Knee osteoarthritis
Author: Dr Tony Williams FFOM, Consultant Occupational Physician, Working Fit Ltd
Date: 13th September 2015
Epidemiology
Few studies break down prevalence of knee osteoarthritis into groups of working age. There are significant ethical constraints now in relation to X-ray studies of populations so many data sets are old. Many patients experience knee pain without underlying degenerative change but these symptoms generally resolve.
Persistent symptoms of knee pain are associated with osteoarthritic changes with a clear link between severity, disability and radiographic changes (Duncan et al., 2007).
Radiographic changes of osteoarthritis increase in prevalence with age, with evidence of significant OA for substantial numbers in the older population. Around half of adults over the age of 50 who have radiographic changes have symptoms (Peat et al., 2006).
The ROAD study in Japan showed a significant rise in knee OA through working age. Prevalence was 22/1000 aged less than 39, 107/1000 aged 40-49, 282/1000 aged 50-59, 508/1000 aged 60-69 and 690/1000 aged 70-79 (Yoshimura et al., 2011).
A UK study found significantly higher numbers of patients with both symptomatic and radiological evidence of knee OA. Prevalence of both symptomatic and radiological knee OA was 200/1000 (men), 190/1000 (women) aged 50-59, 310/1000 (men), 290/1000 (women) aged 60-69 and 360/1000 (men), 340/1000 (women) aged 70-79 (Peat et al., 2008).
The available evidence shows that OA of the knee rarely occurs before the age of 50. Where a patient presents with knee OA at a young age it may be possible to identify a specific cause. Where a patient first presents with knee OA over the age of 50 it will be harder to attribute cause because the condition is so common anyway.
Limits to evidence
There have been significant recent changes in both diagnostic approach and treatments. Arthroscopy was an emerging discipline in the 1980’s. Research prior to this was based on radiographic evidence.
Surgical treatment involved opening the knee, with significant damage to structures simply to gain access. Surgery was also undertaken with the unaided eye using larger instruments. Substantial damage inevitably resulted to surrounding structures, and for example meniscus surgery often involved removal of the complete meniscus. Modern arthoscopy methods involve minimal damage to surrounding structures, surgery using microscopic techniques, and much smaller instrumentation. Outcomes are therefore very different. It is important to understand the surgical procedure a patient had when considering likely aetiology and prognosis. A patient who had an open meniscectomy in 1970 will have a very different outcome to one who had an arthroscopic meniscectomy in 2010, and research papers considering modern methods should be applied with caution to patients who had older procedures.
Studies of occupation are inevitably broad-based using limited definitions. It may not be possible to differentiate between participants who undertook an occupation for one year and those who undertook it for forty years. It may not be possible to differentiate between those who had the same job title or worked in the same industry but actually had widely different roles. Many studies showing a link to occupation may therefore substantially underestimate the effect.
DUNCAN, R., PEAT, G., THOMAS, E., HAY, E., MCCALL, I. & CROFT, P. 2007. Symptoms and radiographic osteoarthritis: not as discordant as they are made out to be? Ann Rheum Dis, 66, 86-91.
PEAT, G., DUNCAN, R. & THOMAS, E. 2008. Data from CAS-K study. [Online]. Arthritis Research UK website. Available: www.arthritisresearchuk.org/arthritis-information/data-and-statistics/osteoarthritis/data-on-knee-oa.aspx.
PEAT, G., THOMAS, E., HANDY, J., WOOD, L., DZIEDZIC, K., MYERS, H., WILKIE, R., DUNCAN, R., HAY, E., HILL, J., LACEY, R. & CROFT, P. 2006. The Knee Clinical Assessment Study-CAS(K). A prospective study of knee pain and knee osteoarthritis in the general population: baseline recruitment and retention at 18 months. BMC Musculoskelet Disord, 7, 30.
YOSHIMURA, N., MURAKI, S., OKA, H., KAWAGUCHI, H., NAKAMURA, K. & AKUNE, T. 2011. Association of knee osteoarthritis with the accumulation of metabolic risk factors such as overweight, hypertension, dyslipidemia, and impaired glucose tolerance in Japanese men and women: the ROAD study. J Rheumatol, 38, 921-30.