Achilles tendonitis is basically inflammation of the Achilles tendon. If sudden trauma is not the cause, it is mostly caused by excessive pronation which causes the heel bone to evert 'roll inwards' increasing the shearing force applied to both the tendon and the protective layer of the tendon. Overtime this causes micro-tearing of tendon fibres which causes pain in the tendon. Pain is usually experienced at the attachment site being the weakest part of the tendon. In some cases bony spurs develop and can be seen on x-rays.
Treatment involves the use of orthotics to reduce pressure on the tendon with the addition of a heel lift to reduce over-stretching of the tendon mainly in the acute phase of injury. Calf stretching is used in the later stages. Dry needling and shockwave therapy are also very effective treatment methods when used in combination with orthotic therapy.