21-07-2012, 11:43 AM
Anatomy of the Body
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The Achilles is the tendonous extension of two muscles in the lower leg: gastrocnemius and soleus . In humans, the tendon passes behind the ankle. It is the thickest and strongest tendon in the body. It is about 15 centimetres (6 in) long, and begins near the middle of the calf, but receives fleshy fibers on its anterior surface, almost to its lower end. Gradually becoming contracted below, it is inserted into the middle part of the posterior surface of the calcaneus, a bursa being interposed between the tendon and the upper part of this surface. The tendon spreads out somewhat at its lower end, so that its narrowest part is about 4 centimetres (1.6 in) above its insertion. It is covered by the fascia and the integument, and stands out prominently behind the bone; the gap is filled up with areolar and adipose tissue. Along its lateral side, but superficial to it, is the small saphenous vein. The Achilles' muscle reflex tests the integrity of the S1 spinal root. The tendon can receive a load stress 3.9 times body weight during walking and 7.7 times body weight when running.
Pathomechanics
Prolonged pronation
As the foot moves from heel strike to foot flat, a certain amount of pronation is necessary to allow the foot to adapt to the surface contour. During excessive pronation, the achilles tendon is at risk for injury. Factors that may cause excessive pronation are forefoot and rarefoot varus, forefoot valgus, and a plantarflexed fifth ray. Internal torsional deformities of hip, femur or tibia, leg lentgh inequalities and muscular shortness of the iliopsoas, hamstrings or gastrocnemius/soleus complex preventing full dorsiflexion of the ankle require abnormal, excessive, subtalar joint pronation.
Prolonged pronation causes tibial internal rotation, pulling the achilles tendon medially. As push off occurs, there is a resultant bowstring or whipping effect, pulling the tendon laterally. This whipping effect may contribute to microtears in the tendon, especially on the medial side.
As the foot moves from mid-stance to push off; the tibia is being externally rotated by knee extension and foot supination. If the foot is excessively pronated and the knee begins to extend, the forces of external tibia rotation at the knee and internal tibia rotation at the ankle occur simultaneously. The resultant torsional force on the achilles tendon mau cause an ischemic “wringing out” at or near the avascular zone, predisposing the tendon to degenerative changes.
Tendon mechanics
Long tendons are most suited for absorbing large forces placed on them during athletic activity, since tendon is stronger than muscle per unit area, it would appear that the achilles tendon is ideally designed to withstand the high forces of running and jumping. However, the tendon is derived from two muscles and has interdigitating fibres that twist as they descend. This may produce areas of high stress concentration.
The achilles tendon absorbs forces in two planes: the sagittal plane(dorsiflexion and plantarflexion), and the frontal plane(eversion and inversion). These combined stresses can create unequal tensile forceson different parts of the tendon. This relates to the torsional ischemic “wringing out”.
Forces that tend to place hoghest stress on the achilles tendon occur during eccentric contraction of the gastrocnemius/soleus muscle complex. Examples of these include: pushing off the weight bearing foot while simultaneously extending the knee, as in uphill running; suddenn ankle dorsiflexion that occurs enexpectedly, such as when stepping up a step and then slipping off with the heel dropping; and rapid involuntary dorsiflexion of a plantarflexed foot.
Poor flexibility
Lack of flexibilty in the calf musculature predisposes an individual to achilles tendon injury. The relationship of length to injury can be described in terms of muscle-tendon unit’s resting length. When the resting length is increased, decreased strain(deformation) takes place during a particular range of movement. A shortened achilles tendon is placed under greater strain than a longer tendon. Also, lack of adequate dorsiflexion may cause unwanted compensation by excessive pronation.
Chronic tendonitis:
Gradual onset of pain over a period of weeks, or even months.
Pain with all exercise, which is constant throughout.
Pain in the tendon when walking especially up hill or up stairs.
Pain and stiffness in the Achilles tendon especially in the morning or after rest.
There may be nodules or lumps in the achilles tendon, particularly 2-4cm above the heel.
Tenderness on palpation.
Swelling or thickening over the Achilles tendon.
redness over the skin.
a creaking is felt when one presses his/her fingers into the tendon and move the ankle.