Development of an internally braced prosthesis for total talus replacement

Abstract

Total loss of talus due to trauma or avascular necrosis, for example, still remains to be a major challenge in foot and ankle surgery with severely limited treatment options. Implantation of a custom made total talar prosthesis has shown promising results so far. Most important factors for long time success are degree of congruence of articular surfaces and ligamentous stability of the ankle. Therefore, our aim was to develop an optimized custom made prosthesis for total talus replacement providing a high level of primary stability. A custom made hemiprosthesis was developed using computed tomography and magnetic resonance imaging data of the affected and contralateral talus considering the principles and technology for the development of the S.T.A.R. prosthesis (Stryker). Additionally, four eyelets for fixation of artificial ligaments were added at the correspondent footprints of the most important ligaments. Two modifications can be provided according to the clinical requirements: A tri-articular hemiprosthesis or a bi-articular hemiprosthesis combined with the tibial component of the S.T.A.R. total ankle replacement system. A feasibility study was performed using a fresh frozen human cadaver. Maximum range of motion of the ankle was measured and ligamentous stability was evaluated by use of standard X-rays after application of varus, valgus or sagittal stress with 150 N. Correct implantation of the prosthesis was technically possible via an anterior approach to the ankle and using standard instruments. Malleolar osteotomies were not required. Maximum ankle dorsiflexion and plantarflexion were measured as 22-0-28 degrees. Maximum anterior displacement of the talus was 6 mm, maximum varus tilt 3 degrees and maximum valgus tilt 2 degrees. Application of an internally braced prosthesis for total talus replacement in humans is technically feasible and might be a reasonable procedure in carefully selected cases with no better alternatives left.

Early Outcomes of 3D Printed Total Talus Arthroplasty

“…10,11 Other authors have shown that total talus replacements can also be used as salvage for total ankles that have significant talar subsidence. [13][14][15] Recently, authors from our institution have shown good radiographic outcomes following third-generation custom 3D printed total talus replacement for talar AVN 8 ; however, there have not been clinical outcomes reported outside of scattered case reports, with the largest series being only 2 patients. 10…”

Custom 3D-Printed Total Talar Prostheses Restore Normal Joint Anatomy Throughout the Hindfoot

“…It has been speculated that proper fit is of utmost importance in TTR, correlating with longevity. 11,14,18 In the 36-year follow-up study by Harnroongroj and Harnroongroj, 11 2 patients failed acutely because of size mismatch. Ando et al 14 described a risk for anterior instability because the deltoid and anterior talofibular ligaments are divided during the procedure.…”

“…The restoration of talar alignment and anatomy, synthetically, could be beneficial in these patients, and early case reports have begun to yield satisfactory results. [16][17][18] Larger case series are needed to appropriate this modality rather than salvage arthrodesis. At the conclusion of this study, there have not been any complications to report.…”

“…Additional case reports have indicated satisfactory results in the short term when using a TTR for talar extrusion and for total ankle arthroplasty salvage procedures. [16][17][18] The largest case series incorporating the use of ceramic third-generation TTR implants included 55 patients with a mean follow-up time of 4.4 years. The authors found significant improvements with pain and functional outcome scores, with no complications reported.…”

A Comprehensive Review of Medical Imaging Equipment Used in Cadaveric Studies

“…X-rays have also been used to measure the cardiopulmonary resuscitation (CPR) force and to look at replacement joint force, and the internal prosthetic forces that can be withstood [ 7 - 8 ].…”