Which bone is primarily involved in the shoulder joint?

The scapula, commonly known as the shoulder blade, is primarily involved in the shoulder joint. It plays a critical role in forming the shoulder joint by articulating with the humerus (the bone of the upper arm) at the glenoid cavity. This connection allows for a wide range of motion in the arm, facilitating various movements such as lifting, pushing, and rotating. The design of the scapula, with its flat, triangular shape, provides a stable base for the shoulder joint while allowing for flexibility and movement.

The other bones listed do not play a role in the shoulder joint. The patella is a knee cap positioned in front of the knee joint, the tibia is one of the major bones in the lower leg, and the metatarsals are the long bones in the foot. Each of these bones has its own functions and associations with different joints, but they are not involved in the mechanics of the shoulder joint.