Comparison of three formal methods used to estimate the functional axis of rotation: an extensive in-vivo analysis performed on the knee joint

Abstract

Estimating the main axis of rotation (AoR) of a human joint represents an important issue in biomechanics. This study compared three formal methods used to estimate functional AoR, namely a cylindrical fitting method, a mean helical axis transformation, and a symmetrical axis approach. These methods were tested on 106 subjects undergoing navigated total knee arthroplasty. AoR orientation in 3D and in the frontal and coronal planes provided by each method was compared to the transepicondylar axis direction. Although all the methods resulted effective, significant differences were identified among them, relatively to the orientation in 3D and in the frontal plane projection. This was probably due to the presence of secondary rotations during the first degrees of knee flexion.

Keywords:

• functional axis
• cylindrical fitting method
• mean helical axis
• symmetrical axis approach
• knee kinematics
• navigated TKA

Acknowledgement

The authors would like to thank Emil “Systemystic” Ferretti for his contribution to the lab IT management.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was partially supported by the “5 × 1000” (2011) funding, provided by Istituto Ortopedico Rizzoli, Bologna (Italy).