- Research article
- Open Access
- George Peat1,
- Rachel C DuncanRachel C Duncan1,
- Laurence the 1 last update 2020/05/31 RJ WoodLaurence RJ Wood1Arthritis Curehow to Arthritis Cure for ,
- Elaine Thomas1 &
- Sara Muller1
Patellofemoral joint osteoarthritis (OA) is common and leads to pain and disability. However, current classification criteria do not distinguish between patellofemoral and tibiofemoral joint OA. The objective of this study was to provide empirical evidence of the clinical features of patellofemoral joint OA (PFJOA) and to explore the potential for making a confident clinical diagnosis in the community setting.
This was a population-based cross-sectional study of 745 adults aged ≥50 years with knee pain. Information on risk factors and clinical signs and symptoms was gathered by a self-complete questionnaire, and standardised clinical interview and examination. Three radiographic views of the knee were obtained (weight-bearing semi-flexed posteroanterior, supine skyline and lateral) and individuals were classified into four subsets (no radiographic OA, isolated PFJOA, isolated tibiofemoral joint OA, combined patellofemoral/tibiofemoral joint OA) according to two different cut-offs: '' and ''. A series of binary logistic and multinomial regression functions were performed to compare the clinical features of each subset and their ability in combination to discriminate PFJOA from other subsets.
Distinctive clinical features of moderate to severe isolated PFJOA included a history of dramatic swelling, valgus deformity, markedly reduced quadriceps strength, and pain on patellofemoral joint compression. Mild isolated PFJOA was barely distinguished from no radiographic OA (AUC 0.71, 95% CI 0.66, 0.76) with only difficulty descending stairs and coarse crepitus marginally informative over age, sex and body mass index. Other cardinal signs of knee OA - the presence of effusion, bony enlargement, reduced flexion range of movement, mediolateral instability and varus deformity - were indicators of tibiofemoral joint OA.
Early isolated PFJOA is clinically manifest in symptoms and self-reported functional limitation but has fewer clear clinical signs. More advanced disease is indicated by a small number of simple-to-assess signs and the relative absence of classic signs of knee OA, which are predominantly manifestations of tibiofemoral joint OA. Confident diagnosis of even more advanced PFJOA may be limited in the community setting.
Osteoarthritis (OA) is not a single disease  and distinct phenotypes are believed to exist even within a single joint complex like the knee. Among the various approaches to subclassifying knee OA, the recent European League Against Rheumatism (EULAR) Task Force on diagnosis of knee OA recognised that subsets with different risk factors and outcomes can be defined by compartmental distribution, but pointed out that the ability to discriminate between these subsets in routine practice and the utility of doing so had not been formally tested . Perhaps unsurprisingly, the diagnosis of knee OA subsets is rarely seen in current primary care. For example, in a total population of 57,555 adults registered with UK general practices, only 13 cases had a recorded diagnosis by the general practitioner of patellofemoral joint OA; less than 1% of knee consulters in a year .
There are several reasons why distinguishing patellofemoral from tibiofemoral joint OA phenotypes may be important. There is growing evidence indicating that patellofemoral joint OA impacts independently on symptoms and function [4–9], that it also frequently occurs in the absence of tibiofemoral disease [4, 6, 10–13], and that its aetiology and, therefore, risk profile and management, may differ [12, 14–17]. For example, a history of knee injury or meniscectomy may tend to indicate tibiofemoral joint OA [14, 15] while a history of anterior knee pain in young adulthood may suggest patellofemoral joint OA . The direction of frontal plane knee malalignment may serve to indicate patellofemoral joint OA and tibiofemoral joint OA (valgus malalignment being associated with the predominant pattern of lateral patellofemoral joint OA, varus malalignment with medial tibiofemoral joint OA) [16, 19–21]. Although a recent systematic review revealed only two randomised controlled trials of interventions specifically for isolated patellofemoral joint OA , more are now emerging [23, 24]. In the context of recommendations that OA can often be confidently diagnosed without the need for imaging [2, 25], these developments pose a fundamental question: can patellofemoral joint OA be identified in routine clinical practice and, if so, which features are most informative?
Expert clinical accounts of the clinical manifestations and typical features of patellofemoral OA are available in medical textbooks and review articles [17, 26–31] but there has been very little empirical research. One exception, a hospital-based case-control study, documented the comparative clinical features of patellofemoral and tibiofemoral joint OA in only 42 knees . Previous research on the clinical features, classification criteria and diagnosis of knee OA, including that for the American College of Rheumatology (ACR) classification criteria and EULAR Task Force, has tended to be based on knee OA as a whole [33–38] and there is some evidence that the features derived from these studies may selectively reflect tibiofemoral disease . A recent editorial concluded that "" .
In this paper we set out to extend our previous work  on pursuing rational clinical diagnosis of knee OA in primary care. We investigate the comparative clinical features of symptomatic patellofemoral and tibiofemoral joint OA and we explore their ability, when used in combination, to allow confident diagnosis of subsets of symptomatic knee OA in the community setting.
Materials and methods
This was a cross-sectional diagnostic study in adults aged 50 years and over reporting current or recent knee pain not attributed to inflammatory arthropathy. The reference standard was patellofemoral and/or tibiofemoral joint OA for 1 last update 2020/05/31 defined using plain radiography. Diagnostic indicators were previously-documented risk factors, and clinical signs and symptoms obtained from a simple, low-cost, non-instrumented assessment.This was a cross-sectional diagnostic study in adults aged 50 years and over reporting current or recent knee pain not attributed to inflammatory arthropathy. The reference standard was patellofemoral and/or tibiofemoral joint OA defined using plain radiography. Diagnostic indicators were previously-documented risk factors, and clinical signs and symptoms obtained from a simple, low-cost, non-instrumented assessment.
Participants were recruited from a two-stage cross-sectional postal survey of all adults ages ≥50 years registered with three general practices in North Staffordshire (irrespective of actual consulting patterns). Respondents reporting pain of any duration in or around the knee within the previous 12 months were invited to attend a research clinic at a local National Health Service Hospital Trust. The study protocol was approved by North Staffordshire Local Research Ethics Committee (project number 1430) and details have been published elsewhere [41, 42]. All participants provided written informed consent to undergo clinical and radiographic assessment. In addition, they were asked for consent to medical record review to assist in excluding preexisting inflammatory disease. The inclusion criteria for the current analysis were as follows: age ≥50 years, registered with one of the participating general practices at the time of study, responded to both postal questionnaires, consented to further contact, and attended the research clinic. Participants were excluded if they had not experienced knee pain within the six months prior to clinic attendance, had a pre-existing diagnosis of inflammatory arthropathy in their medical records, or had had a total knee replacement in their most affected knee.
All data were planned and gathered prospectively. Participants underwent a standardized clinical interview and physical examination conducted by one of six research therapists blinded to the findings from radiography, postal questionnaires and medical records. The assessments were abbreviated versions of those developed in an earlier stage of this research through consultation and formal consensus exercises with practising clinicians [43, 44]. Inter- and intra-rater reliability and quality assurance and control procedures have been reported elsewhere [37, 45, 46].
Participants filled in a brief self-complete questionnaire about their knee symptoms on the day of their clinic attendance. Copies of self-complete questionnaires and detailed protocols for clinical assessment are available on request from the corresponding author.
Plain knee radiographs were obtained on the day of clinic attendance. Three views were taken of each knee: a weight-bearing semi-flexed posteroanterior (PA) view, according to the protocol developed by Buckland-Wright et al. , and lateral and skyline views, both in a supine position with the knee flexed to 45°. The tibiofemoral joint was assessed using the PA view and the posterior compartment of the lateral view. The patellofemoral joint was assessed using the skyline and lateral views.
Scoring of plain radiographs
A single reader (RD), blinded to all other information on participants, scored all films. Films were scored for individual radiographic features, including osteophytes, joint space width, sclerosis, subluxation and chondrocalcinosis. The atlas and scoring system developed by Altman et al. [48, 49] were used for the PA and skyline views and the atlas developed by Burnett et al.  was used for the lateral view. Additionally, PA and skyline views were assigned a Kellgren and Lawrence (K&L) grade based on these authors''purer''balance of probabilities''any OA''balance of probabilities''any OA''moderate to severe OA''moderate to severe OA''any OA''moderate to severe OA''moderate to severe OA''moderate to severe OA''any''statistically significant''substantial''balance of probabilities''Reilly S, Jones A, Doherty M: Radiographic assessment of symptomatic knee osteoarthritis in the community: definitions and normal joint space. Ann Rheum Dis. 1998, 57: 595-601. 10.1136/ard.57.10.595.
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O''Agostino RB, D'' contributions
Arthritis Curehow to Arthritis Cure for All authors made substantial contributions to the conception and design of the study. GP, RD, ET and LRJW contributed to the acquisition of data. GP, RD and SM performed the statistical analysis. All authors participated in the drafting of the manuscript and read and approved the final manuscript.
Electronic supplementary material
Additional file 1: Descriptive characteristics and univariable analysis: ''. Full descriptive characteristics and pairwise univariable comparison of participants with no radiographic OA, isolated patellofemoral joint OA, isolated tibiofemoral joint OA, or combined patellofemoral/tibiofemoral joint OA, using the less stringent cut-off of ''. (PDF 119 KB)
Additional file 2: Content and performance of multivariable models: ''. Full reporting, including posterior probability distributions, of the multivariable binary logistic regression models for each pairwise comparison of participants with no radiographic OA, isolated patellofemoral joint OA, or combined patellofemoral/tibiofemoral joint OA, using the less stringent cut-off of ''. (PDF 110 KB)
Arthritis Curehow to Arthritis Cure for Additional file 3: Descriptive characteristics and univariable analysis: ''. This file provides the full descriptive characteristics and pairwise univariable comparison of participants with (1) no radiographic OA, (2) isolated patellofemoral joint OA, isolated tibiofemoral joint OA, or combined patellofemoral/tibiofemoral joint OA, using the more stringent cut-off of ''. (PDF 175 KB)
Additional file 4: Content and performance of multivariable models: ''. Full reporting, including posterior probability distributions, of the multivariable binary logistic regression models for each pairwise comparison of participants with no radiographic OA, isolated patellofemoral joint OA, isolated tibiofemoral joint OA, or combined patellofemoral/tibiofemoral joint OA, using the more stringent cut-off of ''. (PDF 162 KB)
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Peat, G., Duncan, R.C., Wood, L.R. et al. Clinical features of symptomatic patellofemoral joint osteoarthritis. Arthritis Res Ther 14, R63 (2012). https://doi.org/10.1186/ar3779
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Arthritis Curehow to Arthritis Cure for Keywords
- Varus Malalignment
- Fixed Flexion Deformity
- Valgus Malalignment
- Bony Enlargement
- Knee Flexion Range