[Our Experience with Trabecular Metal Total Ankle System]

One of the surgical treatment options for advanced ankle joint destruction with various etiologies is the total joint replacement. Its significant upside is the preservation of range of motion of the ankle joint and less stress on forefoot joints compared to ankle arthrodesis. Since 2022, we have been using the Zimmer Trabecular Metal Total Ankle inserted via a lateral transfibular approach. This study aims to evaluate the initial outcomes and experience with this implant.

Between 2022 and 2024, 65 total ankle replacements were performed in 63 patients using the lateral transfibular approach. Long oblique osteotomy is newly performed in the frontal plane, replacing the original type of osteotomy in the sagittal plane. After releasing and removing the distal fragment of the fibula distally and dorsally, the lower limb and ankle are placed in an alignment frame, which is fixed with Steinmann pins to the calcaneus, anterior border of the tibia, and the talus bone. The centre of rotation of the ankle is identified using the side bars anchored in the frame. Using the burs, guided by Cutting Guides that are locked to the frame, the talus and distal tibia are removed. After testing, rail holes are drilled in the resected surfaces for the original implants. After releasing the tourniquet, the original components are inserted and osteosynthesis of the fibula is performed. During the study, the previously performed fibula osteosynthesis with LCP was replaced by lag screws. Postoperatively, the ankle is supported with a brace for the period of 5 weeks, after which the patient is permitted to fully weight-bear.

A total of 63 patients (32 women and 31 men) were followed, in whom 65 total ankle replacements were performed. The mean age of the patient was 56 years (age range 30 to 80 years). The mean follow-up period was 14.6 ± 9.3 months (3 to 38 months). The most frequent indication was post-traumatic ankle arthritis, namely in 46 cases (70.8%). Furthermore, there were 5 patients (7.7%) with post-traumatic ankle ankylosis, 9 patients (13.8%) with primary osteoarthritis, and in 5 patients (7.7%) the indication was the damage caused by rheumatoid arthritis. Deep bacterial infection of the prosthesis requiring revision was reported in 3 cases (4.6%). Superficial infection of the surgical wound was seen in 4 other cases (6.2%), which did not require hospitalization. Plate osteosynthesis of the fibula was removed in 7 cases (13.8%), 5 times due to infection and 2 times due to soft tissue irritation. One case of asymptomatic non-union of fibula was observed.

The benefit of total ankle replacement is the preservation of motion of the operated joint, whereas the complication rate is twice as high as in arthrodesis. Contraindications for ankle replacement include significant varus and valgus deformities of the ankle, ankle instability, necrosis of the talus, severe diabetes mellitus, and severe limb ischemia. The advantage of the transfibular approach is the ability to partly correct deformities of the ankle joint and the position of varus or valgus. It provides a better view of the dorsal structures of the ankle and allows accurate identification of the centre of rotation. Another advantage is the low thickness of the components, requiring minimal bone resection. The main disadvantage is the longer operative time and longer learning curve. Other disadvantages include the complications associated with osteosynthesis and fibula healing, such as non-union or soft tissue irritation by plate. The incidence of superficial and deep infection is also slightly higher compared to the anterior approach.

The Zimmer Trabecular Metal Total Ankle system is one of the treatment options for ankle joint destruction provided it is correctly indicated. However, the surgical procedure is a challenge and requires an experienced surgeon. When the indication is correct, the system brings very good short-term outcomes. Nonetheless, longer follow-up period is necessary since the incidence of complications will certainly increase over time.