Stress fractures (SFxs) are debilitating injuries and exact mechanisms that initiate their repair incompletely understood. We hypothesised that osteocyte apoptosis and expression of cytokines and proteins such as sclerostin, VEGF, TGF-β, COX-2 and IL-6 were early signalling events to facilitate the formation of periosteal woven bone and recruitment of osteoclast precursors to the site of remodelling. A SFx was created in the right ulna of mature female wistar rats using cyclic end loading. Rats were killed 1, 4 and 7 days after loading (n=5 per group). Standard histological staining was used to examine SFx morphology and immunohistochemistry to detect the localisation of these proteins and in situ hybridisation to detect mRNA along the SFx line or gene expression to quantify the target genes. Unloaded ulnae served as controls. The labelling index of caspase-3, COX-2 and IL-6 was significantly elevated in the region of SFxs at all time points compared with controls (P<0.001). In addition, the labelling index of sclerostin protein was significantly reduced in osteocytes adjacent to the SFx region when compared with controls at all three time points (P<0.001). Both VEGF and TGF-β expressions were only localised in the woven bone. These data reinforce the involvement of osteocyte apoptosis in the healing of fatigue damage in bone, and demonstrate that local regulation of sclerostin, COX-2 and IL-6 are important signalling events associated with new bone formation and SFx remodelling.

Anomalous muscular variants of pectoralis major have been reported on several occasions in the medical literature. Among them, chondroepitrochlearis is one of the rarest. Therefore, this study aims to provide a comprehensive description of its anatomy and subsequent clinical significance, along with its phylogenetic importance in pectoral muscle evolution with regard to primate posture. The authors suggest a more appropriate name to better reflect its proximal attachment to the costochondral junction and distal attachment to the epicondyle of humerus, as “chondroepicondylaris”; in addition, we suggest a new theory of phylogenetic significance to explain the twisting of pectoralis major tendon in primates that may have occurred with their adoption to bipedalism and arboreal lifestyle. Finally, the clinical significance of this aberrant muscle is elaborated as a cause of potential neurovascular entrapment and as a possible hurdle during axillary surgeries (i.e., mastectomy).

Load-induced extravascular fluid flow has been postulated to play a role in mechanotransduction of physiological loads at the cellular level. Furthermore, the displaced fluid serves as a carrier for metabolites, nutrients, mineral precursors and osteotropic agents important for cellular activity. We hypothesise that load-induced fluid flow enhances the transport of these key substances, thus helping to regulate cellular activity associated with processes of functional adaptation and remodelling. To test this hypothesis, molecular tracer methods developed previously by our group were applied in vivo to observe and quantify the effects of load-induced fluid flow under four-point-bending loads. Preterminal tracer transport studies were carried out on 24 skeletally mature Sprague Dawley rats. Mechanical loading enhanced the transport of both small- and larger-molecular-mass tracers within the bony tissue of the tibial mid-diaphysis. Mechanical loading showed a highly significant effect on the number of periosteocytic spaces exhibiting tracer within the cross section of each bone. For all loading rates studied, the concentration of Procion Red tracer was consistently higher in the tibia subjected to pure bending loads than in the unloaded, contralateral tibia. Furthermore, the enhancement of transport was highly site-specific. In bones subjected to pure bending loads, a greater number of periosteocytic spaces exhibited the presence of tracer in the tension band of the cross section than in the compression band; this may reflect the higher strains induced in the tension band compared with the compression band within the mid-diaphysis of the rat tibia. Regardless of loading mode, the mean difference between the loaded side and the unloaded contralateral control side decreased with increasing loading frequency. Whether this reflects the length of exposure to the tracer or specific frequency effects cannot be determined by this set of experiments. These in vivo experimental results corroborate those of previous ex vivo and in vitro studies. Strain-related differences in tracer distribution provide support for the hypothesis that load-induced fluid flow plays a regulatory role in processes associated with functional adaptation.

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