Equivalent Knee Injury and Osteoarthritis Outcome Scores 12 and 24 Months After Anterior Cruciate Ligament Reconstruction: Results From the Swedish National Knee Ligament Register

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It is not clear whether Knee injury and Osteoarthritis Outcome Score (KOOS) results will be different 1 or 2 years after anterior cruciate ligament (ACL) reconstruction.


To investigate within individual patients enrolled in the Swedish National Knee Ligament Register whether there is equivalence between KOOS at 1 and 2 years after primary ACL reconstruction.

Study Design:

Cohort study; Level of evidence, 2.


This cohort study was based on data from the Swedish National Knee Ligament Register during the period January 1, 2005, through December 31, 2013. The longitudinal KOOS values for each individual at the 1- and 2-year follow-up evaluations were assessed through the two one-sided test (TOST) procedure with an acceptance criterion of 4. Subset analysis was performed with patients classified by sex, age, graft type, and type of injury (meniscal and/or cartilage injury).


A total of 23,952 patients were eligible for analysis after exclusion criteria were applied (10,116 women, 42.2%; 13,836 men, 57.8%). The largest age group was between 16 and 20 years of age (n = 6599; 27.6%). The most common ACL graft was hamstring tendon (n = 22,504; 94.0%), of which the combination of semitendinosus and gracilis was the most common. A total of 7119 patients reported on the KOOS Pain domain at both 1- and 2-year follow-ups, with a mean difference of 0.21 (13.1 SD, 0.16 SE [90% CI, −0.05 to 0.46], P < .001). The same results were found for the other KOOS subscales: symptoms (mean difference −0.54, 14.1 SD, 0.17 SE [90% CI, −0.81 to −0.26], P < .001), activities of daily living (mean difference 0.45, 10.8 SD, 0.13 SE [90% CI, 0.24 to 0.66], P < .001), sports and recreation (mean difference −0.35, 22.7 SD, 0.27 SE [90% CI, −0.79 to 0.09], P < .001), quality of life (mean difference −0.92, 20.0 SD, 0.24 SE [90% CI, −1.31 to −0.53], P < .001), and the combined KOOS-4 score (mean difference −0.41, 14.5 SD, 0.17 SE [90% CI, −0.70 to −0.13], P < .001). Analyses within specific subsets of patients showed equivalent results between the 2 follow-up evaluations.


Equivalent results within patients were found in KOOS values at 1- and 2-year follow-ups after ACL reconstruction. The finding was consistent across all KOOS subscales and for all evaluated subsets of patients. This result implies that there is no additional value in capturing both 1- and 2-year KOOS outcomes after ACL reconstruction. However, these findings of equivalence at 1- and 2-year endpoints do not alleviate the need for longer follow-up periods.

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