Changes in the rotational axes of the tibiofemoral joint caused by resection of the anterior cruciate ligament

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Kinematic alignment is a method of aligning implants in total knee arthroplasty (TKA) that strives to restore the native flexion–extension (F–E) and longitudinal rotation (LR) axes of the tibiofemoral joint. The anterior cruciate ligament (ACL) is typically resected at the time of TKA, which might change the position, and orientation of these axes from that of the native knee. Our objective was to determine whether resecting the ACL causes changes in the F–E and LR axes. A custom designed and validated instrumented spatial linkage (ISL) measured the F–E and LR axes in nine cadaveric knees before and after ACL resection. Changes in these axes were computed for knee flexion from 0° to 120°. For the F–E axis, the two statistically significant yet relatively small changes were internal rotation of 0.5° (p = 0.02) and posterior translation of 0.3 mm (p = 0.04). For the LR axis, the statistically significant and relatively large change was medial translation of 2.1 mm (p = 0.01). Changes to the LR axis in both medial-lateral position and varus-valgus orientation varied widely; 77% of a population of knees would have a medial–lateral position change greater than 1 mm, and 53% of a population of knees would have a varus–valgus orientation change greater than 1°. Knowledge of changes of the F–E and LR axes caused by resecting the ACL provides an important baseline for determining the changes in these axes caused by kinematic alignment and mechanical alignment of bi-cruciate retaining, posterior cruciate retaining, and posterior cruciate substituting implants. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res

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