Annals of the Rheumatic Diseases 1992; 51: 844-849

Radiographic patterns of osteoarthritis of the kneejoint in the community: the importance of thepatellofemoral joint

T E McAlindon, S Snow, C Cooper, P A Dieppe

AbstractThe intimate relation which the patella haswith the knee joint and quadriceps musclesuggests that patellofemoral joint osteoarthritisis likely to be an important cause of knee painand disability. Two hundred and seventythree subjects who reported knee pain in apostal questionnaire survey and 240 controlsubjects consented to have anteroposteriorweightbearing and lateral knee radiographs.Each subject completed a Stanford HealthAssessment Questionnaire (HAQ).

Radiographic knee osteoarthritis was foundin 53% of symptomatic and 17% of asymptom-atic subjects. Three patterns predominatedpateliofemoral, medial, and medial/patello-femoral joint disease in 11, 21, and 7% ofthe men and in 24, 12, 6% of the womenrespectively. The occurrence of isolatedsymptomatic pateliofemoral joint osteoarth-ritis in this sample aged more than 55 yearswas estimated as 8% in women and 2% inmen. All patterns of symptomatic knee jointosteoarthritis increased with age in womenbut peaked at 70 years in men. Medial jointand patellofemoral joint osteoarthritis weresignificantly associated with disability (46 v17% in controls and 64 v 25% in controlsrespectively) but higher HAQ scores weremore common in subjects with pateliofemoraljoint osteoarthritis. Patellofemoral jointosteoarthritis is common, associated withdisability, occurs in the absence of tibio-femoral disease, and can no longer be omittedfrom future studies of osteoarthritis of theknee joint.

(Ann Rheum Dis 1992; 51: 844-849)

Rheumatology Unit,Bristol RoyalInfirmary,Bristol BS2 8HW,United KingdomT E McAlindonS SnowC CooperP A DieppeCorrespondence to:Dr T E McAlindon,Department ofRheumatology,St Thomas's Hospital,Lambeth Palace Road,London SEI 7EH,United Kingdom.Accepted for publication31 December 1991

Osteoarthritis of the knee joint is a common,disabling, and expensive disease which pre-dominantly affects the elderly. ' 2 The knee is a

complex tricompartmental synovial joint.Despite this studies of osteoarthritis of the kneejoint have tended to focus on the tibiofemoralcompartment alone.' 3 4 The patellofemoralcompartment, however, is likely to be important.As a sesamoid bone within the quadriceps

femoris tendon, the patella is an integralcomponent of the knee extension apparatus,acting as a dynamic fulcrum transmitting forcesof up to eight times the body weight duringeveryday activities.5 Its dual role as an articu-lation point and a component of the quadricepsmuscle makes it unique and suggests thatpatellofemoral joint osteoarthritis may be a

potent cause of knee pain and disability.Reviews of this subject indicate that patho-

logical abnormalities of patellar cartilage arecommon and increase with age.6 Minor changesare common and their relevance to knee painremains controversial.7 A distinct subgroup isrecognised, however, with more progressivedamage usually occurring on the lateral patellarface.6 This occurs in older subjects, is morecommon in women,8 and is morphologicallyindistinguishable from patellofemoral osteo-arthritis. It has been observed pathologically6and in radiographic series9 that patellofemoralosteoarthritis can occur in the absence of overttibiofemoral disease. Despite this the patello-femoral joint has received less attention than thetibiofemoral compartment. Its prevalence in thecommunity is not known and the failure toinclude lateral radiographs in any of the largesurveys of knee joint osteoarthritis,' 3 4 mayhave contributed to the low correlations observedbetween symptoms, clinical findings, andradiographic changes.'0

This study investigated the prevalence ofvarious patterns of radiographic osteoarthritis insubjects living in the community who wereasymptomatic and those reporting knee pain.

Subjects and methodsSUBJECTSThe study group has been described pre-viously. " In brief, a postal questionnaire askingabout knee pain and disability was sent to 2101men and women aged over 55 years registered ata general practice in Bristol. The question aboutknee pain was taken verbatim from the Healthand Nutrition Examination Survey'2: (a) haveyou ever had pain in or around a knee on mostdays for at least a month? (b) if so, have you hadany knee pain during the last year?A positive response to the two parts of the

question was required for a subject to bedesignated 'knee pain positive'. The responserate to the questionnaire was 81%. Two sub-groups of this population were then invited toattend the Bristol Royal Infirmary for clinicalassessment of their knee joints and for radio-graphy. These two groups consisted of (a) allknee pain positive respondents and (b) a selectionof asymptomatic control subjects.

RADIOGRAPHYWeight bearing anteroposterior knee radio-graphs and recumbent lateral knee radiographswere obtained for all subjects.

Sconrng systemThe radiographs were scored blindly by the

844

on July 26, 2020 by guest. Protected by copyright.

http://ard.bmj.com

/A

nn Rheum

Dis: first published as 10.1136/ard.51.7.844 on 1 July 1992. D

ownloaded from

Importance ofthe patellofemoraljoint in knee osteoarthritis

same observer (TEM) for the presence ofosteoarthritis using the principles of Kellgrenand Lawrence,13 with joint space narrowingconsidered mandatory for the designation ofdefinite osteoarthritis. Each received an 'on-off'score with respect to the presence of medial,lateral, and patellofemoral compartment diseaseas suggested by Ahlback.9

ReproducibilityFifty sets of knee radiographs were chosen torepresent the spectrum of radiographic changesfrom normal to severe. These were rescoredblindly by the original observer. Their relativereproducibility was assessed using the x

statistic.

ANALYSISCompartmental predilection of knee jointosteoarthritisThe first aim of this study was to determinewhether or not osteoarthritis has stereotypicpatterns of expression at the knee. It is an

analysis which is complicated, however, by thefact that each knee has three compartments andeach subject has two knees, generating 49different patterns of expression of knee jointosteoarthritis per subject. To simplify theprocess we reduced this part of the analysis tothe level of knees rather than subjects. It istherefore important when interpreting the datapresented in this paper to be clear aboutwhether the proportions refer to knees or tosubjects.The two subgroups were investigated

separately. As the symptomatic group containeda proportion of subjects with only unilateralknee pain the number of knee pain positiveknees was not double the number of knee painpositive subjects. These contralateral asymp-tomatic knees were not included in the analysisof knee pain negative knees because it was feltthat they were likely to be unrepresentative ofthis group.The proportions of knees with each of the

seven potential patterns of osteoarthritis were

then calculated separately in the knee painpositive and knee pain negative groups sub-divided by age and sex.

Proportion of subjects with knee joint osteoarthritisSubjects were designated as having knee jointosteoarthritis on the basis of radiographicchanges in one or two knees. Assigning a

compartmental pattern to a subject, however,can be difficult as it is theoretically possible for

different patterns to coexist in each knee.Subjects assigned to a category were thereforerequired to have either unilateral or symmetricaldisease, and subjects with mixed patterns were

not included.To assess the extent to which knee osteo-

arthritis is symmetrical the percentage withbilateral disease from all those with painful kneeosteoarthritis was calculated, and the occurrenceof radiographic changes in the contralateralasymptomatic knees from knee pain positivesubjects was also investigated.

Occurrence of symptomatic patellofemoral jointosteoarthritis in the study groupThis was estimated using the proportions ofknee pain positive subjects found to have osteo-arthritis together with the data on the occurrenceof knee pain derived from the postal question-naire survey. It provides information aboutsymptomatic disease only.

DisabilityDisability was assessed using the lower limbcomponents of the health assessment question-naire (HAQ).'4 The prevalence of disability insubjects with medial or patellofemoral compart-ment knee osteoarthritis was investigated in acase control manner. Controls were required tobe asymptomatic and have radiographicallynormal knees.

StatisticsThe age and sex distribution of the studysample and knee pain positive subgroup was

investigated using the x2 test. The proportion ofsubjects with each possible pattern of compart-mental disease was determined in the knee painnegative and positive groups stratified by ageand gender. Confidence intervals around theseproportions and around other proportionsreported in this study were derived using themethodology of Gardner and Altman.'5

ResultsSUBJECTSA total of 273 knee pain positive subjects and240 controls attended for radiography. Table 1

presents the detailed breakdown. Comparedwith the study group minor differences were

apparent in the subgroups of men due to over

representation of knee pain positive men in the65-74 year old age group and controls in the75-84 year old group but this did not reachstatistical significance (X2 7-031, degrees of

Table I Number (percentage) of men and women in the study, groups by age

Age tvears) Studv group Kinete painl positive grinup Knee paiii negativevt group

Men Womeni Aflen Women Mn Women

55-64 319 (38) 289 (28) 21 (24) 54 (29) 22 (28) 51 (32)65-74 276 (32) 302 (30) 43 (50) 63 (34) 25 (32) 54 (33)75-84 211 (25) 319 (31) 18 (21) 51 (27) 29 (37) 45 (28)85+ 48 (6) 107 (11) 4 (5) 19 (10) 2 () 12 (7

Total 854 1017 86 187 78 162

845

on July 26, 2020 by guest. Protected by copyright.

http://ard.bmj.com

/A

nn Rheum

Dis: first published as 10.1136/ard.51.7.844 on 1 July 1992. D

ownloaded from

McAlindon, Snow, Cooper, Dieppe

freedom=3, p<0-1; x2 4-965, p<0(1 respec-tively). No differences were found in the age orsex distributions of the subgroups of womencompared with the study group (x2 1-112;0-547 respectively, degrees of freedom=3).One hundred and twenty eight subjects from

the knee pain positive group had unilateralsymptoms. As the asymptomatic knees wereexcluded from the analysis of knee joint osteo-arthritis patterns this generated 418 knees in theknee pain positive and 480 in the knee painnegative sample.

REPRODUCIBILITY OF RADIOGRAPHSTable 2 presents the x values for the designationof compartmental osteoarthritis.

PATTERNS OF KNEE JOINT OSTEOARTHRITISFigure 1 shows the frequency of compartmentalpatterns of knee joint osteoarthritis in thesymptomatic men, symptomatic women, andasymptomatic subgroups respectively. Theanalysis of knees in these samples showed thatfrom seven potential patterns only three arecommon: lone medial compartment; lonepatellofemoral; and medial/patellofemoral over-lap. These are consistent between the samplesand between genders. The results of thisanalysis are summarised in fig 1.Any differences which were apparent occurred

in the knee pain positive group. Among menwith symptomatic knees lone medial compart-ment disease was the most common pattern,significantly exceeding patellofemoral osteo-arthritis overall (21 v 11%, p<0 05). Itsapparent frequency increased with age andsignificantly exceeded the frequency of medialcompartment osteoarthritis found in womenover the age of 65 (p<0 05).

In women with symptomatic knees theconverse applied with lone patellofemoralosteoarthritis being more common (24 v 12%overall; p<005) and tending to increase infrequency with age. Lone medial compartmentdisease was present in 12% of knee joints andwas not influenced by age.The third most common pattern, medial/

patellofemoral disease, had similar occurrencein men and women (7 v 6%, NS) which tendedto increase with age though this did not reachstatistical significance.

Other patterns of knee joint osteoarthritisoccurred relatively rarely and did not differbetween the groups of men and women.The same patterns were observed in the

asymptomatic knee joints but at much lowerfrequencies. The occurrence of medial andpatellofemoral patterns tended to increase withage (p<005) and medial compartment osteo-arthritis was approximately twice as common as

Table 2 Reproducibility of radiographic features

Radiogi,raphic feature x Statistic

Medial compartment osteoarthritis 100Lateral compartment osteoarthritis 0-69Patellofemoral osteoarthritis 0-61

patellotemoral osteoarthritis. These results didnot differ between the subgroups of men andwomen, which have therefore been presented asa single group in fig 1.

KNEE JOINT OSTEOARTHRITIS IN THE STUDYGROUPSOne hundred and forty six knee pain positivesubjects (54%) and 40 asymptomatic subjects(17%) had evidence of knee joint osteoarthritis.The sensitivity and specificity of knee pain for

Men: knee pain positive

Women: knee pain positive

Men and women: knee pain negative

Figure 1 Frequency ofcompartmental patterns ofkneejoint osteoarthritis in the symptomatic men and women andthe asvmptomatic subgroups. PFJ -patellofemoral joint.

846

on July 26, 2020 by guest. Protected by copyright.

http://ard.bmj.com

/A

nn Rheum

Dis: first published as 10.1136/ard.51.7.844 on 1 July 1992. D

ownloaded from

Importance ofthe patellofemoral joint in knee osteoarthritis

radiographic knee joint osteoarthritis were 67and 70% respectively.The proportions of subjects with radio-

graphically detected kneeosteoarthritis increasedwith age in all subgroups; the occurrence of allpatterns and of lone patellofemoral osteoarthritiswas significantly greater in the knee painpositive group (p<005) (tables 3 and 4).

In knee pain positive subjects with knee jointosteoarthritis approximately halfofthe subgroupof men and three quarters of the subgroup ofwomen had disease in both knees (see table 5).

Table 3 Percentages of subjects with knee joint osteoarthritis (all patterns), lonepatellofemoral osteoarthritis, and lone medial compartment knee osteoarthritis among the studysamples. Men and women in the knee pain negative sample have been amalgamated due tosmall numbers. 95% confidence intervals are given in parentheses

Patterns of knee Knee pain positive Knee pain negativejoint osteoarthritis

Men Women Men Women

All 48 (38 to 59) 56 (48 to 63) 15 (8 to 25) 17 (11 to 23)Patellofemoral 12 (5 to 20) 26 (20 to 33) 5 (2 to 8) 5 (2 to 8)Medial 23 (15 to 34) 14 (9 to 20) 9 (6 to 11) 9 (6 to 11)

Table 4 Proportions of subjects with knee joint osteoarthritis, lone medial, and lonepatellofemoral patterns, in the knee pain positive subset according to age and sex.95% confidence intervals are given in parentheses

Age (vears) All patterns Medial Patello/emoral

Men55-64 24 (8-2 to 47-2) 10 (1-7 to 27-1) 14 (4 0 to 32-9)65-74 53 (37 7 to 88 8) 28 (17-0 to 41 3) 12 (5 0 to 22 9)75+ 64 (40 7 to 82-8) 27 (12-6 to 33-6) 9 (1 6 to 25-9)

Women55-64 39 (25-9 to 53-1) 19 (10-4 to 294) 17 (9 0 to 27 3)65-74 59 (45-6 to 71-0) 14 (7-7 to 23-6) 30 (20-7 to 41-0)75-84 59 (44-2 to 72-4) 10 (3-9 to 19-5) 31 (20 8 to 43-7)85+ 84 (60-4 to %96) 16 (4 4 to 35-9) 26 (1 1-0 to 47-6)

Table 5 Proportions of subjects with bilateral disease fromthe subsample with symptomatic knee joint osteoarthritis.95% confidence intervals are given in parentheses

Age (years) Men Women

55-6465-7475+

', 20co

0~

0

30

CD

2) 200~

20 (0-5 to 71-6)52 (30-6 to 73-2)64 (35-1 to 87 2)

76 (52 8 to 91-8)70 (53-0 to 84- 1)74 (58-9 to 85-7)

A Men

75+

Women

_ PFJ OA1 Knee OA

_

10 _

0

Figure 2joint.

11

55- 64 65-74 75-84

Age (years)

Prezvalence ofkneejoint osteoarthritis in the studv group. 1' 7-J patello/fenwral

Table 6 Proportions of subjects with medial andpatellofemoral osteoarthritis (OA) reporting disabilitycompared with controls. 'Any disability' is equivalent to aHealth Assessment Questionnaire score >0, 'severe'disability :2. 95% confidence intervals are given inparentheses

Subject group l'ercentage with Percentage withanv disabilitv severe disabilitv

Medial compartment OAControls 18 (8-2 to 31-8) 5 (1-0 to 13-3)Patients 46 (33 4 to 59 1) 13 (5-6 to 32 5)Ratio 2-6 2-6

Patellofemoral OAControls 25 (14-4 to 384) 4 (04 to 12-3)Patients 64 (50 4 to 76-6) 16 (7-6 to 28-3)Ratio 2 6 4-5

Further evidence of the bilateral nature ofthis disease was provided by the contralateralknee joints from 128 subjects with unilateralknee pain. Over 50% of these had radiograph-ically detected osteoarthritis, significantly more(p<005) than was found in the asymptomaticgroup. Furthermore all but 12% of subjectswith knee pain osteoarthritis could be assignedto a compartmental pattern by the presence ofeither unilateral or symmetrical disease.

PREVALENCE OF KNEE JOINT OSTEOARTHRITIS INTHE COMMUNITYThe estimated prevalences of symptomaticmedial, patellofemoral, and medial/patello-femoral knee joint osteoarthritis, extrapolatedfrom the knee pain positive study sample andfrom knowledge of the occurrence of knee painin various age ranges in the study population,are presented in fig 2A and B.

DISABILITY RATES AND RADIOGRAPHIC PATTERNSAge and sex matched controls were found for 63subjects with medial and 56 with patellofemoralcompartment knee joint osteoarthritis. Thegroups were mutually exclusive and the numbersof subjects with other patterns were insufficientfor analysis. Subjects with either medial orpatellofemoral compartment knee osteoarthritishad significantly (p<0-01) higher occurrencesof reported disability (table 6). The prevalenceof disability in subjects with medial compart-ment disease was 2-6 times that of their controlsubjects. This ratio remained constant whenhigher levels of disability (HAQ score greaterthan one or two) were considered. For patello-femoral compartment osteoarthritis the ratiowas 3-1 overall and increased for these higherlevels of disability.

DiscussionWe believe that this is the first study to showthe prevalence of patellofemoral osteoarthritisin the community. The condition is commonand associated with disability. As a cause ofsevere disability it may be even more importantthan medial compartment knee osteoarthritis.The most important conclusion of this paper isthat epidemiological and clinical studies of kneeosteoarthritis can no longer be performed

847

on July 26, 2020 by guest. Protected by copyright.

http://ard.bmj.com

/A

nn Rheum

Dis: first published as 10.1136/ard.51.7.844 on 1 July 1992. D

ownloaded from

McAlindon, Snow, Cooper, Dieppe

without consideration of the patellotemoralcompartment.One of the main difficulties encountered in

this study related to the development of aradiographic scoring system. Previous work inthis field' 3 4 10 has relied on a system adaptedfrom the original standard knee radiographs ofKellgren and Lawrence.'3 These, however, donot include the patellofemoral compartmentand investigations of the relative reproducibilityof the radiographic features of osteoarthritis indifferent compartments of the knee jointsuggest increased variability in scoring patello-femoral osteoarthritis.'6The radiographs in this study were therefore

scored by the same observer using an 'on-off'measure as opposed to a severity scale. Thereproducibility of this score in each of the threecompartments was re-evaluated using the xstatistic. The results were favourable using thismethod, although the x statistic for patello-femoral osteoarthritis compartment was lowerthan that for medial or lateral compartmentosteoarthritis. In contrast with the tibiofemoraljoint little attention has been paid to thedevelopment of a scoring system for patello-femoral osteoarthritis, and this therefore is at anearlier stage of evolution. As no better systemcurrently exists, our 'on-off' score was consideredadequate for use in this study. For futureresearch further work is needed to optimise asystem with which to grade the severity ofpatellofemoral osteoarthritis.The inclusion of patellofemoral imaging in

this survey appears to improve concordancebetween knee pain and radiographic changes.Claessens et al showed a sensitivity, specificity,and predictive value of knee pain againstradiographic osteoarthritis of 24, 90, and 36%respectively'0 (see table 7). Our results showimprovements in the sensitivity and predictivevalue, probably as a result of detecting subjectswith predominant patellofemoral osteoarthritiswhich would have been missed using antero-posterior radiographs alone.

Specificity is decreased, however, whichsuggests that other differences are operativebetween the scoring systems. For example, it islikely that the threshold for the designation oftibiofemoral osteoarthritis was higher in thisstudy than in the work of Claessens et al 'o andthis could account for a reduction in specificityby reducing the proportion of true negativecases.The next problem related to the large number

of potential patterns of knee joint osteoarthritisper subject. To simplify the process of patternanalysis within each knee joint, this part of thestudy was conducted at the levels of kneesrather than subjects. This manoeuvre was helpfulin indicating the most common compartmentalpredilection of osteoarthritis within the kneejoint, but as the disease cannot automatically be

Table 7 Knee pain as a predictor of knee osteoarthritis

I'arameter McAlindon etila" Claessens et al "'

Sensitivitv (%/>) 67-3 24Specificity ("i,) 70-1 90Predictive value (O) 47-8 36

assumed to be symmetrical it is important to beclear whether the data relate to proportions ofknees or proportions of subjects. It showedthat, despite a large number of potentialcompartmental patterns, medial and patello-femoral patterns predominate. They appear tobe relatively exclusive but with a small potentialfor overlap. Other patterns seem rare.Within the pooled subgroup of painful knees

the occurrence of medial compartment kneeosteoarthritis appears to increase with age inmen whereas patellofemoral disease increases inwomen. As these figures relate to percentages ofknees it cannot necessarily be inferred that thepercentages of subjects with these patterns alsoincrease. For example, it is possible that theincrease in medial compartment disease in menresults from increased bilaterality with increasingage rather than an increase in the number ofsubjects with the disease. The rates of bilateraldisease seen in knee pain positive men supportsthis (table 4).A broader picture of the nature of knee joint

osteoarthritis can be achieved by looking at theknee pattern data together with the informationabout bilaterality and the proportions of subjectsfound to have osteoarthritis. In men thesesuggest a trend of increasing bilaterality withage in what is predominantly medial compart-ment disease. The increase in occurrence ofoverall knee osteoarthritis appears to beaccountable to mixed patterns of expression asthe rates of medial, medial/patellofemoral, andpatellofemoral patterns do not alter in men afterthe age of 65. In women neither the bilateralityrates nor the occurrence of medial or patello-femoral disease increases after 65 years. Thissuggests that the increase in overall knee jointosteoarthritis is attributable to a genuineincrease in the numbers of subjects with medial/patellofemoral or mixed patterns of expression.These patterns may either reflect different

disease processes or a similar predispositionwith various risks or environmental factorsresulting in different patterns of expression. Itis tempting to speculate that the increase in themedial/patellofemoral pattern in women is dueto patellar problems developing in subjects withestablished medial compartment disease as aresult of tracking abnormalities. If so, this couldcontribute to the apparent plateau in theoccurrence of lone medial disease in women. Itis, however, difficult to address cause andeffect relations in a cross sectional survey suchas this.An attempt to estimate the prevalence of

symptomatic knee joint osteoarthritis in thestudy group was made based on the occurrencefound in the knee pain positive subgroup andthe known knee pain rates derived from thepostal questionnaire survey. There are anumber of problems with this. Firstly, thefigures refer to symptomatic disease only, andas such are inevitably an underestimate of theoverall prevalence. Also it is possible that kneeosteoarthritis is associated with comorbidity.The issue of coexistent disease was not addressedin this work, but if present might be a sourceof bias at the level of response to the postalquestionnaire and with respect to attendance for

848

on July 26, 2020 by guest. Protected by copyright.

http://ard.bmj.com

/A

nn Rheum

Dis: first published as 10.1136/ard.51.7.844 on 1 July 1992. D

ownloaded from

Importance ofthe patellofemoraljoint in knee osteoarthritis

assessment. Such bias might in part explain theunusual finding of an apparent decrease in theprevalence of knee joint osteoarthritis after theage of 70 years in men. Alternative explanationsare that a cohort effect is operative (though asimilar decrease in prevalence might have beenexpected in women) or the influence of selectivemortality for which there is some evidence. 17 18These factors, together with the possibility thata higher threshold for the designation of kneejoint osteoarthritis was adopted in this study,may account for the lower estimated prevalencefound here than in previous surveys. 14

Finally both medial and patellofemoral osteo-arthritis are strongly associated with disability.Higher levels of disability (as judged by HAQscores of greater or equal to one or two) seemmore common in subjects with patellofemoraldisease, a plausible result given the closeanatomical and functional relation of the patellato the quadriceps apparatus.

In summary, patellofemoral disease is acommon manifestation of knee joint osteo-arthritis. It is often bilateral, is significantlyassociated with pain and disability, and can nolonger be disregarded in studies of knee jointosteoarthritis.

We thank Dr I Watt, Department of Radiology, Bristol RoyalInfirmary for his advice and help with this study, Dr T Paine andpartners, Whiteladies Health Centre for their collaboration, andfinally their patients, without whose willing cooperation thiswork would not have been possible. This project was funded bythe Arthritis and Rheumatism Council.

1 Van Saase J L C M, Van Romunde L K J, Cats A,Vandenbroucke J P, Valkenburg H A. Epidemiology ofosteoarthritis: Zoetermeer survey. Ann Rheum Dis 1989;48: 271-80.

2 Wright V. Osteoarthritis. BMJ 1989; 299: 1476-7.3 Lawrence J S, Bremner J M, Bier F. Osteoarthrosis:

prevalence in the population and relationship betweensymptoms and x-ray changes. Ann Rheum Dis 1966; 25:1-23.

4 Felson D T, Naimark A, Anderson J, Kazis L, et al. Theprevalence of knee osteoarthritis in the elderly. ArthritisRheum 1987; 30: 914-8.

5 Hungerford D S, Barry M. Biomechanics of the patello-femoral ioint. Clin Orthop Rel Res 1979; 144: 9-15.

6 Meachim G. Cartilage lesions on the patella. In: Pickett J C,Radin E L, eds. Chondromalacta of the patella. Baltimore:Williams & Wilkins, 1983.

7 Cascells W. Chondromalacia patellae and its relationship toanterior femoral pain. In: Pickett J C, Radin E L, eds.Chondromalacia of the patella Baltimore: Williams &Wilkins, 1983.

8 Meachim G, Pedley R B. Implications of a sex difference inosteoarthrosis. Ann Rheum Dis 1980; 39: 199.

9 Ahlbach S. Osteoarthritis of the knee: a radiographicinvestigation. Acta Radiologica Suppl 1968; 277: 1-61.

10 Claessens A A M C, Schouten J S A G, Van den OuwelandF A, Valkenburg H A. Do clinical findings correlate withosteoarthritis of the knee? Ann Rheum Dis 1990; 49: 771-4.

11 McAlindon T E, Cooper C, Dieppe P. Knee pain anddisability in the community. Br J Rheumatol 1990; 29(suppl 2): 87.

12 National Center for Health Statistics. Basic data on arthritis oJthe hip, knee and sacro-itiac joints in adults ages 25-74, UnitedStates, 1971-1975. Series 11, No 213, 1979.

13 Kellgren J H, Lawrence J S. Radiological assessment ofosteoarthrosis. Ann Rheum Dis 1957; 16: 494-501.

14 Fries J F, Spitz P, Young D Y. The dimensions of healthoutcomes: the Health Assessment Questionnaire, disabilityand pain scales. J Rheumatol 1982; 9: 789-93.

15 Gardner M J, Altman D G, eds. Calculating confidenceintervals for proportions and their differences. Statisticswith confidence. London: BMJ, 1989: 28-33.

16 Cooper C, Cushnaghan J, Kirwan J R, et al. Radiographicassessment of the knee joint in osteoarthritis. Ann RheumDts. 1992; 51: 80-2.

17 Bergstrom G, Bjelle A, Sundh V, Svanborg A. Joint disordersat ages 70, 75 and 79 years-a cross sectional comparison.BrJ Rheumatol 1986; 25: 33341.

18 Hochberg M C, Lawrence R C, Everett D F, Cornoni-Huntley J. Epidemiologic associations of pain in osteo-arthritis of the knee. Semin Arthritis Rheum 1989; 18: (supp2): 4-9.

849

on July 26, 2020 by guest. Protected by copyright.

http://ard.bmj.com

/A

nn Rheum

Dis: first published as 10.1136/ard.51.7.844 on 1 July 1992. D

ownloaded from