Primary total ankle total talus replacement





Definition




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    Surgical treatment of end-stage ankle arthritis with concomitant avascular necrosis (AVN) of the talus utilizing a combination of patient-specific 3D-printed and off-the-shelf (OTS) components for joint preservation and restoration of function.


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    3D printing has evolved and now allows surgeons to partner with technology that facilitates a continuity of care to maintain ankle joint range of motion (ROM) and avoid the need for tibiotalar calcaneal joint arthrodesis.


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    This chapter focuses on the niche situations that involve significant talar body loss from AVN or posttraumatic changes where plafond and arthritic changes are evident.



Anatomy




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    The talus is a uniquely shaped bone that articulates with the tibial plafond, fibular malleolus, calcaneus and navicular bones.


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    The talus is without tendon attachments therefore stability is provided by its articulations and ligament attachments.


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    Sixty percent of the talar surface is covered by cartilage, thus minimizing available area for vascular perforators.


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    The primary source of vascular influx is provided by the posterior tibial artery via perforators within the deltoid ligament and to the tarsal canal. The dorsal neck and sinus tarsi rely on vascular supply from the dorsalis pedis artery while the perforating peroneal artery serves the posterior body.



Pathogenesis




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    AVN results from a temporary or permanent loss of vascular supply to a bone. Interruption in any part of the vascular supply (arteries, capillaries, sinusoids, or veins) can lead to AVN. Bones with a single terminal vascular source are known to be at higher risk for AVN.


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    Within 3 hours of vascular impairment, anoxia causes osteocyte necrosis. Over time the resultant osteonecrosis can progress to subchondral fracture, loss of normal bony architecture, and collapse, leading to cartilage destruction and arthritis.


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    Much of the pathogenesis is not fully understood, although trauma, drug-induced, and idiopathic causes can result in vascular impairment. Trauma remains the most common cause of talar AVN. The more severe talar trauma, the more likely AVN will develop.


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    The physiologic response to AVN is to resorb necrotic bone by revascularization and reossification, which can be observed radiographically.



Patient history and physical exam findings




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    Patients will typically present with a history of isolated injury to the ankle, or a history of drug-induced ankle pain only sought out upon further investigation of the patient’s past medical history, typically a high dose of steroid. Presentation will almost always be very similar to posttraumatic arthritis or secondary arthritis of the ankle.


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    Patients often have failed to respond to nonsurgical treatment including but not limited to corticosteroid and/or regenerative injection therapy, rigid ankle-foot orthoses, various braces, nonsteroidal antiinflammatory drugs (NSAIDs), and physical therapy.


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    Particularly in the chronic and more advanced cases, patients often have failed to respond to previous surgical intervention aimed at revascularizing the talus, such as core decompression.


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    Early stages of AVN may be somewhat vague but often present as generalized ankle/hindfoot pain, which is worse with weight-bearing activity and ROM. As the disease advances, the symptoms become more apparent.


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    Limited and painful ROM of the ankle and/or hindfoot.


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    Antalgic gait.


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    Deformity may or may not be apparent on exam depending on the presence and degree of collapse.


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    Patients with AVN often have an unremarkable dermatologic and neurovascular exam.



Imaging




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    Currently, no radiographic classification system exists for talar AVN, however plain radiographs reveal characteristic areas of opacity or sclerosis of the talar dome and/or body. As the disease advances and collapse occurs, AVN is more apparent and can cause secondary deformity.


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    Advanced AVN will demonstrate collapse with articular degeneration of the tibiotalar and/or subtalar joints while the talonavicular joint is least commonly affected.


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    Advanced imaging is indicated for diagnostic and treatment planning purposes. Prior to the advent of 3D printing, AVN was a strict contraindication for total ankle replacement (TAR).


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    The authors recommend CT and MRI, which will highlight areas of osteoblastic and osteoclastic activity within the talus and surrounding bones.


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    MRI is the imaging modality of choice for early diagnosis. When AVN is apparent on plain radiographs CT may be more valuable for surgical planning ( Fig. 8.1 ).




    • Fig. 8.1


    Talar avascular necrosis seen on this MRI T1-weighted sequence. This patient underwent previous core decompression, which failed to alleviate symptoms and slow progression of the avascular necrosis.


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    In addition to imaging, infection is ruled out with blood work and, if necessary, a joint aspiration or bone biopsy.



Nonoperative management




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    Immobilization and non–weight bearing.


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    Bracing.


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    NSAIDs and other pain-management modalities.


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    Shoe and activity modification.


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    Over-the-counter versus custom orthotics.



Traditional surgical management




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    Core decompression may be indicated in early-stage AVN without evidence of collapse. In these select cases, core decompression with adjunct injection of bone marrow mesenchymal stem cells (MSCs) did improve the natural history of the disease compared to core decompression alone.


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    AVN with collapse is not an indication for core decompression. Advanced cases with collapse have traditionally been treated with fusion with a variety of fixation options, including plates/screws, intramedullary nails, and external fixation.


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    Tibiotalar calcaneal (TTC) fusion may be considered when AVN is focal. Necrotic bone must be excised with preservation of the talus to maintain limb length.


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    If AVN is geographic, which requires talectomy, tibiocalcaneal (TC) fusion has traditionally been recommended. TC fusions historically have lower fusion rates, require more extensive bone grafting, and result in limb length discrepancy.


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    Contaminant distraction osteogenesis may be considered to maintain limb length when TC fusion is necessary. However, this requires staged treatment, prolonged external fixation, which carries increased risk of pin site infection, and patient intolerance (“cage rage”) in addition to increased cost.


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    Below-knee amputation should be considered but is generally not recommended as a primary option. In the authors’ practice, below knee amputation (BKA) is reserved for failed fusions, infections, and those patients not amenable to reconstruction.



3D-printed implant and instrumentation considerations




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    As per previous chapters, preoperative planning involves partnering with industry to create a 3D-printed custom talus based on the contralateral and ipsilateral CT scans.



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      The 3D printing manufacturer can provide radiographic specifications to ensure the necessary data points are obtained.


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      CT scans should include the tibial tubercle, which will accurately establish alignment and location of the ankle joint axis.



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    It is the surgeon’s preference as to which OTS tibial and polyethylene components will be used. The talar dome will mirror the size and shape of the polyethylene component.


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    Three sizes of the total talus implant are typically available and the authors prefer nominal and ±5% by volume or by implant height alone.



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      In the authors’ experience nominal is most commonly used ( Fig. 8.2 ).




      • Fig. 8.2


      Intraoperative sizing of custom talar implants is important. Typically three sizes are offered based on preoperative templating and sizing.


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      Sizes may differ (based on surgeon’s preference) on total volume where all aspects of the implant are larger or smaller versus only differing in talar implant height. By maintaining a constant anterior-to-posterior length, the surgeon may prevent increasing friction on the navicular bone while having some degree of freedom to restore the anatomic axis of the tibiotalar joint.


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      If requested sizing differs on height alone, consider nominal ±2 mm or another absolute value based on the patient’s needs and planned tibial resection.



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    Additional features, such as eyelets to accommodate suture passage for ligament attachment, may be surgeon or patient specific. For nonarticular portions of the talus corresponding to attachment of the deltoid slips and anterior talofibular ligaments, the authors recommend considering focal areas of roughness and porosity to promote soft tissue ingrowth, which may help stabilize the talar implant ( Fig. 8.3 ).




    • Fig. 8.3


    Anterior and medial view of computer-aided design images of a total talus implant with eyelets for suture passage for ligament attachment. Between the eyelets, focal areas of porosity to promote soft tissue ingrowth correspond to extraarticular portions of the talus and the location of ligament attachment.

    (Reprinted with permission from Restor3d, Durham, NC.)


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    The authors recommend a cobalt chrome (CoCr) 3D-printed talus. CoCr can be highly polished and yields a lower coefficient of friction compared to titanium. Titanium may lead to expedient polyethylene wear, which may result in aseptic loosening.


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    In cases where a previous wound infection was present, these may require a staged approach to AVN of the talus with tibial plafond arthritic changes. The authors recommend a staged approach, with the first stage being resection of talar bone, bone biopsy, wound debridement, and closure with placement of an antibiotic cement spacer. An antibiotic cement spacer is placed for 6 weeks as well as intravenous antibiotics for 6 weeks. If blood work is still negative, the authors will move forward with the second stage of talus implantation ( Fig. 8.4 ).




    • Fig. 8.4


    (A) A 47-year-old male with an isolated open medial talus extrusion from a fall from a ladder. Subsequent wound infection occurred which required a staged reconstruction. (B) An antibiotic-impregnated cement spacer was placed and used in combination with intravenous antibiotics. Once infection was cleared, total ankle total talus replacement was performed.





Surgical management with 3D-printed devices




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    The incisional approach for a primary total ankle arthroplasty with custom total talus involves a standard 10- to 12-cm incision overlying the anterior ankle with dissection through the superior extensor retinaculum. The interval is taken down between the tibialis anterior tendon and extensor hallucis longus. The extensor hallucis longus is maintained within its sheath. Dissection is carried down medial to the neurovascular structures, which are maintained in adipose tissue. An anterior capsulotomy is performed with resection of any hypertrophic anterior capsule. Deep retraction is utilized with a sharp self-retaining retractor on deep tissue only.


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    Next, the authors recommend performing the procedure as if doing a standard total ankle arthroplasty by starting with the tibial alignment and resection:



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      A standard jig or patient-specific tibial cut guide may be used per the surgeon’s preference. Using standard technique according to the manufacturer’s instructions, the distal tibia is cut using a sagittal saw after alignment in orthogonal planes is confirmed.


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      If the tibial resection is easily removed then it may be excised at this juncture, which allows for more efficient talectomy. If much difficulty is encountered, the surgeon may consider proceeding with talectomy, thereby making tibial resection easier.



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    Multiple techniques have been anecdotally described to resect the talus:


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Jul 15, 2023 | Posted by in ORTHOPEDIC | Comments Off on Primary total ankle total talus replacement

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