Hip osteoarthritis

Who gets osteoarthritis of the hip?

Risk factors can be divided into general, intrinsic, and extrinsic. General factors include age, sex, and genetics. Hip osteoarthritis is almost twice as common in women than in men,1 2 and genetic studies show a 50% heritability caused by European genetic variants. Intrinsic factors include incongruency (such as dysplasias) and joint laxity: they cause abnormal wear and loading, and therefore accelerate articular degeneration. Extrinsic factors such as increasing body mass index, high levels of certain exercise, and heavy manual labour are thought to increase the incidence and progression of hip osteoarthritis.3 4 5

Most often the cause of hip osteoarthritis is multifactorial.6 A series of risk factors lead to instability, malalignment, increased joint load, microtrauma and structural damage. The joint responds through subchondral and synovial inflammation, and bone hypertrophy. This is visible on radiographs as narrowed joint space, sclerosis, and cyst or osteophyte formation.7

Hip osteoarthritis is associated with other diseases, but there is often no proven causal relationship. A population based cohort study showed that hip osteoarthritis is associated with frailty, with an odds ratio after adjustment for confounding variables of 1.57 (95% confidence interval 1.1 to 2.22).8 Hip osteoarthritis is also associated with an increased risk of all-cause mortality (hazard ratio 1.14)9 and higher rates of mental health problems.10 One large, population based cohort study also suggests an increase in cardiovascular mortality associated with osteoarthritis (hazard ratio 1.24).9 A prospective, population based cohort study11 suggests this is probably because of ensuing disability rather than the presence of osteoarthritis itself.

What are the symptoms and clinical signs of hip osteoarthritis?

Patients with hip osteoarthritis typically develop pain over months to years rather than acutely. They describe an achy groin pain, which is at first intermittent, worse at the end of the day, and activity related (particularly while walking or climbing stairs). Rest and night pain may feature in all disease stages, but severity increases as the disease progresses.12 Night pain, particularly when atypical or out of context of other osteoarthritis symptoms, may be a sign of a more serious diagnosis (see table 1⇓ for examples). Similar hip pain can occur in other conditions, some of which are highlighted in table 2⇓. Cases of hip osteoarthritis may be considered “severe” if symptoms are a substantial barrier to mobility and independence. Several scoring systems score the severity of symptoms. The Oxford Hip Score is perhaps the most commonly used and forms part of the Patient Reported Outcome Measures (PROMs) in England for total hip replacements.13