The fractures of the coronoid process of the ulna have been observed in 2% to 15% of patients diagnosed with elbow dislocation. More often than not, fractures are observed in an injury called the 'terrible triad of the elbow'. This injury is associated with the fracture of the coronoid process of the ulna, posterior or posterolateral elbow dislocation, and a radial head fracture.
The term 'coronoid process' has been used for describing the bony process or prominence of the ramus of the mandible (lower jaw), as well as triangular-shaped bony prominence that projects from the inner side of the point that is nearest to the attachment of the ulna (one of the two bones of the forearm). The coronoid process of the mandible has been observed to be of different shapes. It might be triangular, round, or hook-shaped. Chewing habit, hormones, and the attachment and action of temporalis muscle are believed to be the factors responsible for the different shapes.
While the coronoid process of the mandible is clinically significant in case of maxillofacial surgery that is done for reconstructive purposes, the coronoid process of the ulna is believed to be instrumental in resisting the partial displacement of the posterior elbow.
Coronoid Process of the Mandible
Maxilla and mandible refer to the upper and lower jaw respectively. The mandible is a large facial bone that holds the lower set of teeth. Masseter, temporalis, medial pterygoid, and lateral pterygoid are the four paired muscles that facilitate the side-to-side and up-and-down movement of the lower jaw. The mandible consists of a horizontal horseshoe-shaped body with ramus, which is the posterior and vertical part of the mandible that projects upward at each end. The ramus includes two processes that are called coronoid process and the condylar process (mandibular condyle).
While the coronoid process is located at the front or the upper border of the ramus, the condylar process is located at the posterior. The muscles that facilitate the process of chewing attach to the coronoid processes, whereas the condylar process joins with the tissues of the temporal bones. The mandibular notch separates these two bony processes from each other. While the temporalis muscle inserts into both the medial and lateral surfaces of the coronoid process, the masseter muscle and temporalis muscle inserts to its lateral and medial surface respectively.
The common sites of mandibular fracture include the body, angle, condylar processes, etc. Around 30-40% of fractures involve the body of the mandible, and 25% fractures involve both the condylar process and angle of the mandible. The fractures of the coronoid process, ramus, and alveolus account for 2-3% only. Isolated fractures of the coronoid process are quite rare. In fact, fractures of the coronoid process account for just 1% of the mandibular fractures. It is believed that the low incidence of the fracture is due to the protection provided to the process by the zygomatic arch, which is the arch of bone that forms the prominence of the cheek. More often than not, surgeons look for the fracture of the zygomatic arch, if the coronoid process has been fractured.
Drug therapy, open/closed reduction, fixation, immobilization, rehabilitation, etc., are some of the aspects of the treatment. In very severe fractures, the jaw needs to be wired shut for immobilization during the recovery period.
Coronoid Process of the Ulna
The elbow joint of the human body is a hinge joint. The hinge is formed by the trochlea of the humerus (which is the bone that extends from the shoulder to the elbow), the trochlear notch of the proximal ulna (a cavity formed by the olecranon and the coronoid process which is present at the end of the ulna that is nearest to its attachment), the radial head, and the capitulum.
The ulna is medial to the radius bone in the forearm, and is also longer than the radius bone. Olecranon, which is a bony process that forms the outer bump of the elbow, is at the posterior surface of the trochlear notch.
The coronoid process is the triangular-shaped projection that forms the anterior section of the trochlear notch. It provides stability during flexion. The trochlear notch articulates with the trochlea of the humerus bone.
The radial notch is an oblong-shaped depression that is present on the lateral or the outer side of the coronoid process for the head of the radius bone. It is a rounded structure that bends inwards. The soft tissue attachments or the insertions of the coronoid process include the brachialis muscle (anteriorally and distal to the capsule), anterior bundle of medial ulnar collateral ligament (distally and medially on the sublime tubercle of the distal ulna), and the anterior joint capsule of the elbow (close to the tip).
The ulnar tuberosity lies under the coronoid process for the attachment of brachialis muscle, which is a muscle in the upper arm that helps flex the elbow joint. The supinator crest lies below the radial notch for the attachment of supinator muscle, which is a muscle that curves around the upper third section of the radius bone. It helps rotate the forearm, allowing us to move our hands in such a way that the palms face upwards. This muscle attaches at the concave-shaped supinator fossa that is located between the supinator crest and coronoid process. The ulna bone is thick, and tapers towards the distal end, which comprises the head and the styloid process. The fractures of the coronoid process are relatively uncommon. These are classified into three types:
The type 1 fracture is associated with the avulsion of the tip of the process.
The type 2 fracture involves less than 50% of the coronoid process.
The type 3 fracture involves more than 50% of the coronoid process.
While closed reduction of the dislocation and short-term use of a splint is recommended for the type 1 and 2 injuries, surgery would be required for type 3 fractures.
On a concluding note, the coronoid process of the ulna and mandible are anatomical structures that play a vital role. The coronoid process of the ulna is important for the stability of the ulnohumeral joint, whereas the process of the mandible inserts into muscles that are essential for chewing and swallowing. Thus, medical assistance must be sought to correct abnormalities associated with these bony prominences. For instance, the elongation of the coronoid process of the mandible can cause restricted mouth opening. Under such circumstances, surgery is recommended to correct this structural abnormality.