Nerve Compression Syndromes Flashcards
How is nerve conduction in the carpal tunnel reported?
In terms of “latency,” with the unit being milliseconds (ms).
What is “latency”?
The time it takes for an electrical stimulus to travel along a nerve from the site of stimulation to a recording
electrode in a target muscle.
What is the normal value for motor latency at the carpal tunnel?
Less than 4.0 ms.
How is nerve conduction at the elbow reported?
In terms of velocity (m/s).
What is a clinically significant decrease in velocity at the elbow?
10 or more m/s.
What is the difference between compressive neuropathies and peripheral neuropathies?
In peripheral (systemic) neuropathies, the nerve conduction is decreased diffusely both proximally and distally in
multiple nerves.
What are typical electromyography (EMG) findings for long-standing nerve compression and axonal damage?
Wide biphasic fibrillation potentials.
What is the double crush syndrome?
A proximal site of nerve compression predisposes the peripheral nerve to a second distal site of compression. For
example, patients with cumulative or repetitive trauma or stress often have problems from the neck to the hand.
What nerve is affected with thoracic outlet syndrome (TOS)?
Lower trunk of brachial plexus with symptoms mimicking cubital tunnel syndrome.
What are the contents of the “thoracic outlet”?
Subclavian vein, subclavian artery, and brachial plexus.
TOS is more common in what gender?
Female (3.5:1).
Within the population of patients with cervical ribs, how many are bilateral?
50%.
When do patients with TOS typically get their symptoms (ulnar-sided numbness)?
When their arms are above their heads.
What is Adson maneuver?
Dampening of radial pulse with inhalation, neck extension, and head rotation to the affected side in patients with
TOS. There are varying descriptions of how to perform this maneuver.
How accurate is an Adson maneuver?
False positives are so common that test is thought of in terms of historical interest only.
What is Wright maneuver?
Reproduction of TOS symptoms or dampening of radial pulse with arm hyperabducted and head in neutral or
turned away from the affected side.
How accurate is Wright maneuver?
It is positive in 7% of normal patients and thus should be used only to support a diagnosis of compression in
patients with arterial symptoms.
What is Roos maneuver?
Both arms are put into 90◦ of abduction and external rotation and the patient is asked to open and close the hands for 3 minutes. Many patients will have forearm fatigue, but patients with TOS have reproduction of their symptoms.
How accurate is Roos maneuver?
It is the most reliable of the three maneuvers noted. However, some patients with carpal tunnel syndrome (CTS) and no TOS will develop symptoms limited to the median nerve distribution.
What are the electrodiagnostic testing results seen with TOS?
Negative EMG for ulnar nerve, positive somatosensory evoked potentials with arm in offending position.
What is the first-line therapy for TOS?
Conservative treatment with exercises to strengthen the shoulder girdle, weight loss, and occasionally breast
reduction in women.
Name the two approaches to the thoracic outlet.
Supraclavicular and transaxillary.
What is similar and what is different about the presentation of TOS and cubital tunnel syndrome?
Similar: ulnar distribution numbness; different: TOS has medial forearm numbness.
How do you tell the difference between ulnar nerve compression at the cubital tunnel from compression at the wrist (Guyon canal)?
Sensory changes on the dorsoulnar hand.
The dorsal sensory branch of the ulnar nerve branches from the main ulnar nerve approximately 7 cm proximal to the pisiform, providing sensation to the dorsoulnar hand. Therefore, patients with cubital tunnel compression should have some difference in sensation of the dorsoulnar hand between the affected side and the unaffected side.
What is the distribution of motor weakness seen with cubital tunnel syndrome?
Flexor digitorum profundus (FDP) of ring and small fingers, ulnar intrinsic muscles.
Describe Froment sign.
With ulnar nerve palsy, patients compensate for lack of adductor pollicis (ulnar innervated) function by flexing the thumb interphalangeal (IP) joint (pinch power then provided entirely by the median innervated flexor pollicis longus [FPL]).
What are potential sites of ulnar nerve compression?
- Arcade of Struthers—an upper arm fascial arcade through which the nerve passes. Present in 70% of patients.
- Intermuscular septum between the brachialis and medial head of triceps. Can cause compression even in absence of arcade of Struthers so they are distinct.
- Medial head of triceps—whether by hypertrophy (bodybuilders) or anterior subluxation over medial epicondyle.
- Osborne ligament—a fascial arcade formed between the two heads of the flexor carpi ulnaris (FCU). The most
common site of compression. - Flexor-pronator aponeurosis—a fascial band between the flexor digitorum superficialis (FDS) and the FDP.
- Guyon canal—at the wrist (see Figure 34-1). Second most common site of entrapment.
Where is the arcade of Struthers?
8 cm proximal to the medial epicondyle of the elbow.
What is the cubital tunnel?
Floor—medial collateral ligament of elbow (spans from medial epicondyle to olecranon).
Roof—Osborne ligament.
Sides—medial epicondyle and olecranon (to which the above two structures attach).
What are implicated as the main compressive structures in cubital tunnel syndrome?
Arcade of Struthers, intermuscular septum, Osborne ligament or band (fascia connecting ulnar and humeral heads
of FCU), and the flexor–pronator aponeurosis.
Explain why the elbow hyperflexion test elicits symptoms of cubital tunnel syndrome?
- Elbow flexion increases the distance the ulnar nerve has to travel to traverse the elbow.
- Feel your own olecranon and medial epicondyle with your elbow extended. Now flex your elbow and feel how the distance between them grows, tightening Osborne ligament and compressing the nerve.
How sensitive is electrodiagnostic testing at the elbow?
50% false-negative rate for nerve compression in this region.
What is a Martin–Gruber anastomosis, and what is its significance in relation to cubital tunnel syndrome?
Interconnection between the median and ulnar nerves at the level of the forearm; presence of this anomalous interconnection can result in spared intrinsic muscle function with cubital tunnel syndrome (because the median nerve innervates the intrinsics in this situation).
What is a Riche–Cannieu anastomosis?
Interconnection between the median and ulnar nerve in the hand, typically the deep or motor branch of the ulnar nerve. Again, there may be confusion for the examiner as muscles usually innervated by the ulnar nerve continue to function.
What are the key steps involved in anterior submuscular ulnar nerve transposition?
Release of FCU origin, transposition of ulnar nerve anterior to medial epicondyle, resuturing of FCU to epicondyle.
So you have to do at least a submuscular transposition of the nerve, right?
Maybe not. In 1957, Geoffrey Osborne, a British orthopedic surgeon, reported 13 cases of cubital tunnel syndrome in which he released the ligament or band that now bears his name noting that it was tight in elbow flexion but lax in extension. These patients did no differently than those patients having a formal transposition. Several studies since then have supported this treatment.
