Simulated operation combines patient-specific guide technology is superior to conventional technology for supramalleolar osteotomy: a retrospective comparative study CURRENT STATUS:

Background: Over the past seven years, our team has designed a simulated operation combines patient-specific guide (SO-PSI) assisted supramalleolar osteotomy (SMOT) method and applied it to the clinic. This study aimed to determine the difference between SO-PSI technology and conventional operation (CO) technology for SMOT in preoperative planning, intraoperative application and postoperative curative effect. Methods: We retrospectively analyzed the data of SMOT in our hospital between October 2014 and December 2018; 28 patients were enrolled and divided into CO group (n=17) and SO-PSI group (n=11); the mean follow-up time was 33.4 (range, 13 to 59) months. We analyzed and compared perioperative data, accuracy of preoperative planning and intraoperative application, difference between pre- and post-operative of radiologic ankle angles, and change of AOFAS score, VAS, range of motion of ankle and Takakura stage after operation. Then we performed statistical analyses. Results: All ankle alignments and positions of two groups have been recovered. Compared with CO group, SO-PSI group has a shorter operative time and a postoperative hospital stay, a decreased number of fluoroscopies and a reduction of albumin, a longer preoperative planning time and a preoperative hospital stay and an increased hospitalization expenses. In SO-PSI group, the ankle angles between preoperative planning and postoperative shown good correlation, but not in CO group; the mean tibial ankle center discrepancy of SO-PSI group was 1.86±1.06 mm. After follow-up, all radiologic parameters of two groups significantly improved, but the improvement of tibial anterior surface angle and tibiotalar tilt angle of SO-PSI group were more obvious than that of CO group; AOFAS score, VAS, range of motion of ankle and Takakura stage of two groups improved after operation; but overall the improvements of SO-PSI group were better than the CO group. Conclusions: SO-PSI technology can carry out the preoperative plan accurately and quickly in SMOT;

3 Background Supramalleolar osteotomy (SMOT) is an effective procedure for the treatment of midstage asymmetric ankle osteoarthritis [1][2][3][4]. Related studies have proved that the key factors affecting the postoperative curative effect of SMOT are the postoperative ankle Takakura stage [5], lower limb power line [6] and ankle angles [7]; but SMOT uses conventional operation (CO) method often does not perfectly accomplish these surgical aims leading to some patients have unsatisfactory outcomes [8,9]. The reasons include preoperative planning dependence on freehand drawing, and surgeons determine the operative procedure all depend on the surgeon's experiences and fluoroscopies [10].
Some studies have demonstrated that simulated operation combines patient-specific guide (SO-PSI) can optimize preoperative planning and operative process, and make operation personalized and precision [11][12][13]. Over the past seven years, our team has designed a SO-PSI assisted SMOT method and applied it to the clinic. The surgeons can complete preoperative evaluation and operation simulation on three-dimensional (3D) digital model, and get the best planning after repeated confirmation; then accurately execute the preoperative planning with the help of PSI during the operation.
Therefore, we collected the data of preoperative planning; intraoperative application and postoperative follow-up of SMOT performed by CO and SO-PSI technology, and conducted a retrospective comparative study to determine whether CO or SO-PSI was more effective.

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 followup time was 33.4 (range, 13 to 59) months.

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][15][16][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][16][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 preop 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 preand post-operation.   Moreover, the mean TACD of SO-PSI group was 1.86 ± 1.06 mm (range, 0.51 to 4.2 mm) ( Table 3).

Follow-up outcomes
All patients were followed up, for radiologic evaluation at post-op one year, all of the included parameters of both two groups significantly improved. But the improvement of TAS and TTS of SO-PSI group were more obvious than that of CO group (TAS: P = 0.006, TTS: P = 0.005) ( Table 3). The AOFAS score of SO-PSI group and CO group increased from 51.7 ± 10.9 and 52.5 ± 10.6 before operation to 88.2 ± 5.7 and 83.1 ± 4.5 respectively at the final follow-up; The AOFAS score of SO-PSI group were better than that of CO group post-op six months (P = 0.014), one year (P = 0.048) and final follow-up (P = 0.024) (Fig. 4a). The VAS of SO-PSI group and CO group decreased from 7.3 ± 1.6 and 7.7 ± 1.4 before operation to 3.7 ± 0.7 and 3.1 ± 0.9 respectively at the final follow-up; The VAS of SO-PSI group was only better than that of CO group post-op six months (P = 0.006) (Fig. 4b). The ROM of ankle of SO-PSI group and CO group increased from 31.8 ± 8.4 and 31.2 ± 6.8 before operation to 37.8 ± 4.4 and 35.9 ± 5.5 respectively at the final follow-up; The ROM of ankle between two groups has no significant difference at each time point (Fig. 4c). Takakura stage of both two groups improved after the operation, but the improvement of SO-PSI group seemed to be better than that in CO group. In CO group at the final follow-up, compared to preoperative four patients improved their Takakura stage by two levels (23.5%), nine patients by one level (52.9%), three patients had similar stage (17.6%) and one patient became worse (5.9%) (Fig. 5a). In SO-PSI group at the final follow-up, compared to preoperative six patients improved their Takakura stage by two levels (54.5%), four patients by one level (36.4%) and one patient had similar stage (9.1%) (Fig. 5b).

Discussions
This study aimed to determine whether there is a difference between CO and SO-PSI technology in terms of preoperative planning, intraoperative application and postoperative follow-up for SMOT.
Referring to relevant studies and combining with own experience, it is strongly suggested that accurate preoperative analysis of condition and the ideal postoperative ankle angles, line of force and arthritis stage are very important for SMOT, which has also become the focus of current research [1, 2, 6-10, 15-17, 21].
Analyzing results of the study, we found that SO-PSI technology have advantage over CO technology in preoperative planning, intraoperative application and postoperative follow-up. There should be four reasons: (1) Preoperative 3D analysis on computer can accurately understand original state of the disease, which is much more reliable than the conventional hand-painted two-dimensional analysis and simple observation of three-dimensional reconstruction of CT images; many studies have reached similar conclusions, and it is generally believed that preoperative 3D digital analysis will greatly deepen surgeons' cognition of the original state of the disease [22,23]. (2) Still consistent with similar studies, the surgeon has performed repeated simulated operations on a digital model before surgery, they must to face difficulties and detail ready prepared ahead of time; at this time the feasibility and perfectness of the preoperative planning are preferable because it is well thought out [24]. (3) Compared with conventional technology, the use of PSI in operation can make the traditional osteotomy and alignment process faster and more accurate; relevant studies have shown that PSI can reduce the number of surgical procedures and fluoroscopies during the operation, and with the help of PSI, many procedures no longer require repeated attempts [11]. (4) Another possible reason is that our team's rich digital orthopedic operation experience [12] provides this new technology with good personnel, technical reserves and execution ability.
However, there are also shortcomings of the SO-PSI technology: Firstly, the preoperative planning time of SO-PSI group was much longer than that of the CO group in the study, which is due to the addition of many preoperative steps, including copying the original CT data, 3D digital model reconstruction, simulated operation completion and PSI 3D printing. These steps are very timeconsuming [25]. Secondly, the average hospitalization expenses of SO-PSI group were 1,400 dollars higher than that of the CO group in the study; the reason is that the designer labor fee and 3D printing production fee need to be increased, and it is not included in the medical insurance in our country. However, with the improvement of health care policies, software upgrades and rapid development of 3D printing technology [26,27], it is gradually getting easier and faster for doctors to complete these steps, and the corresponding costs will gradually drop too.
Moreover, there are some limitations: First, designing the PSI is a complex procedure, usually the surgeon needs a technologist who is skilled at the software to assist to make the PSI. Second, it is necessary to research the survival rate of ankle joint in each group after surgery on the basis of longterm observation in the future. Third, this study is only a retrospective study; a prospective study should be conducted, even randomized controlled trial.

Conclusions
Our results indicate that SO-PSI technology can carry out the preoperative plan accurately and quickly in SMOT; In general, compared with the conventional technology, SO-PSI technology has advantages in preoperative planning, intraoperative application and postoperative curative effect.    We can see from error bar charts that compared with CO group, AOFAS score, VAS and ROM of ankle of SO-PSI group gradually improved after operation. But specifically: (A) AOFAS score of SO-PSI group was better than that in CO group at each time point; (B) VAS of SO-PSI group was better than that in CO group postoperative six months; (C) there was no significant difference in ROM of ankle between two groups at each time point.

Figure 5
A graph plots the individual changes of Takakura stage of (A) CO group and (B) SO-PSI group with time respectively, each circle indicates one ankle (patient); Takakura stage of both two groups improved after the operation, but the improvement of SO-PSI group seemed to be better than that in CO group.