Knee Stiffness can occur after any surgery which is done with in the joint(intra-articular) as in your case.
You have mentioned that you are doing physiotherapy since last 6 weeks. In usual circumstances , patients regain full knee motion in this period. This hasn't happened in your case.
Next Steps
You should ask physiotherapist whether further motion cam be achieved with physiotherapy. If yes then continue with physiotherapy. If no then consult orthopaedic surgeon for further treatment.
This might require surgery.
Health Tips
Don't do physiotherapy with undue force as it can cause fracture also. With that in mind , do not worry as there are good chances that you'll improve with physiotherapy.