Why is the procedure for Total Knee Replacement (TKR) done for?
Total Knee Replacement (TKR) is done to establish a pain free function of the knee joint when the joint becomes painful due to destruction of cartilage. There are many reasons when knee joint cartilage can be destroyed, like osteoarthritis, rheumatoid arthritis, ankylosing spondylitis, tubercular infection, septic arthritis, following fracture around knee, meniscus and ACL injury. TKR is being done to improve joint stability, alignment and range of motion by balancing all the ligament around the knee both in flexion and extension of joint as well as reduce pain by replacing arthritic surface.
What are the different choices for TKR prosthesis?
Main components of TKR are femur component fits at lower end of it, tibial baseplate fits at its upper end, spacer between femur and tibia and button articular surface for under surface patella. Femur and tibia component are made of metal, patella button and spacer are made of polyethylene. Metal component are made off either cobalt-chromium steel alloy (CoCr), titanium, oxidized zirconium (oxinium) or Titanium Niobium Nitride (TiNbN) coating (looks like gold but not true gold).
Type of TKR prosthesis can vary depending on preservation or sacrifice of posterior cruciate ligament (PCL) and mechanism of prosthetic joint stability. The main design change happens at the femur implant and at the polyethylene surface. If PCL is sacrificed then knee stability is maintained by cam and post technique which is called PS knee and if PCL is not sacrificed then it is called CR knee where the stability is maintained by continuity of PCL. In PCL sacrificed knee prosthesis stability can also be maintained by deep curve and elevated anterior margin of polyethylene insert. Philosophy wise each knee designee has its superiority but on survivorship the differences are marginal. The advances in the quality of the polyethylene, highly crosslinked polyethylene has made major changes in prosthesis survivorship. Design wise the most appreciating development in knee prosthesis design happened to increase range of knee movement. The articulation surface in knee prosthesis does not have much choice like THR. Metal on polyethylene is being used in more than 99% cases worldwide. For bonding of the implant with bone either bone cement can be used or the implant surface may have special design and material choice for direct bonding with bone. But in India, uncemented implants are not available.
How is the procedure done?
TKR surgery is being done either under regional anaesthesia or general anaesthesia. The major concern of anaesthesia in TKR is post operative pain management as the postoperative period of TKR is very painful. Recent advances in surgical technique understanding of dissection has made postoperative period less painful than previous. Improvement in selective nerve block technique has made a revolution in post TKR pain management. Now in most centres TKR is being done with single dose spinal anaesthesia and selective nerve block. Due to advances in post operative pain management post TKR patients can get out of the bed on the same day of surgery.
Skin incision for TKR is given at the centre of the knee on the front side. Following cutting the skin joint is accessed either by cutting the quadriceps muscle or by lifting the muscle as a whole and retracting on the lateral side. Bone ends are shaped according to the design of the prosthesis with the help of recommended instruments, jigs and technique. Following the bony surface preparation trial implant is placed and the joint is reduced to check stability and range of motion. After a satisfactory trial original implants are fixed to the bone with bone cement. We rarely transfuse blood in TKR. Judicial use of tranexamic acid has made huge changes in preserving blood loss in TKR.
How does recovery happen?
Due to advances in the understanding of surgical approach, technique in anaesthesia, postoperative pain management, and blood loss management, post TKR recovery has become a cake walk. Most of our patients can walk on the same day of surgery and can get discharged in one or two days after surgery. Physiotherapy is required only to regain muscle strength and balance in walking. By the end of 3-4 weeks pain medication requirement becomes negligible. Swelling and stiffness recovers in 2-3 months and one starts feeling normal and starts forgetting the surgical event usually by the end of 6 months.
What should you expect from the procedure?
Following TKR one should expect significant pain relief, better stability of the joint, increased range of motion and improvement in the quality of life. TKR cannot be the replacement of the original knee but it can give significant relief from the agony of pain and disability of arthritis knee and one can enjoy the near normal function form a replaced knee. Success of TKR does not depend on the perfect postoperative x-ray and successful surgical outcome but on a satisfied patient. If the patient’s expectation and understanding regarding post TKR function is unrealistic then the patient may remain unsatisfied even with a technically successful surgery. Structured preoperative psychological counselling regarding desired postoperative outcome and goal can ensure a happy patient following successful TKR.