OTA 2008 Posters

Scientific Poster #25 Basic Science OTA-2008

Posterior Approach to the Shoulder: The Effect of Shoulder Position on the Proximity of the Neurovascular Structures

Sunny Cheung, MD (n); Michael Fitzpatrick, MD (n); Joey Pirolo, BS (n); Thay Q. Lee, PhD (n);
Orthopaedic Biomechanics Laboratory, Long Beach VA Healthcare System,
Long Beach, Callifornia, USA

Background: The posterior approach to the shoulder is used for treatment of posterior glenoid rim, glenoid neck, and certain glenoid fossa fractures. However, the surgical anatomy of the axillary nerve, suprascapular nerve, and posterior humeral circumflex artery (PHCA), which may be at risk during such an approach, have not been well characterized across a full range of shoulder positions.

Hypothesis: Vertical abduction, forward flexion, and humeral axial rotation affect the proximity of the axillary nerve, suprascapular nerve, and PHCA with respect to the glenohumeral joint.

Methods: The Brodsky posterior approach was performed on 9 fresh-frozen shoulders. A screw was placed in the intersection of the posterior glenoid rim and the lateral scapular ridge as a reproducible bony landmark. The positions of the suprascapular nerve, axillary nerve, and PHCA were measured with a Microscribe 3DLX to the bony landmark, with the humerus placed in permutations of vertical abduction (20°, 40°, 60°), forward flexion (0°, 45°, 60°), and axial rotation (45° and 30° internal rotation, neutral, 30° and 45° external rotation) with respect to the glenoid. Repeated measures analysis of variance statistical analysis was used to compare the results.

Results: At neutral shoulder position, the distance from the posterior glenoid rim landmark to the suprascapular nerve inserting into the infraspinatus was 18.8 ± 6.55 mm; axillary nerve entering the quadrilateral space was 37.7 ± 5.3 mm; axillary nerve closest to the glenoid (often found along the nerve to the teres minor) was 27.6 ± 4.3 mm; axillary nerve insertion to the teres minor was 27.5 ± 6.8 mm; and PHCA closest to the glenoid was 45.2 ± 5.2 mm. Vertical abduction moves distal structures (posterior axillary nerve to the deltoid, anterior axillary nerve to the deltoid, PHCA at the quadrilateral space, PHCA closest to the glenoid, and PHCA insertion into the humerus) farther laterally from the glenoid by 6, 3, 2, 1, and 5 mm, respectively (P <0.05). Forward flexion moved the anterior axillary nerve to the deltoid, PHCA insertion into the humerus, and the nerve to the teres minor farther anteriorly by 5, 3, and 3 mm, respectively (P <0.05). External humeral rotation moved the anterior axillary nerve to the deltoid closer posteriorly by 2 mm, the PHCA closest to the glenoid farther anteroinferiorly by 2 mm, and the PHCA at the quadrilateral space farther anteroinferiorly by 1 mm (P <0.05).

Conclusion: Although vertical abduction, forward flexion, and external rotation can cause a statistically significant effect on the positions of the neurovascular structures in relation to the posterior glenoid, the magnitude may not be clinically significant. Still, knowledge of the absolute distances and positions of the neurovascular structures to the glenoid may help avoid iatrogenic injury during internal fixation of the posterior glenoid. In addition, surgeons should be aware that the nerve to the teres minor is about 1 cm closer to the glenoid than the main trunk of the axillary nerve.

If noted, the author indicates something of value received. The codes are identified as a-research or institutional support; b-miscellaneous funding; c-royalties; d-stock options; e-consultant or employee; n-no conflicts disclosed, and *disclosure not available at time of printing.

• The FDA has not cleared this drug and/or medical device for the use described in this presentation   (i.e., the drug or medical device is being discussed for an “off label” use).  ◆FDA information not available at time of printing. Δ OTA Grant.