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UNIVERSITY OF TORONTO MEDICAL JOURNAL
The Impact of Gender and Socioeconomic Status on
Patients Outcomes in Hip Resurfacing Arthroplasty
Michael Olsen, Ph.D.*
Emil H. Schemitsch, M.D., F.R.C.S.(C).
Investigation conducted at St. Michael’s Hospital
University of Toronto
Toronto, Canada
Primary and Corresponding Author
Michael Olsen, Ph.D.
Martin Orthopaedic Biomechanics Laboratory
St. Michael’s Hospital, University of Toronto
5-066 Shuter Wing, 30 Bond Street
Toronto, ON, Canada
M5B1W8
T: (416) 864-5482
F :(416) 359-1601
Email: michael.olsen@utoronto.ca
Senior Author
Emil H. Schemitsch, M.D., F.R.C.S.(C).
Head, Division of Orthopaedic Surgery
Department of Surgery
St. Michael’s Hospital
800-55 Queen Street East
Toronto, ON, Canada
M5C1R6
Email: schemitsche@smh.ca
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ABSTRACT
Hip resurfacing is a bone-conserving alternative to total hip replacement for the young and
active adult with end-stage hip disease. Determinants of health including gender and
socioeconomic status have been demonstrated to impact outcomes in total hip arthroplasty but
little is known of their effect on patient outcomes in hip resurfacing. The aim of this study was to
investigate whether there are differences in post-operative functional outcomes, and rates postoperative complications and revisions for patients of different gender and socioeconomic status
receiving a hip resurfacing arthroplasty. Between November 2004 and December 2008, 204
consecutive hip resurfacings were performed in 187 patients by a single surgeon in a highvolume academic hospital. The impact of patient gender and socioeconomic status was
analyzed with respect to post-operative functional outcome scores and complication and
revision rates. There were no significant differences between males and females with respect to
functional outcomes or rates of complication or revision.
Socioeconomic status was not
significantly correlated with complication or revision rate. Of the patients residing in Toronto
receiving a hip resurfacing, 54% lived in neighbourhoods of highest socioeconomic status while
only 14% lived in neighbourhoods of low socioeconomic status. The current work did not
demonstrate a correlation between patient gender nor socioeconomic status and outcomes
following hip resurfacing arthroplasty in this single surgeon series. Toronto residents receiving a
hip resurfacing tended to reside in neighbourhoods of higher household income and thus this
study demonstrates a propensity for individuals of higher socioeconomic status to receive a hip
resurfacing arthroplasty.
KEYWORDS: Hip resurfacing, gender, socioeconomic status, functional outcome, complication,
revision
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INTRODUCTION
The aim of joint replacement is to replace a diseased joint with a pain-free and functional joint,
restoring the patient’s quality of life and in many cases improving the overall health of the
patient.
While the benefits of joint replacement include the former, the detriments include
infection, bleeding, nerve palsies, mechanical malalignment and malfunction and even revision
surgery to repair or replace the prosthesis.
Total hip arthroplasty (THA) effectively replaces
both the acetabulum and proximal femur of the patient to restore a functioning and pain free hip
joint.
Traditionally, THA has been indicated for an older population with end-stage hip disease.
However, in recent years, the demographics for patients receiving THA have been changing. 1
Patients are receiving hip replacements at younger ages and THA is no longer a procedure for
the elderly. Younger patients with hip disease are increasingly looking to restore their quality of
life earlier rather than live with their degenerative condition until an older age. Younger patients
place greater demand on their hip replacements and as a result require growing numbers of
revision surgeries compared to their aged counterparts.2 The notion of a single hip joint
replacement in a patient’s lifetime is becoming outdated and rather the notion has now has
shifted to providing the patient a continuum of care with respect to their hip replacement.
A movement has evolved to preserve acetabular and femoral bone stock in patients to ensure
they will be good candidates for revision surgery in the future. Hip resurfacing arthroplasty has
become the preferred choice for the young, active adult with end-stage hip disease.3,4 Prudent
patient selection is key to minimizing the likelihood of premature failure, because as with THA,
hip resurfacing arthroplasty ultimately requires revision surgery in the future. 5
Numerous
studies have looked at THA to determine those patient characteristics that increase the risk of
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revision.6-9
Santaguida et al. performed an extensive meta-analysis investigating the influence
of patient characteristics on outcomes in hip replacement. 8 They showed that younger age and
male sex increased the risk of revision 3-fold. These findings have not been echoed in hip
resurfacing. In fact, women tend to have poorer outcomes with higher revision rates. 5,10-12
Gender as a prognostic factor in hip resurfacing has been demonstrated in numerous
studies.5,10-14 However, there is recent literature to suggest that it is not a patient’s gender, but
rather the size of the component, that influences the likelihood of revision. Shimmin et al.
reviewed the Australian Orthopaedic Association National Joint Replacement Registry and
concluded that femoral component sizes less than 44 mm had a 5-fold increased risk of revision
compared to implants 55 mm or greater, irrespective of gender. 15 This leads one to speculate
that gender may be a surrogate for the size of the patient’s anatomy and that those patients with
larger bones and implants fare better.
In addition to implant related factors, socioeconomic status (SES) is a patient factor that has been
purported to impact outcomes in not only total hip replacement16 but also in other facets of surgery
including colorectal surgery17 and
liver18 and renal transplantation19.
Investigating the
association of implant factors as well as socioeconomic status on outcomes following total hip
replacement, Allen Butler et al. randomized 102 patients to receive either a titanium or cobaltchrome femoral stem.20 They demonstrated that socioeconomic factors including education and
household income have a greater influence on the outcomes following hip replacement than
specific implant factors.
Currently, no such work has looked at this relationship in hip
resurfacing.
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The scope of the current work is to further refine selection criteria for patients eligible for
conservative hip arthroplasty. The main aetiology for revision following hip resurfacing is femoral
neck fracture.21 This has been attributed mainly to mechanical risk factors including femoral neck
notching or varus femoral component alignment during preparation of the femoral head.22,23
However, there has also been speculation regarding vascular insufficiency of the femoral remnant,
local and systemic metal ion levels, and gender as possible explanations for early failure.6,15-18 To
this end, there have been recommendations regarding patient selection in hip resurfacing.5,24 The
aim of this work is to further enhance the literature supporting patient selection in hip resurfacing
and specifically address the health determinants of gender and SES in this regard. The outcome
of the work is to better help surgeons offer conservative hip arthroplasty to patients that will benefit
greatest from this intervention with the least likelihood of postoperative morbidity and risk of
revision surgery.
Therefore, the aim of the current study was to investigate within a single surgeon’s hip
resurfacing practice whether there are differences in post-operative functional outcomes, and
rates of post-operative complications and revisions for patients of different gender and
socioeconomic status.
METHODS
Between November 2004 and December 2008, 204 consecutive hip resurfacings were
performed in 187 patients by the senior surgeon (EHS). There were 153 males and 34 females.
The dominant etiology was primary osteoarthritis (OA) in 187 hips, OA second to hip dysplasia
in two hips, OA second to slipped capital femoral epiphysis in one hip and avascular necrosis
(AVN) in 14 hips. The mean age at time of surgery was 51.8 years (SD 8.5, Range 25-82) and
mean Body Mass Index (BMI) was 29.3 kg/m2 (SD 5.1, Range 19.5-51.9).
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Patients with a minimum 2-year clinical and radiographic follow-up were included in functional
outcome analysis in which there were 154 patients (165 hips). There were 124 males and 30
females. The dominant etiology was primary OA in 153 hips, OA second to hip dysplasia in 2
hips and AVN in 10 hips. The mean age at time of surgery was 51.8 years (SD 8.5, Range 2582) and mean BMI was 29.3 kg/m2 (SD 5.1, Range 19.5-51.9).
Ethics approval was obtained through the Research Ethics Board at St. Michael’s Hospital to
collect patient data from a prospectively updated hip replacement database. Data including date of
birth, date of surgery, operative hip, gender, BMI, postal code, postoperative complications, length
of follow-up, postoperative functional scores, and date of revision were included in the analysis.
Post-operative functional scores were tracked using the St. Michael’s Hospital (SMH) hip score
(Table 1).25 Scored out of a total of 25 points, this score evaluates the domains of pain, function
and range of motion. Patients were followed up at 6 weeks, 3 months, 6 months and yearly
thereafter.
Analysis of socioeconomic status included only those patients residing in the City of Toronto at the
time of surgery. Postal code was used in this study as a surrogate for socioeconomic status.
Data for median neighbourhood household income published by the City of Toronto was used in
place of individual SES.26 The subset of patients used in this analysis consisted of 60 patients
(65 hips). There were 49 males and 11 females. Diagnoses included primary OA in 62 hips,
OA second to hip dysplasia in 1 hip and AVN in 2 hips. The mean age at time of surgery was
53.3 years (SD 8.1, Range 38-73) and mean BMI was 28.3 kg/m2 (SD 3.9, Range 20.7-41.3).
The socioeconomic status classification for individuals residing in Toronto established by
Hulchanski was used to segregate patients into one of three categories. 27 Patients were divided
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into (1) neighbourhoods in which the average individual income increased 20% or more from
1970 to 2000, (2) neighbourhoods in which the average individual income increased or
decreased less than 20% from 1970 to 2000, and (3) neighbourhoods in which the average
individual income decreased 20% or more from 1970 to 2000.
Statistical analysis was performed using Microsoft Excel (Microsoft Corp. Redmond, WA, USA)
and the statistical software package SPSS (SPSS Inc, Chicago, IL). A repeated measures
ANOVA was used to compare differences in SMH hip scores at the different follow-up time
points. A Pearson Chi-Square test was used to compare differences in complication rates and
rates of revision between genders. Correlations between gender and socioeconomic status and
rates of complication and revision were evaluated using Pearson’s correlation coefficient (r).
Kaplan Meier survival estimates were calculated using Stata 10 (Statacorp, College station,
Texas, USA).
RESULTS
The mean follow-up time for the study cohort was 3.2 years (Range 2-6 years). There was no
significant difference in SMH hip scores at any follow-up time period between males and
females (p=0.322, Figure 1). There were 11 complications in the series (5.4%, Table 2). There
was no significant difference in complication rate between males (7/153, 4.6%) and females
(4/34, 11.8%, p=0.107). Gender was not significantly correlated with complication rate (r=0.118,
p=0.108). There were 5 revisions in the series (2.5%, Table 3). The mean time to revision was
26.6 months (SD 14.2, Range 12-42 months). Etiologies included OA in 4 hips and AVN in one
hip. There was no significant difference in revision rate between males (4/153, 2.6%) and
females (1/34, 2.9%, p=0.611).
Gender was not significantly correlated with revision rate
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(r=0.008, p=0.915). The Kaplan Meier survival estimate at 6 years for males was 96% (95% CI
0.87-0.99) and for females was 89% (95% CI 0.43-0.98).
There was no significant difference in SMH hip scores at any follow-up time period between
individuals residing in Toronto and the remainder of the patient cohort (p=0.317, Figure 2). One
complication occurred in a female with elevated serum metal ion levels, and one revision
occurred in a male for deep joint sepsis complicated by femoral neck fracture. Median Toronto
neighbourhood household income was not significantly correlated with SMH hip score at latest
follow-up (r=0.174, p=0.165), rate of complication (r=0.045, p=0.720), or rate of revision (r=0.051, p=0.686). According to the Hulchanski classification, 54% of Toronto patients receiving a
hip resurfacing resided in neighbourhoods of high socioeconomic status (Figure 3). In contrast,
only 14% of Toronto patients receiving a hip resurfacing lived in neighbourhoods of lower
socioeconomic status.
DISCUSSION
Hip resurfacing is a bone-conserving alternative to total hip replacement for the young and
active adult with end-stage hip disease.
socioeconomic
status
have
been
Determinants of health including gender and
demonstrated
to
impact
outcomes
in
total
hip
arthroplasty7,8,16,20,28,29 but little is known of their effect on patient outcomes in hip resurfacing.
The current study was unable to demonstrate significant correlations between gender or
socioeconomic status and post-operative functional outcomes, complication rates or rates of
revision.
This study demonstrates, however, the tendency for individuals of higher
socioeconomic status to receive hip resurfacing arthroplasty.
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Several studies have speculated that female gender negatively impacts outcomes in hip
resurfacing arthroplasty.5,10-12 Early work by one of the pioneers of modern hip resurfacing,
Harlan Amstutz, looked at 400 hip resurfacings performed between 1996 and 2000. 10 The
overall survivorship for those patients was 94.4% at 4 years. The most important risk factors for
femoral component loosening and substantial stem radiolucencies, precursors to failure and
revision, were large femoral head cysts (p = 0.029), patient height (p = 0.032), female gender (p
= 0.005), and smaller component size in male patients (p = 0.005). Carrothers et al. showed that
the prevalence of revision was significantly higher in women compared to men receiving hip
resurfacing (women = 5.7%; men = 2.6%, p < 0.001). 11 Jameson et al. compared revision rates
between 100 females receiving a hip resurfacing and 100 males receiving a hip resurfacing and
demonstrated that females had 3 times the number of revisions than male patients (7.4% vs.
2.2%).12 In contrast, female gender was not shown to impact functional outcomes nor increase
the risk of failure in the current study. This finding is in keeping with recent literature suggesting
that implant size, and not gender, is a prognostic indicator for patient outcomes in hip
resurfacing.15,30
Socioeconomic status for patients residing in Toronto did not appear to impact functional
outcomes or rates of complication or revision in the current study. This is in contrast to previous
work looking at patient outcomes in total hip arthroplasty. 9,16,20,28,29,31 Clement et al. looked at
1312 patients undergoing primary total hip replacement and concluded that social deprivation
increased the risk of post-operative dislocation as well as early mortality.16 Looking at infection
rates in total hip patients, Webb et al. demonstrated an increased risk of infection postoperatively with patients of lower socioeconomic background.31
Similarly, in a multicity,
longitudinal study, Agabiti et al. analyzed 6140 patients undergoing elective hip replacement
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and showed that low income was associated with higher risk of acute adverse medical events
and infections within the first 90 days following surgery.28
A compelling finding in the current study is the tendency for Toronto patients receiving a hip
resurfacing arthroplasty to reside in neighbourhoods of higher household income.
Equal
opportunity to adequate health care is a hallmark in a universal health care system such as that
employed within Canada, however, this study highlights that limitations to access of care
remain. Agabiti et al. demonstrated a similar finding when looking at patients receiving total hip
replacement in Italy, a country that has universal health care, in that low-income individuals
were less likely than high-income counterparts to receive total hip replacement. 28 There are
several possible explanations for this variation across socioeconomic groups. 32 Firstly, there
may be diminished need among lower social classes; however, this is unlikely as persons with
lower socioeconomic position not only have worse symptoms and disability33 but also have a
similar willingness to undergo hip replacement in comparison to those of higher socioeconomic
status.34 Secondly, it is plausible that a lack of knowledge about hip resurfacing and its benefits
is higher among individuals of lower socioeconomic status, specifically with hip resurfacing in its
infancy in Canada in the early 2000’s. The tendency for individuals of higher rather than lower
socioeconomic status to receive hip resurfacing points toward the possibility that perhaps better
educated patients employ more extensive resources, particularly with the advent of easy access
to information via the internet, and thus fervently seek out new and emerging health care
alternatives. The impact of the internet on patient preferences and the distribution of resources
is an interesting area for further investigation.
There are several limitations to the current study. Firstly, the patient cohort used in this study is
drawn from a single surgeon series in a large academic centre and may not adequately
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represent the spectrum of patients receiving hip resurfacing arthroplasty. However, the study
cohort represents one of the earliest and largest such cohorts in Ontario and thus provides
insight into the preliminary use of this intervention in Canada. Secondly, patient data specifically
detailing a patient’s education and income is not collected by St. Michael’s hospital and thus
postal code was used as a surrogate marker for socioeconomic status. Postal code is limited to
the area of residence of the patient at the time of surgery and may not directly indicate a
patient’s social or economic background.
In conclusion, the current work did not demonstrate a correlation between patient gender nor
socioeconomic status and outcomes following hip resurfacing arthroplasty in this single surgeon
series.
Interestingly, Toronto residents receiving a hip resurfacing tended to reside in
neighbourhoods of higher household income and thus this study demonstrates a propensity for
individuals of higher socioeconomic status to receive a hip resurfacing arthroplasty.
ACKNOWLEDGMENTS
The Authors would like to thank Kerry Ann Griffith-Cunningham and Jane Morton for their help in
acquiring data for this work.
CONFLICTS OF INTEREST
The Authors do not have any conflicts of interest with respect to the current investigation.
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Webb, B. G.; Lichtman, D. M.; and Wagner, R. A.: Risk factors in total joint arthroplasty:
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FIGURES AND FIGURE CAPTIONS
Figure 1. SMH hip scores for males and females
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Figure 2. SMH hip scores for individuals residing in and out of Toronto
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Figure 3. Distribution of patients residing in Toronto according to the classification established by
Hulchanski.27
Area (1) denotes neighbourhoods in which the average individual
income increased 20% or more from 1970 to 2000, (2) neighbourhoods in which the
average individual income increased or decreased less than 20% from 1970 to 2000,
and (3) neighbourhoods in which the average individual income decreased 20% or
more from 1970 to 2000.
Percentage of patients residing in the three areas are
indicated by arrows
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TABLES AND TABLE TITLE
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