Trochlear notch is a deep notch facing anterior in the ulna’s thick proximal end. It is the articular surface that is covered with cartilage and it receives the trochlea of humerus— a pulley like structure. On its lower end, it borders the coronoid process while on its upper border there is the anterior projection of olecranon. The term trochlear comes from a Latin term, which implies one or more pulleys. Notch is a term referring to an indentation in margin of bone.
The trochlear notch of ulna or the semilunar notch is also called the greater sigmoid cavity and it forms a large depression from the coronoid process and olecranon. The trochlear notch of ulna serves as an articulation point with trochlea of humerus. In either sides of the notch at the middle is an indentation. This indentation make the notch to contract and it indicates a junction of coronoid process and olecranon.
It is a concave notch from above down. A smooth ridge that runs from high point of olecranon divides the notch into a medial as well as lateral portion. That smooth ridge running from olecranon ends up at the coronoid process.
In structure, the medial part is usually large and it appears slightly transversely concave. The lateral part is convex at its top and lightly concave at its lower part or below. In order to understand the structure and function of trochlear notch, it is important to look at the elbow joint.
Elbow is a kind of hinge of joint, which is formed by distal end of humerus along with the proximal ends of the ulna bones and the radius. The elbow moves into extension and flexion. The trochlear together with capitulum of humerus both articulate with trochlear notch of ulna as well as radial head correspondingly.
Ulna bone is longer and large usually more medial of the bones of the lower arm. A majority of the muscles of the arm tend to attach to ulna and they help in movement of the hand, wrist, and arm. In everyday functions for instance driving a car, or throwing a ball, the movement of ulna plays a big role.
Ulna extends from the elbow to wrist through the forearm and it narrows down significantly, as it reaches the distal end. In the proximal end, ulna creates the elbow joint together with humerus of upper arm alongside the radius of forearm. Ulna further extends to pass the humerus where it forms a tip of elbow referred to as olecranon.
Olecranon fits into olecranon fossa, which is a small recess found in the humerus. The olecranon mainly helps prevent the elbow from extending beyond a 180 degree. And, just distal to olecranon, you find concave trochlear notch, which surrounds trochlea of humerus thus forming a hinge of elbow joint.
In its distal lip, the trochlear notch then protrudes anteriorly thereby forming the coronoid process. The coronoid process helps in locking ulna in place. Ulna provides a point of muscle attachment to over dozens muscles found in the forearm and upper arm. In the upper arm, you find muscles such as the anconeus and triceps brachii, which form insertions that extend the forearm at elbow.
Ulna is categorized as a bone due to its narrow long shape and as other long bones; it has a similar structure of having a hollow shaft that is surrounded by some compact bone reinforced at ends with bones that are spongy. At the center of ulna, there is the hollow medullary cavity, which is filled with soft and greasy substance referred to as the yellow bone marrow. It is this marrow, which stores energy needed by the body in form of fats and triglycerides.
The spongy bone reinforces the ends of ulna and increases its strength near the joints without necessarily increasing the bone mass. In each part of spongy bone, it consists of tiny columns, which are referred to as trabeculae, and these columns act like steel girders of bridge meaning they can withstand stress that is placed on the ulna bone.
In children, fracture of trochlear notch can occur due to differences in bone density as well as cartilage surfaces. When there is an injury that affects parts of the elbow joint, it causes disability of the joint. Loss of motion is one of the most complications, which arise due to injuries.
Traumatic elbow injuries especially those, which are associated with dislocations, may lead to instability of elbow by causing damage on bony structures and the soft tissues. When injuries are experienced in elbow joint, they will impair the range of motion and are accompanied by symptoms such as swelling and tenderness. Examination through imaging like X-ray may be conducted to determine which part of the joint is damaged and the right treatment procedure to apply.