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, infraspinatus 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, infraspinatus 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% to 127% when the greater tubercle fracture was displaced by 5-10 mm. While the required 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. 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 fixation 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 fixation 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%) involved both the supraspinatus and infraspinatus facets, leading to superior and posterior greater tubercle displacement. With an intact infraspinatus tendon, posterior displacement is particularly important to note because it is often underestimated. 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 fixation effects. The network structure formed by the high-strength thread crossing is able to firmly fix the avulsion bone and rotator cuff. Lin et al. [24] reported that the supraspinatus muscle has obvious superiority to the traction tension of the greater tuberosity fragment using suture bridge in comparison to tension screw fixation. The fracture fragment covered 100% of the rotator cuff footprint by suture bridge technique. It not only reduces the tension of the supraspinatus muscle, but also provides maximum contact area, which increases the fixation strength of the fracture block and decreases gap formation.
In this study, clinical examination was conducted at 3 weeks, 6 weeks, 3 months, 6 months and 12 months after surgery and then every 6 months to observe the effect of our technique. Figure 4 showing good reduction of the greater tuberosity and firmly fixed of the fracture mass. Operative records (Table 2) and follow-up results (Table 3) showed that the surgical trauma was small, postoperative complications were few, pain was light and recovery was quick. It has achieved good therapeutic results and brought great benefits to patients. Minimally invasive open reduction by a modified suture bridge with anchors are conducive to reconstruct the original footprint area of rotator cuff. and allows increase surface and fixation area. Simultaneously, our technique allows for a broad contact surface and fixation area, the stability of the greater tuberosity was enhanced, which was beneficial for fracture union and conducive to early functional exercise. Additionally, we found that a more even distribution of load was provided by the four fixation points, which can disperse the stress, reduce the reduction and loss, and is conducive to the recovery of rotator cuff function.
The double-row anchor bridge suture technique has been widely used in arthroscopic surgery. Compared with traditional surgical methods, it has better biomechanical advantages for repairing rotator cuff injuries and fixing fractures of the greater tubercle [15]. However arthroscopic surgery also has some 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 even damage the rotator cuff [26]. Using minimally invasive open reduction with suture bridge technology can overcome the disadvantages of cancellous bone screw fixation and steel plate internal fixation, reduce the risk of implants fixed weakly or loosely, avoid secondary operations to remove the screw and plate internal fixation and decease the cost compared with arthroscopy. This technique is more beneficial to the good reduction of bone mass and the examination and repair of rotator cuff injury through limited incision and direct vision operations.
Rouleau et al.[3] presented a similar surgical approach to ours. Three anchors may be used by them in the proximal row, two anchors or an interference screw placed distal to the fracture bed make up the distal row. Unlikely them, a bone tunnel of appropriate length was drilled by us at the distal outer edge of the fracture line at approximately 5-10 mm, according to the size of the fracture fragment. Clearly, both techniques use the suture bridge technique to cover the fracture block 100% of the rotator cuff footprint, providing maximum contact area and increasing fixation strength of the fracture block. However, our technique eliminates the use of knotless anchors, which not only saves the cost of implants, but also reduces the rejection reaction of some patients with external anchors and reduces the risk of surgical infection. For some patients with osteoporosis, the use of knotless anchors also carries the risk of anchors extraction, leading to failure of fixation. In addition, in the process of positioning and inserting the knotless anchor, there are more operation steps, operation time and operation growth curve are longer. Although there is a possibility of suture cut-out with our surgical approach to bone tunnel, our follow-up results (Table 3) indicate that the efficacy of this technique is reliable.We have more than three sutures through the bone tunnel, and by selecting the right location of the bone tunnel, so we can reduce the pressure and reduce the risk of suture cut-out. In short, our technique not only has good effect, but also has fewer implants, lower cost, simpler operation and easier promotion in comparison to their technique.
However, this technique is only suitable for avulsion fracture of the greater tubercle of the humerus. The greater tuberosity fractures were classified into 3 types based on analyzing 199 cases by Mucth et al.[16] in 2014, including avulsion type (smaller fracture mass, horizontal fracture line) , crackle type (larger fracture mass, vertical fracture line) and compression type (internal displacement of fracture mass into the cancellous bone). The classification of greater tuberosity fractures helps to analyze the mechanism of injury, guide the treatment and evaluate the prognosis. In this study, the average height and width of the fracture blocks were 22.69±1.88mm (10-33mm), 16.94±1.71mm (8-26mm). Due to relatively small fracture fragments, it is difficult for hollow screws to fix avulsion fracture blocks. The avulsion fracture block is often located above the greater tuberosity, and the plate cannot be selected in the proper position, which leads to more complications and even failure of fixation. However, the split fracture block is so large that difficult to maintain the stability of the fracture fragment only by suture bridge technology. And 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. It could increase the strength of fixation and enhance the strength of repair tendon. 2) For greater tuberous humeral fracture with a large fracture block, the anchors should be placed 5-10 mm from the most lateral margin of the fracture. It can not only prevent iatrogenic fracture caused by the anchor too close to the lateral edge of the large fracture block, but also prevent the failure of the anchor. 3) The outlet position of the anchor and suture should be in the same plane to avoid the suture being wedged between the bone blocks, which could affect the fracture. 4) When the suture is fixed, the tightness should be moderate to maintain a certain tension on the rotator cuff.
Our study has some limitations. First, this retrospective study had no control group using other fixation techniques, such as locking compression plates or arthroscopic fixation. 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.