Sleeping Positions from an Anatomical Perspective

By Jan Willem Elkhuizen, ©2025

How sleeping position affects your neck: three anatomical points of attention

Below, three anatomical aspects of the cervical spine are highlighted, explaining the influence of certain (sleep) postures on them. 

• C0-2 complex
• C1-2
• C2-3 and lower

The C0-2 complex

The connections between skull (C0), atlas (C1), and axis (C2) form an ingenious movement unit. C2 is directly connected to C0 by three ligaments. C1 is relatively free in between. This is where C1 derives its enormous rotational capacity relative to C2: about 45 degrees, roughly half of the total neck rotation.

From this video it appears:

• The three drawn ligaments have a guiding function for the movements between C0 and C1 and between C1 and C2
• The movements of the three bone parts are directly linked and dependent on each other
• It is not the muscles that control the movement, but the ligaments
• If a ligament is torn, this can lead to a blockage of the C0-2 complex involving both C0-1 and C1-2
  
• Ligament injury can lead to locally increased muscle tension, which can be very useful

C1-2

The main movement of C1 relative to C2 is rotation. Remarkably and factually incorrect that C2 is called the rotator: it is the atlas that rotates. This rotation is mainly guided by one strong ligament through the vertebral canal, the lig. transversum.

The right photo is taken from an anatomical specimen. All tissues between C1 and C2 have been dissected away except for this ligament. A short video has been made of it, clearly showing how the rotation of C1-2 is guided by this ligament: Video Specimen C1-2.

This video also shows that the Lig. Transversum in this specimen is partially torn. Remarkably, despite this weakening, the ligament is not excessively loaded during rotational movement. However, this is the case when C1 moves forward relative to C2: this heavily stresses the ligament and makes the tear more visible. Below are two close-up images of this specimen.

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In the images above, it can be seen that the Lig. Transversum is heavily loaded when C1 is bent forward relative to C2. This occurs with a kinked head position (chin on chest). This position is especially stressful when a force is applied to the head. For example, this happens when the head rests on a pillow that is too high.

This 'resting' of the head is a misleading term in this case: in fact, the pillow exerts a reaction force (counterpressure) on the head, causing sustained load on this ligament. Moreover, this kinked position also stresses the ligaments of the C0-2 complex.

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Sleeping on the stomach: effect on the facet joints

Explanation: There is little or no lateral bending here, so the C2-C7 segments can contribute little to the neck's rotational movement (this is further explained below under the heading 'The facet joints of C2-3 and lower'). The neck must rotate further than C1-2 alone can manage in this posture. As a result, the C1-2 segment is pressed firmly into the end position. The lower segments are also loaded, but not at their end position. Therefore, the load on the lower segments is moderate.

If one is not lying purely rotated, but with a slight forward bend as well (chin towards chest), some lateral bending and thus rotation can occur in the vertebrae between C2-7. Even then, the C1-2 segment will remain heavily loaded at or near the end position.

When sleeping on the stomach with the head on a pillow, the lower segments can contribute to the rotation of the neck. This also creates tension. Meanwhile, the load on C1-2 will remain significant.

The facet joints of C2-3 and lower

The position of the joints of C2-3 is from front-top to back-bottom, see the photo below. This makes it impossible to only rotate or only laterally bend in these joints. These movements always occur combined and resemble the swinging movement of an airplane: the left wing goes down, the right wing goes up. The airplane tilts (lateral bending) and simultaneously makes a turn (rotation).

Sleeping in the 3/4 position

There is strong evidence that the 3/4 position is especially stressful for the vertebral joints of C2-3. This is also the segment where most headaches originating from the neck are caused.

Several aspects are important here:

1. In the 3/4 position, there is a combination of rotation and lateral bending of the neck. Both in the same direction (in the drawing below: lateral bending to the left and rotation to the left). This movement fits exactly with the range of motion of C2-3 and the lower segments.

2. The lateral bending capacity of C0-1 and C1-2 is not sufficient to absorb the lateral movement that occurs in the 3/4 position. This must therefore be absorbed by the lower segments, starting with C2-3.

3. Viewed from the head, C2-3 is 'the first in line'. The range of motion here is not very large, so the joints can reach their end position.

A non-maximal lateral bend and a non-maximal rotation of the neck can already cause the C2-3 segment to reach its end position. This puts tension on the connective tissue in the capsules, ligaments, and intervertebral disc. This is precisely why the ¾ position is a risky posture. Neck complaints can result, and as far as C2-3 is concerned, also headaches. Pain and dysfunction in lower segments than C2-3 only lead to neck complaints and not to headaches.

Without lateral bending, the load on C2-3 in the 3/4 position is much less. It is therefore important that the pillow is not too high , especially for people who know from experience that they sometimes end up in the 3/4 position during sleep.

For more information about complaints that can result from an incorrect sleeping position, click on: 'Headache: location and source'.