Syndesmosis Fusion in the Agility Total Ankle Arthroplasty

CHAPTER PREVIEW

CHAPTER SYNOPSIS:

A solid syndesmosis fusion is critical for the success of the Agility ankle replacement system. This chapter will deal with both preventing and managing nonunions of syndesmosis fusions.

IMPORTANT POINTS:

1

Syndesmosis fusion is of utmost importance for the success of an Agility total ankle arthroplasty.
2

Adequately prepare both the fibula and tibia.
3

Always bone graft the syndesmosis.
4

Adequately compress across the syndesmosis—a plate and screw system will give better compression than screws alone.

CLINICAL/SURGICAL PEARLS:

1

Remove all soft tissue from the fusion site.
2

Drill or “feather” the opposing bony surfaces.
3

Do not overstuff the joint. It is easier to fuse the syndesmosis if there is primary contact.
4

Use copious amounts of bone graft.
5

Ensure good compression across the fusion site
6

Consider use of platelet-rich concentrate, especially in nonunions.

CLINICAL/SURGICAL PITFALLS:

1

Syndesmosis nonunion is the single most common reason for failure of the Agility total ankle arthroplasty.
2

The fibula is posterolateral to the tibia. Adequate exposure could be difficult in posttraumatic cases.
3

Do not hinge the syndesmosis open. It might result in a fracture. Releasing the anterior and posterior tibiofibular ligaments will allow the syndesmosis to spread open without hinging on the posterior tibiofibular ligaments.

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HISTORY/INTRODUCTION/SCOPE OF THE PROBLEM

The Agility (DePuy, Warsaw, IN) total ankle was introduced in 1984 and is still the most frequently implanted ankle replacement in the United States. To address problems encountered in first-generation total ankle arthroplasties, the Agility design incorporates a fusion of the syndesmosis. Syndesmosis fusion increases the surface area available for both bone in-growth and weight-bearing and allows for resurfacing of both malleolar articulations. Therefore, the addition of a syndesmosis fusion potentially results in enhanced fixation, decreased tibial subsidence, and partial load transfer to the fibula ( Fig. 16-1 ).

Multiple studies have confirmed that syndesmosis fusion is paramount to the success of the Agility total ankle arthroplasty. Pyevich et al. found delayed or nonunion of the syndesmosis to be associated with migration of the tibial component, ballooning lysis at the bone implant interface, and circumferential lucency around the tibial component. The risk ratio for tibial migration in the setting of syndesmosis nonunion was 8.5 ( Fig. 16-2 ).

Although this study did not demonstrate a significant association between syndesmosis nonunion and pain, a longer-term follow-up study by the same group did find that delayed or nonunion of the syndesmosis predicted both a higher pain score and a higher disability score. This group also found that bony lysis halted with definitive radiographic evidence of syndesmosis fusion and continued to progress in cases of nonunion. In the study by Saltzman et al., 67% of the ankles with migration of the tibial component had delayed or nonunions of the syndesmosis ( Fig. 16-3 ).

Unfortunately, delayed or nonunion of the syndesmosis continues to be one of the most common complications of the Agility total ankle arthroplasty and a frequent cause of reoperation.

For most surgical procedures, that would be an unacceptable nonunion or delayed union rate even though not all cases require subsequent surgical treatment. Spirt et al. reported a 4.6% reoperation rate for radiographic evidence of syndesmosis nonunion and “substantial pain” with no other identifiable source, and 8.9% of the cases reported by Saltzman et al. required refusion of the syndesmosis. In addition, since delayed or nonunion of the syndesmosis is strongly associated with tibal loosening, failure to achieve union of the syndesmosis may be the underlying reason for a larger number of revision procedures than is reported.

INDICATIONS/CONTRAINDICATIONS

Fusion of the distal tibiofibular syndesmosis is indicated in, and is critical to, every Agility total ankle arthroplasty. Any contraindication to syndesmosis fusion would constitute a contraindication to the Agility total ankle arthroplasty itself.

SURGICAL TECHNIQUE

In the original technique guide for the Agility replacement system, it was advocated to use the standard midline anterior approach for the ankle replacement part and use a separate lateral incision for the syndesmosis. This is still an acceptable approach, but the reality is that it is very simple to prepare the syndesmosis through the anterior incision as well. Using one incision potentially limits the risk of vascular compromise to the skin flap ( Fig. 16-4 ).