Treatment For Calcaneonavicular Coalition: Better But Not Perfect

Orthopedic surgeons are often faced with the frustration of knowing that a commonly accepted and used surgical technique doesn't always work. In this article, surgeons who treat children for a problem called calcaneonavicular coalition present their technique for dealing with this condition.

Calcaneonavicular coalition refers to the fusing of two bones in the foot: the calcaneus (heel bone) and the navicular bone. The navicular is an important bone because it joins with many other bones in the foot and ankle. It is located on the medial side of the foot (side closest to the other foot). It articulates (moves against) the four and sometimes five other ankle bones.

When calcaneonavicular coalition occurs, the affected individual (usually a child between the ages of eight to 12 years old) reports ankle pain with loss of motion. They are no longer able to point the foot down all the way. Turning the foot and ankle inward can also be limited. The loss of these motions makes it difficult to walk, run, and participate in daily activities at school.

It appears that the bones are fused or held together with a thick, binding cartilage. It's likely the child was born with this problem but sudden, rapid growth during the later childhood years just before puberty brings it to the attention of parent or child. Sometimes ankle or foot injuries (sprains or fractures) occur because of reduced hindfoot motion. An X-ray brings to light the cause of the underlying loss of motion as the coalition is visible with radiographs.

Treatment is usually surgical with resection (removal) of the extra bone. Left untreated, besides being painful and limiting, the joint eventually develops degenerative arthritis. Removing the cartilage that bridges the two bones leaves a deep hole in the foot. The hole that is filled with muscle from the extensor digitorum brevis (EDB) in the foot. The muscle is detached and pulled into the hole with its tendon rolled up to fill the space.

The problem is that in some patients, the coalition grows back. And even for those whose bone doesn't grow back, the bump that's left after surgery is unsightly and rubs against the shoes. In this study, they tried using a fat graft instead of the muscle and tendon, thinking it would fill the hole more completely and prevent regrowth. But even with more than enough fat to fill the area, there were still a fair number of recurrences.

The surgeons asked, Why? What happened? If they were careful to get all of the coalition, why did it grow back, a process called reossification? Patients with regrowth had good results at first with the excision and fat graft. Everything looked good on X-rays and then foot pain returned and loss of motion developed.

The surgeons had hoped that using fat instead of the muscle/tendon to fill the hole would be a better way to prevent regrowth. And, in fact, there were fewer cases of regrowth when using a fat graft compared with tendon, but fibrous regrowth still occurred. The use of fat as a filler has several advantages over tendon interposition. For one thing, the tendon really isn't long enough to fill the entire hole. Fat is always plentiful. For another, it's easier to shape the results with fat, avoiding cosmetic disasters, such as obvious lumps and bumps that rub against shoes and sandals.

The authors conclude that fat grafts have better overall results than tendons to fill the hole left by excision of the calcaneonavicular coalition. But the outcomes aren't perfect yet, so further study is needed to find out why not. Is it something about the individual patient that could be predicted ahead of time? Is there a better technique than even the fat graft? What is it that stimulates regrowth of the coalition? These and other questions will help guide future studies in this area.

Reference: 

Scott J. Mubarak, MD, et al. Calcaneonavicular Coalition. Treatment By Excision and Fat Graft. In Journal of Pediatric Orthopaedics. July/August 2009. Vol. 29. No. 5. Pp. 418-426.

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