Inclusion criteria
① patients with primary or traumatic ankle arthritis ② Patients with asymmetric varus and 50% of tibial articular surface were preserved ③ Mild or moderate ankle osteoarthritis(Takakura stage 1-3a) ④ have some clinical symptoms, including weight-bearing or walking pain, claudication or daily activity limitation, which was unrelieved or even deteriorated by conservative therapy with a period of at least 6 month .
Exclusion criteria
① Patients with acute or chronic ankle infection ② Patients with severe coagulation dysfunction or severe cardiovascular and cerebrovascular diseases ③ Bone destruction, severe osteoporosis and rheumatoid arthritis caused by long term use of steroids ④ Patients with neuromuscular diseases or severe equinovarus ⑤ Patients and their families refused to sign informed consent.
General information: Basing on the criteria listed above, a total of 24 patients was included in this study, including 12 males and 12 females; the patients were enrolled in two cohort: the PSI group and the traditional method group. In the 3D guide group, the average age was (55.6 ± 11.3 ) years old versus (54.6 ± 10.4) in the traditional group; There were 6 males in both groups; Takakura stage: stage 1(1 in 3D guide group,1in traditional group), stage 2(5 in the 3D guide group;9 in the traditional group) and stage 3a(4 in 3D guide group,4 in traditional group)(Table 1). General photographs were routinely taken before surgery, and required imaging were obtained (Fig. 1, 2). All operations were performed by the same doctor who engaged in foot and ankle surgery for 20 years in our hospital. This study has been approved by the ethics committee of Shanghai Sixth People's Hospital (2020 − 135). The Clinical Trials identifier (IDE number) was ChiCTR2000035728. All the subjects have informed consent and signed the informed consent form.
Evaluation Criteria Of Postoperative Efficacy
General indicators: operation time, intraoperative blood loss, intraoperative fluoroscopy times were recorded.
Imaging measurement: the anteroposterior and lateral X-ray films of ankle was taken before and after operation, and the following were measured and recorded: ① TAS, the angle between the distal tibial plateau and the mechanical axis of tibia on the anteroposterior X-ray films; ② TT is the angle between the articular surface of the distal tibia and the articular surface of the talar dome on the anteroposterior X-ray film; ③ The tibial lateral surface angle (TLS) is the angle between the distal articular surface of the tibia and the mechanical axis of the tibia (Fig. 3, Table 2).
Production Of 3d Printing Patient-specific Instrumentation
CT data acquisition
The ankle joint was scanned with thin slice CT before operation. The scanning conditions were as follows: slice thickness and interval were 0.625 mm, voltage was 120 KV, current was 125 ma. The image data are saved in DICOM format.
Bone 3D- reconstruction
The DICOM data were imported into the 3D-reconstruction software Arigin 3D pro (Shanghai Xinjian Medical Technology Co., Ltd.) to reconstruct the 3D model of ankle. Adjust the window width and window level in the software operation interface to obtain an appropriate effect; Filtering, noise reduction and other means are used for two-dimensional image preprocessing, and then the corresponding regions are selected on the cross-section, coronal plane or sagittal plane, and different gray thresholds are set to distinguish bone and soft tissue. After that, the interested parts are separated by region growing operation, and the 3D-reconstruction of bone model is completed (Fig. 4A ~ D). The reconstructed data is optimized and saved in STL format.
Modeling
The reconstructed 3D model data were imported into the surgical planning software system Arigin 3D surgical templating system (Shanghai Xinjian Medical Technology Co., Ltd.). The characteristic points and lines were marked on the three-dimensional model of ankle to determine the tibial anterior surface angle (TAS) and talar tilt angle (TT). The osteotomy line is determined through the sketch line function of the software to draw the osteotomy plane, so as to simulate the tibial osteotomy (Fig. 4E ~ G), and take the contralateral model data as reference. Then, the TT angle, the space between tibia and talus, and the space between fibula and talus were determined by opening the distal end of valgus tibia. Using the above parameters, the patient-specific instrumentation was drawn on the original bone. Arigin 3D surgical templating system software can automatically generate the surgical guide model, and make it into real object through 3D printer. The finite element mechanical property analysis module is used to optimize the structure of the surgical guide plate, and the Boolean operation method is used to obtain the inner surface of the guide plate which fits firmly with the characteristic parts of the bone, so as to complete the design process.
Features of patient-specific instrumentation
The surgical guide plate has its unique features in the design process, which helps to achieve more functions, that is, on the basis of ensuring the accurate osteotomy position and osteotomy direction, the advantages listed bellowed could also obtained: ① ensure the depth of operation, protect the lateral hinge; ② After osteotomy, the angle of orthopedic distraction was determined; ③ Disassemble the guide plate separately, keep the angle of distraction, and do not hinder the installation of steel plate.
Surgical Methods
All patients received general anesthesia, inflatable tourniquet was used at the proximal end of the affected limb, and the contralateral anterior superior iliac spine was disinfected and covered for autologous iliac bone graft.
The ankle joint was cleaned before osteotomy, and the involvement of tibiotalar joint surface was observed. Conventional open osteotomy of the medial tibia outside the joint is adopted. Firstly, the split surgical guide plate designed by arigin 3D surgical templating system is attached to the medial part of the distal tibia of the patient, fixed with 2.0 mm Kirschner wire, and osteotomy is carried out according to the osteotomy knife groove on the guide plate. The osteotomy plane is planned and determined in the above software, generally 5 cm at the proximal end of the medial malleolus, The medial metaphysis of tibia was obliquely osteotomized. During osteotomy, the hinge can be used to limit the guide plate, limit the depth of osteotomy, and reserve the contralateral periosteum and soft tissue. Then, according to the preoperative planning, the wedge-shaped block with the corresponding angle designed in advance can be inserted into the guide plate osteotomy groove, and the osteotomy depth can be gradually expanded until the force line is restored to satisfaction. The angle of distraction should be maintained, the split surgical guide and wedge-shaped block should be removed, and the wedge-shaped iliac bone with corresponding width can be used to fill the osteotomy distraction. Then the distal tibial metaphyseal locking plate was used for fixation, and the distraction angle was removed to maintain the guide plate (Fig. 5).
For the patients who need fibular osteotomy, correct the varus according to the angle that needs to be corrected according to the preoperative plan. Fluoroscopy confirms that the limb alignment is satisfactory. The fibular plate is placed posterolateral and fixed with screws. Finally, fluoroscopy confirms the reduction and fixation effect. The lateral collateral ligament injury and ankle instability were found during the operation. The lateral soft tissue stability of ankle joint was reconstructed with suture anchors or autogenous peroneal longus tendon. Immediate postoperative imaging showed that the internal fixation position was good and the line of force was acceptable (Fig. 6).
Postoperative Management
The patients were guided to take active and passive training for ankle joint on the second day after operation, and short leg support was used to protect them at night. The suture was removed 2 weeks after operation, and the patients were guided to gradually carry out the function of supporting the abduction and load at 6 weeks after operation. The X-ray film of 3 months after operation indicated that the osteotomy and bone healing could start to carry out complete weight-bearing (Fig. 7).
Statistical analysis
Continuous variables were described as mean ± standard deviation (SD), while qualitative variables were described as proportions. Statistical analysis was performed using SPSS software (version 26.0; IBM, Armonk, NY, USA). Independent sample T-test and Fisher’s exact test were used for statistical analyses to compare the two groups. All statistical tests are two-sided and at the 0.05 level of significance.