Basics
Description
-
PINS occurs when muscles innervated by the posterior interosseous nerve are affected secondary to entrapment of the posterior interosseous nerve by 1 of several structures.
-
The related, but separate, radial tunnel syndrome is characterized by pain and weakness on the lateral side of the elbow after activities with forceful elbow extension or forearm rotation.
Epidemiology
-
Most common in individuals 20-50 years old
-
Male and females are affected approximately equally.
Incidence
Uncommon
Risk Factors
Repetitive supinating or gripping motions are risk factors.
Genetics
No Mendelian pattern is known.
Etiology
-
Typically, involvement of >1 of the following structures:
-
Fibrous edge of the supinator muscle (most common cause), known as the arcade of Frohse
-
Fibrous bands over the radial head
-
Radial recurrent vessels to the elbow, known as the leash of Henry
-
Fibrous edge of the extensor radialis brevis muscle
-
Distal edge of the supinator
-
Associated Conditions
Lateral epicondylitis
Diagnosis
Signs and Symptoms
-
Aching pain in the muscles of the lateral forearm, just distal to the elbow (the extensor-supinator mass)
-
Symptoms usually occur after muscular effort.
-
Numbness is rare in PINS because the course of the sensory nerve is separate from that of the motor nerve.
Physical Exam
-
Complete neurovascular examination of the affected limb:
-
The area of tenderness in PINS is ~4 fingerbreadths distal to the lateral epicondyle of the elbow.
-
Pain is worsened by active supination of the forearm (turning the palm up) or extension of the wrist.
-
Pain is worsened by pressing down on the extended long finger.
-
Sensation of the forearm and hand is normal.
-
Motor strength may be diminished in chronic cases because of longstanding compression.
-
-
Diagnostic local anesthetic injection:
-
Inject local anesthetic into the extensor-supinator mass and lateral side of the elbow, on separate days, to determine where pain relief occurs.
-
Tests
Lab
Laboratory tests are not helpful for this diagnosis.
Imaging
Imaging studies are not needed unless an unusual mass is felt in the area.
Pathological Findings
-
On surgical exploration, compression of the radial nerve
-
Nerve possibly having constricted area from long-standing pressure
Differential Diagnosis
-
Lateral epicondylitis (tennis elbow): Usually a more proximal pain, directly over the lateral epicondyle or radial head (i.e., over the elbow itself)
-
Cervical radiculopathy (nerve compression in the neck): Usually associated with a more radiating pain
-
Cheiralgia paresthetica (Wartenberg symptom): Entrapment of the radial sensory nerve, producing numbness
Treatment
General Measures
-
Rest from the causative activity, if one can be identified
-
If no cause identified, immobilization of the elbow and forearm in a splint
-
Surgery if nonoperative measures are not successful
-
After nonoperative or surgical cure, slow resumption of activity
-
Repetitive supination or gripping activities limited to the extent that they do not cause discomfort
Special Therapy
Physical Therapy
-
Occupational therapy for gradual mobilization and strengthening of the elbow is begun when the splint is removed.
-
Therapy should be performed by an experienced hand therapist.
Medication
NSAIDs
Surgery
-
Surgical exploration of the path of the posterior interosseous nerve in this region, which may be an outpatient procedure
-
Release of constricting structures
-
Usually satisfactory results
-
No permanent deficit resulting from release
Follow-up
Prognosis
-
Most patients have a good result after nonoperative or surgical cure.
-
Causative activities should be modified or eliminated, if possible.
Complications
Recurrence is possible.
Patient Monitoring
Patients are followed every 3 months until the symptoms resolve.
Miscellaneous
Codes
ICD9-CM
723.4 Brachial neuritis or radiculitis not otherwise specified
Patient Teaching
-
Demonstrate motions that constrict the nerve.
-
Explain the dosing and side effects of analgesics.
-
Explain that changing manual jobs or repetitive motions may prevent the development of full-blown PINS.
FAQ
Q: How do patients with PINS present?
A: Patients present with pain at the proximal lateral forearm and weakness in the extensor muscles of the digits and wrist.
Q: Is radial tunnel syndrome different from PINS entrapment?
A: Yes. Radial tunnel syndrome affects only the sensory component of the radial nerve, and patients present with pain but not motor weakness.