.A PSI guide helps execute the preoperative plan. 
​If the surgeon choses to check the position of the guide using the floor as a reference to check inclination, an error may occur because of the positioning of the scapula.
​This may happen if an assist arm is used

Which is the best option for glenoid baseplate fixation in the elderly?
Here are some variables to consider:
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1. A 6.5 mm screw is often used. Will this gain sufficient purchase in the elderly?
2. A central post has the potential of ingrowth but has a larger diameter of a 6.5 mm screw. 
3. A revision of a post will need at least a 9.5 mm screw or a completely different hole position
​4. The dimensions of the glenoid vault will determine post perforation which may not be desirable