Uncalcified Fibrocartilage Research Articles

Dynamic Deformation Behavior of the Porcine Anterior Cruciate Ligament Enthesis Under Anterior Tibial Loading.

This study determined the insertion angle at the porcine anterior cruciate ligament (ACL) enthesis under joint loading to provide information on the structure and mechanical function of the enthesis. Ten intact porcine knee joints were harvested, and an anterior tibial load was applied using a robotic testing system. After dissecting a portion of the ACL enthesis along ligament fibers, the remaining enthesis was imaged using a digital microscope while reproducing the three-dimensional intact knee motion. Fiber orientation angles (FOAs) in the enthesis region (0-300µm from the ligament-bone boundary) and the ligament region (500-2000µm from the ligament-bone boundary) were analyzed in the femoral and tibial entheses of the anteromedial bundle (AMB) of the ACL under loading. On the femoral side, the FOA in the enthesis region was significantly higher than that in the ligament region by approximately 10 degrees under loading (n = 5, p < 0.05 in paired t-test). In contrast, the FOAs in the enthesis and ligament regions on the tibial side were nearly equal under loading, with no significant difference (n = 5, p > 0.15 in paired t-test). Histological examination indicated that uncalcified fibrocartilage (UF) was abundant in the enthesis region of the AMB femoral enthesis while the UF was not observed in the enthesis region of the AMB tibial enthesis. Thus, the current data suggest that the regional dependence and independence in FOA are caused by the presence or absence of UF and contributes to a moderate and subtle load-transduction in the ACL enthesis.

Compositional, Structural, and Biomechanical Properties of Three Different Soft Tissue-Hard Tissue Insertions: A Comparative Review.

Connective tissue attaches to bone across an insertion with spatial gradients in components, microstructure, and biomechanics. Due to regional stress concentrations between two mechanically dissimilar materials, the insertion is vulnerable to mechanical damage during joint movements and difficult to repair completely, which remains a significant clinical challenge. Despite interface stress concentrations, the native insertion physiologically functions as the effective load-transfer device between soft tissue and bone. This review summarizes tendon, ligament, and meniscus insertions cross-sectionally, which is novel in this field. Herein, the similarities and differences between the three kinds of insertions in terms of components, microstructure, and biomechanics are compared in great detail. This review begins with describing the basic components existing in the four zones (original soft tissue, uncalcified fibrocartilage, calcified fibrocartilage, and bone) of each kind of insertion, respectively. It then discusses the microstructure constructed from collagen, glycosaminoglycans (GAGs), minerals and others, which provides key support for the biomechanical properties and affects its physiological functions. Finally, the review continues by describing variations in mechanical properties at the millimeter, micrometer, and nanometer scale, which minimize stress concentrations and control stretch at the insertion. In summary, investigating the contrasts between the three has enlightening significance for future directions of repair strategies of insertion diseases and for bioinspired approaches to effective soft-hard interfaces and other tough and robust materials in medicine and engineering.

Pathogenesis of the Hallux Valgus: Enthesopathy of the Metatarsosesamoid Ligament

Category: Bunion; Basic Sciences/Biologics Introduction/Purpose: It is generally accepted that failure of the medial supporting soft tissue structure of the metatarsophalangeal joint plays an important role in the development of hallux valgus. The metatarsosesamoid ligament (MSL), a component of the medial soft tissue, is an important structure that connects the metatarsal head and the sesamoid complex. The sesamoid complex works as a dynamic stabilizer of the metatarsal head. We hypothesized that the failure of the medial MSL causes instability of the first metatarsal bone, which leads to hallux valgus deformities. Therefore, the present study aimed to describe the detailed structure and degenerative findings of MSL and to clarify the mechanical stress of the MSL enthesis, considering the mechanism of failure of the medial supporting soft tissue structure. Methods: The first metatarsal heads and sesamoid bones with soft tissue were collected from twelve cadavers. Serial 4-μm thick section4-μm intervals and stained with toluidine blue (Fig. 1a). We described the detailed histological structures and degenerative findings of MSL. In addition, morphometric comparisons were made between the medial and lateral MSL entheses at the metatarsal head to evaluate the mechanical stress they. First, we measured the thickness of the uncalcified fibrocartilage (UF thickness) following a protocol adopted previously (Fig. 1b). Second, the degree of irregularity of the interface between the zones of calcified fibrocartilage and bone (CFB) at each enthesis was assessed as the ratio between the lengths of the CFB and the enthesis (CFB/ E ratio) (Fig. 1c). The differences in these parameters were evaluated using the paired T test and Wilcoxon signed-rank test (P &lt; 0.05). Results: We identified that the MSL entheses were fibrocartilaginous entheses, which consisted of four tissue zones. The region in which the MSL wraps around the articular surface of the metatarsal head contains a metachromatic area accompanied by fibrocartilage cells at the deep surface of the MSL, called the sesamoid fibrocartilage. At the MSL enthesis, pathological findings indicating enthesopathy were observed. One specimen showed the tear of the MSL at the wrap around region. The MSL enthesis tear was observed in two specimens with hallux valgus. Both UF thickness (P = 0.12, effect size r = 0.89) and CFB/E ratio (P = 0.17, effect size d = 0.35) were significantly greater in the medial MSL enthesis than those in the lateral MSL enthesis. Conclusion: In the present study, the MSL showed enthesis protecting structures such as enthesis fibrocartilage which contributes to dissipating bending forces during insertional angle change, complexed CFB interface which guards an enthesis against shearing forces and wrap around region which contributes to dissipating the shearing force to the enthesis. However, the medial MSL subject to the greater forces and the degenerative findings of enthesopathy were observed. On top of that, all four hallux valgus specimens with sesamoid complex dislocation showed MSL enthesis tear. Enthesopathy, particularly at the medial MSL, may be the cause of hallux valgus.

Mineral tessellation in mouse enthesis fibrocartilage, Achilles tendon, and Hyp calcifying enthesopathy: A shared 3D mineralization pattern

The hallmark of enthesis architecture is the 3D compositional and structural gradient encompassing four tissue zones – tendon/ligament, uncalcified fibrocartilage, calcified fibrocartilage and bone. This functional gradient accommodates the large stiffness differential between calcified bone and uncalcified tendon/ligament. Here we analyze in 3D the organization of the mouse Achilles enthesis and mineralizing Achilles tendon in comparison to lamellar bone. We use correlative, multiscale high-resolution volume imaging methods including μCT with submicrometer resolution and FIB-SEM tomography (both with deep learning-based image segmentation), and TEM and SEM imaging, to describe ultrastructural features of physiologic, age-related and aberrant mineral patterning. We applied these approaches to murine wildtype (WT) Achilles enthesis tissues to describe in normal calcifying fibrocartilage a crossfibrillar mineral tessellation pattern similar to that observed in lamellar bone, but with greater variance in mineral tesselle morphology and size. We also examined Achilles enthesis structure in Hyp mice, a murine model for the inherited osteomalacic disease X-linked hypophosphatemia (XLH) with calcifying enthesopathy. In Achilles enthesis fibrocartilage of Hyp mice, we show defective crossfibrillar mineral tessellation similar to that which occurs in Hyp lamellar bone. At the cellular level in fibrocartilage, unlike in bone where enlarged osteocyte mineral lacunae are found as peri-osteocytic lesions, mineral lacunar volumes for fibrochondrocytes did not differ between WT and Hyp mice. While both WT and Hyp aged mice demonstrate Achilles tendon midsubstance ectopic mineralization, a consistently defective mineralization pattern was observed in Hyp mice. Strong immunostaining for osteopontin was observed at all mineralization sites examined in both WT and Hyp mice. Taken together, this new 3D ultrastructural information describes details of common mineralization trajectories for enthesis, tendon and bone, which in Hyp/XLH are defective.

ACL Graft Matching: Cadaveric Comparison of Microscopic Anatomy of Quadriceps and Patellar Tendon Grafts and the Femoral ACL Insertion Site

Background: The optimal graft choice between the bone–patellar tendon–bone (BPTB) and the quadriceps tendon remains controversial. Studies evaluating the microscopic anatomy of the quadriceps tendon–patellar bone (QTB) and BPTB grafts for anterior cruciate ligament (ACL) reconstruction are currently lacking. Hypothesis: The relationship between post–ACL reconstruction graft bending angle (GBA) and the angle corresponding to the GBA (cGBA) would indicate that the BPTB can bend more than the QTB at the femoral tunnel aperture. Study Design: Controlled laboratory study. Methods: Twenty paired human cadaveric knees fixed at <10° of knee joint flexion (mean age, 82.5 years) underwent histological sectioning and staining with Masson trichrome and toluidine blue. The femoral ACL insertion, QTB graft, and BPTB graft were microscopically analyzed. The width of the direct insertion, thickness of the uncalcified fibrocartilage and calcified fibrocartilage, ligament attachment angle, and cGBA for each group were measured. Eighteen patients who underwent ACL reconstruction with QTB or BPTB autograft were included for the evaluation of GBA using computed tomography images at 1 week postoperatively. Results: The mean insertion widths of the femoral ACL, QTB, and BPTB were 7.81, 9.07, and 6.54 mm, respectively. The QTB was 16% wider than the ACL, while the BPTB was 16% narrower than the ACL. The mean insertion thicknesses of the femoral ACL, QTB, and BPTB were 0.53, 0.94, and 0.38 mm, respectively. The QTB was 77% thicker than the ACL (P < .001), while the BPTB was 28% thinner than the ACL (P = .017). The mean ligament attachment angles of the femoral ACL, QTB, and BPTB were 20.3°, 30.2°, and 33.3°, respectively, and the QTB and the BPTB were 49% and 64% larger, respectively, than the ACL. The mean cGBAs of the femoral ACL, QTB, and BPTB were 33.9°, 35.1°, and 12.3°, respectively. The BPTB was 64% smaller than the ACL, while there was no significant difference between the QTB and the ACL. The mean GBA was 57.7°. Conclusion: The insertion width and thickness were significantly greater and smaller in the QTB and BPTB grafts, respectively, than in the ACL. The relationship between GBA after ACL reconstruction and cGBA in knee extension indicates that at the femoral tunnel aperture, the BPTB can bend more than the QTB. Clinical Relevance: QTB graft may allow more anatomic ACL reconstruction to be performed.

Focal Synovial Inflammation Versus Enthesitis Theory in Distal Psoriatic Arthritis: A Pioneer Histopathologic Study.

The aim of this analysis was to re-examine the classical concept of distal interphalangeal joint (DIP) psoriatic arthritis (PsA) as an entheseal-driven disease. Two cadaveric fingers with severe psoriatic arthritis were analyzed. Our results demonstrate that inflammation of DIP PsA is multifocal without interconnection between entheses and articular cartilage of the DIP. We found a clear association between synovitis and focal loss of articular cartilage at the head of the intermediate phalanx. By contrast, the articular cartilage adjacent to the zone of severe enthesitis did not show notable damage. Fibrocartilaginous destructions of enthesis were characterized by either a multifocal lymphocytic inflammation, accompanied by osteoclastic resorption, beginning on the interface between the uncalcified and calcified fibrocartilage and then extending into the bone or a subchondral bone inflammation which insidiously destroyed first the bone and then the fibrocartilage. Some sections well showed an inflammation either mild or prominent starting at the level of vascular foramina of flexor enthesis, with secondary invading into the interface between bone and enthesis. The different anatomic sites examined showed a slight predominance of CD8+ T cells over CD4+ T cells: 52% up to 63% for CD8+ T cells vs. to 36% up to 48% for CD4+ T cells. Sparse interspersed CD1a+cells and PS100+cells were also seen with a predominance of PS100+ cells on CD1a+ cells. CD20+ B cells, plasmocytes, neutrophils, and mastocytes were absent or rare. CD123 positive cells were not observed. In DIP PsA, 3 findings predominate: (1) cartilage invasion by the thin pannus offers a more rational explanation for the focal joint destruction than does inflammation of the enthesis which is independent from articular cartilage, (2) the thick ventral plate and to a lesser extend the thin dorsal plate constitute a barrier between the inflamed entheses and the articular cartilage, and (3) an unusual form of minute vascular foramen contributes to the early stage of enthesitis. This small study suggests that DIP PsA is a complex disease. It affects anatomical micro sites which, although close, are in fact relatively independent of each other. Further studies are needed to test this hypothesis.

Osteoarthritic meniscal entheses exhibit altered collagen fiber orientation

ABSTRACT Purpose/Aim The knee menisci are vital for maintaining the stability of the joint, allowing for force distribution, and protecting the underlying articular cartilage during loading. Each meniscus is attached to the underlying bone via two ligamentous entheses composed of collagen fibers that are continuous throughout all four zones of the attachment: ligament, uncalcified fibrocartilage, calcified fibrocartilage, and subchondral bone. The collagen fibers of the meniscal entheses are important for proper functionality of the entheses, particularly in preventing meniscal extrusion which is a common hallmark of osteoarthritis. The goal of this work was to assess changes in collagen fiber orientation present in osteoarthritic knee joints. Materials and Methods Entheses were harvested from patients undergoing total knee arthroplasties and prepared histological sections were stained with picrosirius red to identify collagen fiber angle and fiber deviation. Results In the calcified fibrocartilage the collagen fibers of the lateral anterior enthesis inserted at significantly (p < 0.1) shallower angles, and the fiber deviation was significantly (p < 0.1) less compared to the lateral posterior enthesis. These differences in the calcified fibrocartilage may occur as an adaptation to loading regimes of the osteoarthritic joint. When compared to the collagen fiber orientation of healthy entheses, collagen fibers in osteoarthritic tissue inserted at shallower insertion angles and demonstrated higher levels of deviation. Conclusions Changes to meniscal enthesis collagen fiber orientation with end stage osteoarthritis could offer an explanation for the change in functionality of diseased tissue and may contribute to meniscal extrusion and ultimately the degeneration of articular cartilage.

The effect of estrogen-like compound on rotator cuff tendon healing in a murine model.

Estrogen deficiency has been shown to negatively influence rotator cuff tendon healing. Therefore, the addition of an estrogen-like-compound (ELC) in a nonestrogen-deficient animal may improve the quality of a rotator cuff repair. The purpose of this study was to evaluate the effects of an ELC, diethylstilbestrol (DES), on tendon healing in a murine rotator cuff repair model. Thirty-three male wild-type mice (C57BL/6NJ) were randomly divided into three study groups. Group 1-unoperated mice with normal rotator cuff tendons. Groups 2 and 3 consisted of surgically repaired rotator cuff tendons; Group 2 (repair-only) was the standard repair group (no DES injected), whereas Group 3 (repair + DES) was the experimental repair group (injected with DES). Comparing the maximal thickness of calcified fibrocartilage to uncalcified fibrocartilage, the ratios for the control (intact tendon), repair-only, and repair + DES groups were 2:1, 0.9:1, and 1.7:1. RNA expression data demonstrated upregulation of chondrogenic, angiogenic, and tendon modulation genes in the repair- only group compared to the control (intact tendon) group (p < 0.04 for all), and that addition of DES further increased the osteogenic, angiogenic, and tendon modulation gene expression compared to the repair-only group (p < 0.02). Immunohistochemical analysis indicated that the addition of DES further increased osteogenic, angiogenic, and tendon maturation protein expression at the enthesis compared to standard repairs.

Functional Adaptation of the Fibrocartilage and Bony Trabeculae at the Attachment Sites of the Anterior Cruciate Ligament.

The direct insertion of an enthesis is composed of uncalcified fibrocartilage (FC) and calcified FC, believed to function as buffers for multidirectional forces applied to the ligament. This study was performed to investigate the relationship between the FC thickness and bony trabecular orientation of the anterior cruciate ligament (ACL) on both the femoral and tibial sides. Six cadavers were examined (age at death: 73-92 years). Both femoral and tibial insertions of the ACL were harvested and used to make 0.5 mm interval semi-serial sections. Microdigital images were taken and used to measure the maximum thickness of both the uncalcified FC and Calcified FC. Two-dimensional discrete Fourier analysis was also performed to determine the orientation angle and orientation intensity of bony trabeculae directly under the FC. The mean thicknesses of the uncalcified FC at the femoral and tibial insertions were 0.98 mm and 0.49 mm, respectively. The mean thicknesses of the calcified FC were 0.47 mm and 0.38 mm, respectively. There was a significant difference in the uncalcified FC thickness, but not in the calcified FC thickness. The bony trabeculae showed a prominent orientation parallel to the ACL fiber on both sides, but it was more intense on the tibial side than on the femoral side. The trabecular orientation was prominent in the proximal-posterior part of the femoral side and in the anteromedial part of the tibial side, suggesting that mechanical stress is greater in these parts. The dominant bony trabecular angle was 69.0° on the femoral side and 59.8° on the tibial side when the tidemark was set at 0°. These findings suggest that the femoral side receives multidirectional stresses, while relatively unidirectional stress is loaded on the tibial side. Furthermore, stress is considered to be greater in the proximal-posterior part of the femoral insertion and in the anteromedial part of the tibial insertion. At the time of ACL reconstruction, attention should be paid to assign a robust portion of the graft to the posterior part of the femoral insertion and anteromedial part of the tibial insertion. Clin. Anat., 33:988-996, 2020. © 2019 Wiley Periodicals, Inc.

An anatomic study on the origin of the long head of the triceps brachii

BackgroundPosterior shoulder instability was reported to be more common than had been previously reported. However, the detailed morphology of the origin of the long head of the triceps brachii (LHT), which is located at the posteroinferior part of the glenohumeral joint and associated with the stability of the head of the humerus, has been unknown. The purpose of the current study was to clarify the detailed morphology of the origin of the LHT.MethodsA total of 64 specimens from 36 cadavers (11 males and 25 females) were used. After dissecting the origin of the LHT in 54 specimens of 27 cadavers, the width of the origin of the LHT was measured with a caliper by 2 observers. The origin of the LHT was also investigated histologically in 18 specimens. Sections were analyzed with Masson’s trichrome staining and Safranin O staining.ResultsSome fibers of the LHT originated more from the cranial area than from the infraglenoid tubercle and descended along the posterior rim of the glenoid cavity. The width of the origin on the dorsal surface of the scapula was 31.2 mm. The origin from the bone had a developed uncalcified fibrocartilage histologically. In addition, the LHT was fused with the glenohumeral joint capsule and was attached to the glenoid labrum directly.ConclusionsThe LHT could affect the glenohumeral joint capsule or the glenoid labrum because of their connections to each other and be associated with the posterior shoulder instability indirectly.

Histological study of the posterior cruciate ligament femoral insertion

ObjectivesTo describe the microscopic anatomy of the posterior cruciate ligament femoral insertion in order to identify and establish differences between the direct and indirect insertions of this ligament. MethodsTen cadaveric knees were used for this study. The posterior cruciate ligament femoral insertion was observed microscopically. Hematoxylin and eosin staining was performed to observe the morphology of the posterior cruciate ligament insertion. Alcian blue staining was performed to determine the location of the cartilage matrix and better assist in the observation and differentiation between direct and indirect insertions. ResultsThe direct insertion was observed to be a more complex structure than the indirect insertion because it showed four different histological layers (ligament, uncalcified fibrocartilage, calcified fibrocartilage, and bone). Chondrocytes were observed in the uncalcified and calcified fibrocartilage layers. It was observed that the indirect insertion was composed of two layers in which the ligament was anchored directly to the bone by collagen fibers. Indirect insertion was located in the marginal region of the posterior cruciate ligament between the direct insertion and the anterior articular cartilage. ConclusionThrough histological analysis, it was demonstrated that the indirect insertion was adjacent to the anterior articular cartilage and presents a histological pattern where the collagen fibers insert directly into the bone (two-layer insertion). The direct insertion is posterior to the indirect insertion and has four histologically distinct layers.

An anatomic study on the attachment of the joint capsule to the tibia in the lateral side of the knee.

The purpose of the current study was to examine the width, area, and histological characteristics of the capsular attachment to the tibia in the lateral side of the knee. A total of 27 knees were used in this study. The joint capsule of the knee was peeled away from the tibia and the width of the capsular attachment to the tibia was measured by two independent observers using a caliper. Interclass correlation coefficients for each value were calculated to evaluate the validity of the measurement. The capsular attachment to the tibia of the seven knees was histologically analyzed using Masson's trichrome staining. At the posterior border of Gerdy's tubercle, the capsular attachment was wide; the average width was 8.6mm (SD 3.0). Toward the posterolateral aspect of the knee, the capsular attachment gradually tapered. Finally, the capsular attachment was linear at the apex of the head of the fibula. Histological analysis at the posterior border of Gerdy's tubercle revealed developed uncalcified fibrocartilage on the capsular attachment. In contrast, at the apex of the head of the fibula, the joint capsule was adhered to the capsule of the proximal tibiofibular joint. Fibrous connective tissue was directly attached to the calcified fibrocartilage. The attachment width of the knee joint capsule at the lateral side varied according to location. We consider that this finding on the capsular attachment will facilitate an understanding of the pathology or mechanism of diseases on the lateral side of the knee joint.

Estudo histológico da inserção femoral do ligamento cruzado posterior

ObjectivesTo describe the microscopic anatomy of the posterior cruciate ligament femoral insertion in order to identify and establish differences between the direct and indirect insertions of this ligament. MethodsTen cadaveric knees were used for this study. The posterior cruciate ligament femoral insertion was observed microscopically. Hematoxylin and eosin staining was performed to observe the morphology of the posterior cruciate ligament insertion. Alcian blue staining was performed to determine the location of the cartilage matrix and better assist in the observation and differentiation between direct and indirect insertions. ResultsThe direct insertion was observed to be a more complex structure than the indirect insertion because it showed four different histological layers (ligament, uncalcified fibrocartilage, calcified fibrocartilage, and bone). Chondrocytes were observed in the uncalcified and calcified fibrocartilage layers. It was observed that the indirect insertion was composed of two layers in which the ligament was anchored directly to the bone by collagen fibers. Indirect insertion was located in the marginal region of the posterior cruciate ligament between the direct insertion and the anterior articular cartilage. ConclusionThrough histological analysis, it was demonstrated that the indirect insertion was adjacent to the anterior articular cartilage and presents a histological pattern where the collagen fibers insert directly into the bone (two‐layer insertion). The direct insertion is posterior to the indirect insertion and has four histologically distinct layers.

On the heterogeneity of the femoral enthesis of the human ACL: microscopic anatomy and clinical implications.

BackgroundMost ruptures of the native anterior cruciate ligament (ACL) and ACL graft occur at, or near, the femoral enthesis, with the posterolateral fibers of the native ligament being especially vulnerable during pivot landings. Characterizing the anatomy of the ACL femoral enthesis may help us explain injury patterns which, in turn, could help guide injury prevention efforts. It may also lead to improved anatomic reconstruction techniques given that the goal of such techniques is to replicate the knee’s normal anatomy. Hence, the aim of this study was to investigate the microscopic anatomy of the ACL femoral enthesis and determine whether regional differences exist.MethodsFifteen human ACL femoral entheses were histochemically processed and sectioned along the longitudinal axis of the ACL at 20, 40, 60, and 80 % of the width of the enthesis. Four thick sections (100 μm) per enthesis were prepared, stained, and digitized. From these sections, regional variations in the quantity of calcified and uncalcified fibrocartilage, the angle at which the ligament originates from the bone, and the shape profile of the tidemark were quantified.ResultsAt least 33 % more calcified fibrocartilage and 143 % more uncalcified fibrocartilage were found in the antero-inferior region, which corresponds to the inferior margin of the origin of the anteromedial ACL fibers, than all other regions (Ps < 0.05). In addition, the anteromedial fibers of the ACL originated from the femur at an angle six times greater than did its posterolateral fibers (P = 0.032). Finally, average entheseal tidemark profiles correlated bilaterally (Pearson’s r = 0.79; P = 0.036), the most common profile being convex with a single re-entrant.ConclusionsSystematic regional differences were found in fibrocartilage quantity and collagen fiber attachment angles. The marked differences may reflect differences in the loading history of the various regions of the ACL femoral enthesis. These differences, which could affect the potential for injury, should also be considered when developing new ACL reconstruction approaches.

Calf Muscle Contributions To Achilles Tendon Architectures And Injuries Using Finite Element Modeling

Clinically the sites of Achilles Tendon (AT) overuse conditions occur primarily within the tendon mid-portion and the osteotendinous attachment. PURPOSE: We propose an anatomical and finite element model of the muscle-tendon-bone units that could provide a possible anatomic explanation for these 2 sites of injury. METHOD: Twelve cadavers (age 74 ± 7 years) were studied. In both legs, calf muscles (lateral gastrocnemius (LG), medial gastrocnemius (MG) and soleus (SL)) were dissected and their volumes measured. A finite element model based on a von Mises criteria of tendon coupled to a rupture index was developed to investigate the AT response to mechanical load. Three simulations were performed corresponding to three load cases (Force from GM= Force from GL = Force SL, Force from GM=1.5×Force from GL and Force from GL= 1.5×Force from GM). The SL load was kept constant during the three cases. Histological sections of the enthesis and thickness of both the uncalcified fibrocartilage and subchondral plate were evaluated. RESULTS: Muscle volume was highest for the soleus (p=0.02), followed by the MG (p=0.04), and LG (p=0.04). Uncalcified fibrocartilage was significantly thicker medially than laterally (P = 0.02). Finite element modeling predicted rupture propagation and final patterns depending on the load cases indicating that non-uniform stress in the AT can occur through modifications of individual muscle contributions (p=0.02). As the load increased, the pressure converged at the middle area between 4.6cm and 7.9cm from the AT enthesis. CONCLUSION: Our data suggest that the AT muscle-tendon-bone units are composed of anatomically distinct parts that undergo non-uniform mechanical loading. Finite element modeling can be used for identifying localized material property changes due to muscle atrophy or hypertrophy as well as in response to mechanical loading seen during normal gait and running.

Implications of the calf musculature and Achilles tendon architectures for understanding the site of injury

Clinically the sites of Achilles Tendon (AT) overuse conditions can be divided into the tendon mid-portion and osteotendinous attachment. Purpose: We propose an anatomical analysis of the triceps surae musculotendon unit that could provide a possible anatomic explanation for these 2 sites of injury. Method: Twelve cadavers (age 74±7 years) were studied. In both legs, calf muscles (lateral gastrocnemius (LG), medial gastrocnemius (MG) and soleus) were dissected and their volumes measured. Fine saw cuts were made in the sagittal plane, either side of the midline of the calcaneus. Each strip contained the distal part of the tendon and its insertion, together with the superior tuberosity of the calcaneus. Trabecular architecture was analyzed from X-rays taken with Faxitron radiography. Histological sections of the enthesis and the thickness of the uncalcified fibrocartilage and the subchondral plate were evaluated. A finite element model of tendon coupled to a rupture index was developed to investigate the AT response to mechanical load. Results: Muscle volume was highest for the soleus, followed by the MG, and LG. Within the AT, the soleus fibers occupy the antero-medial parts, the MG fibers form the posterior lateral layer, yet the LG head fibers retain the antero-lateral part. The quantity of bone and the apparent trabecular thickness at the enthesis were greatest in the central part of the enthesis. Thickness of calcified fibrocartilage tissue was significantly greater in the central part than medially (P=0.04) and laterally (P=0.03). Uncalcified fibrocartilage was significantly thicker medially than laterally (P=0.02). Finally, finite element analysis showed that AT mechanical stress increased with muscle load and converged at 4.6–7.9cm of the enthesis. Conclusion: Our data suggest that the triceps surae musculotendon unit is composed of anatomically distinct parts that undergo non-uniform mechanical loading. There are two sites where potentially tendon mechanical stress increases, the medial/central portions of the enthesis and the tendon midportion.

Characterization of calcium and zinc spatial distributions at the fibrocartilage zone of bone–tendon junction by synchrotron radiation-based micro X-ray fluorescence analysis combined with backscattered electron imaging

Tendon attaches to bone through a functionally graded fibrocartilage zone, including uncalcified fibrocartilage (UF), tidemark (TM) and calcified fibrocartilage (CF). This transition zone plays a pivotal role in relaxing load transfer between tendon and bone, and serves as a boundary between otherwise structurally and functionally distinct tissue types. Calcium and zinc are believed to play important roles in the normal growth, mineralization, and repair of the fibrocartilage zone of bone–tendon junction (BTJ). However, spatial distributions of calcium and zinc at the fibrocartilage zone of BTJ and their distribution–function relationship are not totally understood. Thus, synchrotron radiation-based micro X-ray fluorescence analysis (SR-μXRF) in combination with backscattered electron imaging (BEI) was employed to characterize the distributions of calcium and zinc at the fibrocartilage zone of rabbit patella–patellar tendon complex (PPTC). For the first time, the unique distributions of calcium and zinc at the fibrocartilage zone of the PPTC were clearly mapped by this method. The distributions of calcium and zinc at the fibrocartilage zone of the PPTC were inhomogeneous. A significant accumulation of zinc was exhibited in the transition region between UF and CF. The highest zinc content (3.17 times of that of patellar tendon) was found in the TM of fibrocartilage zone. The calcium content began to increase near the TM and increased exponentially across the calcified fibrocartilage region towards the patella. The highest calcium content (43.14 times of that of patellar tendon) was in the transitional zone of calcified fibrocartilage region and the patella, approximately 69μm from the location with the highest zinc content. This study indicated, for the first time, that there is a differential distribution of calcium and zinc at the fibrocartilage zone of PPTC. These observations reveal new insights into region-dependent changes across the fibrocartilage zone of BTJ and will serve as critical benchmark parameters for current efforts in BTJ repair.

Association Between Individual Calf Muscle Volume And Achilles Tendon Enthesis Morphology

Although chronic Achilles tendinopathy (AT) is one of the most frequent injuries in sport, it is generally difficult to treat as the etiology and background to the pain mechanisms has not yet been clarified. Anatomically, as calf muscles travel distally, the AT internally rotate, consequently the initially posterior fibers of the soleus insert mainly on the medial aspect of the AT enthesis whereas those of the gatsrocnemuis insert mainly on the lateral aspect. Recently, it has been suggested that the AT undergoes non-uniform deformation under in vivo loading conditions PURPOSE: We investigated whether there are regional differences in calf muscle volumes, in the trabecular architecture of the calcaneus or in the histology of the AT enthesis that could suggest unequal force transmission from muscle to tendon and from tendon to bone. METHOD: We studied 12 cadavers (age 74 ± 7 years). For both legs, individual calf muscles (lateral gastrocnmius (LG), medial gastrocnemius (MG) and soleus (SL) were dissected and their volumes measured. Fine saw cuts were made in the sagittal plane, either side of the midline of the calcaneus, so that approximately 8-mm-wide strips of tissue were sampled from the insertion site. Each strip contained the distal part of the tendon and its insertion, together with the superior tuberosity of the calcaneus. Trabecular architecture was analysed from X-rays taken with a Faxitron radiography. Histological sections were made at the enthesis and regional differences in the thickness of the uncalcified fibrocartilage and the subchondral plate were evaluated. RESULTS: The radiological studies showed that the quantity of bone and the apparent trabecular thickness in the calcaneus were greatest in the center. The thickness of calcified fibrocartilage tissue was significantly greater in the central part of the enthesis than medially (P = 0.04) and laterally (P = 0.03). Uncalcified fibrocartilage was significantly thicker medially than laterally (P = 0.02). Muscle volume was highest (P <0.05) for the SL, followed by the GM, and GL. CONCLUSION: Overall, the results indicate that mechanical stress at the AT enthesis is asymmetrically distributed and greater on the medial than on the lateral side. Thus, we suggest that the functional anatomy of the AT is closely related to regional variations in force transmission, which in turn relates to the site of pain and pathology in AT.

Regional fibrocartilage variations in human anterior cruciate ligament tibial insertion: a histological three-dimensional reconstruction

Purpose: We studied anterior cruciate ligament (ACL) tibial insertion architecture in humans and investigated regional differences that could suggest unequal force transmission from ligament to bone. Materials and methods: ACL tibial insertions were processed histologically. With Photoshop software, digital images taken from the histological slides were collaged, contour lines were drawn, and different gray values were filled based on the structure. The data were exported to Amira software for three-dimensional reconstruction. Results: The uncalcified fibrocartilage (UF) layer was divided into three regions: lateral, medial and posterior according to the architecture. The UF zone was significantly thicker laterally than medially or posteriorly (p < 0.05). Similarly, the calcified fibrocartilage (CF) thickness was significantly greater in the lateral part of the enthesis compared to the medial and posterior parts (p < 0.05). Conclusions: The UF quantity (more UF laterally) corresponding to the CF quantity (more CF laterally) at the ACL tibial insertion provides further evidence suggesting that the load transferred from the ACL to the tibia was greater laterally than medially and posteriorly.

Influence of gradual elongation to the patella tendon insertion in rabbits.

The purpose of this study was to examine the histological changes at the patella tendon (PT) insertion site under gradual elongation in rabbits. Gradual elongation of the PT was performed using external fixation for 4 weeks, with a lengthening speed of 0.5 mm/day (elongation group; n = 24). Rabbits in the sham group underwent the same surgical procedure without gradual elongation (sham group; n = 24). Eight animals were sacrificed 1, 2 and 4 weeks after surgery in each group, respectively. Average thicknesses of stained glycosaminoglycan (GAGs) areas by Safranin-O staining in the total cartilage layer and the uncalcified fibrocartilage layer in the elongation group were significantly higher than that in the sham group at 4 weeks (p < 0.05) and that in the intact PT group (n = 6, p < 0.05). In the elongation group, the peak in the average thicknesses of the stained GAGs areas in the total cartilage layer and the uncalcified fibrocartilage layer were observed at 4 weeks. Gradual elongation of PT insertion significantly affected the increase in the average thicknesses of the stained GAGs areas in the cartilage layer especially in the uncalcified fibrocartilage layer at 4 weeks in rabbits. Clinically, insertions of tendon and ligament can extend during gradual elongation using external fixation more than 4 weeks after the operation.