Total talus replacement with a titanium nitride-coated 3D-printed titanium implant

Total talus replacement (TTR) is a surgical procedure which involves the removal of a pathologic talus and replacement with a patient-specific 3D-printed titanium (Ti) prosthesis coated with titanium nitride (TiN).

DICOM data from a CT scan is used with specialized software to determine the size and dimensions of a TTR prosthesis.

CT scans of bilateral ankles are preferable and recommended; however, data only from a CT scan of the ipsilateral (pathologic) talus may be used if there is no collapse, deformity, or bony deficit.

Diffuse talus avascular necrosis (AVN) is a primary indication for TTR; however, other causes of bony deficit within the talus may be an indication for TTR, such as high-level trauma or malignancy.

Isolated TTR may be considered in patients with talar pathology but without pathology of the adjacent joints.

TTR may be combined with a total ankle replacement in the setting of talar pathology with secondary changes to the distal tibia.

Contraindications for TTR include active infection, neuropathy, gross deformity in the sagittal or coronal planes, and AVN of the calcaneus, distal tibia, or navicular bones.

The talus ( Taxillus , referring to the ankle bone of a horse) is the second largest bone in the hindfoot with an irregular saddle-shaped architecture. It is composed of a head that forms the talonavicular joint with the navicular bone anteriorly and the anterior talocalcaneal joint inferiorly; a neck that connects the head and the body. The latter has three processes (medial, lateral, posterior), two facets (middle and posterior), two tubercles, and one talar dome ( Figs. 5.1 to 5.3 ).

The middle facet articulates with the sustentaculum tali. The posterior facet forms with the calcaneus the posterior talocalcaneal joint.

The talar dome or trochlea located superiorly forms the tibiotalar joint with the tibia and fibula.

The talus is covered by more than 60% of articular cartilage.

There are no muscle attachments, but the talus does possess multiple ligament attachments, including the deltoid complex and spring ligaments medially, and the anterior talofibular and posterior talofibular ligaments laterally.

The modified Boyan Classification is used to describe the variable morphology of the subtalar joint facets based on the number of facets present and the distance between those facets.

The tenuous blood supply is provided by three arterial sources ( Fig. 5.4 ):

• The posterior tibial artery breaks into the tarsal canal artery that supplies most of the talar body except the medial third, which is supplied by the deltoid branch of the tarsal canal artery.

• The anterior tibial artery (becoming the dorsalis pedis artery) gives off the lateral tarsal artery, which anastomoses with the peroneal artery to form the tarsal sinus artery.

• The tarsal sinus and tarsal canal arteries anastomose in the sinus tarsi.

• The medial branches of the dorsalis pedis artery supply the superomedial talar neck.

• The inferior talar neck branches of the tarsal sinus artery or tarsal canal artery supply the inferolateral talar neck.

The tenuous vascularity combined with a lack of periosteal blood supply increases the risk of talar AVN.

AVN may be secondary to fractures and trauma, prolonged steroid use, alcoholism, or vasopressors.

The extent of necrosis along with the severity of bone compromise dictates treatment management.

Extensive AVN has a higher risk of talar dome collapse, which can lead to degenerative changes in the ankle and subtalar joints.