Final answer:
Perpendicular insertion of GB-21 (jianjing) carries a substantial risk of injuring the lungs, especially in thin patients. Careful technique is needed to avoid a pneumothorax. The trapezius muscle, phrenic nerve, and suprascapular artery are not at high risk for injury at this particular point. Option 3.
Step-by-step explanation:
When considering perpendicular insertion of GB-21 (jianjing), especially in thin patients, there is a substantial risk of injuring the lungs option 3. The GB-21 acupuncture point is located on the shoulder and is in proximity to the lungs, particularly if the patient is thin or has less muscle mass. Perpendicular insertion at this point can potentially lead to a pneumothorax, which is a collapsed lung, if the needle punctures the pleura (the membrane surrounding the lungs). Hence, careful insertion technique and depth control are crucial to avoid this serious complication.
In contrast, injuring the trapezius muscle or the suprascapular artery would not typically be associated with perpendicular insertion at this point, as these structures are not located in a position that would be at high risk for puncture. The phrenic nerve also does not typically run in the immediate area of GB-21 and would be unlikely to be injured through acupuncture at this site.