The Achilles tendon is one of the most frequently injured tendons in humans, and yet the mechanisms underlying its injury are not well understood. This study examines the ex vivo mechanical behavior of excised human Achilles tendons to elucidate the relationships between mechanical loading and Achilles tendon injury. Eighteen tendons underwent creep testing at constant stresses from 35 to 75 MPa. Another 25 tendons underwent sinusoidal cyclic loading at 1 Hz between a minimum stress of 10 MPa and maximum stresses of 30-80 MPa. For the creep specimens, there was no significant relationship between applied stress and time to failure, but time to failure decreased exponentially with increasing initial strain (strain when target stress is first reached) and decreasing failure strain. For the cyclically loaded specimens, secant modulus decreased and cyclic energy dissipation increased over time. Time and cycles to failure decreased exponentially with increasing applied stress, increasing initial strain (peak strain from first loading cycle), and decreasing failure strain. For both creep and cyclic loading, initial strain was the best predictor of time or cycles to failure, supporting the hypothesis that strain is the primary mechanical parameter governing tendon damage accumulation and injury. The cyclically loaded specimens failed faster than would be expected if only time-dependent damage occurred, suggesting that repetitive loading also contributes to Achilles tendon injuries.
The results of this study show that the X STOP interspinous process implant prevents narrowing of the spinal canal and foramina in extension.
This investigation used capsaicin to selectively lesion unmyelinated sensory neurons in rats. Neuronal lesioning induced a loss of trabecular integrity, reduced bone mass and strength, and depleted neuropeptides in nerve and bone. These data suggest that capsaicin-sensitive sensory nerves contribute to trabecular bone integrity.Introduction: Familial dysautomia is an autosomal recessive disease in which patients suffer from unmyelinated sensory neuron loss, reduced BMD, and frequent fractures. It has been proposed that the loss of neurotransmitters synthesized by unmyelinated neurons adversely affects bone integrity in this hereditary syndrome. The purpose of this study was to determine whether small sensory neurons are required for the maintenance of bone integrity in rats. Materials and Methods: Ten-month-old male Sprague-Dawley rats were treated with either capsaicin or vehicle. In vivo DXA scanning and CT scanning, and histomorphometry were used to evaluate BMD, structure, and cellular activity. Bone strength was measured in distal femoral sections. Body weight and gastrocnemius/soleus weights were measured and spontaneous locomotor activity was monitored. Peroneal nerve morphometry was evaluated using light and electron microscopy. Substance P and calcitonin generelated peptide (CGRP) content in the sciatic nerve and proximal tibia were determined by enzyme immunoassay (EIA). Substance P signaling was measured using a sciatic nerve stimulation extravasation assay. Results: Four weeks after capsaicin treatment, there was a loss of BMD in the metaphyses of the tibia and femur. In the proximal tibia, the osteoclast number and surface increased, osteoblast activity and bone formation were impaired, and trabecular bone volume and connectivity were diminished. There was also a loss of bone strength in the distal femur. No changes occurred in body weight, 24-h grid-crossing activity, weight bearing, or muscle mass after capsaicin treatment, indicating that skeletal unloading did not contribute to the loss of bone integrity. Capsaicin treatment destroyed 57% of the unmyelinated sensory axons, reduced the substance P and CGRP content in the sciatic nerve and proximal tibia, and inhibited neurogenic extravasation. Conclusion: These results support the hypothesis that capsaicin-sensitive sensory neurons contribute to the maintenance of trabecular bone integrity. Capsaicin-sensitive neurons have efferent functions in the tissues they innervate, effects mediated by transmitters released from the peripheral nerve terminals. We postulate that the deleterious effects of capsaicin treatment on trabecular bone are mediated by reductions in local neurotransmitter content and release.
Mild traumatic brain injury (mTBI, also referred to as concussion) accounts for the majority of all traumatic brain injuries. The consequences of repetitive mTBI have become of particular concern for individuals engaged in certain sports or in military operations. Many mTBI patients suffer long-lasting neurobehavioral impairments. In order to expedite pre-clinical research and therapy development, there is a need for animal models that reflect the long-term cognitive and pathological features seen in patients. In the present study, we developed and characterized a mouse model of repetitive mTBI, induced onto the closed head over the left frontal hemisphere with an electromagnetic stereotaxic impact device. Using GFAP-luciferase bioluminescence reporter mice that provide a readout of astrocyte activation, we observed an increase in bioluminescence relative to the force delivered by the impactor after single impact and cumulative effects of repetitive mTBI. Using the injury parameters established in the reporter mice, we induced a repetitive mTBI in wild-type C57BL/6J mice and characterized the long-term outcome. Animals received repetitive mTBI showed a significant impairment in spatial learning and memory when tested at 2 and 6 months after injury. A robust astrogliosis and increased p-Tau immunoreactivity were observed upon post-mortem pathological examinations. These findings are consistent with the deficits and pathology associated with mTBI in humans and support the use of this model to evaluate potential therapeutic approaches.
The implant does not significantly change the intradiscal pressures at the adjacent levels, yet it significantly unloads the intervertebral disc at the instrumented level in the neutral and extended positions. On the basis of the current findings, it does not appear that the implant causes accelerated disc degeneration at the adjacent levels.
This study demonstrated the chondrogenic effect of hydrostatic pressure on human bone marrow stromal cells (MSCs) cultured in a mixed medium containing osteogenic and chondrogenic factors. MSCs seeded in type I collagen sponges were exposed to 1 MPa of intermittent hydrostatic pressure at a frequency of 1 Hz for 4 h per day for 10 days, or remained in identical culture conditions but without exposure to pressure. Afterwards, we compared the proteoglycan content of loaded and control cell/scaffold constructs with Alcian blue staining. We also used real-time PCR to evaluate the change in mRNA expression of selected genes associated with chondrogenic and osteogenic differentiation (aggrecan, type I collagen, type II collagen, Runx2 (Cbfa-1), Sox9, and TGF-beta1). With the hydrostatic pressure loading regime, proteoglycan staining increased markedly. Correspondingly, the mRNA expression of chondrogenic genes such as aggrecan, type II collagen, and Sox9 increased significantly. We also saw a significant increase in the mRNA expression of type I collagen, but no change in the expression of Runx2 or TGF-beta1 mRNA. This study demonstrated that hydrostatic pressure enhanced differentiation of MSCs in the presence of multipotent differentiation factors in vitro, and suggests the critical role that this loading regime may play during cartilage development and regeneration in vivo.
ABSTRACT:The structure and function of the proximal hip joint capsule and the zona orbicularis are poorly understood. We hypothesized that the zona orbicularis is an important contributor to hip stability in distraction. In seven cadaveric hip specimens from seven male donors we distracted the femur from the acetabulum in a direction parallel to the femoral shaft with the hip in the neutral position. Eight sequential conditions were assessed: (1) intact specimen (muscle and skin removed), (2) capsule vented, (3) incised iliofemoral ligament, (4) circumferentially incised capsule, (5) partially resected capsule (distal to the zona orbicularis), (6) completely resected capsule, (7) radially incised labrum, and (8) completely resected labrum. The reduction of the distraction load was greatest between the partially resected capsule phase and completely resected capsule phase at 1, 3, and 5 mm joint distraction (p ¼ 0.018). The proximal to middle part of the capsule, which includes the zona orbicularis, appears grossly and biomechanically to act as a locking ring wrapping around the neck of the femur and is a key structure for hip stability in distraction. ß
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