Radiologic Technologist Practice Exam

What type of joint is formed between the dens of the axis and the anterior arch of the atlas?

1. Ellipsoidal

2. Gliding

3. Pivot

4. Saddle

The correct answer is: Pivot

The joint formed between the dens of the axis (the second cervical vertebra) and the anterior arch of the atlas (the first cervical vertebra) is classified as a pivot joint. This type of joint allows for rotational movement around a single axis, which is crucial for the head's ability to turn from side to side. In this specific case, the dens acts as a peg around which the atlas pivots. This unique anatomic design permits significant rotational motion of the head while also providing stability to the cervical spine. The pivot mechanism is key for actions such as shaking one's head "no," exemplifying the functionality of this joint type. The other joint types, such as ellipsoidal, gliding, and saddle, do not accurately describe this specific articulatory relationship. Ellipsoidal joints allow for movement in two planes but do not permit the rotational movement seen in the pivot joint. Gliding joints permit limited movement and are not designed for significant rotation. Saddle joints offer a greater range of motion than a pivot but do not suit the specific structural arrangement and movement capabilities seen between the atlas and axis. Thus, the pivot classification accurately captures both the structure and function of the joint in question.