The Spatial Weaving Screw Technique Combined With Minimally Invasive Treatment of Calcaneal Fracture

Background: The conventional surgical method for calcaneal fractures is the extensile lateral approach to reduce and x fractures using plates and screws, Unfortunately, this method has been associated with high rates of wound and steel plate complications. Similarly, it is still dicult for minimally invasive surgical methods to achieve effective reduction and internal xation. Therefore, this article proposes a new method of lateral minimally invasive incision combined with percutaneous, screw-only xation and the screws are individually knitted according to the type of fracture. Methods: Between October 2015 and October 2019, 31 patients who underwent the spatial weaving screw technique combined with minimally invasive were recruited. Any operative complication was recorded. The clinical results were evaluated based on pre-operative X-rays (axial and lateral calcaneus), CT and three-dimensional reconstruction, AOFAS, VAS during follow-up. Results: Bone healing was achieved in all patients, with an average healing time of 7.3±4.2ml weeks. No serious complications occurred after operation, no case of reduction failure or screw displacement were found. The evaluation of the posterior subtalar and calcaneocuboid articular surface respectively showed 80.6% and 90.3% cases got excellent and good reduction. The average AOFAS score was 89.5 at the end of 1 year after the operation, the mean VAS in our series was 2.4 at the last follow-up. Conclusion: Combined with minimally invasive screw spatial weaving technique, displaced Sanders type II and III can be successfully treated displaced Sanders type II and III fractures. The method allows for adequate reduction and effective xation by screws. It also clearly avoids the major wound complication problems, improve the accuracy of reduction and implantation, simplify surgical procedure. SPSS IL USA). measurement data recorded with "Mean ± SD". A P value of <0.005 was considered to be statistically signicant. Independent t-test was used to compare the difference between Preoperative and postoperative Bohler (3.2%) follow-up.


Background
The calcaneus plays an important role in the body's weight bearing and walking. The mechanism of calcaneal fracture is usually high energy axial load injury caused by a fall from a height or a road tra c accident, 65-70% of calcaneal fractures involve displacement of the subtalar articular surface [1]. The mainstream treatment of the calcaneal fractures involving the displacement of articular surface is surgical intervention [2]. Currently, there is still no standard procedure for surgical treatment of the calcaneus [3]. The surgical treatment of calcaneal fractures is still a challenge to orthopedist [4].
In the past 2 decades, operative treatment using an extensile lateral open approach has grown in popularity. This approach provides excellent exposure of the fracture to reduce by separate the lateral skin ap, it has some advantages in the reduction and xation of the calcaneus [5].
Nonetheless, the incidence of soft tissue complications is high including skin necrosis, infection, wound dehiscence, and delayed wound healing [6]. In addition, the stress concentration around the steel plate causes internal xation failure and osteoporosis around the steel plate [7]. Therefore, minimally invasive method is more and more popular for the treatment of calcaneal fracture nowadays [8]. A variety of minimally invasive techniques can reduce the above complications, but there are also some controversies [9,10]. There are three main disadvantages of minimally invasive surgery: 1. Di culty in achieving accurate reduction of fractures. 2. Di culty in internal xation implantation, and inaccurate implant position. 3. The internal xation of minimally invasive implants cannot provide effective stable xation. Ebrahimpour A. et al [11]. believed that for treatment of various types of calcaneal fracture percutaneous reduction and screw xation obtain satisfactory clinical results. Smerek J P et.al [12]. demonstrated that screw xation of calcaneal fractures had similar strength comparing to that of the standard perimeter plating technique in a cadaver model. However, few scholars have proposed systematic and accurate studies on the theory that whether screws alone can provide enough mechanical strength for calcaneal growth. Therefore, this study attempts to look into the problems by using minimally invasive, 3D printing and spatial weaving screw (SWS) technology.
The purpose of this research: 1. To design a new minimally invasive incision which reduces the injury of important lateral calcaneal structures; 2. To improve the accuracy of minimally invasive incision reduction using 3D technology. 3. To design a percutaneous wove screw internal xation based on the type of fracture in which the mutually supported structure can provide enough the mechanically stability for the calcaneal fracture heeling.
The procedure of the current study: 1. The spatial weaving screw xation were divided into three categories according to the xation method. SWS structure should be designed according to the type of fracture and combined with preoperative 3D printing technology preoperative, to improve the accuracy of screw placement. 2. The minimally invasive incision on the lateral calcaneus was performed according to the pre-operative protocol. The screws were implanted percutaneously forming a SWS structure to improve the rmness of screw xation. 3. Clinical follow up the clinical outcomes were evaluated, including incision-related complications the quality of reduction and the stability of internal xation. the patient's the American Orthopedic Foot and Ankle Society (AOFAS) score and visual analog scale (VAS) score were evaluated.

Methods
This research was reviewed and approved by the Ethics Committee of the Ningbo No. 6 Hospital (No.2018-006). All patients signed the informed consent form, reviewed the written surgical plan and alternative regimen before the procedure.
Inclusion criteria Unilateral closed calcaneal fracture. Sander types II and III. Intra-articular step-off ≥2 mm and Depression of the posterior facet of the calcaneus. Age 18-65.
Exclusion criteria accompanied by serious injury of other important organs. The time interval between fracture and operation is more than 4 weeks and it is di cult to fracture reduction. severe medical diseases cannot tolerate surgery. Infected or grossly contaminated soft tissue.

Operative technique of SWS xation
Preoperative CT value data of the calcaneus were imported into MIMICS15.0 software (Mterialise Co. Leuven, Belgium) for 3D modeling of the calcaneus, which was used for subsequent surgical simulation and 3D model printing (Fig.2). The virtual 3D model of the calcaneus was reconstructed by MIMICS software. In this model, the displacement of the fracture fragment is measured and virtual reduction is performed to establish the reduction sequence. In addition, according to the direction of fracture line extends, SWS xation was designed to simulate treating calcaneal fracture. SWS are 3.5mm full-thread screws. The screws are divided into three categories: Sustentacular screw(SS) Long axis screw of calcaneal (LAS) High axis screw of calcaneal (HAS) Screw method: 1. SS The fracture was xed with 2-3 screws perpendicular to the fracture line, A well-restored lateral subtalar joint was xed on sustentaculum tali medially which is the relatively stable position (constant fragment) According to the trends of fracture line running, 1-2 screw insert interfragmentary perpendicular to fracture line, the aim is achieved interfragmentary between calcaneal medial and lateral fracture fragment compression and a good stability of xation. the other 1-2 screws insert on the center of the sustentaculum tali through the lateral wall, where the bone density was relatively high. Several SS screws not only xed the fracture fragment but also played the role of anti-rotation maintaining the integrity of the subtalar articular surface. 2. LAS LAS x lateral reduced fracture fragment from posterior calcaneal tuberosity portion to the calcaneocuboid joint, It passes through the bottom of the lateral fragment to avoid it collapse again. 1-2 LAS also can maintain the length of the calcaneus after reduction. 3. HAS HAS implant into the calcaneus from the inferior to superior tuberosity of the posterior calcaneus along the posterior side of the calcaneus trabecula orientation. It is inserted into the lateral fragment to support and strengthen stabilize the subtalar articular surface, while maintaining the height of the calcaneus after reduction. In total, the three types of screws form a mutually staggered structure in space, evenly distribute the stress and achieve a rm xation of the calcaneal fracture Fig.1 .

Minimally invasive, traction reduction technology
The minimally invasive technique was used to reduce the displaced calcaneal fracture. All patients were carried out with in the lateral decubitus position to permit access to the lateral aspect of the hindfoot. A nonsterile tourniquet is applied on the affected extremity at the level of the thigh to reduce intraoperative bleeding. A rolled-up sterile towel be placed under malleolus medialis to suspended the foot parallel to operating table. This position is facilitated to reduce fracture intraoperative. (Fig.2d-e) Intraoperative procedure In the rst, the three-point distraction approaches applied to reduce fracture [13]. 4.0 Schanz pins were placed on the posterior tuberosity of calcaneus, which is used as a handle for traction. During traction, the front, middle foot and distal leg were xed with hand. Through three-point distraction, ligamentotaxis technique restore the length, width and height of calcaneus and correct the varus/valgus alignment as well as the width of the calcaneal tuberosity. If the displacement of the medial calcaneus column cannot be corrected, a medial side 2-4cm arcshaped incision should be assisted to restore. After a satisfactory reduction of the calcaneal fracture, continuous traction is still needed to maintain, the reduced fracture block is xed by Kirschner wire inserting into the subtalar joint temporarily. Fig.2a-c , An transverse arc-shaped incision was made laterally, which approximately 3-6 cm and about 2-3cm below the tip of the bula in length. The small lateral approach was carried below to calcaneo bular ligament and avoid exposure of important lateral structures, lateral calcaneal artery, lateral calcaneal cutaneous nerve, calcaneo bular, the sheath of the peroneal tendons. Once the sural nerve and the lateral calcaneal artery were identi ed and retracted. Corticotomy of the broken lateral wall of the calcaneus is done keeping the soft tissue attaches to the lateral wall, and avoid separation by dissection, then the lateral wall of the calcaneus was opened like a window to allow access to reduce the articular fragment (Fig.2f). The lateral posterior fragment was exposed and restored by opening the window with a thin osteotome or periosteal elevator. The quality of the reduction was evaluated by intraoperative imaging or ankle arthroscopy. The depressed fracture fragment is reduced and xed using 2.0 K-wires temporarily. After obtaining a satisfactory reduction, the screw can be implant into calcaneus according to the technique of SWS.

Postoperative treatment and functional rehabilitation
The incision was routinely cleaned every other day postoperatively, the affected limb was elevated through the lower extremity cushion. gentle strengthening exercises for the muscles controlling the foot and ankle were started. Initiating active range of motion exercises is encouraged after anesthesia recovery. Rehabilitation exercises as early as possible is critical in restoring motion. As long as the patient can tolerate, it is encouraged to do the activity training of exion, extension of toes, ankle, knee and hip joint. The sutures were removed about 14 days after surgery, patient was routinely followed up every month for over two years. At 6 weeks after surgery, the patient was allowed to walk with partial weightbearing with crutches when the fracture had healed radiographically, and the weight-bearing was increased gradually. Thereafter After 8 weeks, the full weightbearing without support and gait training was gradually resumed. According to the imaging result in the outpatient follow-up, the intensity of the rehabilitation exercise was adjusted.

Postoperative evaluation
The Bohler's angle, the Gissane's angle, and the calcaneus width and height were measured in the lateral and axial view of the heel after and before surgery. The condition was evaluated to reduction of the articular surface of the posterior subtalar and calcaneocubic after 1 year followed up by CT scan(Philips Brilliance 64 CT, Philips Medical Systems, The Netherlands). The articular surface was evaluated according to the displace steps, the degree of defect, the degree of angulation Table 1 CT was used to evaluate the degree of arthritis on the subtalar posterior articular and the calcaneocubic surface. Osteoarthrosis was graded as follows: grade 0 -a normal joint space. with no evidence of degenerative cysts or subchondral sclerosis: grade 1-subchondral sclerosis, osteophytes. and cyst formation, without narrowing of the joint space: grade 2 -narrowing of the joint space, with sclerosis and cyst formation: and grade 3 -complete loss of the joint space. CT scan also observes the internal xation to determine whether the internal xation is displaced or broken. (Table 2) Clinical follow-up Monthly outpatient follow-up within 3 months after operation, and once a year thereafter. Incision-related complications were recorded, including surface, deep infection, wound dehiscence, and necrosis. Additionally, a physical examination was careful checked to identify local sensitivity, such as wound irritation, tenderness, and sensory neurological de cit. The American Orthopaedic Foot and Ankle Society (AOFAS) hindfoot score was applied to evaluation of function 1 year after operation. Scoring criteria were graded excellent for >90 points, good for >80, fair for >70, and poor when≤70. Pain was assessed by a visual analog scale (VAS), ranging from 0 (no pain) to 10(maximum pain). The ability of patient returning to work was also assessed. days (range 2-6 days),11 patients had the medial and lateral fractures, among which 9 patients had reduction after traction during operation. 2 cases were found that the closed reduction of the medial column could not achieve satisfactory reduction during operation, and then the medial incision reduction was assisted. 4 patients with severe osteoporosis were treated with autologous iliac bone graft to ll the void of lateral compression. Mean operating time,39.8 ±12.8min range 20-71min Average blood loss, 31.8±14.0ml range 10-55ml . Bone healing was achieved in all patients, with an average healing time of 7.3±4.2ml weeks (range 6-12 weeks). Recurrence collapse of subtalar articular surface was not founded at the nal follow-up. Slightly super cial skin necrosis around the wound occured in 1 case (3.2%), which resolved with a regular wound care. 1 patient (3.2%) had paresthesia around the incision after surgery, and sural cutaneous neuritis was considered. Anatomical or approximate anatomical reduction was obtained in the rest cases. 21 cases (67.7%) backed to their formerly work normally, while 8 cases (9.7%) returned to the same job but with little restriction, and 2 (64.5%) cases changed their job for limited foot function. The 2 cases had a type III severe fracture types, associated with severe osteoporosis, which had the relatively low score results of functional postoperatively.
The average AOFAS score was 91.1 (range,76-96) at the end of 1 year after the operation, 21 cases were excellent (67.4%), 6 cases were good The evaluation of the posterior subtalar articular surface reduction showed excellent restore in 15 patients (48.4%), good in 10 cases (32.3%), fair in 5 cases (16.1%), and poor in 2 cases (6.5%). The excellent and good reduction rate was 80.6%. The reduction of the articular surface of the calcaneus cuboid: Excellent 18 cases (58.1%), Good 10 cases (32.3%), Fair 2 cases (6.5%), Poor 1 case (3.2%). The excellent and good reduction rate was 90.3%. CT evaluation of the degree of articular arthritis of the posterior subtalar surface were19 cases of grade 0, 9 cases of grade 1, 2 cases of grade 2, and 1 case of grade 3. CT assessment of the degree of articular arthritis of the calcaneus cuboid surface were 21 cases were grade 0, 9 cases were grade 1, 1 case was grade 2, 0 cases were grade 3. (Figure 3).

Discussion
The main trend has developed toward open reduction and internal xation with an extensile L-shaped approach and plate for displaced intraarticular calcaneus fractures. It affords excellent exposure, allowing obtain to operate and x the fracture fragments [14]. yet controversy still exists on this surgical procedure for approach and plate [6,14]. The important structures of the lateral calcaneus are extensively damaged which can lead to the soft tissue-related complication such as the infection and necrosis of the lateral incision in this surgical method. the calcaneal plate can lead to rejection reaction. In addition, the plate is eccentrically xed and may lack effective xation on the opposite side from the aspect of biomechanics.
Therefore, many had tried to develop minimally invasive methods attempts to avoid this method related complications throughout the history of calcaneal fracture treatments, and some have become more popular for selected fracture patterns over the others. Bremer et.al [15]. reported that the 240 consecutive patients that had been used a lateral subtalar approach and screw xation treating for a displaced intra-articular calcaneal fracture were followed for more than 24 months. The presented approach has remained unmodi ed for 16 years and resulted in consistently good functional results. Ebrahim pour A et.al [16]. believed that for treatment of various types of calcaneal fracture compared with ORIF the percutaneous reduction and screw xation may lead to better clinic outcome Fractures of the calcaneus with involvement of the subtalar joint should be treated by anatomical reduction, absolute stable xation, and early mobilization like any other intra-articular fractures. Minimally invasive method usually cannot achieve good reduction and stable xation. The biomechanical stability of internal xation is limited by minimally invasive treatment. Khurana et.al [17]. note minimally invasive surgery methods minimized soft tissue complications and achieved comparable radiological reductions but clinical outcomes were poorer, with percutaneous methods having the worst outcomes. Currently, few studies show how to x percutaneous screws to achieve stable structure. In this study, 3 category SWS xation was designed according to the fracture line characteristics of Sanders II-III and combined with preoperative 3D printing technology preoperatively. Intraoperative manipulation can be carried out according to the preoperative plan. SS screws x the lateral collapsed fracture fragment on the medial sustentaculum tali, compressing the fractures to promote fracture healing; LAS prevents to collapse again of the reduced articular surface while maintains the length of the calcaneus. HAS supports for the lateral fragment furtherly, maintaining the height of the calcaneus. The three types of screws build an interlocking weaving structure in space, which mechanically supports each other to form an effective rigid xation. CT examination showed that only 1 case (3.7%) underwent a postoperative less than 4mm collapse of subtalar articular surface, and others were not found articular surface collapse, calcaneal valgus deformity, calcaneal deformity obviously after more than 1year follow-up. In addition, the percutaneous screw implantation method can also avoid problems such as screw tract infection and the di culty of wound care caused by exposure of implantation.
Calcaneal fractures are usually high-energy mechanism and associated with soft tissue injuries. Soft tissue protection is an important role in calcaneal recovery after operation [18]. The extensile lateral approach has been the most frequently used surgical approach for the last 3 decades [19]. However, the soft tissue-related complication rate is high such as wound dehiscence necrosis, infection, plate exposure, etc. For this reason, there has been increase interest in small-incision operation try to change for calcaneal fractures. Ragab A.H et al [20]. reported they treated displaced intra-articular calcaneal fractures by the trans-osseous limited lateral approach and achieved satisfactory results. In addition, minimally invasive to reduction have become popular because of the lower incidence of wound complications. Among these, sinus tarsi incisions are currently popular [21]. The calcaneus can be restored the fracture of subtalar articular surface on direct vision. However, this approach can damage important lateral structures of calcaneus, Niall A. et al [22]. suggested that the extensile lateral approach to the calcaneus (ELA) and the sinus tarsi approach (STA) could cause lateral sural nerve injury, calcaneo bular ligament, which can result in impaired lateral stability and subtalar articular surface arthritis. Based above all, this study via a small incision below the fracture line and "open the window" from lateral wall. It protects the calcaneo bular ligaments that are attached to the lateral wall and exposes the bottom of the collapsed lateral subtalar articular directly. The depressed subtalar joint fragment can be directly to restore through this approach to avoid the damage of the lateral important structures. The calcaneo bular ligament and the sheath of the peroneal tendons are protected. There were 1 case (3.2%) of peroneal tendon irritation for incomplete reduction of the lateral wall at 1year follow-up. The height of the posterior talocalcaneal joint, the width of the calcaneal tuberosity and the varus/valgus malalignment were restored by ligamentotaxis distraction indirectly. Important structures attached to the lateral wall is prevented from being exposed. Meanwhile, percutaneous reduction and implantation with screws only decreases the risk of the irritation and injury soft tissues. Therefore, it is also not limited to the timing of surgery, even if accompanied by severe soft-tissue trauma, early surgical intervention can be permitted, decrease hospitalization days.
It is essential to anatomical reduction of the subtalar articular surface and restore calcaneal alignment. The surgeon must have integrally spatially accurately understanding of the fracture in order to manipulate anatomic reduction by minimally invasive approach. Computer-aided technology has been widely used in orthopedics, which is of great signi cance for preoperative planning and intraoperative decision-making [24]. The duration of operation time is also considered to be a high-risk factor for postoperative complications of calcaneal surgery [25]. In this study, the surgical method was designed on the virtual reconstructed 3D model in MIMICS. To each individual, the fracture model was dragged and separated in MIMICS to further check the injury mechanism and type of fracture types, the sequence of reduction and xation of calcaneal fractures was rstly established in the virtual software. The simulated operation was performed on the real-size 3D printed model and the operation procedure and screw xation structure were designed for different types of calcaneal fractures individually. Full understanding of the fracture feature are essential prerequisites preoperatively. The 3D technique could give surgeons a better understanding of fractures morphology and su cient preparation preoperatively. In actual operation, it could expand the possibility of improving surgical pro ciency precision and decreasing both the operative duration, intraoperative exposure and the di culty of operation. In this study, the rate of reduction was 81.4% (22/27) to anatomical or approximate anatomical reduction, and the success rate of the operation was signi cantly increased.
A study published by Baca Emre et.al [26]. demonstrated that 114 displaced calcaneal fractures were xed by kirschner wire, followed up for 42.33±18.33 months, AOFAS Score was 80.4 (Range, 47 to 92) Sanders II 81.25, Sanders III. Veltman's et al [27]. found that the average AOFAS score for percutaneous treatment was 86.4 through statistical analysis of literature review involving 1730 calcaneal fractures. Cong et al [28]. applied MIPO technology to treat 29 displaced calcaneal fractures, and AOFAS score was 84.4 ± 4.9 points at end of followed up 1 year postoperatively. Postoperative AOFAS scores in this study were higher than those minimally invasive surgery in the literature.

Conclusions
The minimally invasive approach and opened "window" to the lateral wall was reduced the depressed articular surface, which avoid damage to the Important structure of the lateral calcaneus. And then through three-point distraction, ligamentotaxis technique restore the length, width and height of calcaneus and correct the varus/valgus alignment. According to 3D printing technology, percutaneous weaving structure implantation was carried out, evenly distribute the stress and achieve a rm xation providing mechanical support for calcaneal fracture healing. Despite the sample size is limited in this study, the methods can be proved to be an effective, simple and safe strategy for the displaced calcaneal fractures. The study was approved by the Ethics Committee of the Ningbo No 6 Hospital (No.2018-006). Informed written consent was obtained from all the patients. All procedures were performed in accordance with relevant guidelines.

Consent for publication
A written informed consent was obtained from the patient for publication of this report and any accompanying images.

Availability of data and materials
The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Competing interests
The authors declare no con ict of interest.