Statistical atlas-based morphological variation analysis of the asian humerus: towards consistent allometric implant positioning

Positioning existing humeral implants into Asian patients poses significant challenges due to the inconsistent statistical shapes between Western population and Asian population. Current humeral orthopedic fixation devices and implants have a generic shape and are not designed for Asian patients who exhibit different sizes and shapes compared to their Western counterparts for which present day designs have been based on. To address this problem, it is necessary to develop Asian-specific implants that accommodate the morphology of Asian humeri. Existing morphological studies of humeri in Asian populations are rare and most previous analyses are either based on the manual measurement of dry bones or the use of dual energy X-ray absorptiometry scans. The purpose of this pilot morphological study is to explore the characteristics of Asian humeri using statistical atlas-based analysis. Forty-four CT scans of normal upper limbs were obtained from the National University Hospital, Singapore and used to construct statistical humerus atlases. The atlases were subsequently used to study the morphology of the humeri in an Asian population. Humeral shapes of different patient clusters were analyzed based on statistical shape models. Comparison between different clusters was conducted with regard to centerline, length, width and surface curvature. The statistical humerus atlases reflected the mean shape and modes of variation of humeri in an Asian population. Analyses based on these atlases indicated that curvature and shape of the internal humeral canal were similar in males and females while humeral length and width were greater in males. Most importantly, surface curvatures were explicitly different between clusters. Morphologic analysis based on statistical atlases is novel and useful to characterize the Asian humerus. The humerus demonstrates gender-specific morphology. This unique approach provides information that is useful to the clinician and biomedical engineer, not only in the modification of current or design of future humeral implants, but also in the precise dynamic positioning of Asian-specific humeral implants to Asian patients. Our findings support the need for further development of humeral implants, curvilinear robotics, and the questioning of whether gender-specific devices are necessary.