Definition
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Excision of the talus and navicular in total, which is then replaced with a metallic, patient-customized 3D-printed implant.
Indications
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Avascular necrosis (AVN) of the talus and/or the navicular.
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Comminuted fracture of talus and navicular.
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Post-traumatic arthritis with poor bone quality and cystic formation.
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Osteolysis or bone resorption secondary to an infection.
Anatomy
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The talonavicular joint (TNJ) is a ball and socket type of joint that consists of the articulation between the concavity produced by the proximal posterior aspect of the navicular and the convex, ellipsoid surface of the talar head.
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The articulation of the TNJ is maintained by various ligaments, including the talonavicular ligament, the bifurcate ligament, and the calcaneonavicular (spring) ligament.
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The TNJ composes the transverse tarsal joint and is an essential joint in the medial column, forming a portion of the medial longitudinal arch.
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The primary plane of motion for the TNJ is from dorsal lateral to plantar medial. Its primary function is as part of the transverse tarsal joint along with the calcaneocuboid joint, which acts in unison with the subtalar and ankle joint during gait.
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Talonavicular motion and function is closely paired with the subtalar joint. Fusion of either joint tremendously affects the other in terms of remaining functional motion.
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Vascular supply of the talus and navicular is delicate, with the predominant vascular supply coming from two main suppliers, the dorsalis pedis and the medial branch of the posterior tibial artery. ,
Pathogenesis
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AVN is characterized by osseous cell death secondary to vascular compromise. AVN can result from a variety of causes, including corticosteroid use, trauma, osteomyelitis, septic arthritis, alcoholism, sickle cell disease, diabetes, and systemic lupus erythematosus (SLE). ,
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Spontaneous osteonecrosis of the navicular and talus (SONNT) is an idiopathic disease that is characterized by symptomatic osteonecrosis of both the navicular and talus simultaneously with associated osteoarthritis of the TNJ. While the cause of SONNT is unknown, possible atraumatic causes are insufficient blood supply and developmental reasons.
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Comminuted fractures frequently occur after high-impact trauma and can result in the splintering of bone into multiple fragments as well as the disruption of vascular supply.
Patient history and physical exam findings
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A typical presentation of this injury involves an inability to bear weight and an inability to tolerate midtarsal range of motion, along with pain on ambulation.
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Patients often complain of point tenderness over the navicular or TNJ with or without erythema, edema, or temperature increase.
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Patients may have an antalgic gait with increased weight bearing to the lateral aspect of their foot.
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Previous history of trauma to the TNJ or rheumatoid arthritis is common among these patients, especially with risk factors that could cause AVN ( Figs. 10.1 and 10.2 ).
• Fig. 10.1
Anteroposterior view of the surgical foot preoperatively.
• Fig. 10.2
Lateral view of the surgical foot preoperatively.
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Frequently patients will have a history of failing conservative treatment methods such as casts, boots, and a series of corticosteroid injections.
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In longstanding TNJ injuries you will see a progressive valgus deformity as the longitudinal arch continues to collapse, resulting in an alteration of subtalar joint motion.
Imaging and other diagnostic testing
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Radiographs often demonstrate initial minor osteopenia, patchy sclerosis with rim calcification of affected bones, possible subchondral cyst formation, late cortex collapse with “crescent sign,” and associated soft tissue edema.
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If there is any suspicion of AVN, MRI and CT scans are indicated to allow for appropriate preoperative evaluation of the extent of the AVN.
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If 3D printing technology is being utilized, CT is the preferred imaging modality.
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Vascular studies to ensure that the patient has adequate blood supply to the anterior ankle angiosomes are required with the anterior ankle incisional approach due to the nature of this incision having issues with healing.
Treatment options
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Nonoperative management includes:
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Conservative treatment is suggested prior to consideration for surgical intervention; however, frequently patients will experience no relief and AVN will progress.
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Prolonged non–weight bearing through the use of casting or controlled ankle motion (CAM) boots.
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Activity modification.
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Custom orthotics.
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Bracing.
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Corticosteroid injections.
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Extracorporeal shockwave therapy.
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Electrical bone stimulation using a pulsed electromagnetic field.
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Traditional/alternative surgical management
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Vascularized bone graft with a plate fixation technique. ,
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Talus removal with a tibiotalocalcaneal (TTC) arthrodesis technique utilizing an osseous graft.
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Core decompression of the talus and navicular technique. ,
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Conservative care and other midfoot and/or hindfoot fusions.
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By utilizing more traditional options, such as those listed here, you are eliminating the possibility for a revisional surgery down the line by early fusion of multiple joints or utilizing autologous or allograft bone.
3D-printed implant design specifications and considerations
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A 3D-printed implant comprising both the talus and navicular for total TNJ replacement allows for precise restoration of medial column length but also avoids ankle arthrodesis by restoring the articular surface of the talar dome ( Figs. 10.3 to 10.6 ).
• Fig. 10.3
Plantar view of the talonavicular implant.
• Fig. 10.4
Lateral view of the talonavicular implant.
• Fig. 10.5
Medial view of the talonavicular implant.
• Fig. 10.6
Anterior-lateral view of the talonavicular implant.
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A CT scan should be obtained to help create and design implants. If there is any collapse or significant deformity at the TNJ, a contralateral CT can be obtained in order to create inverted variants for nominal anatomy of the affected TNJ.
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The implant material may vary according to the surgeon’s preference. The implant featured in this chapter is made from titanium alloy (Ti6Al4V). Cobalt chromium (CoCr) is also a common 3D-printed material. The implant can contain multiple-sized honeycomb lattice–shaped pores, which are also made up of CoCr (see Figs. 10.1 and 10.2 ). This is the senior author’s preference, as this specific pattern has been shown to allow for better ingrowth than the roughened surface of the implant alone. Larger diameter pores are located plantarly and smaller diameter pores are located on the medial aspect of the talonavicular implant.
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The shape of the implant was in the form of a fused talus and navicular bone. The senior author prefers the implant to be shaped like a truncated cone that is wider anteriorly than posteriorly, with an extension off the distal aspect in the shape of a boat that allows for seamless integration with the medial, intermediate, and lateral cuneiform.
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Polished surfaces were located on the dorsal aspect of the implant extending from the articular surface of the talus distal to the navicular cuneiform joint.
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Rough surfaces with a porous lattice were located on both the distal navicular portion and the plantar aspect of the talonavicular implant to promote osseous ingrowth.
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Holes should be designed within the implant to allow fixation into the calcaneus and individual cuneiforms. The holes can be designed to accommodate screw or staple fixation.
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Fixation of the implant to the intended arthrodesis sites can also vary according to preference; however, the authors’ experience includes utilizing multiple types of fixations from the implant across the cuneiforms. This includes individual staples into respective cuneiforms and multiple screws in divergent patterns from the implant into the cuneiforms. Screws should be headed to allow for contact with the implant. Screw sizes can vary based on availability and surgeon preference; however, 4.0 and 7.0 mm into the cuneiform and calcaneus, respectively, have worked well.
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In regard to fixating the subtalar arthrodesis, there are multiple options. Larger diameter fixation with a screw seems optimal. The plantar surface can be designed according to the native contour of the contralateral talus, or another available option in design is building a convex surface to the plantar aspect of the talar portion of the implant. When prepping the subtalar joint, utilizing an acetabular reamer allows an increased surface area of implant to bone interface. In addition, the convex-concave relationship allows for rotation of the calcaneus for any potential need for deformity correction. If the convex portion is pursued in implant design, ensure the same sized reamer is used as the implant.
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Areas for intended arthrodesis should be designed to be rough, trabecular, and porous to promote bony ingrowth.
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Articulating portions of the implant, specifically the talar dome, should be smooth and highly polished.
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Certain designs for potential soft tissue reattachment can be incorporated with rough surfaces and additional eyelet anchor sites.
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There is a fine balance to be achieved when incorporating an increased amount of fixation options for a stable construct, as a higher number of clearances designed into the implant decrease the opportunity for bony ingrowth that facilitates implant adherence.
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Although there are varying concomitant procedures that are ultimately up to the surgeon’s preference, it is the senior author’s recommendation to incorporate arthrodesis of the subtalar and cuneiform interface to increase the stability of a large sized total implant.
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Small loops can be incorporated into the device designs to allow for reattachment of ligament and tendon insertions, specifically the posterior tibial (PT) tendon.
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To account for variations in sizing intraoperatively, the senior author prefers to have three different sizes of the implant available, which range from nominal and ±5% to 10% of the length of the nominal-sized implant. The size of the implant used is determined by press fitting it into the operative site.
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Trial guides are used to confirm which size of the implant fits optimally in an intraoperative setting. Trial guides can be made from radiopaque material, which eases visualization prior to implantation.
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Harvested bone autograft can be morselized and packed into porous surfaces at the intended fusion implant interface.
Surgical management with 3D-printed devices
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All surgical planning was performed with an engineering design team from the product manager and included multiple options for this specific patient as well as adjunct fixation options due to the less than ideal quality of the patient’s bone for fusion.
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The surgeon’s preference is general anesthesia with a preoperative regional nerve block.
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The surgical approach is best achieved through the supine position with a hip bump.
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Incision planning should be well planned in accordance with the adjunctive procedures that are to be performed. However, direct visualization of the talus and navicular is vital to the procedure. An incision interval for anterior ankle exposure is used. The incision starts approximately 5 cm proximal to the ankle joint lateral to the tibialis anterior tendon, and then continues distal along the tendon but then medially deviates towards the extensor hallucis longus tendon as the incision extends to its completion distal to the ankle joint. The incision should end distal to the level of the cuneiform metatarsal joint to allow for complete exposure ( Fig. 10.7 A,B).
Related posts:
Historical perspectives on 3D printing
Material science for 3D printing in medicine
Distraction subtalar joint fusion using a custom 3D-printed implant
Custom constrained 3D total talus/navicular replacement
3D-printed total cuboid replacement for lateral column pathology
3D-printed custom hemi-talus replacement
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