What is Primary Knee Replacement?
Primary knee replacement, also referred to as primary total knee arthroplasty, is a surgical procedure in which the worn out or damaged parts of the knee joint are removed and replaced with artificial knee joints called prostheses or implants. Artificial knee joints are usually made of metal, plastic, or ceramic and consist of the femoral and the tibial components. The main objective of the procedure is to relieve knee pain and restore normal range of motion and function to the knee joint when conservative treatment, such as medications, injections, and physical therapy have failed to provide desired results.
Anatomy of the Knee
The knee is made up of the femur (thighbone), tibia (shinbone) and patella (kneecap). The lower end of the femur meets the upper end of the tibia at the knee joint. A small disc of bone called the patella rests on a groove on the front side of the femoral end. The fibula, another bone of the lower leg, forms a joint with the shinbone. The bones are held together by protective tissues, ligaments, tendons, and muscles. Synovial fluid within the joint aids in the smooth movement of the bones over one another. The meniscus, a soft crescent-shaped area of cartilage between the femur and tibia, serves as a cushion and helps absorb shock during motion.
Indications for Primary Knee Replacement
Primary knee replacement is commonly indicated for severe osteoarthritis of the knee. Osteoarthritis is the most common form of knee arthritis in which the joint cartilage gradually wears away. It often affects older people.
In a normal joint, articular cartilage allows for smooth movement within the joint, whereas in an arthritic knee the cartilage itself becomes thinner or completely absent. In addition, the bones become thicker around the edges of the joint and may form bony “spurs.” All of these factors can cause pain and restricted range of motion in the joint.
Your doctor may advise primary knee replacement for the following conditions that have not responded to non-surgical remedies. These include, but are not limited to:
- Severe knee pain which limits your daily activities, such as walking, getting up from a chair, or climbing stairs
- Moderate to severe pain that occurs during rest or awakens you at night
- Chronic knee inflammation and swelling
- Knee deformity with loss of cartilage and pain
- Injury or fracture of the knee
- Instability of the knee
Preparation for Primary Knee Replacement
Preoperative preparation for primary knee replacement may involve the following steps:
- A review of your medical history and physical examination are performed by your doctor to check for any medical issues that need to be addressed prior to surgery.
- Depending on your medical history, social history, and age, you may need to undergo tests such as blood work and imaging to help detect any abnormalities that could compromise the safety of the procedure.
- You will be asked if you have allergies to medications, anaesthesia, or latex.
- You should inform your doctor of any medications, vitamins, or supplements that you are taking or any conditions you have such as heart or lung disease.
- You may be asked to avoid medications such as blood thinners, aspirin, or anti-inflammatories for a specific period prior to surgery.
- You should refrain from alcohol or tobacco at least a few days prior to the surgery and several days after as it can hinder the healing process.
- You should not consume any solids or liquids at least 8 hours prior to surgery.
- You need to arrange for someone to drive you home after surgery.
- A signed informed consent will be obtained from you after the pros and cons of the surgery have been explained in detail.
Procedure for Primary Knee Replacement
Primary knee replacement is performed under spinal or general anaesthesia. Your surgeon will make an incision in the skin over the affected knee to expose the knee joint. Then, the damaged portions of the femur bone are cut at appropriate angles using specialised jigs. The femoral component is attached to the end of the femur with or without bone cement.
Your surgeon then cuts or shaves the damaged area of the tibia and the cartilage. This removes the deformed part of the bone and any bony growths, as well as creates a smooth surface on which the implants can be attached. Next, the tibial component is secured to the end of the bone with bone cement or screws.
Your surgeon will place a plastic piece called an articular surface between the implants to provide a smooth gliding surface for movement. This plastic insert will support the body’s weight and allow the femur to move over the tibia like the original meniscus cartilage.
The femur and the tibia with the new components are then put together to form the new knee joint.
To make sure the kneecap glides smoothly over the new artificial knee, its rear surface is also prepared to receive a plastic component.
With all the new components in place, the knee joint is tested through its range of motion. The entire joint is then irrigated and cleaned with a sterile solution. The incision is carefully closed, and a sterile dressing is placed over the incision.
Postoperative Care and Recovery
In general, postoperative care instructions and recovery after primary knee replacement may involve the following steps:
- You will be transferred to the recovery area where your nurse will closely observe you for any allergic or anaesthetic reactions and monitor your vital signs as you recover.
- You may notice pain, swelling, and discomfort in the knee area. Pain and anti-inflammatory medications are provided as needed.
- Antibiotics are also prescribed to address the risk of surgery-related infection.
- You are advised to keep your leg elevated while resting to prevent swelling and pain.
- You will be given assistive devices such as crutches with instructions on restricted weight-bearing for a specified period of time. You are encouraged to walk with assistance as frequently as possible to prevent blood clots.
- Instructions on surgical site care and bathing will be provided to keep the wound clean and dry.
- Eating a healthy diet rich in vitamin D is strongly advised to promote healing and a faster recovery.
- Refrain from strenuous activities for the first few months and lifting heavy weights for at least 6 months. A gradual increase in activities over a period of time is recommended.
- An individualised physiotherapy protocol will be designed to help strengthen knee muscles and optimise knee function.
- You should be able to resume your normal activities in a couple of months, but with certain activity restrictions. Return to sports or high-intensity activities may take at least 6 months or longer.
- Refrain from driving until you are fully fit and receive your doctor’s consent.
- A periodic follow-up appointment will be scheduled to monitor your progress.
Risks and Complications
Primary knee replacement surgery is a relatively safe procedure; however, as with any surgery, some risks and complications may occur, such as the following:
- Blood clots
- Anaesthetic/allergic reactions
- Injury to nerves and blood vessels
- Implant wear and loosening
- The need for revision surgery