Deformity-Correcting Ankle Fusions With Patient-Specific 3D Operative Planning and 3D-Printed Cut Guides: Report of 2 Cases : JBJS Case Connector

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Deformity-Correcting Ankle Fusions With Patient-Specific 3D Operative Planning and 3D-Printed Cut Guides

Report of 2 Cases

Bouchard, Maryse MD, MSc, FRCSC1,2,a; Da Costa, Sophia BSc Candidate at the University of Waterloo1,4; Peel, Brandon BSc, BEng1,3

Author Information
JBJS Case Connector 12(4):e22.00553, October-December 2022. | DOI: 10.2106/JBJS.CC.22.00553
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  • Disclosures

Abstract

Complex ankle deformities in patients with arthrogrypotic clubfeet are challenging to treat. Owing to high risk of relapse, most patients have many surgeries by the time they reach adolescence, resulting in atypical multiplanar deformities1–6. Joint sparing procedures are preferred in younger patients; however, in the setting of arthrogryposis, the joints tend to become extremely stiff. When joint motion is already markedly reduced, arthrodesis may be the optimal solution6–8.

Deformity-correcting ankle fusions are not commonly performed in pediatric patients. Restoring alignment in children with ankle deformities, such as those seen in arthrogrypotic clubfeet, is challenging because the surgeon must often free-hand bone cuts in multiple planes while avoiding neurovascular structures.

To address these complex cases with improved surgical precision and to decrease surgical risks, a new technique of preoperative planning and intraoperative deformity correction was developed using 3D digital modeling and 3D printing of patient-specific cut guides.

Others have used 3D guides in orthopaedic surgery, including cut guides for osteotomies of the hindfoot, midfoot, and knee9–11, and k-wire positioning guides for both arthroscopic ankle fusions12 and ankle ligament reconstruction13. All reported reductions in operation time and intraoperative fluoroscopy. To the best of our knowledge, these are the first cases using custom 3D-printed cutting guides for fusion in the foot or ankle.

We present 2 patients with arthrogrypotic clubfoot and complex multiplanar ankle deformities who were treated with deformity-correcting ankle fusions using 3D preoperative planning and custom 3D-printed intraoperative cutting guides. It is important to note that in these cases the concurrent foot and ankle deformities were managed with deformity correction entirely through the ankle joint to mitigate surgical risk.

The patients were informed that data concerning the case would be submitted for publication, and they provided consent.

Case Reports

Case 1. A 12-year-old male patient presented with multiply casted and operated arthrogrypotic clubfeet. He had persistent severe stiff deformities affecting his mobility and balance preventing independent standing and gait. He used ankle-foot orthoses (AFOs) and knee-AFOs (KAFOs).

Both feet had limited subtalar and ankle motion and persistent adductus, cavus, and significant hindfoot varus, with the left more severe than the right. Preoperatively, his responses on the Oxford Ankle Foot Questionnaire for Children (OxAFQ-C) physical, school and play, emotional and footwear domains were 14.0 (58.3%), 9.0 (56.2%), 15.0 (93.8%), and 4.0 (100%), respectively, with a higher score representing better function.

Owing to his extreme deformity primarily at the ankle with stiffness and degenerative changes, deformity-correcting ankle fusion was indicated as a powerful option for improving alignment of both feet.

Surgical Planning

Segmentation of the Digital Imaging and Communications in Medicine images was performed by a biomedical engineer using Mimics Medical 23.0 (Materialise NV) software to generate a 3D model of the ankle and foot. The 3D model was further processed using 3-matic Medical 15.0 (Materialise NV) software for preoperative planning with the surgeon. Materialise software was selected because it is the industry-standard software for medical segmentation, planning, and design and has U.S. Food and Drug Administration clearance for 3D printing.

The original 3D anatomical model of the patient was 3D-printed with the Fortus 380mc (Stratasys) 3D printer with ABS-M30i material to allow better visualization for preoperative planning purposes (Fig 2A). The surgeon and engineer collaborated to determine the desired corrected position by using 3-matic Medical software to visualize overlapping bony anatomy needing to be removed (Fig 2B). The final corrected position was defined as one with the foot tripod restored between first and fifth metatarsal heads and calcaneus with a plantigrade position of the foot relative to the tibia. Cut planes are then used to mimic the cuts produced by the surgeon in the operating room (Fig 2C). Patient-specific cut guides were designed by reverse engineering the corrected foot position with cut planes back to the original deformity position (Fig 2D). The patient-specific cut guides are printed with the J750 Digital Anatomy (Stratasys) 3D printer using MED610 material. The postoperative models with predesigned cuts are printed with the Fortus 380mc (Stratasys) 3D printer to use in the operating room for reference and to cue positioning of the cut guides. Both 3D printers were selected because of the printability of sterilizable materials.

fig1
Fig. 1:
Clinical photograph (Fig. 1-A) and radiographs of case 1. Fig. 1-B 3 foot standing x-ray demonstrating leg length discrepancy from prior femoral fracture. Fig. 1-C through 1-F Anteroposterior (AP) and lateral x-rays of right and left feet demonstrating residual equinocavovarus deformities with significant dysplastic and degenerative changes in the ankle, hindfoot, and midfoot.
fig2
Fig. 2:
Case 1 3D digital images of the anatomical models of left foot and ankle for surgical planning; (Fig. 2-A) original anatomical position. (Fig. 2-B) Corrected-deformity position. (Fig. 2-C) Original anatomical position with cut planes. (Fig. 2-D) Original anatomical position with patient-specific cut guides.

All design, manufacturing, and postprocessing of the models and patient-specific cut guides were performed at The Hospital for Sick Children.

Surgical Technique

An incision was made over the anterior distal tibia curving slight lateral distally to expose the distal tibia and ankle joint. Neurovascular structures were carefully protected. After exposing the anterior surface of the tibia and dorsal surface of the talar neck, the custom 3D-printed cutting guides were positioned and secured with k-wires through precut holes over the predetermined anatomical landmarks to resect a dorsolateral wedge through the ankle joint. The bone cuts were confirmed with fluoroscopy and made with an oscillating saw. The guides and bone wedge were removed, and the reduction held temporarily with k-wires. Clinical and radiographic alignment were confirmed. The only freehand adjustment required was resection of the distal tip of the lateral malleolus to avoid impingement. A compression screw and anterolateral locking ankle fusion plate, preselected based on the 3D-printed model of the postoperative foot, were implanted. The patient was immobilized in a splint and kept non–weight-bearing for 6 weeks. He used a combination of AFOs and KAFOs for comfort until he gained endurance and balance in gait. The second foot was corrected in the same manner with patient-specific guides 6 months later.

At 1 year, both ankles were fused radiographically. He was able to walk 5 km with increased independence and transitioned to walking without a brace on the right side and weaning the KAFO on left. There was an increase in OxAFQ-C physical score (Table I). He rated his current level of functioning near normal with a functional score for activities of daily living of 90% on the Foot Ankle Ability Measure (FAAM).

TABLE I - Case 1 OxAFQ-C Functional Scores Preoperatively and Postoperatively
Months from First Procedure OXFAQ Child Functional Scores
Physical School and Play Emotional Footwear
0.5 preoperative 14.0 (58.3%) 9.0 (56.2%) 15.0 (93.8%) 4.0 (100%)
9.5 postoperative 15.0 (62.5%) 13.0 (81.2%) 16.0 (100%) 2.0 (50.0%)
13.5 postoperative 16.0 (66.7%) 7.0 (43.8%) 13.0 (81.2%) 1.0 (25.0%)

case 2.A 12-year-old female patient presented with severe residual arthrogrypotic clubfeet. She had no prior surgical treatment. Her left foot was corrected with a combination of soft tissue releases, serial casting, and joint sparing osteotomies. The right midfoot was corrected with similar joint sparing techniques, but owing to a flat-top talus, a deformity-correcting ankle fusion was performed to correct the equinus given her stiff ankle and to avoid worsening the calcaneus deformity (Figures 7 and 8). Preoperatively, she reported OxAFQ-C physical, school and play, emotional, and footwear scores of 12.0 (50%), 11.0 (69%), 11.0 (69%), and 3.0 (75%) respectively.

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Fig. 3:
Case 1 intraoperative clinical photographs of right foot with (Fig. 3-A) use of model to ensure appropriate landmarking; (Fig. 3-B) intraoperative cut guide placement; (Fig. 3-C) lateral radiograph with blue line representing distal talar cut to confirm correct guide placement; (Fig. 3-D) lateral radiograph with blue line representing proximal tibial cut to confirm correct guide placement.
fig4
Fig. 4:
Case 1 3D digital images of the anatomical models of right foot and ankle for surgical planning; (Fig. 4-A) and (Fig. 4-F) original anatomical AP and lateral position with cut guides (Fig. 4-B) and (Fig. 4-E) corrected AP and lateral deformity position with first planned cut. (Fig. 4-C) and (Fig. 4-D) corrected AP and lateral deformity position with second planned cut for additional correction as needed intraoperatively. AP = anteroposterior.
fig5
Fig. 5:
Case 1 intraoperative clinical photographs of left foot with (Fig. 5-A) use of model to ensure appropriate landmarking with proximal cut performed. (Fig. 5-B) Anatomy with bone wedge resected and guides removed. (Fig. 5-C) Reduced position of ankle. (Fig. 5-D) Lateral view demonstrating plantigrade foot position once reduced.
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Fig. 6:
Clinical photographs (Fig. 6-A – AP view, Fig. 6-B – anterior view with 1" block under left foot) and lateral radiographs of both ankles (Fig. 6-C – right, Fig. 6-D – left) in case 1. Note some residual equinus left on purpose to accommodate knee flexion contractures. Fusion achieved in both ankles.
fig7
Fig. 7:
Clinical photograph (Fig. 7-A) and radiographs of left foot for case 2 preoperatively. Fig. 7-B Lateral x-rays of left foot demonstrating flattop talus and severe midfoot cavus. Fig. 7-C AP x-ray with significant adductus of forefoot.
fig8
Fig. 8:
Fig. 8-A and 8-B Clinical AP and lateral photographs of case 2 left foot after plantarmedial soft tissue releases and serial casting. Fig. 8-C Lateral radiograph at same time point highlighting calcaneus deformity and flattop talus. Corrected midfoot cavus and adductus. AP = anteroposterior.
fig9
Fig. 9:
Fig. 9-A Intraoperative photograph showing tibial and talar guide placement for deformity-correcting ankle fusion. Fig. 9-B Preoperative 3D-printed models of resected bone wedges and actual bone wedges resected. Fig. 9-C and 9-D Lateral and AP preoperative models of same resections. AP = anteroposterior.
fig10
Fig. 10:
Fig. 10-A and 10-B Postoperative clinical photographs of case 2 AP and anterior views showing plantigrade feet and normal hindfoot alignment with mild residual adductus on left. Fig. 10-C and Fig. 10-D AP and lateral radiographs at 1 year of left foot showing residual calcaneus deformity and mild adductus but plantigrade position with corrected cavus and healed ankle fusion. AP = anteroposterior.

The surgical planning and technique followed the same as Case 1.

At 1 year, the ankle was fused radiographically. The patient reported occasional heel pain in the left foot when not wearing AFOs due to the calcaneus deformity. Her OxAFQ-C functional scores – except footwear - increased (Table II). She rated her level of functioning normal with a functional score of 75% for activities of daily living on the FAAM.

TABLE II - Case 2 OxAFQ-C Functional Scores Preoperatively and Postoperatively
Months from Procedure OXFAQ Child Functional Scores
Physical School and Play Emotional Footwear
2.25 preoperative 12.0 (50.0%) 11.0 (68.8%) 11.0 (68.8%) 3.0 (75.0%)
7 postoperative 11.0 (45.8%) 9.0 (56.2%) 14.0 (87.5%) 2.0 (50.0%)
11 postoperative 13.0 (54.2%) 13.0 (81.2%) 13.0 (81.2%) 2.0 (50.0%)

Discussion

Deformity-correcting fusions of the foot and ankle in adolescence are rare and often complex. They include risks such as shortening of the foot, recurrence of deformity, nonunion, and neurovascular injury6–8. In extreme cases of severely relapsed clubfoot, there may not be other suitable options14.

In the cases presented, using patient-specific 3D guides reduced surgical complexity and improved accuracy of deformity correction in ankle fusions for arthrogrypotic clubfoot patients. There is only 1 study in the literature that reported using 3D guides in ankle fusions, and these were designed for k-wire and screw placement12. To the best of our knowledge, our cases are the first description of patient-specific 3D-printed cut guides reported in the literature for arthrodesis in the foot and ankle.

While increasing numbers of hospitals have access to 3D printing and planning expertise, our cut guide design process using 3D reverse engineering is novel. This technique allowed the surgeon to accurately control the correction in each plane, which is often difficult to achieve during traditional surgery without continual adjustments. Our process also applied Boolean intersection design methods to the corrected model to better visualize bony overlaps for guide creation. Modeling of various degrees of correction was visualized instantaneously through this method allowing the surgeon to precisely plan the procedure on a personalized level.

Fixation and surgical approach can affect outcomes of ankle fusion15. In these cases, the use of 3D preoperative planning offered a 3D anatomical model of the foot making it possible to choose implants and their placement ahead and plan appropriate incisions. This saved time intraoperatively and ensured the best implant choice. The total cost for each anatomical model was approximately $200.00 CAD with each set of sterilizable guides approximately $50.00 CAD.

In conclusion, deformity-correcting ankle fusions in adolescents are challenging. The use of 3D-planning and 3D-printed patient-specific guides is an optimal adjunct for complex cases enabling a safer procedure for the patient and a more efficient and accurate procedure for the surgeon.

References

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10. Arnal-Burró J, Pérez-Mañanes R, Gallo-del-Valle E, Igualada-Blazquez C, Cuervas-Mons M, Vaquero-Martín J. Three dimensional-printed patient-specific cutting guides for femoral varization osteotomy: do it yourself. Knee. 2017;24(6):1359-68.
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12. Duan X, He P, Fan H, Zhang C, Wang F, Yang L. Application of 3D-printed personalized guide in arthroscopic ankle arthrodesis. Biomed Research Int. 2018;2018:1-8.
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Keywords:

3D-printing; surgical cut guides; preoperative planning; CAD surgery simulation; patient-specific; pediatric; foot and ankle; ankle fusion; adolescent; male and female; clubfoot; arthrogryposis; ankle arthrodesis; surgical guides; deformity; clubfeet; ankle; OxAFQ-C; bony fusion; deformity correction; tibia; relapsed clubfoot

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