A motion segment is defined as which of the following?

A motion segment is defined as which of the following?

• A. Three vertebrae and a disc
• B. One vertebra and a disc
• C. Two vertebrae and a disc
• D. Two vertebrae and two discs

Answer: (C)

A motion segment is the smallest unit of the spine that can move, and it consists of two adjacent vertebrae with the intervertebral disc between them. This pairing allows the relative motion between those vertebrae, with the disc providing load transmission and permitting sliding, while the facet joints and supporting ligaments guide and stabilize the movement. Thinking of it this way, two vertebrae together with the disc between them captures exactly the functional unit that undergoes motion; adding another vertebra or another disc would span more than one motion segment and isn’t the basic unit being described.

A motion segment is the smallest unit of the spine that can move, and it consists of two adjacent vertebrae with the intervertebral disc between them. This pairing allows the relative motion between those vertebrae, with the disc providing load transmission and permitting sliding, while the facet joints and supporting ligaments guide and stabilize the movement. Thinking of it this way, two vertebrae together with the disc between them captures exactly the functional unit that undergoes motion; adding another vertebra or another disc would span more than one motion segment and isn’t the basic unit being described.