Younger age and hamstring tendon graft are associated with higher IKDC 2000 and KOOS scores during the first year after ACL reconstruction

Purpose: Although reference values in healthy subjects have been published for both the International Knee Documentation Committee 2000 subjective knee form (IKDC 2000) and the Knee injury and Osteoarthritis Outcome Score (KOOS), data obtained during the first year after anterior cruciate ligament reconstruction (ACL-R) are sparse. The aim was to establish patient reference values for both questionnaires at different time points and depending on nine individual patient characteristics during the first year after ACL-R. Methods: Prospectively recorded data from a hospital-based registry were retrospectively extracted from the database. IKDC 2000 and KOOS questionnaires were self-administered pre-operatively and 6 weeks, 3 months, and 6 and 12 months following primary ACL-R. Score values were compared according to nine individual patient criteria: gender, age, body mass index, level of activity, involvement in competition, previous contralateral knee injury and/or surgery, graft type, meniscal repair and/or cartilage lesions. The feature which had a significant and consistent impact on the outcomes was considered as main reference. Results: Two-hundred and nighty-eight patients met the inclusion criteria. Overall, the score values increased over time after ACL-R. At 12 months, they were significantly greater than at any other time point (p < 0.05). The main individual feature influencing the IKDC 2000 score was age. Patients below 30 years of age had up to 9 points higher IKDC 2000 score values at all time points (p < 0.05). The main individual characteristic influencing the KOOS score was graft type. Patients with hamstring tendon grafts (STGR) had up to 15 points higher KOOS score values than patients with bone–patellar tendon–bone (BPTB) grafts during the first months after ACL-R (p < 0.05). At 12 months, no differences in KOOS score values could be identified anymore. Conclusions: Younger age (< 30 years) and STGR grafts were related to higher IKDC 2000 and KOOS score values within the first year after primary ACL-R. The patient reference values adjusted to age and graft provided in this study may help to identify patients with lower outcomes within the first year after ACL-R. Level of evidence: Level III.