A diagnosis often missed by physical therapists and often slides under the radar is Posterior Interosseous Nerve Entrapment Syndrome (PINS). Often the physical therapist (PT) receives a script from a specialist or primary care physician (PCP) and follows those directions to a “T”. It is important for the PT to perform a thorough physical therapy examination in order to corroborate or deny the prescription from the MD/DO. PT’s must not forget that all lateral elbow pain is not “tennis elbow”. PINS are part of the differential diagnosis and should not be overlooked.
The posterior interosseous nerve runs from cervical vertebrae seven and eight (C7 and C8) and descends on the interosseous membrane, in front of the Extensor pollicis longus muscle. The posterior interosseous nerve may be entrapped at the Arcade of Frosche, which is part of the Supinator muscle. Posterior interosseous neuropathy is purely a motor syndrome resulting in finger drop and radial wrist deviation on extension. The PIN innervates the following muscles Extensor carpi radialis brevis, Extensor digitorum, Extensor digiti minimi, Extensor carpi ulnaris, Supinator, Abductor pollicis longus, Extensor pollicis brevis, Extensor policis longus, & Extensor indicis. Patients commonly have tenderness over lateral epicondyle & almost always have tenderness more distally over the arcade of Frosche. Pain complaints are almost always experienced with resisted supination of the forearm and frequently with resisted pronation. Full pronation of forearm produces pressure on the PIN by the sharp tendinous edge of the origin of ECRB muscle. This is why most often we correlate this injury with lateral epicondylitis in its early stages. Also the Tinel Test usually proves positive and the patient may feel buzzing in the forearm hand after this provocative test.
Treatment for this at the initial onset of the complaint is optimal. The research shows an indirect relationship between time to treatment and prognosis. The physical agent of choice is moist heat and paraffin if available. Longitudinal and cross friction massage is prescribed along with radiocapitular joint mobs, Radio-Ulnar mobs, active and passive release treatments along with neural flossing of the peripheral nerve. Positional release techniques work great, both static and dynamic flexibility exercises are critical, and strength exercises is also prescribed for both acute and long term maintenance.
Next time your patient points to that point two to three fingers below their elbow at the fleshy part of their forearm (near the brachioradialis muscle adjacent to the wrist extensors), make sure PINS is in your differential diagnosis.
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