Background: The proportion of patients perceiving their symptoms as either acceptable or as a failure of treatment after anterior cruciate ligament reconstruction (ACLR) is unknown. Commonly used outcome scores such as the Knee injury and Osteoarthritis Outcome Score (KOOS) suffer from poor interpretability, and little is known about which scores represent an acceptable or failed postoperative outcome.
Purpose: To determine the proportion of patients reporting acceptable symptoms or treatment failure at 6 to 24 months after ACLR and to define KOOS values corresponding to the patients’ perceptions of treatment outcome.
Study Design: Cross-sectional study; Level of evidence, 3. 
Methods: In 2012, a total of 1197 patients were randomly extracted from the Norwegian Knee Ligament Registry at 3 postoperative time points: 397 at 6 months, 400 at 12 months, and 400 at 24 months. The inclusion criterion was unilateral primary ACLR. Questions about acceptable symptoms and treatment failure and the KOOS questionnaire were sent to the patients, and those who answered “yes” to the acceptable symptoms question were considered to have acceptable symptoms. Patients who answered “no” to the same question and “yes” to the treatment failure question were considered to have treatment failure. Mean KOOS values and 95% CIs were calculated for each category.