A motion segment includes which components?

A motion segment includes which components?

• A. Two adjacent vertebrae, intervertebral disc, posterior joints, and various ligaments
• B. Two adjacent vertebrae and intervertebral disc only
• C. Three adjacent vertebrae and ligaments
• D. A single vertebra with surrounding soft tissue

Answer: (A)

The motion segment is the smallest functional unit of the spine and includes two adjacent vertebrae with the disc between them, plus the posterior facet joints and the ligaments that stabilize this unit. The intervertebral disc provides cushioning and the ability to move, while the facet joints (the posterior joints) guide and constrain motion, especially rotational and flexion-extension movements. The surrounding ligaments—such as the anterior and posterior longitudinal ligaments, ligamentum flavum, interspinous, and supraspinous ligaments, along with the facet capsules—tether the segments together and limit excessive movement, maintaining stability. This combination of two vertebrae, the intervening disc, the facet joints, and the stabilizing ligaments is what defines a motion segment. The other descriptions miss one or more essential components, or describe the wrong number of vertebrae.

The motion segment is the smallest functional unit of the spine and includes two adjacent vertebrae with the disc between them, plus the posterior facet joints and the ligaments that stabilize this unit. The intervertebral disc provides cushioning and the ability to move, while the facet joints (the posterior joints) guide and constrain motion, especially rotational and flexion-extension movements. The surrounding ligaments—such as the anterior and posterior longitudinal ligaments, ligamentum flavum, interspinous, and supraspinous ligaments, along with the facet capsules—tether the segments together and limit excessive movement, maintaining stability. This combination of two vertebrae, the intervening disc, the facet joints, and the stabilizing ligaments is what defines a motion segment. The other descriptions miss one or more essential components, or describe the wrong number of vertebrae.