Clavicular hook plate has been widely used to treat acromioclavicular joint dislocation and clavicular acromion fracture since the 1970s. It has become one of the most critical methods for the treatment of this type of injury. The plate's specially designed "hook" was inserted under the acromion to reduce and fix the acromioclavicular joint dislocation and clavicular acromion fracture using the lever principle. The clavicular hook plate has sufficient fixation strength to allow early active shoulder abduction after surgery. However, the clavicular hook may slide in various degrees with the movement of the shoulder joint due to three-dimensional irregular space under the acromion. It has been confirmed by numerous literature reports that there is good clinical efficacy with few complications in the treatment of acromioclavicular joint dislocation and clavicular acromion fracture with clavicular hook plate. The abnormal sound of the shoulder joint and acromion bone erosion after operation have not yet been paid enough attention, for the symptoms are released to a greater extent after removal of internal fixators. The acromioclavicular joint is flexible, and its unique multi-dimensional activities will cause friction and cutting between the clavicular hook and acromion. Bone erosion will occur at the stress concentration point under the acromion. Many biomechanical studies on the length, angle, and height of clavicular hook plates have been reported in recent years. The research mainly focuses on the factors of the clavicular hook plate itself. There are few reports on the related complications after internal fixation due to the morphological difference of acromion.

To investigate the causes of acromion bone erosion in patients with distal clavicle fractures or acromioclavicular joint dislocations after internal fixation with a clavicular hook plate and determine whether it is related to the matching of plate hook and acromion.

From August 1, 2015 to August 31, 2018, the clinical data of 210 patients with acromioclavicular joint dislocation or distal clavicle fracture treated with clavicular hook plate in the department of orthopedics, Shanghai Pudong Hospital were retrospectively analyzed. There were 110 males and 100 females, and the ages ranged from 24 to 76 years old (44.60 years±8.75 years) . There were 70 acromioclavicular joint dislocations and 140 cases of distal clavicular fractures. The relevant data were measured on the anteroposterior X-ray films of the acromioclavicular joint collected after the surgeries and final follow-ups. According to whether the acromion bone erosion occurred after clavicular hook plate fixation, the patients were divided into no bone erosion group, bone erosion with clavicular hook displacement group, and bone erosion without clavicular hook displacement group, and the matching degree (β) of plate hook-acromion was measured respectively. The relationship between acromion bone erosion and plate hook and acromion matching degree was statistically analyzed.

All patients were followed up for 24 to 64 weeks (32.0 weeks±6.5 weeks) . Group A (no acromion bone erosion group) included 115 cases, group B (bone erosion with clavicular hook displacement) included 54 cases, and group C (bone erosion without clavicular hook displacement) included 41 cases. There was a significant difference in matching degree (β) between group A (β=3.72 mm±0.48 mm) and group B (β¹=6.91 mm±0.84 mm) (P<0.05) . The matching degree of group A (β=3.72 mm±0.48 mm) was significantly different from that of group C (β²=5.88 mm±0.65 mm) (P<0.05) . There was a significant difference in matching degree between group B (β¹=6.91 mm±0.84 mm) and group C (β²=5.88 mm±0.65 mm) (P<0.05) .

Acromion bone erosion after clavicular hook plate fixation is significantly correlated with the matching degree (β) of plate hook-acromion. The better matching the plate hook and acromion is, the less the possibility of acromion bone erosion.