Tibia knee fracture healed MRI clear still knee pain anf pain when bending knee. When standing leg not straight?

Nerve injury. Knee injuries may be associated with nerve damage at times which is quite painful- many people guard their knees (avoid use due to fear of pain) and may develop contraction deformities and adhesions which may explain your lack of range of motion. You may need to revisit with your surgeon or seek expert opinion with pain specialist.
Need therapy. Pain and stiffness of joints around a fracture are common. To recover from a fracture it takes more than just having the bones heal. If your knee doesn't go all the way straight that alone can cause problems and pain due to an altered gait. Speak to the doctor that treated your fracture. I think that you would benefit from a physical therapy evaluation.