Monday, June 22, 2020

Coronoid Fracture


The coronoid process provides anterior buttress against posterior subluxation or displacement. The radial head prevents valgus instability, and the coronoid process prevents varus instability. The coronoid process also provides attachment for the anterior bundle of the MCL and attachment to the anterior capsule. The anterior capsule attaches 6mm distal to the tip of the coronoid process. The anterior bundle of the medial collateral ligament attaches to the sublime tubercle 18mm distal to the tip of the coronoid process. You need to know the difference between the insertion of the MCL and the insertion of the brachialis as seen here. If the fracture of the coronoid process tip is small, the brachialis should insert distal to the tip of the coronoid process. There are two types for the mechanism of injury: posterolateral rotatory displacement and varus and posteromedial rotatory displacement. Posterolateral rotatory displacement is a fracture of the radial head, fracture of the coronoid process tip, and dislocation of the elbow. Varus and posteromedial rotatory displacement are associated with fracture of the anteromedial coronoid process. The LCL tears from the humerus, and the MCL may not be ruptured. In posterior elbow dislocation and posterolateral instability, the lateral side fails first with the medial side failing last. This valgus and supination can result in the terrible triad. Patient with instability after elbow fracture dislocation always has a coronoid fracture, and it can redislocate in a cast or after surgery. Elbow dislocation with Type II coronoid process fracture and non-reconstructable comminuted radial head fracture. Treated by repair of the lateral collateral ligament, do radial head arthroplasty, and do ORIF of the coronoid process. This is an example of the terrible triad (dislocation of the elbow, coronoid fracture, and radial head fracture) and you need to fix all these injuries. Address each injury to restore elbow stability. If you have an elbow dislocation with fracture of the olecranon tip fracture and a radial head fracture, the likely pattern of instability is valgus posterolateral rotatory instability. There will be rupture of the LCL from the humerus and varus force will cause medial facet fracture, and this is the malignant fracture pattern. To recognize the posteromedial facet injury, look at the AP view x-ray in addition to the lateral view x-ray (in the lateral view you may miss it). In large medial coronoid fracture and elbow dislocation, there probably will be varus posteromedial rotatory instability, and it will affect the anteromedial facet of the coronoid. In fracture of the coronoid process, the x-ray is difficult to interpret. The fracture may be mistaken for a radial head fracture. The structures overlap, and we may miss the fracture. In the lateral view radiograph, you find a chip a bone. AP view radiograph will find a nondislocated elbow with an anteromedial coronoid process fracture. if you miss the anteromedial coronoid process fracture, you will get progressive narrowing of the joint space from lateral to medial between the medial trochlea and the coronoid process. This entity (anteromedial facet fracture) that gives posteromedial instability, occurs in conjunction with lateral collateral ligament injury. When you see this fracture, suspect anteromedial coronoid fracture, especially when you cannot find a radial head fracture. You may also find narrowing of the joint space between the medial trochlea and the coronoid process. CT scan is usually very helpful. There are two known classification systems: Regan & Morrey Classification and O’Driscoll Classification. Regan & Morrey Classification is based on viewing the lateral x-ray. In Regan & Morrey Classification, there are three fracture types based on viewing the lateral x-ray. Type I is a shear fracture of the tip of the coronoid process. Type II involves up to 50% of the coronoid process. Type III involves more than 50% of the coronoid process. This is a very simple classification system, but the problem is that it does not show the malignant fracture pattern. The O’Driscoll classification is very helpful, and it will show the anteromedial facet fracture that will create posteromedial instability. The O’Driscoll classification can be the tip, anteromedial facet, or basal. The O’Driscoll classification recognized the anteromedial facet fracture caused by varus posteromedial rotatory force. This fracture could be missed on the x-ray and can cause degenerative joint disease.