Radiographic change is common in new presenters in primary care with hip pain

F. Birrell, P. Croft1, C. Cooper2, G. Hosie3, G. J. Macfarlane4 and A. Silman on behalf of the PCR Hip Study Group

ARC Epidemiology Unit, University of Manchester, Manchester M13 9PT,
1 Centre for Primary Care Sciences, University of Keele, Stoke-on-Trent ST4 7QB,
2 MRC Environmental Epidemiology Unit, University of Southampton, Southampton SO9 4XY,
3 Great Western Health Centre, Glasgow G13 2SW and
4 Unit of Chronic Disease Epidemiology, University of Manchester, Manchester M13 9PT, UK


    Abstract
 Top
 Abstract
 Introduction
 Subjects and methods
 Results
 Discussion
 References
 
Objective. To determine the prevalence of radiographic osteoarthritis in subjects with hip pain newly presenting to primary care.

Methods. The study was cross-sectional in design, set in 35 general practices across the UK. It included 195 men and women aged 40 yr and over (median 63 yr) presenting with a new episode of hip pain. Hip radiographs were scored for minimum joint space (MJS) and overall—Croft's modification of the Kellgren and Lawrence (Croft)—grade of osteoarthritis.

Results. In all, definite evidence of radiographic change in the painful joint was common: Croft grade >= 2 in 44%, >= 3 in 34%. MJS of 2.5 mm or less was seen in 30% of whom half were below 1.5 mm. There were no significant gender differences in radiographic severity.

Conclusions. Radiographic change is common in patients newly presenting with hip pain and many already have advanced disease.

KEY WORDS: Radiographic change, Hip pain, Osteoarthritis, Primary care.


    Introduction
 Top
 Abstract
 Introduction
 Subjects and methods
 Results
 Discussion
 References
 
Hip osteoarthritis (OA) is not the most common form of OA [1], but represents an important subtype for three reasons. First, the hip is often the sole joint involved, suggesting it is a separate disease entity [2]. Second, the hip is crucial to locomotion and therefore to independent function. Finally, effective treatment is currently available, in the form of total hip arthroplasty, for end-stage disease, with an estimated 46 000 total hip arthroplasties performed in the UK in 1996 [3].

Pain is a common presentation of hip OA but, by the time patients with hip pain attend a hospital, their disease is often advanced [4]. It is unknown how common X-ray evidence of OA is earlier in the natural history of this disease, in particular at the time of first presentation for health care. The aim of this study was to enrol subjects presenting with a standardized definition of hip pain to primary care and to determine the prevalence of radiographic OA in this group.


    Subjects and methods
 Top
 Abstract
 Introduction
 Subjects and methods
 Results
 Discussion
 References
 
Design
This study was part of a prospective multicentre outcome study of patients presenting with new episodes of hip pain in primary care. General practices from all over the UK were used both to ensure the generalizability of the study results and to maximize the recruitment rate. General practitioners (GPs) enrolled consecutive new attenders aged 40 yr or older with hip pain.

GPs
We recruited 36 GPs from 35 practices. All were members of the Primary Care Rheumatology Society and have a particular interest in musculoskeletal pain. This approach was designed to maximize recruitment by motivated GPs. The practices represented a broad mix of urban, suburban and rural areas and had between two and nine partners. Ethical permission was secured locally for each practice, prior to study commencement.

Definition of hip pain episode
As no standardized definition for hip pain exists, a working case definition was derived by a consensus group of the study co-ordinators and the participant GPs and validated by pilot testing. This was defined as pain within a pre-shaded area on a body manikin (Fig. 1Go) which on GP clinical assessment was considered as not arising from structures outside the hip (e.g. low back, trochanteric bursa). For the purposes of this study an arbitrary definition of a new episode was adopted: a patient presenting with pain in the hip who had not attended their GP with the same problem in the previous 12 months.



View larger version (24K):
[in this window]
[in a new window]
 
FIG. 1. Standardized pain drawing for hip pain. A, Iliac crest; B, ischial tuberosity; C, anterior superior iliac spine; D, pubic tubercle; E, 1/3 way down thigh.

 

Pain history
All eligible patients completed a simple questionnaire covering pain severity [using a numerical rating scale (1–10)]. Duration of pain was based on the interval since the start of the current episode.

Radiographs
An anterioposterior supine pelvic radiograph was requested on each subject, with a set of standard instructions given to recruiting hospitals. As there is no consensus definition for radiographic OA [57], X-rays were graded for both (a) Croft's modification of the Kellgren and Lawrence (Croft) grade: 0, no OA; 1, osteophytosis alone; 2, joint space narrowing alone; 3, two; and 4, three, separate individual radiographic features; 5, as 4, but also secondary collapse of the femoral head; and (b) minimal joint space (MJS). Gradings were made by two independent observers, blinded to the clinical status of the subject, with adjudication of any discrepancies made by a third observer. The frequency of radiographic OA was summarized by age and sex, with 95% confidence intervals. Four thresholds for OA were analysed: Croft grade (cut-offs of >=2 and >=3 and MJS, cut-offs of <2.5 mm and <1.5 mm).

Analysis
The percentage of patients with radiographic OA using the four cut-offs was calculated with 95% confidence intervals and stratified by gender and age (above/below median). Pain duration was stratified into the categories <3 months, 3–12 months and >12 months. To assess the possibility of selection bias, subgroup analyses were undertaken comparing the data from patients recruited from low-recruiting practices (<8 subjects per GP), with those from higher-recruiting practices.


    Results
 Top
 Abstract
 Introduction
 Subjects and methods
 Results
 Discussion
 References
 
One hundred and ninety-five patients (63 males, 132 females) with a median age of 63 yr [interquartile range (IQR) 54–71 yr] were recruited. In all, 53% had pain affecting the right hip alone, 45% the left hip alone and only 3% had bilateral pain at presentation. The median pain severity was 5 (IQR 3–7). Hip pain duration was less than 3 months in 30%, between 3 and 12 months in 42% and longer than 12 months in 28%. In all, 38% reported a prior episode of hip pain, although none had attended for hip pain in the 12 months prior to recruitment.

Frequency of radiographic OA
Radiographs were available on all 195 subjects (100%). The prevalence of hip OA in the affected hip of new hip pain attenders is presented in Table 1Go. Nearly half had definite OA (Croft >=2) with 17% having advanced disease, defined by a Croft score of 4 or greater. In all, 30% had a MJS of 2.5 mm or less, with 14% having a MJS of 1.5 mm or less. There were no significant sex differences in the radiographic severity of the cases recruited and thus subsequent analyses pooled data across gender. Not surprisingly, those above the median age of 63 yr were more likely to have joint space narrowing by both cut-offs, although one in eight below that age had severe disease as judged by a Croft grade of 4 or 5.


View this table:
[in this window]
[in a new window]
 
TABLE 1. Frequency of OA by age and sex

 
Table 2Go shows the frequency of OA by pain duration. Those reporting longer pain duration at presentation had a trend towards higher radiographic grades and a significant trend to severe joint space narrowing.


View this table:
[in this window]
[in a new window]
 
TABLE 2. Frequency of OA by pain duration

 
A comparison of the radiographic findings, however, between patients from high- (n = 78) and low- (n = 117) recruiting GPs did suggest evidence of selection bias with twice the frequency in the latter group with the most severe grades of OA (MJS <= 1.5 mm: 8 vs 19%, P<0.05; Croft grade >=3: 26 vs 40%, P<0.05).


    Discussion
 Top
 Abstract
 Introduction
 Subjects and methods
 Results
 Discussion
 References
 
This study has found a high frequency of radiographic change in those newly presenting with hip pain even at first presentation to primary care. In this group, the clinical decision had been made that the pain had arisen from the hip and not from the spine or other periarticular structures. Thus, it is reasonable to conclude that OA is the predominant cause of isolated hip pain presenting to primary care and is often advanced at first presentation, particularly in older individuals.

More severe OA was found with a longer duration of hip pain. This demonstrates that individuals have different thresholds for attendance at their GP. It is unknown whether this results from an individual's pain severity, periodicity, or the attendant disability. It is clear that many individuals present even to primary care with advanced disease.

Primary care-based studies are valuable for two main reasons. First, the cases are unselected for severity in comparison with hospital series, where referral of the more severe cases leads to referral bias. Second, the consultation is closer in time to the episode of interest, allowing the examination of early disease. The current study was a multicentre study to enhance the external validity of the study. Such an approach, however, would be adversely affected by differences in patient attendance, GP assessment and study compliance. Such differences were minimized by using a standardized pragmatic definition of a hip pain episode and a pain drawing, aiming to maximize reliability across several centres and over time. A comparison of the radiographic findings, however, between patients from high- and low-recruiting GPs did suggest evidence of selection. Although some of this difference might reflect variation in GP behaviour, there may be differences in patient attendance. We are currently undertaking a community-based survey to ascertain the extent of this.

Second, the evaluation of the radiographs is an important aspect of our study. Grading was performed in random order, blinded to the side of pain. Reliability of grading was assessed prior to reading the study films, showing good intra-observer (dichotomized kappa statistic 0.7–0.9) and interobserver (dichotomized kappa statistic 0.5–0.8) reliability. This was further enhanced by using independent adjudication of discrepant gradings. We used the supine approach to assess MJS, which is at least as reliable as weight bearing, and has the benefit of better image quality [8, 9].

The lack of consensus definitions for clinical or radiographic OA [7, 10] makes comparison with previous studies difficult. In particular, differing severity and duration have been used, which may explain all or part of the differences observed between populations.

The major unanswered question is how frequent is radiographic change in asymptomatic subjects, i.e. how far do the figures presented in this study reflect an association with hip pain. A recent review of population-based radiographic surveys in Europe [11] showed the prevalence of radiographic OA in middle-aged and elderly adults to range from 2 to 6%, depending on age, gender and radiographic cut-off. These proportions are all substantially lower than those found in the current study population of hip pain attenders.

In summary, the most important clinical finding is that in these new attenders, with a median age of 63 yr, there was an important proportion of subjects who radiographically already had end-stage disease which in part was related to the duration of symptoms. Like studies of hospital attenders, it is difficult to extrapolate from one study. It does seem reasonable, however, to conclude that careful clinical and radiographic evaluation is appropriate for all new primary care attenders with a likely high pick-up rate for significant disease.


    Acknowledgments
 
The co-operation of the patients and recruiting GPs from the Primary Care Rheumatology Society is much appreciated. The PCR Hip Study Group comprises: Dr M. Allen, Dr F. Birrell, Dr T. Birnie, Dr S. Bradbury, Dr D. Child, Dr A. S. Chopra, Professor C. Cooper, Professor P. Croft, Dr T. Davies, Dr B. Dennis, Dr E. Dickson, Dr J. Dickson, Dr I. L. Foster, Dr R. Gadsby, Dr I. Gilchrist, Dr C. Goldwyn, Dr M. W. Hall, Dr A. Harris, Dr B. M. Heap, Dr S. G. Hill, Dr M. J. L. Hopkins, Dr G. Hosie, Dr D. Jobling, Dr M. John, Dr F. Kavalier, Dr P. Lindsay, Professor G. Macfarlane, Dr J. Machen, Dr I. Robertson, Dr J. D. A. Robertson, Dr W. Rumfeld, Dr R. W. Shaw, Professor A. Silman, Dr R. Simpson, Dr L. K. R. Smith, Dr T. G. Stammers, Dr M. Stevenson, Dr A. Vaghmaria, Dr H. Watkin, Dr A. Watson, Dr D. Wheeler, Dr J. Wilcock and Dr M. Young. We are also grateful to L. Nahit, L. Robinson and C. Afzal for their unstinting efforts in recruitment and follow-up of the study patients. Funding was provided by Arthritis Research Campaign core funding. F. N. B. is an ARC Clinical Epidemiology Training Fellow. There were no conflicts of interest.


    Notes
 
Correspondence to: F. Birrell, ARC Epidemiology Unit, University of Manchester, Stopford Building, Oxford Road, Manchester M13 9PT, UK. Back


    References
 Top
 Abstract
 Introduction
 Subjects and methods
 Results
 Discussion
 References
 

  1. Cooper C. Epidemiology and natural history of osteoarthritis. In: Klippel JH, Dieppe PA, eds. Rheumatology, 2nd ed. London: Mosby, 1998: Chapter 8.02.
  2. Solomon L. Geographical and anatomical patterns of osteoarthritis. Br J Rheumatol1984;23:177–80.[ISI][Medline]
  3. Birrell F, Johnell O, Silman A. Projecting the need for hip replacement over the next three decades: influence of changing demography and threshold for surgery. Ann Rheum Dis1999;58:569–72.[Abstract/Free Full Text]
  4. Cushnaghan J, Dieppe P. Study of 500 patients with limb joint osteoarthritis. I. Analysis by age, sex, and distribution of symptomatic joint sites. Ann Rheum Dis1991;50:8–13.[Abstract]
  5. Spector TD, Hochberg MC. Methodological problems in the epidemiological study of osteoarthritis. Ann Rheum Dis1994;53:143–6.[Abstract]
  6. Croft P, Cooper C, Wickham C, Coggon D. Defining osteoarthritis of the hip for epidemiologic studies. Am J Epidemiol1990;132:514–22.[Abstract]
  7. Croft P, Cooper C, Coggon D. Defining hip osteoarthritis: osteophytosis or joint space narrowing. J Rheumatol1994;21:590–2.
  8. Auleley GR, Rousselin B, Ayral X, Edouard-Noel R, Dougados M, Ravaud P. Osteoarthritis of the hip: agreement between joint space width measurements on standing and supine conventional radiographs. Ann Rheum Dis1998;57:519–23.[Abstract/Free Full Text]
  9. Pessis E, Chevrot A, Drape JL, Leveque C, Sarazin L, Minoui A et al. Study of the joint space of the hip on supine and weight-bearing digital radiographs. Clin Radiol1999;54:528–32.[ISI][Medline]
  10. Altman R, Alarcon G, Appelrouth D et al. The American College of Rheumatology criteria for the classification and reporting of osteoarthritis of the hip. Arthritis Rheum1991;34:505–14.[ISI][Medline]
  11. Petersson IF. Occurrence of osteoarthritis of the peripheral joints in European populations. Ann Rheum Dis1996;55:659–61.[ISI][Medline]
Submitted 20 August 1999; revised version accepted 17 January 2000.