Tarsal Coalition is an uncommon cause of flatfeet usually seen in children and young adults. It is caused by the formation of an abnormal join (coalition) between two or more of the bones of the hindfoot, most commonly the talus and calcaneum or calcaneum and navicular. The condition is present from birth but does not usually cause any problems until late childhood or early adolescence when the coalition stiffens up.
Tarsal coalition differs from the flexible flatfoot, much more commonly seen in children, in that the hindfoot becomes stiff and lacks side to side motion. No arch forms when the child goes up onto tiptoes and there may be pain in the foot or muscles of the lower leg. If the condition is left untreated arthritis may develop in the affected joint.
Tarsal coalition can be treated with orthotics (insoles) or steroid injection, but surgery to remove the abnormal bone is required if movement of the affected joint is to be restored. This can often be carried out with arthroscopic (keyhole) techniques. If the joint has become significantly arthritic, surgery to fuse it gives good relief of pain.