Thanks both of you for guiding me.
My patient is having pain during extension and walking and it relieves after rest in supine lying with knee flexed. Prone lying is also painful.
His orthopaedic had advised not to wear corset as it would cause extension of the spine and he has to prevent extension at this stage.
His lumbo sacral angle is also increased about 10 degree.
His hamstrings are also tight and pelvis is posteriorly tilted.
As stated by sd kashif I think it is posterior elemental pain and we have to start flexion exercise as the acute stage of pain subsides.