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MS: 5088249348284415
4/3/2013
Thank you for the opportunity to revise and resubmit our manuscript. We have followed all of
your suggestions, as well as addressed the reviewers’ concerns, as outlined below:
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Reviewer: Michael G. Zywiel
This is a review of the manuscript entitled ‘The outcomes of hip resurfacing compared to standard
primary total hip arthroplasty in men.’ The authors compared the clinical and radiographic outcomes of
120 consecutive hip resurfacing arthroplasties performed in 114 men at a single institution to those of 120
consecutive total hip arthroplasties in 117 men performed over the same time period. The authors found
similar revision rates, and Harris hip scores at final follow-up, with higher UCLA activity scores in the
hip resurfacing cohort. Overall, the manuscript is clear, concise and well-written, and the methodology is
generally sound within the limitations of the study design (retrospective comparative study).
Thank you
While this reviewer does have a few comments concerning the study, assuming that these are addressed
by the authors I expect that the manuscript will be suitable for publication following re-review.
Thank you
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Major Revisions:
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1-My principal comment for the authors is concerning the presentation and analysis of the UCLA activity
scores. Both in the introduction as well as the discussion the authors bring attention to the continuing
controversy concerning activity levels in patients undergoing hip arthroplasty, namely whether the
superior post-operative activity levels reported by several authors for patients with hip resurfacings are
inherent to the procedure itself, or whether they represent a selection bias with higher pre-operative
activity levels in these patients. However, while the authors did present a statistical comparison of postoperative activity levels in both study groups, they failed to compare pre-operative activity levels between
the two groups. It is this reviewer’s opinion that the authors should also include a statistical comparison
of pre-operative activity levels, as well as magnitude of change in UCLA activity levels between the two
groups. Based on the data presented I suspect the authors will find significantly higher pre-operative
activity levels in the resurfacing group. Regardless of the findings, these should also be placed into
context in the Discussion.
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We have now included a comparison of pre-operative activity levels, as well as magnitude of
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change in UCLA activity levels between the two groups. When evaluating activity levels, the mean pre-
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operative UCLA activity scores in the resurfacing cohort were 3.6 points (range, 1 to 5 points) which
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were significantly higher than 2.7 points (range, 1 to 4 points) in the standard THA cohort (p=0.005).
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Resurfacing patients also had achieved significantly higher mean post-operative (6.7 vs. 5 points;
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p=0.001) and mean gains in activity scores (3.1 vs. 2.3 points; p=0.002) compared to standard THA
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cohort. The authors believe that the higher UCLA activity scores in the resurfacing group can be
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contributed to a combination of patient selection as well as the prosthetic design. This is evident in
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higher pre-operative activity scores of the resurfacing group which can be contributed to patient
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selection, as well as, higher overall gains in activity scores in this group which can be contributed to the
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prosthetic design. We have clarified these in the manuscript and added the following:
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Line 167 to 171:
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When evaluating activity levels, the mean pre-operative UCLA activity scores in the resurfacing
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cohort were 3.5 points (range, 2 to 5 points) which were significantly higher than 2.7 points (range,
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1 to 4 points) in the standard THA cohort (p=0.005). Resurfacing patients also had achieved
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significantly higher mean post-operative (6.7 vs. 5 points; p=0.001) and mean gains in activity levels
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(3.1 vs. 2.3 points; p=0.002) compared to standard THA cohort.
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Line 229 to 233:
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However, patients in the resurfacing cohort had achieved a significantly higher post-operative
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UCLA activity score. This may be contributed to the combination of patient selection as well as the
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prosthetic design. This is evident in higher pre-operative activity scores of the resurfacing group
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which can be contributed to patient selection, as well as, higher overall gains in activity scores in
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this group which can be contributed to the prosthetic design.
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2. Additionally, it would be helpful to the reader if the authors would briefly mention at some point in the
Materials a comparison of pre-operative demographics and clinical scores between the two groups. From
the tables it would appear these were similar except perhaps for the activity scores.
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We have added a brief statement regarding comparison of the demographic data between the two
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patient cohorts in the Methods section of the manuscript. A more detail complete comparison can also be
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found in Table 1 as follows:
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Line:
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There were no significant differences between age, gender, height, weight, body mass index, mean
Hip resurfacing
cohort
Standard total hip
arthroplasty
P-value
Number of patients
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117
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Number of hips
120
120
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All men
All men
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Gender
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follow-up, and etiology of end-stage arthritis between the two cohorts (p= 0.09 to 48) (a complete
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description of these findings is summarized in Table 1).
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Table 1: Summary of Demographic Findings
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Mean age in years (range)
50 (20 to 85 )
53 (18-78)
0.11
Mean height in meters (range)
1.79 (1.59-2.1)
1.81 (1.55-2.07)
0.63
Mean weight in kilograms (range)
90.5 (58.5- 165)
93.9 (57- 171)
0.09
Mean body mass index in Kg/m2 (range)
28.2 (19-45)
28.7 (19-51)
0.48
Mean follow-up in months (range)
42 (24 -55)
40 (24 to 58)
0.23
Osteoarthritis
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106
Osteonecrosis
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Etiology of end-stage arthritis
0.38
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Minor revisions:
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3. Line 48: delete ‘also.’ Survival rates were numerically different in the two groups (98% vs 99%)
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We have now deleted the word ‘also” from line 48.
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4. Line 61: “…hip disease and who have failed…”
We have modified line 61 to read as “…hip disease and who have failed…”.
5. Line 62: Is this the correct referencing style for BMC (both parentheses and square brackets)? If not
please correct throughout the manuscript.
We have corrected the reference style throughout the manuscript.
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6. Lines 95-96: The authors stated that inclusion criteria were patients with minimum 24 month followup. Why were patients lost after 24 month follow-up excluded? Did the authors mean 10 patients were
lost prior to 24 month follow-up?
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Yes, we had attempted to report the minimum 24 months outcomes and thus, had excluded these
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patients who were lost prior to that period. We have clarified this in the manuscript and added the
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following:
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Line 95 to 98:
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One patient had been deceased due to metastatic cancer (with an intact prosthesis) and 10 patients
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(10 hips) were lost to follow-up (7%) prior to their 24-months post-operative visit and consequently
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were excluded from this study; although they had well-functioning prosthesis at last-follow-up.
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7. Line 118: Did the authors mean “…based on the senior author’s…”?
Yes, we have corrected the line to read “…based on the senior author’s…”.
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Lines 138-139: Why was removal/exchange of components for infection not included in the definition of
revision surgery? Were these in a different category of failure?
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Removal/exchange of components for infection was included in the definition of revision surgery,
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however, we had attempted to evaluate the aseptic survivorship of the implants. Thus Aseptic survivorship
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was defined as revision surgery due to any aspartic reasons. We have clarified this in the manuscript and
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added the following:
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Revisions were defined as a change of the femoral or acetabular components for any reason
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including component loosening, peri-prosthetic fracture, osteolysis, component malalignment, or
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infection. Failure was defined as revision surgery due to any septic or aseptic reasons. Aseptic
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survivorship was defines as revision due to any aseptic failure.
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8. Line139: Please be more specific in what constitutes ‘failure’ of hip arthroplasty resulting in revision
procedures.
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As explained in Question 7, failure was defined as revision surgery due to any septic or aseptic
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reasons. Aseptic survivorship was defines as revision due to any aseptic failure. We have clarified this in
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the manuscript and added the following:
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Failure was defined as revision surgery due to any septic or aseptic reasons. Aseptic survivorship
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was defines as revision due to any aseptic failure.
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9. Line 140: “All data were recorded…”
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We have corrected this typographic error.
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10. Line 157: Unclear how one patient achieved two different Harris hip scores at a single follow-up
period. Presumably only one of these values (84 or 82) is correct.
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This patient achieved HHS of 82 points and we have corrected this typographic error as follows:
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This patient was treated successfully with a femoral component revision and achieved a Harris hip
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score 82 at 36 months follow-up.
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11. Line 197: I’m not sure that the WOMAC instrument would be considered a broader quality of life
measure so much as a patient-reported outcome measure.
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We have removed WOMAC for this statement. This line now reads:
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Line:
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Patient satisfaction and broader quality of life measures (such as SF-12 or SF-36, etc.) were also not
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evaluated or compared between the cohorts.
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Reviewer: Michel Le Duff
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Reviewer's report:
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Although hip resurfacing is not a new concept and modern designs have been in use for well over a
decade, there is still a debate about its place in the prosthetic options offered to treat end stage
osteoarthritis of the hip. The present study does not provide new information per se but consolidates the
value of a procedure in a specific patient population and therefore has definite merits for publication.
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Thank you.
The two groups in this study are of sufficient size to confer enough statistical power in support of the null
hypothesis when no difference was found between groups.
Thank you
The conclusions are supported by the data and do not extrapolate short-term results beyond what is
reasonable.
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Thank you
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Some improvements however, are needed, particularly in the Methods and Materials and the Results
sections.
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1. The statistical analysis needs to be better defined in the M&M section and reflect precisely what test
was used in what analysis.
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We have now attempted to better describe the statistical analyses in the M&M section to reflect
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precisely what test was used in what analysis. We have clarified this in the manuscript as follows:
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All data were recorded using an Excel spreadsheet (Microsoft Corporation, Redmond, Washington)
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and all statistical data analyses were performed using SPSS software (Version 19, IBM
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Corporation, New York). Implant survivorship was evaluated and compared between the
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resurfacing and standard THA cohorts using Kaplan Meier analysis and Log-ranked test statistics.
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Clinical outcomes and activity scores were compared using Mann-Whitney U test. Complication
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rate were compared using odds ratio statistics. A p-value of less than 0.05 was used as a threshold
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for significance.
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2. A Kaplan-Meier survival estimate requires that the % survival be reported at a given time of follow-up
(and that is not the average follow-up of the cohort). Also, the 95% confidence intervals are usually
reported in the results section.
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We have compared survivorship between the two cohorts using Kaplan Meier analysis and Log-
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ranked test statistics with SPSS software (Version 19, IBM Corporation, New York). We have also added
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the 95% confidence intervals in the results section of the manuscript as follows:
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The Kaplan-Meier implant survivorship in the hip resurfacing cohort was 98% (95 CI: 93.4 to
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99.5%) at 36 and 48 months follow-up which were not significantly different than 99% (95% CI:
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94.1 to 99.9%) in the standard total hip arthroplasty cohort (p = 0.95)
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3. The Fisher Exact test is not a time-dependent test and should not be used to compare 2 survivorship
curves. If the 2 groups are established as comparable, a Log-ranked test is the appropriate tool because it
will take into consideration both the number of failures and when they happened. These tests are not
available in Excel and a specific statistical package (e.g. Stata or SPSS) will be needed.
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We have removed Fisher Exact statistics from survivorship analyses of this manuscript and have
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used SPSS software (Version 19, IBM Corporation, New York) to evaluate Log-ranked test and compare
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Kaplan-Meier survivorship between the two cohorts. We have clarified this in the manuscript and added
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the following:
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Implant survivorship was analyzed using Kaplan-Meier and Log-ranked test analysis with a 95%
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confidence interval.
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4. The Student t-test is designed for parametric data (although it is quite robust to a violation of this
assumption). The UCLA activity score is likely to show non-parametric characteristics so the MannWhitney U test is probably more appropriate. My guess is that this will not change the findings of this
study but in case of a closer result, this could be important.
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We evaluated UCLA activity scores using SPSS software (Version 19, IBM Corporation, New
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York) and the Mann-Whitney U test and found similar p-values compared to our initial Student t-test
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evaluations. Thus, we are only reporting the p-value from the Mann-Whitney U test in this manuscript as
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requested. We have clarified this in the manuscript and added the following:
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Harris hip scores and UCLA activity scores were compared using Mann-Whitney U test.
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Minor Essential Revisions
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1.Table 1: the goal of a table associated with the Materials and Methods section is to establish that the 2
groups are comparable with respect to the variables that could affect the results of the main research
questions. For example, patient height, weight, BMI, and etiologies should be reported and compared in
this table.
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We have revised Table 1 to only emphasize and compare patient demographic data in both
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cohorts. We have added patient height, weight, BMI, and etiologies of end-stage arthritis to this table as
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follows:
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Table 1: Summary of Demographic Findings
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2. Table 2: (Also labeled table 1 – this is confusing) should be associated with the results section and
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compare the results of the main research questions only. Right now there are redundant variables between
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the 2 tables.
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We have revised Table 2 to only compare the results of the main research questions only and
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have deleted redundant variables between the 2 tables. This table now reads as:
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Table 2: Summary of the clinical results
Hip resurfacing
cohort
Standard total hip
arthroplasty
P-value
Number of patients
114
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Number of hips
120
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All men
All men
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Mean age in years (range)
50 (20 to 85 )
53 (18-78)
0.11
Mean height in meters (range)
1.79 (1.59-2.1)
1.81 (1.55-2.07)
0.63
42 (24 -55)
40 (24 to 58)
0.23
Osteoarthritis
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Osteonecrosis
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Gender
Mean follow-up in months (range)
Etiology of end-stage arthritis
0.38
Resurfacing hip
Standard total hip
arthroplasty
arthroplasty
P-value
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Implant survivorship (%)
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99
0.95
Complication rate (%)
0.8
0.8
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Mean pre-operative Harris hip score (range)
47 (31-62)
41 (21-56)
0.75
Mean post-operative Harris hip score in points (range)
96 (72-100)
94 (70-100)
0.9
Post-operative activity score in points (range)
3.6 (1-5)
2.7 (1-4)
0.005
Post-operative activity score in points (range)
6.7 (2-8)
5 (3-7)
0.001
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3. A comment is warranted in the discussion about the difference in UCLA activity score. Considering
that all patients had the same post-operative protocol and recommendations with respect to activity, do
you believe it is a consequence of patient selection or prosthetic design?
The authors believe that the higher UCLA activity scores in the resurfacing group can be
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contributed to the combination of patient selection as well as the prosthetic design. This is evident in
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higher pre-operative activity scores of resurfacing group which can be contributed to patient selection, as
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well as, higher overall gains in activity scores in this group which can be contributed to the prosthetic
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design. We have clarified this in the manuscript and added the following:
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Line 230 to 233:
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The authors believe that the higher UCLA activity scores in the resurfacing group can be
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contributed to the combination of patient selection as well as the prosthetic design. This is evident
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in higher pre-operative activity scores of resurfacing group which can be contributed to patient
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selection, as well as, higher overall gains in activity scores in this group which can be contributed to
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the prosthetic design.
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Discretionary Revisions:
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1.Figure 3 does not seem necessary as it does not provide any additional information compared with a
proper report of prosthetic survival in the text.
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We have removed Figure 3 from this submission.
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