While many people preparing for their USMLE Step 1 exams tend to focus on the tougher subjects like Pathology and Pharmacology, it is imperative that you do a good review of your Anatomy material because you are guaranteed to get a few really easy questions. If you take just a little bit of time to go through the high-yield anatomy notes from your review books or course, you are going to get an easy 5-7 points on your exam, which as you may know can be the difference between a sub-200 score and an above-200 score.
In order to make this process as easy for you as possible, I am going to outline five common injuries that are related to the brachial plexus, which is a very high-yield USMLE topic.
Here we go:
Median Nerve Injury – this commonly results from an injury to the supracondyle of the humerus, and results in a loss of the following:
– forearm pronation
– wrist flexion
– finger flexion
– thumb movement
And it also results in a loss of sensation to the thumb, lateral aspect of the palm, and the first 2.5 fingers.
Radial Nerve Injury – this occurs commonly when there is an injury to the shaft of the humerus, and results in the following:
– loss of triceps reflex
– loss of brachioradialis reflex
– loss of carpi radialis longus
These symptoms lead to the commonly known “wrist drop”, as well as a loss of sensation to the posterior antebrachial cutaneous and the posterior brachial cutaneous nerves.
Ulnar Nerve Injury – this occurs with injury to the medial epicondyle of the humerus, and causes the following problems:
– impaired flexion and adduction of the wrist
– impaired adduction of the ulnar two fingers and the thumb
There is also a loss of sensation to the medial aspect of the palm, as well as loss of sensation to the medial half of the ring finger and the pinky.
Axillary Nerve Injury – occurs as a result of injury to the surgical neck of the humerus and/or an anterior dislocation of the shoulder, resulting in the following:
– complete loss of deltoid movement
– loss of sensation over the deltoid muscle as well as the skin covering the inferior aspect of the deltoid
These are four common brachial plexus related injuries, and are very likely to present themselves on your USMLE Step 1 and/or Step 2 CK exams. Be aware that they will be disguised as clinical vignettes, but also refer back to your basic knowledge in order to choose the most accurate answer.