Systemic versus local patterns of limb joint articular morphology inferred from relative distances from morphological centroid.

Joint morphogenesis is a complex process known to require the interaction of developmental cascades and mechanical loading, yet many details of this interaction are incompletely understood. While prior work has established populational patterns of joint morphological (co)variance, exploring how these patterns manifest within the individual provides information on the deployment of morphogenic processes as either systemic or local influences on joint shape. To better identify the patterns of variance-generating morphogenic processes, this study investigates the degree to which individual joint shapes deviate from population averages systematically across the body. Using three-dimensional landmark data from 200 adult skeletons, we ranked individuals based on their distances from morphological centroids for eight major joints. Spearman correlations assessed associations between ranks across various articular pairings, testing hypotheses regarding systemic versus localized variance. Results reveal low coordination between deviations observed in conarticular surfaces, functional analogs, and same-bone surfaces; however strong associations exist between antimeres, suggesting the left-right deployment of variance-generating morphogenic patterns is highly consistent. These results support a model of localized rather than systemic processes driving variation in joint shape. While more remains to be elucidated about the specifics of articular surface morphogenesis, these findings advance our understanding of the systems of variance generation at play during development and growth of our definitive joint morphology.

Covariance in human limb joint articular morphology.

OBJECTIVES: Limb synovial joints exhibit complex shapes that must accommodate often-antagonistic demands of function, mobility, and stability. These demands presumably dictate coordination among joint articular shapes, but the structure of morphological covariance within and among joints is unknown. This study analyzes the human shoulder, elbow, hip, and knee to determine how articular covariance is structured in relation to joint structure, accessory cartilage, and function. MATERIALS AND METHODS: Surface models were created from the CT scans of 200 modern skeletons from the University of Tennessee Donated Skeletal Collection. Three-dimensional landmarks were collected on the shoulder, elbow, hip, and knee joints. Two-block partial least squares were conducted to determine associations between surfaces of conarticular shapes, functionally analogous articulations, and articulations belonging to the same bone. RESULTS: Except for the components of the shoulder, all conarticular pairs exhibit covariance, though the strength of these relationships appears unrelated to the amount of accessory cartilage in the joint. Only the analogous articulations of the humerus and femur exhibit significant covariance, but it is unlikely that this pattern is due to function alone. Stronger covariance within the lower limb than the upper limb is consistent broader primate patterns of within-limb integration. DISCUSSION: With the exception of the elbow, complementary joint function does not appear to promote strong covariance between articulations. Analogous humeral and femoral surfaces are also serially homologous, which may result in the articular associations observed between these bones. Broadly, these patterns highlight the indirect relationship between joint congruence and covariance.

Variation in human limb joint articular morphology.

OBJECTIVES: Synovial joints in human limbs strike a balance between mobility, stability, and articular fit, yet little is known about how these conflicting demands pattern intraspecific variation in articular shape. In this study, we use geometric morphometrics to establish the apportionment and magnitude of morphological variance of the articular surfaces of the human shoulder, elbow, hip, and knee. We hypothesize that variances will be comparable between articulating surfaces within a joint and will be larger in joints with smaller ranges of motion, given their plurality of functional demands. MATERIALS AND METHODS: Three-dimensional landmarks were taken on the articular surfaces of the glenohumeral, humeroulnar, acetabulofemoral, and tibiofemoral joints from CT scans of 200 skeletons from the University of Tennessee Donated Skeletal Collection (84 females, 116 males). Root mean-squared distances between articulations calculated from Procrustes shape coordinates were used to determine variance distributions. RESULTS: We found no difference in variances for each articular surface between the sexes or between left and right articular surfaces. A high range of motion is associated with greater morphological variance; however, this pattern is largely driven by the concave articular surfaces of each joint, which consistently exhibit statistically greater variance than their convex counterparts. DISCUSSION: The striking pattern of differential variance between articulating morphologies points to potential disparities in development between them. Consistently higher variance in concave surfaces may relate to chondral modeling theory for the formation of joints. Establishing intraspecific morphological variance patterns is a first step in understanding coordinated evolution among articular features.

The Influence of Body Size on the Expression of Sexually Dimorphic Morphological Traits.

Skeletal sexual dimorphism manifests as size or shape differences between males and females in a population. Certain dimorphic traits are used in sex estimation methods, and populational variation in the expression of these traits can result in inaccurate sex estimation. However, the underlying causes of variation in trait expression remain unclear. This study explores body size, which also exhibits sexual dimorphism, as a potential factor influencing trait expression. To test this, skeletons of 209 individuals of varying body size were analyzed, and morphological traits were scored according to the Walker (2008), Klales et al. (2012), and Rogers (1999) sex estimation methods. Statistical analyses found significant correlations between body size parameters and expression of traits, with stature explaining more relative variance in trait expression than body mass. However, the relationships are weak and few in number, suggesting that body size has a minimal impact on the expression of these morphological traits.