Patterns and variations in morphology of glenoid cavity in mammals: Implications for locomotion efficiency

Abstract

The aim of this study was to evaluate and compare the morphology and dimensions of glenoid cavity and examine their relationship with body size  and locomotion efficiency. The study was performed on 356 glenoid cavities from 178 mammals, representatives of all major taxa from rodents, sirenians, marsupials, pilosa, cetaceans, carnivores, ungulates, primates and apes. Parameters measured included cranio-caudal and lateral-medial diameters and their ratios; areas of articular surfaces; glenoid cavity index; angles-alpha, -beta and -gamma and length of supraglenoid tubercle and coracoid process. Images were taken using computed tomographic (CT) scanning technology (CT-Aquarium, Toshiba and micro CT- LaTheta, Hotachi, Japan) and measurement values were acquired and processed using Avizo computer software and CanvasTM 11 ACD systems. Statistical analysis was performed using Microsoft Excel 2013. Results obtained showed that mammals exhibit various patterns in the morphology of glenoid cavities that may be associated with adaptation of the glenohumeral joint to robust mobility for locomotion. When the diameters of glenoid cavities were compared between groups of mammals, significant difference was observed in diameters of articular surfaces between rodents and ungulates (1.34±0.32); carnivores and primates (1.39±0.16); primates and rodents and carnivores (1.3±0.12) and between ungulate and carnivores, rodents and primates (1.19±0.18). The mean values of glenoid cavity index in ungulates were found to be lower (0.15±0.13) than those of carnivores (0.22±0.71)  and apes (0.26±0.16), indicating that the depth of glenoid cavities of ungulates is shallow compared to those of carnivores and apes. The inclination of the scapula relative to the trunk was found to be tilted lateromedially in apes; mediolaterally in primates (monkeys); craniocaudally in carnivores; vertically in ungulates and cranially in diggers. Significantly, the angles were wider in apes but narrower in ungulates. The length of supraglenoid  tubercle was long in ungulates but short in carnivores while the coracoids process was short in ungulates but long in primates and moderately in carnivores and other mammals. The morphological characteristics of the glenoid cavities and the functional interpretation of the parameters in mammals are discussed in detail.

Keywords: Mammalian, Glenoid cavity, Morphology, CT analysis