Primary Total Knee Replacement

The knee is basically a hinge joint with strong, smooth articular cartilage which lines the bone ends within the joint.

When articular (or hyaline) cartilage in the knee wears away, the underlying bone comes into contact with the bone of the opposing joint surface. This leads to pain, restricted movement and deformity of the joint. Patients with established osteoarthritis notice pain on movement and at night (which wakes them), decreased walking distance and a general decrease in the ability to carry out daily activities like walking the dog, shopping, climbing stairs and putting on shoes and socks.

X-ray of a normal knee.                 X-ray of an arthritic knee – note the complete loss of joint space.

Total knee replacement reduces pain and improves mobility and function as well as correcting any deformity.  This is done by resurfacing the damaged joint surfaces with metal and plastic so that the new joint surfaces glide over each other. Last year about 85,000 TKR’s were carried out in the UK

A picture of a knee replacement showing the 3 main components: the tibial tray, the curved femoral component and the high density plastic in between.

This photograph also includes a high density plastic button which is used to resurface the underside of the kneecap (if it is worn)

Post-operative X-rays of a knee replacement

The quality of the materials and bearing surfaces used to make knee replacements have improved vastly over the last few years. Knee replacements tend to last about 20 years (depending on how much it was used).

The operation

You will be admitted on the day of surgery. The operation takes 60-90 minutes. You will have a bulky bandage around the knee which should feel numb (due to local anaesthetic infiltration around the knee during the operation and /or the spinal anaesthetic). You can walk on your new straight away on return to the ward, but make sure you ask for help before doing so.

The wound is about 20cm down the front of the knee. It will heal in 2 weeks so keep it dry until then.

Typical TKR wound

After the operation

You will be given exercises to do by the physios. Average length of stay in hospital is 3 days. You will be able to climb stairs before you go. You will be discharged with crutches in most cases.

The recovery from a TKR can be slow and important to have realistic expectations.

As you can see from the table, it can take your new knee up to a year to completely settle. It is important to know that although your pain has gone and you are functioning normally, the new knee will not feel like a normal knee. This is normal and is due to absence of ligaments which need to be removed during the operation. The range of movement column is just a rough guide – in general you will regain the range of movement that you had before the operation. That’s why it’s important not to leave the operation too late.

What are the risks?

Complications are rare following TKR.

During the operation

Damage to nerves and blood vessels

The incision damages some skin nerves and you will have a patch of numbness over the outer part of the kneecap. Everyone who’s had a TKR has this. The main nerves and vessels to the foot are tucked away at the back of the knee. In some severely deformed knees, the nerve to foot can sometimes be stretched – again –  don’t leave it too long.

Fracture

If the bone quality is very poor, fractures can occur. This is extremely rare and will be dealt with during the operation.

After the operation (0 – 12 weeks)

Blood clots

Clots in the calf veins (DVT) can form after TKR. To prevent this we give you special stockings to wear and medication which thins the blood slightly to prevent clots from forming. The best way to prevent clots is by walking on your new knee as soon as possible. If a DVT forms, some of it can break off and travel in the bloodstream to the lungs. This is a pulmonary embolus (PE) and is very rarely fatal (less than 1 in 1000). The stockings should be worn for 6 weeks. The daily injection under the skin (as an inpatient) and tablets (as an outpatient) are to be taken for 2 weeks after the operation

Infection

The rate of wound infection is about 1 in 100 (1%). This can be treated with antibiotics. Deep infection of the joint is much less common (0.1%).

Stiffness

The first few weeks after a TKR are painful but its important to push on and persevere with your exercises.  Not doing so is a cause of long term stiffness and decreased range of movement.

Heart attack / stroke

If you do not suffer with these conditions, it is extremely unlikely that this will occur. If you do, then you will need to see the anaesthetist at pre-assessment clinic. I may refer you to the cardiologist or stroke unit before the operation.

After the operation (12 weeks onwards)

Leg length discrepancy (LLD)

The bone taken away at the time of surgery is accurately replaced with metal and plastic (to the mm). If both knees are affected with arthritis, it is possible for the operated knee to feel longer. In general we can tolerate up to 1cm of LLD.

Loosening

After about 20yrs, the cement that is used to hold the implants in place can start to crumble causing the implants to loosen. This presents as pain and instability of the knee. Revision surgery is usually required in these cases.