Abstract & Commentary
Synopsis: This descriptive, anatomic, cadaveric study evaluates and confirms the safety of a low-posterior arthroscopy portal to access the inferior capsular recess of the glenohumeral joint.
Source: Davidson PA, Rivenburgh DW. The 7-o’clock posteroinferior portal for shoulder arthroscopy. Am J Sports Med. 2002;30:693-696.
Davidson and Rivenburgh studied the 7-o’clock posterior-inferior portal for safety with regard to proximity of the axillary and suprascapular nerves in addition to the risk of injury to the articular cartilage. They evaluated the relationship of the 2 closest nerves in 6 paired cadaveric shoulders using both the outside-in and inside-out techniques. They used an anterosuperior portal for passing the inside-out Wissinger Rod. They studied the distance in millimeters and the angle of divergence necessary to injure the nerves.
Davidson and Rivenburgh showed that the suprascapular nerve (28 mm) and the axillary nerve (39 mm) are sufficiently far from the posteroinferior portal to be considered safe. The inside-out technique resulted in a portal approximately 5 mm further from either nerve than the outside-in technique. There was no significant difference in the distance between both nerves and the posterior-inferior portal with varying arm position: flexion-extension or abduction-adduction. The angle of divergence from the intended portal path necessary to injure the axillary nerve was 47° and 33° to injure the suprascapular nerve.
Davidson and Rivenburgh showed that the portal penetrated the teres minor muscle in all cases. They note that with the inside-out technique, it is essentially impossible to injure the suprascapular neurovascular structures since they are medial to the glenoid. However, with a tight shoulder, the Wissinger Rod may cause iatrogenic injury to the articular surface.
Comment by Marc R. Safran, MD
Accessory portals for arthroscopy of any joint are helpful to gain access to areas that may otherwise be difficult or impossible to reach. The safety of a posterior inferior shoulder portal is important to establish and have the information disseminated for several reasons. First, the anterior inferior portal for shoulder arthroscopy has been shown to not be entirely safe for routine use. Access to the inferior capsular recess is important, however, to help remove loose bodies from the axillary pouch and for arthroscopic shoulder stabilization and capsulorraphy procedures.
There is the concern for crowding with 2 posterior portals; however, not any more so than with 2 anterior portals, which is routinely performed with shoulder stabilization. However, with a 9-o’clock posterior portal, these 2 portals may be too close for easy manipulation of instrumentation. Thus, it would be recommended to have a 10:30 posterior portal in addition to the 7-o’clock posterior portal.
It would be advisable for the arthroscopic surgeon to practice this posterior-inferior portal in cadavers and in patients with loose shoulders using the inside-out technique before attempting the outside-in technique. Using the inside-out technique in a tight shoulder risks injury to the articular surfaces and thus should be reserved for those without a tight shoulder. The surgeon not familiar with this portal should not begin with the outside-in technique until he is familiar with the correct angle of portal insertion. Knowing the correct path of the portal helps reduce divergence from the appropriate path, as divergence may result in neurologic injury. Once familiar with the correct angle of inclination of the trocar and sheath, using the outside-in technique appears to be safe, provided the trocar is blunt. Arthroscopic identification of the proposed portal with a spinal needle can also be helpful.
Dr. Safran, Co-Director, Sports Medicine, Associate Professor, UCSF Department of Orthopaedic Surgery, San Francisco, CA, is Associate Editor of Sports Medicine Reports.
This descriptive, anatomic, cadaveric study evaluates and confirms the safety of a low-posterior arthroscopy portal to access the inferior capsular recess of the glenohumeral joint.
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