The conoid tubercle is a small, roughened, elevated prominence on the surface of the clavicle, the bone that connects the upper limb to the trunk. It serves as a specialized site for anchoring soft tissues. This feature is crucial for force transmission and stability within the shoulder complex. Understanding its location and function is foundational to comprehending the biomechanics of the upper torso.
The Conoid Tubercle’s Exact Location
The conoid tubercle is situated on the clavicle, or collarbone. This prominence is located on the clavicle’s inferior surface, the side facing downward toward the ribs and chest. It is positioned toward the outer, or lateral, end of the bone, near the junction of the lateral one-third and the medial two-thirds of the clavicle shaft.
The bony feature is a slight, rounded elevation. It is positioned slightly posterior on the inferior surface, marking the start of a small ridge, known as the trapezoid line, which extends laterally from it.
Role in Stabilizing the Shoulder Girdle
The primary function of the conoid tubercle is to serve as the attachment site for the conoid ligament. This ligament is the medial component of the coracoclavicular ligament complex. This complex provides a strong link between the clavicle and the coracoid process, a hook-like projection extending from the scapula.
By connecting the clavicle to the scapula, the ligament complex establishes vertical stability in the shoulder girdle. It acts as a mechanical restraint, preventing the clavicle from moving excessively upward and backward relative to the scapula. This tethering action is essential for the proper alignment of the acromioclavicular (AC) joint. The integrity of the tubercle ensures the necessary anchor point for these restraints, allowing the shoulder to transmit forces from the upper limb to the axial skeleton.
Relevance in Clavicle and Shoulder Injuries
The conoid tubercle is important clinically, particularly in the context of shoulder trauma. Injuries that result in a high-grade AC joint separation, such as a Type III or higher, often involve a complete rupture of the coracoclavicular ligament complex anchored at the tubercle. When these ligaments are torn, the scapula and attached arm drop downward due to gravity, while the unopposed force of the sternocleidomastoid muscle pulls the medial end of the clavicle upward. This visible deformity is a direct consequence of the loss of the stabilizing function provided by the conoid ligament.
The tubercle also serves as an important anatomical landmark for orthopedic surgeons during fracture repair. The region of the clavicle where the tubercle resides is frequently the site of fractures, and stabilization plates must be contoured to this specific anatomy.
A less common but notable clinical feature is the occasional development of a coracoclavicular joint (CCJ), an anomalous joint that can form between the conoid tubercle and the coracoid process. While often asymptomatic, this extra articulation can sometimes lead to localized shoulder pain or contribute to degenerative changes in the surrounding joints, underscoring the importance of this small bony feature in overall shoulder health.