Abstract
Background
Reverse Geometry shoulder replacement requires fixation of a base plate (called a metaglene) to the glenoid to which a convex glenosphere is attached. Most systems use screws to achieve this fixation. The suprascapular nerve passes close to the glenoid and is known to be at risk of injury when devices and sutures are inserted into the glenoid. We investigate the risk posed to the suprascapular nerve by placement of metaglene fixation screws.
Materials and Methods
Ten cadaveric shoulder specimens were used. A metaglene was inserted and fixed using 4 screws. The suprascapular nerve was dissected and its branches identified. The screw tips and their proximity to the nerve and branches were identified and recorded.
Results
The superior and posterior screws posed most risk to the suprascapular nerve. The nerve was engaged by the posterior screw on 4 occasions and was within 5 mm of the nerve or a branch of it in 5 others. The superior screw was extra osseous on 4 occasions, making contact with the nerve on 3 of those 4 specimens and being within 2 mm of it on the 4th.
Conclusion
Metaglene fixation using screws poses a significant risk to the suprascapular nerve. Caution should be used when inserting the posterior and superior screws in particular. Short locking screws may allow adequate fixation while minimizing the risk of neurological injury.
