Comparative anatomy of rabbit and human achilles tendons with magnetic resonance and ultrasound imaging.
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We sought to describe the comparative anatomy of the Achilles tendon in rabbits and humans by using macroscopic observation, magnetic resonance imaging, and ultrasonography. The calcaneus-Achilles tendon-gastrocnemius-soleus complexes from 18 New Zealand white rabbits underwent ultrasound (US) and magnetic resonance (MR) imaging and gross anatomic sectioning; these results were compared with those from a cadaveric gastrocnemius-soleus-Achilles tendon-calcaneus specimen from a 68-y-old human male. The medial and lateral gastrocnemius muscle tendons merged 5.2 +/- 0.6 mm proximal to the calcaneal insertion macroscopically, at 93% of their course, different from the gastrocnemius human tendons, which merged at 23% of their overall course. The rabbit flexor digitorum superficialis tendon, corresponding to the flexor digitorum longus tendon in human and comparable in size with the gastrocnemius tendons, was located medial and anterior to the medial gastrocnemius tendon proximally and rotated dorsally and laterally to run posterior to the Achilles tendon-calcaneus insertion. In humans, the flexor digitorum longus tendon tracks posteriorly to the medial malleolus. The soleus muscle and tendon are negligible in the rabbit; these particular comparative anatomic features in the rabbit were confirmed on the MR images. Therefore the rabbit Achilles tendon shows distinctive gross anatomical and MR imaging features that must be considered when using the rabbit as a research model, especially for mechanical testing, or when generalizing results from rabbits to humans.Keywords:
Cadaveric spasm
Gastrocnemius muscle
Flexor Digitorum Longus
Calf muscle
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We dissected 12 fresh-frozen leg specimens to identify the insertional footprint of each fascicle of the Achilles tendon on the calcaneum in relation to their corresponding muscles. A further ten embalmed specimens were examined to confirm an observation on the retrocalcaneal bursa. The superficial part of the insertion of the Achilles tendon is represented by fascicles from the medial head of the gastrocnemius muscle, which is inserted over the entire width of the inferior facet of the calcaneal tuberosity. In three specimens this insertion was in continuity with the plantar fascia in the form of periosteum. The deep part of the insertion of the Achilles tendon is made of fascicles from the soleus tendon, which insert on the medial aspect of the middle facet of the calcaneal tuberosity, while the fascicles of the lateral head of the gastrocnemius tendon insert on the lateral aspect of the middle facet of the calcaneal tuberosity. A bicameral retrocalcaneal bursa was present in 15 of the 22 examined specimens. This new observation and description of the insertional footprint of the Achilles tendon and the retrocalcaneal bursa may allow a better understanding of the function of each muscular part of the gastrosoleus complex. This may have clinical relevance in the treatment of Achilles tendinopathies. Cite this article: Bone Joint J 2014; 96-B:1344–8
Fascicle
Periosteum
Plantar fascia
Deep fascia
Fat pad
Facet (psychology)
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To evaluate the ultrasound (US) appearance of the normal Achilles tendon at increasing frequency and establish an anatomical correlation for US findings, 30 normal tendons were examined in vivo and three in vitro with 10 MHz and 15 MHz mechanical sector probes. Side-by-side comparison was performed in vitro between the sonograms and the corresponding anatomical sections. Two tendinous portions were detected by presence of an internal acoustic interface which had different appearances: one (type I) or two (type II) continuous lines of increased thickness and greater reflectivity than adjacent fibrils; or displacement (type III) of the distal portion of the well insonated sector of the tendon body. When, on coronal scans of the tendon, no intratendinous linear echoes of increased reflectivity were visible, the two portions of the tendon were identified through the converging course of their bundles (type 0 pattern). Different echogenicity allowed the detection of two tendinous portions, also on axial images. Scanning of isolated tendons allowed precise location of these interfaces at the boundary between anatomically distinct tendinous portions arising from the soleus and gastrocnemius muscles. Although the normal Achilles tendon is commonly regarded as a uniform structure by US, the use of high resolution probes allows identification of its constituent portions. Their identification may be useful to avoid misdiagnoses of pathological findings.
Echogenicity
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Introduction:The insertion footprint of the different muscles tendon fascicles of the Achilles Tendon on the calcanium tuberosity has not been described before.Method:Twelve fresh frozen leg specimens were dissected to identify the different Achilles Tendon fascicles insertion footprint on the calcaneum in relation to their corresponding muscles. Further ten embalmed cadaveric leg specimens were examined to confirm an observation on the retrocalcaneal bursa.Results:The superficial part of the AT insertion is made by tendon fascicles from the medial head of the gastrocnemius muscle which insert over the entire width of the inferior facet of the calcaneal tuberosity. In three specimens, this insertion had continuity with the plantar fascia in the form of periostium. The deep part of the TA insertion is made of fascicles from the soleus tendon which insert on the medial aspect of the middle facet of the calcaneal tuberosity while the lateral head of the gastrocnemius tendon fascicles insert on the lateral as...
Cadaveric spasm
Plantar fascia
Deep fascia
Fat pad
Fascicle
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Tendons consist of collagen (mostly type I collagen) and elastin embedded in a proteoglycan‐water matrix with collagen accounting for 65–80% and elastin approximately 1–2% of the dry mass of the tendon. These elements are produced by tenoblasts and tenocytes, which are the elongated fibroblasts and fibrocytes that lie between the collagen fibers, and are organized in a complex hierarchical scheme to form the tendon proper. Soluble tropocollagen molecules form cross‐links to create insoluble collagen molecules which then aggregate progressively into microfibrils and then into electronmicroscopically clearly visible units, the collagen fibrils. A bunch of collagen fibrils forms a collagen fiber, which is the basic unit of a tendon. A fine sheath of connective tissue called endotenon invests each collagen fiber and binds fibers together. A bunch of collagen fibers forms a primary fiber bundle, and a group of primary fiber bundles forms a secondary fiber bundle. A group of secondary fiber bundles, in turn, forms a tertiary bundle, and the tertiary bundles make up the tendon. The entire tendon is surrounded by a fine connective tissue sheath called epitenon. The three‐dimensional ultrastructure of tendon fibers and fiber bundles is complex. Within one collagen fiber, the fibrils are oriented not only longitudinally but also transversely and horizontally. The longitudinal fibers do not run only parallel but also cross each other, forming spirals. Some of the individual fibrils and fibril groups form spiral‐type plaits. The basic function of the tendon is to transmit the force created by the muscle to the bone, and, in this way, make joint movement possible. The complex macro‐ and microstructure of tendons and tendon fibers make this possible. During various phases of movements, the tendons are exposed not only to longitudinal but also to transversal and rotational forces. In addition, they must be prepared to withstand direct contusions and pressures. The above‐described three‐dimensional internal structure of the fibers forms a buffer medium against forces of various directions, thus preventing damage and disconnection of the fibers.
Fibrocyte
Dense connective tissue
Collagen fibril
Matrix (chemical analysis)
Type I collagen
Collagen fiber
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The objectives of this study were to evaluate the morphology and biomechanical function of Achilles tendons regenerated using knitted poly-lactide-co-glycolide (PLGA) loaded with bone marrow stromal cells (bMSCs). The animal model used was that of an adult female New Zealand White rabbit with a 10-mm gap defect of the Achilles tendon. In group I, 19 hind legs with the created defects were treated with allogeneic bMSCs seeded on knitted PLGA scaffold. In group II, the Achilles tendon defects in 19 hind legs were repaired using the knitted PLGA scaffold alone, and in group III, 6 hind legs were used as normal control. The tendon-implant constructs of groups I and II were evaluated postoperatively at 2, 4, 8, and 12 weeks using macroscopic, histological, and immunohistochemical techniques. In addition, specimens from group I (n = 7), group II (n = 7), and group III (n = 6) were harvested for biomechanical test 12 weeks after surgery. Postoperatively, at 2 and 4 weeks, the histology of group I specimens exhibited a higher rate of tissue formation and remodeling as compared with group II, whereas at 8 and 12 weeks postoperation, the histology of both group I and group II was similar to that of native tendon tissue. The wound sites of group I healed well and there was no apparent lymphocyte infiltration. Immunohistochemical analysis showed that the regenerated tendons were composed of collagen types I and type III fibers. The tensile stiffness and modulus of group I were 87 and 62.6% of normal tendon, respectively, whereas those of group II were about 56.4 and 52.9% of normal tendon, respectively. These results suggest that the knitted PLGA biodegradable scaffold loaded with allogeneic bone marrow stromal cells has the potential to regenerate and repair gap defect of Achilles tendon and to effectively restore structure and function.
Histology
PLGA
Hindlimb
Enthesis
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The aim of the study was to describe anatomy of the common calcaneal tendon in rat (Rattus norvegicus) and to correlate individual parts of the tendon with the muscles that act with the aid of them. Ten pelvic extremities of adult rats were fixed in 10% of formaldehyde and were dissected layer-by- layer method with microsurgical instruments under the operating microscope (4 and 10 fold magnification). The fascicles of the soleus muscle and the lateral head of the gastrocnemius muscle compose the deepest layer of the tendon. The fascicle of the medial head of the gastrocnemius muscle is located more superficially. The strong tendon of the plantaris muscle covers the fascicles listed above. The common calcaneal tendon in rat is composed of twisted fascicles attaching on the tuber calcanei. Fascicles of the following muscles: gastrocnemius and soleus are twisted along the long axis of the common calcaneal tendon, which is additionally strengthened from behind by the plantaris tendon. A detailed knowledge of anatomy of the common calcaneal tendon in rats provides a better understanding of pathology of the tendon. Conclusions are often extrapolated to the human calcaneal tendon.
Fascicle
Muscle belly
Plantaris muscle
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Abstract Forty embalmed cadaver lower limbs were dissected to identify the morphology of the conjoint junction of the tendons of gastrocnemius and soleus and the location of the gastrocnemius tendon relative to bony landmarks. Five patterns of conjoint junction morphology were found: transverse (25%), oblique passing distally and medially (45%), oblique passing distally and laterally (5%) and arcuate as an inverted U (17.5%) and a U‐shape (7.5%). Left‐right asymmetry of the junction was observed in 31.6% of 19 paired cadaver legs. On the medial side of the calf the gastrocnemius tendon could be located between 38 and 46% of the proportion of the distance between the upper border of the calcaneus and the fibular head. Corresponding values for the midline and lateral side of the calf were 45–58% and 48–51%. The location of the gastrocnemius tendon relative to bony landmarks may help to guide incision planning for open or endoscopic division of the tendon. Clin. Anat. 20:924–928, 2007. © 2007 Wiley‐Liss, Inc.
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Flexor Digitorum Longus
Foot (prosody)
Tendon transfer
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he Achilles tendon is among the most frequently injured tendons of the body with a variety of types of traumatic and overuse conditions affecting it. These conditions are common, often come to clinical attention, and are frequently imaged. The pathophysiology of Achilles disorders is complex, and the nomenclature is irregularly applied; this leads to miscommunication between clinicians and radiologists and inconsistencies in the literature. Therefore, we review the anatomy, MR imaging findings, and pathologic findings in an attempt to develop a systematic nomenclature. Gross Anatomy The Achilles tendon originates in the mid leg and is formed by the junction of the two heads of the gastrocnemius muscles and the soleus muscle [1, 2]. The bulk of the Achilles is formed from the gastrocnemius muscle. The larger medial head originates almost entirely from just proximal to the medial femoral condyle, and the smaller lateral head arises from both the posterior and lateral surfaces of the lateral femoral condyle. At the junction of the proximal and mid calf, the two heads of the gastrocnemius muscles and their tendons approximate midline. The gastrocnemius tendon origin is gradual, occurring over approximately 3‐4 cm. The fibers of the medial head originate slightly lower than those of the lateral head. The Achilles tendon is not formed until the soleus muscle inserts onto the gastrocnemius tendon, approximately 3‐4 cm more distally [2]. The plantaris muscle originates from the lateral meniscus and the lateral femoral epicondyle in close association with the lateral head of the gastrocnemius muscle. The plantaris tendon then crosses obliquely between the soleus and gastrocnemius muscles and continues just medial to the Achilles. Various plantaris insertions are seen, but most fibers insert on the medial aspect of the superior calcaneal tuberosity or 1 cm anterior and medial to the Achilles on the calcaneus, a distinct insertion point separate from that of the Achilles. The Achilles‐plantaris complex is termed the “triceps‐surae complex” [3].
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