A Modied Sinus Tarsi Approach for Treatment of Displaced Intra-articular Calcaneal Fractures Sanders type (cid:0) or (cid:0) Compared to Extended Lateral Approach

Background: We have designed a modied sinus tarsi approach (MSTA) to treat sanders type (cid:0) or (cid:0) intraarticular calcaneal fractures, providing sucient surgical eld exposure and operation space, and signicantly reducing the rate of wound complications. We compared the radiologic results, clinical outcomes, and complications of patients operated on via the MSTA and the extended lateral approach (ELA) for treatment of displaced intraarticular calcaneal fractures Sanders type (cid:0) or (cid:0) . Methods: We retrospectively studied the utility of the ELA (32 patients, 34 feet) and the MSTA (33 patients, 36 feet) operated on from January 2013 to January 2018. The average follow-up time of the two groups was 58 months. We assessed the preoperative and nal x-rays, clinical outcomes and complications at the last follow-up. Clinical outcomes were evaluated using the American Orthopaedic Foot and Ankle Society (AOFAS) score and visual analog scale (VAS). Results: In both groups, the average nal width, height, Bohler angle were signicantly restored compared with the preoperative width, height, and Bohler. The last follow-up calcaneal length, width, height, Bohler angle, Gissane angle did not differ signicantly between the 2 groups. In terms of the clinical outcomes, the average AOFAS score of the ELA group checked to 82.1 points, yielding a 77.8% excellent or good rating, and the average VAS score was 1.76 points. In contrast, the average AOFAS score of the MSTA group checked to 81.0 points, yielding a 79.4% excellent or good rating, and the average VAS score was 1.68 points. There was no signicant difference in AOFAS score and VAS score between the 2 groups. The wound-healing complication rate was 2.9% in MSTA group and 22.2% in ELA group (p = .040). 4 cases of sural nerve injury occurred in ELA group, and 2 in MSTA group. 1 cases of peroneal tendon complication only occurred in ELA group. Compared


Background
Calcaneal fractures comprise 1% to 2% of all fractures and 75% of calcaneal fractures involving the subtalar joint [1] . Surgical treatment of displaced intra-articular calcaneal fractures (DIACFs) has been widely accepted [2 3 4] . Among all the approach, the extended lateral approach (ELA) has been recognized as the gold standard of treatment for intra-articular calcaneal fractures [5 6 7] . This approach can fully expose the calcaneal fracture, reduce it under direct vision, and provide enough space to insert the plate and screws. The reduction effect and functional recovery of this approach are satisfactory, but the high rate of wound complications has become a troublesome problem for clinicians [8 9] .
In order to limit the wound complications, various minimally invasive approaches have been proposed, including Palmer approach [10] , Olier approach [11] , and sinus tarsi approach (STA) [12] . The minimally invasive approach to treat sanders or displaced intra-articular calcaneal fractures can achieve a clinical effect comparable to that of the ELA, and the wound complications rate is signi cantly reduced [13] . The STA is the most widely used minimally invasive approach. This approach is limited incision, the dissection of soft tissue is mild, and the incidence of wound complications is low [14 15 16 17 18] . This approach can reduce the subtalar joint under direct vision, but the body of the calcaneal fractures cannot be fully exposed, so reduction and placement of the plate and screws are di cult. It requires experienced surgeons and a longer learning curve.
In attempt to overcome the high incidence of wound complications in ELA and the di cult operation of STA, we designed a modi ed sinus tarsi approach (MSTA). The approach is only about 5cm, and the soft tissues including the peroneal tendons, the sural nerve, and the lateral calcaneal artery are pulled together and protected as a whole, then the calcaneal fracture is fully exposed through the anterior and posterior windows. This approach combines the advantages of ELA whose operation eld was fairly visible and STA whose wound complications rate is low. We have retrospectively analyzed and reported the operative times, radiographic results, and clinical outcomes of 29 patients with Sanders or intra-articular calcaneal fractures treated with MSTA. It showed adequate fracture reduction and satisfactory functional recovery. Also, the wound complications rate was signi cantly reduced [19] . However, there was no conclusive conclusion about the comparison between MSTA and ELA. This investigation aims to solve this problem. This investigation retrospectively analyzed the 65 patients (70 feet) of Sanders or intraarticular calcaneal fractures treated in our hospital from January 2013 to January 2018, using MSTA or ELA. Our primary goals were to compare the operative time, radiographic results, and clinical outcomes afforded by MSTA and ELA.

Methods
From January 2013 to January 2018, 96 patients with displaced intra-articular calcaneal fractures were admitted to the hospital. Inclusion criteria were patients (1) diagnosed with closed displaced intraarticular calcaneal fractures of Sanders type or (2) age more than 18 years and less than 65 years at the time of surgery. Exclusion criteria were patients (1) Patients who refused surgery or follow-up, (2) diagnosed with closed displaced intra-articular calcaneal fractures of Sanders type or 3 Patients with severe medical diseases who cannot tolerate surgery. 14 patients were Sanders type . 9 patients refused or lost follow-up. 1 patient was younger than 18 years old, and 2 patients were older than 65 years old. 3 patients decided to treat conservatively after preoperative conversation. 2 patients were open fractures.
Finally, 65 people were included. 65 people were included in this retrospective study, consisting of 33 patients 36 feet in the ELA group, and 32 patients 34 feet in the MSTA group. All surgeries including hardware removal were performed by the same senior surgeon who is pro cient in both techniques. The minimum follow-up for each technique was 24 months. This study was approved by our institutional review board.

Preoperative Management
Calcaneal lateral and axial radiographs and CT were taken before operation. The calcaneus length, width, height, Böhler angle, and Gissane angle were measured on calcaneal lateral and axial radiographs, and Sanders classi cation was performed according to the CT. All operation was not performed until the swelling diminished, which depended on the doctor's opinion that the planned approach can be applied. The duration between injury and operation were recorded for both groups.

Operative Techniques
Modi ed sinus tarsi approach After general or spinal canal anesthesia, the patient was placed in a lateral position (bilateral calcaneal ipped, secondary disinfected) and tourniquet was used for the injured limb. An approximately 5-cm incision was made from 1.5 cm inferior to the bular tip, paralleling to the sole of the foot, and ended at the base of the fourth metatarsal. The incision spanned the peroneal tendons and sural nerve, and these soft tissues need to be properly protected. After sharp dissection of the skin and subcutaneous tissue, the peroneal tendons was de ned as the boundary, the exposed area in front of the tendon sheath was de ned as the anterior window of the surgical eld, and the exposed area in the rear of the tendon sheath was de ned as the posterior window of the surgical eld. First, the skin of the anterior window was pulled, and the lower part was exposed as extensor digitorum brevis tendon. The calcaneal anterior tuberosity and the calcaneocuboid joint could be exposed by dissecting from the attachment point of the extensor digitorum brevis tendon along the bone surface. The posterior facet could be exposed by pulling the skin of the peroneal tendon sheath and the sinus tarsi to both sides, opening the posterior joint capsule and cleaning up the soft tissue and blood clots. Then the skin of posterior window was pulled and the deep fascia was cut along the back of the peroneal tendons. The posterior edge of the tendon sheath was dissected sharply and the soft tissue was separated along the bone surface. Finally, the anterior and posterior edges of the tendon sheath were sharply dissected, deep to the bone surface, the tendon sheath was isolated from the bone surface. The operation eld was exposed by using ribbon gauze to pass under the tendon sheath and the sural nerve and pulling up these tissues to protect them. Through above operations, the calcaneal anterior tuberosity, the calcaneocuboid joint, the posterior facet, the lateral wall and the calcaneal posterior tuberosity could be exposed.
Fracture reduction followed the sequence from medial to lateral. First, the ribbon gauze was pull forward, so the anterior window was exposed. The fracture segments of the lateral wall were opened and the blood clot was cleaned to expose the deep medial fracture segment. The calcaneal varus deformity was corrected by using a periosteal stripper to insert the medial fracture line combined with a 3.5 mm Steinman pins inserted through the calcaneal tuberosity to pull downward. Meanwhile, the calcaneal tuberosity was reduced to the medial sustentacular fragment and was temporary xed with 1.5 mm Kwires to restore the calcaneal height, Böhler angle and Gissane angle. Then, the ribbon gauze was pulled backward, so the posterior facet could be viewed directly through the posterior window. After the reduction of the posterior facet, a 1.5 mm K-wire was temporarily xed from the medial to the lateral. Finally, the lateral wall was reduced. The fracture reduction and the bone defect were observed with intraoperative uoroscopic and determined whether the bone graft was needed. The plate could be placed from the anterior window by pulling up the ribbon gauze. After placing the plate and con rming it to be in the proper position, the screws was xed on it. Then, the incision was washed and closed by layers over a drain. Figure 1 Extended Lateral Approach The ELA was the standard approach [20 21] . The reduction technique and the implants used for xation were the same as MSTA. (Figure 2) The operative times were recorded for both groups.

Postoperative Management
All patients were treated with antibiotics for 1 day after operation. Antibiotics was not stopped until the wound was dry. The wound dressing was changed 24 hours after the operation. The drain was removed when the volume was less than 30ml / 24h. The subtalar circle motion exercises and the active extension and exion of the ankle and toes were guided under the condition of analgesia, 48 hours after the operation. The wound dressing was changed once every 2 or 3 days, and the sutures were removed 2 or 3 weeks after operation. Partial weight bearing began gradually at 6 weeks after operation. Full weight bearing began when the radiological results showed that the fracture had healed.

Follow-up Evaluation
Wound healing of patients after operation were recorded. Postoperative follow-up was at 6 weeks, 3, 6, and 12 months after operation, and every six months thereafter. Early complications were recorded 3 months after operation. Measurement of calcaneus length, width, height, Böhler angle, Gissane angle were at the last follow-up. Meanwhile, the American Orthopaedic Foot and Ankle Society (AOFAS) hindfoot score was used to assess the e cacy, the visual analog scale (VAS) score was used to assess pain relief and the complications were recorded. All measurements and scoring were performed by two clinicians.

Statistical Analysis
Statistical analysis was performed using IBM SPSS version 23 software for Windows. The distributions of age, duration between injury and operation, operation time, calcaneal length, width, height, Bohler angle, Gissane angle of pre-operation and nal follow-up, and AOFAS scores of the two groups were normal, and the independent t test was employed to compare these data between the 2 group. The paired t test was performed to compare the preoperative and nal length, width, height, Bohler angle, Gissane angle angles and calcaneal widths of both groups. The Mann-Whitney U test was used to compare follow-up duration, VAS scores between the 2 groups. Pearson's chi-square test or Fisher's exact test was performed to compare gender, other fracture complications, injury severity, prevalence of complications between the 2 groups. P < .05 was considered signi cant.

Results
The 2 groups did not differ in terms of age, gender, or injury severity. However, the duration between injury and operative differed signi cantly. Also, there was signi cant difference in the operation time. (Table 1)

Radiologic Results
The mean preoperative calcaneal length, width, height, Bohler angle, Gissane angle did not differ signi cantly between the 2 groups. In both groups, the mean nal width, height, Bohler angle were signi cantly restored compared with the preoperative width, height, and Bohler. The last follow-up calcaneal length, width, height, Bohler angle, Gissane angle did not differ signi cantly between the 2 groups. (Table 2)  Values are expressed as the mean (range).

Clinical Results
At the last follow-up, the average AOFAS score of ELA was 82.1 points. The result was excellent in 12 cases (33.3%), good in 16 cases (44.4%), fair in 8 cases (22.2%) and no poor case. The average AOFAS score of MSTA was 81.0 points. The result was excellent in 10 cases (29.4%), good in 17 cases (50.0%), fair in 7 cases (20.6%) and no poor case. There was no signi cant difference in AOFAS score and VAS score between the 2 groups (Table 3).   Values are expressed as the mean (range) unless otherwise indicated.

Discussion
This study compared the radiographic results, the clinical outcomes and the complications of the MSTA group with the ELA group in the treatment of Sanders or intra-articular calcaneal fractures. The radiographic results, the clinical outcomes of the MSTA group were comparable to that of the ELA group. The preoperative waiting time and operation time of the MSTA group were shorter, and the rate of wound complications and complications were lower than that of the ELA group.
The ELA is the most commonly used surgical approach for intra-articular calcaneal fractures. This approach is completely exposed, and the fracture can be reduced under direct vision and insertion of the plate is simple and practicable. Therefore, Satisfactory radiographic results and clinical outcomes can be achieved through this approach [22] . The mean postoperative Böhler angle and width were signi cantly restored compared with the preoperative Böhler angle and width in both groups. Also, the postoperative and the last follow-up Böhler angles and calcaneal widths did not differ signi cantly between the 2 groups. These results indicate that the MSTA can obtain radiographic results comparable to the ELA. In terms of the clinical outcomes, the average AOFAS score of the ELA group checked to 82.1 points, yielding a 77.8% excellent or good rating, and the average VAS score was 1.76 points. Roberto Buzzi et al. reported 44 cases of ELA for intra-articular calcaneal fractures, with an excellent or good rating of 72.7% [23] , whose results are similar to that of ours. In this study, the average AOFAS score of the MSTA group checked to 81.0 points, yielding a 79.4% excellent or good rating, and the average VAS score was 1.68 points. This was not signi cantly different from the ELA group, achieving the same good clinical outcomes.
Compare to ELA, MSTA can achieve equivalent radiographic results and clinical outcomes in the treatment of Sanders II and III intra-articular fractures. The reasons are as follows. Although the incision of MSTA is small, the calcaneal anterior tuberosity, the calcaneocuboid joint, the posterior facet are exposed via anterior window and the lateral wall, the calcaneal tuberosity are exposed via posterior window to obtain a su cient operative eld by pulling up the soft tissues including the peroneal tendons, the sural nerve, and the lateral calcaneus artery as a whole. For the reason that there are only two or three fracture segments in Sanders or intra-articular calcaneal fractures, this approach can provide enough space for reduction. Insertion of the plate is also simple and practical by putting one side of the plate through the anterior window, pulling up the ribbon gauze, and dragging the other side of the plate into the incision. Therefore, MSTA can completely replace the ELA in the treatment of Sanders or intra-articular calcaneal fractures. A signi cant advantage of MSTA over other minimally invasive approaches is simple operation and short learning curve.
Although the ELA can provide a good operation eld, the biggest problem is that the soft tissue is stripped too much, making the rate of wound complications reached about 30% [8] . In order to solve this problem, various minimally invasive approaches have been proposed in recent years, of which the STA is the most widely used. In a retrospective study, Je-Hyoung Yeo et al. reported that overall incidence of the wound complications was 5% and 13.3% in STA and ELA respectively [16] . The wound complication rate of the STA was very low. In our study, 8 case of the wound complication occurred in the ELA group, yielding a 22.2% wound complication rating, while only 1 case of the wound complication occurred in the MSTA group, yielding a 2.9% wound complication rating. The rate of wound complications in the MSTA was much lower than the ELA, which is comparable to the STA in previous studies by others. The MSTA is only about 5 cm in length, which is equivalent to the length of the STA and has less damage to soft tissues. The blood supply of the lateral calcaneal ap is mainly derived from the lateral calcaneal artery which is the branch of the peroneal artery [24 25] . The MSTA can avoid damage to the lateral calcaneal artery by pulling up the lateral calcaneal artery together with the tendon sheath and the sural nerve to protect them, coupled with a smaller incision and less damage to the surrounding soft tissues, so the MSTA signi cantly can reduce the risk of skin necrosis and infection of the lateral calcaneal ap.
In addition to the low rate of wound complications, MSTA have some advantages in reducing other complications. Operation eld is achieved by pulling up the soft tissues with the ribbon gauze in MSTA instead of retracting the lateral ap with the K-wires in ELA, doing much less damage to the peroneal tendons and the sural nerve, so that vascular and neurological complications may reduce. The pain after MSTA was much slighter than that after ELA due to shorter incision, milder soft tissue damage and new exposure method. Therefore, patients with MSTA may have greater range and intensity of early subjective exercise and lower rate of late subtalar joint stiffness.
In addition, the average duration between injury and operation for ELA group was 10.4 d and the average operation time was 116.9 minutes. While the average duration between injury and operation for MSTA group was 7.8 d and the average operation time was 101.1 minutes. The duration between injury and operation and the operation time were shorter in MSTA than that in ELA and the differences were signi cant.
ELA requires completely diminishment of swelling, which is con rmed by positive wrinkle sign [26] . However, the incision of the MSTA is short and the requirements for the degree of swelling diminishment are lower, so the duration between injury and operation of MSTA is also lower than that of ELA. The ELA need full-thickness subperiosteal ap, deep wound closure with the interrupted gure-of-eight technique, and skin closure with the Allgöwer-Donati technique to minimize the rate of wound complications, which require more time than the MSTA. The ELA takes longer operation time and cause more damage to soft tissues, and soft tissue swelling and exudation risks are greater after surgery and recovery time is longer. Therefore, the duration between injury and operation, the operation time and the hospital time of MSTA are shorter than that of ELA, and the hospitalization cost is lower.
The MSTA can completely replace the ELA in the treatment of Sanders or intra-articular calcaneal fractures, whose radiographic results and clinical outcomes are comparable to the ELA, and the rate of complications is signi cantly lower. Compared with other minimally invasive approaches, the MSTA can provide su cient surgical eld, and the reduction of fracture and insertion of plates are more convenient, with simpler operation and shorter learning curve. Therefore, the MSTA is more suitable as a conventional approach for Sanders or intra-articular calcaneal fractures.
As for Sanders intra-articular calcaneal fractures, due to severity of fracture, more fracture segments and obstruction of a soft tissue sheath, the MSTA is di cult to reduce the fracture well. Therefore, it is more appropriate for Sanders intra-articular calcaneal fractures to choose the ELA. In the surgical treatment of intra-articular calcaneal fractures, the indications of various approaches should be carefully selected. The most appropriate surgical approach should be selected according to the fracture classi cation to reduce the pain and nancial burden of patients as much as possible.
This study also had some limitations, including retrospective studies, too short follow-up time, and too few cases. In addition, the reduction of the posterior facet evaluated by CT is closely related to the clinical outcomes [27] . This study lacked postoperative CT and failed to evaluate the reduction of the posterior facet after surgery. Further research is needed to clarify these issues.

Conclusion
In summary, the MSTA can combine the su cient operation eld of ELA and low wound complication rate of STA, achieving satisfactory radiographic results and clinical outcomes comparable to ELA, and having the advantage of simple operation and short learning curve. The MSTA is more appropriate in the treatment of Sanders II and III calcaneal intra-articular fractures.