The Durom Acetabular Component. A Concise Follow-Up of Early Revision Rates at a Minimum of 2 Years

Abstract

We report our experience with 143 Durom acetabular components. Our data show a survivorship of 99.2% at 5 years, (95% CI 94.8-99.9), which is not consistent with other reports in the literature of high early failure rates. The true natural history of this component is yet to unfold completely.

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© 2012 Wichtig Editore - ISSN 1120-7000
Hip Int (2012 ;:05 ) 562 - 56522
562
The Durom acetabular component. A concise follow-up
of early revision rates at a minimum of 2 years
Jonathan Hutt 1, Matthew Dodd 2, Nikolai Briffa 2, Henry Bourke 2, Alexandra Hazlerigg 2, David Ward 2
1 Epsom and St. Helier NHS Trust, Epsom - UK
2 Department of Trauma and Orthopaedics, Kingston Hospital, Kingston-Upon-Thames, Surrey - UK
AbstrAct: We report our experience with 143 Durom acetabular components. Our data show a survi-
vorship of 99.2% at 5 years, (95% CI 94.8-99.9), which is not consistent with other reports in the litera-
ture of high early failure rates. The true natural history of this component is yet to unfold completely.
Key words: Uncemented, Durom, Survivorship, Revision
Accepted: May 21, 2012
ORIGINAL ARTICLE
DOI: 10.5301/HIP.2012.9743
INTRODUCTION
Large diameter metal on metal bearings in hip replacement
surgery are attractive options due to their wear and sta-
bility characteristics. The Durom acetabular component,
(Zimmer, IN, US), is a monoblock, flattened hemispherical
implant made of CoCr alloy with a Metasul Bearing. Initial
fixation is via press fit augmented by three cutting fins on
the peripheral rim: The component has a 0.3 mm thick-
ness pure titanium plasma sprayed porous coating without
hydroxyapatite. Initial reports of its use produced worrying
early revision rates with little demonstrable bony ongrowth
on explanted prostheses (1, 2). This led to a suspension
of activity in the US, where a number of class action law-
suits are currently in preparation. Other recent publications
have raised concerns about high early revision rates (3, 4),
but not all reported series have demonstrated such signifi-
cant problems (5, 6). We undertook a review of the Durom
acetabular components implanted at our institution.
MATERIALS AND METHODS
A retrospective review was undertaken to identify all
Durom acetabular components implanted for either total
hip replacement or hip resurfacing as a primary procedure
between March 2003 and June 2008. The senior author
performed all procedures. An anterolateral approach was
used for both total hip replacement and hip resurfacing, in
a theatre with vertical laminar flow.
Acetabular preparation was performed according to the
manufacturers guidelines and reaming was line to line. In-
traoperative seating of the acetabular component was a
priority in the senior surgeon’s operative technique. The
femoral component was either a Durom cemented femo-
ral resurfacing component or an uncemented CLS stem
coupled with a large metal bearing, (both Zimmer, IN, US).
The clinical outcome was established by reviewing the
patient notes and radiographs. Those patients without
documented follow-up of at least two years were con-
tacted by telephone to establish their clinical status and
whether they had undergone revision surgery.
Statistical methods
Survival curves were constructed using the life table meth-
od with 95% confidence intervals calculated according to
Rothman (7, 8). Three curves were constructed, with failure
defined as revision for any reason, or revision for aseptic
loosening with a best and worst case scenario. Patients

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Hutt et al
lost to follow-up were censored at the latest time point at
which the outcome of their acetabular component was
known.
RESULTS
143 hips in 139 patients were identified between March
2003 and June 2008, consisting of 84 total hip replace-
ments, (THR), and 59 resurfacings. The average age at
surgery was 59 (Range 28-84) with a male to female ratio
of 75:64. The mean follow up was 4.3 yrs (range 2-7 yrs).
Nine patients (9 Hips) were uncontactable despite signifi-
cant efforts, and were lost to follow-up.
There were 4 acetabular component revisions in 3 hips.
One was revised for component malposition 3 years after
initial surgery. At this revision, the cup was well fixed. Fur-
ther revision was required a year later for infection. There
was 1 further revision for deep infection. One patient with
a THR underwent revision for thigh pain at 6 years and
both components were noted to be loose at surgery. One
patient is being monitored for potential adverse metal re-
action with an elevated chromium level. Further imaging
has not revealed any evidence of pseudotumour and the
patient is currently under annual review. All other patients
were functioning well with no significant symptoms.
Fig. 1 - Sur vivorship cur ve - revision for any reason. Fig. 2 - Sur vivorship cur ve - revision for aseptic loosening (Best Case).
Survivorship at 5 yrs was 99.2% (95% CI 94.8-99.9) with
revision for any reason as the endpoint (Fig. 1). Figure 2
and Figure 3 show survivorship with revision for aseptic
loosening as the endpoint in a best and worst case sce-
nario respectively. For the worst case, all patients lost to
follow-up are assumed to have failed at a time point just
after their last known status, and in this setting, survivor-
ship for aseptic loosening at 5 years would fall from 100%
(95% CI 96.2-100) to 93.4% (95% CI 87.6-96.8). The full
survivorship curves with confidence intervals are shown
for completeness, but we have used the 5 year survival
rates as the study was about establishing early revision
rates and after this time period the estimated number at
risk falls below 50% of our total cohort numbers.
DISCUSSION
Uncemented hemispherical acetabular components with a
porous coating have a good pedigree. With revision for loos-
ening or evidence of radiographic loosening as an endpoint,
survival rates of 96% at twenty years for some components
have been reported (9), and are considered as a benchmark
for new designs (10). The Durom acetabular component,
however, is the subject of some controversy, and the pub-
lished success of this particular implant in the literature varies.

© 2012 Wichtig Editore - ISSN 1120-7000
564
The Durom acetabular component. A concise report of early revision rates
Long et al reported high levels of revision in a series of
206 hips, predominately implanted in female patients (2).
At two years, 15% (30 hips) of implanted cups had been
revised for loosening, including one case of deep infection.
12 further patients had clinical failure, and of the 176 hips
remaining in the study, a further 29 had radiographic evi-
dence of failure at last follow-up. Analysis of the 13 cups
removed in the second postoperative year showed no
evidence of bony ongrowth on the porous surface of any
cups. In this series, preparation of the acetabular bed was
modified to account for the shape of the cup, with reamers
not fully seated. The size was initially reamed line-to-line.
If this did not provide stability of a trial cup, then over or
under-reaming was performed to allow a stable fit.
Berton et al reported on a series of 100 hips at a mean
follow-up of 43 months (3). In all these cases, the acetabu-
lum was under-reamed by 2 mm according to the manu-
facturer’s instructions, but 7 acetabular components had
been revised, 2 for deep infection, 1 for metallosis, and
4 for aseptic loosening. Analysis of these 14 components
showed no bony growth on the porous coating.
Not all published results are so concerning. The latest
report from the Swedish Hip Arthroplasty Register records
a survival of 99.7% at 7 yrs of 326 Durom acetabular com-
ponents (11). Of the published series, similar good results
were reported by Panousis et al (6), with no acetabular
revisions at a mean of 4.6 yrs in a consecutive series of
200 hips. Vendittoli et al had no failures of the acetabular
component at a mean follow-up of 32 months (5).
Notwithstanding the variation in results, the reports of a
lack of bony ongrowth on the surface of the cups at revi-
sion are concerning. Neither of the series above report-
ing a high revision rate could attribute the poor results to
problems of orientation. The single acetabular component
revised in our series for aseptic loosening ‘popped free’ in
the manner described initially by Dorr, and did not show
any significant bony ongrowth.
There are a number of features of this implant that may
affect its success. Although hemispherical reamers are
used, the cup itself is not a hemisphere, with a sector an-
gle of 165 degrees and a peripheral flare at the rim (2). In
addition, the rim has 2 mm sharp circumferential fins for
rotational stability to be embedded in the bone. Because
of these features, when combined with seated hemispheri-
cal reamers for acetabular preparation, it is not possible
to fully seat the prosthesis even if the fins are embedded,
and gaps remain between the contact surfaces (2, 3). The
surface is a porous plasma spray coating, with a pore size
of 20-60 um. Porous surfaces have shown good fixation to
bone both in the laboratory (12, 13) and clinically (9, 10).
Pore sizes between 50 and 400 um give the best fixation
strength within the shortest time period (12), whilst a pore
size in the range of the Durom cup gives lower strengths
of fixation. The bony ongrowth will be further affected by
the surface contact problems associated with the shape of
the implant. In addition, without this contribution to initial
stability, the inevitable movement between the implant and
surrounding bone that will ensue will further compromise
bone formation at the implant surface (14).
The problems with the series of cups paper by Long et al
were reported in an earlier letter to members of the Ameri-
can Association of Hip and Knee Surgeons (1). In 2008,
Zimmer announced a voluntary suspension of US market-
ing and distribution whilst the company undertook a review
of labelling and surgical training, citing poor surgical tech-
nique as a cause for failure. The product was relaunched
later that year, with a new surgical training programme
initiated. This included a change to line to line reaming,
use of trials in every case, correct cup positioning and ap-
propriate impaction techniques with no repositioning of the
cup. Sales were not suspended in Europe. The same year,
Zimmer published a letter saying that the implants used
in Europe and the US were identical apart from indicating
Fig. 3 - Sur vivorship cur ve - revision for aseptic loosening (Worst Case).

© 2012 Wichtig Editore - ISSN 1120-7000 565
Hutt et al
tive probability of survival in life table analysis. J Chronic Dis.
1978;31:557-60.
8. Murray DW, Carr AJ, Bulstrode C. Survival analysis of joint
replacements. J Bone Joint Surg Br. 1993;75:697-704.
9. Della Valle CJ, Mesko NW, Quigley L, Rosenberg AG,
Jacobs JJ, Galante JO. Primary total hip arthroplasty with a
porous-coated acetabular component. A concise follow-up,
at a minimum of twenty years, of previous reports. J Bone
Joint Surg Am. 2009;91:1130-5.
10. Huo MH, Parvizi J, Bal BS, Mont MA. What’s new in total hip
arthroplasty. J Bone Joint Surg Am. 2009;91:2522-34.
11. Kärrholm J, Garellick G, Herberts P. Annual Report 2008:
Swedish Hip Arthroplasty Register 2008. Available at: http://
www.jru.orthop.gu.se/. Accessed December 3, 2011.
12. Bobyn JD, Pilliar RM, Cameron HU, Weatherly GC. The op-
timum pore size for the fixation of porous-surfaced metal
implants by the ingrowth of bone. Clin Orthop Relat Res.
1980;150:263-70.
13. Welsh RP, Pilliar RM, Macnab I. Surgical implants. The role of
surface porosity in fixation to bone and acrylic. J Bone Joint
Surg Am. 1971;53:963-77.
14. Cameron HU, Pilliar RM, MacNab I. The effect of movement
on the bonding of porous metal to bone. J Biomed Mater
Res. 1973;7:301-11.
that the plasma spray coating in the US was modified by
increasing its thickness by 0.1 mm to meet FDA abrasion
testing requirements.
Our findings of 99.2% survivorship at 5 years for revision
for any reason with a minimum 2 year follow-up of all cases
are not consistent with the findings of high rates of early
failure. However, as a result of the problems reported else-
where and the ongoing controversy regarding large metal
on metal bearings, this prosthesis is no longer in use by
the senior author and all patients have been contacted to
continue annual follow-up. The full natural history of the
Durom acetabular component is yet to unfold.
Financial support: This paper has received no external funding.
Conflict of interest: The authors have no significant financial interest or
other conflict of interest relating to this paper.
Address for correspondence:
Jonathan Hutt
6 Nevis Road
Tooting
London SW17 7QX, UK
drhutt@hotmail.com
REFERENCES
1. Dorr LD. Memo to American Association of Hip and Knee
Surgeons. Available at: http://www.csengerilaw.com/drDor-
rLetter.html. Accessed 3 December, 2011.
2. Long WT, Dastane M, Harris MJ, Wan Z, Dorr LD. Failure
of the Durom Metasul acetabular component. Clin Orthop
Relat Res. 2010;468:400-5.
3. Berton C, Girard J, Krantz N, Migaud H. The Durom large
diameter head acetabular component: early results with a
large-diameter metal-on-metal bearing. J Bone Joint Surg
Br. 2010;92:202-8.
4. Illgen RL 2nd, Heiner JP, Squire MW, Conrad DN. Large-
head metal-on-metal total Hip arthroplasty using the Durom
acetabular component at minimum 1-year nterval. J Arthro-
plasty. 2010;25 (6 suppl):26-30.
5. Vendittoli P-A, Mottard S, Roy AG, Dupont C, Lavigne M.
Chromium and cobalt ion release following the Durom high
carbon content, forged metal-on-metal surface replacement
of the hip. J Bone Joint Surg Br. 2007;89:441-8.
6. Panousis K, Meek R, Roberts P, Grigoris P. The Durom hip
resurfacing - results at an average follow up of 4.6 years. J
Bone Joint Surg Br. 2010;92 (SUPP_II):307.
7. Rothman KJ. Estimation of confidence limits for the cumula-