hi vishal,welcome to healthcare magic,your father must be suffering from osteoarthritis
of knee joint.In this disease there is degenration of joint cartilage
due to which joint space seems to be reduced on x-Rays.
Knee replacement surgery involves replacement of articular surfaces with artificial implants.this is the best option when conservative treatment fails to give result interms of pain and mobility.
where as ilizarov surgery involves lengthening of bones by creating an artificial fracture
and both ends separated on regular interval of time.
Ilizarov surgery is done on the shaft of bone not on the articulating surfaces of bone. so, in your father case total knee replacement
surgery is best option.
Drawbacks are : its a costly surgery. other disadvantages are same as in case of any other major surgery.
Patient has to make lots of effort after the surgery and physiotherapy
is the key to achieve success.