Table 2.

Reference axes or measurement methods of normal patellar tracking (from 2005).

References	Reference axes of shift	Reference axes or measurement methods of flexion	Reference axes or measurement methods of tilt	Reference axes or measurement methods of rotation
Laprade and Lee [37]	TEA	—	—	—
Nha et al. [31]	TEA	TEA	Longitudinal axis of the patella	AP axis of the patella
Wilson et al. [38]	TEA	TEA	Longitudinal axis of the patella	Floating axis perpendicular to the first two axes
Suzuki et al. [30]	TEA	The angle between the superior-inferior axis of the patella and long axis of the femur projected onto the sagittal plane of the femur	The angle between the ML axis of the patella and the TEA projected onto the transverse plane of the femur	The angle between the ML axis of the patella and the TEA of the femur projected onto the coronal plane of the femur
Yao et al. [32]	TEA	TEA	Longitudinal axis of the patella	AP axis of the patella
Amis et al. [39]	Axis perpendicular to the long axis of the femoral shaft and parallel to the plane containing the most posterior points of the femoral condyles	Same to the axis of shift	Longitudinal axis of the patella	Floating axis perpendicular to the first two axes
Merican and Amis [15]	Axis aligned with the most posterior points of the femoral condyles	Same to the axis of shift	Longitudinal axis of the patella	AP axis crossing geometric center of the patella
Philippot et al. [40]	TEA	—	Longitudinal axis of the patella	AP axis of the patella
Philippot et al. [41]	—	—	—	AP axis of the patella
Philippot et al. [42]	ML axis of patella	—	Longitudinal axis of the patella	AP axis of the patella
Stephen et al. [43]	—	—	Longitudinal axis of the patella	—
Cheung et al. [44]	TEA	TEA	The line joining the greater trochanter and midpoint between two femoral epicondyles	Cross product of the first two axes