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 ① Unilateral closed calcaneal fracture. ② Sander types II and III. ③ Intra-articular step-off ≥2 mm and Depression of the posterior facet of the calcaneus. ④ Age 18-65.
Exclusion criteria ① accompanied by serious injury of other important organs. ② The time interval between fracture and operation is more than 4 weeks and it is difficult to fracture reduction. ③ severe medical diseases cannot tolerate surgery. ④ Infected or grossly contaminated soft tissue.
Operative technique of SWS fixation
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 fixation 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 fixed with 2-3 screws perpendicular to the fracture line, A well-restored lateral subtalar joint was fixed 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 fixation. 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 fixed the fracture fragment but also played the role of anti-rotation maintaining the integrity of the subtalar articular surface. 2. LAS: LAS fix 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 firm fixation 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 first, 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 fixed 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 arc-shaped 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 fixed by Kirschner wire inserting into the subtalar joint temporarily.
The second step is semi-open reduction(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 fibula in length. The small lateral approach was carried below to calcaneofibular ligament and avoid exposure of important lateral structures, lateral calcaneal artery, lateral calcaneal cutaneous nerve, calcaneofibular, the sheath of the peroneal tendons. Once the sural nerve and the lateral calcaneal artery were identified 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 fixed 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 flexion, 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 fixation to determine whether the internal fixation 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 deficit. 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.
Statistical analysis
Statistical data analysis was performed with SPSS 19.0 statistical software (version 19.0 SPSS Inc., Chicago, IL USA). The measurement data were recorded with "Mean ± SD". A P value of <0.005 was considered to be statistically significant. Independent t-test was used to compare the difference between Preoperative and postoperative Bohler Angle (B), Gissane's Angle (G), calcaneal width (W), height (H).