An Infamous Point
GB21 is a famous point – or should I say “infamous”.
Not just because is it helpful for many neck and shoulder issues, helpful for inducing labour (therefore, contraindicated in pregnancy!) and the milk reflex but also famous for not so great things – it is the most common point for people to cause a pneumothorax with.
Please note that although it is the most common point for a pneumothorax, it does not happen very often.
If you know what you are doing and how to needle this point, you will never have to worry about causing this totally preventable issue. Just be sure to be extra cautious with thin subjects when needling GB21.
The Location
Location of GB21 requires some anatomical landmarking.
The first anatomical landmark to locate is the midline or in this case, C7. Finding the midline, however, is all you really need. The next anatomical landmark is the lateral tip of the acromion. Be sure you’re on the lateral tip…a lot of people seem to measure from the AC joint rather than the most lateral tip of the acromion.
Once you have these two landmarks, split the distance in half.
Now we need to find the highest point of the shoulder. To do this, you need to get down to eye level and find the highest point of the shoulder – not too far in front (anteriorly) and not too far towards the back (posteriorly) – enough so that your pen mark is just barely visible when you are looking at this point at eye level. Midway between the midline and the lateral tip of the acromion at the highest point of the shoulder – this is GB21.
Common Mistakes
Common location errors mostly include incorrect anatomical landmarking.
Finding the midline should be easy. Finding the lateral tip of the acromion seems to give people trouble – literally look for the most lateral end of the bone.
The other error is that people are too far towards the front of the body or too inferior to the point (often putting you on top of SJ16. Get down to eye level before you make your mark for GB21 and this will prevent this error.
Watch my video on the details of why GB21 is associated with pneumothorax – and never let this happen in your practice.
