What Causes Difficulty In Lifting The Leg Post Removal Of Screws In Hip?

Hi. Im in the ER with my 85 yo dad. He had acrews removed from right hip 5 days ago anticipating THA in 8 weeks. Im a FNP. i zee no new dx on XRAY. severe OA especially mexial acetabular margins. Why is it that he suddenly can t lift leg at a 90-90 degrees. Just curious about the possible pathophysiology.