Functional anatomy of the Achilles tendon

Abstract

The Achilles tendon is the strongest and thickest tendon in the human body. It is also the commonest tendon to rupture. It begins near the middle of the calf and is the conjoint tendon of the gastrocnemius and soleus muscles. The relative contribution of the two muscles to the tendon varies. Spiralisation of the fibres of the tendon produces an area of concentrated stress and confers a mechanical advantage. The calcaneal insertion is specialised and designed to aid the dissipation of stress from the tendon to the calcaneum. The insertion is crescent shaped and has significant medial and lateral projections. The blood supply of the tendon is from the musculotendinous junction, vessels in surrounding connective tissue and the osteotendinous junction. The vascular territories can be classified simply in three, with the midsection supplied by the peroneal artery, and the proximal and distal sections supplied by the posterior tibial artery. This leaves a relatively hypovascular area in the mid-portion of the tendon where most problems occur. The Achilles tendon derives its innervation from the sural nerve with a smaller supply from the tibial nerve. Tenocytes produce type I collagen and form 90% of the cellular component of the normal tendon. Evidence suggests ruptured or pathological tendon produce more type III collagen, which may affect the tensile strength of the tendon. Direct measurements of forces reveal loading in the Achilles tendon as high as 9 KN during running, which is up to 12.5 times body weight.

Ultrasonography and Low-field Magnetic Resonance Imaging of the Common Calcanean Tendon in a Rabbit Model for Tendinopathy Research: a Descriptive Study of Normal Anatomy

“…The calcaneal tendon is accompanied by the superficial digital flexor tendon and together they form the common calcanean tendon. As these tendons track distally, they rotate in a lateral direction, which reflects the spiral arrangement of the fibers and fascicles of the human Achilles tendon (Doherty et al 2006, Szaro et al 2009, Doral et al 2010). Due to the lateral rotation, at the level of the calcaneal tuber the superficial digital flexor tendon is positioned immediately caudal to the calcaneal tendon insertion (Doherty et al 2006).…”

“…Consequently, we do not distinguish the common calcanean tendon in a man and all described Achilles tendinopathies refer clearly to the calcaneal tendon, i.e. the tendons of the gastrocnemius and soleus (Szaro et al 2009, Doral et al 2010. It should be kept in mind that, the analysis of the experimental research with laboratory animals utilizing the components of the common calcanean tendon, like superficial digital flexor tendon or tendons of the medial or lateral head of the gastrocnemius, are applied to the human calcaneal tendon pathologies only by analogy and not by straightforward translation.…”

Achilles tendon: functional anatomy and novel emerging models of imaging classification

“…The medial and lateral heads fuse in a single muscle belly occupying the posterior superficial compartment of the lower leg [41,45]. Deep to the gastrocnemius there is the soleus, a large flat, pennate muscle [14]. Together with the gastrocnemius, it forms the three-headed triceps surae, which acts to plantarflex the ankle joint via its conjoint tendon, the Achilles tendon.…”

A Study on the Structure and Morphologic Development of Calcaneal Tendon and Triceps Surae Muscle in Human Fetuses during the Fetal Period and the Evaluation of Clinical Importance of Calcaneal Tendon

“…Separately, plantaris muscle may also participate in the formation of calcaneal tendon (Doral et al, 2010;Grechenig et al, 2004;O'Brien, 2005;Pichler et al, 2007;Standring et al, 2008). The length of the tendon in adults is approximately 15 cm.…”

“…During running, jumping and skipping, calcaneal tendon is exposed to strain ten times as much as the body weight and can lengthen by 4% more before sustaining any injury and therefore, tendon ruptures commonly occur (Doral et al; O'Brien). It is expressed that tendon ruptures occur more in males due to the fact that calcaneal tendon is of a rigid character in them (Doral et al, 2010). Besides, it is stated in studies that achilles tendinopathy occurs commonly in athletes (Zafar et al, 2009).…”