Characteristics of the Diseased Ankle.- Ankle Arthrodesis.- Anatomic and Biomechanical Characteristics of the Ankle Joint and Total Ankle Arthroplasty.- History of Total Ankle Arthroplasty.- Current Designs of Total Ankle Prostheses.- Preoperative Considerations for Total Ankle Arthroplasty.- Surgical Techniques.- Postoperative Care and Follow-Up.- What is Feasible in Total Ankle Arthroplasty?.- Complications of Total Ankle Arthroplasty.- Future Directions.
Chapter 8 SURGICAL TECHNIQUES (p. 105)
Although many surgical approaches have been described in the literature, most current total ankle prostheses are implanted using the standard anterior ankle approach. Because of the fragility of the soft tissues around the ankle, however, and scars from previous injuries or surgeries, the approach sometimes demands a modified technique in order to prevent wound healing problems. Various techniques are used to implant current ankle prostheses. In most cases, however, a jig is used to align a tibial resection block with respect to the longitudinal axis of the tibia. Talar resection is made, to some extent, as a free-hand surgery. In some cases (with the AGILITYTM ankle, for example), an external fixator/ distractor is used to realign the ankle and tension the ligaments.
8.1 Preoperative Planning
Recognizing critical preoperative risk factors and doing careful preoperative planning are important factors for limiting complications and obtaining satisfactory results. Meticulous clinical and radiological assessment is required. Clinically, the surgeon should examine and document the softtissue conditions, hindfoot alignment, ankle stability, foot deformities, foot vascularization, and sensibility. Lateral and anteroposterior weightbearing radiographs of the foot and ankle are mandatory, and may help to identify possible osteoarthritis in adjacent joints, as well as varus and valgus deformities of the hindfoot and longitudinal arch. The use of MRI may also help to determine the condition of the subchondral bone, particularly with respect to potential osteonecrosis.
8.2 Surgical Approach to the Ankle
Most of the current total ankle prostheses (the Buechel-PappasTM ankle [15], the HINTEGRA® ankle [8], the TNK ankle [19], the Ramses ankle [16], the SALTO® ankle [2], and the S.T.A.R. ankle [14]) are implanted using the standard anterior ankle approach, which uses a single incision between the anterior tibial and extensor hallucis longus tendons. The AGILITYTM ankle uses the same anterior incision, as well as a lateral incision over the distal fibula to mobilize and bridge the tibiofibular syndesmosis [17]. The ESKA ankle, by contrast, is implanted using a single lateral (transfibular) approach [18].
8.2.1 Anterior Approach to the Ankle
The patient is positioned supine, with the heel of the foot on the edge of the table. A support beneath the ipsilateral hip, and/or tilting the table serves to get the foot in an upright position so that the ankle is seen from the front side of the leg (Fig. 8.1). A longitudinal skin incision is made over the center of the ankle (Fig. 8.2), taking care to identify and retract the medial branch of the superficial peroneal nerve (Fig. 8.3). The approach is made longitudinally between the extensor hallucis longus and anterior tibial tendons, through the tendon sheet of the extensor hallucis longus [5, 21] or of the anterior tibial tendon [8, 10]. Once the distal tibia is exposed just beneath the anterior tibial tendon ("safety area"), the soft tissues are pushed sideways using a raspatory subperiosteally. Then, the neurovascular bundle is retracted laterally, and two Hohmann retractors are inserted (Fig. 8.4). The ankle capsule is incised vertically over the midpoint of the ankle. Note that it may be necessary to excise the central part of this capsule to gain good exposure.
