Achilles Tendonitis

Achilles Tendonitis - A violent strain can cause injury to the calf muscles or the achilles tendon. This can happen during a strong contraction of the muscle, as when running or sprinting. Landing on the ground after a jump can force the foot upward, also causing injury. The strain can affect different portions of the muscles or tendon. For instance, the strain may occur in the belly of the muscle. Or it may happen where the muscles join the achilles tendon (called the musculotendinous junction). Chronic overuse may contribute to changes in the achilles tendon as well, leading to degeneration and thickening of the tendon.

The achilles tendon joins three muscles: the two heads of the gastrocnemius and the soleus. The gastrocnemius heads arise from the posterior portions of the femoral condyles. The soleus arises from the posterior aspect of the tibia and fibula. The gastrocnemius is a muscle that crosses three joints: the knee, the ankle, and the subtalar joint. The functioning of these joints and influence of other muscles on these joints has a significant effect on the tension that occurs within the achilles tendon. As an example tight hamstrings impact the functioning of the ankle joint, the subtalar joint, and increase tension in the achilles tendon. The soleus does not cross the knee and is a biarticualar muscle. The plantaris is a nearby muscle that has its separate tendon. It arises from the lateral condyle of the femur. It has a thin tendon that passes between the gastrocnemius and soleus and inserts into the calcaneus. When this musclculotendinous structure is injured it is frequently felt as a "pellet shot" in the back of the leg. The tear is usually about eight inches below the knee joint. The bulk of the achilles tendon inserts into the posterior superior third of the calcaneus. Some fibers course distally and continue to where portions of the plantar fascia insert into the plantar aspect of the calcaneus. The achilles tendon does not have a rich blood supply. It is not invested within a true tendon sheath. A paratenon composed of other soft tissue surround it. The outer layer is a portion of the deep fascia, the middle layer is called the mesotenon and the inner layer is a thin layer. The blood supply to the proximal portion of the tendon comes from the branches of the muscles themselves. The distal portion is supplied by branches from the tendon-bone interface. The mesotenon supplies the major blood supply to the Achilles tendon.