Brief communication: Developmental versus functional three‐dimensional geometric morphometric‐based modularity of the human proximal humerus

Abstract

The proximal humerus is formed by three secondary ossification centers during the postnatal trajectory of the human infant. The ossification centers later grow into the structures of the articular surface, major tubercle, and minor tubercle. There is a purported functional division between the articular surface and the tubercles, with the articular surface mainly responsible for the range of movement of the shoulder joint, and the tubercles bearing the insertions of the rotator cuff muscles, mainly devoted to securing the joint against humeral displacement. Using three-dimensional geometric morphometrics, we tested the presence of such developmental and functional divisions in the proximal humerus, applying the RV coefficient of Escoufier to these a priori hypothesized modules. Our results indicate that the proximal humerus might be a generally integrated structure. However, a weak signal for modular configuration was present, with slightly stronger support for the two modules depicting the boundaries between the purported functional regions of the epiphysis: the articular surface and the tubercles.

In search of morphological modules: a systematic review

“…Various studies approach the modularity of limbs by comparing patterns of morphological integration among these three units in the same limb, between left and right limbs, or between forelimb and hindlimb (see also Goswami et al , ; Martín‐Serra et al , ). A less‐common approach is the study of modularity within a single bone, such as the scapula (Young, ), the humerus (Árias‐Martorell et al , ), and the tibia (Tallman et al , ).…”

Shape Covariation (or the Lack Thereof) Between Vertebrae and Other Skeletal Traits in Felids: The Whole is Not Always Greater than the Sum of Parts

“…Modularity is a prevailing characteristic of the vertebral column in felids (Randau et al 2016a ; Randau and Goswami 2017a , b ), and most likely of mammals in general (Buchholtz 2007 ; Buchholtz et al 2012 ). In fact, modular organisation is ubiquitous across multiple levels of structures in the skeleton of organisms, observed across functionally linked elements (e.g., modular organisation within entire limbs; Schmidt and Fischer 2009 ; Fabre et al 2014 ; or across the vertebral column; Randau and Goswami 2017a ) and within different components of individual elements (e.g., within the skull; Goswami 2006a ; Goswami and Polly 2010a ; within humeral shape; Arias-Martorell et al 2014 ; or within vertebrae; Randau and Goswami 2017b ). It may therefore be hypothesised that modularity is a universal characteristic of complex traits and may be expected to exist at even higher levels of organisation within organisms, such as between the vertebral column and the limbs or the skull.…”

Ossification center of the humeral shaft in the human fetus: a CT, digital, and statistical study

“…The proximal end of the humerus develops from the three secondary ossification centers located in its head, greater and lesser tubercles [ 34 ], with the fusion of these ossification centers starting at the age of 3 years and progressing in the anteroposterior direction. The humeral head ossification center appeared between the age of 6 and 20 months, while the ossification centers in the greater and lesser tubercles appeared between the age of 1 and 3 years [ 1 ]. However, earlier ossification was reported in a radiographic study by Ogden et al [ 28 ] in human cadavers ranging from full-term stillborn to fourteen years old, in which the ossification of the humeral head began between the age of 2 and 3 months, while that of the greater tubercle began at the age of roughly 7 months.…”