RTS + PIN Palsy

Radial tunnel syndrome and posterior Interosseous Nerve palsy are both a result of compression of the Posterior interosseous nerve with a more severe compression occurring in posterior interosseous nerve palsy.

Pathology

Radial Tunnel Syndrome (RTS) and Posterior Interosseous Nerve (PIN) Palsy are both a result of compression of the posterior interosseous nerve.

RTS results from more mild compression, and PIN Palsy occurs with more severe compression.

Posterior Interosseous Nerve (PIN) is the motor branch of the radial nerve. It arises at the lateral border of the elbow when it splits from the sensory part of the radial nerve, the superficial radial nerve.

Common Causes of PIN Compression

  • A tight fascia (layer of fibrous tissue) at the carpi radialis brevis muscle, forearm muscle that extends and abducts the wrist
  • Dense less elastic entry at the Arcade of Froshe, a fibrous arch over the PIN
  • Presence of fibrous bands along the course of the PIN
  • A arterial array of vessels branching off the radial artery called the leash of Henry vessels
  • A cystic mass or ganglion from the joint pressing on the nerve in patients with rheumatoid arthritis

Symptoms of Radial Tunnel Syndrome (RTS)

  • Pain
  • Weakness
  • Arm fatigue as a result of repetitive use or from a direct traumatic event

When the compression is more severe, there is severe weakness and an inability to raise the fingers, which is the hallmark of PIN palsy.

RTS can accompany tennis elbow in 5%-30% of cases. RTS must be considered when treating tennis elbow because not addressing existing RTS will result in persistent lateral elbow and dorsal forearm pain.

A PIN palsy in a patient without injury and that is severe or progressive is considered to be the result of a tumor until proven otherwise. An MRI of the forearm in this case is indicated.

If there is no tumor, the MRI can confirm atrophy of the muscles innervated by the PIN.

Treatment

Nonsurgical Treatment of RTS

Most RTS cases can be resolved with:

  • Activity modification
  • Home exercise program
  • A steroid injection
  • Properly conducted therapy program

The key in the therapy program is stretching the tight fascia elements of the muscles that trap and bind the posterior interosseous nerve (PIN).

About three months of supervised therapy is usually needed to fully resolve the problem. The exercise program is directed at stretching tight muscles and their respective fascia.

If tight bands, ganglion cysts or vascular leashes which are an anatomic static change are the cause of compression, these will usually not respond to stretching and will often require surgical release.

Surgery involves a short incision over the dorsal forearm that takes about fifteen minutes to perform. Only the arm is put to sleep and the use of the hand after surgery is allowed immediately.