Definition
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Resection of damaged cartilage and subchondral bone in the talus which is then replaced with a metallic, patient-specific, 3D-printed implant without the need for malleolar osteotomy.
Indication(s)
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Chronic, medium-to-large osteochondral defects (OCDs) of the talar dome which are often uncontained (i.e., involving the talar shoulder) and have mixed cystic and sclerotic subchondral bone.
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Prior failed arthroscopic OCD repair which may include debridement, microfracture, or morselized cartilage allografting.
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Prior failed open treatment of the OCD which may include structural allograft resurfacing or osteochondral transfer.
Anatomy and pathogenesis
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60% of the talus is covered by articular (hyaline) cartilage which contains no nervous, vascular, or lymphatic vessels.
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The exact etiology of talar OCDs has been theorized to be direct trauma, microtrauma secondary to instability or deformity, and spontaneous focal avascular necrosis (AVN).
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With time, OCDs may progress in size, develop cystic bone and sclerosis, subchondral collapse, and higher, asymmetric contact stresses.
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There is concern for the development of localized arthritis but, in general, OCDs do not progress to diffuse arthritis.
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Classically, acute lateral OCDs tend to be more shallow and anteriorly located, whereas acute medial lesions are cup-shaped, deeper, and located in the central to posterior aspects of the talar dome. In our experience, chronic lesions, especially if prior surgical intervention, are more irregularly shaped, have a variable/nonuniform depth, and a degree of local AVN.
Patient history and physical exam findings
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In the authors’ experience, patients complain of anterior or “deep” aching ankle pain with or without clicking, popping, or catching of the ankle, which is worse with activity.
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If trauma is reported, which often is not, it most often involves remote or recurrent ankle sprain. Less often the patient will report a previous malleolar fracture.
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Patients may limp or complain of inability to perform athletic or recreational activities.
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Stiffness is a common symptom, especially with chronic OCDs.
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Stability testing may elicit guarding, pain, or frank laxity.
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Immobilization often improves but does not eliminate symptoms.
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Patients may report that prior corticosteroid injection provided temporary relief.
Imaging and diagnostic tests
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Chronic, large OCDs are often seen on X-rays depending on their size and location, but detailed description of the lesion is not clear with X-rays alone and advanced imaging is indicated.
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MRI is great for diagnosis of OCDs and assessment of common concurrent problems such as lateral collateral ligament and/or peroneal tendon pathologies. However, bone marrow edema may cause an overestimation of size and decrease the clarity of the lesion’s shape and location.
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CT is the preferred imaging modality to determine size and characterize the depth and extent of subchondral bone involvement.
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In the authors’ experience, obtaining both MRI and CT scans is very beneficial in preoperative planning and gives an excellent overview of the extent of talar pathology.
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Diagnostic injections can be considered and may alleviate symptoms temporarily, but, in the authors’ opinion, injections should be avoided if possible due to the deleterious effect of intra-articular local anesthetics and corticosteroids on chondrocytes.
Nonoperative management
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In the authors’ experience, conservative treatment modalities may show temporary improvement but are unsuccessful in younger or more active patients with chronic talar OCDs. However, they should still be attempted.
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Rest, ice, compression and elevation (RICE) therapy.
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Activity modification.
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Bracing.
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Oral or topical nonsteroidal antiinflammatories (NSAIDs).
Traditional surgical management
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Bone marrow stimulation (BMS) techniques such as microfracture, subchondral drilling, and abrasion chondroplasty are often a reasonable option for smaller, contained OCDs:
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BMS techniques encourage fibrocartilage ingrowth, which is inferior to native hyaline cartilage.
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BMS may lead to an increase in lesion size and depth within 1 year.
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Long-term results for BMS have mixed functional results and are associated with the development of arthritis and decreased athletic activity.
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BMS plus cellular allograft, acellular allograft, scaffold, and/or growth factors:
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To encourage ingrowth of “hyaline-like” cartilage augmentation with an allograft, scaffold or growth factors may be considered; however, few are commercially available in the United States compared to Europe and other countries.
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BMS plus graft or scaffold is a good option for small primary OCDs of the talus and may yield satisfactory results in select patients.
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Autologous chondrocyte implantation/transplantation (ACI):
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First described by Brittberg et al. for treating deep cartilage defects in the knee.
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Arthroscopic ACI has led to the possibility of a valid option for regenerating the osteochondral layer with less morbidity than open-field surgery.
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Staged procedures have been described, which in the authors’ opinion is a disadvantage to this technique as it puts the patient through an additional procedure despite there being satisfactory outcomes. ,
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Subchondral cysts may be treated with subchondral drilling and retrograde bone grafting:
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Treatment of subchondral cysts was first described in the knee and was performed in an effort to prevent patients from having to undergo a total knee arthroplasty (TKA).
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The procedure involves percutaneous injection of a flowable nanocrystalline calcium phosphate synthetic bone graft into the cancellous trabeculae of the subchondral bone. It is hypothesized that the calcium phosphate improves the structural integrity and biomechanical strength of pathologic subchondral bone without damaging the existing bone scaffold.
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It is important to note that the subchondral bone provides support for the overlying articular cartilage and absorbs most of the mechanical force transmitted during joint loading.
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Osteochondral transfer with allograft or autograft:
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Osteochondral autograft transfer/transplantation has also been described as a method to replace damaged cartilage with either allograft or autograft.
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Autograft transplantation, also known as knee-to-ankle mosaicplasty, has been described, but not without caution. In a study by Valderrabano et al., they concluded that there was significant donor-site morbidity at the knee joint which potentially led to incipient patellofemoral osteaoarthritis.
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In addition, elevated graft placement leads to significant increases in joint contact pressure at the graft site. Recessed graft placement leads to transfer of pressure from the graft site to the opposite facet of the talus.
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3D-printed implant and instrumentation considerations
Materials:
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Cobalt-chromium is used owing to its low coefficient of friction, which reduces wear with adjacent bones of the foot that need to be kept intact to preserve motion in the joint (i.e., subtalar and talonavicular joints).
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Polished versus rough surfaces:
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Articulating aspects of the implant should be polished to lower the coefficient of friction over the adjacent cartilage.
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Rough and porous surfaces are needed where bony ingrowth is desired.
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Pore size:
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The gyroid is porous and measures 6 mm × 6 mm × 6 mm, with a 0.5-mm separation of pores.
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Shape:
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The shape of the implant must match that of the resected area of the talus. Naturally, the superior surface of the implant must be convex to be continuous with the remaining portion of the talus and to articulate appropriately with the tibia. The inferior surface of the implant is flat, with two 10 mm–long pegs for fixation into the body of the talus and associated pores to facilitate bone ingrowth ( Fig. 7.1 ).
• Fig. 7.1
Implant design correlating with the contour of a resected portion of the talus.
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Sizing:
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The surgeon’s preference is nominal ± 5% to 10%.
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Special features:
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The pegs can be placed in any orientation depending on the patient’s given anatomy.
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Options for screw fixation may be advantageous where additional/increased stability may be needed.
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Rationale for patient-specific instrumentation:
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CT and CAD images are extremely useful to determine nominal sizing in all planes.
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Patient-specific imaging also aids in accurately cutting an appropriately sized portion of the talus ( Fig. 7.2 ).
• Fig. 7.2
Preoperative CAD image showing appropriate positioning of guide and respective talus cuts. CAD , Computer-aided design.
(Reprinted with permission from restor3d, Inc, Durham, NC.)
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Surgical management with 3D-printed devices
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Special off-the-shelf instrumentation:
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The authors recommend utilizing a Hintermann distractor to help distract the ankle joint for better exposure of the ankle joint and for easier retrieval of the resected portion of the talus.
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A power rasp can be used to smooth the area of resected talus for easier insertion of implant and for quick adjustments to the resected surface of the talus.
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A 4-mm osteotome can be used for mobilization of the resected portion of talus.
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Positioning and anesthesia:
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The patient is positioned supine with a well-padded thigh tourniquet and ipsilateral thigh bump to ensure the foot and ankle are perpendicular to the operative table.
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General anesthesia with a local block is administered for postoperative pain control.
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Approach and technique:
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A mini anterior ankle incision is made between the interval of the tibialis anterior and extensor hallucis longus tendons.
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The ankle capsule is reflected utilizing sharp dissection and a Cobb elevator.
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Exposure is maintained using Gelpi and Weitlaner retractors placed deep so as not to compromise healing of the incision.
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A Hintermann distractor is utilized to maintain exposure of the ankle joint. Usually the distractor is placed on the side of the talus that is being replaced ( Fig. 7.3 ).
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
A 3D-printed solution for evans calcaneal osteotomy nonunion
3D-printed total cuboid replacement for lateral column pathology
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