Patients
For this research, Acromioclavicular(AC) joint dislocation were classified using the method described by Rockwood et al(9). The inclusion criteria for the research were as follows: (1) acute, AC joint dislocation (grade III, IV, V, and VI ) determined according to the classification described by Rockwood et al; (2) no more than 14 days of trauma; (3) signed informed consent. The exclusion criteria were as follows: (1) other types (grade I, II) of AC joint dislocation; (2) no signed informed consent; (3) previous surgery on the shoulder; (4) history of AC joint dislocation or other shoulder trauma.
We retrospectively analyzed the prospectively collected data from 310 consecutive patients with AC joint dislocation between December 2014 and August 2019 at our institute. The research protocol was approved by the Institutional Review Board of the authors’ institute. Written informed consent was obtained from all of the participants, and the research methods were carried out in accordance with approved guidelines.
Operation
Surgery was performed under brachial plexus anesthesia or general anesthesia. Patients with supine position, and placed a pillow under the medial margin of the scapula of sick shoulder. After the routine disinfection and covering surgical position, took an incision to the arcuate of the shoulder from the distal end of the clavicle, followed by cutting the skin, subcutaneous and plastric muscles, separating the trapezius fascia to exposure the acromioclavicular joint. The dislocated lateral clavicle was reduced and temporarily stabilized by transarticular Kirschner wires from lateral acromion. The hook of the pre-curved clavicular hook plate was inserted below the acromion, the plate body was placed above the clavicle and the locking screws were fixed. Repaired the acromioclavicular joint capsule in the surgery, stitched the distal end of the clavicle angle and trapezius muscle. After intraoperative fluoroscopy and passive activities of the shoulder joint, rinsed and sutured the wound.
Dependent variable
Moderate-to-severe postoperative shoulder pain at the last follow-up when the internal fixation will be removed was presence as the dependent variable. Patients rated the average intensity of postoperative shoulder pain using an 11-point numerical rating scale (NRS) (0: no pain; 10: worst pain imaginable). The cut-off point between mild and moderate-to-severe postoperative pain intensity was set at NRS ≥ 4 (10). For logistic regression analysis, patients were categorized into two groups: (1) those who had moderate-to-severe neck pain (NRS ≥ 4); (2) those who had no or mild neck pain (NRS < 4).
Independent variables
Patient characteristics
Age at the time of surgery, sex, body-mass index (BMI), smoking status and alcohol consumption were included in the patient characteristics. According to the smoking status, the patients were categorized into two groups: current smokers and current non-smokers. The current non-smokers included the past smokers or those who never smoked (11). As for the definition of alcohol consumption, the standard we set was Alcohol > 15 drinks/week. A standard drink is 12 oz of 5% alcohol beer, 8 oz of 7% malt liquor, 5 oz of 12% alcohol wine or 1.5 oz of 40% alcohol liquor (12).
Injury mechanism
The types of injuries were divided into four major categories: (1) Car accident injury; (2) Falling injury; (3) Fell and hurt; (4) Other injuries. According to Rockwood Classification (9), all cases were divided into four categories: (1) Rockwood Ⅲ; (2) Rockwood Ⅳ; (3) Rockwood Ⅴ; (4) Rockwood Ⅵ. The site of injury was distinguished by right and left shoulders.
Surgical factors
The first was the operation time, which was specifically from the beginning of the skin incision to the final suture of the skin. The second was the time from injury to surgery which calculated in days.
Hook plate factors
Regarding the hook plate factors, this research included a total of three items. (1) The hook depth (DH), it specifically referred to the distance between the connection point between the hook body and the hook tip and the cortical bone below at the distal of the clavicle (Fig. 1). (2) The hook plate angle (AHP), the angle with hook plate body and hook tip (13) (Fig. 2). (3) The distance between hook and acromion articular surface (DHA), its definition was the closest distance from the acromial articular surface to the hook body (Fig. 3).
Statistical analysis
Means and standard deviations (SDs) were used to describe distributions for continuous variables, and proportions were used to summarize categorical variables. One-way ANOVA tests were used to compare the means of continuous and ordinal variables; values of 0.05 represent a statistically significant difference. For categorical variables, the Pearson chi-square analysis was used, and a P value of 0.05 represented a statistically significant difference. Binary logistic regression analysis was performed to account for confounding significant variables. P < 0.05 was considered significant. Odds ratios and 95% confidence intervals were calculated for each of the risk factors included in the logistic regression models. Analyses were performed using SPSS version 21 (IBM).