Knee arthroplasty is a surgical procedure for the treatment of end-stage knee osteoarthritis. It is commonly known as knee replacement surgery, as the patient’s knee is replaced with an artificial joint made from plastic and metal. This surgery is mainly performed to treat knee pain from knee osteoarthritis, but has the effect of potentially improving knee function, in terms of knee range of motion, and knee alignment.
Osteoarthritis is a disease of the joints, where the cartilage over the knee joints is damaged and worn out over time. This results in uncovered bone in the joint surfaces, which results in severe knee pain, as well as progressive knee deformity. Patients with end-stage knee osteoarthritis often have a bow-legged deformity and have their quality of life adversely affected. Patients with knee osteoarthritis often find themselves unable to walk for long distances, are unable to squat, and have difficulty climbing up stairs. With activity, they may develop painful knee swelling.
Knee arthroplasty is performed through an incision made at the front of the knee joint. Through this incision, the damaged bone and cartilage in the patient’s knee are removed and the bone ends are shaped to receive the new artificial joint. This surgery can be performed with the aid of computers and robots to increase the accuracy of joint replacement. There is no difference in outcomes between the use of robotic surgery and the use of computer-aided surgery, with computer-aided (navigation) surgery having a cost advantage.
After the artificial joints are inserted, the cut joint is stitched up again, the skin is repaired and the patient is sent to rest in the inpatient ward. In general, this surgery will take about 2 hours, and patients are usually placed under general anaesthesia for the surgery.
After surgery, patients typically stay for 2 to 5 days in the hospital to receive pain relieving medications and antibiotics and undergo knee physiotherapy. After their stay in the hospital, some patients opt to return home, whilst others may choose to be transferred to a step-down facility such as a community hospital, where they will undergo more intensive rehabilitation to improve knee function and balance before returning home.
After knee replacement surgery, patients will find themselves having increased pain due to the surgery for the first few days. This is the reason why prolonged inpatient stays are usually necessary for pain management. Once the pain has subsided, the patient is required to undergo physiotherapy, which will focus on a range of knee motion exercises, and strengthening exercises for the thigh muscles. Patients are usually advised to start with the use of walking aids such as crutches and walking frames for the initial 2 to 6 weeks. Thereafter, as their balance and strength improve, they may be able to downgrade to walking sticks or even walk without the use of any walking aids. In general, most patients undergoing knee replacement surgery will be able to walk independently by 6 weeks after surgery. Most patients will be able to return to normal activities after 3 months, though some patients find themselves having difficulty due to pain from the other unoperated knee.
In general, younger patients under the age of 65 years of age can undergo bilateral knee replacement surgery, meaning that they can have both knees replaced during the same surgery. This is more cost-effective, but carries a higher overall surgical risk, and should only be performed on younger patients. For patients above the age of 65, it is safer to perform staged surgery, meaning that knee replacement surgeries are not performed concurrently. The time interval between surgeries should be at least 3 months to allow for the first operated knee to recover. This ensures optimal rehabilitation for both knee surgeries.
In general, most knee replacement options are similar in design and function, with the difference being the accuracy of the instruments used for the knee replacement. Most implants consist of metal components used to replace damaged bone at both ends of the knee, which sandwich a plastic component that is meant to replace the function of the cartilage in the knee joint. Additionally, the cartilage over the patella or kneecap is replaced with a piece of plastic, which is cemented in place.
Computer-assisted surgery improves the accuracy of bone cuts during knee replacement surgery, without sacrificing surgical time or significantly increasing complexity. It is especially useful if there are subtle deformities in the shin or thigh bones, which may not be recognized prior to surgery. When compared to robotic surgery, computer-assisted surgery has the great advantage of being much cheaper, with shorter surgical time. Shorter surgical time translates to lower overall surgical risk, without significant changes to outcomes.
Knee replacement surgery is considered major surgery and has some rare complications. There is a risk of infection from the surgical wounds and the implants. In severe cases, the surgical wound may need to be reopened and revision surgery may need to be performed.
There are also major nerves and blood vessels behind the knee joint, which are rarely injured during knee replacement surgery. Damage to these structures can result in numbness, and weakness of the foot. In severe cases, revision surgery may be necessary to repair any damaged blood vessels.
Due to the prolonged period of rehabilitation and rest needed for recovery, some patients may also develop deep vein thrombosis, which refers to the formation of blood clots in the veins in the leg. These blood clots can result in pain and swelling of the leg, and may also travel to the lungs, where they can cause a condition known as pulmonary embolism, which can threaten life. As a result, most patients are encouraged to move as soon as possible, and patients undergoing knee replacement surgery are often given anti-platelet or anti-coagulant medications to prevent blood clots.
Some patients may find themselves developing knee stiffness after knee replacement surgery. This is frequently due to inadequate rehabilitation after surgery. Most patients are encouraged to enter into a structured post-operative rehabilitation schedule after surgery, where they are taught a range of motion exercises and stability exercises. These help to prevent knee stiffness after knee replacement surgery. Should post-operative rehabilitation be neglected, patients may be required to undergo additional procedures, such as knee manipulation under anaesthesia. Or even revision knee replacement surgery to treat post-operative knee stiffness.