The mechanical behavior of tendons has been well studied in vitro. A noninvasive method to acquire mechanical data would be highly beneficial. Elastography has been a promising method of gathering in vivo tissue mechanical behavior, but it has inherent limitations. This study presents acoustoelasticity as an alternative ultrasound-based method of measuring tendon stress and strain by reporting a relationship between ultrasonic echo intensity (B mode ultrasound image brightness) and mechanical behavior of tendon in vitro. Porcine digital flexor tendons were cyclically loaded in a mechanical testing system while ultrasonic echo response was recorded. We report that echo intensity closely follows the applied cyclic strain pattern in time with higher strain protocols resulting in larger echo intensity changes. We also report that echo intensity is related nonlinearly to stress and nearly linearly to strain. This indicates that ultrasonic echo intensity is related to the mechanical behavior in a loaded tissue by an acoustoelastic response, as previously described in homogeneous, nearly incompressible materials. Acoustoelasticity is therefore able to relate strain-dependent stiffness and stress to the reflected echo, even in the processed B-mode signals reflected from viscoelastic, inhomogeneous material such as tendon, and is a promising metric to acquire in vivo mechanical data noninvasively.
Summary The structure of the collagen fibers that composes tendon and ligament are disrupted or damaged during injury and healing. Quantification of these changes is traditionally a laborious and subjective task. In this work we apply two automated techniques, Fourier transformation (FFT) and fractal dimension analysis (FA) to quantify the organization of collagen fibrils. Using multi-photon images we show that for healing ligament FA differentiates more clearly between the different time-points during healing. Using scanning electron microcopy images of overstretched tendon we show that combining FFT and FA measures separates the damaged and undamaged groups more clearly than either method individually.
Ligament healing follows a series of complex coordinated events involving various cell types, cytokines, as well as other factors, producing a mechanically inferior tissue more scar-like than native tissue. Macrophages provide an ongoing source of cytokines to modulate inflammatory cell adhesion and migration as well as fibroblast proliferation. Studying interleukins inherent to ligament healing during peak macrophage activation and angiogenesis may elucidate inflammatory mediators involved in subsequent scar formation. Herein, we used a rat healing model assayed after surgical transection of their medial collateral ligaments (MCLs). On days 3 and 7 post-injury, ligaments were collected and used for microarray analysis. Of the 12 significantly modified interleukins, components of the interleukin-1 family were significantly up-regulated. We therefore examined the influence of interleukin-1 receptor antagonist (IL-1Ra) on MCL healing. Transected rat MCLs received PBS or IL-1Ra at the time of surgery. Inhibition of IL-1 activation decreased pro-inflammatory cytokines (IL-1α, IL-1β, IL-12, IL-2, and IFN-γ), myofibroblasts, and proliferating cells, as well as increased anti-inflammatory cytokines (IL-10), endothelial cells/blood vessel lumen, M2 macrophages, and granulation tissue size without compromising the mechanical properties. These results support the concept that IL-1Ra modulates MCL-localized granulation tissue components and cytokine production to create a transient environment that is less inflammatory. Overall, IL-1Ra may have therapeutic potential early in the healing cascade by stimulating the M2 macrophages and altering the granulation tissue components. However, the single dose of IL-1Ra used in this study was insufficient to maintain the more regenerative early response. Due to the transient influence on most of the healing components tested, IL-1Ra may have greater therapeutic potential with sustained delivery.
Despite a complex cascade of cellular events to reconstruct damaged extracellular matrix, ligament healing results in a mechanically inferior, scar-like tissue. During normal healing the number of macrophages significantly increases within the wound site. Then, granulation tissue expands into any residual, normal ligamentous tissue (creeping substitution), resulting in a larger region of healing, greater mechanical compromise, and an inefficient repair process. To study the effects of macrophages on the repair process, rats underwent bilateral, surgical rupture of their medial collateral ligaments. Treatment animals received liposome-encapsulated clodronate 2 days before rupture to ablate phagocytosing macrophages. Ligaments were then collected at day 5, 11, and 28 for immunohistochemistry and/or mechanical testing. Clodronate treatment reduced both the M1 and M2 macrophages at day 5 and altered early healing. However, the macrophages effectively returned to control levels after day 5 and reinitiated a wound healing response. Our results suggest that an early macrophage response, which is necessary for debridement of damaged tissue in the wound, is also important for cytokine release to mediate normal repair processes. Additionally, non-specific inhibition of macrophages (without regard to specific macrophage populations) can control excessive granulation tissue formation but is detrimental to early matrix formation and ligament strength.
Background:Shoulder pain is becoming increasingly problematic in young players as volleyball gains popularity. Associations between repetitive motion and pain and overuse injury have been observed in other overhand sports (most notably baseball). Studies of adult athletes suggest that there is a shoulder pain and overuse problem present in volleyball players, but minimal research has been done to establish rates and causes in juvenile participants.Purpose:To establish rates of shoulder pain, regardless of whether it resulted in a loss of playing time, in female high school volleyball players. A secondary goal was to determine whether high repetition volumes correlated with an increased likelihood of experiencing pain.Study Design:Descriptive epidemiology study.Methods:A self-report survey focusing on the prevalence of pain not associated with a traumatic event in female high school youth volleyball players was developed. Survey questions were formulated by certified athletic trainers, experienced volleyball coaches, and biomechanics experts. Surveys were received from 175 healthy, active high school volleyball players in Iowa, South Dakota, and Minnesota.Results:Forty percent (70/175) of active high school volleyball players remembered experiencing shoulder pain not related to traumatic injury, but only 33% (23/70) reported taking time off to recover from the pain. Based on these self-reported data, activities associated with significantly increased risk of nontraumatic shoulder pain included number of years playing competitive volleyball (P = .01) and lifting weights out of season (P = .001). Players who reported multiple risk factors were more likely to experience nontraumatic shoulder pain.Conclusion:When using time off for recovery as the primary injury criterion, we found that the incidence of shoulder pain is more than twice as high as the incidence of injury reported by previous studies. Findings also indicated that the incidence of shoulder pain may be correlated with volume of previous volleyball experience.
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