A Prospective Evaluation of the Anatomy of the First Dorsal Compartment in Patients Requiring Surgery for De Quervain's Tenosynovitis.

 We prospectively evaluated the surgical anatomy during first dorsal compartment release for De Quervain's tenosynovitis, with special attention to the superficial branch of the radial nerve (SBRN). Additionally, the incidence of tendon instability during surgery was assessed.  This prospective cohort study consisted of 130 De Quervain's patients undergoing first dorsal compartment release. The treating surgeons recorded the type of incision used, the number of abductor pollicis longus (APL) and extensor pollicis brevis (EPB) tendon slips, the number of SBRN branches encountered, additional subcompartments created by any septations, and active/passive tendon stability.  A singular first dorsal compartment was found in 37% of cases, whereas 55% of patients had two subcompartments and 8% had three. Multiple APL tendon slips (range: 1-4) were identified in 78% of patients. In contrast, a single EPB tendon was found in 92% of patients (range: 0-2). At least one SBRN was encountered in 61% of cases. Following surgery, instability was evident in 9% of patients, who had tendons perch with passive wrist flexion. In one of these patients (<1%), the tendons dislocated volarly out of the first dorsal compartment during active flexion.  The anatomical findings in our relatively large, prospective study of De Quervain's patients undergoing first dorsal compartment release are consistent with previous smaller and/or retrospective studies. Overall, we expect to encounter the SBRN during first dorsal compartment release in more than 50% of patients but are unconcerned if it is not visualized during a careful approach. Tendon instability has an incidence of 9%; however, dislocation is rare (<1%).