Transient synovitis in adults?

Hey super physios.
I would like to know what causes transient synovitis in adults. To be specific this condition affected the right hip which was constantly subjected to stress. The patient is a 35 year old physiotherapist with a history of hormonal imbalance who was using her left knee as a fulcrum when performing passive hamstring stretching on his clients.
The pain started suddenly and was aggravated by movement. SLR was possible by slightly painful durIng. eccentric return.
She was given a thrust in the hip by other physios and the pain seemed to spread to the mid thigh.
The pain got worse and SLR became impossible. Investigations revealed low levels of vitamin D with a sickle cell trait.
X-ray showed a ?? pseudo hairline fracture ?? of the proximal 1/3 of neck of femur.
There was a positive trendelenburg's sign and gait.
After three months of strict bed rest, the pain subsided and MRI only revealed oedema in the right hip with a probable diagnosis of ??Transient Synovitis??
How common is TS in adults with such a history?