Total Knee Replacement

Knee Replacement Surgery

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Knee arthroplasty or Knee replacement is a surgical procedure where the weight-bearing worn out bony ends of the knee joint is replaced in order to relieve pain and disability. Ideally it should be called resurfacing rather than replacement. It is one of the five most commonly performed surgeries worldwide, most commonly for osteoarthritis  and also for other knee diseases such as rheumatoid arthritis . In patients with severe deformity from trauma, advanced rheumatoid arthritis or long standing osteoarthritis, the procedure may be more complicated and may incur risks.

Knee replacement surgery can be performed as a partial or a total knee replacement. Generally, the surgical procedure involves replacement of the diseased and damaged joint surfaces of the knee using metal and plastic components that are shaped in order to allow continued motion of the knee.

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Knee replacement surgery should be considered when conservative treatment options have been exhausted.  Replacement of the entire knee is also an option to correct the significant knee joint or bone trauma in younger patients.

Pre-operative preparation

Knee arthroplasty is major surgery. Pre-operative preparation begins immediately following decision. Anaesthetist would like to meet the patient and discuss various issues regarding anaesthesia and pain management. Whole battery of tests are done to find out the fitness levels of heart, lungs kidney,liver etc. Blood cross-matching is also done to facilitate possible transfusion.  Close to a month before the surgery, the patient is usually prescribed supplemental iron to boost the level of haemoglobin in the blood. It is required to have accurate X-rays of the affected knee to measure the size of the components and to understand specific requirements.  Blood thinner medications such as warfarin and aspirin will be stopped some days before surgery to reduce the amount of bleeding. Physiotherapist assesses the patient, tell them the various stages of recovery and expectations. Home exercise plan is started to strengthen the muscles which hasten up the recovery period.

Technique

The surgery involves exposure of the knee from the front. The knee cap (patella) is displaced to one side of the joint allowing exposure of the  ends of the femur and tibia. Tight tissues on one side are released to straighten the joint. The ends of these bones are then accurately cut to shape using cutting guides oriented to the long axis of the bones. All tissues inside the joint are removed except for the posterior cruciate ligament which may be preserved along with the collateral ligaments.

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A round ended implant is used for the femur that mimics the natural shape of the joint. The component on the tibia is flat. It has a stem that sometimes goes down inside the bone for improved stability.  A flattened or slightly dished high density polyethylene surface is then inserted onto the tibial component so that the weight is transferred from metal to plastic. These implants are fixed to the bone using bone cement. Before closure of the wound, ensure that the knee has a good range of movement and is aligned and stable. In certain cases, the articular surface of the patella is also removed and replaced by a polyethylene button cemented to the posterior surface of the patella. In other cases, the patella is left unaltered.

Variations

Lot of research is still going on regarding what constitutes a happy knee. Different issues prevalent are- Posterior cruciate ligament retaining or sacrificing, patella esurfacing or not, mobile bearing or fixed.

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Minimally invasive procedures have been developed in total knee replacement (TKR) that do not cut the quadriceps tendon. Various definitions exist for minimally invasive knee surgery that may include a shorter incision length, retraction of the patella without rotating out and specialized instruments. However, there have been no studies that have shown the long term benefits of the same.

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