3D Printed Talus Replacement

Jisun J. Lee, Ms, DPM; Mica Murdoch, DPM; Ashley Mcclain, DPM, Broadlawns Medical Center

Osteoarthritis (OA) is one of the most common causes of chronic disabling medical conditions in the United States, which affects about 27 million people and approximately 15% of the adult population. 1,2Among these, ankle OA occurs in 1% of the world population.3Unlike the hip or the knee joint, the ankle joint is unique in the sense that it is more resistant to primary OA with efficient dispersing of greater body weights than the hip or the knee joint. It has been reported that the primary ankle OA comprises only 7% of ankle OA origin.4

However, the talus is an irregular saddle–shaped bone that articulates with the tibia and fibula with minimal thickness of the cartilage of 1 to 1.7 mm.5Tenuous vascular supply due to devoid muscular structure attachment of the talus further makes the talus predispose at risk of severe pathologic processes, especially with incongruity. Approximately 80% of the ankle OA cases are attributable to the posttraumatic origin, which will lead to ankle instability and joint incongruity.3 Moreover, posttraumatic OA develops nearly 10 years earlier than primary OA and affects individuals at a younger age.6The talus is also the 3rd most common anatomic location to develop avascular necrosis after a traumatic event. Other reported etiologies of advanced ankle OA are including but not limited to osteomyelitis, septic joint, rheumatoid, hemochromatosis, hemophilia, gout, neuropathic disease, bone tumor, and osteochondral lesions.7,8

Treating end-stage ankle OA is still a challenge, yet tibiotalar arthrodesis is currently considered as an effective operative treatment. Total ankle replacement (TAR) is also considered as a safe and effective alternative. However, previous reports have demonstrated that the reoperation rateis approximately 20% and up to 50% tibiotalar arthrodesis and TAR, respectively.9,10In case of poor bone quality with talar osteonecrosis, loss of talus due to trauma or infection, or failed TAR due to hardware loosening or significant substance, 3D printed talus replacement is a valid and promising operative management option.

A custom designed talus replacement was first published by Harnroongroj T and Vanadurongwan V with first-generation talar body prosthesis in 1997. First-generation talar prosthesis preserved the head and neck of the talus to allow the insertion of the prosthetic peg into the bone.11 Then, in 1999, Tanaka Y et al. designed second-generation alumina-ceramic talar body prosthesis without a peg for the neck of the talus.12In 2005, Taniguchi et al. reported excellent pain and functional outcomes in 55 ankles with a total talar replacement (TTR).

The contralateral talus is utilized for radiographic data and computed tomography (CT) to obtain 3dimensional model to replicate its biomechanical and anatomical properties. Patient specific and anatomic based design talar prosthesis will be constructed with 3D printed using polymeric biocompatible powders.14,15Production of TTR generally requires 4 to 6 weeks for completion and stainless still, titanium, alumina ceramic, and cobalt chrome are the most commonly used materials.

The most commonly used surgical approach is the anterior ankle approach, where a 10 to 14 cm anterior longitudinal midline incision is made to the talonavicular joint level. Care should be taken to identify and protect all vital neurovascular structures. Upon performing an anterior capsulotomy, the ankle joint is exposed after elevation of the periosteum. Then the talar body is carefully dissected out for complete extrusion. Any remaining osteophyte should also be removed. Then appropriate soft tissue manipulation was performed to maintain a functional ankle joint space. The new custom-built implant was then fitted into the patient's ankle, and the most appropriate fit of the polyethylene component is inserted after trial polyethylenes were tried. Insertion of the tibial portion of the arthroplasty system is also carried out with the system based on the surgeon’s choice. A gastrocnemius recession or Achilles tendon lengthening is required when it is clinically indicated. A below-knee cast will be applied for 2 weeks then the patient will begin weight-bearing in a CAM boot. Then supportive shoes and a lace up ankle brace will be used at 6 to 8 weeks. Outcomes will be measured by inspecting maintained postoperative ankle range of motion as well as clinical and functional surveys such as the AOFAS score and SF–36.

Highlighted benefits of the TTR are good restoration of the physiological motion without limb length shorteningas demonstrated in multiple studies.14,16,17 TTR also produces stability with preventing degenerative changes to adjacent joints and dispersing pressures appropriately. Thus, TTR is an excellent surgical treatment option for patients with advanced OA from trauma, talar osteonecrosis, infectious origin, talus bone tumor, and failed TAR.

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