The entrapment of posterior interosseous nerve (PIN) on the forearm is a compressive neuropathy of the upper arm, which is characterized by weakness of finger and wrist extension and pain on the affected area. The diagnosis of PIN compression syndrome requires thorough clinical evaluation and differential diagnosis. The inability of finger extension, the presence of space-filling lesion and the failure of conservative treatment require surgical decompression. Purpose of the report is the presentation of a series of cases with PIN compression syndrome, with non-traumatic etiology, which were surgically treated.

25 patients (12 male, 13 female) with an average age 38 years old (28–60) were surgically treated for PIN decompression from May of 2018 until June of 2023. 18 patients were manual laborers and 8 performed sports with the use of the affected arm. No patient presented with a neurologic or rheumatologic co-morbidity. All patients were submitted to plain radiographs, magnetic resonance imaging and EMG study. 22 patients presented PIN compression on the course of the nerve that passed through the supinator muscle or extensor capri radialis brevis or the leash of Henry or the arcade of Fröhse. 3 patients developed compression due to a lipoma. All patients at the time of the surgery had presented symptoms on the average 3.5 months (2–11 months). In 15 cases was performed posterior approach and in 10 anterior. In all cases nerve decompression was performed in all possible sites of its course. In 3 cases intraoperatively was recognized and removed fibrous connective tissue with PIN compression.

3 patients presented with postoperative haematoma, without the need of drainage. 20 patients (80%) regained their finger extension in 2–7 months. 5 patients (20%) did not regain their finger extension, 3 of them were submitted to tendon transfers. The median quickDASH score was improved from 51 to 87. No patient developed infection or recurrence of the compression syndrome.

PIN decompression has shown the most impressive results concerning the finger and wrist motion.

The differential diagnosis and surgical treatment of PIN compression syndrome are challenging. The surgical decompression has positive results in patients who are treated on the early onset of symptoms and the conservative treatment has failed. The pre-op imaging is necessary, and the interpretation of electromyography is substantial to the prognosis of the re-enervation.