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International Orthopaedics
ISSN 0341-2695
International Orthopaedics (SICOT)
DOI 10.1007/s00264-013-2256-z
The effect of a collar and surface finish
on cemented femoral stems: a prospective
randomised trial of four stem designs
Jonathan Hutt, Alexandra Hazlerigg,
Ansari Aneel, Geoffrey Epie, Husam
Dabis, Roy Twyman & Andrew Cobb
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ORIGINAL PAPER
The effect of a collar and surface finish on cemented femoral
stems: a prospective randomised trial of four stem designs
Jonathan Hutt &Alexandra Hazlerigg &Ansari Aneel &
Geoffrey Epie &Husam Dabis &Roy Twyman &
Andrew Cobb
Received: 6 November 2013 /Accepted: 9 December 2013
#Springer-Verlag Berlin Heidelberg 2014
Abstract
Purpose The optimal design for a cemented femoral stem
remains a matter of debate. Over time, the shape, surface
finish and collar have all been modified in various ways. A
clear consensus has not yet emerged regarding the relative
merits of even the most basic design features of the stem. We
undertook a prospective randomised trial comparing surface
finish and the effect of a collar on cemented femoral compo-
nent subsidence, survivorship and clinical function.
Methods One hundred and sixty three primary total hip re-
placement patients were recruited prospectively and
randomised to one of four groups to receive a cemented fem-
oral stem with either a matt or polished finish, and with or
without a collar.
Results At two years, although there was a trend for increased
subsidence in the matt collarless group, this was not statisti-
cally significant (p= 0.18). At a mean of 10.1 years fol-
low-up, WOMAC scores for the surviving implants were
good, (Range of means 89–93) without significant differ-
ences. Using revision or radiographic loosening as the end-
point, survivorship of the entire cohort was 93 % at 11 yrs, (CI
87–97 %). There were no significant differences in sur-
vivorship between the two groups with polished stems
or the two groups with matt stems. A comparison of the
two collarless stems demonstrated a statistically significant
difference in survivorship between polished (100 %) and
matt (88 %) finishes (p=0.02).
Conclusions In the presence of a collar, surface finish did not
significantly affect survivorship or function. Between the two
collarless groups a polished surface conferred an improved
survivorship.
Keywords Arthroplasty .Hip .Randomised .Bone Cement .
Stem
Introduction
Since the earliest cemented total hip replacement, many dif-
ferent stem designs have been used; shape, surface finish and
collar have all been modified in various ways. Comparison of
the impact of each of these variables across published series is
difficult, as the stems being investigated often differ in more
ways than one. Each factor has a potential effect on the
mechanics of the stem and the stem–cement interface; thus,
the relative contribution of each is hard to elicit. In addition,
there are significant contributions from both patient character-
istics and surgical techniques that may influence outcome [1].
The number of factors contributing to success or failure may
explain why a clear consensus has not yet emerged regarding
the relative merits of even the most basic design features of the
stem. Variability of results even between different surgeons
using the same implant demonstrates the unreliability of com-
parisons between published results of individual implants.
The only way to establish the optimal design of implant is
by rigorous scientific assessment through a prospective
randomised trial, and such studies are few [2].
The design rationale of modern stems and the mechanism
of stability within the cement mantle can be broadly divided
J. Hutt (*):A. Hazlerigg :A. Aneel :G. Epie :H. Dabis :
R. Twyman :A. Cobb
Department of Trauma and Orthopaedics, Epsom General Hospital,
Dorking Road, Epsom, Surrey KT18 7EG, UK
e-mail: drhutt@hotmail.com
International Orthopaedics (SICOT)
DOI 10.1007/s00264-013-2256-z
Author's personal copy
into loaded-taper and composite-beam designs [3]. Loaded-
taper stems are expected to migrate in the initial phases after
implantation to a stable position. A polished finish, and thus a
weak cement bond, might be preferred with this concept, as
this, along with a hollowed centraliser used in some designs,
allows progressive subsidence to a position of stability with-
out generating metal and cement debris at the cement–stem
interface as a result of micromovement whilst also reducing
the development of channels at the interface in which debris
can travel [4].
A composite-beam stem has features such as a collar or
altered geometry or surface finish intended to achieve and
maintain initial stability, prevent subsidence and transmit load
directly to the cement mantle [3]. The advantage might lie in
reducing micromotion at the cement/implant interface, there-
by reducing generation of particulate debris, variation in hy-
draulic pressure, and tensile stresses within the cement that
might lead to cracking. These benefits may not be achieved,
however, if debonding of the interface occurs; features such as
surface roughening designed to prevent movement may then
compound the adverse consequences when movement does
occur [5,6]. This may account for some of the concerns
reported when matt surfaces are used with loaded-taper-
design stems [7,8]. The usefulness of a collar on a stem is a
matter of some debate. Its presence has the potential to transfer
load directly from the implant to the medial cement mantle
and the medial femoral neck; the ensuing benefit is reduced
stress in the proximal cement mantle and decreased stress
shielding of the proximal femur [9]. This altered loading
may in turn have a detrimental effect on distal cement stresses
[10,11]. Even with a collar, micromotion can still occur, and it
does not alwaysprevent early resorption of the medial femoral
neck [12,13]. This indicates that a collar may not be of
primary importance in preventing implant instability, and
evidence of disuse atrophy of calcar bone under a well-
fitting collar suggests that with a well-fixed stem, the collar
may be redundant even when particular effort has been taken
to ensure close contact between collar and bone.
We undertook a prospective, randomised trial in order to
determine the effect of a collar and alterations in surface finish
on cemented femoral stems.
Patients and methods
The Ultima LX stem, (Depuy, IN, USA) is a cobalt–chromium
(CoCr) alloy, straight tapered stem with a lateral flange
(Fig 1), and four variations were used in this study. Collared
and collarless versions were polished to give a surface rough-
ness of 0.1 μm, or sand blasted to give a matt finish with a
surface roughness of 2 μm. The stems were otherwise
identical.
The regional ethics committee approved the study design.
All patients aged between 60 and 80 years with a diagnosis
of primary osteoarthritis were invited to enrol. Patients un-
dergoing revision surgery, with a history of previous hip
sepsis or those likely to remain housebound once rehabilita-
tion was complete, were excluded from the study. Power
calculations were performed for the primary outcome of stem
subsidence using analysis of variance (ANOVA) to detect a
difference between treatment group means of 0.5 standard
deviations (SD) at a significance level of p<0.05. In order to
achieve 80 % power, a minimum of 160 patients, 40 in each
group, was required. In the end, 163 patients (163 hips) were
prospectively recruited between 1997 and 2003. Recruitment
was then ceased, as the stems, manufactured specifically for
the trial, were reaching the end of their useable shelf life. All
operations were performed at a single centre by one of four
consultant surgeons. Randomisation was via a previously
prepared sealed envelope opened in theatre once the patient
had been anaesthetised. A standard anterolateral approach
and cementing technique were used in all cases. The stems
were coupled with 28-mm ceramic heads and cemented
polyethylene acetabular components (Ultima™DePuy,
Warsaw, IN, USA). Three tantalum marker beads were im-
planted into the proximal femur at the time of surgery
(Fig. 2). Patients followed a standard rehabilitation pro-
gramme, with full weight bearing from the first postoperative
day.
The primary outcome measure was stem subsidence over
the first two years postoperatively. This was calculated after
digitising radiographs taken on the first postoperative day,
then at six months and one and two years. Measurements
were taken from the centre of the femoral head to marker
beads in the femur that were visible on all follow-up
Fig. 1 Anteroposterior (AP) profile of collared and noncollared stems
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radiographs. Secondary outcome measures were clinical func-
tion and implant survivorship. During the final follow-up
period, between April and May 2010, all surviving patients
were contacted via telephone or post. Function was evaluated
using the Western Ontario and McMaster Universities
Arthritis Index, (WOMAC). Those who were able to travel
were invited to attend for a follow-up radiograph. Hospital
notes were reviewed for all revisions, and all latest radio-
graphs were evaluated for any evidence of loosening in the
zones as defined by Gruen et al. [14].
Statistical analysis
Differences in mean stem subsidence at two years were
analysed using analysis of variance (ANOVA). Differences
in WOMAC scores between groups were analysed with the
Kruskal–Wallis test. Survival analysis was performed using
the life table method, with binomial confidence intervals (CIs)
calculated from the effective number at risk using Rothman’s
equation [15,16]. The endpoints were defined as stem revi-
sion for aseptic loosening or radiographic evidence of loosen-
ing as shown by progressive radiolucency in one or more
Gruen zones.The cumulativesurvival rates for the four groups
were compared using the log-rank test. Statistical significance
for all analyses was set at p< 0.05. The Consolidated
Standards of Reporting Trials (CONSORT) flow diagram for
the study is shown in the Appendix.
Results
The groups were well matched in terms of numbers, mean
age, preoperative hip score and mean follow-up time
(Table 1). At the last review of our 163 patients, at a mean
of 10.1 range 6.5–12.9) years, 44 patients had died, eight had
undergone revision (5.5 %) and five had been lost to follow-
up and were untraceable, which left 105 patients with surviv-
ing stems. All patients recorded a WOMAC score; 18 patients
across all four groups were unable to travel for a follow-up
radiograph at last review, as shown in the CONSORT dia-
gram. Two patients, one in group A and one in group C, had
radiographic evidence of stem loosening.
Three patients had significant complications, none of
which impacted on stem survival. There were two
periprosthetic fractures in the collarless matt stem groups:
One occurred at six months that was thought to be related
to a breach of the femur during broaching the femur at
surgery. The other followed a road accident eight months
after operation. Both were treated at the time of injury with
internal fixation, and both are still functioning well, with
WOMAC scores of 90 at 12.4 years and 10.3 years, re-
spectively. The latter stem had migrated only 0.4 mm at
six months prior to the accident. One patient with a matt
collarless stem had two dislocations at nine days and
four weeks postoperatively but then achieved stability and
a WOMAC score of 97 at 8.7 years postoperatively.
Subsidence at two years of individual stems in each group
is shown in Fig. 3. There was a trend for the collared matt
stems to migrate less than other groups, but this was not
statistically significant (p= 0.18). In all groups, the majority
of subsidence happened in the first six months, and all stems
were stable between 12 and 24 months (Fig. 4). There was no
correlation between the level of subsidence of individual
stems and eventual failure or loosening.
There were no significant differences in WOMAC scores
between groups for the surviving stems (p=0.29) (Fig. 5). The
mean for the entire cohort was 91. Survival curves with
cumulative survival at 11 years and 95 % CI (Fig. 6)were:
Tabl e 1 Breakdown of the four
groups after randomisation Group Number Mean Sex Preoperative Harris
Hip Score
Mean length
of follow-upAge M:F
A (matt collared) 43 72 15:28 29 9.7
B (polished collared) 41 71 20:21 25 10.3
C (matt collarless) 40 71 14:26 27 9.9
D (polished collarless) 39 71 14:27 29 10.2
Fig. 2 Radiograph showing positions of marker beads implanted in
proximal femur
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polished collarless 100 % (89–100 %), matt collared 97.4 %
(85–100 %), polished collared 93.8 % (80–98 %) and matt
collarless 81.2 % (63–91 %). The only statistically significant
difference was between the two collarless stems, with the matt
surface leading to an inferior outcome, (p=0.02).
Discussion
The two most commonly used stems in the Swedish
Arthroplasty Register are the Lubinus Sp II, (Waldemar
Link, Hamburg, Germany), a collared, CoCr, matt-surface
stem; and the Exeter (Stryker, NJ, USA), a tapered, highly
polished, collarless stem made of stainless steel. Both
designs show excellent long-term clinical survival [17].
Individual series show excellent clinical results with col-
lared polished [1], collared matt [18], collarless polished
[19] and collarless matt [20] stems, which indicates that
the two features we assessed in this study are only two of
many that could affect long-term survival. Other studies
concentrated on the effect of surface finish and presence
of a collar. Lachiewicz et al. reported on a prospective
randomised trial of a collared, precoated stem and a
collarless, polished stem and found no difference in sur-
vival at a mean of six years [21]. Vaughn et al. compared
a collared, satin-finish stem with a morphologically iden-
tical precoated stem and found that the latter performed
worse at four years of follow-up [22]. Vail et al. compared
a polished, collared stem with a grit-blasted stem and
found no revisions or difference in radiographic loosening
at five years, which led them to conclude that the surface
finish may be secondary in importance to optimal stem
design and good cement technique for short-term success
[23]. The same grit-blasted, collared stem was compared
in a study by Sherfey et al. with a polished, collarless
stem and found to have significantly worse results of
67 % survival at five years [24]. A case–control study
comparing collared stems with satin or rough finishes
showed increased levels of radiographic failure with the
latter type at between four and eight years [25]. Other,
less powerful, studies comparing stem finish also found
worse outcomes for stems with increasing degrees of
surface roughness [8,26–28].
Two prospective randomised studies compared stems with
and without a collar. One trial with published data at both five
and ten years found no difference in outcomes between a
Fig. 4 Western Ontario and
McMaster Universities Arthritis
Index (WOMAC) scores at latest
follow-up
Fig. 3 Individual subsidence of stems within groups at 2 years
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collared or collarless matt CoCr stem [13,29]. In that study,
there were no revisions in those stems defined as having good
collar to bone contact, although this was only achieved in
47 % of cases. Meding et al. compared a collared and collar-
less titanium stem and found no differences in clinical out-
comes at six years [30]. Whereas the variability of these
studies does not allow any firm conclusions, it would appear
that roughening the surface of the stem to increase cement
bonding does not confer a survival benefit. However,
implantation of roughened stems may be more unforgiv-
ing once a cycle of loosening is initiated due to the
increased wear debris produced. Grose et al. reported high
early failure rates with a modified design of a previously well-
performing stem. The addition of an extra roughened proximal
coating resulted in debonding, leading to accelerated
osteolysis and loosening. [31].
There are limitations to our study. The sample size would
only be able to detect large variations in survival between groups
[21]. In addition, we were unable to follow-up all patients with
evaluation of clinical outcomes and radiology. Although all
patients contacted had good WOMAC scores, they might in-
cludesomepatientswithearly subclinical loosening.
This paper reports the medium-term results of a prospective
randomised trial designed to investigate the effect of a collar
and altered surface finish on the survival of cemented femoral
stems of the same profile and material. Overall survival of all
Fig. 6 Survival curves showing
cumulative survival at 11 years,
with 95 % confidence intervals
Fig. 5 Mean stem subsidence in
each group over 2 years
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stems in our study was 93 % (95 % CI 87–97 %). In the
presence of a collar, the surface finish of the cemented femoral
stem in this study did not significantly affect survivorship or
function. Without a collar, a matt finish was associated with a
lower survivorship of 81 % at 11 years. Collared matt stems and
collarless polished stems gave equivalent excellent results.
Acknowledgments The authors thank William Twyman for his assis-
tance with digitising and analysis of radiographs.
Conflicts of Interest and Funding Johnson and Johnson (now Depuy,
IN, USA) provided funding for the implants used in the study and for a
research nurse over a 2-year period. None of the authors have any other
financial disclosures relevant to this study.
Appendix
Fig. 7 Consolidated Standards of Reporting Trials (CONSORT) flow diagram
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