OTA 2008 Posters

OTA 2008 Posters

Scientific Poster #26 Basic Science OTA-2008

Morphometric Analysis of Vulnerable Neurovasculature (“Danger Zones”) with a Posterior Approach to the Scapula

Coen A. Wijdicks, MSc1 (n); Bryan M. Armitage, MSc1 (n); Jack Anavian, MD2 (n); Peter A. Cole, MD2 (a-Zimmer);
1Department of Orthopaedic Surgery, University of Minnesota, Minneapolis, Minnesota, USA;
2Division of Orthopaedic Trauma, Department of Orthopaedic Surgery, University of Minnesota,
Regions Hospital, Saint Paul, Minnesota, USA

Purpose: A recent study found that 90% of surgically treated scapula fractures required a posterior surgical approach to facilitate open reduction and internal fixation. To our knowledge, there have been no comprehensive studies that quantitatively describe spatial relationships of the suprascapular nerve and ascending branch of the circumflex scapular artery to the posterior surgical approach to the scapula. We aimed to define the topographic distribution in which these vulnerable structures are most commonly found, thus establishing “danger zones”.

Methods: 24 nonpaired fixed cadaveric specimens were dissected for analysis. The infraspinatus and teres minor musculature were elevated off the posterior scapula body to reveal the suprascapular artery and nerve as they emanated from the spinoglenoid notch. Additionally, the plane between the infraspinatus and teres minor was carefully dissected down to the lateral scapula border to visualize the ascending branch of the circumflex scapular artery and its associated bony groove. Radial coordinates were established using a goniometer pinned to the medial extent of the scapular spine to determine location of critical structures relative to osseous landmarks. These coordinates were then converted into a frequency map for the neurovascular structures. We therefore identified critical areas where arteries and nerves are vulnerable to injury (danger zones).

Results: The suprascapular neurovasculature was exposed along the undersurface of the infraspinatus muscle and its trunk was always adjacent to the base of the acromion as it traversed the spinoglenoid notch. The mean distance from the spinoglenoid notch to the medial border of the suprascapular nerve where it entered the muscle was 2.5 ± 0.6 cm (range, 1.3-3.8 cm). The mean distance from the spinoglenoid notch to the inferior border of the suprascapular nerve danger zone was 2.4 ± 0.6 cm (range, 1.2-3.8 cm). The mean distance from the medial extent of the scapular spine to the medial border of the suprascapular nerve danger zone was 4.3 ± 0.8 cm (range, 3.0-6.7 cm). The entry of the ascending branch of the circumflex scapular artery was located 5.6 ± 0.7 cm (range, 4.5-7.0 cm) inferior to the spinoglenoid notch at the lateral border and 8.0 ± 1.2 cm (range, 5.6-9.5 cm) superior to the inferior angle apex of the scapula. A normalized scapula with pertinent bony landmarks was overlaid with both the suprascapular nerve and ascending branch of the circumflex scapular artery, and reflected as shaded danger zones to demonstrate these distance measurements.

Conclusion and Significance: This is the first study with a detailed morphometric, anatomical assessment of the suprascapular nerve and the ascending branch of the circumflex scapular artery. The suprascapular nerve was located in a vulnerable location, where it curves around the base of the acromion through the spinoglenoid notch. Similarly, the ascending circumflex scapular artery also curves around the lateral aspect of the scapula and thus is highly vulnerable to common fracture patterns and possibly retractors placed over the lateral border. Familiarity with these anatomical landmarks can help the surgeon determine risk for suprascapular nerve injury and aid in the selection of surgical approach and intraoperative surgical maneuvers.