Knee replacement is, by and large, a reliable and successful surgery. However, a small number of people may have problems following surgery. The success rate of surgery is 90 to 95% at 10 years.
The potential problems include:
1. Infection in the knee
Infection in the replaced knee joint is a serious but rare problem and the risk is less than 1%. Superficial infections in the wound present as discharge from the wound, and generally respond to antibiotics and dressing. Deep infection presents as persistent wound discharge, formation of sinus over the wound, or persistent pain. Deep infection may often require revision knee surgery - removal of the artificial knee joint and insertion of a new joint.
The surgery is done in clean air operating theatres, and with use of appropriate antibiotics, along with antibiotic in the cement, the risk of infection is very low. Meticulous surgical technique and strict asepsis allows us to achieve an infection rate which is nearly zero. The infections encountered are generally blood borne infections from a remote site in the body - like the chest, or urinary tract.
2. Swelling and stiffness
Knee replacement is a major surgery and inevitably results in local swelling. This is usually temporary and settles in 3 to 6 months as knee movements are regained. Mild to moderate swelling in the knee after surgery is expected and is not a cause for concern.
Some patients experience stiffness and this gradually improves with progression of physiotherapy. It is important to do exercises to fully straighten the knee and to bend the knee.
Almost everyone will regain knee bending to a right angle and most will regain even more bending. The final range of knee bending after surgery is largely dictated by the range of movement prior to surgery. At the time of surgery, a lot of effort is made to maximise the range of movement.
About 1 % people may experience problems in bending their knee fully. In this situation a manipulation of the knee under general anaesthetic is needed to break the adhesions. Intense physiotherapy after manipulation helps to improve the range of motion.
3. Deep vein thrombosis and Pulmonary Embolism
Deep vein thrombosis is development of a blood clot in the veins of the calf, thigh or pelvis. This is a risk with any hip or knee surgery and prophylaxis against this provided in the form of oral tablets or by injections. Foot pumps are also used to physically help blood circulation. The duration of anticoagulant therapy is 2 weeks after operation.
Deep vein thrombosis causes swelling of the leg and pain, and temporarily delays rehabilitation following surgery. Clots require treatment with Warfarin.
Pulmonary Embolism is a very rare complication where a clot from the leg travels to the lungs and blocks circulation. Small clots are inconsequential and may not be noticed or detected. Large clots are potentially life threatening.
4. Ongoing pain in the knee
A small number of people (about 1%) may experience pain the knee after apparently successful surgery. This may be referred pain from the hip or spine, or it may be an undetectable deep infection. This requires investigations and sometimes further surgery may be needed to alleviate the pain.
Following knee surgery, walking aid in the form of Zimmer frame, crutches and sticks are needed temporarily. As muscle strength improves, the gait improves and by two months, most people are able to walk without sticks. Some people can take a longer time, and this is within normal expected recovery patterns.
6. Rare complications
Rare complications of knee surgery include chest infection, urinary tract infection, or injury to the nerves. Some people may require a urinary catheter for the first day or two after surgery, if there are preexisting problems of the urinary tract. The surgical incision of the knee is a vertical cut on the front of the knee. This results in unavoidable damage to some small nerves in the skin, which leads to numbness on the outer side of the knee adjoining the scar. This numbness may be permanent but is not a cause for concern.
In some instances, there may be a crack in the thigh or leg bone during fixation of the components. These are generally detectable and treatable at the same time.
The risk of dying as a result of knee replacement is extremely low – a fraction of 1%. Pulmonary embolus, heart attack or stroke, especially with a history of such an event in the past, are the underlying factors for this.
7. Long term complications
In the long term (years), the fixation of the artificial joint into the bone may become loose, or the polyethylene liner may wear out. These situations result in pain and damage to bone around the knee joint. Revision to a new knee joint is required to correct these problems.
Revision of the knee is more extensive operation than the primary surgery and the risk of complications is also higher in revision surgery.
Despite all the risks mentioned here, most patients (90%) have a speedy and uneventful recovery after knee surgery and do well. 5 to 8% may have a minor complication which delays rehabilitation, but does not affect the outcome. Only 1 or 2 percent end up with a significant problem. It is advisable that the surgery is undertaken only when the expected benefit outweighs the potential risks.