Family Practice Advance Access originally published online on November 1, 2004
Family Practice 2005 22(1):118-125; doi:10.1093/fampra/cmh609
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Prospective study of elderly people comparing treatments following first primary care consultation for a symptomatic hip or knee
a Division of Public Health and Primary Health Care, Old Road, Oxford OX3 7LF, b School of Health and Social Care, Oxford Brookes University, Marston Road Campus, Jack Straws Lane, Oxford OX3 OFL, c Wellcome Trust Centre for Human Genetics, University of Oxford and d Nuffield Orthopaedic Centre, Windmill Road, Oxford OX3 7LD, UK
Correspondence to Dr Jill Dawson, School of Health and Social Care, Oxford Brookes University, Marston Road Campus, Jack Straws Lane, Oxford OX3 OFL, UK; Email jdawson{at}brookes.ac.uk
Received 26 April 2004; Accepted 19 June 2004.
Linsell L, Dawson J, Zondervan K, Randall T, Rose P, Carr A and Fitzpatrick R. Prospective study of elderly people comparing treatments following first primary care consultation for a symptomatic hip or knee. Family Practice 2005; 22: 118–125.
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Abstract |
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Background. Symptomatic knee problems in elderly people are considerably more common than hip problems, yet far more hips are replaced.
Objective. The purpose of this study was to investigate whether systematic differences occur in early primary care management of elderly patients who first consult with hip versus knee symptoms.
Methods. A prospective analysis was carried out of anonymized records in the MediPlus general practice database. This was a 3 year (1996–1998) prospective study of 310 843 patients aged 65+ regarding consultations about a new hip or knee problem. Survival analysis techniques were used to analyse time to and frequency of various interventions.
Results. A total of 1410 new hip and 3152 new knee consulters were identified. Baseline characteristics of the two groups were very similar. By 3 years following the first consultation, more of the hip cases had referral to a specialist (38.2% hips versus 31.5% knees, P < 0.001) and joint replacement (9.6% hips versus 1.8% knees, P < 0.001) recorded. Non-steroidal anti-inflammatory drug (NSAID) prescribing was high for both groups, with 
51% prescribed one of the safer forms and 15% prescribed one with a lower safety record within 3 years.
Conclusion. Rates of specialist referral and joint replacement in older people are much lower, or slower, for those with symptomatic knees relative to hips. In the absence of surgery, prescriptions for pain killers are similar for both groups. Elderly people with symptomatic knees are therefore at increased risk of drug side effects relative to those with symptomatic hips. This may represent another facet of unmet need for surgery in people with knee disease.
Keywords. Hip pain, knee pain, NSAIDs, primary care.
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Introduction |
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Hip and knee pain represent major causes of disability and social isolation in elderly people. In older people, persistent hip or knee pain is generally due to osteoarthritis (OA). This diagnosis is frequently made solely on clinical grounds due to the lack of agreement between the presence of radiographic signs of OA and symptoms.1,2 For severe symptoms, hip or knee replacement (arthroplasty) is the treatment of choice, and both surgical procedures are now considered similarly effective in the long term.3–7
Studies consistently report knee symptoms (or confirmed knee OA) to be more prevalent than hip symptoms (or confirmed hip OA), yet considerably more hips than knees are replaced in England and Wales.8 This has led to the assertion that people with knee problems have unmet health care needs relative to those with hip problems,3 but there is little evidence available to support this. Few data exist regarding primary care management of symptomatic hips or knees, or on out-patient attendance and management. We therefore undertook an analysis of records in a general practice database—IMS Disease Analyzer-Mediplus UK (MediPlus)—comparing consultation rates for new hip or knee problems and subsequent treatment strategies in a cohort of people aged 
65 years.
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Methods |
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The study obtained ethical approval from the Applied and Qualitative Research Ethics Committee (AQREC) (reference A01.060).
Data
The MediPlus database is collated by International Medical Statistics (IMS Health Ltd). Available since 1991, and containing >3 million anonymized patient records, MediPlus is currently used by 604 GPs in 198 practices dispersed throughout the UK. Symptoms, diagnoses, referrals and procedures are coded using the Read code system; drug prescriptions are coded using Anatomic Therapy Class (ATC) codes, with 16 classes corresponding to different body systems. The database is commonly used to examine prescribing practices in the UK. Provided limitations inherent in primary care databases are borne in mind, studies have concluded that the MediPlus database is generally reliable and consistent.9 These limitations are: (i) the amount of detail with which diagnoses, but in particular symptoms, are coded is left mainly at the discretion of the GP; and (ii) the population registered on MediPlus represents a dynamic rather than a static group: practices and patients enter and leave the database.
Selection of cohort
We included only practices in the database that had complete data up to February 2002 (112 out of 198, 56.6%). A cohort of people aged 65 or above was identified from their first GP consultation ('index consultation') about either a hip or knee condition. The selection strategy was designed to minimize heterogeneity between the two groups and to identify first consultations where the differential diagnosis could reasonably include primary or secondary hip or knee OA.
Consultations initially included were those with any Read code indicative of a symptomatic hip or knee, e.g. hip joint pain, OA of the hip joint, knee joint pain, internal derangement of knee (details of codes are given in Table 1). The time period during which these symptoms had to occur was 1 January 1996 to 31 December 1998.
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To allow identification of new symptoms and allow follow-up, inclusion criteria for individuals into the cohort required the existence of (i) at least 3 years of records prior to the index consultation from which a medical history could be derived; and (ii) 3 years of records following the date of the index consultation. Cases were excluded if: (i) first presentation involved simultaneous hip and knee problems; (ii) records indicated previous replacement or surgical treatment of a hip or knee joint, or provided evidence of previous symptomatic hip, knee or multiple joints; (iii) records suggested a history of a chronic condition likely to produce hip or knee symptoms unrelated to OA, e.g. rheumatoid arthritis, or a condition over-riding OA problems (often involving aggressive treatment such as steroids, radiotherapy, opiates), e.g. metastatic cancer, systemic lupus erythematosus (SLE); and (iv) recent (within 12 months) evidence of trauma, injury or acute systemic condition, likely to produce the current symptoms (e.g. polymyalgia rheumatica).
Longitudinal analysis
Records of patients in the hip versus knee groups were followed-up for 3 years beyond the index consultation regarding: relevant medications [simple and narcotic analgesics, non-steroidal anti-inflammatory drugs (NSAIDs), steroids, antidepressants, gastroprotective agents]; investigative or therapeutic procedures (intra-articular injections and lavage, hydrotherapy, physiotherapy and arthroplasty) and referrals.
Oral NSAIDs were grouped on the basis of their relative safety regarding risk of upper gastrointestinal bleeding:10,11 (i) ibuprofen, aspirin, diclofenac and fenoprofen (safest); (ii) NSAIDs + gastroprotective agent in one preparation; (iii) cyclo-oxygenase (COX)-II-selective inhibitors; and (iv) 'other oral NSAIDs' (least safe).
The assumption underlying all analyses was that any coding inconsistencies or missing data should equally affect records of people with hip versus knee problems.
Statistical analysis
Survival analysis techniques were employed to analyse time to and frequency of treatment. The log-rank test, adjusted for age and sex, was used to test for differences in treatment patterns between hips and knees during the 3 year period following the index consultation. The binomial test was used to investigate change in NSAID prescriptions before and after arthroplasty, in patients already using these drugs. Differences in the proportion of hip and knee cases prescribed NSAIDs following arthroplasty were compared using Fisher's exact test. Analyses were conducted using STATA software.
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Results |
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The case selection process (Table 1) identified 310 843 people aged
65 years on 31 December 1998 of whom 212 642 (68.4%) had consulted their GP at least once during the period 1991–1992. Of these, 5602 people (2.6%) consulted their GP from 1 January 1996 to 31 December 1998 about a hip problem, and 10 489 (4.9%) consulted about a knee problem. At this stage (step II: case inclusion criteria, stage 1), 218 people [218/ (5602 + 10 489 + 218) = 1.3%] were excluded who had hip and knee codes recorded simultaneously at their index consultation. The requirement of 3 years' complete follow-up data reduced these numbers to 4443 hip and 8701 knee cases; the exclusion criteria further reduced numbers to 1410 (1410 out of 212 642, 0.7%) new hip cases versus 3152 (3152 out of 212 642, 1.5%) new knee cases.
Table 2 presents demographic details comparing hip and knee cases. The age and sex distribution of the two groups were very similar; the ratio of men to women was 2:3. Limited information on height and weight allowed patients' body mass index (BMI) to be calculated for less than half of the sample (hips, 615 out of 1410, 43.6%; knees, 1291 out of 3152, 41.0%).
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Table 3 shows that rates of investigations, referrals and prescriptions were strikingly similar between people in the hip and the knee groups during the 12 month period prior to their index consultation, with rates generally higher than those for all people aged 65+.
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Table 4 compares the cumulative number of patients who received selected treatments or procedures at the index consultation, and within the following 12 and 36 months. Patient observations have been censored at the point where a hip case developed a new knee problem or received a hip replacement; equivalent censorship was applied to knee cases. Thus the proportions in the table represent the cumulative number of patients receiving a particular treatment by month 't' divided by the number of patients not yet censored.
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During the 3 year period, a higher proportion of people who first presented with a hip problem also subsequently developed a knee problem than was the case vice versa (P = 0.004). The proportion of patients who had a hip or knee replacement recorded differed substantially between the hip (9.6%) and knee (1.8%) groups (P < 0.001). No significant differences were found in the number of hip and knee cases sent for blood tests, screening or imaging; more hip (38.2%) than knee (31.5%) cases were referred to a clinical specialist by the end of 3 years (P < 0.001).
The proportion of hip and knee cases prescribed NSAIDs was high compared with all people aged 65+ receiving such prescriptions in a 1 year period (Tables 3 and 4). By the end of 3 years, around half of the hip and knee cases (excluding those who underwent arthroplasty) had received a safer form of NSAID. NSAIDs with a lower safety record were also (equally) well represented amongst hip and knee cases, with 15% of cases prescribed one within the 3 year period.
Within the 3 year period post-index consultation, over a quarter of hip and knee cases had been prescribed a gastroprotective agent [H-2 antagonist, proton pump inhibitor (PPI) or 'misoprostol/other anti-ulcerant'], while over one-fifth had received an antacid/antiflatulant. Around 10% of hip cases versus 8% of knee cases had received oral NSAIDs in the form of a combined NSAID/gastroprotective formula.
The use of topical NSAIDs was consistently higher amongst the knee than hip cases, as was the use of injected corticosteroids. Around three-quarters of all cases had prescriptions for non-narcotic analgesics by the end of 3 years, although significantly more hip cases had received these than knee cases (79.4 versus 72.3%, respectively, P < 0.001).
Amongst hip and knee patients who were prescribed an oral NSAID during the 12 months prior to joint replacement (arthroplasty), there was a significant decrease in these prescriptions during the 12 month period beginning 3 months post-surgery (hips, n = 76 before versus n = 38 after, P < 0.001; knees, n = 25 before versus n = 8 after, P < 0.001). Oral NSAID prescription rates following arthroplasty did not differ significantly between hip and knee cases (P = 0.16).
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Discussion |
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In line with other published work,8 this study revealed over twice as many new knee cases as new hip cases attending primary care in the 65+ age group. Although knee OA is much more common than hip OA, and OA is the most common reason for arthroplasty, considerably more hips than knees are replaced in the UK. Reasons for this are unknown. In the USA, rates of knee and hip arthroplasty are similar, and it is possible that at least part of the explanation could lie with a shortage of knee surgeons in the UK. Another possibility is that, in the UK, there are systematic differences in treatments between people with hip and knee problems in the primary care setting.
In our 3 year, record-based follow-up of 1410 new hip cases and 3152 new knee cases, we found that hip cases were referred to a specialist significantly more often (38.2 versus 31.5%) and that a higher proportion of hip cases received joint replacement (9.6 versus 1.8%). This confirms recent evidence of differential rates of hip and knee referral and surgery.12 However, our study also found evidence that knee cases were more often managed medically through NSAIDs, corticosteroid injections and therapeutic procedures.
The finding that significantly more new hip cases developed subsequent knee problems than vice versa warrants further research. People with two symptomatic joints are likely to be more disabled (and at potentially greater risk of side effects from pain-killing drugs) than those who have only one, which might prompt specialist referral. However, this finding did not explain why hip cases were referred to specialists sooner than knee cases in the current study, as such cases were censored from the comparative analysis of interventions at the point when a second symptomatic joint was registered.
There was some evidence that GPs tried extra forms of treatment for knees, such as intra-articular steroid injections. This might partially explain a delay in referring new knee cases to a specialist, relative to hips, but cannot explain the huge disparity in arthroplasty rates between the two joints. Our finding that 7.1% of new hip cases had a hip replacement recorded within 24 months is in line, given the likely waiting time, with another study that found that 7% of primary care attenders with a new hip problem were put on a surgical waiting list for hip replacement within 12 months of being seen.13
Our analysis of prescribed medications revealed that at least half of the hip and knee cases were prescribed oral NSAIDs and 15% had had at least one prescription for a type of NSAID considered less safe than others, a finding which we believe should arouse some concern. The use of any NSAIDs in people aged 65 is associated with a high risk of gastrointestinal complications, which can be life threatening.10,14,15 In addition, only around one-quarter of the cases had been prescribed a gastroprotective agent (e.g. H-2 antagonist, PPI or misoprostol) within the same period, which could offer partial protection, with one-fifth having received an antacid/antiflatulant (concomitantly, or alone). This would appear to fall short of optimal protection.16
The proportion of people prescribed tricyclic antidepressants (11%) within 3 years after onset of the joint problem was similar in both the hip and knee groups. Serotonin re-uptake inhibitors (SSRIs) were prescribed in the ratio of 3:2 for hip and knee cases, respectively. A recent study has confirmed SSRIs to be associated with upper gastrointestinal tract bleeding, especially if co-prescribed with NSAIDs or aspirin.17
Our sample selection aimed to reduce heterogeneity between the hip and knee groups, and to identify first consultations about a localized hip or knee condition which excluded acute injury. In older people, persistent hip or knee pain is generally due to OA, although it would be difficult to confirm the extent to which the cohort was based on OA. Also, MediPlus data will only reveal problems that patients have consulted about, which are subject to the coding accuracy and consistency of GPs. Although the scope for assessing absolute rates is limited, the data do allow a valid comparative analysis, as coding inconsistencies should not have differed systematically between the hip and knee groups. This assumption was supported by the similarity of characteristics unrelated to OA between the two groups, and rates of prescriptions and procedures recorded during the year prior to index consultations. However, rates of referral, and prescriptions for NSAIDs and gastroprotective agents were raised for both groups by comparison with all people aged 65+ in MediPlus. It is therefore possible that a small proportion of the 'new' hip or knee cases had in fact consulted about this joint problem before but not had an appropriate diagnostic code recorded.
One possible explanation for our study's findings is that the natural progression of hip OA may be faster than is the case for knee OA, and this has to remain at least a partial potential explanation since we could find no examples of studies that have compared the progression of symptoms in people with hip versus knee disease. We were unable to examine this issue as MediPlus does not contain information on symptom severity. Although we cannot judge the levels of symptoms experienced by the two groups relative to one another, it is nevertheless reasonable to assume that a prescription for analgesics or an NSAID represents a 'more than mild' level of symptoms. A recent study has reported that, following adjustment for symptom severity, people with knee disease are slightly more likely to consult a GP than those with hip disease.12
While no evidence-based guidelines or measures exist to help clinicians decide who might best benefit from arthroplasty, there are consensus criteria which address indications for both referral and surgery.18–20 These recommendations emphasize the importance of pain not managed by medical means, followed by progressive disability, as the main reasons for undertaking surgery for hip and knee OA.
Most people with advanced hip or knee disease are elderly, yet none of the recommendations seriously address the issue of drug side effects which are particularly relevant to elderly people. This includes situations where pain is managed adequately by medications which nevertheless carry high risks when used over the longer term, and which are not recommended for particular categories of patient—such as NSAIDs, antidepressants or hypnotics, in elderly people.10,14
Once side effects appear, a person awaiting joint surgery may face many months without adequate pain management due to a reduced range of safe options. This could represent an argument for recommending that joint replacement is considered appropriate in elderly people from the moment that drugs which have the potential to carry serious side effects are regularly required in order to manage pain, irrespective of whether they manage the pain effectively or not. We showed that there was a significant decrease in NSAID prescriptions following hip or knee arthroplasty surgery (albeit based upon small numbers).
When patients consult their GP (or specialist) about an increasingly painful hip or knee, one of the factors which may influence whether specialist referral occurs is the patient's willingness to proceed to surgery.12 This will probably be tempered by their assessment of the risks associated with such surgery, and doctors can play an important role in counselling patients in this regard. While the risk of serious perioperative complications associated with hip or knee arthroplasty increases with older age, the risk is nevertheless low.21 Evidence from studies regarding the risks and recommendations surrounding NSAID usage in elderly people, together with evidence from our own data—revealing the widespread use of these drugs for people with hip and knee disease—emphasizes the point that there are also risks associated with not proceeding to arthroplasty.
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Declaration |
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Funding: financial support provided by a grant from the NHS Executive (South-East Region).
Ethical approval: obtained from the Oxford Applied and Qualitative Research Ethics Committee (ref.A01.060).
Conflicts of interest: none.
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Acknowledgments |
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We greatly appreciate the considerable assistance provided by Mary Thompson at IMS Health Ltd in relation to MediPlus data extraction and coding interpretation.
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