Study design and patients
This study has been approved by the Ethics Committee of our hospital. We retrospectively reviewed the clinical and imaging data of patients with SMOT used or did not used SO-PSI between October 2014 and December 2018. The inclusion criteria were as follows: (1) more than 18 years old; (2) primary surgery; (3) unilateral SMOT; (4) with Takakura stage II, IIIA or IIIB; (5) with clinical symptoms, like 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 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 the end, 28 patients were included; we divided them into CO group (n = 17) and SO-PSI group (n = 11). Basic information of the patients is presented in Table 1; the demographics and preoperative situation of two groups have no significant difference. Follow-up was conducted at 3, 6, and 12 months postoperatively, and at least one follow-up after postoperative 12 months. The 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 in combination with the surgeon’s experience. First, we drew anatomical axis of tibia and angles of ankle (Figs. 1a and 1b), such as tibial anterior surface angle (TAS), tibiotalar tilt angle (TTA), malleolar angle (MA) and tibial lateral surface angle (TLS); then we drew osteotomy plan on the X-ray, the aim of osteotomy was to make the ankle angles ideal while keeping the force line correct [7, 14–17] (Fig. 1c). However, only target value of TAS and TLS can be accurately designed in preoperative plan.
In the SO-PSI group, first in order to understand the disease quickly, we drew anatomical axis of tibia and angles of ankle as same as the CO group (Figs. 1a and 1b). Second, the CT data were entered into E-3D V17.08 software (Huiqing, LTD., Nanjing, China) and was built into a 3D digital model, then we performed a simulated operation on the digital model (Fig. 1d). The simulated operation was usually divided into five steps: (1) We drew the axis and angles on the digital model to understand the disease further. (2) We did osteotomy, reduction and other special operative step on the digital model, at this point, we could repeatedly adjust the osteotomy, reduction and special operative step until the parameters became the most perfect (Fig. 1c). (3) We chose one to four suitable plates and appropriate screws from our virtual database of internally fixed models, after that, we installed the virtual internal fixation on the digital model. (4) We designed a PSI to help with the operation; usually we created an osteotomy guide plate to assist in osteotomy, and a temporary fixation guide plate to maintain the normal position of bone blocks. (5) We checked repeatedly to see if the simulated operation was satisfactory, and did some actively modified until it became perfect. Third, after satisfactory simulated operation, all procedures, tools and internal fixation were recorded and prepared accordingly. In addition, we used nylon material to construct the PSI and life-sized 3D model, using the selective laser sintering (SLS) technique (Fig. 1e).
Operation and rehabilitation
In the CO group, as same as the conventional SMOT [1, 2, 7, 15–17], the medial point of osteotomy line was about 3 cm to 5 cm above the joint surface. According to the preoperative plan, we did osteotomy and other steps to perfect the ankle alignment and position assisted by multiple intraoperative fluoroscopies.
In the SO-PSI group, most steps were as same as the CO group, but there were still differences. (1) The position of the osteotomy line was determined, according to the osteotomy guide plate; then an osteotomy could be performed accurately without repeated confirmations and attempts (Fig. 1f). (2) Perfect axes and angles were obtained through the assistance of temporary fixation guide plate; when the plate was installed on bone blocks and then form a rigid whole reciprocally, the ankle alignment and position will be consistent with the preoperative plan (Figs. 1d and 1 g). (3) Suitable plates and appropriate screws were installed on skeleton according to the preoperative plan (Fig. 1d). The ankle alignment and position in the mortise were verified fluoroscopically before and after final fixation.
For both two groups, the patient wore a plaster slab until the stitch of wound was removed, then wore a below-knee protective plaster cast. Patients were encouraged to mobilize partially weight bearing for the first 3–6 weeks; after that, full weight-bearing without plaster cast began after the osteotomy site reached bony union radiographically.
Measurement and follow-up
To compare the difference between the two groups during the perioperative period, we carefully searched and collected: pre-op planning time, number of plate, op-special step, op-time, number of fluoroscopies, op-blood loss, reduction of albumin (ALB, the difference of albumin value between pre-op two days and post-op two days), total hospital stay, hospitalization expenses, complication rate and union time.
To evaluate the accuracy of preoperative planning and intraoperative application, preoperative planning and postoperative three to six months actual imaging data were compared. In CO group, we compared the TASs and TLSs; in SO-PSI group, we compared the TASs, TTAs, MAs, TLSs and tibial ankle center discrepancy (TACD, the distance between tibial ankle center of preoperative SO plan data and actual postoperative three to six months CT data) (Figs. 1h and 1j).
To compare the postoperative follow-up of the two groups, we carefully searched and collected the imaging data to compare the changes of the ankle angles and Takakura stage. Moreover, the American Orthopaedic Foot & Ankle Society (AOFAS) ankle-hindfoot score [18], range of motion (ROM) of ankle [19] and visual analogue scale (VAS) [20]were used to evaluate the functional outcomes pre- and post-operation.
Statistical analysis
Independent Samples t-test was used to analyze the difference of the age, BMI, AOFAS score, VAS, ROM of ankle, follow-up time, pre-op planning time, op-time, number of fluoroscopies, op-blood loss, reduction of ALB, hospital stay, pre-op hospital stay, post-op hospital stay, hospitalization expenses and union time. Chi-squared test was used to analyze the difference of the gender, etiology, diabetes, smoker, Takakura stage, number of plate, special op-step and complication rate. Independent-samples t-test was used to analyze the changes of angles before and after operation. Linear correlation regression analysis was used to analyze the accuracy of pre-op plans in both two groups. Significance was defined as p < 0.05. Statistical analysis was performed with SPSS 20.0 software (SPSS Inc., Chicago, IL, USA).