Arthrodesis in the foot and ankle is sometimes an ideal solution for our patients; unfortunately, this procedure does not come without several potential complications that can prove to be challenging.1 Even when fusion is successful, poor alignment can cause stability issues, poor gait mechanics, difficulty with shoe fit, and decreased function.2

Special attention is paid to the subject of nonunion, as it is one of the most common and challenging adverse outcomes following arthrodesis procedures.1 Diagnosis of symptomatic nonunion is an important step in order to establish an optimum treatment plan. There are many imaging techniques [plain radiography, bone scan, computed tomography (CT), and magnetic resonance imaging] but none of these are as important as the physician’s clinical evaluation. A high index of suspicion and appropriate treatment are paramount for successful outcomes.3 Early and aggressive treatment of any arthrodesis complication is essential for good clinical outcomes.1 If anatomic reduction and arthrodesis position are stable and the patient shows evidence of good bone-healing potential, then nonoperative methods are appropriate,1 but the presence of a fibrous or cartilaginous pseudoarthrosis in a symptomatic patient is an operative indication,2 and resection of the nonviable pseudoarthrosis tissue is critical to allow boney ingrowth.1

However, finding the accurate nonunion plane intraoperatively could be challenging. Through a traditional open approach, in the beginning, nothing but a bone wall is visible, and landmarks are scarce to decide an appropriate cutting plane. Therefore, the only way to begin the resection is by slowly progressing, by “blind” bone excision with osteotomes and rongeurs.4 Different operative tips have been suggested to identify and mark the nonunion plane, such as using intraoperative fluoroscopy, bony landmarks and/or needles. Notwithstanding these tips could help us to find part of the nonunion plane, it is a 3-dimensional (3D) deformity and could be difficult to identify it completely. This is crucial as the complete resection of the nonviable pseudoarthrosis is critical to allow bony ingrowth.1

The advancements in 3D printing technology have allowed for the use of custom-designed implants for difficult-to-treat pathologies.5 Previous surgeries present a unique challenge to arthrodesis, nevertheless, in symptomatic patients revision surgery is needed if the position of the fusion is not mechanically sound, or if fixation has failed.1

We present a technical tip to identify the nonunion plane, by using a customized 3D printed surgical guide for resection and hindfoot rearthrodesis.

TECHNIQUE Design of the Cutting Guide

A CT scan of the patient’s foot and ankle is performed for preoperative planning. The CT scan DICOM images are then imported into radiologic post processing open-source software 3DSlicer (https://www.slicer.org/). The 3D-nonunion plane is obtained by creating a point cloud. To obtain the point cloud, the nonunion is marked in the 2D CT scan with spheres using axial, sagittal, and coronal views (Fig. 1). All this procedure is made inside 3D Slicer, along with the image processing and 3D-surface rendering so the images are exported as a stereo lithography file. The stereo lithography file files are then uploaded into the free Autodesk Meshmixer 3.3 (http://www.meshmixer.com/) to view and edit the 3D digital model of the foot. Once the point cloud is loaded, a virtual plane is drawn to guide the main resection cut (Figs 2A, B; Supplemental Fig. 1, Supplemental Digital Content 1, https://links.lww.com/TIO/A42). Once the nonunion plane is obtained, a resection-positioning guide is designed. The guide consists of four 10×3.5 mm cannulated cylinders attached to a template of the lateral aspect of the hindfoot and can only fit on the specific patient in the predefined position. The predefined position is based on the bony contour of the patient, using at least 3 bony landmarks (anterior, posterior, medial, and/or lateral). While designing the guide, we can choose as many bony landmarks as we need (bony spurs, osteophytes, tuberosities, etc.). The more bony landmarks used to define the position, the more the guide will adapt to an unique position. The central lumen of each cylinder is 1.5 mm in diameter and is designed to guide a K-wire (Supplemental Fig. 2, Supplemental Digital Content 1, https://links.lww.com/TIO/A42). Since it will be in contact with the patient during the operative procedure, a biocompatible material is needed. Dental LT Clear Resin (FormLabs, MA), with ISO Certificate 134485, is used to print the custom medical device in-house. Subsequently, the resin resection guide is sterilized using ethylene oxide for operative use.3

FIGURE 1:

The three-dimensional nonunion plane is obtained by creating a point cloud based the two-dimensional computed tomography scan with spheres using axial, sagittal, and coronal views.

FIGURE 2:

Virtual plane and point cloud in three-dimensional digital model of the foot. A, A virtual plane is drawn to guide the main resection cut based on the point cloud. B, Lateral view.

Nonunion Rearthrodesis

The patient is placed supine on the operating table with a sandbag under the ipsilateral buttock to internally rotate the affected leg in order to better expose the lateral aspect of the foot. Previous ostheosynthesis material (cannulated screws) were removed using a plantar approach. An extended lateral approach was performed exposing the distal third of tibia, the fibula and the hindfoot. The peroneal tendons were retracted, and the bone surface was exposed.

Then the 3D positioning guide was placed over the exposed rim of bone using the anatomic references (Supplemental Fig. 3, Supplemental Digital Content 1, https://links.lww.com/TIO/A42) and four 1.5-mm K-wires were inserted through the guide sleeves. Subsequently, the custom guide was removed leaving the K-wires as a reference. The plane defined by the K-wires is used to align an oscillating saw and perform the main resection cut, which has an oblique direction from dorsal-lateral to plantar-medial (Supplemental Figs 4 and 5, Supplemental Digital Content 1, https://links.lww.com/TIO/A42). The osteotomy was finished using an osteotome to prevent neurovascular bundle damage at the medial side (Supplemental Figs 6 and 7, Supplemental Digital Content 1, https://links.lww.com/TIO/A42). A second osteotomy was performed to obtain a lateral base wedge to correct the hindfoot varus, and the fibrous nonunion plane osteotomy plane was refreshed. Compression was achieved at the osteotomy plane and stabilized using an ankle fusion plate (Ortholoc Lateral TTC plate, WRIGHT, Arlington, TX) (Supplemental Figs 8 and 9, Supplemental Digital Content 1, https://links.lww.com/TIO/A42).

EXPECTED OUTCOME

Rearthrodesis after failed previous surgeries is a complex and challenging complication for the orthopedic surgeon. The arthrodesis may fail because of nonunion and/or malunion, causing pain, instability, and poor functional outcomes.2 Complete resection of the nonviable fibrous tissue is critical to allow boney ingrowth,1 but despite excellent preoperative planning, the nonunion plane may be little, or even not visible at all, with the intraoperative use of the fluoroscope. In contrast, the bone may look like an authentic wall in which no nonunion plane can be identified. In our opinion, 3D printing technology can be a valuable tool for this situation. The main advantages of the 3D printing guide are intraoperative time saving, the improved accuracy, and the reduction in x-ray exposure.4

This innovative technology not only assists medical staff but is also beneficial for the patients. The use of 3D printing technology is becoming more widespread for patient-specific guides in the medical field, and the applications of 3D printing in the field of medicine are yielding promising results.

The accuracy of 3D printing technology is essential for clinical applications. In this case, cannulated cylinders for K-wires placement were used to simulate the position and direction of the resection cut. We opted out of designing a cutting slot on the guide, because dental resin may not be hard enough to be used as an insertion guide for an oscillating saw. Besides, direct contact of the guide with the saw blade could produce a significant amount of debris and the device can easily be broken. In order to occupy the whole plane, a total of 4 cannulated cylinders were required because of the extent of cut needed to excise the bone wedge from the complete nonunion block. However, in other cases, less or more K-wires could be needed to guide the cut. Based in our experience we recommend to use as many K-wires as possible, placing 1 K-wire for each cm length, spacing 1 cm apart in each side.

The use of 3D printing can substantially reduce operative time and the number of fluoroscopy shots. We cannot quantify how much intraoperative time and x-ray exposure was saved, but this is a technically demanding 3D deformity, and we believe this technical tip may improve the accuracy of the nonunion excision. Identifying the nonunion plane preoperatively could be easy, but intraoperatively prove more difficult. Recognizing and treating the nonunion plane is crucial, and using a custom made cutting guide with an oscillating saw instead of a progressive bone resection using osteotomes and rongeurs is more precise. The nonunion planes could be difficult to identify in the operating room, as they are complex spatial deformities. This technique could be helpful as a intraoperative guide, and leads the surgeon to be bone conserving in nonunions that have little real estate on one side.

Advances in 3D reconstruction of radiologic studies have provided tools for virtual preoperative planning.4 Unique patterns such us the nonunion planes could be highly demanding to identify in the operating room, as they are complex multiplanar deformities. Although this technique is more relevant in smaller bones needing more precise bony resection, it could be used as a guide for long bones, helping the surgeon to minimize human error and improve the intraoperative accuracy. We believe that the utility of this tip lies on the creation of a point cloud (Supplemental Fig. 6, Supplemental Digital Content 1, https://links.lww.com/TIO/A42). Using the paint tool in the 2D CT scan, we can mark with spheres in both axial, sagittal and coronal views creating a point cloud which help us to create the nonunion plane preoperatively, leading us in the operating room with the cutting plane. This do-it-your-self model based on spheres is highly useful to create the cutting plane, but in our opinion, this method could be improved by using a total least squares algorithm. Further studies are needed to learn more about this technique tip, although the preliminary results are encouraging, and in our opinion, this can be performed safely with the described technique.

3D images are easier to interpret, including by less experienced surgeons4 and 3D printing allows translation from computer simulation to a tangible model, allowing the surgeon better appreciation of the geometry, size, and exact relationship between tissues.

COMPLICATIONS

Preoperative planning is the most common use of 3D printing in most orthopedic surgery subspecialties, and it has a potential usefulness in operative procedures of high spatial complexity.4 Future studies are needed, although the application of this new technique tip in clinical practice in our center brings encouraging results (Supplemental Fig. 10, Supplemental Digital Content 1, https://links.lww.com/TIO/A42). No complications have been observed yet with this technique tip. We believe that digitally planned and executed osteotomies facilitated by 3D printed patient-specific guides help the surgeon to minimize human error, improving intraoperative accuracy, while reducing surgical time and intraoperative x-ray exposure, but further studies are needed to determine if this technical tip really improve the clinical results.

REFERENCES 1. Martone J, Poel LV, Levy N. Complications of arthrodesis and nonunion. Clin Podiatr Med Surg. 2012;29:11–18. 2. Taylor JC Crenshaw A. Delayed union and nonunion in fractures. Campbell’s Operative Orthopedics. St. Louis, MO: CV Mosby; 1992:1287–1345. 3. Pérez-Mañanes R, Arnal J, Rojo J, et al. 3D surgical printing cutting guides for open- wedge high tibial osteotomy: do it yourself. J Knee Surg. 2016;29:690–695. 4. Sobrón FB, Benjumea A, Alonso MB, et al. 3D printing surgical guide for talocalcaneal coalition resection: technique tip. Foot Ankle Int. 2019;40:727–732. 5. Dekker TJ, Steele JR, Federer AE, et al. Use of patient-specific 3D-printed titanium implants for complex foot and ankle limb salvage, deformity correction, and arthrodesis procedures. Foot Ankle Int. 2018;39:916–921.