Anatomical Reference Frames for Long Bones: Biomechanical Applications

The definition of anatomical reference frames is necessary both for in vitro biomechanical testing, and for in vivo human movement analyses. Different reference frames have been proposed in the literature, for the different applications. Reference frames for in vivo use must rely on anatomical landmarks that can be accessed non-invasively in living subjects. This limits the operator to certain regions of the bone segments, and possibly to anatomical landmarks that are scarcely reproducible. Conversely, when the bone is fully accessible in vitro, direct measurements are possible of diameters, lengths, and angles. This enables the selection of anatomical reference planes that rely upon anatomical landmarks that are better reproducible. In this section, anatomical reference frames are discussed for the most important long bones of the human skeleton: femur, tibia, fibula, metatarsal bones, humerus, radius, ulna, metacarpal bones, and phalanges. The different reference frames proposed for each bone segment are discussed: this includes the guidelines proposed by the Standardization and Terminology Committee of the International Society of Biomechanics (ISB) for in vivo movement analysis, and also reference frames proposed by different authors for in vitro testing. Optimal reference frames are proposed for each bone segments. Detailed guidelines (including suggested materials and methods) are provided to correctly identify the anatomical landmarks and the anatomical frames. For each bone segment, an estimate of the intra-operator repeatability (i.e. when the same operator repeatedly identifies the reference frame on the same specimen) and of the inter-operator repeatability (i.e. when different operators identify the reference frame on the same specimen) is reported for the recommended reference frame. This confirms the reliability of the approach proposed.