Abstract
Introduction: Classical studies have defined axes from prominent scapular landmarks that have been used to synthesise many applications. The morphology of the scapula is however known to be highly variable between individuals1,2,3. This introduces significant variability on the use of these classical axes for various clinical applications. Also, some of the literatureapplied landmarks were highly dependant on the presence of pathology, thus introducing more variability in the products they parented. This limits accuracy in inter-subject comparisons from such applications. Therefore there is a need to identify and define pathology-insensitive anatomical landmarks that are less variable between individuals than the variability of the overall scapular shape. The aim of this study was to define more scapular axes from clearly identifiable landmarks, analysing these and other classical definitions for the best axis that minimizes variability and is closely related to the scapular clinical frame of reference.
Materials and Method: Fourteen different axes of new and classical definitions from clearly identifiable landmarks were quantified by applying medical images of 21 scapulae. The orientations of the quantified axes were calculated. The plane of the blade of the scapula was defined, bounded by the angulus inferior4, the spine/medial border intersection5 and the most inferolateral point of the infra-glenoid tubercle. This was applied to grade the alienation of the quantified axes from the scapular blade. The angular relationships between individual axes of a spcapula were quantified, averaged over the 21 specimens and their standard deviations (SD) applied to grade the sensitivity of each axis to interscapular variations in the others. The volume of data required to define an axis (VDA) was noted for its dependency on pathology. These three criteria were weighted according to relative importance such that
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axes bearing 10° or more from the blade deviated significantly and were eliminated;
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insensitivity to scapular morphological variations based on the smallest SD and axes applicability in pathology based on VDA of the remaining axes were graded for the final result.
Results: A least square line through the centre of the spine root was the most optimal medio-lateral axis. The normal to the plane formed by the spine root line and a least square line through the centre of the lateral border ridge was the most optimal antero-posterior axis.
Conclusion: These body-fixed axes are closely aligned to the cardinal planes6 in the anatomical position and thus are clinically applicable, specimen invariant axes that can be used in generalised and patient-specific kinematics modelling.
Correspondence should be addressed to Diane Przepiorski at ISTA, PO Box 6564, Auburn, CA 95604, USA. Phone: +1 916-454-9884; Fax: +1 916-454-9882; E-mail: ista@pacbell.net
References:
1 Gallino et al., 1998; J Should Elbow Surg7, 284–291. Google Scholar
2 Monk et al., 2001; Clin Anat14, 320–323. Google Scholar
3 Stehle et al., 2007; J Should Elbow Surg16, 135–142. Google Scholar
4 Wu et al., 2005; J Biomech38, 981–992. Google Scholar
5 Wong et al., 2003; J Should Elbow Surg12, 360–364.CrossrefPubMed Google Scholar
6 Amadi et al., 2008; J Biomech41, 2144–2149. Google Scholar
