Why is the procedure for Partial Knee Replacement (UKR) done for?
Partial knee replacement done for selective arthritis for the medial side of knee. Osteoarthritis of the knee commonly starts either from the medial side of knee or from patellofemoral joint. Arthritic change of medial side of knee joint starts from anterior part of femur and tibia. With the progression of arthritis cartilage damage extends posteriorly. This happens due to progressive changes in ACL due to arthritis and its loss of integrity. In advance stage ACL becomes incompetent and femur joint sublux posterior on tibia and cartilage degeneration happens on entire length of medial tibia surface. With further progression of arthritis other parts of knee joint cartilage also start getting degeneration. It has been seen that 40% of all grade IV osteoarthritis (full thickness cartilage loss) only the medial side of the joint is affected. Due to this selective involvement of cartilage all ligaments of the knee joint remain functional and cartilage of other parts of the joint remains as healthy as normal joints. This pattern of arthritic involvement is called anteromedial OA (AMOA). For AMOA replacing all the surfaces of joints with TKR is an overdo. Only replacing the damaged medial part of the joint can solve the problem of arthritis disability. Though no ligament is sacrificed in partial knee replacement normal feeling and full functional recovery is possible.
What are the different choices for UKR prosthesis?
Mainly there are two types of UKR prosthesis available: mobile bearing and fixed bearing implant. In mobile bearing the spacer articulation moves along with the femur during full range of knee movement. Whereas in fixed bearing design femur roles on polyethylene surface. Implant components are fixed at the bony surface either with the help of bone cement or the uncemented implant are designed to develop bony ingrowth and bonding to hold the implant in place. Mobile bearing implant is the most popular one which is known as ‘OXFORD’ knee.
How is the procedure done?
Skin incision is the same as TKR but is smaller and the joint can be accessed only by incising capsule and muscle need not to cut. No ligament need to sacrifice and no tissue release is required. Space between femur and tibia is equalised in flexion and extension and surface prepared to place the femur and tibia component. All these are done with the help of recommended jigs, instruments and technique specific for the implant to be used.
How does recovery happen?
Anaesthesia and perioperative management protocol is the same as TKR. Though surgical insult is far less than TKR the recovery is very fast in comparison to TKR. If good postoperative pain control is possible it’s like nothing has been done and the patient can perform all day to day activities like preoperative status. Within 2 weeks of surgery one can resume all their normal day to day activity without any restriction. Requirement of analgesic and other supportive treatment post-surgery is far less than TKR. As no ligaments are sacrificed in this surgery, normal reflexes of the knee joint is maintained.
What should you expect from the procedure?
One should expect full functional recovery and be able to do all normal activities, even recreational sports and dance. Regains full range of knee movement as normal knee, so can sit cross legged and squat.