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ORIGINAL ARTICLE
The use of a dual mobility cup in the management of recurrent
dislocations of hip hemiarthroplasty
Christian Carulli
1
•
Armando Macera
1
•
Fabrizio Matassi
1
•
Roberto Civinini
1
•
Massimo Innocenti
1
Received: 29 December 2014 / Accepted: 15 June 2015
Ó The Author(s) 2015. This article is published with open access at Springerlink.com
Abstract
Background Dislocation is one of the most frequent
causes of failure of hemiarthroplasties of the hip, which is
the most common treatment for femoral neck fractures in
elderly patients. A revision with conversion to total hip
arthroplasty is the gold standard in case of failure of closed
reduction: however, the use of standard or modular com-
ponents shows variable outcomes. The use of a dual
mobility cup has been evaluated in patients with unstable
implants, given the good outcomes obtained in primary and
revision surgery. The aim of this study was to assess the
results of revisions by dual mobility cups in unstable
hemiarthroplasties.
Materials and methods Thirty-one patients (mean age
75.4 years) were retrospectively evaluated between 2006
and 2010 after conversion to total hip arthroplasty with
dual mobility cups for recurrent dislocations. The mean
number of dislocations was 2.6 (range 2–5). The evaluation
was performed by the American Society of Anesthesiolo-
gists physical function score (ASA) and the Harris hip
score, and several radiologic criteria.
Results The mean follow-up was 3.8 years. No recurrence
of dislocation was recorded. The ASA score remained
unchanged, and the mean Harris hip score improved from
62.2 before dislocation to 76.0 points postoperatively.
Conclusions Dual mobility cups may be a useful option
in the treatment of a hemiarthroplasty dislocation. No risk
of a new revision due to instability after insertion of dual
mobility cups resulted in our experience, and this option
may be strongly considered in cases of revisions of
unstable hemiarthroplasties.
Level of evidence IV.
Keywords Dislocation Hemiarthroplasty of the hip
Dual mobility cups Revision
Introduction
Dislocation is one of the major causes of failure of a
hemiarthroplasty of the hip (HAH). Its incidence is rated at
6–10 % with respect to 2–3 % for total hip arthroplasty
(THA) [1, 2]. Dislocations occur typically within 6 months
after surgery [3], particularly in the first 2–6 weeks. Sev-
eral factors have been advocated, such as sex, cognitive
status, anatomy of the acetabulum (related to patients);
femoral head diameter, femoral stem rotation and off-set,
surgical approach and excessive removal of joint capsule
(related to surgeons) [4, 5]. It is crucial to understand the
causes of dislocation before facing surgery with an ade-
quate strategy, in order to limit the recurrence of the
instability. Several procedures have been proposed
depending on the cause of the dislocation: repositioning of
femoral stem [6], conversion to THA [6, 7], revision with
traditional or modular neck components [7–10], use of
constrained components [11, 12], trochanteric advance-
ment [13], removal of acetabular or femoral osteophytes
[6], and repair of the abductor muscles and of the joint
capsule [14, 15]. However, all these procedures showed
rates of success ranging from 60 to 80 %, independently by
the cause leading to instability [6, 10, 13, 16–19]. Partic-
ularly, the conversion of HAH to THA demonstrated dis-
couraging results with reports of even worse failure rates
than a full revision [6, 7]. The implant of constrained
& Christian Carulli
christian.carulli@unifi.it
1
Orthopaedic Clinic, University of Florence,
Largo P. Palagi 1, 50139 Florence, Italy
123
J Orthopaed Traumatol
DOI 10.1007/s10195-015-0365-8
acetabular inserts also showed variable results, with a high
risk of increased wear, osteolysis, and instability in THA
[11, 12]. Revisions of unstable THAs are generally con-
sidered technically demanding procedures [20–22].
Recently, good results have been obtained by the use of
‘‘dual mobility’’ cups for revisions of unstable THAs [23–
31] and primary implants after femoral neck fractures [32],
in terms of limitation of dislocation recurrence and
preservation of a wide range of motion (ROM): low wear is
also expected. To date, no report addresses similar out-
comes for the management of unstable HAHs treated by
revisions with dual mobility cups.
The purpose of this study was to assess the short-term
results of a series of patients affected by unstable HAHs
managed by a conversion to THA with dual mobility cups.
Materials and methods
We retrospectively reviewed 31 patients (31 hips) affected
by recurrent dislocations of HAH, treated by a conversion to
THA with dual mobility cups between 2006 and 2010. All
patients had been given bipolar cemented implants for
femoral neck fractures: the index operation was performed
with a mean interval of 2.4 days (range 1–3) after patient
admission to the emergency room. Eighteen patients were
female and 13 male, with a mean age of 75.4 years (range
71–86) at the time of fracture. The right side was affected in
17 cases; the left side in 14 cases. Eleven patients were
operated on in other hospitals, while 20 were operated on at
the authors’ institution. All patients were operated on by a
lateral approach at the time of HAH. The mean interval to
the first dislocation after HAH was 23.2 days (range 1–46).
The mean number of dislocations was 2.6 (range 2–5).
Dislocations were mostly posterior (29 cases); one subject
showed a dislocation in an anterior direction; only one case
was multidirectional (a single patient with five episodes of
instability).An evaluation of the associated risk factors of
patients was made before proceeding to revision. The mean
time between the HAH and the revision in arthroplasty was
3.2 years (range 7 months–6 years). The American Society
of Anesthesiologists physical function (ASA) score based
on the severity of patients’ comorbidities was evaluated
[33]. The ASA score at the time of revision was III in 19
patients, IV in six subjects, and II in the remainder. Several
pathologies were present, and a high risk of dislocation was
considered in some patients: three cases of Parkinson&s dis-
ease, three cases of diabetes mellitus with severe peripheral
neuropathy, one case of critical peripheral arterial disease,
two severe cognitive impairments related to Alzheimer&s
disease, one hemiparesis as the result of a previous stroke,
and one of severe pluriarticular rheumatoid arthritis. The
Harris hip score (HHS) was also recorded [34]. A
radiographic study by anteroposterior and lateral views was
conducted to study the femoral stem position according to
Loudon and Charnley [35], and the stability of the compo-
nents as described by Engh et al. [36]. The presence of
radiolucent lines and osteolysis of periprosthetic bone were
assessed by the criteria of DeLee and Charnley, and Gruen
et al. [37, 38]. Cup inclination was assessed in the anterior–
posterior projection, measuring in degrees the angle formed
by a line drawn along the bottom of the acetabular com-
ponent intersecting with the horizontal inter-teardrop line.
Hip centre restoration was assessed by calculating the per-
pendicular distance from the prosthetic centre of rotation to
a horizontal line drawn between the tips of the teardrops.
Limb length was evaluated. Finally, the presence of peri-
articular ossification was also evaluated by Brooker’s
classification [39]. Collaborative patients, or relatives of
poorly oriented subjects were adequately informed, and
approved the treatment and follow-up. Surgery was per-
formed by two surgeons, in all cases by a direct lateral
approach through the previous surgical scars. In 19 cases a
general anaesthesia was performed (ASA score: IV in six
patients, III in 13); in 12 cases, a locoregional anaesthesia
was chosen. In 25 cases, a capsular laxity was present, while
in the remaining patients the capsule was mostly absent.
When possible, capsulae were sutured and soft tissues
reconstructed after the cup positioning. In all cases a dual
mobility acetabular cup was implanted as porous coated
press-fit or cemented (Avantage
Ò
, Biomet, Warsaw, IN,
USA). This component consisted of a metal cup with a
polished inner surface articulating with a high molecular
weight polyethylene bipolar insert (acting as a large diam-
eter head) containing a 28-mm chrome–cobalt head. In 20
cases, a press-fit cup was implanted (Fig. 1): three cups
needed a further fixation by two or three acetabular screws.
In the remainder, a cemented cup was implanted (Fig. 2).
Criteria leading to the use of a cemented cup were poor bone
quality or a significant enlargement of the native diameter of
the acetabulum as tested intraoperatively during acetabular
preparation. Cups sizes between 44 and 56 mm were used.
Actually, in a single case we also proceeded to the revision
of the cemented femoral stem, given the remarkable rota-
tional malposition of the component and the length dis-
crepancy (2 cm): a new larger cemented femoral stem was
used (MS-30
Ò
, Biomet, Warsaw, IN, USA). In 12 patients, a
long (eight cases) or extra-long (four cases) 28-mm head
was implanted to ensure an adequate offset and further
stability. The prophylaxis of heterotopic ossifications was
made by Indometacin 25 mg t.i.d. for 3 weeks in patients
without any contraindications related to other comorbidities
or concomitant therapies. Parameters such as blood loss,
following the criteria of Liu et al. [40], surgical time, and
early postoperative complications were recorded. Postop-
erative care consisted of a short period of immobilization
J Orthopaed Traumatol
123
with a pillow between the legs in order to limit adduction of
the hips. An assisted passive motion protocol from the 3rd
postoperative day was then performed. Active exercises,
partial weight-bearing, and assisted gait activities were then
specifically prescribed for each case, depending on pain and
patients’ collaboration. All patients were clinically and
radiographically evaluated at 1 month after surgery, and
after 3, 6, and 12 months. After this follow-up, all the
subjects were encouraged to attend a yearly follow-up.
Considering the small size of the study population, only
the Wilcoxon signed rank test was used to compare pre-
and postoperative HHS scores.
Results
All patients were followed at least for 2 years, with a mean
follow-up of 3.8 years (range 2–7 years). The average
blood loss was 210 cc (range 100–400), and the mean
surgical time was 57.8 min (range 45–120). Seven patients
were assisted after surgery in an intensive care unit for
24–48 h. No intraoperative complication was recorded.
Postoperative complications were present in six cases
(19.3 %): three deep vein thromboses (one unilateral, one
bilateral) managed by a mechanical compression and ther-
apeutic doses of low-molecular-weight heparin; one case of
urinary tract infection, treated by antibiotics; one case of
superficial wound infection, managed by an advanced
wound care treatment and oral antibiotics; and one case of
an acute imbalance in diabetes mellitus, managed by tai-
lored insulin therapy.
No case of dislocation was recorded during the mentioned
follow-up. Radiographic studies revealed radiolucent lines in
zone 2 according to DeLee and Charnley in three patients (all
with cementless cups). However, these were not progressive
and were less than 2 mm in width: these cups were correctly
implanted. In three additional cases radiolucent lines of about
1 mm without progression around the femoral component
Fig. 1 A left femoral fracture of a 72-year-old male patient, treated by a hemiarthroplasty of the hip (a); 3 weeks postoperatively, a dislocation
of the implant occurred (b), and conversion to total hip replacement by a pressfit dual mobility cup was performed (c)
Fig. 2 A left femoral fracture of a 79-year-old female patient,
affected by Alzheimer’s disease, and treated by a hemiarthroplasty of
the hip (a); 4 days after surgery, a dislocation occurred, treated by
closed reduction under anaesthesia (b). A second dislocation recurred
after 5 days, thus a cemented dual mobility cup was implanted (c)
J Orthopaed Traumatol
123
were found in zone 1 (the only patient with the stem revision)
and zone 5 (two patients) according to Gruen et al. The mean
cup inclination was 45.4° (range 42–49°). An adequate hip
centre restoration was achieved in 23 cases. A suboptimal hip
centre was achieved in the remaining subjects; however, due
to good stability, the patients accepted well the residual
length discrepancy (in all cases \1.5 cm). No osteolysis,
significant subsidence, or cement mantle fractures were
noted, according to the criteria of Loudon and Charnley. No
implant was found to be unstable or poorly stable according to
Engh’s classification. We recorded three cases (9.6 %) of
heterotopic ossifications grade 1 and one grade 2 (the patient
with the revised stem), without, however, referred symptoms
or functional impairments: two of them did not undergo
prophylaxis due to clinical contraindications.
The pillow was maintained for an average interval of
2.8 days (range 2–4). The mean HHS improved from 62.2
points (range 34–75) before the dislocation to 76.0 points
(range 71–80) postoperatively with a significant difference
(p = 0.002). The ASA score remained basically stable after
surgery in all the patients. Symptoms and functional dis-
ability progressively decreased over the follow-up period,
allowing all patients without neurologic impairments to
return to their common daily activities. Poorly or uncol-
laborative patients were not substantially able to complete a
full functional recovery, however, without further episodes
of dislocation.
Discussion
Dislocations of HAHs are generally associated with an
insufficient restoration of the centre of rotation or other
mechanical problems due to a wrong primary implantation.
The conversion of an unstable HAH to a standard THA is a
procedure with a high risk of further dislocations, with an
incidence often higher than revision THA itself [2, 20–22,
41, 42]. Several reasons have been advocated: the reduc-
tion of the diameter and offset of the femoral head, which
may produce an inadequate soft tissues tension; the inap-
propriate positioning of a retained femoral stem, frequently
maintained to avoid long surgical procedures in critical
patients; and the insufficient retaining properties of the
acetabular cup/liner complex. Several other options such as
the use of a cemented cup with a structural bone graft fixed
with screws, threaded cups with or without bone grafting,
constrained cups, reinforcement rings, or ‘‘anti-protrusio’’
cages have been proposed over the decades. Variable
results have been obtained in cases of acetabular discon-
tinuity or severe bone loss, poor acetabular rim coverage,
and substantial alterations of shape of the acetabulum [43,
44]. In the remaining cases, outcomes were not
satisfactory.
Figved et al. [20] reported a lower risk of complications,
including instability, based on the Norwegian Arthroplasty
Register, in cases of conversion of HAH to THA with stem
revisions, compared to stem retaining procedures. More-
over, in the same series, modular implants for revision
presented more advantages related to head size, neck
length, and worn head replacement. However, no mention
of dual mobility cups has been described.
Only a few studies showed no relationships or even
higher rates of dislocation between large diameter heads
and the risk of instability in primary and revision implants
[41, 42]. Llinas et al. [21] reported the long-term outcomes
of a series of failed HAHs treated with THA with tradi-
tional components: higher rates of earlier radiologically
detected loosening of acetabular components inserted fol-
lowing HAH failure were found with respect to primary
THAs. No mention of dual mobility cups was made in this
series.
Constrained cups and liners have been proposed over the
years with variable results [11, 12]. Reduction of ROM
related to component impingement, increased wear related
to high local stresses, and higher risk of loosening were
considered the reasons related to significant rates of failure
of these implants [23–25].
Dual mobility cups and large femoral heads have their
rationale in limiting instability, ensuring a wide ROM with
respect to traditional implants, and maintaining low wear in
primary and revision hip arthroplasties. Satisfactory long-
term outcomes have been reported in several series in
primary and revision hip arthroplasty [23–31, 45]. A single
multicentre study reported the use of this type of implant
for the primary replacement in patients affected by a
femoral fracture: a dislocation occurred in three cases out
of 214 patients (1.4 %) within the first 3 months [46]. The
authors found no recurrence of the dislocation in these
patients treated by closed reduction under general anaes-
thesia, even if they used a posterior approach, generally
associated with a higher risk of dislocation with respect to
the direct lateral approach [47, 48]. However, to date there
has been no significant experience regarding series of
HAHs failed for instability and managed by revision with
dual mobility cups. Bouchet et al. reported a statistically
lower risk of dislocation for the dual mobility cup com-
pared to a conventional 28-mm head and polyethylene
inserts implanted through a posterior approach. The insta-
bility rate was 0 % compared with 4.63 % for the con-
ventional prostheses [25]. In our series, we recorded
improvements in the HHS, and complication rates were
comparable to other reports in the literature. Nonetheless,
we had no recurrence of dislocation, and no specific failure
related to choice of implants. A specific mechanism of
failure of dual mobility cups is effectively represented by
the intraprosthetic dislocation [49–
51]. It consists of the
J Orthopaed Traumatol
123
loss of the polyethylene retentive rim, with escape of the
femoral head from the liner that may manifest particularly
in younger, high-demand patients undergoing a primary
THA with this implant [28, 51]. No similar complication
was recorded in our series.
The present study has some limitations. It is a retro-
spective analysis with a small number of patients, and
without a control group. However, we do not usually per-
form revisions with standard or constrained cups for
unstable HAHs, using in most cases a dual mobility com-
ponent: related costs are similar to other choices of treat-
ments. Nevertheless, at short-term follow-up we had no
recurrence of instability, with both versions (cemented and
cementless) of the dual mobility cup.
We feel that dual mobility cups may be a useful and
effective option worth considering in the treatment of HAH
dislocations.
Compliance with Ethical Standards
Ethical standards The authors state that the study conforms to the
1964 Helsinki declaration and its later amendments; the study was
approved by the local or institutional Ethical Review Board; all the
patients provided informed consent before being enrolled.
Open Access This article is distributed under the terms of the
Creative Commons Attribution 4.0 International License (http://crea
tivecommons.org/licenses/by/4.0/), which permits unrestricted use,
distribution, and reproduction in any medium, provided you give
appropriate credit to the original author(s) and the source, provide a
link to the Creative Commons license, and indicate if changes were
made.
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