Rheumatoid arthritis: epidemiology of hip and knee replacement in the UK

Takeaway

• The overall incidence rates of total hip replacement (THR) and total knee replacement (TKR) were 6.38 per 1000 person-years (PYs) and 8.57 per 1000 PYs in newly diagnosed rheumatoid arthritis (RA) patients, respectively, over a maximum of 20 years.
• Incidence rates of TKR but not THR increased according to body mass index (BMI).
• Increased deprivation was associated with a declining trend in both THR and TKR.

Why this matters

• Findings provide physicians, patients, and commissioners a better understanding of the long-term prognosis of RA.

Study design

• Study identified 27,607 patients with RA (mean age, 61 years; 70.6% females; mean BMI, 27.3 kg/m²) using data from the UK Clinical Practice Research Datalink (CPRD).
• Outcome: first occurrence of TKR and THR following RA.
• Funding: None.

Key results

• A total of 1028 THRs and1366 TKRs were identified.
• THR and TKR had overall:
  • incidence rates per 1000 person-years of 6.38 (95% CI, 6.00-6.78) and 8.57 (95% CI, 8.12-9.04),
  • 10-year cumulative % probability of 5.2% (95% CI, 4.9-5.6%) and 7.0% (95% CI, 6.6-7.4%) and
  • 20-year cumulative % probability of 8.4% (95% CI, 7.3-9.7%) and 11.1% (95% CI, 10.0-12.4%), respectively.
• Incidence rates for TKR increased with increasing BMI (P<.001) but remained the same for THR.
  • lowest among underweight (4.98 [95% CI, 3.46-7.17] per 1000 PYs) and
  • 3 times higher in those with BMI ≥35 kg/m² (14.58 [95% CI, 12.72-16.72] per 1000 PYs).
• Most deprived patient vs least deprived had:
  • >30% lower THR estimate rates (5.07 [95% CI, 4.02-6.40] per 1000 PYs vs 7.49 [95% CI, 6.45-8.71] per 1000 PYs) and
  • 20% lower TKR estimate rates (7.30 [95% CI, 6.00-8.87] per 1000 PYs vs 9.06 [95% CI, 7.90-10.39] per 1000 PYs).

Limitations

• Likely delay in a patient’s record between onset of RA symptoms and coding of the disease.