Tibiotalocalcaneal (TTC) fusion is a salvage procedure for patients with substantial ankle and subtalar arthritis or severe malalignment of the ankle-hindfoot complex. In many cases, this procedure is the only option available to provide patients with a stable, painless, plantigrade foot for ambulation. General indications for TTC include severe symptomatic hindfoot and ankle deformity or combined ankle and hindfoot arthritis for which nonsurgical management has failed. What makes this treatment modality even more challenging is the often-associated bone loss, especially in cases of neuropathic arthropathy or Charcot arthropathy. As the indications for TTC fusion expand, the number of procedures performed continues to rise.

Specific conditions for which such fusion is commonly indicated include inflammatory arthropathies; congenital deformity; neuropathic arthritides secondary to diabetes mellitus or inherited polyneuropathies; failed total ankle arthroplasty; severe pes planovalgus deformity; fracture malunion and nonunion; and bone loss and collapse secondary to trauma, tumor, osteonecrosis, Charcot arthropathy, or infection.

Patient factors that have been shown to affect outcomes of TTC fusion include medical comorbidities such as diabetes mellitus, previous ulcerations, peripheral vascular disease, renal disease, immunosuppression, chronic steroid use, rheumatologic disease, malnutrition, and smoking. In addition, a history of surgical intervention, particularly with postoperative complications (e.g., deep infection, problems with wound healing), may affect postoperative outcomes. In several studies of TTC arthrodesis, 20% to 40% of patients had a history of diabetes mellitus or smoking, resulting in poorer than average outcomes in these patients. ^,

The ankle joint is a ginglymus (hinge) joint involving the tibia, talus, and fibula. The talar dome is biconcave with a central talar sulcus. Viewed axially, the joint is trapezoidal and wider anteriorly than posteriorly. The talus is the only tarsal bone without muscular or ligamentous insertions.

The syndesmosis is the tibiofibular articulation composed of the tibial incisura fibularis and its corresponding fibular facet. It has three ligamentous structures that are variably responsible for its support: the anterior inferior tibiofibular ligament, the interosseous ligament, and the posterior tibiofibular ligament.

The subtalar joint has three facets: posterior, middle, and anterior. The posterior facet is the largest, the middle facet rests on the sustentaculum of the calcaneus and is located medially. The anterior facet is often continuous with the talonavicular joint.

The transverse tarsal joint (Chopart joint) is composed of the talonavicular and calcaneocuboid joints and acts in concert with the subtalar joint to control foot flexibility during gait. The talonavicular joint is supported by the spring ligament complex, which has two separate components: the superior medial calcaneonavicular ligament and the inferior calcaneonavicular ligament. The calcaneocuboid joint is saddle-shaped. It is supported plantarly by the inferior calcaneocuboid ligaments (superficial and deep) and superiorly by the lateral limb of the bifurcate ligament.

The ankle joint’s primary motion is dorsiflexion and plantarflexion. With the foot fixed, dorsiflexion is accompanied by internal tibial rotation and plantar flexion is accompanied by external tibial rotation. The bimalleolar axis runs obliquely at 82 degrees ± 4 degrees in the coronal plane and defines the main motion of the ankle. The talus is wider anteriorly than posteriorly, and the contact area of the dome of the talus increases and moves anteriorly with dorsiflexion. Increased load transmission in the malleoli also occurs with dorsiflexion. The fibula transmits approximately 10% to 15% of the axial load. The tibiofibular syndesmosis allows rotation and proximal and distal migration of the fibula with the tibia but little motion in the sagittal or coronal planes.

The subtalar and Chopart joint act through a series of coupled motions to create inversion and eversion of the hindfoot and to lock and unlock the midfoot. Inversion of the subtalar joint locks the transverse tarsal joint; eversion unlocks the joint. The joints are parallel during heel strike when the calcaneus is in eversion, allowing the midfoot to be flexible for shock absorption as the foot accepts the body’s weight. The joint axes are deviated as the subtalar joint moves to inversion (e.g., during push-off), making the foot inflexible so that it provides a rigid lever arm for push-off.

The hindfoot articulations include the subtalar, talonavicular, and calcaneocuboid joints. Arthritides of the hindfoot are most often posttraumatic in origin but can also develop from inflammatory arthritis, primary osteoarthritis (OA), end-stage tibialis posterior tendon disorders, tarsal coalitions, or neurologic disorders including Charcot arthropathy.

The pathogenesis of Charcot arthropathy (also termed Charcot foot) has been explained using two major theories—neurotraumatic and neurovascular:

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  The neurotraumatic theory attributes bond destruction to the loss of pain sensation and proprioception, combined with repetitive and mechanical trauma to the foot.

  
  
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  The neurovascular theory suggests that joint destruction is secondary to an autonomic stimulated vascular reflex causing hyperemia and periarticular osteopenia with contributory trauma.

  
  
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  There is a growing body of evidence that dysregulation of inflammatory and bone metabolism pathways, with upregulation of receptor activator of nuclear factor-kappa B ligand (RANK-L), lead to osteoclast overactivation and bone resorption.

Clinically, midfoot osteoarthropathy manifests as a noninfectious, osteolytic process that may ultimately result in profound deformity and instability from bone and joint collapse. Deformity with neuropathy may lead to ulceration and potentially to a limb-threatening condition.

In 1966, orthopedic surgeon Sidney N. Eichenholtz published clinical, radiographic, and pathologic data used to define three stages of Charcot arthropathy based on the natural history of the condition. The three stages he described were (I) development; (II) coalescence; and (III) reconstruction and reconstitution.

Clinical signs (such as swelling, warmth, and erythema) regularly precede the radiographic findings seen with Eichenholtz stage I arthropathy. As such, in 1990 Shibata et al. added a fourth stage, stage 0, to the conventional Eichenholtz classification ( Table 11.1 ).

An examination of the skin and the presence of ulceration or impending ulceration is to be noted and considered in procedure selection.

Vascular examination should include palpation of pedal pulses, the presence or absence of pedal hair, and degree of swelling. If there is any question about the vascular status of the limb in which TTC fusion is being considered, further workup is warranted and may include vascular studies or consultation with a vascular surgeon.

A neurologic evaluation should include sensation testing with a 5.07-gauge monofilament, a tuning fork, or pin-prick test. Further, Achilles reflexes should also be tested.

Alignment while standing and walking is of particular importance. Deformity and instability in the sagittal and coronal planes of the ankle, hindfoot, and forefoot should be assessed in detail. To assess the need for forefoot correction, the hindfoot can be held in the corrected position while the clinician assesses the position of the forefoot in the coronal plane relative to the long axis of the tibia while the patient is seated.

Bony prominences, rocker-bottom deformity, and potential areas of increased pressure are prone to ulceration and must be addressed.

Weight-bearing radiographs of the ankle and foot are mandatory in the evaluation for TTC fusion.

Radiographic evidence of arthrosis, bone loss, shortening, existing implants from prior surgeries (particularly broken screws), and deformity should be noted.

Weight-bearing anteroposterior (AP) views of both ankles gives an excellent indication of the degree of actual or functional shortening caused by bone loss or malalignment.

CT may be indicated in patients with substantial disruption of the normal bone architecture of the foot and ankle, and is useful in revision arthrodesis for determining the status of a previous fusion.

MRI may be used in select cases to evaluate the extent of osteonecrosis in a foot and ankle being considered for TTC fusion.

Nonsurgical treatment of arthritis of the ankle and foot include nonsteroidal anti-inflammatories (systemic or topical), activity modification, corticosteroid injections, shoe modifications, and bracing.

Most cases of acute Charcot arthropathy can be treated effectively with pressure-relieving methods such as total contact casting.

Chronic and/or unstable ankle and hindfoot Charcot deformities are prone to fail nonsurgical treatment.

A transfibular approach is most often used for TTC fusion. Prior surgical incisions or soft tissue flaps may dictate variations in the location of the incision for such an approach. Occasionally, if the lateral skin is compromised and a lateral approach cannot be used, a posterior approach may be used to access both the subtalar and ankle joints.

Traditional TTC fixation methods include external fixation, cannulated versus solid screws, intramedullary nailing, and plating. Currently, there is no accepted standard technique for this procedure, with the type of implant typically being determined by the discretion or familiarity of the surgeon.

Autograft sources for TTC fusion grafts include the iliac crest for cancellous and corticocancellous bone, the tibia or femur for cancellous bone harvested with a reamer-irrigator aspirator device, and the fibula for interpositional struts.

Allograft options include cancellous chips, bulk allograft obtained from the femoral head, and struts of corticocancellous bone from the iliac crest or the fibula.

The use of a femoral head allograft to span bone defects has recently gained popularity since it can restore normal limb length and offer a conduit for fusion. However, this technique has led to mixed results, with reported rates of successful arthrodesis as low as 50%. There is also an infection risk with the use of a large bulk allograft and the potential for graft subsidence or collapse.

In patients at high risk of complications after TTC fusion, augmentation with bone marrow aspirate, platelet-rich plasma, or an orthobiologic material may be used.

Materials: all implants are fabricated via laser powder bed fusion (L-PBF) of medical-grade titanium alloy (Ti6Al4V ELI).

Polished versus rough surfaces: after printing, the implants undergo multiple postprocessing steps before being delivered for surgery. The first of these steps is known as hot isostatic pressing (HIP, “hipping”), a process during which the implants are subjected to both high temperature and pressure to relieve the implants of residual thermal stresses and close any internal voids. Next, the parts undergo microblasting, during which titanium powder is blown at the implant surface under high pressure to remove any partially adhered particles of powder. Finally, the implants are subjected to a chemical passivation process which results in a thin surface oxide layer that improves the corrosion resistance of the implants.

Shape: the implants are typically spherical with or without modifications. This geometry was selected after proving to offer significant intraoperative flexibility in terms of repositioning. Modification to the spherical implant shape may be considered, for example, a flattened lateral implant surface can aid in soft tissue closure ( Fig. 11.1 ).

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