The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 94, Issue 10

Scientific Articles | May 16, 2012

Validation of the Western Ontario Meniscal Evaluation Tool (WOMET) for Patients with a Degenerative Meniscal Tear: A Meniscal Pathology-Specific Quality-of-Life Index

Raine Sihvonen, MD¹; Timo Järvelä, MD, PhD²; Heikki Aho, MD, PhD¹; Teppo L.N. Järvinen, MD, PhD³

¹ Department of Orthopaedics and Traumatology, Hatanpää Hospital, Hatanpäänkatu 24, 33900 Tampere, Finland. E-mail address for R. Sihvonen: raine.sihvonen@fimnet.fi. E-mail address for H. Aho: heikki.aho@elisanet.fi
² Sports Clinic and Hospital Mehiläinen, Itäinekatu 3, 33210 Tampere, Finland. E-mail address: timo.jarvela@sci.fi
³ Department of Orthopaedics and Traumatology, Helsinki University Central Hospital, Topeliuksenkatu 5, Helsinki PL 266, 00029 HUS, Finland. E-mail address: teppo.jarvinen@uta.fi

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Investigation performed at the Department of Orthopaedics and Traumatology, Hatanpää Hospital, Tampere, Finland

J Bone Joint Surg Am, 2012 May 16;94(10):e65 1-8. doi: 10.2106/JBJS.K.00804

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Abstract

Background:

Arthroscopic partial meniscectomy is the most common orthopaedic procedure and is often carried out to treat a degenerative meniscal lesion. The purpose of the present study was to determine the psychometric properties of the Western Ontario Meniscal Evaluation Tool (WOMET) for patients with an arthroscopically verified degenerative meniscal tear.

Methods:

Four hundred and eighty-five patients with an arthroscopically verified degenerative meniscal tear were included. Two groups of patients were formed: one consisted of 385 patients for the purpose of psychometric testing of the WOMET and the other consisted of 100 patients for the assessment of criterion validity. The reliability of the WOMET questionnaire was assessed by determining both internal consistency and test-retest repeatability; for the latter, a subgroup of forty patients completed the form two weeks preoperatively and again on the day of the operation. Validity assessment included determination of content validity (floor and ceiling effects), criterion validity (completion of the WOMET, the Lysholm knee score, and a generic quality-of-life questionnaire by a group of 100 patients), and construct validity (hypothesis testing). Finally, the responsiveness of the WOMET was determined with two successive assessments (on the day of surgery and six months postoperatively).

Results:

The WOMET showed acceptable internal consistency, test-retest reliability, floor and ceiling effects, criterion validity (agreement with both Lysholm and 15-D scores), and construct validity (all hypotheses were significant). The WOMET was also found to be responsive to change.

Conclusion:

The WOMET score demonstrated acceptable psychometric performance as a patient-administered outcome measure for patients with an arthroscopically verified degenerative meniscal tear.

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Introduction

Introduction | Materials and Methods | Results | Discussion

Meniscal pathology can be classified into two distinct entities: (1) traumatic or sports-related tears that typically occur in younger individuals and (2) degenerative lesions in older patients^1-3. When otherwise healthy meniscal tissue tears as the result of an excessive force, a meniscal repair is indicated if technically feasible⁴. However, the majority of meniscal pathology is considered to be degenerative in nature, is usually attributable to low-energy trauma, and is commonly accompanied by early signs of osteoarthritis of the knee^3,5. These lesions typically are treated with arthroscopic partial meniscectomy, the most common orthopaedic procedure, with estimates of approximately half a million of these procedures being performed each year in the United States alone⁶.

Various instruments have been developed to assess the outcome of treatment of knee pathology^7,8. Early attempts included generic tools such as the Tapper and Hoover system, the Knee Injury and Osteoarthritis Outcome Score (KOOS), the Lysholm knee score, the International Knee Documentation Committee (IKDC) subjective knee form, the Cincinnati knee rating scale, and the Tegner activity scale. However, with improved understanding of the complexity of knee pathology, we have witnessed a recent upsurge in attempts to develop more valid instruments for the assessment of various knee complaints.

But what is a valid measurement instrument? Perhaps the simplest definition of validity is that proposed by Guyatt et al.⁹: “A measurement tool is valid if it is measuring what it is supposed to measure.” In essence, we should be convinced that the measurement tool does what we suppose it to do and that the results are as near to the truth as possible. Ideally, the measurement instrument should be disease-specific, particularly if the purpose is to measure outcome after the treatment of a selected patient group¹⁰. A measurement tool should also ideally quantify and measure not only impairments and disabilities such as pain and function but also the individual’s quality of life¹¹. Of the available knee outcome measurement tools, only the Lysholm knee score and the IKDC have been specifically validated for patients with meniscal injury^12,13. In addition, the KOOS has been validated for patients with various knee injuries, including meniscal injury¹⁴. However, the Western Ontario Meniscal Evaluation Tool (WOMET) is the first meniscal pathology-specific health-related quality-of-life instrument¹⁵ to demonstrably measure the symptoms most relevant to patients with a meniscal tear¹⁶.

Despite the obvious differences between the two types of meniscal injuries in terms of patient and trauma characteristics, symptoms, and possible additional pathology of the knee, surprisingly few studies in general—and none of those specifically assessing the validity of an outcome instrument in patients with meniscal lesions—have made this distinction. For example, in the validation of the Lysholm knee score and the IKDC score for patients with meniscal injury, population studies included patients with clearly traumatic lesions requiring meniscal repair and patients with obvious degenerative lesions^12,13. Similarly, the psychometric properties of the WOMET were validated with use of a population of patients with meniscal pathology requiring repair (i.e., traumatic lesions) in most cases¹⁵.

Although arthroscopic partial meniscectomy for degenerative meniscal tear is the most common orthopaedic procedure in most Western countries^17,18, there is no validated outcome measurement instrument for this specific patient group. Accordingly, the purpose of the present study was to determine the psychometric properties of the WOMET for patients with an arthroscopically verified degenerative meniscal tear.

Materials and Methods

Introduction | Materials and Methods | Results | Discussion

Outcome Measures

WOMET

The WOMET is a disease-specific tool designed to evaluate health-related quality of life in patients with meniscal pathology¹⁵. The WOMET contains sixteen items addressing three domains: nine items addressing physical symptoms; four items addressing disabilities due to sports, recreation, work, and lifestyle; and three items addressing emotions. The best and least symptomatic score is 0, and the highest and most symptomatic score possible is 1600. The score may be reported as a total overall score, as a total score for each domain, or as a percentage of normal by subtracting the total score from 1600, dividing by 1600, and multiplying by 100¹⁵. In this study, the percentage of normal score is used, and accordingly, 100 (%) represents the best possible score and 0 (%) represents the worst possible score. Before being used in the target language, the WOMET questionnaire was translated according to the principles of the MAPI Research Institute¹⁹. Briefly, the original English-language version of the questionnaire was first translated into the target language by two orthopaedic surgeons independently of each other. Then a consensus version of these two versions was drafted under the supervision of a director of the translation process. This version then underwent backward translation into English by a bilingual orthopaedic surgeon. Finally, in a meeting of all three above-mentioned translators (orthopaedic surgeons), an English-language professional, and the director of the translation process, the final version in the target language was made. The practicality (ease of use and unambiguity) of the translated questionnaire was confirmed by subjecting it to pilot testing on thirty individuals.

Lysholm Knee Score

The Lysholm knee score is an eight-item questionnaire designed to evaluate knee function and symptoms in activities of daily living in patients with anterior cruciate ligament insufficiency²⁰. It has been adjusted and validated for the evaluation of meniscal injuries^12,21. The Lysholm knee score also has been used extensively in clinical research as a patient-administered instrument for the evaluation of patients with articular cartilage injuries and patellar dislocations^22,23.

15-D (Generic Health-Related Quality-of-Life Instrument)

Health-related quality of life was measured with use of the generic 15-D instrument, comprising fifteen dimensions²⁴. The responsiveness, reliability, and validity of 15-D have been thoroughly established, and this instrument has been used extensively in clinical and health-care research^25,26.

Study Population

The records for 485 patients with an arthroscopically-verified degenerative meniscal tear with no previous knee trauma were retrieved; this group was part of a prospectively collected cohort of patients who underwent knee arthroscopy at our institution in the period 2007 to 2009. The findings at the time of arthroscopy were registered with use of a structured form. Patients with trauma, bilateral arthroscopy, or reoperation during a six-month follow-up were excluded. The mean age of the patients was fifty-three years (range, eighteen to eighty-one years); 217 patients were female, and 268 were male.

Methods

The scheme used for determining the psychometric properties of WOMET is presented in Table I. From the entire cohort of 485 patients, two groups of patients were formed: 100 patients for the assessment of criterion validity and 385 patients for all other psychometric testing (including a subgroup of forty patients for test-retest repeatability). Although there is no single universally accepted and standardized protocol for this process, our analysis followed the principles proposed by Irrgang and Anderson¹¹ with minor modifications.

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TABLE I Process for Validating the WOMET

	Question	Statistical Method
Reliability	Can we rely on the WOMET and the consistency of the results it yields?
Test-retest repeatability (n = 40)	Does the WOMET provide the same result on repeated assessments?	Agreement of repeated tests, CV_rms*
Internal consistency (n = 385)	Do all items of the WOMET assess the same phenomenon?	Cronbach alpha
Validity	Does the WOMET adequately measure health-related quality of life in patients with a degenerative meniscus tear?
Content validity (n = 385)	Does the WOMET cover all symptoms commonly experienced by patients with a degenerative meniscus tear?	Floor and ceiling effects
Criterion validity (n = 100)	Are the results of the WOMET comparable with a “gold standard?”	Correlation to Lysholm and 15-D
Construct validity (n = 385)	Does the WOMET follow the theory on which it is based?	Five hypotheses for convergent validity and one for discriminate
Responsiveness (n = 385)	Does the WOMET score change over time or in response to treatment?	Effect size, standardized response mean

*CV_rms = root-mean-square coefficient of variation.

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TABLE I Process for Validating the WOMET

	Question	Statistical Method
Reliability	Can we rely on the WOMET and the consistency of the results it yields?
Test-retest repeatability (n = 40)	Does the WOMET provide the same result on repeated assessments?	Agreement of repeated tests, CV_rms*
Internal consistency (n = 385)	Do all items of the WOMET assess the same phenomenon?	Cronbach alpha
Validity	Does the WOMET adequately measure health-related quality of life in patients with a degenerative meniscus tear?
Content validity (n = 385)	Does the WOMET cover all symptoms commonly experienced by patients with a degenerative meniscus tear?	Floor and ceiling effects
Criterion validity (n = 100)	Are the results of the WOMET comparable with a “gold standard?”	Correlation to Lysholm and 15-D
Construct validity (n = 385)	Does the WOMET follow the theory on which it is based?	Five hypotheses for convergent validity and one for discriminate
Responsiveness (n = 385)	Does the WOMET score change over time or in response to treatment?	Effect size, standardized response mean

*CV_rms = root-mean-square coefficient of variation.

Reliability

Test-Retest Repeatability

Test-retest repeatability was studied in a subgroup of forty patients (seventeen female and twenty-three male) with a mean age of 57.3 years (range, forty-two to seventy-three years). The WOMET was administered twice within a two-week interval (first approximately two weeks preoperatively and then again on the day of the operation) as this time interval has been shown to provide the most reliable estimate of test-retest ability²⁷. The repeatability of the WOMET was defined as the 95% limit of agreement for the differences in the two repeated measurements (i.e., the mean difference ± twice the standard deviation of the differences) according to the study by Bland and Altman²⁸. In addition, the average root-mean-square coefficient of variation (CV_rms) was determined as a proportionate measure of repeatability²⁹.

Internal Consistency

Internal consistency was determined in three groups: (1) the entire population of 385 patients with preoperative radiographs, (2) seventy-two patients with osteoarthritis (Kellgren-Lawrence grade ≥2)³⁰ on radiographs, and (3) 313 patients with no osteoarthritis on radiographs. The overall internal consistency for all sixteen items of the WOMET and for the three domains was determined separately. A Cronbach alpha of >0.70 was considered acceptable³¹.

Validity

Content Validity

Preoperative WOMET scores were also used to establish content validity. Floor effects (expressed as a percentage of the lowest possible score) and ceiling effects (expressed as a percentage of the highest possible score) were determined for the overall WOMET score, for the three domains of the WOMET score, and for the sixteen items separately. Floor and ceiling effects of <30% were considered acceptable.³¹

Criterion Validity

The criterion validity was determined in the group of 100 patients (forty-five women and fifty-five men) with a mean age of 52.0 years (range, twenty-seven to fifty-two years) who also completed the Lysholm knee score and the 15-D questionnaire. Correlation of the overall WOMET score with the Lysholm knee score and the 15-D score was determined to establish criterion validity.

Construct Validity

Six hypotheses (constructs) were developed by consensus and were tested, including five hypotheses for convergent evidence of construct validity and one hypothesis for discriminate evidence of construct validity (Table II). The five convergent hypotheses were chosen to reflect the general condition of the knee, possible impairments, pain, and symptoms/findings associated with early osteoarthritis (morning stiffness and chondral lesions observed at the time of arthroscopy).

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TABLE II Hypotheses for Construct Validity

Hypothesis	N*	WOMET Score†	P Value
1. Patients with a lower self-rating of the knee (0 to 5) (on a scale from 0 to 10, with 10 being the best possible) would have lower WOMET scores than patients with higher self-rating (6 to 10).			<0.001
Self-rating: 0 to 5	263	42 ± 17
Self-rating: 6 to 10	111	56 ± 19
2. Patients with abnormal subjective assessment of the affected knee function would have lower WOMET scores than patients with normal or nearly normal assessment of their knee function.			<0.001
Subjective assessment: abnormal	330	44 ± 18
Subjective assessment: normal	51	62 ± 16
3. Patients with knee pain on most days in the past month would have lower WOMET scores than patients with no pain on most of these days.			<0.001
Knee pain most days	334	45 ± 18
No knee pain most days	44	62 ± 15
4. Patients with morning stiffness with their knee would have lower WOMET scores than patients with no stiffness.			<0.001
Morning stiffness	158	37 ± 16
No morning stiffness	216	54 ± 17
5. Patients with meniscal tears associated with deep (Grade-II, III, or IV) chondral lesion in weight-bearing areas seen at arthroscopy according to ICRS‡ classification³² would have lower WOMET scores than patients with no or superficial (Grade-0 or I) chondral lesions.			<0.001
Deep chondral lesions	225	42 ± 17
No or superficial chondral lesions	150	52 ± 19
6. Patients with an even value for age in years would not have a different WOMET score than patients with an odd value for age (discriminate or internal control).			0.384§
Even value for age	187	47 ± 18
Odd value for age	198	45 ± 20

*The values are given as the number of patients who answered the question/fulfilled the criterion.
†The values are given as the mean and the standard deviation.
‡ICRS = International Cartilage Repair Society.
§No significant difference for discriminate hypothesis.

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TABLE II Hypotheses for Construct Validity

Hypothesis	N*	WOMET Score†	P Value
1. Patients with a lower self-rating of the knee (0 to 5) (on a scale from 0 to 10, with 10 being the best possible) would have lower WOMET scores than patients with higher self-rating (6 to 10).			<0.001
Self-rating: 0 to 5	263	42 ± 17
Self-rating: 6 to 10	111	56 ± 19
2. Patients with abnormal subjective assessment of the affected knee function would have lower WOMET scores than patients with normal or nearly normal assessment of their knee function.			<0.001
Subjective assessment: abnormal	330	44 ± 18
Subjective assessment: normal	51	62 ± 16
3. Patients with knee pain on most days in the past month would have lower WOMET scores than patients with no pain on most of these days.			<0.001
Knee pain most days	334	45 ± 18
No knee pain most days	44	62 ± 15
4. Patients with morning stiffness with their knee would have lower WOMET scores than patients with no stiffness.			<0.001
Morning stiffness	158	37 ± 16
No morning stiffness	216	54 ± 17
5. Patients with meniscal tears associated with deep (Grade-II, III, or IV) chondral lesion in weight-bearing areas seen at arthroscopy according to ICRS‡ classification³² would have lower WOMET scores than patients with no or superficial (Grade-0 or I) chondral lesions.			<0.001
Deep chondral lesions	225	42 ± 17
No or superficial chondral lesions	150	52 ± 19
6. Patients with an even value for age in years would not have a different WOMET score than patients with an odd value for age (discriminate or internal control).			0.384§
Even value for age	187	47 ± 18
Odd value for age	198	45 ± 20

Responsiveness

To assess responsiveness, the preoperative WOMET scores for 385 patients were compared with the corresponding scores at six months after arthroscopic partial meniscectomy. The effect size was calculated by subtracting the mean postoperative score from the mean preoperative score and dividing the result by the standard deviation of the preoperative scores for all patients. The standardized response mean was calculated by subtracting the mean postoperative score from the mean preoperative score and dividing the result by the standard deviation of the mean change in the score. Values between 0.20 and 0.50 were considered to be small effects; those between 0.51 and 0.80 were considered to be moderate effects; and those of >0.80 were considered to be large effects³¹. As another measure of responsiveness, the change in the WOMET score during the six month follow-up period was compared with the patients’ global impression of change of the knee as assessed on a 5-point Likert scale. Specifically, the patients were asked the question “How do you rate your knee at the moment compared with the situation before the operation?” and answered “much better”, “better”, “same”, “worse” or “much worse”.

All data were collected after obtaining approval from a local institutional review board.

Statistical Methods

The preoperative WOMET scores and patient ages demonstrated normal distribution. The mean values were used to describe scores and ages. The medians were used for the postoperative values as the distribution was not normal. The independent t test was used for two-group comparisons of preoperative WOMET scores. The Spearman correlation coefficient (r) was used to assess associations between the WOMET and the Lysholm and 15-D scales as the latter two were not normally distributed. The Mann-Whitney test was used to compare two postoperative WOMET scores. Statistical analyses were performed with use of SPSS (version 11.5; SPSS, Chicago, Illinois). All reported p values are two-tailed with an α of 0.05 indicating significance.

Source of Funding

There was no external funding source for this investigation.

Results

Introduction | Materials and Methods | Results | Discussion

Test-Retest Repeatability

Thirty-seven of forty patients completed all sixteen items with no missing items at both two weeks preoperatively and on the day of surgery. The mean WOMET score (and standard deviation) was 47 ± 17 at the time of the first assignment and 47 ± 18 at the time of the second assignment. The CV_rms values of the corresponding measurements are provided as a measure of repeatability (Table III). The 95% limits of agreement for the differences in the two repeated measurements for the overall WOMET score were 20.10 and −20.11 (Fig. 1).

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TABLE III Repeatability of the WOMET

	First Assessment*	Second Assessment*	CV_rms†(%)
Overall WOMET score	47 ± 17	47 ± 18	9.9
Physical symptoms	58 ± 19	56 ± 19	17.3
Feeling of giving way or instability	56 ± 23	51 ± 23	24.4
Pain or soreness after activities	45 ± 20	44 ± 22	22.8
Loss of range of motion	54 ± 26	51 ± 27	26.7
Numbness	75 ± 24	70 ± 27	43.6
Stiffness after rising or sitting	52 ± 30	53 ± 27	19.6
Weakness	54 ± 29	54 ± 26	37.6
Swelling	72 ± 30	71 ± 28	42.6
Sharp pains after full weight-bearing	52 ± 29	47 ± 24	32.6
Cracking, grinding, or popping	62 ± 30	61 ± 27	38.7
Sports/recreation/work/lifestyle	32 ± 19	34 ± 18	12.3
Fear of reinjury	38 ± 31	40 ± 28	35.7
Effect on the ability to participate in activities	23 ± 22	26 ± 18	18.4
Ability to perform specific skills	30 ± 22	32 ± 22	20.5
Squatting ability	39 ± 31	37 ± 28	25.4
Emotions	36 ± 22	40 ± 23	20.6
Consciousness of the knee	31 ± 23	36 ± 24	22.3
Concern about the future of the knee	31 ± 26	36 ± 25	24.1
Frustration or discouragement	45 ± 29	50 ± 31	33.7

*The values are given as the mean WOMET score (and standard deviation) for thirty-seven patients.
†The values are given as the average root-mean-square coefficient of variation (CV_rms) for the overall WOMET score, the three domains, and all sixteen items.

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TABLE III Repeatability of the WOMET

	First Assessment*	Second Assessment*	CV_rms†(%)
Overall WOMET score	47 ± 17	47 ± 18	9.9
Physical symptoms	58 ± 19	56 ± 19	17.3
Feeling of giving way or instability	56 ± 23	51 ± 23	24.4
Pain or soreness after activities	45 ± 20	44 ± 22	22.8
Loss of range of motion	54 ± 26	51 ± 27	26.7
Numbness	75 ± 24	70 ± 27	43.6
Stiffness after rising or sitting	52 ± 30	53 ± 27	19.6
Weakness	54 ± 29	54 ± 26	37.6
Swelling	72 ± 30	71 ± 28	42.6
Sharp pains after full weight-bearing	52 ± 29	47 ± 24	32.6
Cracking, grinding, or popping	62 ± 30	61 ± 27	38.7
Sports/recreation/work/lifestyle	32 ± 19	34 ± 18	12.3
Fear of reinjury	38 ± 31	40 ± 28	35.7
Effect on the ability to participate in activities	23 ± 22	26 ± 18	18.4
Ability to perform specific skills	30 ± 22	32 ± 22	20.5
Squatting ability	39 ± 31	37 ± 28	25.4
Emotions	36 ± 22	40 ± 23	20.6
Consciousness of the knee	31 ± 23	36 ± 24	22.3
Concern about the future of the knee	31 ± 26	36 ± 25	24.1
Frustration or discouragement	45 ± 29	50 ± 31	33.7

Fig. 1

Scatterplot illustrating the difference in the WOMET score for each patient between the first assessment (two weeks preoperatively) and the second assessment (on the day of surgery).

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Internal Consistency

There was acceptable internal consistency (Cronbach α >0.70) for the preoperative overall WOMET score and for the domains of physical symptoms, sports/recreations/work/lifestyle, and emotions (Cronbach α = 0.917, 0.890, 0.749, and 0.824, respectively). The Cronbach alpha was also acceptable for the overall WOMET score for the patients with a meniscal tear without osteoarthritis on radiographs (α = 0.913) and for the patients with osteoarthritis (α = 0.931).

Content Validity

The overall WOMET score, the three domains, and all sixteen items had acceptable floor and ceiling effects (<30%). Also, the WOMET had acceptable floor and ceiling effects for the patients with and without radiographic evidence of osteoarthritis (Table IV).

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TABLE IV Floor and Ceiling Effects

	Floor Effect*			Ceiling Effect†
	All (N = 385)	Without OA (N = 313)	With OA (N = 72)	All (N = 385)	Without OA (N = 313)	With OA (N = 72)
Overall WOMET score	0 (0%)	0 (0%)	0 (0%)	0 (0%)	0 (0%)	0 (0%)
Physical symptoms	0 (0%)	0 (0%)	0 (0%)	4 (1.0%)	3 (1.0%)	1 (1%)
Feeling of giving way or instability	12 (3%)	10 (3.2)%	2 (3%)	1 (0.3%)	1 (0.3%)	0 (0%)
Pain or soreness after activities	2 (0.5%)	1 (0.3%)	1 (1%)	2 (0.5%)	2 (0.6%)	0 (0%)
Loss of range of motion	8 (2.1%)	7 (2.2%)	1 (1%)	3 (0.8%)	3 (1.0%)	0 (0%)
Numbness	67 (17.4%)	62 (19.8%)	5 (7%)	0 (0%)	0 (0%)	0 (0%)
Stiffness after rising or sitting	18 (4.7%)	17 (5.4%)	1 (1%)	5 (1.3%)	5 (1.6%)	0 (0%)
Weakness	28 (7.3%)	25 (8.0%)	3 (4%)	1 (0.3%)	1 (0.3%)	0 (0%)
Swelling	52 (13.5%)	49 (15.7%)	3 (4%)	4 (1.0%)	3 (1.0%)	1 (1%)
Sharp pains after full weight bearing	6 (1.6%)	6 (1.9%)	0 (0%)	2 (0.5%)	2 (0.6%)	0 (0%)
Cracking, grinding, or popping	31 (8.1%)	29 (9.3%)	2 (3%)	1 (0.3%)	1 (0.3%)	0 (0%)
Sports/recreation/work/lifestyle	0 (0%)	0 (0%)	0 (0%)	0 (0%)	0 (0%)	0 (0%)
Fear of reinjury	9 (2.3%)	8 (2.6%)	1 (1%)	9 (2.3%)	8 (2.6%)	1 (1%)
Effect on the ability to participate in activities	2 (0.5%)	2 (0.6%)	0 (0%)	22 (5.7%)	19 (6.1%)	3 (4%)
Ability to perform specific skills	2 (0.5%)	2 (0.6%)	0 (0%)	17 (4.4%)	15 (4.8%)	2 (3%)
Squatting ability	3 (0.8%)	3 (1.0%)	0 (0%)	20 (5.2%)	16 (5.1%)	4 (6%)
Emotions	0 (0%)	0 (0%)	0 (0%)	1 (0.3%)	0 (0%)	1 (1%)
Consciousness of the knee	1 (0.3%)	1 (0.3%)	0 (0%)	14 (3.6%)	12 (3.8%)	2 (3%)
Concern about the future of the knee	4 (1.0%)	3 (1.0%)	1 (1%)	12 (3.1%)	8 (2.6%)	4 (6%)
Frustration or discouragement	10 (2.6%)	7 (2.2%)	3 (4%)	12 (3.1%)	8 (2.6%)	4 (6%)

*The values represent the number and percentage of patients who received the lowest possible score (floor effect). OA = osteoarthritis.
†The values represent the number and percentage of patients who received the highest possible score (ceiling effect). OA = osteoarthritis.

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TABLE IV Floor and Ceiling Effects

	Floor Effect*			Ceiling Effect†
	All (N = 385)	Without OA (N = 313)	With OA (N = 72)	All (N = 385)	Without OA (N = 313)	With OA (N = 72)
Overall WOMET score	0 (0%)	0 (0%)	0 (0%)	0 (0%)	0 (0%)	0 (0%)
Physical symptoms	0 (0%)	0 (0%)	0 (0%)	4 (1.0%)	3 (1.0%)	1 (1%)
Feeling of giving way or instability	12 (3%)	10 (3.2)%	2 (3%)	1 (0.3%)	1 (0.3%)	0 (0%)
Pain or soreness after activities	2 (0.5%)	1 (0.3%)	1 (1%)	2 (0.5%)	2 (0.6%)	0 (0%)
Loss of range of motion	8 (2.1%)	7 (2.2%)	1 (1%)	3 (0.8%)	3 (1.0%)	0 (0%)
Numbness	67 (17.4%)	62 (19.8%)	5 (7%)	0 (0%)	0 (0%)	0 (0%)
Stiffness after rising or sitting	18 (4.7%)	17 (5.4%)	1 (1%)	5 (1.3%)	5 (1.6%)	0 (0%)
Weakness	28 (7.3%)	25 (8.0%)	3 (4%)	1 (0.3%)	1 (0.3%)	0 (0%)
Swelling	52 (13.5%)	49 (15.7%)	3 (4%)	4 (1.0%)	3 (1.0%)	1 (1%)
Sharp pains after full weight bearing	6 (1.6%)	6 (1.9%)	0 (0%)	2 (0.5%)	2 (0.6%)	0 (0%)
Cracking, grinding, or popping	31 (8.1%)	29 (9.3%)	2 (3%)	1 (0.3%)	1 (0.3%)	0 (0%)
Sports/recreation/work/lifestyle	0 (0%)	0 (0%)	0 (0%)	0 (0%)	0 (0%)	0 (0%)
Fear of reinjury	9 (2.3%)	8 (2.6%)	1 (1%)	9 (2.3%)	8 (2.6%)	1 (1%)
Effect on the ability to participate in activities	2 (0.5%)	2 (0.6%)	0 (0%)	22 (5.7%)	19 (6.1%)	3 (4%)
Ability to perform specific skills	2 (0.5%)	2 (0.6%)	0 (0%)	17 (4.4%)	15 (4.8%)	2 (3%)
Squatting ability	3 (0.8%)	3 (1.0%)	0 (0%)	20 (5.2%)	16 (5.1%)	4 (6%)
Emotions	0 (0%)	0 (0%)	0 (0%)	1 (0.3%)	0 (0%)	1 (1%)
Consciousness of the knee	1 (0.3%)	1 (0.3%)	0 (0%)	14 (3.6%)	12 (3.8%)	2 (3%)
Concern about the future of the knee	4 (1.0%)	3 (1.0%)	1 (1%)	12 (3.1%)	8 (2.6%)	4 (6%)
Frustration or discouragement	10 (2.6%)	7 (2.2%)	3 (4%)	12 (3.1%)	8 (2.6%)	4 (6%)

Criterion Validity

There was a significant correlation between the WOMET score and the Lysholm knee score (r = 0.558, p < 0.001). A significant correlation was also found between the overall WOMET score and the overall 15-D scale (r = 0.311, p = 0.002).

Construct Validity

All five convergent hypotheses were significant and the one discriminate hypothesis showed no significant difference between the two groups of patients (Table II).

Responsiveness

Of the 385 patients, 323 (84%) returned the six-month follow-up questionnaire completely filled in. The median preoperative and postoperative WOMET scores were 44 (range, 6 to 97) and 77 (range, 0 to 100), respectively. There was a large overall effect size (1.17) and a large overall standardized response mean (0.90) for the WOMET score. Also, when compared with the patients’ global impression of knee function, the observed mean change in the WOMET score was greater for patients who reported that the knee was much better or better after the operation (31 ± 21) than for patients who reported that the knee was the same or worse (−3 ± 16) (p < 0.001).

Discussion

Introduction | Materials and Methods | Results | Discussion

The present study demonstrated that, with use of the standard principles of assessing the psychometric properties of knee-specific measurement tools (Table I), the patient-administered WOMET tool showed acceptable test-retest reliability, internal consistency, content validity (floor and ceiling effects), criterion and construct validity, and responsiveness for measuring meniscal pathology-specific health-related quality of life in patients with arthroscopically verified degenerative meniscal lesions (both with and without osteoarthritis on radiographs).

Reliability is classically considered to comprise two domains: test-retest repeatability and internal consistency (Table I). Although intraclass correlation coefficients (ICCs) commonly have been used as a measure of reliability (test-retest) in previous validations of various knee instruments^12-14, a more appropriate approach is to calculate the 95% limits of agreement for the differences in the two repeated measurements²⁸. This analysis showed acceptable agreement for the WOMET (Table III). Also, the WOMET showed acceptable internal consistency (with Cronbach alpha values clearly above 0.70) for the preoperative overall WOMET score as well as for the subdomains of physical symptoms, sports/recreations/work/lifestyle, and emotions. In essence, the analysis confirmed that all items of the score reflect the same phenomenon. The overall internal consistency of the WOMET in our analysis (α = 0.917) was also very similar to those obtained previously for patients with general meniscal pathology (α = 0.923 for the WOMET¹⁵, α = 0.729 for the Lysholm knee score¹², and α = 0.773 for the IKDC¹³).

Validity is classically divided into external and internal validity, and the latter can further be divided into the domains of content, criterion, and construct validity (Table I). In our assessment, the WOMET covered the entire area of interest as the overall WOMET score, each of the three domains, and all sixteen separate items showed acceptable floor and ceiling effects. However, although the domains of “numbness” and “swelling” were within acceptable limits, they did show clearly higher floor effects than the fourteen other items. The absence of numbness or swelling was also far more common in patients with an isolated tear (20% and 16%) than in those with concomitant osteoarthritic changes (7% and 4%) (Table IV). Overall, our findings are very much in agreement with the findings of the original WOMET validation study by Kirkley et al.¹⁵, except for the two domains noted above, which were more common in their patient group than in our population. As also noted previously, the original cohort in the study by Kirkley et al.¹⁵ included a substantial number of patients with acute, traumatic meniscal injuries. Taken together, these findings suggest that numbness and swelling may not be as prevalent (and relevant) symptoms for patients with degenerative meniscal lesion as for those with an acute traumatic tear. As for the content validity of the other tools validated for the assessment of patients with meniscal injuries, the Lysholm knee score has an unacceptable floor effect for squatting and unacceptable ceiling effect for swelling, limp, instability, support, and locking¹². The IKDC, in turn, has an unacceptable floor effect in the domains of catching, kneeling, sitting, running, and jumping and a ceiling effect in the domain of catching¹³.

Criterion validity, or instrumental validity as it is also called, is used to demonstrate the accuracy of the instrument by comparing it with the truth or at least with another instrument that has been proven to be valid. We chose the Lysholm knee score as our gold standard as it has been validated as a meniscus-specific instrument¹². Similar to the findings of Kirkley et al.¹⁵ (r = 0.414, p < 0.015), we also observed a significant correlation between the WOMET score and the Lysholm knee score (r = 0.558, p < 0.001). We also performed interclass correlations between the WOMET and the 15-D, a validated, fifteen-dimension, generic self-administered measure of health-related quality of life²⁴. Although significant (p < 0.002), the observed correlation (r = 0.311) was clearly lower than that between the WOMET and the Lysholm knee score.

By assessing the agreement between the WOMET and five hypotheses that should have been theoretically related (convergent) and one hypothesis that should not have been related (discriminative), we were able to show that the construct of the WOMET score works as predicted (Table II). The fact that there was a high level of agreement with the overall WOMET score (Table II) as well as with the two subgroups (patients with isolated lesions and patients with concomitant osteoarthritis) (data not shown) suggests that the developers of the WOMET succeeded in choosing constructs that adequately reflect the aspects of patient-relevant symptoms present in both degenerative meniscal tears and in early osteoarthritis. When considered in light of the fact that the hallmark symptoms of degenerative meniscal tears³² are also the most common symptoms of early osteoarthritis and that these cannot be reliably distinguished from each other³³, our findings are actually very logical.

The indices most commonly used to quantify responsiveness or to measure the magnitude of a treatment effect are the effect sizes and the standardized response mean (Table I). In our study, both the effect sizes and the standardized response mean showed treatment effe0ct of a large magnitude (1.17 and 0.90, respectively). These values concur well with the findings of earlier validation studies: N/D (i.e., not recorded) and 0.65 for the WOMET¹⁵, 1.2 and 0.97 for the Lysholm¹², and 2.11 and 1.5 for the IKDC¹³, respectively. The responsiveness of an outcome instrument can also be determined with a method that involves rating by the patients themselves; this is done by comparing a change observed in the score from one assessment point to another with the patients’ impression of whether their condition has improved, deteriorated, or stayed the same. Our analysis showed that patients’ subjective “transition changes” (as determined by global impression of change in the knee) corresponded well with the changes observed in the WOMET score, a finding further corroborating that the responsiveness of the WOMET is acceptable.

The group of patients used in the development of the WOMET was heterogeneous with respect to the prevalence of coexisting knee pathology, such as articular cartilage damage or ligament injury¹⁵, prompting the authors to suggest that the WOMET should be tested in a more homogenous group with isolated meniscal pathology. This was indeed one of the primary objectives of the current paper. However, as also noted previously, recent investigations^34,35 have lent support to the idea that rather than being a clinical entity on its own, a degenerative meniscal lesion could actually represent an early phase of knee osteoarthritis. Accordingly, our current sample consisted of patients with an isolated degenerative meniscal tear and those with concomitant osteoarthritis and was analyzed both as one large group and as two separate groups. The inclusion of patients with and without concomitant osteoarthritic changes hopefully ensures that the instrument can be applied equally to patients with isolated meniscal lesion and those with more generalized articular cartilage pathology. We concede that categorizing the patients according to their primary diagnosis or reason for treatment is inherently flawed to some extent as it does not create pure categories. However, as also stated previously¹⁶, the advantage of this procedure is that it is consistent with clinical practice.

It has been claimed that disease-specific measures of health-related quality-of-life are important because they tend to be more sensitive for detecting quality-of-life deficits than more general health measures for the assessment of patients with specific, localized pathology³⁶. Accordingly, a meniscus-specific measure, such as the WOMET, may discriminate better between patients or groups of patients after evaluations of different treatments for meniscal pathology, such as in the setting of a randomized trial³⁷. As doubt has been cast over the potential benefits of arthroscopic procedures for the treatment of degenerative meniscal tears in patients with or without osteoarthritis^38-40, this issue seems particularly important and timely. Our current analysis demonstrated that the WOMET has acceptable psychometric properties for the evaluation of patients with a degenerative meniscal tear.

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Disclosure: None of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of any aspect of this work. None of the authors, or their institution(s), have had any financial relationship, in the thirty-six months prior to submission of this work, with any entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. Also, no author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.

Topics

knee joint ; quality of life ; knee meniscus tears

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Raine Sihvonen, Timo Järvelä, Heikki Aho, Teppo L.N. Järvinen; Validation of the Western Ontario Meniscal Evaluation Tool (WOMET) for Patients with a Degenerative Meniscal TearA Meniscal Pathology-Specific Quality-of-Life Index. The Journal of Bone & Joint Surgery. 2012 May;94(10):e65 1-8.

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