Trends in arthroscopy-documented cartilage injuries of the knee and repair procedures among 15-60-year-old patients.

We validated a registry-based method of identifying patients with knee cartilage injury and estimated temporal changes in the incidence of arthroscopy-documented cartilage injuries of the knee and the proportion leading to repair procedures in Denmark. After excluding patients with diagnosed osteoarthritis, we identified 21,392 patients aged 15-60 years with a first recorded procedure code indicating knee cartilage injury in the Danish National Registry of Patients (DNRP) from 1996 to 2011. Using the surgical descriptions of arthroscopy findings in medical records as gold standard, the positive and negative predictive value of procedure codes for knee cartilage injury was 88% and 99%, respectively. The arthroscopy-documented overall incidence of cartilage injury of the knee was 40/100,000 person-years (py) [95% confidence interval (CI): 39.5-40.6] during the period 1996-2011. The arthroscopy-documented age-standardized annual incidence of knee cartilage injury increased from 22 (95% CI: 20.5-23.7) in 1996 to 61 (95% CI: 58.7-64.0) in 2011, per 100,000 py. An increase occurred in all age groups and both sexes. Only 1/6 (17%) patients with knee cartilage injury had a repair procedure. The validity of procedure codes for knee cartilage injury in the DNRP is high. The arthroscopy-documented incidence of knee cartilage injuries increased substantially during the 15-year period.