The split portal: Description of a new accessory posterior portal for arthroscopic shoulder instability procedures.

ABSTRACT

PURPOSE: Open approach to the posterior shoulder during bone block for posterior shoulder instability is challenging. Anatomical study was performed to identify landmarks of a portal, avoiding soft tissue damage, between the infraspinatus (IS) and teres minor (TM) muscles and distant from the supra-scapular nerve (SSN) for arthroscopic shoulder bone block. METHODS: Eight fresh-frozen cadaveric shoulder specimens were used. The arthroscope was introduced through the soft point (SP). A guide wire was placed through the SP, in the rotator interval direction. A posterior open dissection exposed the split between the IS and TM. A new guide wire was placed into the split, parallel to the first wire, to locate the new posterior arthroscopic approach. Ten distances were measured to define the safe position. RESULTS: The mean values were SP to split IS-TM 2 ± 0.2 (2-2.8); spinal bone to split IS-TM 5 ± 0.5 (3-6.2); split IS-TM to posterior glenoid 6 o'clock 1.3 ± 0.3 (0.6-1.6), 9 o'clock 1.5 ± 0.3 (1-1.9), and 12 o'clock 2 ± 0.1 (2.1-2.4); SSN to posterior glenoid 6 o'clock 2.4 ± 0.2 (2.1-2.6), 9 o'clock 1.7 ± 0.1 (1.5-1.8), and 12 o'clock 1.5 ± 0.3 (1.2-2.1); and SSN to split IS-TM 2 ± 0.3 (1.2-2.1). CONCLUSION: This preliminary anatomical study described a posterior arthroscopic portal located 2 cm under the SP, parallel to the SP portal direction, and finishing between 7 and 8 o'clock at the posterior rim of the glenoid. For arthroscopic shoulder bone block, this portal can avoid muscle and SSN lesions.