A prediction model for the 40-year risk of knee osteoarthritis in adolescent men.

OBJECTIVES: To simplify the previously published Nottingham 12-year risk prediction model for knee osteoarthritis (OA) and examine whether it can be used to predict the 40-year risk of knee OA in young men.

METHODS: We included 40 118 men aged 18 undergoing military conscription in Sweden 1969-70. Diagnostic OA codes were obtained from the Swedish National Patient Register 1987-2010. The original Nottingham model included predictors age, sex, body mass index (BMI), knee injury, occupational risk and family history of OA with area under receiver operating characteristics curve (AUC)=0.70, 95% CI=0.61-0.79 in the model development sample and AUC=0.60, 95% CI=0.58-0.63 in an external validation sample. We used predictors available in adolescence only (age, BMI and knee injury) and studied the discrimination of the simplified model using AUC in our sample.

RESULTS: The AUC-statistic of the modified knee OA model to predict 40-year risk was 0.60 (95% CI=0.59-0.61). Hence, using the reduced model; an 18-year old man having a BMI of 30 and a knee injury would have a three times higher risk of developing knee OA within 40 years compared to a similarly aged man having a BMI of 25 and no knee injury (predicted risks 22% and 7%, respectively).

CONCLUSION: The individual and population 40-year risk of knee OA is predictable in 18-year olds from a few easily measured covariates with moderate discrimination. The discrimination of this simplified model based on data available in adolescence was comparable to that of the full Nottingham model in middle age. This article is protected by copyright. All rights reserved.