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Causes of Ankle Fracture After Ankle Replacement

Posted on: 05/29/2013
It doesn't happen very often but ankle fracture after a total ankle replacement (TAR) is possible. Every effort is being made to reduce the number of these cases. In fact, in this study of over 500 patients, surgeons note that their own work has improved over time. In the first 100 cases, the rate of intraoperative fractures (those that occurred during the surgery) went from three out of every four patients down to one of every three. By the end of the study, only two per cent of the last 100 patients experienced an intraoperative periprosthetic (around the implant) fracture.

What made the difference? There were several possible factors contributing to the improved results. Surgeons gained experience over time. Operative techniques improved as did surgical instruments. And even the implant designs improved over time. Some patients still developed post-operative fractures but these were from stress (overload) and trauma (injury).

The authors expect that as results following total ankle replacement continue to improve, more and more surgeons will choose ankle replacement over ankle fusion (called arthrodesis). Preserving motion and function (especially in younger, active patients) is the number one reason for this choice. And along with the increasing number of candidates for total ankle replacement may come an increasing number of periprosthetic ankle fractures (both intraoperative and postoperative).

Because of this expectation, there is a need for a classification system that will assist surgeons in making decisions about what to do after such a fracture occurs. The authors of this study offer their proposed classification system. This classification model is centered around three key factors: 1) cause of the fracture, 2) location of the fracture, and 3) stability of the implant (also known as the prosthesis).

Using their patient base of 503 people, they divided the classification of periprosthetic ankle fractures based on cause into three categories: Type 1 - intraoperative fracture, Type 2 - postoperative traumatic fracture, and Type 3 - postoperative stress fracture. The classification model divides fracture location into four groups (A, B, C, and D) based on whether the fracture occurred in the medial malleolus, lateral malleolus, tibia, or talus.

And the last classification variable (implant stability) has two possibilities: stable or unstable. A stable implant is not loose and the fracture does not affect the implant. An unstable implant has signs of loosening with loss of bone around the implant. Each of these three classification parameters (location, type, implant stability) helps determine and guide treatment.

For example, a nondisplaced fracture (the bones have not separated at the fracture site) with no sign of implant loosening can be managed nonoperatively (without surgery). But when there is fracture displacement, implant shifting or loosening, or malpositioning of the implant, then it becomes necessary to perform corrective surgery. And each one of those problems calls for a different surgical approach ranging from bone graft to joint fusion.

In summary, the authors of this study used the results of their 503 patients to design a decision-making classification model to aid and assist management of periprosthetic fractures. The fractures may occur during or after surgery. They may develop as a result of improper implant size or position, mechanical overload of the implant, or weakening of the bone from the surgery. This classification model is practical and easy to apply. How effective it is (i.e., how good are the outcomes of each decision based on this method) remains to be determined in future studies.

Sebastian Manegold, MD, et al. Periprosthetic Fractures in Total Ankle Replacement: Classification System and Treatment Algorithm. In The Journal of Bone and Joint Surgery. May 2013. Vol. 95A. No. 9. Pp. 815-820.

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