials, roughness ...) and their biomechanical environment (range of motion, impingement, decoaptation/separation, lubrication, increase of the temperature gradient, wear, creep, deformation) so as to avoid the deleterious effects that may lead to intra-prosthetic dislocation (IPD) which is a specific mechanical failure of this process (despite it is typically a late complication and it has become very rare).

The retention collar (RC) is the part of the polyethylene (PE) insert that articulates with the head and neck, defining the third articulation of a dual mobility (DM) device. This collar ensures stability of the device due to its retentive effect. The RC is solicited during the impaction of the head into the insert and during hip movements. While introducing the head into the insert, it must not be damaged.  Its effectiveness depends on the way the surgeon handles it, the elastoplastic nature of the material, the dimensions of the surfaces and the shape of the collar, which must work like a hook providing easy entry of the head without causing damage while ensuring a difficult extraction.

We describe the factors influencing the wear of the RC by the neck of the implant according to the condition of the involved surfaces. The dimensions of the cup and the thickness of the PE also influence the wear of the RC and can lead to the “bottle-opener effect” causing an intra-prosthetic dislocation. The size of the heads, the surfaces in contact and the geometry of the RC determine the ability of the system to ensure stability of the head in the PE and fluidity of contact between the head, neck, and insert.

Knowledge of these considerations and the mechanics of the RC are required to extend the longevity of a DM device, the reference implant in the fight against luxation.  In the “Polarsystem”, the Polarcup used since 1999 respects these rules and minimizes the risk of intra-prosthetic dislocation.  A good RC is needed to ensure the stability and fluidity of the implant and the future of the DM, which is on its way to becoming the reference implant for THA. 

Background

Dual mobility concept has been successful in improving the range of motion and reducing the number of dislocations of total hip arthroplasty. It has been shown that during normal activity of the hip, the major motion of the prosthesis occurs between the femoral head and the inner surface of the insert, but there is still little motion between the insert and the shell. Several studies have tried to illustrate the behaviour of total hip prosthesis using standard radiography on patient, motion analysis or stereo camera on isolated prostheses, however the behaviour of dual mobility implant remains unclear.

Objectives

Therefore, the global aim of our work is to propose the use of the non-invasive ultrasound technique to assess the in vivo behaviour of a dual mobility implant. The method proposed to monitor a dual mobility implant is presented and validated using an isolated prosthesis.

Design and Methods

A 3D ultrasound probe (Aixplorer®, Supersonic Imagine) that enables the acquisition of ultrasound images in 3 perpendicular planes was used. Five ultrasound acquisitions of the implant immersed in water were realized. For each acquisition the insert position relative to the shell position was different. The acquired ultrasound images were used to reconstruct the position of the 3 parts of the implant thanks to a custom made mathematical algorithm.

Together with the ultrasound acquisitions, 3D acquisitions of the implant in the same positions were performed using a laser scanner (NextEngine 3D scanner), and used as a reference for the comparison with ultrasound measurements. Indeed, in order to check the ultrasound method’s reliability, the diameters of each part of the implant, and the angle between the plane of the shell and of the insert were compared to the 3D scan measurements.

Results

The average difference between θ angle measured with 3D or US method was 2.2°. The average difference between reality and diameter of the parts of the THA obtained by the US method is respectively 3.2 mm for the shell, 2 mm for the insert and 2.7 fort the head.

Conclusion

Regarding to the range of motion of a THA, the difference between reference method and our US method is very reliable. We have shown that US are a good option to monitor a dual mobility implant in vitro. The best way to follow a total hip arthroplasty in vivo would be to implant some markers on the different part of the implant, but with the very strict registration, it would be very difficult.

Introduction

Double mobility (DM) cups are an increasingly popular option for elderly patients, those at high risk of joint instability and/or poor compliance with post-operative protocols.The aim of this study was to establish whether a DM cup would generate metal ions to similar extent as metal-on-metal implants.

Methods

Between 2012 and 2015, 16 patients (13 women, three men) underwent primary hip replacement for advanced arthritis, with a Biolox® (CeramTec, Plochingen, Germany) ceramic head, a Corail® (DePuy Synthes, Warsaw, IN) femoral stem and a stainless steel (19% Chromium (Cr), 13-15% Nickel (Ni))  Novae® (SERF, Décines-Charpieu, France) DM cup with a polyethylene mobile insert. The mean patient age was 69.6 years [62 - 85]. All cases were performed by a single surgeon, the principal investigator (TASS).Serum levels (µg/mL) of Ni and Cr were measured by an independent laboratory (Biomnis®), using Inductively Coupled Plasma Mass Spectrometry pre-operatively and at two years post-surgery. Upper limits for Cr and Ni were <0.87 µg/mL and <1.0 µg/mL, respectively.Pelvis radiographs were taken pre- and post-surgery and analysed for radiolucent lines and features of prosthetic loosening. The Postel-Merle-d’Aubigné scoring system (PMA) was recorded pre-operatively and at each follow-up visit. 

Results

The mean follow-up was 29 months [13-39].

Preoperatively, seven patients had serum metal ion assays. The serum Ni levels were <1 µg/mL for six patients (86%) and >1 µg/mL for one patient (14%). The preoperative Cr level was 0.2 µg/mL [0-0.8 µg/mL]. Post-operatively, all 16 patients had serum metal ion assays, at an average of 29 months post-surgery. The serum Ni levels were <1 µg/mL for four (25%) patients and >1 µg/mL for 12 (75%) patients (four had levels >2 µg/mL).

No signs of radiographic loosening were demonstrated on pelvic radiographs at most recent follow-up. The average PMA at two years of follow-up was 17.8.

Conclusion

In the current study, DM cups generated elevated serum nickel ion levels but no significant elevation of serum chromium ion levels. These levels were still significantly lower than those demonstrated in studies related to metal-on-metal hip prostheses and metal spinal implants. The clinical significance of such increased serum metal ion levels remains unclear. Critically, analysis of the study cohort, did not reveal any significant negative clinical or radiographic outcomes, irrespective of the various serum metal ion levels.

Introduction

Based on a matched cohort of 231 cases of primary DM-THA and 231 cases FC-THAs, the purpose of this study was to assess whether 1) Revisions for infection are more frequent when using DMC-THA than FC-THA 2) Causes for revision are significantly different between DMC-THA and FC-THA.

Material and method

During two year period (2010, 2011), a prospective multi centre study (40 centres involved in France) was carried out by the French Society of Orthopaedic and Traumatology. Inclusion criteria were an exhaustive collection of first revision THA (at least one component revised, re-revision excluded). 2044 first revision cases were prospectively collected; 251 (13.5%) were revision of DMC-THA and 1793 were revision of FC-THA (87.7%). We defined a matching process (matching ratio 1:1) between the 2 cohorts. 231 DMC-THAs were eligible for comparison with to 231 FC-THAs.

Results

Forty-seven (20.3%) FC-THAs were revised for infection and 54 (23.3%) in DM-THAs. There was no statistical difference between the 2 series (p-value 0.65.). Forty-one (17.7%) FC-THAs were revised for dislocation, compared to 11 (4.7%) DMC-THAs (p value is 0.00014).

Discussion

Main finding of our study is that DM cup are not associated with an increased risk of revision for infection compared to standard THA. Revision THA for infection is not correlated to the type of cup used (DMC-THA or FC-THA).

Dual Mobility (DM) acetabular components are designed to enhance stability which is particularly useful for patients that are at risk for dislocation. DM technology is more than 30 years old  and many clinical studies attest to their low dislocation rates and high survivorship.Intra Prosthetic Dislocation (IPD) of the head from the polyethylene (PE) inner is unfrequent and late in the outcome of DM . 5874 documented DM were performed from 1991 to 2009 in the same institution.The mid term survival of a consecutive serie of 153 isolated replacements of the conventional PE mobile inner as treatment of the IPD of the femoral head is reported. The prosthetic metal head  was 22.2mm; the metal cup was a non-cemented hemispheric metal cup; the prosthetic femoral stem and neck was in titanium alloy.In 2017 42 were deceased . 111 IPD were reported at the latest follow-up. IPD succeeded after a mean age of implantation 17,8 years. The mean patients follow-up was 89,2+/-14,2m. 9 patients required an iterative exchange due to the absence  of the exchange of a damaged femoral prosthetic head with a good outcome after a new exchange head and inner; 10 underwent a revision  with new acetabular component because 3 recurent dislocations and major osteolysis with fracture of the greater trochanter. The isolated exchange is efficient concerning the age of the patients because non aggressive versus a revision but the exchange of the femoral head is imperative. Revision of the cup is performed  when the metalic cup is damaged or /and when a metallosis is noted; Metal-Metal impingement  creates a third body wear  which induces IPD and osteolysis of the proximal femur. DM needs to conserve the adequate positioning of the metal components .

The isolated exchange of the inner has to be associated with the exchange of the prosthetic femoral head. The limit of the process is the metallosis symptomatic of the Metal-Metal impingement  of the metal components .

Purpose :

Dislocation is a complication in total hip arthroplasty that could be minimized by the choice of implant. A good radiological follow-up and score of auto-evaluation are essential to assess potential failure of the implant. We retrospectively followed 86 dual-mobility cup (DMC) prosthesis in 78 patients younger than 65 years at operation to collect all the significant events.

Method :

We enrolled 86 primary DMC prosthesis in 78 consecutive patients in a retrospective study and contacted them for evaluation. Mean interval between operation and convocation is 4,2 years, mean age at surgery is 58,4 years. Two types of cementless DMC (Avantage ®) were used: 71 press-fit and 11 3Pegs and 6 cemented implants. We collected all the events and usual information about the patients.

We evaluated the evolution of these implants and compared them between the direct post-operative X-ray and the last one in order to observe the presence of radiolucent lines, osteolysis, loosening, ossifications and position of the cup. The patients were also invited to answer two scoring system of auto-evaluation (Oxford Hip Score and the HOOS).

Results:

The ten years follow-up cup survival rate was 90,2 %. One early dislocation occurred on a fall, no intra prosthetic dislocation, 9 hips were revised (1 dislocation, 1 aseptic loosening, 6 lavage and 1 fracture), 7 patients died with 8 DMC, 12 were lost to follow-up and 59 hips were still in situ. We observed a significant difference in the presence of radiolucency around the cup and the stem over the years whatever the kind of cup chosen.

Conclusion:

Considering the outcomes of this series of young patients, dual mobility cup is safe from early dislocation and intra prosthetic dislocation.  Nevertheless the increase of radiolucency and osteolysis need further follow up to evaluate their clinical implications. We might expect a better outcome with the apparition of the new E1 Highly Crosslinked Polyethylene.

Introduction

We report the results of a 12-year follow-up retrospective series of 310 total hip arthroplasties using cementless, press-fit, dual-mobility acetabular cups. The aim of our study was to evaluate the clinical and radiographic results of this acetabular cup at last follow-up.

Patients and methods

This continuous and homogeneous series included 310 primary total hip arthroplasties performed during the year 2001 to 2005. The THA combined a Integral® stem (Amplitude®, Valence, France) with a stainless steel Saturne® (Amplitude®, Valence, France) acetabular cup.

RésultS

At 12.6 years follow up, 170 patients (194 hips) were died without revision,  and 6 patients were lost to follow up. Among the 99 remaining patients (110 hips), 3 stems had been revised for femoral fracture without revision of the cup. The global survival rate at an average follow up of 12.6 years was 98% and the survival rate of the cup was 100%. The Harris hip score increased by 49 points and PMA score by 6 points. The radiological  analysis revealed no sign of loosening or intra prosthetic dislocation.

Conclusion

Dual mobility is a good alternative for primary hip arthroplasty, which seems to be a competitive option compared to other strategies  in patient of 60 years and more.

Background:  The POLARCUP is a dual mobility system designed to provide enhanced stability and reduce the risk of dislocation in total hip arthroplasty (THA) patients.  Despite having over 15 years of market history, there are currently no descriptions of long-term outcomes with this system. 

Objectives:  The objective of this study was to determine the long-term component survivorship and functional outcomes for subjects implanted with this dual mobility system.

Design and Methods:  Between 2002 and 2005, there were 502 THAs performed using the subject dual mobility system at 3 centers in France.  All subject records were reviewed for baseline Merle D’Aubigne, revisions, and complications.  Unrevised subjects were invited to attend a single follow-up visit that included WOMAC Scores, Merle D’Aubgine Scores, and standard radiographs.

Results:  At a mean follow-up of 11.9 years, the mean WOMAC total, pain, stiffness, and function scores were 13.9 (range, 0-75), 2.3 (range, 0-14), 1.1 (range, 0-6), and 10.7 (range, 0-56), respectively.  Mean Merle D’ Aubigne Scores improved from 9.9 (range, 6-15) to 17.0 (range, 10-18).  The cumulative 10-year survivorship was 98.7% (95% CI, 96.6-99.5) with revision of the acetabular component for any reason as the endpoint.  The acetabular component was revised in 14 subjects for aseptic loosening and secondary to fracture of the femur in 1 subject.  Radiographic analysis revealed a single subject with acetabular medial migration and osteolysis in Gruen Zones I, II, IV, and V. 

Conclusion:  This study is the first to report long-term results with this dual mobility system.  The system was associated with excellent long-term component survival and satisfactory functional outcomes. 

I use the dual mobility since 2006 in the fracture of the femoral neck in elderly patient

The serie include 356 ( cotyle Ades Dedienne Sante - Zimmer ) procedures with a minimal fellow ship of 1 year

The middle age is 82.5 years old

The range of dislocation is very low, less than 1%

There is no intra prothetic dislocation,  the range of reintervention is less than 1%

The range of death in this serie is less than 15% in the first year

The dual mobility is a very good solution for the take care of this population with a high risk of complication and dislocation

Background: Acetabular bone loss in revision hip surgery in the elderly represent a noteworthy surgical challenge. The Burch-Schneider reinforcement cage is widely accepted as a practicable option in managing Paprosky type III bone defects. In addition, Literature reports that implementing a dual mobility cup is useful to avoid dislocation of the prosthetic components, even in high-risk patients.

Methods: We consecutively studied 83 patients that undergone acetabular revision surgery. In 25 (30.12%) we find a Paprosky type III bone defect and managed it with a Burch-Schneider reinforcement cage. The mean age of these patients at the time of surgery was 80.3 years. The mean length of follow-up was 18 months. In 15 patients (60%) we employ a cemented polyethylene cup, in 10 (40%) a cemented dual mobility cup. 5 patients (20%) died (within 11 months after surgery) and 1 (4%) was lost to follow-up.

Results: We did not observe dislocation of the components in the dual mobility cup group and 2 dislocations (13.33%) in the polyethylene cup group. In both groups, we did not observe loosening of the components, nor other major complications (superficial and/or deep infection / implant breakage / peri-prosthetic fractures).

Conclusions: the Burch-Schneider reinforcement is a practicable option in managing severe acetabular bone defect in acetabular revision surgery, even in the elderly. Furthermore, the association with a dual mobility cup is useful to minimize the incidence of implant dislocation in the short as much as in the long term.