Total Talar Replacement: Surgical Technique.

BACKGROUND

Total talar replacement is a salvage procedure for end-stage osteonecrosis of the talus. A customized total talar implant is designed with use of computed tomography scans of the healthy opposite side and made of alumina ceramic. The use of such an implant is potentially recommended, with a guarded prognosis, for the treatment of traumatic, steroidal, alcoholic, systemic lupus erythematous, hemophilic, and idiopathic pathologies. The talus is surrounded by the tibia, fibula, calcaneus, and navicular bones, which account for a large portion of the articular surface area. Yoshinaga reported that alumina ceramic prostheses were superior in terms of congruency and durability of articular cartilage compared with 316L stainless steel in an in vivo test in dogs. Therefore, alumina ceramic is an ideal material for replacement of the talus to preserve postoperative hindfoot mobility.

DESCRIPTION

Total talar replacement is performed with the patient in a supine position. The anterior ankle approach is utilized to exteriorize the talus, facilitating dissection of the ligaments and joint capsule attached to talus. The first osteotomy is performed around the talar neck, perpendicular to the plantar surface of the foot. The talar head fragment is then removed. Subsequent talar osteotomies are performed parallel to the first cutting line, at approximately 2-cm intervals. The attaching articular capsule and ligaments are dissected in each step. The removal of the posterior talar bone fragments is succeeded by careful dissection of the ligament and joint capsule under the periosteum. After dissecting the remaining interosseous talocalcaneal ligament, the foot is distally retracted and a customized talar implant is inserted. After testing and confirming the stability and mobility of the implant, the wound is irrigated with use of normal saline solution. A suction drain is placed anterior to the implant, and the skin is closed after repairing the extensor retinaculum.

ALTERNATIVES

In cases with a limited area of necrosis, symptoms may improve with a patellar tendon-bearing brace. However, in many cases of symptomatic osteonecrosis of the talus, nonoperative treatment is not expected to improve symptoms. Alternative surgical procedures include ankle arthrodesis and hindfoot arthrodesis, but there are risks of nonunion, leg-length discrepancy as a result of extensive bone loss, and functional decline because of loss of hindfoot motion.

RATIONALE

Total talar replacement is a fundamentally unique treatment concept in which the entire talus is replaced with an artificial implant. Compared with ankle or hindfoot arthrodesis, this procedure preserves the range of motion of the foot and allows for earlier functional recovery. Postoperative results were satisfactory in the subjective evaluation, with no failure requiring revision. This procedure reduces the risk of postoperative failure in patients who are elderly and/or have underlying diseases, who often require a long recovery time. As the talus is a small bone with uniquely vulnerable vascularity, treatment of talar pathology is usually difficult; however, total talar replacement is a potential treatment option for patients with end-stage osteonecrosis of the talus without obesity.

EXPECTED OUTCOMES

The greatest advantage of total talar replacement is the preservation of ankle and hindfoot mobility. Second, a customized talar prosthesis based on a mirrored model of the contralateral, unaffected talus will allow the smooth transfer of body weight from the lower leg to the heel and forefoot-a requirement for a stable gait. Third, the artificial talar prosthesis has a potential advantage in that it minimizes leg-length discrepancy, preventing daily inconvenience for the patient. Twenty years after the development of the implant, replacement with a total talar prosthesis resulted in a median score of 97 out of 100 on the Japanese Society for Surgery of the Foot (JSSF) Ankle-Hindfoot Scale as an objective evaluation and yielded a significant improvement in the subjective evaluation of the Ankle Osteoarthritis Scale (AOS) in a follow-up study over 10 years. The median ankle joint range of motion was 45°, and complications requiring implant replacement never occurred.

IMPORTANT TIPS

The skin incision should be placed at the center of the inferior tibial articular surface and curved medially to avoid the medial branch of the superficial peroneal nerve.During the resection of the talus, the attaching ligament and joint capsule are recommended to be debrided prior to osteotomy.Bone fragments should be removed as an entire block in order to avoid leaving small fragments.When inserting the artificial talus, pull the entire foot distally by grasping the heel in order to avoid excessive plantar flexion.During wound closure, the extensor retinaculum should be repaired to avoid skin bowstringing.Although favorable long-term results have been reported, postoperative outcomes in patients with high body mass index have not been adequately investigated. This procedure should be carefully selected on the basis of the physical characteristics of the patient.

ACRONYMS AND ABBREVIATIONS

AVN = avascular necrosis (osteonecrosis)SLE = systemic lupus erythematousCAD = computer-aided designCT = computed tomographyJSSF = Japanese Society for Surgery of the FootIQR = interquartile rangeAOS = Ankle Osteoarthritis ScalePWB = partial weight-bearingW = weeks.