The Knee Replacement Operation

Total knee replacement is a major operation but now routine in major hospital units. Good preparation with the help of a physiotherapist can make your recovery quick and successful. This is a general description only and will vary with circumstances.

The Anaesthetic

The most commonly used technique is general anaesthetic where the person is fully asleep throughout the procedure and looked after by the anaethetist.

If a general anaesthetic is not suitable for a medical reason a spinal anaesthetic may be given. Here the anaesthetist gives an epidural injection into the area surrounding the spinal cord to numb the lower body and the person is sedated to some extent so they are less aware of what is occurring.

An epidural may also be performed to allow post-operative pain control for a day or two following the operation.

The Operative Procedure

• The person is positioned on the operating table and the leg is swabbed down with skin disinfectant. This may colour the leg yellow, pink or brown.

• A tourniquet may be applied round the thigh so the surgeon can work in a blood-free field.

• The joint is opened through an incision about 6-10 inches long over the front of the knee or slightly towards the inner side. The kneecap is moved across to the outer side of the knee to expose the knee joint behind it.

• Any extra bone which has formed is removed and the tight soft tissues are gently loosened so that the knee can be correctly aligned.

• The arthritic ends of the bones are removed with a power saw guided by precision instruments called jigs. These are fitted to the leg bones during operation and have slots to guide the cutting blades so that the cuts are made very precisely. A difference of only one millimeter of bone removal can be important in fitting the joint components precisely.

• Most knee replacement components come in five different size ranges to reflect the differences in the size of individuals. The plastic spacer may come in up to 10 different thicknesses to fit whatever space is needed between the femoral and tibial components.

• Once the initial preparations have been performed, a trial joint is fitted to check that the joint is stable and moves in the correct manner. It is then removed, the last adjustments made, the bone surfaces are cleaned and the joint is ready for the insertion of the final components.

• The metal components of the joint are positioned either using cement as a fixator or using the press-fit technique. The plastic spacer is then inserted and the patellar button fitted to the back of the kneecap.

• A plastic tube called a drain is inserted in the wound to collect any oozing from the cut tissues into a bottle by the side of the bed.

• The tourniquet is released to check for bleeding.

• The wound is closed with stitches or clips.

• A dressing or splint is applied.

Overall the operation takes one and a half to three hours, but may be longer if there are technical problems to deal with. Antibiotics may be used for a short period during and after the operation to prevent infection.