The surgical efficacy of clavicular hook plates in the treatment of distal clavicle fractures has been widely recognised [13, 14]. The clavicular hook plate can reduce and stabilise distal clavicle fractures through leverage; thus, promoting fracture healing . Compared with other fixation methods, the clavicular hook plate anatomical design is closer to the biomechanical characteristics of the acromioclavicular joint, and can better stabilise the clavicular distal fracture block. At the same time, the acromioclavicular ligament, beak lock ligament, and surrounding soft tissue provide a stable environment without tension, greatly improving the quality of fracture healing and soft tissue repair.
Acromion osteolysis and SIS are common complications of the standard clavicular hook plates. The incidence of SIS after clavicular hook plate surgery is about 19–25% [7, 16]. There are several reasons for this SIS. Soft tissues in the subacromial space, such as supraspinatus tendon, infraspinatus tendon, coracoclavicular ligament, and bursa may be damaged during preoperative trauma, and the insertion of the steel plate at the hook end, scar tissue, and calcification formed during fracture healing also occupy the joint space . The hook portion of the hook plate inserted into the gap under the acromion can lead to a decrease in the shoulder peak. If the hook angle of the hook plate selected during the operation is mismatched or pre-bent poorly, it further reduces the clearance under the shoulder peak. Other studies have shown that elderly patients undergoing hook plate surgery have a higher risk of SIS, which may be related to shoulder tissue degeneration [7, 17]. Macdonald  believed that SIS after clavicular hook plate surgery was related to the acromial type, and curved and hooked acromions were more likely to cause SIS than flat acromions. Additionally, the hook portion of the hook plate was fixed under the acromion without screws, and there was fretting in the horizontal direction, which could rub the soft tissue under the acromion to aggravate inflammatory response of the tissue and cause pain, resulting in SIS . ElMaraghy  believed that for women, the hook board and tip of the hook board should be pre-bent when necessary, and a hook board with a smaller depth should be selected when necessary. In this study, the incidence of SIS in the experimental group was lower, and the postoperative functional score in the experimental group was higher than that in the control group. This study proved that the acromion height metre combined with the new hook plate can reduce the incidence of SIS. However, the extent to which the difference between the height of the acromion and depth of the hook plate during surgery can minimise the incidence of subacromial impingement syndrome remains to be further studied.
In this study, the incidence of acromion osteolysis in the two groups was not statistically significant. Researchers have continuously explored acromion osteolysis caused by clavicular hook plates. Currently, it is believed that the risk factors for acromion osteolysis mainly include the stress of the hook plate on the acromion, micromotion of the acromioclavicular joint, long duration of internal fixation, and difference in acromial morphology [9, 20, 21]. According to Anshuman , 62.5% of patients treated with hook plates required removal of the internal fixation due to shoulder joint irritation or SIS. Due to loss of the coracoclavicular ligament, the proximal fracture is shifted backwards and upwards by the sternocleidomastoid muscle, while the distal bone is shifted inwards and downwards due to upper limb gravity. A clavicular hook plate is used to treat distal clavicular fractures using the lever principle. When the clavicular hook plate is used for fixation, this stress is transferred to the hook portion of the hook plate and acromion [14, 23]. The contact area between the acromion and hook portion of the hook plate determines the pressure between the acromion and hook. The smaller the contact area, the greater the pressure, and the higher the risk of osteolysis, osteotomy, and acromion fractures . Other studies have observed the reaction force of the acromion on the clavicular hook plate and found that the larger the hook angle implanted into the clavicular hook plate, the greater the force on the acromion, and a larger hook angle makes the contact position between the steel plate hook and acromion. Under the same stress through leverage, the shorter the moment arm, the greater the load on the acromion . The lower surface of the human acromion is irregular; however, the shape of the hook portion of the hook plate is different. It cannot be well attached to the inclined surface, but forms point contact, which constantly rubs against the lower surface of the acromion during the movement of the shoulder joint and may cause acromion osteolysis.
Although this study showed that the acromial height measurement device combined with the new clavicle hook plate had less shoulder pain, better functional score, lower incidence of SIS, and obvious advantages over the traditional method, the complications of the hook plate were still not completely resolved. Some scholars believe that early removal of the internal fixation after fracture healing can reduce the incidence of acromion osteolysis . In this study, the hook plates were removed 12 months after confirming good fracture healing. Currently, clavicular locking plates are widely used in the treatment of distal clavicle fractures with relatively fewer complications . However, some scholars believe that the effect of locking plate fixation is not ideal for small fracture pieces, especially for distal clavicle comminuted fractures caused by traction and trauma of the coracoclavicular ligament or other reasons or elderly osteoporotic fractures, and hook plates are very suitable for such fractures [5, 15]. The authors believe that the clavicular hook plate can be selected according to the location of the clavicular fracture line, the size and degree of comminution of the fracture fragment, and whether the fracture is osteoporotic. Hook plates can provide more reliable fixation in patients with relatively small distal fractures, heavily comminuted fractures, and some loose fractures.
This study has several limitations. First, the influence of different acromion types was not considered. Second, in this study, the difference between the height of the acromion and depth of the hook plate was controlled to be < 6 mm, which was a clinical study based on the previous imaging study of our team, but the results of the imaging study were different from the actual intraoperative measurement results and hook plate. The difference between the depth and height of the acromion was not as small as possible. If the difference is too small, it may cause stress fracture of the clavicle after surgery. The extent to which the difference between the height of the acromion and depth of the hook plate during surgery can minimise the incidence of subacromial impingement syndrome remains to be further studied. Third, the sample size of the study was small, and there was a lack of other case investigations in multiple centres and hospitals. A large sample size is required for further studies. Fourth, in this study, the traditional plate group belonged to the early surgical group, while the acromion measurement combined with the new plate group belonged to the late surgical group. During this period, the accumulation of clinical experience and updating of surgical concepts also had a certain influence on the results of the study.