The coronoid process is an important stable structure of the elbow joint. The coronoid process is formed by the forward and medial extension of the proximal metaphysis of the ulna, which increases the area of the joint matching the humerus block and maintains the stability of the elbow varus. However, nearly 60% of the anteromedial articular surface lacks the bony support of the metaphysis. Under the varus stress, it is easy to cause fracture, which leads to varus posterior medial rotational instability of the elbow. According to the characteristics of the coronoid fracture, O’Driscoll divided the fracture into three parts, the tip, the anteromedial side and the base according to the fracture location and injury mechanism. Among them, type 2 fracture, anteromedial articular surface fracture, was divided into three subtypes, type 2-1, anteromedial side fracture; type 2-2, anteromedial side + tip fracture; type 2-3, anteromedial Articular surface + sublime fractures ± tip fractures. O'Driscoll believes that the mechanism of injury to type 2 fractures is varus-posterior medial rotational instability, which is often accompanied by complete or partial rupture of the lateral collateral ligament.

1. General information: In this retrospective analysis, from July 2012 to July 2016, Tianjin Hospital received 19 patients with anteromedial fractures of the ulnar coronoid process, including 17 males and 2 females, aged 22-58 years, with an average of 37.1 years. All 19 patients were freshly injured and had no open wounds. Causes of injury: 14 cases were falls and 5 cases were car accidents, which showed swelling of the elbow joint, pain, limited mobility, and no obvious neurological and vascular symptoms. Among them, 6 patients with elbow dislocation, closed reduction in emergency department, were all achieved; 1 patient had comminuted fracture of the distal radius; 1 patient had arthritis in the elbow joint. 2. Preoperative evaluation: Preoperative examination includes the patient's skin, soft tissue swelling, presence or absence of dislocation, with or without blood vessels, nerve damage. The anterior-posterior and lateral X-ray films of the elbow joint and the three-dimensional CT of the elbow joint were routinely examined before operation. MRI examination was used to determine the integrity of the medial and lateral collateral ligament. The preoperative dislocation was restored and the elbow was immobilized at 90 degrees. 3. Surgical method: Brachial plexus block anesthesia was used. First fix the coronoid process, the incision uses the ulnar carpi flexor approach: 2-3 cm up the medial epicondylar center, extending down 5-6 cm to the forearm longitudinal axis. Cut the skin and subcutaneous tissue in turn, and pull open to both sides of the incision, reveal the ulnar nerve, first reveal the release to the medial muscle interval, and then reveal between the two ends of the ulnar carpi flexor, free the first muscle branch. Support, give protection, lead to the posterior side, turn the ulnar carpi flexor tendon and the entire flexor tendon forward, the broken joint capsule and displaced fracture block could be seen. Clear the fracture end. According to the size and position of the fracture block, the steel plate, the screw and the auxiliary lasso are selected to fix the anterior joint capsule. Through the incision, the integrity of the medial collateral ligament is checked under direct vision. Once there is tearing, anchor reconstruction and the suture of the collateral ligament would be done. After fixation of the coronoid process and the medial structure was repaired, the forearm pronation position and neutral position were given. Under the C-arm fluoroscopy, the varus stress was applied respectively to see if the medial space of the ulnar joint was narrowed, and whether the lateral joint space was widened. If there was significant widening, suggesting that the lateral collateral ligament complex was damaged. The Kocher approach was used. The lateral collateral ligament was checked from humeral insertion to ulna insertion, repair using suture anchor was indicated if tear was confirmed. After repairing, look at the medial and lateral gaps again under C-arm fluoroscopy to determine the stability of the elbow joint. 4. Postoperative treatment: All patients were treated with hinged splint at 90-degree of flexion for 3 days. Under the protection of the hinge brace, the autonomous passive flexion and extension activities were performed, the extetion was not more than 30 degrees, and the forearm was in the neutral position after 3 days. After 6 weeks, the active flexion and extension exercises were carried out, and the flexion and extension angle were not restricted. After 12 weeks, the brace was used intermittently, and after 4 months, the normal life was gradually restored. 5. Eficacy evaluation: Postoperative evaluations use the Mayo elbow performance score (MEPS) , disability of arm shoulder and hand (DASH) and visual analogue scale (VAS) Evaluation of elbow joint function and symptoms. X-ray films were reviewed periodically after surgery, and osteoarthritis was graded using the Broberg-Morrey imaging score.

All patients underwent anatomical reduction of ulnar coronoid process fractures, no fracture fixation failure, no ulnar coronectomy or bone grafting. One patient with a distal radius fracture and one patient had a history of arthritis were excluded. All other patients were followed up for a period of 12-30 months with an average of 19.7 months. The coronoid process was healed after operation, and no fracture malunion and internal fixation failure were found. Type of fracture: O'Driscoll 2-1 type 4 cases, 2-2 type 9 cases, 2-3 type 4 cases. Cases of elbow dislocation: 6 cases; varus stress test (-) , 4 cases of unrepaired lateral ligament, varus stress test (+) , repair of lateral collateral ligament: 13 cases; intraoperative medial collateral ligament found rupture and repair: 3 cases; at the last follow-up, the patient's elbow function score was recorded: MEPS: 85-100 points, mean: 97.6 points, excellent 16 cases, good 1 case; DASH: 0-10.8 points, average : 4.13 points; VAS: 0-2 points, average: 0.4 points; arthritis 5 cases of I degree. According to the fracture type grouping, non-parametric test was used to analyze whether the functional scores of type 1, 2, and 3 fractures were significantly different. On the basis of effective fixation of coronoid fractures, the multilateral analysis of the lateral collateral ligament repair, whether to repair the medial collateral ligament, arthritis grade and the presence of joint dislocation, the impact on joint function score. The arthritis and functional scores were assessed by Spearman test. all are not-significant different.

The injury mechanism of the anteromedial coronoid process is the fracture and instability of the elbow joint caused by the varus-posterior medial rotation, often with partial or complete rupture of the lateral ligament complex. After the medial bone mass is effectively fixed in the anterior coronoid process, the varus test can truly reflect the injury of the lateral ligament and the stability of the elbow joint. Under the premise of stable elbow joint, the lateral collateral ligament can be under the protection of the brace, functional exercise can achieve good treatment results.

Elbow joint; Anteromedial coronoid fracture; Fracture fixation; Lateral collateral ligament injury; Ligament repair