When an achilles tendon rupture is misdiagnosed and not treated for a long time (often defined as over 4 weeks), the rupture is classified as a chronic one rather than an acute one. In most instances of chronic neglected ruptures, the gap between ruptured tendon ends exceeds a few centimeters, and surgery becomes far more complicated.
There is usually a need for grafting and tendon transfer, and a number of options exist. Among these include the use of allografts (another person’s tissue), autografts (patient’s own tissue), xenografts (animal tissue) or synthetic grafts. Below are some useful links that cover this subject:
Chronic Achilles Tendon Ruptures and Surgical Treatment
Flexor Hallucis Longus Tendon Transfer
Ligament Advanced Reinforcement System (LARS) graft