Abstract
The identification of femoral landmarks is a common procedure in multiple academic fields. Femoral bone coordinate systems are used particularly in orthopedics and biomechanics, and are defined by landmarks, axes and planes. A fully automatic detection overcomes the drawbacks of a labor-intensive manual identification. In this paper, a new automatic atlas- and a priori knowledge-based approach that processes femoral surface models, called the A&A method, was evaluated. The A&A method is divided in two stages. Firstly, a single atlas-based registration maps landmarks and areas from a template surface to the subject. In the second stage, landmarks, axes and planes that are used to construct several femoral bone coordinate systems are refined using a priori knowledge. Three common femoral coordinate systems are defined by the landmarks detected. The A&A method proved to be very robust against a variation of the spatial alignment of the surface models. The results of the A&A method and a manual identification were compared. No significant rotational differences existed for the bone coordinate system recommended by the International Society of Biomechanics. Minor significant differences of maximally 0.5° were observed for the two other coordinate systems. This might be clinically irrelevant, depending on the context of use and should, therefore, be evaluated by the potential user regarding the specific application. The entire source code of the A&A method and the data used in the study is open source and can be accessed via https://github.com/RWTHmediTEC/FemoralCoordinateSystem.
Highlights
The identification of femoral landmarks is a common procedure in multiple academic fields
The median manual method’s differences (MMD) of the Euclidian distance to the reference landmarks ranged from 0.3 mm for the femoral head center (FHC) to 4.4 mm for the MEC
Excluding the point of the trochanteric crest (PTC), superior point of the greater trochanter (SGT) and lesser trochanter (LT), the median differences of the Euclidian distance between the landmarks determined by the A&A method (AMD) and the reference landmarks ranged from 0.4 mm for the FHC to 4.0 mm for the MEC
Summary
The identification of femoral landmarks is a common procedure in multiple academic fields. Femoral bone coordinate systems are used in orthopedics and biomechanics, and are defined by landmarks, axes and planes. A new automatic atlas- and a priori knowledge-based approach that processes femoral surface models, called the A&A method, was evaluated. Landmarks, axes and planes that are used to construct several femoral bone coordinate systems are refined using a priori knowledge. Automatic methods for landmark detection should provide reproducible results, be robust against the spatial alignment of the femur and handle the large interindividual v ariability[17] of the femoral morphology. For the sake of clarity, this paper deals with the fully automatic identification of femoral landmarks and parameters based on a three-dimensional (3D) surface model. A robust identification method has to consider that the anatomical planes of the patient can differ highly from the coordinate system of the medical imaging system and that the anatomical orientation of the coordinate system of the medical imaging system can vary
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