Is there something called tmj joint lavage .. if there is how its done & why ?

Actually yes.: Lavage usually refers to injecting saline into the tempero mandibular space (under anesthesia) to free up a displaced/stuck tempero mandibular disc.

TMJ lavage: Tmj lavage is an office procedure done under i v sedation to decrease the discomfort . The operator will do what we call it TMJ dis tension and flushing of the joint with sterile saline and/or medications to increase the mobilization of the joint.

Flushing joint: A tube is placed into the joint and flushed out. Make sure your TMJ surgeon is VERY experienced with this technique.