30/10/2023 at 3:19 pm #55292Debbie HodderParticipant
I have been working on setting up dedicated protocols for nerve imaging of the upper limb. Was wondering do you use set protocols or do you guide the study according to the distribution of symptoms, or do you image the nerve according to the syndrome in particular that is being questioned? i.e carpal tunnel, pronator teres syndrome, anterior interosseous nerve syndrome etc.
Also wondering what protocol if any do you follow for the radial nerve? Do you assess the entire length of the nerve or do you concentrate on the potential entrapment sites?
Any helpful tips and tricks would be greatly received.
30/10/2023 at 3:30 pm #55293Stephen BirdKeymaster
I do have a protocol of sorts for median, ulnar and radial nerve examinations and then I flex the exam as the patients presentation requires.
I will outline how I go an=bout a basic median, ulnar and radial nerve examination for you. This is not comprehensive, but it is a good starting point for a basic examination for you:
Carpal tunnel protocol:
Assess median nerve starting in the mid forearm where it is easy to identify between FDS and FDP muscle bellies.
Follow the nerve in axial orientation distally and when you see pronator quadratus stop and measure the cross sectional area of the nerve. At this level also observe the pronator quadratus echogenicity, as if it showing signs of atrophy it may be due to anterior interosseous nerve dysfunction. This is most commonly caused by neuralgic amyotropy (Parsonage Turner) neuritis in the upper arm.
Then keep heading distal until you come off the radius and you see the lunate bone. At this level you will not see the scaphoid or pisiform (if you can, you have gone too far distal and need to back up a bit). At this level with the lunate measure the cross sectional area again. Now you can do a ratio between the two measurements and if the lunate measurement is more than 1.4 times greater than the pronator quadratus measurement you have a swollen nerve.
Then head distal a little more and the scaphoid and pisiform come into view with the bone between them now being the capitate.
You are now in the tunnel and may see the nerve being flattened.
Look for synovitis changes in the flexor sheaths with hypoechoic material surrounding the tendons and vascularity with Doppler. Be careful that this is not muscle belly extension from the forearm, especially if the patient is younger and their hand is open with the fingers extended.
Look at the carpal floor for arthritis changes.
Look at dynamic glide of the median nerve medially and laterally in relation to the transverse carpal ligament above the nerve during flexion and extension of the metacarpo-phalyngeal joints.
Scan a little more distal and you will see the trapezium and the hamate appear and you are now in the distal tunnel. Repeat the steps I have just described.
Then scan longitudinally and watch the nerve going into the tunnel looking for a sharp “step sign” compression as the nerve enters the tunnel.
Stay longitudinal and perform MCP joint flexion and extension again looking for glide of the nerve relative to the transverse carpal ligament above and also the flexor sheath beneath.
Look at the exit point of the tunnel for “nerve flaring” as it exits the tunnel.
Then scan into the palm of the hand and see the individual median nerve branches form.
Scan the thenar eminence in short axis to the 1st M/C and look for muscle wasting of abductor pollicis, opponens pollicis and the superficial head of flexor pollicis brevis as these are median nerve driven muscles. (You can see a detailed explanation about this trick on the website by watching the thenar eminence lesson)
Then I follow the nerve from the mid forearm proximally, through the gap between the pronator teres heads, over the elbow joint and all the way to the arm pit. I do this in short axis only and it is a quick sweep. It means I never miss a nerve sheath tumour like a neurofibroma or schwannoma etc. It also means I don’t miss other random causes of compression or displacement.
I think this makes a nice exam.
I would extend further depending on the clinical presentation.
For example if the symptoms are palm related I would include the palmar cutaneous branch.
If the anterior interosseous nerve was suspected I would look at the pronator quadratus, FDP index and FPL muscle bellies for atrophy, compare to the other side and then extend the exam to the upper arm looking for localized swellings in the postero-medial aspect of the median nerve suggesting neuralgic amyotropy.
Whatever it takes really to get the answer !
Ulnar nerve protocol:
I start with the patient supine , arm above the head, supported on a pillow. Scan in the proximal forearm where I see the ulnar nerve sitting beneath the FCU muscle. This is the cubital tunnel. Track it proximally and you see the FCU divide into the ulnar and humeral heads and the membrane between the heads is the Osborne fascia. Scan proximally until you see the bony landmarks of the medial epicondyle of humerus and the olecranon of the ulna appear and you are now in the retroepicondylar groove. Make sure there is no muscle between your transducer and the nerve. If there is, you have found an accessory muscle, the anconeus epitrochlearis.
Observe the nerve in this location looking for a muscle above it or arthritis below it as it now sits on the posterior elbow joint capsule. Follow the nerve proximally, into the upper arm and it sits on top of the medial head of triceps muscle. Look for a band of collagen displacing the nerve at this location as it enters Struthers Canal.
The I go back to the retroepicondylar groove and assess the nerve with the elbow in flexion. Simply ask the patient to bring the back of their hand in front of their chin and scan the nerve in this position. If the nerve subluxes you will find it medial to the medial to the medial epicondyle. If you find it there ask the patient to extend and flex their elbow slowly while you watch what happens to the nerve. Mostly the medial head of triceps carefully gets under the nerve and gently subluxes it over the medial epicondyle (this is gentle subluxation and of little significance). Sometimes the subluxation is rapid and the nerve snaps out of the grove, over the medial epicondyle creating symptoms and neural oedema (this vigorous subluxation is more significant.
Look at the nerve during flexion for extrinsic compression by the Osborne ligament. This is common and causes the nerve to get a “pacman” shape. This is a common cause of ulnar neuritis.
Look at the nerve in long axis assessing for any localised area of oedema or compression.
Back in short axis follow the nerve to the armpit and then down the forearm to the wrist. Distally the nerve sits deep to FCU.
I do this in short axis only and it is a quick sweep. It means I never miss a nerve sheath tumour like a neurofibroma or schwannoma etc. It also means I don’t miss other random causes of compression or displacement.
Sit the patient in a chair opposite you and look at the elbow joint for arthritis changes, effusions etc.
Then assess the ulnar nerve at the wrist. Locate the pisiform bone and the ulnar nerve sits between it and the ulnar artery. This is Guyons canal. You will see it divide into two branches. The ulnar sided branch is the motor nerve. You can follow it distally and watch it pass around the hamate and into the palm of the hand. Look for any displacement as it passes the hamate.
The sensory branch on the radial side passes into the palm of the hand and goes both sides of the little finger and the ulnar side of the ring finger.
There is a branch just before the Guyons canal called the dorsal cutaneous branch. You can follow it easily onto the dorsal / ulnar hand. It comes off before the Guyons canal so if there are sensory symptoms affecting the dorsal / ulnar hand it suggests the problem is proximal to the Guyons canal.
Then scan the thenar eminence in short axis to the 1st M/C and look for muscle wasting of 1-2 interosseous, Adductor pollicis and the deep head of flexor pollicis brevis as these are median nerve driven muscles. (You can see a detailed explanation about this trick on the website by watching the thenar eminence lesson)
Then extend the exam as necessary depending on the clinical presentation.
This makes a nice exam.
Radial nerve examination.
I start short axis above the elbow and locate the radial nerve sitting between brachioradialis and brachialis. It is easy to see here. Follow it proximally and it hugs the humerus. Keep following it as far proximal as you can to the arm pit.
In the upper arm you can see the dorsal antecubital cutaneous nerve arise from the radial nerve.
Follow the radial nerve distally towards the elbow and it divides into a deep (motor) and superficial (sensory) branch. We call the deep branch the posterior interosseous nerve (PIN).
I follow the PIN in short axis and watch the recurrent radial artery (Leash of Henry) pass by it and see if it compressed or displaced the nerve and if there is a localized PIN swelling in this area. Then I watch the PIN pass between the two heads of the supinator (this is the arcade of Frohse). Watch the nerve make its way into the supinator and see if there is an echogenic fibrous band in this location. Use resisted supination as a provocative maneuver.
Watch the PIN pass through the supinator and exit into the dorsal wad of the forearm where it splits up to motor drive the extensor muscles except ECU which is serviced by the ulnar nerve.
Look at the extensor muscle bellies and compare to the other side for atrophy changes.
Assess the PIN at the arcade of Frohse in the long axis.
Then go back to the common radial nerve and follow the superficial branch distally where it passes deep to brachioradialis and eventually emerges from beneath the brachioradialis distal tendon to enter the subcutaneous space adjacent to APL and EPB. It then divides into branched to provide sensory function on the dorsal / radial hand.
The terminal branch of the PIN can also be visualized deep to EDC (extensor compartment 4 of the wrist) where it can be followed into the dorsal wrist capsule as a pain receptor nerve.
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