Apparent density patterns in subchondral bone of the sloth and anteater forelimb

Department of Biomedical Sciences, Ohio University College of Osteopathic Medicine, Athens, OH 45701, USA.
Biology letters (Impact Factor: 3.25). 10/2008; 4(5):486-9. DOI: 10.1098/rsbl.2008.0297
Source: PubMed


Vertebrate morphologists often are interested in inferring limb-loading patterns in animals characterized by different locomotor repertoires. Because bone apparent density (i.e. mass per unit volume of bone inclusive of porosities) is a determinant of compressive strength, and thus indicative of compressive loading, recent comparative studies in primates have proposed a structure-function relationship between apparent density of subchondral bone and locomotor behaviours that vary in compressive loading. If such patterns are found in other mammals, then these relationships would be strengthened further. Here, we examine the distal radius of suspensory sloths that generally load their forelimbs (FLs) in tension and of quadrupedal anteaters that generally load their FLs in compression. Computed tomography osteoabsorptiometry was used to visualize the patterns in subchondral apparent density. Suspensory sloths exhibit relatively smaller areas of high apparent density than quadrupedal anteaters. This locomotor-based pattern is analogous to the pattern observed in suspensory and quadrupedal primates. Similarity between xenarthran and primate trends suggests broad-scale applicability for analysing subchondral bone apparent density and supports the idea that bone functionally alters its material properties in response to locomotor behaviours.

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Available from: Kristian J Carlson, Oct 13, 2014
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    • "Under compressive loads fibrocartilage differentiates within tendons and ligaments [38]. The absence of fibrocartilage in the SCA in two-toed sloths demonstrates that not only does tensile loading act on the distal limbs [9], but that tension is also transferred to the thorax (Fig. 4). Collagen fibers are differentiated in the SCA of C. didactylus in the same way as Pauwels [37] predicts for a tensile loading regime. "
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    • "In other mammals , researchers have examined variation in subchondral apparent density in the elbow joint of dogs (Samii et al., 2002), as well as the tibial plateau and wrist joint of primates (Ahluwalia, 2000; Carlson and Patel, 2006; Patel and Carlson, 2007), in order to characterize difference in load magnitude, load distribution, and posture. Patel and Carlson (2008) have also examined similar patterns in the wrist joints of sloths and anteaters. Together, these studies demonstrate that subchondral bone can provide information about the loading history of joint surfaces (see also Fischer et al., 1995). "
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