Watches/Warnings   |    
Concern About Early Intraprosthetic Dislocation in Dual-Mobility Implants
Marc Swiontkowski, MD
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Copyright © 2013 by The Journal of Bone and Joint Surgery, Inc.
JBJS Case Connector, 2013 Sep 25;3(3):e91 1-7. doi: 10.2106/JBJS.CC.M.00212
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As outlined in our January 16, 2013 editorial, “The Case Report Redefined with JBJS Case Connector,” one important role of the JBJS Case Connector is to alert the orthopaedic community about a potentially problematic device or therapy. When two or more such cases with similar mechanisms appear, we will identify the procedure or implant as a “watchable” intervention.
While this system is not statistically conclusive and may or may not be supported by other published case reports or registry data, the intention is to sharpen the focus of clinicians on the potential for similar problems and thereby enhance clinical outcomes and patient safety. The “Watch” designation may also encourage others to report related difficulties and enlist the orthopaedic community to either demonstrate that these are isolated, unrelated cases or sharpen the focus further by rigorously evaluating the intervention. Where appropriate, we may identify brand, model, or implant-lot specifics.
The dual-mobility approach to total hip arthroplasty is intended to provide improved stability along with two additional characteristics that are absent in many fixed-implant designs: increased range of motion and low component wear. Surgeons seem especially interested in dual-mobility devices for patients who need revision for recurrent dislocation, and that is the most common application in Europe, where dual-mobility prostheses have been used since the 1970s.
However, these devices are new to the orthopaedic community in the U.S. The first U.S. Food and Drug Administration (FDA)-approved dual-mobility hip implant was introduced by Stryker in February 2011 and is indicated for both primary and revision applications. Recent reports of early intraprosthetic dislocation have prompted us to issue this “Watch.”
Dual-mobility components essentially consist of a small metal femoral head embedded in a larger polyethylene ball, both of which are mobile within a metal acetabular cup. This is a reversal of the usual material configuration in total hip implants, in which the harder surface is the ball and the softer surface is the socket.
The dual-mobility design presents an advantage in range of motion (ROM): when the small femoral head reaches its ROM limit, the larger polyethylene ball can move in the cup. The claim for less wear stems from the lower torque forces generated by the small metal head that is encased in the larger polyethylene head, and the stability comes from the greater jump distances conferred by the large-diameter outer ball. With the polyethylene-on-metal interface, dual-mobility systems provide stability without the metal-on-metal contact that has caused so much concern in recent years.
Several European studies evaluating dual-mobility designs have confirmed high levels of implant stability. Philippot et al. identified “no early or late instability” among 384 cases that were followed for a mean of fifteen years1. Vielpeau et al. tallied only five dual-mobility devices that required revision for dislocation among 668 cases2. Three of these dislocations occurred after ten years or more, and the authors ascribed the two “early” dislocations (at four and six years postimplant) to “technical errors.” Vielpeau et al. concluded that “dual mobility can be recommended for patients over seventy years of age and for younger patients with high risk of dislocation.”
These studies also divulged a complication of dual-mobility systems that is now starting to emerge in the U.S.: intraprosthetic dislocation. The most common manifestation of this complication occurs when the metal femoral head separates from the surrounding polyethylene ball. This can leave the polyethylene component aberrantly positioned in the hip joint and the metallic femoral head in direct contact with the metal acetabular cup.
In a recent case series analyzing eighty-one cases of intraprosthetic dislocations among nearly 2000 dual-mobility hip replacement procedures in France from 1985 through 1998, Philippot et al. divided these dislocations into three types: “pure” intraprosthetic complications without arthrofibrosis or cup loosening, dislocation secondary to blocking of the liner, and dislocation associated with cup loosening3. Of note, these cases represent relatively late dislocations: the mean times to failure of these three types of dislocations were eleven, eight, and nine years after surgery, respectively.
In contrast to late intraprosthetic dislocations, two cases of early intraprosthetic dislocation of dual-mobility components appear in this edition of JBJS Case Connector. In both cases, surgeons chose a mix-and-match strategy to minimize surgical complexity and bone loss and to maximize hip stability. Despite these sound clinical objectives, both cases suggest that mixing dual-mobility components with components from manufacturers of non-dual-mobility systems may increase the risk of adverse events.
It should be noted that the mixed-component approach to dual-mobility devices is an off-label use, but it has appeared in the literature4. The FDA 510(k) clearance and the manufacturer’s surgical guidance for the dual-mobility components used in these cases explicitly instruct against their use with any component from another manufacturer.
Ward et al. report on the intraprosthetic dislocation of a dual-mobility implant where the polyethylene component completely dissociated from the metal head and lodged itself in the gluteal soft tissue. Because this adverse event occurred within two months of the device’s implantation, wear probably did not cause the intraprosthetic dislocation. The patient was an eighty-seven-year-old woman with dementia who had previously undergone two revision hip arthroplasties.
In this case, in order to match a retained femoral stem that had remained well fixed since its original implantation eleven years earlier, the surgeon used a properly sized femoral head from a different company than the maker of the polyethylene component. To use the dual-mobility device as labeled, the surgeons would have had to revise the well-fixed stem, increasing surgical complexity, bone loss, and potential risk to the patient.
While suggesting that the “mismatch of components is a potential etiology for the dissociation of the polyethylene component,” the authors go on to say that there are no known differences between cobalt-chromium heads of the same size from two different manufacturers. They report that the components were coupled in the operating room and that the bearing functioned properly during intraoperative stability testing. They surmise that the metal and polyethylene components had separated during an attempt at closed reduction of the dislocation when the patient had first presented with persistent instability and clunking. They also suggest that early intraprosthetic dislocations may be “generalizable to dual-mobility bearings and not related to the products of specific companies.”
This patient eventually received a constrained polyethylene liner and a metal femoral head manufactured by the maker of the femoral stem. After eight weeks, she was ambulatory with a walker and had not experienced additional dislocations.
In another case report in this edition of Case Connector, Riviere et al. implanted a dual-mobility bearing to revise a large-diameter metal-on-metal implant in a forty-two-year-old man who had an adverse reaction to metal debris and had a pseudotumor in the hip joint. Surgeons left the well-fixed monoblock cup in place to preserve bone and minimize surgical complexity. Six months after revision, the patient was doing well functionally, and the blood chromium and cobalt levels were substantially lower after one year.
However, at fourteen months postrevision, the patient presented with acute, intense groin pain. Radiographs revealed dislocation, and there was considerable metal debris in the joint. Closed reduction was unsuccessful, and during revision surgery, extensive wear of the mobile polyethylene component was apparent, with loose polyethylene particles in the joint and scratches on the dome of the OXINIUM head. Surgeons replaced the existing acetabular cup with a modular trabecular metal cup and implanted a ceramic modular bearing.
In this case, the authors speculate that the mobile polyethylene ball and existing acetabular cup were incompatible in shape and design. They recognize that the matched suprahemispherical dual-mobility cups are well designed for dual-mobility polyethylene bearings, but that the monoblock metal-on-metal cups provide an articular surface that is less than hemispherical and therefore not well suited for use with dual-mobility designs. Thus, they recommend against the use of dual-mobility components with cups designed for metal-on-metal bearings.
One irony about that recommendation is that surgeons are hoping that dual-mobility designs will be a viable option when revising metal-on-metal implants. They may eventually prove to be just that, but as these two cases suggest, early failures seem to arise when all components are not replaced simultaneously.
In another recently published case of intraprosthetic dislocation with the FDA-approved dual-mobility device, Banzhof et al. reported on a sixty-three-year-old woman with a long history of recurrent dislocations following a primary total hip arthroplasty in 20025. The most recent revision (a hemispherical cup and liner and 36.5-mm metal head) had followed an uneventful postoperative course for seven years until she had fallen and experienced two posterior dislocations in quick succession. During subsequent surgery, surgeons retained the original cup but lined it with the dual-mobility metal cup liner. Surgeons also implanted a dual-mobility polyethylene outer head (42 mm) and a metal inner head (28 mm).
Two months later, the hip spontaneously dislocated. After two unsuccessful attempts at closed reduction, radiographs revealed dissociation between the outer polyethylene head and the inner metal head. During surgical revision, surgeons found the metal head sitting in the cup liner and the polyethylene head positioned in the psoas sheath, with no signs of damage to either component. The cup liner was well fixed to the shell, but there was a slight separation of the locking mechanism. Subsequently, surgeons revised the acetabular component with a conventional titanium shell and also used a conventional liner and femoral head. One year later, the patient was walking without assistance, was pain free, and had not experienced any additional dislocations.
In this case, the authors attributed the separation of the metal and polyethylene heads to “impingement of the outer polyethylene head on the edge of the acetabular component” during the attempts at closed reduction. The authors recommend general anesthesia and use of muscle relaxants when attempting closed reduction of dual-mobility implant dislocations.
Cases of early intraprosthetic dislocation in dual-mobility devices are not restricted to revision procedures. In a case from the United Kingdom, Mohammed and Cnudde reported on a 70-year-old man who received a dual-mobility implant during a primary arthroplasty three years prior to presenting with insidious onset of hip pain6. Radiographs revealed an eccentric location of the metal head in the metal socket, abnormal position of the polyethylene liner, and heterotopic ossifications. Computed tomography images revealed a large cyst; aspiration of the cyst yielded 70 mL of black fluid that tested negative for infectious organisms.
While performing a single-stage revision arthroplasty, surgeons noted widespread black staining of all periprosthetic soft tissues. The metal head, dislodged from the polyethylene liner, had eroded through the metal socket. The components were extracted, and the metal head was found to be relatively unscuffed, with only minor wear to the convex surface of the polyethylene liner.
To avoid the numerous complications from metallosis, these authors encourage a “high index of clinical suspicion” for intraprosthetic dislocation in people who have dual-mobility devices and present with hip pain.
Until we know more about the exact etiology of both early and late intraprosthetic dislocation in dual-mobility hip implants, surgeons should consider intraprosthetic dislocation as a diagnosis in people who present with acute hip pain and have one of these implants, and they should use general anesthesia when attempting closed reductions of intraprosthetic dislocations.
Most importantly, until additional studies confirm whether, why, and in whom the mix-and-match approach to dual-mobility components is problematic, surgeons would be advised to adhere strictly to FDA and manufacturer guidance when implanting such devices, or to select an alternative implant design.
Case Connector would like to hear from surgeons who have had experience, either positive or negative, with these newly available prostheses.
Philippot  R;  Camilleri  JP;  Boyer  B;  Adam  P;  Farizon  F. The use of a dual-articulation acetabular cup system to prevent dislocation after primary total hip arthroplasty: analysis of 384 cases at a mean follow-up of 15 years. Int Orthop.  2009 Aug;33(  4):927-32.  Epub 2008 Jun 03.[CrossRef]
Vielpeau  C;  Lebel  B;  Ardouin  L;  Burdin  G;  Lautridou  C. The dual mobility socket concept: experience with 668 cases. Int Orthop.  2011 Feb;35(  2):225-30.  Epub 2010 Dec 24.[CrossRef]
Philippot  R;  Boyer  B;  Farizon  F. Intraprosthetic dislocation: a specific complication of the dual-mobility system. Clin Orthop Relat Res.  2013 Mar;471(  3):965-70.  Epub 2012 Oct 10.[CrossRef]
Verhelst  LA;  Van der Bracht  H;  Vanhegan  IS;  Van Backlé  B;  De Schepper  J. Revising the well-fixed, painful resurfacing using a double-mobility head: a new strategy to address metal-on-metal complications. J Arthroplasty.  2012 Dec;27(  10):1857-62.  Epub 2012 Jul 05.[CrossRef]
Banzhof  JA;  Robbins  CE;  Av  Ven;  Talmo  CT;  Bono  JV. Femoral head dislodgement complicating use of a dual mobility prosthesis for recurrent instability. J Arthroplasty.  2013 Mar;28(  3):e1-3.  Epub 2012 Dec 21.[CrossRef]
Mohammed  R;  Cnudde  P. Severe metallosis owing to intraprosthetic dislocation in a failed dual-mobility cup primary total hip arthroplasty. J Arthroplasty.  2012 Mar;27(  3):e1-3.  Epub 2011 Jul 12.[CrossRef]

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Philippot  R;  Camilleri  JP;  Boyer  B;  Adam  P;  Farizon  F. The use of a dual-articulation acetabular cup system to prevent dislocation after primary total hip arthroplasty: analysis of 384 cases at a mean follow-up of 15 years. Int Orthop.  2009 Aug;33(  4):927-32.  Epub 2008 Jun 03.[CrossRef]
Vielpeau  C;  Lebel  B;  Ardouin  L;  Burdin  G;  Lautridou  C. The dual mobility socket concept: experience with 668 cases. Int Orthop.  2011 Feb;35(  2):225-30.  Epub 2010 Dec 24.[CrossRef]
Philippot  R;  Boyer  B;  Farizon  F. Intraprosthetic dislocation: a specific complication of the dual-mobility system. Clin Orthop Relat Res.  2013 Mar;471(  3):965-70.  Epub 2012 Oct 10.[CrossRef]
Verhelst  LA;  Van der Bracht  H;  Vanhegan  IS;  Van Backlé  B;  De Schepper  J. Revising the well-fixed, painful resurfacing using a double-mobility head: a new strategy to address metal-on-metal complications. J Arthroplasty.  2012 Dec;27(  10):1857-62.  Epub 2012 Jul 05.[CrossRef]
Banzhof  JA;  Robbins  CE;  Av  Ven;  Talmo  CT;  Bono  JV. Femoral head dislodgement complicating use of a dual mobility prosthesis for recurrent instability. J Arthroplasty.  2013 Mar;28(  3):e1-3.  Epub 2012 Dec 21.[CrossRef]
Mohammed  R;  Cnudde  P. Severe metallosis owing to intraprosthetic dislocation in a failed dual-mobility cup primary total hip arthroplasty. J Arthroplasty.  2012 Mar;27(  3):e1-3.  Epub 2011 Jul 12.[CrossRef]
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Marc Swiontkowski
Posted on January 30, 2014
thanks for the continued dialogue
JBJS Case Connector Editor

Many thanks to the MGH group's contribution to the discussion thread about our Dual Mobility Hip Watch. This information will be useful for all hip surgeons who use this prosthetic approach for complex clinical scenarios or on a routine basis. The JBJS Case Connector team hopes that the discussion continues to the ultimate benefit of surgeons and patients where the dual mobility approach is being considered.

Kartik Mangudi Varadarajan PhD, Andrew A. Freiberg MD, Henrik Malchau MD, Harry E. Rubash MD, Orhun K. Muratoglu PhD, Thomas Zumbrunn MS, Michael P Duffy MS
Posted on January 27, 2014
Blocking of dual mobility insert by iliopsoas and hip capsule as mechanism for late intra-prosthetic dislocation
Department of Orthopedic Surgery, Massachusetts General Hospital, Boston, MA, USA

We would like to share our recent laboratory findings, which suggest that blocking of the dual mobility (DM) insert via impingement with the iliopsoas and hip capsule may be an important mechanism for intra-prosthetic dislocation (IPD). Prior to this discussion, we would also like to emphasize that this complication affects a small percentage of DM patients, and DM implants have enjoyed decades of successful use in Europe, especially for difficult-to-treat patient groups. Furthermore, the complication rates of other surgical options should be kept in perspective. Nonetheless, it is the responsibility of the scientific and clinical community to find ways to improve this promising technology further.

In the native hip the iliopsoas muscle/tendon complex has been shown to directly articulate against the native femoral head[1]. Consequently, the iliopsoas can impinge against a large femoral head prosthesis, leading to severe groin pain. This has been documented by Browne et al. for metal-on-metal patients [2]. In bi-polar hemi-arthroplasty, Schaffer et al. have shown that capsular impingement may lead to failure via blockage of the mobile bipolar head [3]. In a dual mobility implant, the large diameter DM insert acts like a large femoral head. This led us to suspect that the DM insert motion may be impeded by soft tissues such as iliopsoas and hip capsule.

We were able to confirm the above via laboratory experiments in cadaver specimens. In extension and low flexion, the DM insert tented the iliopsoas and its motion was impeded via anterior impingement with the iliopsoas. Furthermore, in certain positions the DM insert was fully trapped between posterior engagement with the stem tending to rotate the DM insert, and anterior soft tissue impingement blocking this rotation. A video from this experiment is available at this time on YouTube.

Intermittent and recurrent blocking of DM insert motion would result in increased load transfer from impingement with the femoral stem. This may lead to loss of the retentive rim over time, leading to late IPD. Previous generations of implants using conventional polyethylene may be at a higher risk of late IPD than newer implants using highly cross-linked and antioxidant stabilized polyethylene. The mechanism for the exceptionally rare early IPD is less clear, but may be a combination of soft tissue blocking of the DM insert and insufficient retentive force due to mixing of components or component assembly errors. Regarding the latter, the force required to cause IPD is typically on the order of several hundred newton. Therefore, in the operating room it may be difficult to detect instability even with substantial reduction in retentive force.

In conclusion, our recent laboratory work strongly suggests soft tissue related blocking or trapping of DM inserts as important mechanism for late IPD. We hope that a next generation of implants that can minimize soft tissue impingement, together with use of advance polyethylene materials, may further reduce the risk of this relatively rare complication.

1. Yoshio M, Murakami G, Sato T, Sato S, Noriyasu S. The function of the psoas major muscle: passive kinetics and morphological studies using donated cadavers. J Orthop Sci. 2002;7(2):199-207.
2. Browne JA, Polga DJ, Sierra RJ, Trousdale RT, Cabanela ME. Failure of larger-diameter metal-on-metal total hip arthroplasty resulting from anterior iliopsoas impingement. J Arthroplasty. 2011 Sep;26(6):978 e5-8.
3. Schaffer JL, Wilson MG, Scott RD. Capsular impingement as a source of pain following bipolar hip arthroplasty. J Arthroplasty. 1991 Jun;6(2):163-8.

Javad Parvizi
Posted on January 18, 2014
Could History Repeat Itself?
Rothman Institute, Bensalem, Pennsylvania, USA

No one doubts that total hip arthroplasty is a truly successful surgical procedure that affords relief of pain and return of function to many afflicted patients. A large number of prostheses are available to allow the surgeon to execute the operation well, and in the hands of a proficient surgeon the surgical procedure can be performed with high degree of success and without problems.
It is also clear that orthopedics in general and joint arthroplasty in particular can continue to make strides in making the surgical procedure even more successful and beneficial for our patients. Our profession continues to benefit from the vision of scholar surgeons, scientists and engineers. Invention of highly cross-linked bearing surface is one example of how the field was transformed. There are numerous other examples of progress that has benefited our profession. Conversely, our profession as a whole and total hip arthroplasty in particular suffered a blow to its reputation in recent years with the recall of metal-on-metal and modular femoral stems. Many thousands of patients had to be subjected to revision arthroplasty and many more stand in fear of revision as more and more of these prostheses fail. The question that comes to the mind of many is what issue in arthroplasty were these technologies intending to address? I personally believe that the increase in the use of metal-on-metal bearing surface and the reception it received in the orthopedic community was mostly because of its ability to "reduce" instability and not because of its "superior" wear characteristics. I am still puzzled to know exactly what issue the modular femoral stems were attempting to address during primary THA and remain unconvinced that these stems afforded better restoration of anatomy (offset and limb length) than their monolithic counterparts, at least in the hands of a proficient surgeon.
Dual mobility implants were recently introduced into the US market based on the data generated mostly in France. If one evaluates the literature from France (most of which is in their native language) one notes two striking issues. One is that the French utilized this system mostly in the elderly and just about every high level study that I am aware of had a notable failure of the device (aseptic loosening) in the early years. I realize that our industry partners claim to have "improved" the system by the use of highly cross-linked polyethylene and the use of a modular acetabular component and so on. The main question that still remains is what "issue" in THA is this device trying to address? I am not aware of a single in vivo study that shows superior performance of this device over other bearing surfaces nor do I know of any study that shows the use of this device led to a reduction in instability following THA.
The case report here, and many other anecdotal reports I am aware of, presents a unique failure mode for this device that we have not seen with other available prostheses. Only time will tell whether this device stands to catapult our subspecialty to a higher level by addressing real issues or stands to suffer the same fate as MOM and modular femoral stems. In the meantime one hopes that our patients are not subjected to undue suffering.

Tyler D. Goldberg
Posted on November 25, 2013
Caution about this Report
Texas Orthopaedics, Austin, Texas, USA

I would like to address the recent Watches/Warning regarding dual mobility (DM) implant Intraprosthetic dislocation (IPD). As a successful user of the DM technology for the last 4 years I have yet to experience an IPD or a hip dislocation essentially eliminating this complication from my practice.

I believe that DM technology was first approved in the United States in 2007 with the introduction of the Polar-Cup by Smith Nephew. Other companies followed with FDA introduction soon after. The implant I currently use, Versafitcup DM (Medacta International, SA) was FDA approved in April, 2009.

As with any technology, a meticulous analysis of the literature should be performed before introduction into clinical use. As is well known, DM was introduced by Bosquet in France in the 1970’s to minimize the risk of dislocation. It has been successfully utilized with survivorships>95%.[1,2] In fact Boyer, et. al. reports 80% survivorship at average 22 years utilizing first generation porous coatings and conventional first generation polyethylene.[3]

Few studies directly address IPD, a complication completely unique to DM design. The incidence reportedly ranges from 0.0 – 5.3%. However, it should be noted that when analyzing this complication, it seems to be associated with a 22.2mm femoral head size and occurs over longer term follow-up.[1,3,4] Leiber-Wackenheim et. al. reported a 0% IPD utilizing a 28mm head.[5] Most failures appear to be wear related with neck impingement causing degradation of the locking mechanism and eventual escape of the femoral head. Whether the improvements of Highly cross-linked polyethylene and 28mm heads, as employed in modern designs, continue to prevent IPD remains to be elucidated. Longer term studies are required but initial report such as Leiber-Wackenheim’s would lead us to have guarded optimism for a durable solution.

The Case Connector "Watch" highlights 4 cases. The first case highlights an 87 year-old patient with dementia who had undergone multiple revisions and an off-label “mix and match” DM articulation (mismatch of manufacturers of components). The second case reports a 42 year-old patient revised from a metal-on-metal THA with significant pseudotumor. Once again “mix and match” off label use of implants was utilized. One should not be surprised at unique complications in these settings. The third case once again highlights the use of DM technology in an exceptional setting: a 63 year-old female undergoing multiple revisions for recurrent dislocations. The fourth case reported highlights an unfortunate 70 year-old patient who suffered an IPD 3 years after a primary THA. The etiology of IPD in this case was unclear, but leaves one to wonder if the femoral head was ever truly captured by the surrounding polyethylene.

In conclusion, I would urge the AAOS to yield caution in this report. The 4 cases used to issue such an alert were exceptional by all accounts. The failure of these select patients should not justify the entire category of implants to be discontinued.

1. Philippot R, Farizon F, Camilleri JP, et al. Survival of cementless dual mobility socket with a mean 17 years follow-up. Rev Chir Orthop Reparatrice Appar Mot. 2008;94(8):e23-e27
2. Farizon F, de Lavison R, Azoulai JJ, Bousquet G. Results with a cementless alumina-coated cup with dual mobility. A twelve year follow-up study. Int Orthop. 1998;22(4):219-224
3. Boyer B, Philippot R, Geringer J, Farizon F. Primary total hip arthroplasty with dual mobility socket to prevent dislocation: a 22-year follow-up of 240 hips. Int Orthop. 2012;36(3):511-518
4. Philippot R, Adam P, Farizon F, Fessy MH, Bousquet G. Survival of cementless dual mobility sockets: ten-year follow-up. Rev Chir Orthop Reparatrice Appar Mot. 2006;92(4):326-331.
5. Leiber-Wackenheim F, Brunschweiler B, Ehlinger M, Gabrion A, Mertl P. Treatment of recurrent THR dislocation using a cementless dual-mobility cup: a 59 case series with a mean 8 years’ follow-up. Orthop traumatol Surg Res. 2011;97(1):8-13.

Marc Swiontkowski, MD
Posted on October 15, 2013
Response to Dr. Perona
Editor, JBJS Case Connector

After reading Dr. Perona's comment on the Case Watch article on dual mobility hips, I carefully re-read the manuscript. In it we clearly state that the surgeons involved with managing these two cases chose a "mix-and-match" approach. I basically have no disagreement with Dr. Perona's position, based on the two cases we report, and trust that this manuscript will prompt discussion about appropriate use of the dual mobility technology until we have other information to add to the discussion. I thank him for his comment.

Paul G Perona MD
Posted on October 03, 2013
Misleading Concerns About Early Intraprosthetic Dislocation In Dual-Mobility Implants
St Margaret's Health, Spring Valley, IL, USA

As an orthopedic surgeon who has implanted more than 500 ADM cups, I have concerns with the article that was listed as a "Watches and Warnings" top story. The title, “Early Intraprosthetic Dislocation in Dual-Mobility Implants,” insinuates that there is an inert risk with Dual-Mobility implants; however it does not state that the implants were revision cases, and mixed components from different companies directly against the manufacturers’ recommendation. The manual as well as the sales representatives strongly discourage the practice of mixing different company components.

Revision surgery for recurrent dislocations in multi-operated patients is a challenging situation no matter which approach is used. Failure of a Dual-Mobility implant in this situation should not condemn the practice, but it should be noted that if the hip dislocates it is very difficult to re-reduce. This fact may discourage the use of a Dual-Mobility cup rather than the fact that it may disassociate. Of all the ADMs I have inserted, I have never seen one disassociate. I feel that these are exceptional cases in which the implant was used for a difficult condition in an unorthodox fashion.

In conclusion, I feel that in this litigious society we live in, we as surgeons should be very careful in how we report things that may be construed the wrong way.

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