The Anatomy of the Achilles Tendon
Section snippets
Gastrocnemius
The gastrocnemius is the most superficial muscle. A fusiform muscle, it forms the lower boundary of the popliteal fossa and accounts for the bulge of the calf (Fig. 1) [2], [20]. The medial head of the gastrocnemius arises from the popliteal surface of the femur behind the medial supracondylar line and the adductor tubercle, above the medial femoral condyle. It is larger and longer, and extends more distally in the calf than the lateral head [2].
The lateral head is shorter and arises from the
Soleus
The soleus muscle is a broad, flat pennate muscle. It is wider than the gastrocnemius, and its muscle fibers extend more distally than those of the gastrocnemius. It originates from the posterior surface of the head and upper fourth of the posterior surface of the fibula, from a fibrous arch between fibula and tibia, and from the oblique line and the middle third of the medial border of the tibia. The popliteal vessels and the tibial nerve pass under the fibrous arch.
The soleus consists of two
Plantaris
The plantaris muscle has a variable size, and is absent in 6% to 8% of individuals. It has a short, fleshy origin from the popliteal surface of the femur above the lateral femoral condyle. The muscle belly is usually 5 cm to 10 cm in length, with a long tendon that extends distally between the gastrocnemius and the soleus. The tendon inserts into the medial border of the Achilles tendon, anterior to the Achilles tendon. In 6% to 8% of subjects, it inserts into the flexor retinaculum [21]. This
Achilles tendon
The Achilles tendon is approximately 15 cm long, and starts at the musculotendinous junction of the gastrocnemius and soleus in the middle of the calf. The tendon is flattened at its junction with the gastrocnemius to become rounded until approximately 4 cm from its insertion. At this level, it flattens, then expands and becomes cartilaginous, to insert into a rough area on the middle of the lower part of the posterior surface of the calcaneus. On its anterior surface, it receives the muscular
Structure of the Achilles tendon
Tendons appear white because they are mostly avascular. A tendon is a roughly uniaxial composite that is composed of mainly type I collagen in an extracellular matrix that is composed of mucopolysaccharide and a proteoglycan gel [35]. They consist of 30% collagen and 2% elastin embedded in an extracellular matrix that contains 68% water and tenocytes [36], [37]. Elastin contributes to the flexibility of the tendon. The collagen protein, tropocollagen, forms 65% to 80% of the mass of dry weight
Blood supply
The blood supply of tendons is variable, and usually is divided into three regions: the musculo-tendinous junction, the length of the tendon, and the tendon–bone junction. Blood vessels originate from vessels in the perimysium, periosteum, and by way of the paratenon and mesotenon. The Achilles tendon is supplied at its musculotendinous junction, along the length of the tendon, and at its junction with bone. The blood supply consists mainly of longitudinal arteries that course the length of the
Nerve supply
Tendons are supplied by sensory nerves from the overlying superficial nerves or from nearby deep nerves, the tibial nerve, and its branches [23]. The nerve supply is largely, if not exclusively, afferent [48], The afferent receptors are found near the musculo-tendinous junction [23], either on the surface or in the tendon. The nerves tend to form a longitudinal plexus and enter by way of the septa of the endotenon or the mesotenon if there is a synovial sheath. Branches also pass from the
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