We were interested to read the article by Keurentjes et al (“Patients with Severe Radiographic Osteoarthritis Have Better Prognosis in Physical Functioning after hip and knee replacement: a cohort study”) (1) in the April edition of your journal. While agreeing with the overall message, we wish to point out two concerns, first that the authors do not seem to be aware of recent relevant literature on the subject, and secondly that there are several methodological issues with their study.

The authors imply that their finding of an association between pre-operative radiographic severity of arthritis, and outcomes after joint replacement is new. This is not the case, there are at least three other published studies reporting similar findings, none of which is quoted (2,3,4). Furthermore, in their introduction the authors state that ‘unattained expectations of surgery are thought to play an important role in dissatisfaction after joint replacement’, whereas recent data also suggest the opposite (5).

While the authors acknowledge that there are some methodological weaknesses to their study, we also assert that an ascertainment rate of only 46% is inadequate for drawing a firm conclusion on a study that requires subject reporting. Moreover, the main clinical outcome measure was the SF-36 which is a generic quality of life instrument, and not a disease specific outcome measure. Although there is a physical disability component, it is a poor way of assessing function in patients with osteoarthritis. X-ray grades were reported using the widely used Kellgren and Lawrence method, but grades were collapsed into two categories (0-2 –v- 3+4). Our experience suggests that a graded response was important and that the difference between grades 3 and 4 was particularly so (2).

We look forward to hearing the authors’ response to these points.

Yours sincerely

Michelle Dowsey, Mandy Nikpour, Paul Dieppe and Peter Choong

1. Keurentjes JC, Flocco M, So-Osman C, Onstenk R, Koopman Van Gemert AWMM, Poll RG, Kroon HM, Vlieland TPMV and Nelisson RG. Patients with Severe Radiographic Osteoarthritis Have a Better Prognosis in Physical Functioning after Hip and Knee Replacement: A cohort study. PLOS One 2013; 8(4) e59500
2. Dowsey MM, Nikpour M, Dieppe P, Choong PFM. Associations between pre-operative radiographic changes and outcomes after total knee joint replacement for osteoarthritis. Osteoarthritis and Cartilage 2012; 20; 1095-1102.
3. Valdes AM, Doherty SA, Zhang W, Muir KR, Maciewicz RA, Doherty M. Inverse relationship between preoperative radiographic severity and postoperative pain in patients with osteoarthritis who have undergone total joint arthroplasty. Semin Arthritis Rheum 2011
4. Cushnaghan J, Bennett J, Reading I, Croft P, Byng P, Cox K et al. Long-term outcomes following total knee arthroplasty: a controlled longitudinal study. Ann rheum Dis 2009; 68: 642-7.
5. Judge A, Cooper C, Arden N, Williams S, Hobbs N, Dixon D, Guenther KP, Dreinhoefer K, Dieppe P. Pre-operative expectation predicts 12-month post-operative outcome among patients undergoing primary total hip replacement in European orthopaedic centres. Osteoarthritis and Cartilage 2011; 19: 659-67