Internal rotation of the shoulder in the beach chair position may increase the risk of iatrogenic suprascapular nerve injury at the spinoglenoid notch during surgical treatment for shoulder instability

Purpose Suprascapular nerve (SN) at the spinoglenoid notch is a mobile structure which is vulnerable to iatrogenic injury from screw or guidewire penetration during shoulder surgery such as Latarjet procedure or SLAP/Bankart repairs. The primary objective is to identify the distance between posterior glenoid and SN in different shoulder abduction and rotation. The secondary objective is to identify the distance in standard lateral decubitus position. Methods Nineteen shoulders from 10 Thiel embalmed soft cadavers were used in this study. The dissection of posterior shoulder was done to identify the SN at spinoglenoid notch. The distance between the posterior glenoid rim and the SN was measured. In beach chair position, the SN distance from six combinations of shoulder position was obtained: adduction/90 degrees internal rotation (ADIR), adduction/neutral rotation (ADN), adduction/90 degrees external rotation (ADER), 45 degrees abduction/90 degrees internal rotation (ABIR), 45 degrees abduction/neutral rotation (ABN), 45 degrees abduction/90 degrees external rotation (ABER). Subsequently, the suprascapular nerve distance was measured in standard lateral decubitus position with 10 lbs. longitudinal traction. Results In the beach chair position with the shoulder in adduction, the mean distances between the glenoid and the SN in ADIR, ADN and ADER were 15.0 +/- 3.3, 19.3 +/- 2.6 and 19.5 +/- 3.1 mm, respectively. During shoulder abduction, the mean distances when the shoulder was in ABIR, ABN and ABER were 15.2 +/- 3.4, 19.4 +/- 3.0 and 19.3 +/- 2.6 mm, respectively. The mean distance for the lateral decubitus position was 19.3 +/- 2.4 mm. The distance between the glenoid and SN was significantly shorter when the shoulder was positioned in internal rotation than in neutral (p < 0.001) or external rotation (p < 0.001) when compared to the same shoulder abduction position. The lateral decubitus position had comparable SN distance with the shoulder position of abduction/neutral rotation in beach chair position. Conclusion The SN was closest to posterior glenoid rim if the shoulder was in internal rotation. Therefore, shoulder internal rotation must be avoided during guidewire and cannulated screw placement in the Latarjet procedure and drill bit insertion during anchor placement in SLAP/Bankart repair.