Injury Extra (2004) 35, 111—113

www.elsevier.com/locate/inext

CASE REPORT

Intraprosthetic dissociation of a ‘JRI’ bipolar hiphemiarthoplasty

James Gibbs*, Richard Hargrove

Trauma and Orthopaedic Department, St. George’s Hospital, Blackshaw Road, Tooting,London SW17 0QT, UK

Accepted 4 July 2004

A 78-year-old woman was admitted to hospital hav-ing had a fall down her stairs at home. Five weeksbefore she had had an intracapsular fracture of herright hip which was treated with a cemented bipolarJRI prosthesis (JRI, Sheffield, UK) via a modifiedHardinge approach. The bipolar prosthesis wasassembled correctly, there were no intraoperativecomplications and the operating surgeon was happywith the overall stability once the prosthesis wasreduced. The post-operative X-ray was also satis-factory (Fig. 1). Her admission X-rays for this fallshowed an intraprosthetic dissociation of her bipo-lar hemiarthroplasty (Fig. 2) where the dissociatedinner metallic component of the bipolar cup is stillattached to the femoral stem and the outer poly-thene and metal cup is still within the acetabulum.

Over 19,000 JRI cemented bipolar hemiarthro-plasties have been used in the United Kingdom since1991 (data from manufacturers) when they wereintroduced. This is the first recorded dissociation ofany of their bipolar heads.

The patient was taken to theatre where a closedreduction, under general anaesthesia with paraly-

* Corresponding author. Present address: 8 Gateways, SurbitonHill Road, Surbiton, Surrey KT6 4TR, UK.Tel.: +44 2083399975; mobile: +44 7980843265.

E-mail address: jamesrgibbs@hotmail.com (J. Gibbs).

1572-3461/$ — see front matter # 2004 Elsevier Ltd. All rights resedoi:10.1016/j.injury.2004.07.033

sis, failed. An open reduction showed the femoralstem to be well fixed and so the bipolar head wasrevised to a similar head of the same size. The

Figure 1 Immediate post operative radiograph.

rved.

112 J. Gibbs, R. Hargrove

Figure 2 Post fall radiograph showing dissociation of thebipolar prosthesis.

polythene of the removed bipolar head was notmacroscopically cracked or deformed. The patientmade a good recovery and after 6 weeks hadreturned to her pre-morbid (i.e. pre-dislocation)levels of mobility.

Discussion

Bipolar dissociation is a rare but recognised compli-cation of the bipolar prosthesis. Some older pros-thesis appears to be more prone to thiscomplication. In general, there seem to be fourmechanisms for bipolar disassociation:

(1) W

here the entire bipolar head dislocates andthen a closed reduction leads to an immediateor late disassociation6 due to a ‘bottle opener’effect which locks the cup onto the posterioracetabular rim or where the cup has ‘button-holed’ through the soft tissues.

(2) F

ailure to correctly assemble the bipolar heads.Some bipolar heads have ‘snap-fit’ bipolar com-ponents such as the Hastings (Johnson and John-son, Leeds, UK). This has lead to a number of

reports of dissociation4,8 thought to be due todue to a ‘beginners mistake’ of failing to cor-rectly assemble and ‘snap-fit’ the bipolar com-ponent at the time of surgery.

(3) T

he third is due to a mechanical failure andfracture of the polythene in the bipolar cup ashas been reported with the Bateman prosthe-sis.1

(4) T

he fourth is due to late creep deformation ofthe polythene lining of the cup leading to dis-sociation.5

To these mechanisms we would like to add a fifthmechanism reported by the JRI manufacturers,where a bipolar head was dropped on the floorand then autoclaved (strictly against guidelines)leading to the inner head falling out after cooling(thankfully before surgery!).

Summary

Bipolar dissociation is a rare but serious complica-tion. It almost always leads to an open reduction andit is associated with a high mortality –— 50% in twostudies4,7 but these studies have low numbers in afrail population. This level of mortality also occursafter dislocation of non-bipolar hemiarthroplastieswhere mortality at 6 months can be up to 65%.3

Some authors advocate open reduction of all dis-located bipolar hemiarthroplasties to avoid thecomplication of dissociation.6 However, in astudy of almost 2000 bipolar hemiarthroplastiesonly 29 dislocated, 25 were reduced closed butof these 13 re-dislocated and 7 needed operativeintervention.2

If dissociation occurs it should be reported to themedical devises agency (Hannibal House, Elephantand Castle, London, SE1 6QT) and serious considera-tion given to a primary open reduction and revision.Any failed bipolar head should be kept for laboratoryanalysis and the high morbidity and mortality ofthese dislocations should be recognised and actedon from the initial presentation.

References

1. Barmada R, Mess D. Bateman hemiarthroplasty componentdisassembly. Clin Orthop Relat Res 1987;224:147—9.

2. Barnes CL, Berry DJ. Dislocation after hemiarthroplasty hip. JArthroplasty 1995;10(5):667—9.

3. Blewitt N, Mortimer S. Outcome of dislocation after hemiar-throplasty of the hip. Injury 1992;23(5):320—2.

4. Harvey IA, Jones MW. Separation of the hastings hemiarthro-plasty: a report of 8 cases. J R Coll Edinb 1991;36:202—3.

Intraprosthetic dissociation of a ‘JRI’ bipolar hip hemiarthoplasty 113

5. Kim Y.-H. Late separation of femoral head from bipolar acet-abular assembly. Orthop Rev 1986;15:673—6.

6. Loubignac F, Boissier F. Dissociation de la cupule au cours de lareduction d’une luxaion de prosthese de hanch intermedaire.Revue de Chirugie Orthopedique 1997;83:469—72.

7. Muller BN. Seperation of the Christiansen Prosthetic compo-nents following dislocation of hemiarthroplasty for hip frac-ture. Acta Orthop Scand 1983;54:553—6.

8. Stewart HD, Papagianno G. Hemiarthroplasty: a progression intreatment? J R Coll Edinb 1986;31:345—50.