Is Arthrodesis The Answer For A Severely Deformed Ankle?
Numerous conditions can result in the need for arthrodesis of the ankle joint. In particular, neuropathic osteoarthropathy, post-polio syndrome, neuromuscular disease and severe degeneration secondary to trauma can all make it especially difficult for podiatric surgeons to achieve a successful fusion.1-4 Although implant arthroplasty is gaining acceptance and distraction arthroplasty may postpone the joint destructive procedure, arthrodesis remains a viable and effective treatment for patients with gross deformity of the ankle.
While all patients will require modifications in surgical technique (and there are numerous articles in the literature addressing this at length), let’s take a brief look at some of the principles in successful surgical management of this condition.
Key Preoperative Considerations
Rotational, angular and limb length deformities necessitate the need for appropriate preoperative planning. The goal is not simply to achieve arthrodesis, but to achieve arthrodesis in the optimum functional position. A plantarflexed foot will force the knee into hyperextension. You will need to address any bone loss from previous talar collapse, prior infection or severe trauma. You need to determine if you can accommodate this with postoperative shoe modifications or surgically with extensive bone grafting.
The amount of autogenous bone will determine the graft harvesting site. In the majority of cases, you will need iliac crest bone. In cases of significant shortening, it may be necessary to perform tibial lengthening via distraction osteogenesis.
You must also correct valgus and varus positions. Typically, the rearfoot to leg relationship is positioned in neutral to slight valgus. Be sure to avoid performing a varus biased ankle arthrodesis as it can place significant stress on the knee joint. When it comes to treating significant deformities, I have found that performing a calcaneal osteotomy may also be necessary to completely align the hindfoot.
Also assess proximal deformity prior to performing an ankle arthrodesis. Especially when you’re dealing with cases of previous trauma, evaluating and considering proximal tibial or femoral deformities is a must. A well-positioned ankle arthrodesis is of little value if the overall position is compromised by proximal deformity.5,6
In an uncomplicated ankle arthrodesis, soft tissue structures are rarely a significant component of the deformity. In fact, a moderately contracted Achilles tendon can actually provide a tension-band effect and aid in successful fusion. This is typically not the case in severely deformed ankles. A long-standing deformity may require surgical treatment of the soft tissue. Ankle equinus or other tendinous contractures may require lengthening or a frank tenotomy. Skin contractures may require release, plasty, grafting or rotation flaps. If you do not assess and treat skin contractures at the time of surgery, skin complications can compromise the entire operation.
The form of fixation is also extremely important in this type of arthrodesis. Since there is a higher risk of non- or malunion, using external fixation or a combination of internal and external fixation can give you the ability to adjust the final position postoperatively. As with any surgery, your choice of fixation should be based upon your experience, the type of procedure and what is most suitable for the patient.
Step-By-Step Surgical Insights
Typically, the patient is in a lateral decubitus position under general or spinal anesthesia with a thigh tourniquet. Place the first incision over the distal aspect of the fibula, beginning approximately 10 cm proximal to the distal tip. You may curve the incision distally over the sinus tarsi to aid in exposure. More often than not, you’ll need to make a medial incision as well. This is due to the fact that a severely deformed ankle often requires extensive bone resection to maximize position. When this incision is necessary, make the approximately 5 cm incision over the anterior-medial aspect of the ankle joint.