A novel method for quantifying femoral neck anteversion: A case study in extinct and extant sloths

Abstract

The anteriorly‐projecting femoral head/neck of some extinct sloths has been noted; however, neck angle has never been quantified from a 3D perspective, despite its potential usefulness in taxonomic and functional interpretations. Here, we present a method to quantify femoral neck torsion in extinct and extant sloths. Seventy femora from four genera of extinct (n=49; Megalocnus, Parocnus, Neocnus, Acratocnus) and two genera of extant (n=21; Bradypus, Choloepus) sloths were scanned to create virtual surface models. These models were used to extract morphological and biomechanical axes, such as neck axis, shaft axis, transepicondylar axis (TEA), maximum shaft cross‐sectional dimension at 35% of bone length and an axis between the greater and lesser trochanters. The shaft axis was used to define a transverse plane through the bone to which all other axes were projected. The angles between the neck axis and other three axes were calculated. Multiple angles were calculated to prevent any particular region of the bone from biasing results. Genera were compared using ANOVAs with post hoc multiple comparisons and Bonferroni corrections. Significant differences among species exist for all angles (p<0.001). Multiple comparison results are the same for TEA and cross‐section angles for all but three genera. When Parocnus is compared to Megalocnus and Neocnus only the TEA angle is significant, however for the Megalocnus/Neocnus comparison only the cross‐section angle is significant. These results suggest the condyles are twisted relative to the shaft in these genera. Some genera were significantly different in only trochanter angle, suggesting this angle is capturing a different aspect of morphology. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Functional morphology of the hindlimb of fossilized pygmy hippopotamus from Ayia Napa (Cyprus)

“…P. minor has a prominent "anteverted" femoral neck, similar to that of large-sized Hippopotamus species, but clearly more distinct than in C. liberiensis and H. lemerlei. The femoral anteversion is associated with a more medial inclination of the hindlimb in P. minor, as it occurs in other animals (Harper et al, 2020;Tayton, 2007). Additionally, the neck anteversion can also be related to a more flexed placement of the femur in a standing position for Cypriot hippo, consistent with a more crouched stance in animals with lower body mass (e.g., Álvarez et al, 2013;Biewener, 1989).…”

“…The estimated indices are presented in Tables 5 and 6. The calculation of the femoral anteversion was performed by measuring the angle between the femoral neck axis and the axis of the femoral condyles, following one of the methods that Harper et al (2020) have proposed. The rotation angle of the astragalus on the distal epiphysis of the tibia was estimated by manipulating the skeletal material, and then, the created angle was drawn on paper and measured by a protractor.…”

Accuracy of CT for measuring femoral neck anteversion in children with developmental dislocation of the hip verified using 3D printing technology

“…There are many FNA measuring methods which still remain controversial [ 3 , 9 , 10 ]. Initially, FNA measurement was usually done by biplane X-ray method.…”