|
Year |
2001 |
|---|---|
|
Question Number |
33 |
|
Category |
Select |
Question
Which of the following terms best describes the primary motion at C1-2?
1 – Flexion
2 – Rotation
3 – Lateral bend
4 – Translation
5 – Extension
Figures
Answer (click for answer)
ANSWER: 2
DISCUSSION: The upper cervical spine carries 50% of all cervical mobility. Specifically, 50% of cervical rotation occurs at the C1-2 articulation (correct answer 2) while 50% of cervical flexion/extension occurs at the occiput-C1 articulation (wrong answers 1 and 5). The subaxial spine (C3-T1) comprises evenly the rest of cervical spine motion. Lateral bending occurs mainly in the subaxial spine (wrong answer 3). Translation is usually pathological—as in a fracture-dislocation. To help remember this, think of the shape of the articulations. C1-2 is a ring (C1) about a peg (odontod), so rotation is predominant. The O-C1 joints occur where the convex, downward-pointing occipital condyles meet the concave, upward-pointing C1 articular facets, so flexion/extension is predominant.
Reference: Garfin SR, VAccaro, AR (eds): Orthopaedic Knowledge Update: Spine. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1997, pp 3-17.