Tarsal coalition surgery
I had a long conversation today with a patient regarding surgery for a bilateral tarsal coalition. The patient is a 21 year old female who presented with deep achy pain in the rearfoot bilat. We had sent her for a CT scan that confirmed the presence of a calcaneal-navicular coalition bilaterally.
As described in the link above to our knowledge base page for tarsal coalitions, the evolution of a coalition follows a similar pattern. As a child, the patient has a rigid flatfoot that becomes increasingly more rigid over time. This change from semi-rigid to rigid occurs as the coalition ossifies. As a child, the coalition is a fibrous bridge (syndesmosis). This fibrous coalition is somewhat flexible and moves to accommodate motion. But as the patient reaches skeletal maturity, the fibrous union ossifies and the foot becomes rigid. This rigidity occurs in the late teens and early twenties.
The pain created by the ossification of the tarsal coalition is caused by a number of factors. The primary reason for pain is due to the stress that is placed on adjacent bone and soft tissue structures of the rearfoot. The subtalar joint is particularly effected by this alteration in loading.
My primary reason for obtaining the CT scan was not so much to rule in the CN bar, you could easily see it on plain films taken in the office. The CT scan was ordered to identify the degree of collateral damage that the subtalar joint has already sustained. And in this case, cystic erosion adjacent to the subtalar joint has already occurred. The importance of this finding is that the subtalar joint damage will continue to be painful even following resection of the CN bar. In most cases, this pain is only resolved with a subtalar joint fusion.
In the conversation today with my patient I think she was disappointed with my discussion of the problems associated with these surgeries. I detailed the fact that 50% of my patients will require a subtalar joint fusion due to continued pain. The patient was interested in doing both feet at the same time but I told her that was impossible. We also discussed the possibility of a primary fusion of the subtalar joint rather than doing a two stage surgery. We focused on what the community standard would be and I assured her that all surgeons would begin with just the resection of the tarsal coalition.
But that does bring up a good point. If most patients require a subtalar joint fusion, why aren't we performing that fusion at the time we resect the coalition? I think most surgeons will agree that the earlier the fusion the greater the chance of destruction of adjacent joint. By putting off the subtalar joint fusion you'll be sparing increased load to the ankle and midfoot that will result in early osteoarthritis of the ankle and midfoot.
Treatment of CN bars is just one of those problems that ultimately deserves a better solution.
Jeffrey A. Oster, DPM