The extensor mechanism may be the key to kinematic alignment of total knee arthroplasty. The purpose of this study was to determine any differences in the direction of the quadriceps vector based on gender or ethnicity and to determine which anatomically derived alignment axis is closest to the quadriceps vector.
Computed tomography scans and patient records for 14 Caucasians (9 men and 5 women) and 40 Japanese (19 men and 21 women) were evaluated. Three axes of alignment—anatomic, mechanical, and spherical—were identified, measured, and compared to the quadriceps vector in each case. Principal component analysis was used to determine the quadriceps vector by using 3-dimensional models of muscles on computed tomography scans.
No statistically significant differences in the orientation of the quadriceps vector were found based on gender or ethnicity, and the quadriceps vector was most closely aligned with the spherical axis.
Because the quadriceps is the primary knee extensor, the spherical axis therefore may be a ubiquitous guide to alignment of the arthroplasty knee based on motion.