Should all elective knee radiographs requested by general practitioners be performed weight-bearing?

Osteoarthritis represents a complex musculoskeletal disorder with multiple genetic, constitutional and biomechanical risk factors. It represents the most common form of joint disease in the elderly and ranks amongst the top 5 causes of disability (Murray and Lopez 1997). The prevalence of knee osteoarthritis in patients aged over 45 in the general practice (GP) setting has been estimated at 12.5% in 2005 (Bedson et al. 2005).

The diagnosis of knee osteoarthritis is based on clinical history and examination, followed by radiographic examination of the knee (Altman et al. 1986). Radiographs can be taken with the patient supine or standing. The Kellgren-Lawrence Grading Scale is one measure used to assess knee osteoarthritis severity on plain radiograph (Kellgren and Lawrence 1957). Studies have shown that standing/weight-bearing (WB) views improve the detection of joint space narrowing more reliably than supine views (Brandt et al. 1991). This is probably because WB places compressive stresses on the knee joint that help accentuate any loss of articular cartilage causing joint space narrowing. It is not known whether knee radiographs requested by the general practitioner are routinely performed WB or non-WB in UK hospitals.

Professor Briggs highlighted in his report ‘Getting it right first time’ that 15%-30% of GP consultations will be of a musculoskeletal nature (Briggs 2012). With regard to requesting musculoskeletal investigations, in a survey of GPs in 2003 by Bedson et al. (Bedson et al. 2003), 50% of GPs were confident of diagnosing osteoarthritis on the basis of the plain radiograph. Furthermore, 80% of GPs were likely to request a radiograph if considering referral to an orthopaedic surgeon. The radiological report of the GP-requested knee radiograph is therefore pivotal in determining whether onward specialist referral is undertaken. The radiology report is however, influenced by whether WB or non-WB views are taken (Brandt et al. 1991).

The Royal College of Radiologists has published guidelines on the indications for various imaging investigations, including plain radiography of the knee. In an audit of 1153 knee radiographs requested by GPs, only 50% of those radiographs fell within the RCR guidelines (Morgan et al. 1997). Morgan et al. found in 87% of cases, there was no change in management, apart from continuation of symptomatic treatment. GPs in Morgan’s study reported medico-legal reasons as a significant factor in unnecessary radiograph requests. One further reason that management may not have changed in the case of knee radiographs, could be that non-WB views were taken, which did not fully reveal the joint space loss from degenerative change that WB views would have revealed.

This study shows that, in the absence of a departmental policy for routinely performing WB knee radiographs, the vast majority of non-traumatic knee radiographs requested by GPs in patients over the age of 40 are performed non-WB (98%). In the financial year of 2011 – 2012 the national cost of all diagnostic radiology to the NHS budget was £815 million (Department of Health 2012). To put the extrapolated unnecessary direct costs (£200,052) calculated from our study into context this would account for 0.025% of diagnostic radiology costs. In the current politico-economic climate, this saving, while modest compared to the whole NHS budget, represents a significant and unnecessary cost, which can be readily and easily addressed.

Our department sees approximately 1000 new knee patients annually. Of these patients, approximately 300 patients (in 2012) would fit our inclusion criteria (age over 40, no previous arthroplasty or fixation, no trauma). Therefore, as a representation of patients seen by our department for suspected knee osteoarthritis, 19% (56 out of 300) require an unnecessary repeat of the knee imaging at the time of their outpatient visit. This would therefore support the view that a significant amount of time is wasted in the outpatient setting repeating these radiographs. The overall numbers of patients actually requiring such repeat radiographs remain, however relatively small (n = 56). However, this may be due to the reluctance of specialist clinicians in subjecting patients to further radiation in repeating radiographs as WB.

There is good evidence that tibio-femoral joint space narrowing is good evidence for cartilage loss (Buckland-Wright et al. 1995). In addition, our study confirms that WB compared to non-WB films significantly increase the amount of joint space narrowing on plain radiographs (p = 0.035), and hence the severity of osteoarthritis when reported by a radiologist. This represents an area of possible delayed or missed diagnosis, with its potential costs in terms of complaints and/or litigation.

From the results of our study, the numbers of patients who may be suffering from such a delay could potentially be quite large, with a pool of up to 1867 patients (those who had non-WB radiographs and did not have repeat WB radiographs) being under-diagnosed with regard to the extent of their knee osteoarthritis. This may then result in delayed/inappropriate treatment or referral of such patients to specialist care.

Jayatilaka et al. (2012) in a study of 41 patients over a two-week period found none of the patients referred by GPs to orthopaedic outpatients had WB radiographs requested prior to consultation. A higher proportion of patients in our study had WB knee radiographs requested prior to being seen in our orthopaedic clinic (2.3%), however a significantly lower amount of radiographs initially performed non-WB were repeated in our study (2.9% vs. 25%). In our literature search this was the only study found looking at the requesting trends of GPs with regards to WB and non-WB knee radiographs. Given the time period and sample size of our study, we believe our findings to be a comprehensive representation of plain radiograph requests by GPs investigating knee osteoarthritis.

Our study raises the question whether a national policy to routinely perform elective knee radiographs with the patient WB should be implemented, or at the very least discussed between primary care institutions, radiology and orthopaedic departments. In the absence of such a national policy existing, our study suggests that it would be prudent for doctors in all specialities to request all AP and lateral knee radiographs as weight bearing (or “erect”) views, unless there is a history of trauma or the patient is not able to bear weight on the knee.

Only a small proportion of patients referred for knee radiographs by GPs have WB AP films. The radiographic features of osteoarthritis appear to be more severe on WB plain radiographs of the knee when compared with non-WB plain radiographs of the knee. In London, 46% of hospitals do not routinely perform WB radiographs to investigate suspected knee osteoarthritis, potentially leading to a delay in diagnosis, referral or treatment of these patients. It represents a significant risk and cost burden to the NHS. In the absence of a national policy on WB status on knee radiographs, we would recommend when investigating for knee osteoarthritis, radiographs be requested at “weight bearing” or “erect” when general practitioners complete the request form as part of a national policy.