Communicating foramen between the tendon sheaths of the extensor carpi radialis brevis and extensor pollicis longus muscles: imaging of cadavers and patients.

OBJECTIVE: The purpose of this study was to examine the anatomic features and imaging appearance of the intersection of the extensor pollicis longus (EPL) tendon with the extensor carpi radialis brevis (ECRB) and longus (ECRL) tendons in cadavers and patients.

MATERIALS AND METHODS: MR and CT tenography were performed on 10 cadaveric wrists, and tenosynovial endoscopy and dissection of the EPL tendon sheath were performed on five additional cadaveric wrists. A computer-assisted search of dictated MRI reports identified 12 wrists of patients with simultaneous EPL tenosynovitis and ECRB and ECRL tenosynovitis. The relation between EPL tenosynovitis and ECRB and ECRL tenosynovitis was studied with chi-square testing. Interobserver agreement was calculated with kappa statistics.

RESULTS: MR and CT tenography revealed a communicating foramen between the sheaths of the ECRB and EPL tendons in all 10 cadavers studied. Endoscopic evaluation and dissection of five additional cadaveric wrists further confirmed the presence of foramina. In the patients, the presence of EPL tenosynovitis and that of ECRB and ECRL tenosynovitis had strong correlation (p < 0.001). The incidence of simultaneous EPL tenosynovitis and ECRB and ECRL tenosynovitis in our referral population of wrist MRI examinations was 0.8% (12/1,540).

CONCLUSION: A normal foramen exists between the sheaths of the EPL and ECRB tendons where they intersect in the wrist. Such foramina allow synovial fluid to communicate between the tendon sheaths and probably account for the high prevalence of tenosynovitis in more than one tendon on clinical MRI studies.