Study design and patients
This study was approved by the Ethics Committee of our hospital. We retrospectively reviewed the clinical and imaging data of patients with SMOT, using SO-PSI or not, between October 2014 and December 2018. The inclusion criteria were as follows: (1) > 18 years old; (2) primary surgery; (3) unilateral SMOT; (4) Takakura stage II, IIIA, or IIIB; (5) clinical symptoms, including pain and limitation of daily activities; (6) treated with SMOT, with at least one year follow-up. The exclusion criteria were: (1) refused to participate in the study; (2) Charcot arthropathy, rheumatoid arthritis, or ankle infection; (3) physical activity disorders, caused by other disease, such as neurologic disorders; (4) mental illness.
In total, 28 patients were included and divided into CO (n = 17) and SO-PSI (n = 11) groups. The basic characteristics of the patients are presented in Table 1. There were no significant differences in demographic factors or preoperative characteristics between the two groups. Follow-up was conducted at 3, 6, and 12 months postoperatively, with at least one follow-up after 12 months postoperative. Mean follow-up time was 33.4 (range, 13 to 59) months.
Table 1
Basic information of the patients.
| CO group | SO-PSI group | P values# |
Number of patients | 17 | 11 | |
Gender (male/female) | 5/12 | 4/7 | 0.700 |
Mean of Age (years) | 46.4 ± 11.6 | 53.8 ± 14.4 | 0.147 |
Mean of BMI (kg/m2) | 24.8 ± 4.4 | 25.6 ± 4.6 | 0.622 |
Etiology (No. and %) | | | |
| Osteoarthritis | 4 (23.5%) | 3 (27.3%) | 0.823 |
| Posttrauma arthritis | 13 (76.5%) | 8 (72.7%) | 0.823 |
Diabetes (No. and %) | 2 (11.8%) | 2 (18.2%) | 0.636 |
Smoker (No. and %) | 3 (17.6%) | 4 (36.4%) | 0.264 |
Takakura stage (No. and %) | | | |
| Takakura II | 3 (17.6%) | 1 (9.1%) | 0.527 |
| Takakura IIIA | 9 (52.9%) | 5 (45.5%) | 0.699 |
| Takakura IIIB | 5 (29.4%) | 5 (45.5%) | 0.387 |
Mean of pre-op AOFAS score | 52.5 ± 10.6 | 51.7 ± 10.9 | 0.860 |
Mean of pre-op VAS | 7.7 ± 1.4 | 7.3 ± 1.6 | 0.463 |
Mean of pre-op ROM of ankle (°) | 31.2 ± 6.8 | 31.8 ± 8.4 | 0.850 |
Mean of follow-up time (months) | 28.6 ± 12.4 | 35.9 ± 12.9 | 0.150 |
Abbreviations: CO: Conventional operation group; SO-PSI: Simulated operation combines Patient-specific guide; BMI: body mass index; AOFAS score: the American Orthopedic Foot and Ankle Society score; VAS: visual analogue scale; ROM: range of motion; pre-op: preoperative. |
# P values, α = 0.05, (Age, BMI, AOFAS score, VAS, ROM of ankle and follow-up time: independent-samples t-test; Gender, Etiology, Diabetes, Smoker and Takakura stage: Chi-squared test) |
Preoperative evaluation and planning
In the CO group, preoperative planning was based on radiography images and the surgeon’s experience. First, the anatomical axis of the tibia and angles of the ankle were drawn (Figs. 1a and 1b), including the tibial anterior surface angle (TAS), tibiotalar tilt angle (TTA), malleolar angle (MA), and tibial lateral surface angle (TLS). Then an osteotomy plan was drawn on the X-ray. The aim of osteotomy was to generate ideal ankle angles, while retaining the correct force line [7, 14–17] (Fig. 1c); however, only target values of TAS and TLS could be accurately designed in the preoperative plan.
In the SO-PSI group, initially, to achieve a quick understanding of the disease condition, the anatomical axis of the tibia and ankle angles were drawn, as for the CO group (Figs. 1a and 1b). Next, computed tomography (CT) data were entered into E-3D V17.08 software (Huiqing, LTD., Nanjing, China) and incorporated into a 3D digital model. Then simulated surgery was conducted on the digital model (Fig. 1d). The simulated operation was usually divided into five steps: (1) The axis and angles were drawn on the digital model to further understand the disease condition. (2) Osteotomy, reduction, and other specific operative steps were conducted on the digital model. At this point, the osteotomy, reduction, and specific operative steps could be repeatedly adjusted to optimize the parameters (Fig. 1c). (3) One to four suitable plates and appropriate screws were chosen from our virtual database of internally fixed models, then the virtual internal fixation was installed on the digital model. (4) PSI was designed to assist with the operation. Usually, an osteotomy guide plate was constructed to assist in osteotomy, as well as a temporary fixation guide plate to maintain the normal position of bone blocks. (5) Repeated checks were conducted to determine whether the simulated operation was satisfactory, and active modifications conducted until it was optimal. Finally, after a satisfactory simulated operation had been conducted, all procedures, tools and internal fixations were recorded and prepared accordingly. Nylon material was used to construct the PSI and life-sized 3D model, using selective laser sintering (SLS) (Fig. 1e).
Operation and rehabilitation
In the CO group, as for conventional SMOT [1, 2, 7, 15–17], the medial point of the osteotomy line was approximately 3–5 cm above the joint surface. According to the preoperative plan, osteotomy and other steps were conducted to optimize the ankle alignment and position, assisted by multiple intraoperative fluoroscopies.
In the SO-PSI group, most steps were as same as those for the CO group; however, there were differences, as follows: (1) The position of the osteotomy line was determined according to the osteotomy guide plate, allowing osteotomy to be performed accurately, without repeated confirmations and attempts (Fig. 1f); (2) Optimal axes and angles were obtained with the assistance of a temporary fixation guide plate; when the plate was installed on bone blocks and then used to reciprocally form a rigid whole, the ankle alignment and position were consistent with the preoperative plan (Figs. 1d and 1 g); and (3) Suitable plates and appropriate screws were installed in the skeleton according to the preoperative plan (Fig. 1d). Ankle alignment and position in the mortise were verified fluoroscopically before and after final fixation.
For both groups, the patient wore a plaster slab until the stitches were removed from the wound, then a below-knee protective plaster cast was worn. Patients were encouraged to mobilize, with partial weight-bearing for the first 3–6 weeks; subsequently, full weight-bearing, without a plaster cast, began after the osteotomy site achieved bony union, according to radiography.
Measurement and follow-up
To compare parameters between the two groups during the perioperative period, we carefully searched and collected the following data: pre-operative planning time, number of plates, operation-specific steps, operation-time, number of fluoroscopic examinations, operative blood loss, reduction of albumin (ALB, the difference between the albumin value two days pre-op and two days post-op), total hospital stay, hospitalization expenses, complication rate, and union time.
To evaluate the accuracy of preoperative planning and intraoperative application, actual imaging data for preoperative planning and at three to six months postoperatively were compared. In the CO group, TAS and TLS values were compared, while in SO-PSI group, the values compared were TAS, TTA, MA, TLS, and tibial ankle center discrepancy (TACD; the distance between tibial ankle center in the preoperative SO plan and the actual postoperative position on three to six month CT) (Figs. 1h to 1j).
To compare postoperative follow-up between the two groups, we carefully searched and collected imaging data to evaluate changes in the ankle angle and Takakura stage. Moreover, the pre- and post-operation American Orthopaedic Foot & Ankle Society (AOFAS) ankle-hindfoot score[18], ankle range of motion (ROM) [19], and visual analogue scale (VAS) [20] were used to assess functional outcomes.
Statistical analysis
An independent Samples t-test was used to evaluate differences in age, body mass index, AOFAS score, VAS, ankle ROM, follow-up time, pre-operative planning time, operating time, number of fluoroscopies, operative-blood loss, reduction of ALB, hospital stay, pre-operative hospital stay, post-operative hospital stay, hospitalization expenses, union time, and changes in angles before and after surgery. Chi-squared tests were used to analyze differences in sex, etiology, diabetes, smoker status, Takakura stage, number of plates, specific operation steps, and complication rate. The accuracy of pre-operative plans in both groups was analyzed by linear correlation analysis. Significance was defined as p < 0.05. Statistical analyses were performed using SPSS 20.0 software (SPSS Inc., Chicago, IL, USA).