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The effect of a collar and surface finish on cemented femoral stems: A prospective randomised trial of four stem designs



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 component subsidence, survivorship and clinical function. One hundred and sixty three primary total hip replacement patients were recruited prospectively and randomised to one of four groups to receive a cemented femoral stem with either a matt or polished finish, and with or without a collar. At two years, although there was a trend for increased subsidence in the matt collarless group, this was not statistically significant (p = 0.18). At a mean of 10.1 years follow-up, WOMAC scores for the surviving implants were good, (Range of means 89-93) without significant differences. Using revision or radiographic loosening as the endpoint, survivorship of the entire cohort was 93 % at 11 yrs, (CI 87-97 %). There were no significant differences in survivorship 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). 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.
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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
1 23
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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
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 8993) without significant differ-
ences. Using revision or radiographic loosening as the end-
point, survivorship of the entire cohort was 93 % at 11 yrs, (CI
8797 %). 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
Keywords Arthroplasty .Hip .Randomised .Bone Cement .
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 stemcement 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
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 cementstem
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 cobaltchromium
(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
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 (UltimaDePuy,
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
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
KruskalWallis test. Survival analysis was performed using
the life table method, with binomial confidence intervals (CIs)
calculated from the effective number at risk using Rothmans
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.
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 6.512.9) 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 % (89100 %), matt collared 97.4 %
(85100 %), polished collared 93.8 % (8098 %) and matt
collarless 81.2 % (6391 %). The only statistically significant
difference was between the two collarless stems, with the matt
surface leading to an inferior outcome, (p=0.02).
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 casecontrol 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 [8,2628].
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
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 8797 %). 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.
Fig. 7 Consolidated Standards of Reporting Trials (CONSORT) flow diagram
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... Since the introduction of cementless total hip arthroplasty (THA) in the late 1950s, many design modifications have been proposed to improve the primary stability and long-Electronic supplementary material The online version of this article (doi:10.1007/s00264-017-3524-0) contains supplementary material, which is available to authorized users. term survival of femoral stems [3,4]. Collared designs are thought to enhance primary stability and hence osseointegration by improving resistance to axial, rotational, and varus forces at the bone implant interface [4]. ...
... This might be of importance in view of the current trend to allow for early weight bearing after total hip arthroplasty. However, the use of collared designs is controversial, as concerns in regards to their downsides have been raised [3]. For an optimal load transmission, a perfect contact between the collar and the calcar is a mandatory prerequisite. ...
... Clinical studies have reported no difference in the revision rate of collarless and collared versions of the same stem [3]. In contrast, Demey et al. [4] reported that a collar increased the force required to initiate implant subsidence and intraoperative periprosthetic fractures. ...
Full-text available
Purpose: The aim of this study is to quantitatively compare the difference in primary stability between collarless and collared versions of the same femoral stem. Specifically, we tested differences in subsidence and micromotion. Methods: Collarless and collared versions of the same cementless femoral stem were implanted in two groups of six fresh-frozen cadaveric femurs. Each implanted femur was then subsequently tested for axial compressive and torsional loadings. A micro-CT based technique was applied to quantify implant subsidence and compute the map of local micromotion around the femoral stems. Micromotion of collarless and collared stems was compared in each Gruen zone. Results: Subsidence was higher but not significantly (p = 0.352) with collarless (41.0 ± 29.9 μm) than with collared stems (37.0 ± 44.6 μm). In compression, micromotion was lower (p = 0.257) with collarless (19.5 ± 5 μm) than with collared stems (43.3 ± 33.1 μm). In torsion, micromotion was also lower (p = 0.476) with collarless (96.9 ± 59.8 μm) than collared stems (118.7 ± 45.0 μm). Micromotion was only significantly lower (p = 0.001) in Gruen zone 1 and for compression with collarless (7.0 ± 0.6 μm) than with collared stems (22.6 ± 25.5 μm). Conclusions: Primary stability was achieved for both stem designs, with a mean micromotion below the osseointegration threshold. Under loading conditions similar to those observed in normal daily activity and with good press-fit, the collar had no influence on subsidence or micromotion. Further studies are required to test the potential advantage of collar with higher loads, undersized stems, or osteoporotic femurs.
... Total hip arthroplasty (THA) continues to be one of the most common elective procedures performed worldwide as our current population continues to age [1]. Overtime, the use of un-cemented collarless stems in the United States has become common place [1][2][3]. The relative ease of insertion, proven implant survival, and reliable clinical outcomes have made them popular [4][5][6]. ...
Full-text available
Introduction Fully hydroxyapatite-coated titanium alloy double-tapered stems have been successful implant designs for THA. The Novation Element Stem (Exactech, Gainesville, FL) is one of several of these implants following a modified Corail design philosophy. Although a great deal is known about the results of the Corail stem, little is known about the more recent Corail-inspired implants. The authors evaluated the clinical outcomes, radiographic findings and survival statistics of the collarless version of the Element Stem when used routinely in a diverse patient population. Methods A retrospective review was performed for all primary THR cases from 2010 to 2018. Patient demographics and HHS/OHS/patient satisfaction scores were obtained. Radiographs were evaluated for stem subsidence, radiolucencies, and bone responses to the implant. Results One hundred and fifty seven Element Stems were implanted with greater than 2 years of radiographic follow-up, while 105 Element Stems implanted during the study period had a survival of 5 years or more. Average HHS was 91.7 and average OHS was 44.0. 54 of 157 hips had radiolucencies, all of which included a proximal zonal radiolucency. Average subsidence was 3.33 mm; 18 hips had subsidence > 4 mm. There were 8 revisions for: aseptic loosening (4), trauma-related peri-prosthetic fractures, and early proximal–medial fractures. At 5 years, the all-cause survival rate is 92.4%, 96.2% based only on aseptic loosening and 98.1% based only on proximal medial fractures. Conclusion Clinical outcomes using the collarless Novation Element Stem are good, but early proximal medial fracture is still a factor in patients with poor-quality bone. Proximal radiolucencies progressing to aseptic loosening post-operatively are also a concern. The 11.5% rate of subsidence is comparable to other fully HA-coated collarless stems. This study provides a thorough critical analysis of outcomes and midterm survival data of this dual tapered-wedge fully HA-coated collarless stem used routinely in a diverse patient population.
... With the goal of subsidence-dependent fixation, taper-slip stems are characterized by a smooth polished surface with bi-or tri-planar tapers, thereby ensuring a robust cement-bone bond through cementbone interdigitation. In addition, the weaker stem-cement interface allows for controlled subsidence and micromotion tolerance with minimal debris generation [58]. Of note, there have been reports of proximal bone remodeling in response to the indirect load transmission through the cement mantle; however, the implications of such findings remain unclear [59]. ...
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Purpose of Review To describe the (1) indications, (2) preoperative precautions, and (3) stepwise technical details of modern femoral stem cemented fixation. Recent Findings Femoral stem cementation provides excellent implant longevity with a low periprosthetic fracture rate among patients with compromised bone quality or aberrant anatomy. Unfamiliarity with the details of modern cementation techniques among trainees who may lack frequent exposure to cementing femoral stems may preclude them from offering this viable option to suitable patients in later stages of their careers. As such, maximizing benefit from cemented femoral stem fixation among suitable candidates is contingent upon the meticulous use of modern cementation techniques. Summary In addition to proper patient selection, modern cementation techniques emphasize the use of (1) pulsatile lavage of the femoral canal, (2) utilization of epinephrine-soaked swabs, (3) vacuum cement mixing, (4) retrograde cement introduction, (5) cement pressurization, and (6) the use of stem centralizers. Furthermore, identifying and optimizing the preoperative status of at-risk patients with pre-existing cardiopulmonary compromise, in addition to intraoperative vigilance, are essential for mitigating the risk of developing bone cement implantation syndrome. Further research is required to assess the utility of cemented femoral stem fixation among younger patients.
... The distal anchoring of the stem, the favorable positioning of the SP2 stem, and the avoidance of the stress rising caused by the wedge design of the Exeter stem might be the reasons for the lower risk for PPF in this high-risk population. The effect of collar has been investigated in the literature [27]. In a randomized RSA study of different designs of the Lubinus stems indicated that alternative shapes could be possible and give adequate clinical results [28]. ...
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Background The purpose of this study was to compare the cumulative incidence of postoperative periprosthetic fracture (PPF) in a cohort of femoral neck fracture (FNF) patients treated with two commonly used cemented stems: either a collarless, polished, tapered Exeter stem or the anatomic Lubinus SP2 stem. Methods In this retrospective multicenter cohort study of a consecutive series of patients, we included 2528 patients of age 60 years and above with an FNF who were treated with either hemiarthroplasty or total hip arthroplasty using either a polished tapered Exeter stem or an anatomic Lubinus SP2 stem. The incidence of PPF was assessed at a minimum of 2 years postoperatively. Results The incidence of PPF was assessed at a median follow-up of 47 months postoperatively. Thirty nine patients (1.5%) sustained a PPF at a median of 27 months (range 0–96 months) postoperatively. Two of the operatively treated fractures were Vancouver A (5%), 7 were Vancouver B1 (18%), 10 were Vancouver B2 (26%), 7 were Vancouver B3 (18%), and 13 were Vancouver C (32%). The cumulative incidence of PPF was 2.3% in the Exeter group compared with 0.7% in the SP2 group (p < 0.001). The HR was 5.4 (95% CI 2.4–12.5, p < 0.001), using the SP2 group as the denominator. Conclusions The Exeter stem was associated with a higher risk for PPF than the Lubinus SP2 stem. We suggest that the tapered Exeter stem should be used with caution in the treatment of FNF. Trial registration The study was registered at (identifier: NCT03326271).
We have compared prospectively the incidence of loosening of 20 femoral stems with a matt surface with that of 20 polished stems of an otherwise identical tapered, non-modular design of Exeter hip replacement. The stems were inserted using the same technique at operation and radiographs showed no difference in the adequacy of the cement mantle or of fixation. All the patients were reviewed regularly and none was lost to follow-up. After a minimum follow-up of nine years, four matt but no polished stems had been revised for aseptic loosening. Polished stems subsided slightly within the cement mantle early, but did not loosen.
Survival analysis is a powerful tool for analysing the results of total joint replacement, but it has major drawbacks when the failure rates are very low. We have reviewed 35 recent survival analyses of joint replacements to assess the magnitude of these problems and make recommendations as to how they may be avoided.
To assess the role of surface finish in the survivorship of a cemented femoral stem, we evaluated the midterm clinical and radiographic performances of a cohort of patients who had total hip arthroplasties with two cemented femoral stems that differed only in surface finish. One hundred seventy-five patients [64 total hip arthroplasties with rough, textured stems (radius, 1.75-2.5 mu m) and 138 total hip arthroplasties with satin finish, textured stems (radius, 0.5 mu m)] were followed up clinically and radiographically for 4-8 years. All surgeries were done by one surgeon using the same surgical technique, acetabular cup, cement type, and cementing technique. The groups had similar demographics, diagnoses, preoperative clinical scores, cement mantle qualities, alignments, and lengths of followup. Seven hips in the rough surface group and none in the satin surface group had aseptic loosening. The femoral bone-cement interface showed progressive radiolucent lines or osteolysis in eight of 64 rough stems and in three of 138 satin stems. A rough, textured stem of this design is more likely to fail at intermediate followup than a satin surface stem. We recommend that the surface of cemented stems should be satin or polished with a radius less than 0.5 mu m.
In view of the increasing incidence of stem-type femoral component loosening, a detailed retrospective radiographic zonal analysis of 389 total hip replacements indicated a 19.5% incidence (76 hips) of radiological evidences of mechanical looseness, i.e., fractured acrylic cement and/or a radiolucent gap at the stem-cement or cement-bone interfaces. Detailed serial radiographic examination demonstrated progressive loosening in 56 of the 76 hips and these were categorized into mechanical modes of failure. The 4 modes of failure characterizing stem-type component progressive loosening mechanisms consisted of stem pistoning within the acrylic (3.3%), cement-embedded stem pistoning with the femur (5.1%), medial midstem pivot (2.5%), calcar pivot (0.7%) and bending (fatigue) cantilever (3.3%).
Improved cementing techniques have been shown to decrease the rate of aseptic loosening of femoral components of cemented total hip replacements at five to seven years. We now report our results in 105 hips in 93 patients at 10 to 12.7 years (mean 11.2). The improved techniques included use of a medullary plug, a cement gun, a doughy mix of Simplex P and a collared stem of chrome cobalt. Only three femoral components had definitely loosened, none were probably loose and 24 were graded as possibly loose. In contrast, the incidence of radiographic loosening on the acetabular side was 42%. Improved cementing techniques have produced a marked reduction in the rate of aseptic loosening of the femoral component, but the incidence of acetabular loosening is unchanged.
Four cases are described of localised endosteal bone lysis in the femur occurring in association with cemented femoral components that were not obviously 'loose' radiologically. In each, the area of lysis was shown at operation to be related directly to a region in which there was a local defect in the cement mantle surrounding the stem. Via the space between the stem and cement, such defects provide a route through which the contents of the joint cavity may reach the endosteal surface of the femur, subsequently leading to localised bone lysis, and later to frank loosening.
Unlabelled: We used three-dimensional finite-element models of the proximal end of the femur to examine the influence of stem material, stem geometry, and the use of a calcar collar on the stresses in and around implanted total hip-replacement femoral components. Anatomical bone geometries and realistic prosthetic geometries were considered. A slender titanium-alloy stem with a collar allows creation of calcar stresses of approximately 80 per cent of the anticipated normal levels. A similar stem of cobalt-chromium alloy creates calcar stresses of 67 per cent of these normal values. Stem designs without a collar were shown to generate no more than 40 per cent of normal values while larger, stiffer stems were seen to create less than 30 per cent of normal values, with or without a collar. Proximal cement stresses were increased by the use of titanium-alloy stems, but were reduced to low levels by a functioning collar. The highest cement stresses in the system were found near the tip of the stem, where titanium-alloy stems create lower stresses than do corresponding cobalt-chromium-alloy stems. The achievability of calcar loading with a titanium prosthesis was demonstrated in in vitro strain-gauge tests. Clinical relevance: Loosening of the femoral stem and calcar resorption are problems that are seen in many long-term clinical series of total hip prostheses. In order to reduce the incidence of these problems, the goal of the designer of a prosthesis is to reduce cement and cement interface stresses around the femoral stem and to create stress distributions in the bone that will prevent resorption.(ABSTRACT TRUNCATED AT 250 WORDS)