Elbow joint dislocation accounts for 11%-28% of elbow trauma and is commonly seen in sports injury. The dislocation can be anatomically classified into simple type (no intraarticular fractures) and complex type (complicated with distal humeral fractures, radial head fractures, proximal ulna and/or coronal process fractures) . The simple type of elbow dislocation is more common than the complex type, and it does not mean less damage. The anatomical study , injury mechanism and clinical feature indicate extensive damage to the surrounding soft tissue after elbow joint dislocation. O 'Driscoll et al. expatiate the classic simple type of elbow dislocation mechanism in detail. The elbow joint undergoes axial stress combined with supination and valgus stress. These lead to annular soft tissue injury starting with lateral collateral ligament (LCL) from the anterior joint capsule to the medial collateral ligament (MCL) of anterior and posterior bundles, causing the posterolateral instability and dislocation of elbow joint. With improper treatment, these acute elbow instabilities cause incomplete healing of lateral collateral ligament complex (LCLC) which may develop into chronic elbow instability. The most common one is posterolateral rotatory instability (PLRI) . However, due to the limited awareness and knowledge among most doctors for the elbow joint dysfunction caused by such ligament injuries, the missed diagnosis or the failure of timely and effective treatment will seriously affect the life quality of patients. Currently, the treatment of PLRI is mainly surgical with repair or reconstruction of LCLC.

1. Clinical data:From June 2013 to December 2017, 20 patients with PLRI caused by simple elbow dislocation were admitted into our hospital continuously, among which 11 patients underwent open reduction and LCLC repair, and 9 patients received conservative treatment of external fixation with hinged brace. There were 9 cases of male and 2 cases of female with an average age of 29.4 years (19-52 years) . 9 cases had the dominant elbow affected. Causes of injury: 7 cases of sports injury; 2 cases of traffic injury; 1 case of high fall injury; 1 case of fall damage. Among them, 2 cases were combined with the avulsion fracture of external humeral epicondyle. In the control group, there were 6 males and 3 females with an average age of 28.2 years (17-45 years) . 6 cases had the dominant elbow affected. Causes of injury: 4 cases of sports injury; 1 case of traffic injury; 2 cases of fall injury; 2 cases of fall damage. The diagnosis of PLRI was made based on patient's medical history, physical examination, preoperative X-ray and MRI examination. 2. Surgical methods:Modified Kocher approach was adopted on the lateral side of elbow joint. A 6-8 cm oblique incision was made across humeroradial joint and radial head along the lateral epicondyle of humerus. The gap between extensor carpi ulnaris muscle and anconeus was cut open through the entrance between brachioradialis muscle and triceps muscle, and the common extensor tendon was carefully lifted to fully expose the insertion point of LCLC. Lateral axial test and lateral drawer test were performed during the operation, and the radial head was found unstable with subluxation in posterior and lateral position. A suture anchor was placed in the origin of external epicondylar ligament of humerus. According to the method of Kim et al., the lateral ulnar collateral ligament (LUCL) and LCL were respectively repaired by Mason Allen method with two sutures. 3. Postoperative management:In the operation group, the elbow joint was immobilized in 90° of neutral flexion within 1 week of operation , and the hinged brace was adopted 1 week after operation. Passive flexion and extension started within 3 weeks, and the range of motion was controlled from 30° of elbow extension to 90° of elbow flexion. The rehabilitation training including active and passive flexion and extension began 3 weeks later , and the range of motion was gradually increased to normal (0-150°) 6 weeks after operation. The brace was removed 6-8 weeks postoperatively, and the elbow joint was restored to normal 3 months after surgery. In the control group, the elbow joint was immobilized with plaster in 90° of neutral flexion. 3 weeks later, the plaster was changed into hinged brace for progressive functional exercise. 4. Postoperative evaluation:During postoperative follow-up, VAS score and Mayo elbow performance score (MEPS) were used to evaluate elbow function before and after treatment. Pain (45 points) , range of joint motion (20 points) , joint stability (10 points) and daily life function (25 points) were evaluated according to MEPS: ≥90 points were considered excellent, 75-89 points were considered good, 60-74 points were considered moderate and <60 points were considered poor. 5. Statistical methods:The SPSS19.0 statistical software was used to analyze and process the data in this study,±s was used to represent measurement data, and percentage was used to represent counting data. A P value of <0.05 was considered statistical difference, and t or χ² test was used for comparison between groups.

1. Clinical efficacy analysis:All patients were followed up for an average of 11.8 months (6-24 months) . The excellent and good rates of operation group and control group were 100% and 77.78%, respectively, and the difference was statistically significant. 2.VAS scores and MEPS scores before and after treatment in the two groups.The VAS scores of patients in the two groups decreased significantly after the treatment, but symptoms alleviated more significantly in the operation group. The difference of post-operated VAS scores between the two groups was statistically significant. The MEPS scores of operation group increased significantly after the treatment, and the difference was statistically significant compared with that of the control group.3. Complications in the two groups after the treatment:In the operation group, 11 patients had no wound infection, nerve injury or reoperation, and only 1 patient had slight heterotopic ossification. In the control group, 2 patients showed slight heterotopic ossification, and 1 patient had elbow stiffness.

The correct diagnosis of acute posterolateral rotatory instability of elbow is critical for the selection of treatment option. The LCLC repair with active functional exercise is preferred for restoring normal function and elbow stability.