Enthesis Anatomy and Physiology
TM integrity is also thought to be crucial for maintaining enthesis functionality-. Previous evaluation of TM integrity has remained strictly qualitative; however, the metrics introduced here facilitated quantitative comparisons between healthy and arthritic tissue at each enthesis. In general, OA entheses exhibited higher variance and mean amplitude, suggesting a less organized TM. Specifically, the MA had a significantly greater amount of disorganization, potentially leading to detrimental bone formation extending into the soft-tissue including to osteophyte formation,. These enthesophytes, distinct from the calcium deposits, commonly appear in the Achilles tendon in athletes. However their direct ramifications are unclear as patients can be asymptomatic. In articular cartilage, osteophyte detection is associated with disruption of the adjacent articulating surfaces thereby exacerbating adverse joint mechanics.
What Is the Enthesis? (with pictures) - wiseGEEK
To our knowledge this is the first study to examine pathophysiology of the meniscal entheses. Qualitatively, the entheses exhibited morphological changes including a breakdown of TM organization, double TM formation, clefts and microcracks/fissures, osteophytes, and calcium deposition within the soft-tissue, all of which disrupt functional homeostasis. Quantitatively, the arthritic tissue was found to have significant increases in GAG thickness in the mineralized fibrocartilage, cortical shell thickness, peak and mineral density and mineralization gradient, and mechanical compliance. As there is limited data specifically on the meniscal entheses these findings must be considered in the context of other enthesopathies.
Similar to other fibrocartilaginous entheses, the meniscal entheses are compositionally graded to withstand a myriad of interfacial loading mechanisms. Primarily type I collagen fibrils, extending from the mainbody of the meniscus, form a ligamentous (LI) zone which sustains longitudinal tensile forces manifested by compression on the meniscus,. These fibers then join with type II collagen fibers forming interwoven uncalcified and calcified fibrocartilage zones (UFC and CFC, respectively), separated by a tidemark (TM),,. These proteoglycan rich zones withstand compression and shear generated by dynamic changes in fiber angle and avulsion stress shielding. Lastly, the CFC zone joins the SB at an interdigitated cement line,,. These four zones can vary in size at each meniscal enthesis site, presumably structurally adapting to their unique functional environment,,. Coupling mechanical and magnetic resonance imaging studies typifies this as the posterior sites, known to translate more during flexion, are significantly more compliant than the anterior sites-.
Enthesis - an overview | ScienceDirect Topics
In this study, we investigated the effect of muscle unloading on the postnatal development of the tendon enthesis, and found diminished biomechanical function in BtxA-unloaded tissues. An important distinction must be made between the concepts of material and structure when interpreting biomechanical results. We define material effects as those due to local changes to tissue, including its composition and hierarchical structure, at a specific point along the tendon-to-bone insertion site. We define structural effects as those due to changes in the spatial distribution of material (e.g., cross-sectional area, the spatial distribution of material with different mechanical properties). Clear effects of BtxA-induced unloading were observed in the biomechanical tests performed, and these likely involved both material and structural effects.
The enthesis is defined as the site of ..
GAG thickness in the calcified fibrocartilage (CFC) zone and calcium content were significantly greater in osteoarthritic anterior meniscal entheses. TM integrity was significantly decreased in OA tissue, particularly in the medial anterior (MA) enthesis. The mineralized zone of osteoarthritic meniscal entheses was significantly thicker than in healthy entheses and showed decreased bone mineral density. Fitting of mineralization data to a sigmoidal Gompertz function revealed a lower rate of increase in mineralization in osteoarthritic tissue. Analysis of viscoelastic mechanical properties revealed increased compliance in osteoarthritic tissue.
which promotes the basic function of tendon/ligament anchorage
Muscle forces are essential for skeletal patterning during development. Eliminating muscle forces, e.g., through paralysis, leads to bone and joint deformities. Botulinum toxin (BtxA)-induced paralysis of mouse rotator cuffs throughout postnatal development closely mimics neonatal brachial plexus palsy, a significant clinical condition in infants. In these mice, the tendon-to-bone attachment (i.e., the tendon enthesis) presents defects in mineral accumulation and fibrocartilage formation, presumably impairing the function of the tissue. The objective of the current study was to investigate the functional consequences of muscle unloading using BtxA on the developing supraspinatus tendon enthesis. We found that the maximum endurable load and stiffness of the supraspinatus tendon attachment decreased after four and eight weeks of post-natal BtxA-muscle unloading relative to controls. Tendon cross-sectional area was significantly reduced by BtxA-unloading, suggesting that the reduction of mechanical function resulted in part from geometric changes. However, strength, modulus, and toughness were also decreased in the BtxA-unloaded group compared to controls, indicating a decrease in tissue quality. Polarized-light microscopy and Raman microprobe analysis were used to determine collagen fiber alignment and mineral characteristics, respectively, in the tendon enthesis that might contribute to the reduced biomechanical performance in BtxA-unloaded shoulders. Collagen fiber alignment was significantly reduced in BtxA-unloaded shoulders. The mineral-to-matrix ratio in mineralized fibrocartilage was not affected by loading. However, the crystallographic atomic order of the hydroxylapatite phase (a measure of crystallinity) was reduced and the amount of carbonate (substituting for phosphate) in the hydroxylapatite crystals was increased. Taken together, these micrometer-scale structural and compositional changes partly explain the observed decreases in the mechanical functionality of the tendon enthesis in the absence of muscle loading.