Background Total knee arthroplasty (TKA) surgery accounts for a great part of the costs related to knee osteoarthritis (KOA). There is a scarcity of data on the association between overweight/obesity and clinical progression from KOA diagnosis to TKA.
Objectives We aimed to study the association between overweight/obesity at the time of KOA diagnosis and risk of TKA.
Methods We conducted a retrospective population-based cohort study.
The SIDIAP Database comprises all clinical information as collected in primary care records, and hospital admissions for >5 million people (80% of the population) in Catalonia (Spain).
SIDIAP participants with an incident diagnosis of KOA in 2006-2011 were included, and followed until the end of 2011. Participants with a history of inflammatory arthritis were excluded.
The body mass index (BMI) measurement registered closest to the date of KOA diagnosis was defined as baseline BMI, and categorized following the WHO classification into: normal (<25 kg/m2), overweight(25 to <30), obese I(30 to <35), obese II(35 to <40), and obese III(>=40 kg/m2).
Multivariable Cox regression was used to estimate Hazard Ratios (HR) according to BMI category, after adjustment for: age, gender, smoking, alcohol drinking, Charlson co-morbidity index, hip OA, polyarthritic OA, and socio-economic status. We tested for a priori defined interactions with median age (68 years) and gender.
Results 105,189 participants were studied for a median (inter-quartile range) 2.6 (1.3-4.2) years, and 7,512(7.1%) underwent TKA in this time.
Multivariable adjusted HRs for risk of TKA were: 1.41 [95%CI 1.27-1.57] for overweight, 1.97 [1.78-2.18] for obese I, 2.39 [2.15-2.67] for obese II, and 2.67 [2.34-3.04] compared to normal-weight patients (reference group).
The effect of BMI on risk of TKA was stronger (p for interaction<0.0001) amongst younger participants (HR 1.64 [1.34-2.03], 2.71 [2.21-3.32], 3.61 [2.92-4.45], and 4.17 [3.33-5.23] for overweight, obese I, II and III respectively). No interactions were found with gender.
Conclusions BMI is a strong predictor of clinical progression from KOA diagnosis to TKA: overweight patients are at >40% increased risk of surgery, and the obese have a more than doubled risk compared to KOA patients with normal weight.
This excess risk is stronger in younger patients. Weight reduction strategies could have a big impact on the need for surgery in KOA, especially for younger patients.
Disclosure of Interest D. Prieto-Alhambra Grant/research support from: Unrestricted grant from BIOIBERICA SA, K. Leyland: None Declared, A. Judge: None Declared, M. K. Javaid: None Declared, C. Cooper: None Declared, N. Arden: None Declared