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Vol. 88, No. 1, January 2008, pp. 33-42
DOI: 10.2522/ptj.20060372
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Research Reports

Associations Between Physical Examination and Self-Reported Physical Function in Older Community-Dwelling Adults With Knee Pain

Laurence Wood, George Peat, Elaine Thomas, Elaine M Hay and Julius Sim

L Wood, PhD, BA, BPhysiotherapy, MCSP, is Post-Doctoral Research Fellow in Clinical Epidemiology, Primary Care Musculoskeletal Research Centre, Keele University, Keele, Stoke-on-Trent ST5 5BG, United Kingdom, and works part-time as an Advanced Therapist at the University Hospital of North Staffordshire, Stoke-on-Trent, United Kingdom
G Peat, PhD, MSc, BSc, MCSP, is Senior Lecturer in Clinical Epidemiology, Primary Care Musculoskeletal Research Centre. He is the Principal Investigator of the Knee Clinical Assessment Study
E Thomas, PhD, MSc, BSc, is Senior Lecturer in Biostatistics, Primary Care Musculoskeletal Research Centre
EM Hay, MBChB, MD, FRCP, is Professor of Community Rheumatology and Honorary Consultant Rheumatologist, Haywood Hospital, Stoke-on-Trent, United Kingdom. She is the Director of the Clinical Trials Unit at Primary Care Musculoskeletal Research Centre
J Sim, PhD, MSc(soc), MSc(stat), BA, MCSP, is Professor of Health Care Research, Primary Care Musculoskeletal Research Centre

Address all correspondence to Dr Wood at: l.r.j.wood{at}cphc.keele.ac.uk


Submitted December 12, 2006; Accepted August 20, 2007


   Abstract
 
Background and Purpose: Knee pain is a common disabling condition for which older people seek primary care. Clinicians depend on the history and physical examination to direct treatment. The purpose of this study was to examine the associations between simple physical examination tests and self-reported physical functional limitations.

Subjects and Methods: A population sample of 819 older adults underwent a standardized physical examination consisting of 24 tests. Associations between the tests and self-reported physical functional limitations (Western Ontario and McMaster Universities Osteoarthritis Index physical functioning subscale [WOMAC-PF] scores) were explored.

Results: Five of the tests showed correlations with WOMAC-PF scores, corresponding to an intermediate effect (r≥.30). These were tenderness on palpation of the infrapatellar area, timed single-leg standing balance, maximal isometric quadriceps femoris muscle strength (force-generating capacity), reproduction of symptoms on patellofemoral compression, and degree of knee flexion. Each of these tests was able to account for between 7% and 13% of the variance in WOMAC-PF scores, after controlling for age, sex, and body mass index. Three of these tests are indicative of impairments that may be modifiable by exercise interventions.

Discussion and Conclusion: Self-reported physical functional limitations among older people with knee pain are associated with potentially modifiable physical impairments that can be identified by simple physical examination tests.


   Introduction
Top
 Abstract
 Introduction
Method
 Results
 Discussion
 Conclusion
 References
 
The degree to which musculoskeletal impairments are associated with limitations in physical functional activities is a central question, because proper medical care and timely rehabilitation aimed at such impairments may contribute to reducing functional limitations and disability.1 This notion has been demonstrated in studies of the effectiveness of lower-limb strengthening exercises for knee pain and osteoarthritis (OA).2–5 However, despite this fact, few studies in primary care have investigated the associations between signs of impairment in older people with knee pain and self-reported physical function.6–12 The need to quantify these associations in potential clients seeking primary care is underlined by the fact that knee pain is the most common symptom reported by people over 60 years of age consulting their general practitioner.13 The few previous studies in primary care and the general population have tended to concentrate on just 1 or 2 signs, such as weak quadriceps femoris muscles and reduced knee flexion range of motion.6,10,11 We have been unable to identify any study that has quantified the associations with a comprehensive set of physical examination tests. Our objective, therefore, was to examine the associations between the variables contained in a comprehensive physical examination of the knee, suitable for use in older people seeking primary care, and their self-reports of limitations in physical functional activities.


   Method
Top
 Abstract
 Introduction
 Method
Results
 Discussion
 Conclusion
 References
 
Subjects

A total of 6,108 adults (68% of those contacted), 50 years of age and older and registered with 1 of 3 general practices in North Staffordshire, United Kingdom, responded to a mailed general health questionnaire (see below). Of these responders, 3,106 reported an episode of knee pain in the previous year. Of the responders with knee pain, 1,949 subsequently responded to a further mailed questionnaire concerning regional pain (see below), and 819 of these responders consented to a detailed clinical examination at a research clinic, in which a standardized physical examination (see below) was performed and plain radiographs were obtained. These 819 adults constituted the Knee Clinical Assessment Study [CAS(K)] cohort (full details of this study have been reported elsewhere14).

Demographic and lifestyle characteristics for the 3,106 adults who reported an episode of knee pain in the previous year and the subset of 819 adults attending assessment clinics are provided in Table 1.


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  		Table 1. Characteristics of All Respondents to the Questionnaires Who Reported Knee Pain and of All Subjects Attending Research Clinics

 
Of the 819 adults attending assessment clinics, 12 had had a total joint replacement of the affected or more-affected knee and were excluded from the analyses. Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) physical functioning subscale (WOMAC-PF) scores (from the anatomical regional pain questionnaire) were missing for a further 66 adults. Thus, data from 741 study participants were included in the analyses. The mean age of the 741 study participants was 65.5 years (SD=8.5 years), and 54% were women. Their mean body mass index (BMI) was 29.6 kg/m2 (SD=5.1 kg/m2). The WOMAC was completed by the participants a mean of 60 days (SD=33 days) prior to their being clinically assessed. The mean scores for each of the 3 WOMAC domains were as follows: pain=6.4 (SD=4.4), stiffness=2.7 (SD=1.9), and physical functioning=20.9 (SD=15.2). These scores denote generally mild or mild-to-moderate knee problems and are similar to those for the whole subset of 1,949 people who responded to the regional pain questionnaire described below (6.3, 2.7, and 21.1, respectively).

Two-Stage Postal Survey

The 2-stage postal survey comprised a general health questionnaire followed by an anatomical regional pain questionnaire.15 The questionnaires included questions about anxiety and depression, from the Hospital Anxiety and Depression Scale (HADS),16 and physical functioning, from the ordinal-response version of the WOMAC.17 The WOMAC is a disease-specific, self-completed questionnaire developed as an outcome measure for use in people with hip and knee OA. It has excellent psychometric properties with regard to reliability, responsiveness, internal consistency, and construct validity.18,19

Standardized Physical Examination

A standardized physical examination, consisting of items selected for their appropriateness for everyday clinical practice in primary care, was developed with reference to standard rheumatology textbooks and the opinions of rheumatology experts.20 This physical examination was applied to all 819 members of the CAS(K) cohort.

The standardized physical examination consisted of 24 items whose reliability in a population of 58 people seeking primary care has been described in detail elsewhere.20 Five of the items used some form of simple instrumentation, such as a tape measure or a goniometer. Response options for the majority of the noninstrumented measures were dichotomous (eg, "present" or "absent"), with only 5 having more response categories. Each of the items is described in Table 2. For each participant, a single examiner carried out the entire physical examination. Participants were not randomly assigned to the different examiners. Instead, they were booked into the first available convenient research clinic, regardless of which examiners were staffing it that day.


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  		Table 2. Tests Contained in the Standardized Physical Examination

 
Examiners were 5 research physical therapists and 1 research occupational therapist who had been licensed for a median of 10.5 years (range=8–12 years). Each examiner was provided with a detailed observer manual, which contained in-depth protocols for the clinical interview and examination, for reference during the entire study period. Each examiner received several hours of training in the standardized clinical interview and examination. Quality control sessions were arranged with each examiner after every 100 participants recruited for the study.14 These sessions included observation of assessments in clinics by the principal investigator, structured observation of assessments in volunteers who were healthy, and direct interexaminer comparisons for selected participants. All of these measures were intended to minimize sources of interexaminer variability in the physical examination.21,22

Plain Radiographs

Three views of the knees were obtained for each participant at the assessment clinics: the weight-bearing posteroanterior (PA) semiflexed/metatarsophalangeal view, according to the protocol of Buckland-Wright and colleagues23; a skyline view of the patellofemoral articulation; and a lateral view. The last 2 views were obtained in the supine position with the knee flexed to 45 degrees.

A single reader, unaware of all other information on participants, scored all radiographs. The atlas24 and scoring system25 of Altman and colleagues were used for the PA and skyline views, and the atlas of Burnett et al26 was used for the lateral view. Additionally, PA and skyline views were assigned a Kellgren-Lawrence (K & L) grade.27 For PA and skyline views, the widely accepted minimum score of 2 (ie, a definite osteophyte and unimpaired joint space)28–30 was used to define the presence of radiographically evident OA (ROA). Because of the difficulty in estimating joint space width on the lateral view, the K & L score was not applied to this view; instead, a definite osteophyte was used as a marker of ROA, comparable to a K & L score of 2. The K & L score for PA and skyline views and the osteophyte score for the lateral view were combined to provide a definition of ROA for the whole joint that is comparable to the American College of Rheumatology definition of ROA.31,32

Organization and Analysis of Data

The data were organized on the basis of which knee each participant identified as the affected or more affected. This knee was designated the "index knee." Only findings relating to the index knee were considered for the analyses, because these were likely to be the most salient in clinical decision making. For dichotomous examination items, the prevalence was calculated in order to characterize more fully the clinical sample.

Analysis of the data involved 2 main stages. First, in bivariate analyses, the results of the participants’ physical examinations were compared with their aggregate WOMAC-PF scores (possible range=0–68) by use of Pearson correlation coefficients (r) in most instances. For ordinal data, dummy variables were generated to express each ordinal variable, and the multiple correlation coefficient (R) was calculated. The association between a count of the number of tender points around the knee (0–6 sites) and WOMAC-PF scores also was considered.

Second, with the exception of the tenderness count variable, all physical examination items that demonstrated a correlation with WOMAC-PF scores representing an intermediate effect, according to Cohen33 (ie, r or R of ≥.30), were entered into regression analyses with WOMAC-PF scores as the outcome variable. This was done both with one predictor at a time and with all predictors together, in multiple regression analyses, controlling for age, sex, BMI, and the time lag (days) between the completion of the WOMAC and the physical examinations. As in other studies, linear regression models were used because WOMAC-PF scores generally can be regarded as generating interval-level data.34–38 In each such analysis, the assumptions underlying linear regression analysis were checked.

A series of sensitivity analyses were undertaken in order to test whether the relationships between physical examination findings and physical functioning in older adults persist under the following circumstances: (1) when only people with definite ROA are considered and (2) when the potential psychological confounders of anxiety and depression are removed by considering only people with no anxiety or depression, according to the HADS.16

Finally, in order to facilitate comparison of our results with those of O'Reilly et al,9 maximal isometric quadriceps femoris muscle strength (force-generating capacity) measurements in millimeters of mercury were converted to kilograms of force by methods established in an earlier cross-validation study39 and were placed in 4 ordinal categories (≤10, >10 to ≤20, >20 to ≤30, and >30 kg of force). Logistic regression analyses were used to determine the crude odds ratios for these 4 categories of strength measurements as predictors of the presence or absence of physical functional limitations, as defined by O'Reilly et al9 as a WOMAC-PF score of 19 or ≤19, respectively (0–68 ordinal-response version). Except as otherwise stated, statistical significance was set at P≤.05 (2-tailed).


   Results
Top
 Abstract
 Introduction
 Method
 Results
Discussion
 Conclusion
 References
 
The correlations between all of the individual physical examination findings and the WOMAC-PF scores are shown in Table 3, together with the prevalence of each of these findings. For this set of analyses only, the cutoff for statistical significance was reduced to P≤.01 in order to control the type I error rate.


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  		Table 3. Results of Correlation Analyses of Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) Physical Function Domain Aggregate Scoresa

 
Only 5 of the original physical examination items had intermediate (r or R of ≥.30) correlations with the WOMAC-PF scores. These were tenderness on palpation of the infrapatellar area (r=.30), timed single-leg standing balance (r=.37), maximal isometric quadriceps femoris muscle strength (r=.37), reproduction of symptoms on patellofemoral compression tests (R=.39), and degree of knee flexion (r=.46). In addition, the generated variable of tenderness count demonstrated a similar level of association with the WOMAC-PF score (r=.38). After controlling for age, sex, and BMI, the 5 original examination items, taken individually, were able to account for 7% to 13% of the total variance in WOMAC-PF scores in a multiple regression analysis. In the sensitivity analyses, similar levels of association were demonstrated for subgroups of participants with confirmed ROA (495 out of 716 with readable radiographs), with no depression (608 out of 724 with HADS data), and with neither depression nor anxiety (432 out of 724 with HADS data) (Tab. 4). A modest diminution in the strength of the association between quadriceps femoris muscle strength and the WOMAC-PF score was noted in participants with no depression and in those with no depression or anxiety, although all of the associations remained significant.


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  		Table 4. R2 Valuesa for Associations With Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) Physical Function Domain Aggregate Scores in the Whole Cohort and in Subgroups After Controlling for Age, Sex, and Body Mass Index

 
A multiple regression analysis, in which all 5 of these physical examination items were entered together as the predictor variables, was able to account for an additional 27% of the total variance in WOMAC-PF scores, after adjusting for age, sex, BMI, and the time lag between the completion of the WOMAC and the physical examinations.

Finally, the use of logistic regression to determine the associations among muscle strength categories and physical functional limitations yielded the odds ratios indicated in Table 5. Participants in the weakest muscle strength category were just over 5 times more likely to report such limitations, according to the criterion of WOMAC-PF scores of greater than 19, used by O'Reilly et al,9 than those in the strongest muscle strength category.


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  		Table 5. Comparison of Results of Logistic Regression Analyses From the Present Study and the Study of O'Reilly et al9 (Isometric Quadriceps Muscle Strength Versus Self-Reported Physical Functional Limitationsa)

 

   Discussion
Top
 Abstract
 Introduction
 Method
 Results
 Discussion
Conclusion
 References
 
The present study demonstrated that a minority of the simple physical examination tests contained in a comprehensive physical examination schedule of 24 tests had intermediate correlations with the self-reported physical functional difficulties of older people with knee pain in the community. The tests in question were symptom reproduction on manual patellofemoral compression, goniometric range of knee flexion, maximal isometric quadriceps femoris muscle strength (measured with a sphygmomanometer), timed single-leg standing balance, and palpation for infrapatellar tenderness. Even when the possible confounding factors of age, sex, and BMI were taken into account, these 5 physical examination findings were able, individually, to account for 7% to 13% of the variance in WOMAC-PF scores. Collectively, these variables were able to account for over one fourth of the variance. These findings demonstrate that a few core tests may show sizeable associations with subjects’ perceptions of their functional abilities. This conclusion has important implications for clinical practice, in which potentially modifiable impairments, such as quadriceps muscle weakness, reduced range of knee flexion, and poor standing balance, may be specific targets for rehabilitation interventions that have been shown to lead to a direct reduction in the particular impairment.2,4,40–42

It is less clear how pain on patellofemoral compression tests may affect treatment, although the fact that the lateral retropatellar facet is the most commonly associated with radiologically progressive OA43 may suggest that measures aimed at reducing the loading of this articular facet are warranted.44–46 Of the 5 physical examination findings, infrapatellar tenderness on palpation demonstrated the weakest correlation with the WOMAC-PF scores, and it is difficult to conclude how such a finding might be directly suggestive of a particular treatment option. The fact that the tenderness count demonstrated an even stronger association with the WOMAC-PF scores may suggest that tenderness around the knees of older people with knee pain and OA is related more to central sensitization than to the identification of localized pathology.47

Many of the items in our physical examination schedule demonstrated only very weak correlations with self-reported physical function. Tests of ligamentous laxity and judgments regarding the presence or absence of periarticular swelling were associated with correlations with WOMAC-PF scores of no greater than r=.10. Likewise, measurements of intercondylar and intermalleolar gaps, judgments regarding the presence or absence of knee joint effusions and fixed flexion deformities, and palpation for bony enlargement had correlations with WOMAC-PF scores of no greater than r=.15.

Potential indicators of structural changes, such as palpation for bony enlargement and coarse crepitus, were found to have only weak correlations with WOMAC-PF scores. This finding is important because the American College of Rheumatology clinical algorithm for the classification and reporting of OA of the knees depends greatly on these 2 physical examination findings in its favored classification-tree method.31 Poor agreement among the 6 examiners about what exactly constituted a positive case may have been partly responsible for the poor observed correlations with WOMAC-PF scores in such instances. Although the interrater reliability of the examination items was not formally assessed in the present study, 3 of the 6 examiners who participated in the present study took part in a companion reliability study. That study concluded that for trained but nonexpert examiners (such as those who participated in the present study), agreement was generally poor (kappa= –.06–.58) for dichotomous and ordinal items.20 In the presence of poor agreement regarding the presence or absence of a finding among examiners, the validity of the finding will, necessarily, also be poor. Such poor agreement therefore will be reflected in a poor correlation between the finding and an outcome, such as the WOMAC-PF score. In contrast, reasonable levels of interexaminer reliability (ICC[2,1]=.61–.77) were observed for the simple continuously measured items of isometric quadriceps femoris muscle strength, single-leg standing balance, and degree of knee flexion.

The sensitivity analyses demonstrated that the associations with WOMAC-PF scores persisted in people with knee pain and confirmed ROA, who may be considered to be a more homogeneous group of particular interest to clinicians. They also showed that anxiety and depression, which may be linked to both self-reported functional limitations and impairments,6,9,36,48–50 were not major confounders for the observed associations between response- or volition-dependent tests and WOMAC- PF scores. This finding suggests that the observed associations may not simply be the result of confounding by these psychological variables. However, other psychological variables, such as self-efficacy, may contribute to the associations between response- or volition-dependent tests and WOMAC-PF scores51; no measure of self-efficacy was used in the present study.

Crude measures of malalignment (intercondylar and intermalleolar gaps in standing) and mediolateral laxity (manual varus and valgus stress tests) in the present study were found to have only weak correlations with physical function (r=.01–.13). This finding seems to be in contrast with the 18-month data from the longitudinal study of Sharma and colleagues,52,53 which suggested that malalignment and laxity are both risk factors for the deterioration of self-reported physical function (WOMAC-PF). It is possible that the measurement techniques that we used, which were specifically chosen to be practical for use in primary care, were not sufficiently reliable or sensitive for the small variations in knee alignment or laxity that may be associated with functional decline.

The results of our logistic regression analyses, with quadriceps femoris muscle strength as the predictor variable, confirmed the finding of O'Reilly et al9 that the risk of experiencing difficulties with physical function in the presence of knee pain is greater when isometric quadriceps muscle strength is lower. Slightly lower odds ratios were observed in the present study than in the study of O'Reilly et al, but they fell within the relatively broad 95% confidence intervals quoted in that study and followed the same pattern of association (Tab. 5). This form of analysis, based on quadriceps femoris muscle strength rankings, also confirms that such simple categorizations of quadriceps femoris muscle strength measurements (4 increments) are sufficient to discriminate people with knee pain who are and people with knee pain who are not likely to have significant difficulties with physical function.

There is no perfect instrument for measuring limitations in physical function. Certainly, the responsiveness of the physical function domain of the WOMAC has been shown to vary among studies.3,54–58 However, the WOMAC is specific to the lower-limb-related function of people likely to have OA of the hip or knee, and it is generally agreed that the WOMAC has excellent measurement properties. Given its minor limitations, therefore, and because the primary interest of the present study was self-reported physical functional limitations, the WOMAC was the instrument of choice for this study. Nonetheless, when drawing conclusions from the results of this study, one must bear in mind that although the relationship of musculoskeletal impairments to limitations in physical functional activities is a central question that can identify physical examination tests that may affect treatment, the value of the physical examination is not limited to its association with the physical function of an individual. The physical examination also may be used for other purposes, such as diagnosis or prognosis.59 Clinicians must not be tempted, therefore, to dismiss physical examination items, such as bony enlargement and crepitus, that show only a weak relationship to measures of physical function, because they may be useful, for instance, in classifying the nature of people's joint pain.31


   Conclusion
Top
 Abstract
 Introduction
 Method
 Results
 Discussion
 Conclusion
References
 
The present study has identified—from a comprehensive physical examination suitable for use in the primary care setting—simple physical examination tests that could be used to identify potentially modifiable impairments in older people with knee pain and OA. Our findings suggest a pragmatic mode of assessment, in which tests indicate the tailoring of rehabilitation interventions in the manner suggested by current clinical guidelines.60 Although evidence already exists for a beneficial cause-effect link between quadriceps muscle strengthening exercises and self-reported physical function,2–5 this evidence needs to be extended by similar studies exploring the effectiveness of rehabilitation interventions for treating reduced knee flexion range of motion and poor standing balance.


   Footnotes
 
Dr Wood, Dr Peat, and Dr Sim provided writing. Dr Wood provided data collection. Dr Thomas provided data management. Dr Wood and Dr Sim provided data analysis. Dr Peat provided project management. All authors provided study design and reviewed and approved the final manuscript.

Ethical approval for this study was obtained from the North Staffordshire Local Research Ethics Committee (project no. 1430).

This work was funded by a Programme Grant awarded by the Medical Research Council, United Kingdom (Grant Code G9900220), and by Support for Science funding secured by the North Staffordshire Primary Care Research Consortium for NHS service support costs.

An oral presentation of this research was given at the Annual Scientific Meeting of the American College of Rheumatology; November 12–17, 2005; San Diego, Calif. A poster presentation of this work was given at the 2006 British Society for Rheumatology Annual Meeting; May 2–5, 2006; Glasgow, Scotland, United Kingdom.


   References
Top
 Abstract
 Introduction
 Method
 Results
 Discussion
 Conclusion
 References
 

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