Primary constrained total talus with subtalar joint arthrodesis

Patient-specific 3D custom-printed metallic constrained total talus replacement includes modifications to implant design and technique in order to incorporate subtalar arthrodesis.

The talus, through its articulations, is the link between foot and ankle motion.

The talus is covered by approximately 60% cartilage, with little area remaining for soft tissue attachments or penetration of blood supply. ^,

The neck of the talus allows for ligament attachment such as the deltoid and the anterior talofibular, which aid in ankle stability. It also contains the interosseous talocalcaneal ligament on its undersurface for portions of subtalar joint stability. A majority of the blood supply to the talus enters through this region, making it vulnerable during injury and surgery.

The posterior tubercles of the talus allow posterior ligaments such as the posterior talofibular and components of the deep deltoid to aid in ankle stability, as well as the posterior talocalcaneal ligament of the subtalar joint.

Medial support of the subtalar joint comes from the corresponding talocalcaneal ligament, while the lateral talocalcaneal ligament is aided in its support by the calcaneal fibular ligament.

The blood supply to the talus is fragile and easily compromised by trauma and surgery. ^,

The main blood supply to the body of the talus is from the posterior tibial artery and its branches through the medial deltoid, in addition to its supply to the artery of the tarsal canal. ^,

The dorsalis pedis artery supplies the dorsal neck and sinus taris region of the talus through the artery of the tarsal sinus.

The perforating peroneal artery supplies blood to the posterior body as well as to the tarsal sinus plexus.

The inferior surface of the talus contains facets for articulation with the calcaneus to form the subtalar joint.

The subtalar joint has an oblique axis that allows for supination and pronation, working in conjunction with the ankle, talonavicular, and calcaneal cuboid joints.

The subtalar joint axis runs anterior and superomedial from the posterolateral tubercle toward the neck of the talus and is dynamic, changing as the joint progresses through motion.

The average axis of the subtalar joint is 16 degrees from the sagittal plane, 42 degrees from the transverse plane.

The accepted range of motion of the subtalar joint is approximately 30 to 40 degrees total, with it divided one-third eversion and two-thirds inversion from neutral.

Subtalar joint fusion can be a useful procedure and is performed in deformity corrections, to decrease pain in arthritis, to aid in rearfoot stability, and to provide a stable platform for the talus in complicated reconstructions.

Altered mechanics are still debated after subtalar fusion, with conflicting data. Long-term arthritic changes may not be as definite as once thought but pressure studies show loading shifts after fusion, which may have implication on the ankle joint or implant arthroplasty following fusion. The effects on adjacent joints need to be considered when incorporating subtalar joint fusion into constrained total talus replacement.

Large talar deficits that may necessitate the need to incorporate subtalar arthrodesis include:

• Severe osteoarthritis including both the ankle and subtalar joints.

• Avascular necrosis of the talus with concomitant subtalar arthritis or deformity.

• Other destructive pathology with extensive cystic changes to adjacent bone, such as other arthritides, hemophilic joint pathology, and neoplastic processes.

• Failed arthrodesis with subsequent bone loss.

• Failed total ankle arthroplasty with component subsidence violating the subtalar joint.

Trauma is the most common cause of talar avascular necrosis (AVN), occurring in approximately 75% of cases, with medication and idiopathic trauma also being described. ^,

Arthritides such as rheumatoid arthritis and osteoarthritis can affect both the ankle and subtalar joints leading to cystic changes and joint destruction, which in some cases involves both the ankle and subtalar joints concurrently.

With the increasing number of total ankle joint arthroplasties being performed annually, more complications are being reported. The development of revision techniques is essential and, for certain cases, total talar replacement is a possibility. For implants that have violated or subsided into the calcaneus and subtalar joint, incorporating subtalar arthrodesis has been a valuable tool to add fixation and provide a stable platform for the revision.

Talar deficiency is a challenging dilemma, with surgical options including talectomy, tibiotalocalcaneal arthrodesis with or without bone grafting, tibiocalcaneal arthrodesis, or even major amputation.

Arthrodesis of the ankle and subtalar joints has been the standard of treatment for large talar deficits and patients with concomitant ankle and subtalar pathology.

Local bone quality and quantity can make fixation for arthrodesis around the talus challenging. Without adequate fixation, fusion is more likely to fail.

Unreliable blood supply adds to the challenges of talar deficiency and surgery to address these deformities may disrupt blood supply, further compromising results.

Long-term consequences of arthrodesis include the potential for limb shortening, stress on adjacent structures, and chronic pain.

Arthrodesis can lead to increased disability, decreasing overall dorsiflexion by 63% and plantarflexion by 82%.

Fusion for large talar deficits can have high failure rates including nonunion of 16% to 52%, increased infection rates up to 21.8%, and hardware complications of 14%.

Fusion for large talar deficits can have an overall high rate of reoperation up to 39.6%, or even conversion to major amputation of up to 16%.