Hip OA is increasingly common with age. Those who develop hip OA in middle and old age are more likely to have a genetic predisposition to hip OA, while those who develop it at younger age are more likely to have an underlying developmental defect, or to have developed hip OA because of trauma or high levels of physical activity.
There is no clear evidence to show an increased risk for hip OA from military activity or general military sporting activity.
There is evidence to show an increased risk with frequent heavy manual activity and with frequent or prolonged standing.
There is evidence to show an increased risk for hip OA with elite sport, particularly running and contact sports.
There is evidence to show an increased risk following trauma to the hip joint.
Hip arthroplasty is a good treatment for hip OA with generally excellent outcomes. There is some evidence that joint resurfacing is more appropriate for the younger patient, and care should be taken in choice of prosthesis, probably avoiding ceramics as these may fail with impact activities. Most military activities are compatible with hip arthroplasty without significant increased risk.
There are variations in both diagnostic criteria, and in the application of specific criteria between researchers. Some studies look at radiologic findings, others use MRI, or CT findings. Studies may only assess degree of disability and others use joint replacement as a severity marker.
Prevalence rates vary with age, and different factors appear to be involved as age increases. Many studies only consider older populations, so relating these to a young and active population can be difficult. While some studies show differences between gender and ethnic groups these appear to vary with age, and it is not possible to extrapolate the gender and ethnic differences from many reports which consider wide age groups.
Patient recall is commonly used, either of past symptoms or of activities including occupation, and recall particularly of long past events may be very inaccurate. Even where the patient is currently undertaking an occupation their description of occupational exposure can vary.
Case-control studies may only consider exposure to activity at some point, and may not accurately measure duration or frequency of exposure; working in a role for only six months in a lifetime gives a very different exposure from forty years in that role. Lifting a 40kg load once a month is a very different exposure from lifting 40kg ten or twenty times an hour.
It can be very difficult to control for confounders such as obesity, diet, or other activity such as sport.
Studies of occupation are inevitably broad-based using limited definitions. 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.
Individuals who have served in the Forces may have worked in very different roles. A REME mechanic who served in an Aviation Regiment will have had a very different activity profile from a REME mechanic who served in a Parachute Battalion and was parachute trained.
Most measures of outcome after arthroplasty, and indeed after most orthopaedic interventions, rely on patient reports which are inevitably subjective. The only objective measures are of joint failure, or clear complications such as infection or restricted movement. Care needs to be taken when assessing reported outcomes as there is concern over the reliability of the tools currently in use (Alviar et al., 2011).
Osteoarthritis (OA) of the hip (syn: osteoarthrosis of the hip, coxarthrosis) is a common degenerative condition. Usually progressive, in later stages it is often associated with pain and functional impairment.
Risk estimates for hip OA, as with OA of other joints, vary according to the population studied and the criteria used to diagnose OA. Few studies break down prevalence into groups of working age, most studying older populations, so it is difficult to estimate a baseline expected prevalence in younger populations.
The prevalence of hip pain increases with age. In men, only 30/1000 report hip pain in age range 16-44, increasing to 110/1000 in age range 45-64 and 130/1000 in age range 65-74. Among women the prevalence is higher, with 40/1000 in age range 16-44, 150/1000 in age range 45-64 and 200/1000 in age range 65-74 (Urwin et al., 1998).
A review of the prevalence of radiographic primary hip OA found a wide variation between studies. Overall, prevalence in men increased from 13/1000 age 35-39 to 24/1000 aged 50-54 to 93/1000 age 70-74. In women the corresponding prevalence was 17/1000, 26/1000 and 92/1000. There was a steady increase through middle age, with a significant rise after age 55 (Dagenais et al., 2009).
Around half those with radiographic hip OA present with significant symptoms (National Collaborating Centre for Chronic Conditions, 2008). A major US study, the Johnston County Osteoarthritis Project, compared hip symptoms, radiographic hip OA, symptomatic hip OA and severe radiographic hip OA. Overall this found that although symptoms are common, the prevalence of disease severe enough to limit function is substantially less. In age range 45-54, 307/1000 had hip symptoms, 212/1000 had radiographic OA, 59/1000 had symptomatic OA while only 14/1000 had severe radiographic OA. In age range 55-64 these changed to 359, 230, 89 and 11. These further increased in age range 65-74 to 407, 311, 108 and 36 (Jordan et al., 2009).
The overall rate of primary hip OA in active duty US military service personnel was found to be 35 per 100,000 person-years. Assuming an average term of service of 7 years, this would equate to around 2.5 cases per thousand in serving personnel. Service personnel aged 40 and over had an adjusted incidence rate ratio of 22.21 compared to the 20 year old group. There was an increased risk for the Navy, Army and Marines compared to the Air Force (Scher et al., 2009).
Women serving in the US military had a significantly increased adjusted incidence rate ratio of 1.87 (Scher et al., 2009).
An overall analysis of incidence in personnel serving in the US military found black personnel had an increased incidence rate ratio of 1.32 compared to white personnel (Scher et al., 2009). A study of the general population in the US found African Americans appear to have a significantly lower incidence of hip OA than white Americans (adjusted hazard ratio 0.44) (Kopec et al., 2013). However the US Johnston County OA project found the baseline frequency of radiographic hip OA between Caucasians and African Americans was broadly similar at age 61 (23%), but some radiographic features differed (Foley et al., 2015). Hip OA is less common among Chinese than US Caucasians (Allen, 2010).
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FOLEY, B., CLEVELAND, R. J., RENNER, J. B., JORDAN, J. M. & NELSON, A. E. 2015. Racial differences in associations between baseline patterns of radiographic osteoarthritis and multiple definitions of progression of hip osteoarthritis: the Johnston County Osteoarthritis Project. Arthritis Res Ther, 17, 366.
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