Minimally Invasive Open Reduction by a Modied Suture Bridge with Anchors for Avulsion-type Greater Tuberosity Fracture of the Humerus

Background: This study aims to describe a new procedure of minimally invasive open reduction by a modied suture bridge with anchors for avulsion-type greater tuberosity fracture of the humerus and to evaluate its clinical effectiveness. Methods: From January 2015 to January 2018, 16 patients who were diagnosed with an avulsion-type greater tuberosity fracture of the proximal humerus and treated with minimally invasive open reduction by modied suture bridges with anchors were retrospectively studied. Endpoints were assessed preoperatively and postoperatively and included the visual analog scale (VAS), the University of California Los Angeles (UCLA) shoulders score, the American Shoulder and Elbow Surgeons score (ASES), and the range of motion (ROM) for shoulders. Results: There were 7 males and 9 females with an average age of 44.94 years. Six fractures involved the left shoulder, and 10 involved the right shoulder. The time between injury and operation ranged from 1 to 5 days, with an average of 2.32 days. The average length of stay was 6.5 ± 0.85 days; the mean operation time was 103.1 ± 7.23 minutes; and the mean amount of operative blood loss was 51.88 ± 6.40 ml. All patients achieved bone union within 3 months after surgery. The VAS score signicantly decreased at 3 weeks postoperatively (p = 0.002), as did the average degree of forward elevation (p = 0.047). The mean degree of abduction increased at 6 weeks after the operation (p = 0.035), and the average degree of external rotation and internal rotation improved at 3 months postoperatively (p = 0.012; p = 0.007). The ASES score and the UCLA score improved at the 6-week follow-up (p = 0.092; p = 0.029). No procedure-related death or incision-related supercial or deep tissue infection was identied in any case. No iatrogenic neurovascular injuries or fractures were found in this study. Conclusion: The fracture block was xed rmly by minimally invasive open reduction with a modied suture bridge with anchors. Patients were allowed to move their shoulder early after surgery and recovered quickly. It is an ecient method for the treatment of avulsion-type greater tuberosity fractures of the humerus. and to set up a control group using other treatment methods to evaluate the effect of minimally invasive open reduction and suture bridge techniques for the treatment of humeral greater tubercle fractures. This study highlights that minimally invasive open reduction by a modied suture bridge with anchors for avulsion-type greater tuberosity fracture of the humerus yielded an acceptable clinical result, which was xed rmly and allowed patients early passive shoulder movement postoperatively. It is an ecient and reliable method for the treatment of avulsion-type greater tuberosity fractures of the humerus.


Introduction
Proximal humerus fractures are the most common injuries, accounting for approximately 5% of total body fractures [1]. Greater tuberosity fractures, as a very special type of proximal humeral fracture, account for approximately 20% of proximal humeral fractures [2,3] and are often accompanied by different degrees of rotator cuff injury because the humeral greater tubercle is the attachment point of the rotator cuff, which often pulls the fractured fragments to separate and shift after avulsion.
The treatment for this type of fracture can be classi ed into conservative and surgical strategies. The former uses a shoulder pillow or brace in an abduction position, with poor prognosis [4], often resulting in shoulder joint pain, movement limitation, acromion impingement, limb weakness and other functional disorders [5]. Although the surgical indication for fractures of the humeral greater tubercle is still controversial, most surgeons suggest that if the fracture displacement is more than 5 mm, surgical treatment will be recommended [6]. At present, the main surgical procedures for simple avulsion fractures of the humeral greater tubercle are screw xation, suture anchor xation, and plate xation [3]. Among them, open reduction and internal xation with plates is widely used, but several problems, such as a larger incision, more damage to blood circulation and periosteum, in uence on fracture healing, and acromion impingement will be encountered [7]. Compared with conventional plates, locking plates bring important changes in fracture management, allowing exible biological fracture xation based on the principle of internal xators and reducing the incidence of failed bone healing [8,9]. However, several studies have shown a higher than expected incidence of plate xation complications associated with ischemic necrosis, delayed healing, malunion, nonunion, and implant failure [10,11]. In particular, the incidence of screw-related mechanical complications, such as screw perforation, cutoff, screw rotation, and loosening, should not be overlooked [12]. Cannulated screws and washers in the treatment of humeral greater tubercle fractures have the advantages of simple procedures and short operation times, as well as rm xation of bone mass, but the incidence of postoperative stiffness and pain is higher [13], and these are not suitable in osteoporosis patients because the bone of the greater tubercle tends to be fragile and prone to further commination [14].
The technique of double-row anchor suture under arthroscopy is expensive and complicated to perform. In addition, as a postoperative complication, inadequate reduction can lead to postoperative stiffness due to the di culty of adequate reduction and xation of severely displaced fracture fragments with wire anchors [15]. To reduce surgical complications and provide better treatment for patients, we have been inspired by the repair of rotator cuff injuries using the suture bridge technique to x fractures of the great tubercle of the humerus through a minimally invasive small incision under direct vision.
The purposes of this study were to 1) present a new, minimally invasive surgical technique for the treatment of avulsion fractures of the greater tuberosity of the humerus and 2) evaluate the clinical outcomes of 16 patients, including restoration of work activity, ROM and strength, and patient-based function.

Study population
Inclusion criteria were as follows: 1) X-ray, CT (computed tomography) or MRI(Magnetic Resonance Imaging)of the shoulder showing avulsion fracture of the greater tuberosity, assessed according to the classi cation system of Mutch et al. [16]; 2) fracture displacement between 5 mm and 10 mm; 3) closed fracture; 4) fresh fractures (no more than 3 weeks after surgery); 5) all cases followed up for more than 1 year.
The exclusion criteria were as follows: 1) split fracture and compressed fracture of the humeral greater tubercle; 2) fracture of the humeral greater tubercle associated with proximal humerus fracture; 3) shoulder joint dysfunction before admission; and 4) greater tubercle fracture of the humerus combined with brachial plexus injury.
Between January 2015 and January 2018, 16 patients with avulsion fractures of the humeral greater tuberosity were referred to our hospital. There were 7 males and 9 females, with an average age of 44.94 years (range, 20-65 years). The mechanism of injury was falls in 9 patients, tra c accident injuries in 4 patients, and crash injuries in 3 patients. Six fractures involved the left shoulder, and 10 involved the right shoulder. The time between injury and operation ranged from 1 to 5 days, with an average of 2.32 days. There were 7 patients with other diseases. One patient had a right clavicle fracture, 1 patient had a left tibia and bula fracture, and 1 patient had a left radius fracture. The patients' demographic data are listed in Table 1.

Radiologic assessment
For radiologic evaluation, avulsion fractures of the humeral greater tuberosity were diagnosed preoperatively by X-ray ( Fig. 1A), planar CT scan (Fig. 1B), coronal CT scan (Fig. 1C), and three-dimensional reconstruction image (Fig. 1D)   Operative procedures The operation was performed under general anesthesia in a 20° beach chair position. A 3 cm longitudinal skin incision was made from the anterolateral angle of the acromion. The deltoid muscle was dissected bluntly to expose the subacromial bursa. Supraspinatus and infraspinatus muscle avulsion fractures, great tubercle area fractures, multiple fracture fragments and rotator cuff lacerations were observed ( Fig. 2A). The broken end of the bone was then cleaned, and the free bone fragments were removed. Two 5.0 mm anchors were inserted into the cartilaginous margin of the humeral head, and then the anchor lines were passed through the rotator cuff tissue and knotted (Fig. 2B). Kirschner wire was used for temporary xation of the greater tubercle fracture fragments, and a hole of appropriate length was drilled at the distal outer edge of the fracture line at approximately 5-10 mm, according to the size of the fracture fragment. The large tubercle fracture was reduced and xed by the suture bridge technique, and the torn rotator cuff tissue was repaired. Intraoperative uoroscopy showed the position of the anchors and the reduction of the fracture (Fig. 2C). Figure 3 shows a schematic diagram of the main points of the surgical procedure.

Postoperative rehabilitation
Ice was applied 1-2 days after the operation to relieve pain and swelling of the incision. The patients were encouraged to walk on the ground, and the arm was immobilized with a shoulder abduction brace in a neutral position to prevent internal rotation. The patients began to carry out passive rehabilitation training under the guidance of rehabilitation doctors 3-5 days postoperatively, according to the patient's speci c situation, and continued passive function exercise up to 1-4 weeks after surgery. The external xator was removed 5 weeks postoperatively, and the amount of motion was increased under the guidance of the rehabilitation physician. The patients began to perform active shoulder joint exercise 6 weeks postoperatively.

Functional assessment
Visual analog scale (VAS) for pain assessment, American Shoulder and Elbow Surgeon (ASES) Score, University of California Los Angeles (UCLA) Shoulder score, and ROM of the joint were used to assess the function of the affected shoulder joint. Active joint range of motion is measured based on the forward exion of the scapula plane and the external and internal rotation of the lateral arm. Internal rotation is estimated by determining the highest spinal segment the patient can reach with the thumb. For ease of statistical analysis, spinal segments were converted into numbers: segments T1 through T12 were designated as 1 through 12, segments L1 through L5 were designated as 13 through 17, and the sacrum was designated as 18 [17,18]. The pain scale, shoulder function score, and active ROM were assessed by an independent reviewer.

Operative records and Complications
As shown in Table 2, the average length of stay was 6.5 ± 0.85 days (range, 4-15 days); the mean operation time was 103.1 ± 7.23 minutes (range, 60-150 minutes); and the mean amount of operative blood loss was 51.88 ± 6.40 ml (range, 30-100 ml). 1 day after operation, the radiography and CT demonstrated a good reduction in the greater tuberosity (Fig. 4A, 4B, 4C), and the fracture has healed 1 months after surgery (Fig. 4D). None of the patients developed super cial or deep infections in the surgical site, and there were no wound healing problems in any patients. No sensory loss in the upper arm or shoulder associated with the axillary nerve or displacement was observed among patients in this group during the surveillance period. No procedure-related death was observed in any case.

Functional and radiologic outcomes
All patients were followed up with clinical examination and radiographs at 3 weeks, 6 weeks, 3 months, 6 months and 12 months after surgery and then every 6 months (

Discussion
The greater tuberosity of the humerus is the bony protrusion of the proximal lateral part of the humerus. It is the insertion point of the supraspinatus, subaspinatus and teres minor tendons. After the fracture of the greater tuberosity of the humerus, the fracture block is often displaced posteriorly and upward by the muscle pull, which easily causes acromial impingement syndrome and is often accompanied by rotator cuff injury. If the fracture is not properly reduced, the supraspinatus, subaspinatus or teres minor may be shortened. Muscle strength may also be weakened, which seriously affects the function of the shoulder joint [19]. In addition, the biomechanical test [20] showed that the deltoid force required for abduction of the shoulder joint increased from 116-127% when the greater tubercle fracture was displaced by 5-10 mm. While the abductive force increased by 29% when the fragment was displaced by > 1 cm, active surgical treatment should be used for humeral greater tubercle fractures with displacement over 5 mm. Hence, for the patients in this study, the average displacement of fracture blocks was 19.75 ± 2.05 mm (5-30 mm), and only surgical treatment could provide adequate xation and accurate reduction of the fracture block, which is conducive to the recovery of normal anatomical structure and promotes the rapid recovery of shoulder joint function.
When selecting the optimal surgical xation strategy for fractures of the greater tuberosity of the humerus, the deforming force caused by rotator cuff muscle elongation should be taken into account. The supraspinatus, infraspinatus and teres minor are inserted into the greater tuberosity of the humerus, and their coupling force plays a crucial role in the function of the shoulder joint. Ogawa et al. [21] reported that most fractures of the greater tubercle of the humerus (57%) involve the supraspinatus and supraspinatus joints, resulting in upward and backward displacement of the greater tubercle of the humerus in the same direction as the rotator cuff pull for a complete supraspinatus tendon, and note that posterior displacement is particularly important because it is often underestimated and delays treatment. On the other hand, Mutch et al. [16,22] found that 20% of the fracture blocks of the greater tuberculum shifted downward, and in the study of Bahrs et al. [23], the displacement was up to 25.2%, which suggested that it might be caused by the direct downward force or the impact of the greater tuberculum with the acromion during extreme abduction of the upper limb. In addition, in the case of anterior dislocation of the shoulder, the shear force at the glenoid margin can also lead to greater tuberosity fractures. The suture bridge technique covers the fracture block with the high-strength thread at the end of the anchor, which can effectively disperse the shear force and torsion force of the suture line and obtain satisfactory suture and xation effects. The network structure formed by the high-strength thread crossing is able to rmly x the avulsion bone and rotator cuff. Lin et al. [24] reported superior supraspinatus muscle tension on the greater tubercle fragment. The xation of the greater tubercle with an anchor through the rotator cuff was superior to that with two tension screws. The supraspinatus muscle can be reduced by 100% coverage of the supraspinatus, and the supraspinatus muscle can provide the maximum contact area, which increases the xation strength of the fracture block and decreases gap formation. The double-row anchor bridge suture technique has been widely used in arthroscopic surgery. Compared with traditional surgical methods, it has certain biomechanical advantages for repairing rotator cuff injuries and xing fractures of the greater tubercle [15]. Under arthroscopy turned into a double row of anchors, the suture bridge technology with a tail line will smash the humerus fracture piece for complete coverage of the greater tuberosity, provide anatomical repositioning, and anchor the minimally invasive open reduction with xed line suture bridge technology. This procedure takes the same amount of time of as solid block of fracture xation, reduces the use of outside anchor nails, saves cost, and reduces the operation steps, thereby shortening the operation time.
Although the bridge suturing technique has obvious advantages in the treatment of greater tubercle fractures of the humerus, arthroscopic surgery itself also has certain limitations, including complicated operations and longer operation times that will increase the potential risk of surgery; surgeons must have a higher learning curve [25]. It has also been reported that arthroscopic double-row anchoring is unlikely to adequately reduce and repair severely displaced fracture fragments and can even damage the rotator cuff [26]. Using minimally invasive open reduction with suture bridge technology can overcome the disadvantages of cancellous bone screw xation and steel plate internal xation, reduce the risk of implants xed weakly or loosely, avoid secondary operations to remove the screw and plate internal xation and decease the cost compared with arthroscopy. This technique is more bene cial to the good reduction of bone mass and the examination and repair of rotator cuff injury through limited incision and direct vision operations.
Recently, the minimally invasive open reduction and suture technique with suture anchors for the treatment of greater tubercle avulsion fractures of the humerus has achieved good therapeutic results and brought great bene ts to patients. The advantages of this technique include: 1) less surgical trauma, fewer postoperative complications, and faster recovery of pain; 2) simple operation, no special equipment, all under direct vision operation; 3) suture anchors are more conducive to the reconstruction of original rotator cuff prints; 4) the suture bridge technique xes the bone block at rotator cuff insertion on the surface in a multidirectional, overall and stable manner to the humerus head, forming a two-layer plane xation of rotator cuff insertion, which is accurate and conducive to early functional exercise; 5) suture anchors can form planar multipoint stress xation, which can disperse the stress, reduce the reduction and loss, and is conducive to the recovery of rotator cuff function; 6) suture anchors are suitable for the treatment of comminuted fracture of greater tuberosity or osteoporotic fracture; and 7) avoids secondary surgery to remove the internal xation. However, this technique also has several limitations. Due to relatively small fracture fragments, it is di cult for hollow screws to x avulsion fracture blocks, which are often located above the greater tubercle. The steel plate cannot choose the appropriate location, which leads to more complications and even xation failure. However, the split fracture block is large, and it is di cult to maintain the stability of the fracture fragment only by suture bridge technology. The compression fracture block is relatively stable, and conservative treatment is generally adopted.
Several notes should be considered when using this technique. 1) When repairing the rotator cuff, the footprint area should be covered by 100% to provide more contact area while reducing local tension. In addition, the initial xed strength can be increased to reduce the formation of intertissue space to promote fracture healing and thus enhance the strength of the repaired tendon. 2) For comminuted fracture or small fracture block, xation with a wire anchor can be used to reduce the possibility of iatrogenic fracture caused by plate xation. 3) For greater tuberous humeral fracture with a large fracture block, the anchor should be perforated 5-10 mm from the most lateral edge of the fracture block to prevent the anchor from being too close to the lateral edge of the large fracture block, causing iatric fracture, and to prevent the anchor from failing. 4) The threading position of the anchor suture line should be kept in the same plane, and the suture line should not be inserted between the bone blocks. 5) When the suture is xed, the tightness should be moderate to maintain a certain tension on the rotator cuff but not be loose and affect healing.
Our study has some limitations. First, this retrospective study had no control group using other xation techniques, such as locking compression plates or arthroscopic xation. Second, the sample size was small, with only 16 cases and a follow-up time of no more than 2 years. Therefore, the next step is to continue to accumulate more samples and longer follow-up cases and to set up a control group using other treatment methods to evaluate the effect of minimally invasive open reduction and suture bridge techniques for the treatment of humeral greater tubercle fractures.

Conclusion
This study highlights that minimally invasive open reduction by a modi ed suture bridge with anchors for avulsion-type greater tuberosity fracture of the humerus yielded an acceptable clinical result, which was xed rmly and allowed patients early passive shoulder movement postoperatively. It is an e cient and reliable method for the treatment of avulsion-type greater tuberosity fractures of the humerus. Imaging examination showed signi cant displacement of the fracture block of the humeral greater tubercle of the patient. A) Shoulder joint X-ray orthotopic lm; B) planar CT scan, C) coronal CT scan, D) three-dimensional reconstruction image of the humerus. Intraoperative operation and perspective. A) Avulsion fracture of supraspinatus and infraspinatus stopper, greater tubercle fracture, multiple fracture fragments, rotator cuff tear. B) The anchor lines were passed through the rotator cuff tissue and knotted. C) Intraoperative uoroscopy showed a good reduction of the fracture block. A schematic diagram of the operation process. A) Two 5.0 mm anchors were inserted into the cartilaginous margin of the humeral head, and then the anchor lines were threaded through the rotator cuff tissue. B) Kirschner wire was used for temporary xation of the greater tubercle, and a hole of appropriate length was drilled at the distal outer edge of the fracture line at approximately 5-10 mm, according to the size of the fracture block. C) The greater tubercle fracture block was reduced and xed by the suture bridge technique to repair the torn rotator cuff tissue (because there should not be too many knots, the number of threads should be used according to the size of the fracture fragment. Generally, 3 threads can be rmly xed for avulsion greater tubercle fracture of the humerus).