Although I do a lot of trauma and reconstructive surgery, I still consider bunion surgery to be very challenging and at times, difficult. While we can easily evaluate the X-ray and select an appropriate procedure, we must also consider the function and cosmetic appearance of the foot. Perception of the final result can vary greatly between patients. Of course the patients want the bunion removed, but many want the great toe to be straightened.
The Austin-Akin procedure is the most common bunion procedure that I perform. My initial goal is to remove the bunion and to reduce the intermetatarsal (IM) angle. Preoperatively, I evaluate the bone via X-ray for osteopenia. In addition to looking for the cysts in the medial aspect of the first metatarsal head, I check for osteopenia of the first metatarsal diaphysis. If this is present, I may make the osteotomy slightly more proximal and use additional fixation or select a different procedure.
Often when one is shifting the metatarsal head laterally, if the bone is soft, the medial aspect of the head can drop into the medullary space, resulting in valgus rotation, adduction and dorsiflexion of the head. If this happens, I will insert a portion of bone from the bunion into the dorsal arm of the osteotomy positioned medially. This acts as a strut to prevent displacement and stabilizes the osteotomy as the fixation is inserted.
If the metaphysis and distal diaphysis of the first metatarsal is
essentially hollow, I will pack the entire space with autogenous bone and, if necessary, an allogenic product.
Also when it comes to bone this soft, I may use 0.62 Kirschner wire for fixation rather than screws. In osteoporotic bone, the cortex is usually very brittle and can easily crack when you tighten the screw, even when you are using a headless bone screw. I use a generous countersink to ensure that the head of the screw is flush with the bone as I tighten it.
When I reduce the metatarsal head, I want to reduce the IM space but I do not have a specific distance to achieve. Rather, I focus on correcting the bunion and aligning the joint. Most of the time this involves shifting the head laterally 3 to 4 mm. Excessive lateral positioning can result in instability and varus deformity with malalignment of the joint. also, If I have difficulty shifting the head laterally, it is almost always because we did not release the periosteum dorsally and laterally at the osteotomy site.
Due to the fact that I have had several Austin displacements, I now routinely use two screws for fixation. I insert the first screw through the metatarsal head in a traditional manner. I then insert a second screw on the dorsal surface proximal to distal and plantar. The tip of the screw is in the metatarsal head but does not penetrate the plantar cortex. This screw provides additional protection against axial loading as it prevents dorsal and medial displacement.
The next step is to address the dorsal medial aspect of the metatarsal head. Even with excellent correction of the bunion and no elevatus, I will go back and rasp that area. This is the area that shoes may rub against.
After I have performed and fixated the Austin and akin osteotomy the final step is to evaluate the joint capsule.
Usually, there is redundant capsule. I use and "L"-shaped capsulotomy and I will remove an appropriate section of the capsule medially. This tends to provide nice stability to the joint. I never overlap the capsule. If the edges do not line up perfectly, I remove a larger section. If the capsule is overlapped medially or bunched up, it looks like a portion of the bunion is still present postoperatively and this soft tissue prominence may not resolve with time.
I'm sure everyone is familiar with these techniques, but if your
results are less than optimal, you might benefit form these tips.