Orthopedics

Feature Article 

Hip Disability and Osteoarthritis Outcome Score and Western Ontario and McMaster Universities Osteoarthritis Index Values in Asymptomatic and Arthritic Cohorts

Raymond W. Yu, MBBS, MSurgSci; James M. McLean, MBBS, MS, FRACS; Jasvir S. Bahl, BAppSc; Lucian B. Solomon, MD, PhD, FRACS

Abstract

The primary aim of this study was to determine whether an electronic, multicenter data collection system could be used to establish normal population reference values for the Hip Disability and Osteoarthritis Outcome Score (HOOS) and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). The secondary aim was to investigate differences in asymptomatic HOOS and WOMAC values reported in 2 geographically distinct English-speaking countries and compare these with a symptomatic arthritic patient cohort. A total of 552 participants were recruited. Asymptomatic Australian and Canadian cohorts were compared; combined asymptomatic cohorts were compared with an arthritic cohort. There was a statistically significant association between age and asymptomatic HOOS (P<.0001) and WOMAC (P<.0001) values; as age increased, values worsened. Females had worse HOOS and WOMAC values (P<.0001). When compared with age- and sex-matched asymptomatic participants, arthritic participants had worse scores (P<.0001). Asymptomatic Australians had a statistically significant 3.8% better (higher) HOOS (P<.0001) in all age groups (P<.0001). When compared with age- and sex-matched asymptomatic participants, younger arthritic participants reported worse activities of daily living and sports and recreation HOOS values. This observational study established an electronic HOOS and WOMAC patient-reported outcome measures database of asymptomatic individuals in 2 geographically distinct countries. An asymptomatic control group should be sourced from the same country of origin as the proposed study. Factors that should be considered when recording the HOOS and WOMAC include age, sex, geographic location, history of an inactive hip problem, contralateral hip disease, and active knee, ankle, or foot problems. [Orthopedics. 2019; 42(2):e216–e224.]

Abstract

The primary aim of this study was to determine whether an electronic, multicenter data collection system could be used to establish normal population reference values for the Hip Disability and Osteoarthritis Outcome Score (HOOS) and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). The secondary aim was to investigate differences in asymptomatic HOOS and WOMAC values reported in 2 geographically distinct English-speaking countries and compare these with a symptomatic arthritic patient cohort. A total of 552 participants were recruited. Asymptomatic Australian and Canadian cohorts were compared; combined asymptomatic cohorts were compared with an arthritic cohort. There was a statistically significant association between age and asymptomatic HOOS (P<.0001) and WOMAC (P<.0001) values; as age increased, values worsened. Females had worse HOOS and WOMAC values (P<.0001). When compared with age- and sex-matched asymptomatic participants, arthritic participants had worse scores (P<.0001). Asymptomatic Australians had a statistically significant 3.8% better (higher) HOOS (P<.0001) in all age groups (P<.0001). When compared with age- and sex-matched asymptomatic participants, younger arthritic participants reported worse activities of daily living and sports and recreation HOOS values. This observational study established an electronic HOOS and WOMAC patient-reported outcome measures database of asymptomatic individuals in 2 geographically distinct countries. An asymptomatic control group should be sourced from the same country of origin as the proposed study. Factors that should be considered when recording the HOOS and WOMAC include age, sex, geographic location, history of an inactive hip problem, contralateral hip disease, and active knee, ankle, or foot problems. [Orthopedics. 2019; 42(2):e216–e224.]

The number of total hip arthroplasties (THAs) performed continues to increase.1 Currently, most clinical research and joint registry outcome data involve observation of THA failure and revision rates. Patient-reported outcome measures (PROMs) allow for the evaluation of THA outcomes prior to failure and revision. Patient-reported outcome measures have indicated that 15% of patients undergoing elective THA are not satisfied with their results.2 These data are not routinely collected by most THA registries. Patient-reported outcome measures can provide surgeons and researchers with valuable long-term data on the severity of and change in symptoms before and after THA.

Approximately 20 different hip PROM scoring systems have been described.3,4 The PROMs working group of the International Society of Arthroplasty Registries reported that the Hip Disability and Osteoarthritis Outcome Score (HOOS) and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) are the PROMs most commonly used for THA registries.5 The HOOS is a PROM used to measure subjective hip function and symptoms in adult patients with hip disability.6,7 This includes individuals with or without hip osteoarthritis. The HOOS has the complete and original WOMAC within it.

The HOOS and the WOMAC can be administered quickly, requiring approximately 10 to 15 minutes for patients to complete. Swedish, Dutch, and French versions have been previously validated.6,8 The Swedish and French versions of the HOOS have shown high responsiveness (ie, the ability to detect clinical change) before and after THA in patients with hip osteoarthritis.4,7

The HOOS and the WOMAC incorporate subjective reports of patients' hip and associated problems. Several investigators have reported an inverse relationship between age and PROM scores in asymptomatic populations, suggesting that as age increases, the reported “normal” PROM score decreases.9 It is possible that a similar inverse relationship exists for the HOOS and the WOMAC; however, to the authors' knowledge, this has not been reported.

Despite their widespread use since their description in 1988 and 2003, no study has investigated the effect of administering an English version of the HOOS or the WOMAC to asymptomatic individuals and to individuals with symptomatic end-stage hip osteoarthritis planned for THA.6,10 The primary aim of this study was to determine whether an electronic, multicenter data collection system could be used to establish normal, asymptomatic, population reference values for the HOOS and the WOMAC and to investigate potential regional differences in the reported values by assessing 2 geographically distinct English-speaking countries (Australia and Canada). The secondary aim was to compare this asymptomatic HOOS and WOMAC cohort with a symptomatic patient cohort with end-stage hip osteoarthritis planned for THA. The authors hypothesized that longitudinal data from symptomatic arthritic populations should be compared with data from ageand sex-matched control cohorts sourced from the same country of origin as the study (ie, local cohorts should only be compared with a local control group).

Materials and Methods

Independent ethics board approval was granted from each institution involved in this study. Adult participants were recruited from November 2014 to January 2017. Participants for the asymptomatic cohort were recruited from medical outpatient departments, driver's licensing offices, and community centers. There were no incentives or payment for participation. Informed consent was obtained from all individuals included in the study.

An asymptomatic cohort was established by approaching adult Australian and Canadian participants who identified themselves as having no symptoms of problems in either hip. Inclusion criteria were no self-reported pain or pathology in either hip and fluent in English. No medical notes or radiographs were reviewed for these individuals. Exclusion criteria were cognitive impairment, a history of inflammatory or hip arthritis, significant lumbar spine problems that interfered with function, active hip pathology, previous hip arthroplasty, or any hip surgery within the past 3 years. A history of inactive (ie, asymptomatic) hip pathology, including previous surgery more than 3 years earlier, was recorded. Reports of concurrent knee or ankle pathology or pain affecting function were recorded.

A consecutive sample of English-speaking patients with end-stage, radiographically confirmed osteoarthritis planned for THA were recruited from a single tertiary referral center. Exclusion criteria were cognitive impairment and significant lumbar spine problems interfering with function. A history of active knee or ankle pathology or pain affecting function, as well as a history of contralateral THA or hip problems, was recorded.

A total of 552 participants were recruited (496 asymptomatic and 56 symptomatic arthritic), with 273 being women and 279 being men. They were divided into 5 age subgroups: 40–49, 50–59, 60–69, 70–79, and 80 years and older.

Participants self-administered the HOOS (English version LK 2.0), which consisted of 40 items assessing 5 categories of PROMs: symptoms and stiffness (5 questions); pain (10 questions); function and daily living (17 questions); function, sports, and recreational activities (4 questions); and quality of life (4 questions). Participants were directed to answer each item by selecting 1 of 5 descriptive responses presented as a Likert scale. Each question was scored from 0 to 4, yielding a total score ranging from 0 (severe disability) to 100 (no disability).

The HOOS contained all WOMAC LK 3.0 questions in their original, unchanged form. The WOMAC scores were calculated as described by Nilsdotter et al8 and included subscales for pain, stiffness, and function. All items were scored from 0 to 4, and scores for each of the subscales were calculated from the sum of the included items. A normalized score up to 100 was calculated for each subscale, with 0 indicating maximal problems and symptoms and 100 indicating no problems. A total WOMAC score of 0 to 100 was calculated for each participant, with a higher score indicating worse pain, stiffness, and function.

Chi-square and Fisher's exact tests were used for the analysis of differences between arthritic and asymptomatic cohorts. Ordinal logistic models were used for the analysis of differences in HOOS and WOMAC values because these scores are ordinal (ie, lower scores correlate with worse symptoms for HOOS, and higher scores correlate with worse symptoms for WOMAC). Poisson regression models were used to assess for associations between 5 HOOS and 4 WOMAC subscales and predictors such as country, age, and sex. SAS version 9.4 statistical software (SAS Institute Inc, Cary, North Carolina) was used.

Results

The demographics of each cohort are presented in Table 1. The HOOS values and statistical analyses are presented in Table 2 and Figure 1. On adjustment for sex, asymptomatic Canadian participants had worse (lower) HOOS values across all age groups (P<.0001) compared with asymptomatic Australian participants. Arthritic participants had worse (lower) HOOS values than age- and sex-matched asymptomatic participants (P<.0001). Female participants had worse (lower) HOOS values than age-matched participants (P<.0001).

Demographics of Australian Asymptomatic, Canadian Asymptomatic, and Arthritic Cohorts

Table 1:

Demographics of Australian Asymptomatic, Canadian Asymptomatic, and Arthritic Cohorts

Hip Disability and Osteoarthritis Outcome Scoresa

Table 2:

Hip Disability and Osteoarthritis Outcome Scores

Scattergram showing Hip Disability and Osteoarthritis Outcome Score for each age group among asymptomatic Australian participants (blue), asymptomatic Canadian participants (red), and arthritic cohort (green). Higher scores indicate better outcomes for symptoms, pain, function, and quality of life.

Figure 1:

Scattergram showing Hip Disability and Osteoarthritis Outcome Score for each age group among asymptomatic Australian participants (blue), asymptomatic Canadian participants (red), and arthritic cohort (green). Higher scores indicate better outcomes for symptoms, pain, function, and quality of life.

The HOOS subscale values and univariate Poisson regressions are presented in Table 3. Asymptomatic Australian participants had a HOOS for pain that was 2.1% better (higher) than that of age- and sex-matched asymptomatic Canadian participants (P=.0123; 95% confidence interval, 1.0044–1.0369). Asymptomatic Australian participants also had better (higher) HOOS subscale values for symptoms (P=.0003), activities of daily living (P=.0006), sports and recreation (P<.0001), and quality of life (P<.0001). Overall, asymptomatic Australian participants had a total HOOS value that was 3.8% better (higher) than that of age- and sex-matched asymptomatic Canadian participants (P<.0001).

Univariate Poisson Regressions of Hip Disability and Osteoarthritis Outcome Score Subscale Scores

Table 3:

Univariate Poisson Regressions of Hip Disability and Osteoarthritis Outcome Score Subscale Scores

The WOMAC scores and statistical analyses are presented in Table 4 and Figure 2. On adjustment for sex, when compared with asymptomatic Australian participants, asymptomatic Canadian participants had worse (higher) WOMAC scores in the 70 to 79 years (P=.0025) and 80 years and older (P<.0001) age groups only. No difference in HOOS value was reported for asymptomatic participants younger than 70 years (P>.05). Arthritic participants had worse (higher) WOMAC scores than age- and sex-matched asymptomatic participants (P<.0001). Female participants had worse (higher) WOMAC scores compared with age-matched participants (P<.0001).

Western Ontario and McMaster Universities Osteoarthritis Index Scoresa

Table 4:

Western Ontario and McMaster Universities Osteoarthritis Index Scores

Scattergram showing Western Ontario and McMaster Universities Osteoarthritis Index score for each age group among asymptomatic Australian participants (blue), asymptomatic Canadian participants (red), and arthritic cohort (green). Higher scores indicate worse pain, stiffness, and function.

Figure 2:

Scattergram showing Western Ontario and McMaster Universities Osteoarthritis Index score for each age group among asymptomatic Australian participants (blue), asymptomatic Canadian participants (red), and arthritic cohort (green). Higher scores indicate worse pain, stiffness, and function.

The WOMAC subscale scores and univariate Poisson regressions are presented in Table 5. Asymptomatic Australian participants had a better (lower) WOMAC score on all subscales compared with ageand sex-matched asymptomatic Canadian participants (P<.0001). Overall, asymptomatic Australian participants had a total WOMAC score that was 2.5% lower than that of age- and sex-matched asymptomatic Canadian participants (P<.0001).

Univariate Poisson Regressions of Western Ontario and McMaster Universities Osteoarthritis Index Subscale Scores

Table 5:

Univariate Poisson Regressions of Western Ontario and McMaster Universities Osteoarthritis Index Subscale Scores

Discussion

The HOOS and the WOMAC are PROMs that provide valuable information for surgeons and researchers assessing and quantifying outcomes before and after THA. This study assessed the HOOS and the WOMAC PROMs in asymptomatic and pathological, arthritic cohorts. Comparing both asymptomatic and arthritic hip cohorts enables a more accurate interpretation of the normal, age-related functional changes that will affect THA patients being followed on a longitudinal basis.

Establishment of a PROM reference database for asymptomatic individuals will aid in the interpretation of THA patients' PROM reports on a longitudinal basis. An electronic database allows remote administration, thereby minimizing resources, cost, and personnel required to collect, collate, and process data.11 This theoretical advantage is enabled by the HOOS and the WOMAC PROMs containing only subjective responses and not requiring a face-to-face interaction with an assessor. These PROMs have the potential for remote access by both researchers and patients, who can complete questionnaires when convenient and have electronic reminders set. An electronic database also permits simultaneous data entry and data analyses, allows automated participant reminders or response time points, and has the potential to link to an electronic medical record. This could increase the response rate, which can be low with mailed paper questionnaires.

In this study, females in both the asymptomatic and the arthritic cohorts had worse HOOS and WOMAC values. This finding is similar to that of other studies.12,13

An inverse correlation was found between age and reported PROMs in asymptomatic participants (ie, as age increased, the reported PROM score was worse). This finding was not surprising given the age-related changes that occur with time and the accumulated medical and surgical comorbidities that can affect lower limb function and the resultant reported PROM score. Certainly, as patient age increases, perfect PROMs should not be expected.

Asymptomatic individuals 70 years and older showed great variation in reported HOOS and WOMAC values, with Canadian participants having worse PROM values than with their Australian counterparts. This trend was well demonstrated on comparison of each PROM graph, with national asymptomatic PROMs becoming more divergent in individuals 70 years and older. In contrast to the HOOS, which showed statistical differences between all age groups for all subscales, the WOMAC did not show statistically significant differences for all subscales. The WOMAC did show a significant difference for individuals 70 years and older, but not for younger individuals. This observation may be explained by an increased relevance of these particular subscale questions to younger and more high-demand individuals, as the HOOS was developed as an expansion of the WOMAC (with the inclusion of questions relating to sports and recreation and decreased quality of life). Therefore, the authors recommend that the HOOS be used in preference to the WOMAC to detect differences between cohorts in the younger age groups (40 to 69 years).

Arthritic participants reported statistically worse PROMs compared with their age- and sex-matched asymptomatic counterparts. This finding was not surprising given the end-stage arthritic changes that defined this cohort and the effect that this had on their lower limb function. Interestingly, in contrast to the asymptomatic cohort, in this study a correlation was found between age and reported PROM in the arthritic cohort (ie, as age increased, PROM score improved). The authors postulate that the apparent age-related improvement in PROMs was unlikely to be related to the natural history of osteoarthritis, but rather to the threshold of operative intervention for individuals with radiographically confirmed osteoarthritis. Because, by definition, all of the arthritic participants were indicated and planned for surgery, younger individuals in this cohort required worse symptoms and greater impact on function before reaching the threshold for consideration for THA intervention. Older arthritic individuals likely had a lower threshold indication for THA, given the lower implant demands and lower risk of revision surgery in these age groups.1

Younger arthritic participants were also more likely to report worse activities of daily living and sports and recreation HOOS values than their asymptomatic age-matched counterparts. This study also found that as age increased, the disparity between scores in all cohorts diminished, particularly the subscales (ie, as age increases, asymptomatic and symptomatic PROM values approach one another). This observation highlights the implications of osteoarthritis in younger arthritic individuals, which likely translate to a greater impact on occupation, livelihood, and recreation. Future longitudinal studies should assess the impact of THA on reported PROMs in younger individuals compared with the more common elderly THA patients.

Factors other than age were also found to be associated with differences in PROM values. Participants who reported a history of an inactive (previous) hip problem or an active knee, ankle, or foot problem had worse PROM scores. The asymptomatic Canadian cohort reported a higher incidence of inactive hip problems, as well as more active knee, ankle, or foot problems. This may also have influenced the PROM values reported, as both of these variables were associated with worse PROM scores in the combined asymptomatic cohorts, independent of age.

There is significant overlap in the functional questions contained in the assessment tools, suggesting that these functional tools may not represent hip-specific PROMs and may fail to discriminate a primarily hip source of pathology from other sources of lower limb incapacity. This should be considered when using these tools for patients with multiple, concurrent lower limb pathologies. To the authors' knowledge, few (if any) studies investigating either asymptomatic or arthritic cohorts have considered the effect these variables may have on the reported HOOS and WOMAC values. In addition, most studies do not record the incidence of contralateral hip disease (either active or inactive), concurrent spinal disease, or active bilateral or unilateral knee, ankle, or foot pathology. Rarely is a history of contralateral hip disease or THA reported in arthritic or THA patient cohorts.8,14–16

In this study, efforts were made beyond those reported previously to establish an asymptomatic control group that fulfilled the criteria of being a control group. Exclusion criteria were carefully chosen to minimize the inclusion of participants with active pathology and to collect an asymptomatic population who identified themselves as having normal hips. To the authors' knowledge, this study represents the largest database of normal HOOS and WOMAC values reported in the literature. Although other researchers have recorded normal values for other musculoskeletal assessment tools, most have collected fewer than 150 participants17 or have studied only young, active individuals18 or individuals not first screened for active joint pathology.13

Several studies have indicated that a perfect hip score may not be reported in an asymptomatic or disease-free population.13,19 In a representative sample, it is assumed that a certain percentage of the general population will have asymptomatic, incidental hip pathology. A representative control cohort without active pathology would include a small percentage of participants with the following: a history of inactive hip pathology; a history of previous successful non-arthroplasty hip surgery; incidental subclinical hip pathology; and incidental clinical hip pathology (undiagnosed or not investigated). In this study, all efforts within the constraints of ethics approval, budget, and practical participant selection were made to exclude patients with active hip pathology from the asymptomatic cohort. Many previous studies investigating normal reference values did not attempt to exclude these participants from their sample cohorts.13 Thus, in these studies, the numbers of responders with active hip pathology or a history of hip pathology are unknown. The authors recommend that future studies consider these variables when establishing a control group against which to compare an interventional group using the HOOS and WOMAC PROMs.

This study reported differences between 2 geographically distinct asymptomatic cohorts from 2 English-speaking Western countries. Although this study represents the largest cohort of asymptomatic hip PROM scores reported in the literature, this finding may reflect a true difference between the population cohorts or a selection or reporting bias. Cultural and societal differences may also explain the disparity in scores. Although the distribution of ethnicity was not explored in this study, the 2 countries have Westernized societies and similar distributions based on reports from the Australian Bureau of Statistics20 and Statistics Canada.21 Future studies with larger samples may be able to assess these reported differences. On the basis of their findings, the authors recommend that future studies using the HOOS and the WOMAC be performed with comparisons made against a control group sourced from the same country of origin.

The current study had important limitations that should be considered when interpreting the results. The arthritic cohort represented a sample of consecutive patients with end-stage osteoarthritis planned for THA. In contrast, the asymptomatic cohort was collected randomly, with no specific randomization method regarding participant identification being employed. Because no radiographs were obtained to confirm whether participants had asymptomatic degenerative hip disease, it is possible that some of these individuals were included in the cohorts even though they self-reported as asymptomatic.

As with any observational study, there is the potential for selection bias, particularly when there is no randomization. The primary benefit of randomization is the elimination of both conscious and unconscious bias associated with the selection of a participant. Randomization was not employed in this study secondary to time, resource, and cost constraints.

Another potential source of selection bias involves the use of electronic questionnaires. Patients with severe wrist and hand pathology may be less able to complete electronic questionnaires using computers or tablets. The technology also assumes that the patient is capable of being and willing to be an active participant and that the patient prefers a virtual method of follow-up over a face-to-face clinician–patient interaction. This may not be the case for the entire population and especially for the elderly, who may not be computer savvy.22 Participants may have declined involvement because of the technology. Interviewer bias may have been introduced, especially when elderly participants were assisted with using the technology.

Asymptomatic participants with a history of a prior hip injury may have chosen not to participate in the study, citing that their hip was not normal. Although the authors chose to exclude participants with active hip disease, they did include participants with a history of a previous hip problem that “no longer bothered them” (ie, asymptomatic). Because this is a purely subjective report, it is possible that some asymptomatic individuals with a prior hip problem and only minor functional incapacities who could have been included self-excluded themselves.

The arthritic cohort was sourced from Australia, and from the same city as the asymptomatic Australian cohort. Although differences in PROM values in asymptomatic cohorts from 2 geographically distinct English-speaking Western countries were reported, no such comparisons could be made for the arthritic cohort. Therefore, future THA studies should involve comparison with a control group sourced from the same country of origin.

Because the main goal of this study was the establishment of an asymptomatic control group, longitudinal data were not collected over several time points; hence, response rate could not be assessed and the PROMs could not be validated. Validation, which requires collection of multiple data over different time points, was not within the scope of this study. Formal validity studies have not been published for English translations of the HOOS and the WOMAC. Future studies could collect the WOMAC and the HOOS values in both asymptomatic and arthritic cohorts on a longitudinal basis. However, this would require significant administration, resources, and personnel. A positive step toward this goal is the establishment of an electronic database of population reference values for various ages across the sexes for the HOOS and the WOMAC PROMs.

To the authors' knowledge, this study represents the largest cohort of combined asymptomatic and arthritic participants using the HOOS and the WOMAC PROMs. The authors aim to expand this database to include an arthritic population of equivalent size with longitudinal data. The HOOS and the WOMAC are preferable in the development of a large electronic catalog of normal control population data because they permit remote administration. With resource management and cost justification becoming more of a focus in health care, PROMs that can be administered remotely make future research, especially international multicenter cohort studies, a possibility.

Conclusion

This observational study established an electronic HOOS and WOMAC PROM database of asymptomatic individuals in 2 geographically distinct English-speaking countries for comparison with age- and sex-matched arthritic and THA patients. The HOOS should be used in preference to the WOMAC when assessing for variation in younger age groups (40 to 69 years). An asymptomatic control group should ideally be sourced from the same country of origin as the proposed study. Factors that should be considered when recording the HOOS and the WOMAC include age, sex, geographic location, a history of an inactive (previous) hip problem, contralateral hip disease, and an active knee, ankle, or foot problem.

References

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Demographics of Australian Asymptomatic, Canadian Asymptomatic, and Arthritic Cohorts

CharacteristicAustralian Asymptomatic Cohort (n=247)Canadian Asymptomatic Cohort (n=249)Arthritic Cohort (n=56)Total (N=552)Comparing Australian and Canadian Asymptomatic CohortsComparing Asymptomatic and Arthritic CohortsComparing All Cohorts
Sex, No.
  Male123 (49.8%)123 (49.4%)33 (58.9%)279 (50.5%)P=.9290 (chi-square)P=.4146 (chi-square)P=.4146 (chi-square)
  Female124 (50.2%)126 (50.6%)23 (41.1%)273 (49.5%)
Age group, No.
  40–49 y51 (20.7%)53 (21.3%)5 (8.9%)109 (19.7%)
  50–59 y72 (29.1%)74 (29.7%)8 (14.3%)154 (27.9%)
  60–69 y71 (28.7%)70 (28.1%)19 (33.9%)160 (29.0%)P=.9086 (chi-square)P=.0128 (chi-square)P=.0128 (chi-square)
  70–79 y33 (13.4%)37 (14.9%)16 (28.6%)86 (15.6%)
  80+ y20 (8.1%)15 (6.0%)8 (14.3%)43 (7.8%)
Age, mean (range), y60.1 (40–90)59.8 (40–94)66.9 (43–89)60.7 (40–94)
History of an inactive (previous) hip problem (hip for asymptomatic cohort; contralateral hip for arthritic cohort), No.0 (0%)8 (3.2%)24 (42.9%)32 (5.8%)P=.0074 (Fisher's exact test) (ie, asymptomatic Canadian cohort had a statistically significantly higher incidence of a history of an inactive [previous] hip problem compared with the asymptomatic Australian cohort)P<.0001 (Fisher's exact test) (ie, arthritic cohort had a statistically significantly higher incidence of a contralateral history of an inactive [previous] hip problem compared with all asymptomatic participants)P<.0001 (Fisher's exact test) (ie, arthritic cohort had a statistically significantly higher incidence of a contralateral history of an inactive [previous] hip problem compared with both asymptomatic cohorts assessed independently)
History of an active knee, ankle, and foot problem(s), No.3 (1.2%)39 (15.7%)16 (28.6%)58 (10.5%)P<.0001 (Fisher's exact test) (ie, asymptomatic Canadian cohort had a statistically significantly higher incidence of an active knee, ankle, or foot problem[s] compared with the asymptomatic Australian cohort)P<.0001 (Fisher's exact test) (ie, arthritic cohort had a statistically significantly higher incidence of an active knee, ankle, or foot problem[s] compared with all asymptomatic participants)P<.0001 (Fisher's exact test) (ie, arthritic cohort had a statistically significantly higher incidence of an active knee, ankle, or foot problem[s] compared with both asymptomatic cohorts assessed independently)
Previous hip arthroplasty in contralateral hip, No.NA as exclusion criteriaNA as exclusion criteria20 (35.7%)20 (3.6%)aNA

Hip Disability and Osteoarthritis Outcome Scoresa

CharacteristicAsymptomatic Cohort, Mean HOOSArthritic Cohort Mean HOOSTotal Mean HOOS (Combined Asymptomatic and Arthritic Cohorts)P


AustralianCanadianCombinedComparing Australian and Canadian Asymptomatic CohortsComparing Combined Asymptomatic and Arthritic CohortsComparing All Cohorts
Sex
  Male97.2892.5294.9029.6887.19.0002<.0001<.0001
  Female95.9590.8693.3923.8487.53<.0001<.0001<.0001
Age group
  40–49 y98.7894.9896.844.8893.08.0383<.0001<.0001
  50–59 y97.8894.4796.1519.6392.18.0271<.0001<.0001
  60–69 y94.6391.0992.8824.4584.75.0243<.0001<.0001
  70–79 y94.6988.2591.2934.9680.81.0039<.0001<.0001
  80+ y96.7777.4588.4934.0878.37<.0001<.0001<.0001
Overall96.6291.6894.1427.2987.36<.0001<.0001.0001

Univariate Poisson Regressions of Hip Disability and Osteoarthritis Outcome Score Subscale Scores

HOOS SubscaleAsymptomatic Cohort, Mean Score95% Confidence IntervalP

AustralianCanadian
Pain97.6795.711.0044–1.0369.0123
Symptoms97.2394.441.0133–1.0462.0003
Activities of daily living97.9395.241.0120–1.0447.0006
Sports and recreation94.7487.401.0664–1.1019<.0001
Quality of life96.2592.631.0225–1.0559<.0001
Total score483.83465.411.0321–1.0470<.0001

Western Ontario and McMaster Universities Osteoarthritis Index Scoresa

CharacteristicAsymptomatic Cohort, Mean ScoreArthritic Cohort Mean ScoreTotal Mean ScoreP


AustralianCanadianCombinedComparing Australia and Canadian Asymptomatic CohortsComparing Combined Asymptomatic and Arthritic CohortsComparing All Cohorts
Sex
  Male1.794.973.3661.7910.32.0018<.0001<.0001
  Female2.806.384.6068.439.98.0004<.0001<.0001
Age group
  40–49 y0.963.252.1380.605.72.1237<.0001<.0001
  50–59 y1.473.422.4470.256.01.1231<.0001<.0001
  60–69 y3.655.864.7465.3211.94.0830<.0001<.0001
  70–79 y3.368.846.2657.6315.81.0025<.0001<.0001
  80+ y2.1016.678.3460.6318.07<.0001<.0001<.0001
Overall2.305.693.9964.5210.15<.0001<.0001.0001

Univariate Poisson Regressions of Western Ontario and McMaster Universities Osteoarthritis Index Subscale Scores

WOMAC SubscaleAsymptomatic Cohort, Mean Score95% Confidence IntervalP

AustralianCanadian
Pain0.390.760.42–0.52<.0001
Stiffness0.240.530.35–0.45<.0001
Function1.433.340.38–0.43<.0001
Total score2.074.630.41–0.45<.0001
Authors

The authors are from the Orthopaedic and Trauma Service (RWY, JMM, LBS), Royal Adelaide Hospital, the Centre for Orthopaedic and Trauma Research (JMM, LBS), University of Adelaide, and the Alliance for Research in Exercise, Nutrition and Activity (JSB), Sansom Institute for Health Research & School of Health Sciences, University of South Australia, Adelaide, South Australia, Australia; and the Department of Orthopaedics (JMM), University of British Columbia, Vancouver, British Columbia, Canada.

The authors have no relevant financial relationships to disclose.

The authors thank Mami Okada, Research Assistant, University of British Columbia, for help establishing the study in Canada; Suzanne Edwards, Statistician, Data Management and Analysis Centre, University of Adelaide, for help with statistical analysis of the collected data; Tara-Louise McLean, Research Assistant to Dr James McLean, for help establishing the study in Australia and Canada; Catherine Hill, Professor of Rheumatology, University of Adelaide, for help establishing the study protocol; Tiffany Gill, Senior Research Fellow, University of Adelaide, for help establishing the study protocol; and Danny Awwad, Orthopaedic Registrar, Royal Adelaide Hospital, for help preparing the scattergrams used in this article.

Correspondence should be addressed to: James M. McLean, MBBS, MS, FRACS, Orthopaedic and Trauma Service, Royal Adelaide Hospital, 1 Port Rd, Adelaide, South Australia, Australia 5000 ( james.mc_lean@adelaide.edu.au).

Received: July 31, 2018
Accepted: September 10, 2018
Posted Online: January 31, 2019

10.3928/01477447-20190118-02

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