TOTAL PRIMARY KNEE REPLACEMENT
Knee replacement in the present day continues to present challenges to the Orthopaedic Surgeon.
Major orthopaedic companies continue to develop, test and refine knee replacement designs.
However the overall design of the modern knee replacement has changed little over the last 20 years.
Knee replacement can effectively bring relief of disabling pain, correction of deformity and return of movement.
Primary total knee replacement now shows 90% survival at 25 years for some implants (De Puy PFC)
Knee replacement is a highly successful operation with over 55,000 operations performed in the UK per year.
Whilst the immediate results of knee replacement cannot be compared to hip replacement it is a highly successful operation offering a return of function that patients truly benefit from.
At surgery an incision is made over the front of the knee.
Typically this is 20-25 centimetres long extending from above the kneecap down to the lower leg over the centre of the knee. The incision is carried down through the skin and fat to the muscles and tendons on the front of the knee.
In order to carry out the operation the knee must be opened. Cutting through the tendon as it attaches to the inside half of the kneecap performs this. The kneecap may then be displaced to allow the surgeon to see the inside of the knee.
During surgery remnants of the menisci (cartilages) as well as the cruciate ligaments are then removed together with any excess bone that has formed as part of the process of arthritis. The bony surfaces are cleared to allow preparation for the knee replacement to occur.
During knee replacement very small amounts of bone are actually removed from the end of the thigh bone (femur) and leg bone (tibia).
In order to do this a jig is used to first remove the end of the thigh bone.The thigh bone is then sized. Each individual will have a different sized thigh bone and leg bone and all knee replacement systems come with a range of sizes to accommodate all individuals.
Once the size has been determined the thigh bone can be finished to the appropriate size. This is done using further jigs of the appropriate size. There are a range of jigs in each size necessary. A small amount of bone is then removed from the leg bone again using the jig.
At this stage the surgeon is able to perform a trial using a sterile “dummy” knee to determine that the sizing is correct, that the knee is not too tight or too loose and to make fine-tuning adjustments to ensure that when the real knee is inserted it will be perfect and function properly.
After this the leg bone is usually finished and finally prepared to receive the real implant.
During knee replacement a decision is made as to whether the back of the kneecap will be replaced.
In the UK practice varies between surgeons. Some routinely replace the back of the kneecap and some do not. When performing a knee replacement I will only replace the back of the kneecap if it is seriously degraded and destroyed.
In these instances I feel it is necessary for the knee to function properly. Replacing the kneecap does carry the risk of significant complications and routine replacement has not been shown to be necessary.
Once all the bone surfaces are prepared the final real knee replacement may be inserted. This is made of metal both for the thigh bone and the leg bone. It is held in pace with a “cement” which in reality acts like a grout – just like your bathroom tiles.
Once the components are in place and the cement is drying the surgeon has a final opportunity to decide on the size of the plastic insert that will be in the centre of the new knee.
Whilst waiting for the cement to dry the knee is infiltrated with a combination of local anaesthetic as well as some adrenalin to supplement your post operative pain relief and reduce post-operative bleeding.
Once the cement is dry the correct sized plastic insert is inserted and the new knee thoroughly washed out.
The tissues are then closed in layers with stitches and a final layer of metal clips is placed in the skin.
A dressing is then put over the wound.
Typically the patient will be provided with painkiller through a pump that they can self administer (PCA). The following day after surgery they will begin exercises with the physiotherapist to begin bending the knee. The picture below shows typical scarring 3 days after surgery.
A typical stay is between 2 to 4 days in hospital. Physiotherapy may need to continue following discharge into the community.
Patients can expect to achieve at least 90- 100 degrees of bend from a routine knee replacement. Many will achieve up to 110 degrees. There are knee designs that offer greater degrees of flexion.
Follow up after surgery occurs at 6 weeks and range of movement will be assessed at that stage.
In general knee replacement patients are often slower to recover than hip replacements. This is not surprising as they are two totally different operations and should not be compared.
The first six weeks following replacement are extreemely difficult and require a great deal of effort from any patient. Typically there is alot of swelling, it is difficult to achieve movement and the knee will feel warm and tight.
After the first six weeks the next six weeks are easier but many patients find the first three months after surgery a real challenge.
The majority of knee replacement patients see an ongoing improvement for up to 6 months following their knee replacement and find maximum benefit between 6 and 12 months after their surgery.
The indications for computer navigation, patient selection and whether it should be in routine use continue to be debated amongst Orthopaedic surgeons.