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)
- 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.