Knee replacement

Knee replacement

Introduction

Knee replacement, also called arthroplasty, is a surgical procedure to resurface a knee damaged by arthritis. Metal and plastic parts are used to cap the ends of the bones that form the knee joint, along with the kneecap. This surgery may be considered for someone who has severe arthritis or a severe knee injury.

Various types of arthritis may affect the knee joint. Osteoarthritis, a degenerative joint disease that affects mostly middle-aged and older adults, may cause the breakdown of joint cartilage and adjacent bone in the knees. Rheumatoid arthritis, which causes inflammation of the synovial membrane and results in excessive synovial fluid, can lead to pain and stiffness. Traumatic arthritis, arthritis due to injury, may cause damage to the cartilage of the knee.

The goal of knee replacement surgery is to resurface the parts of the knee joint that have been damaged and to relieve knee pain that cannot be controlled by other treatments.

Anatomy of the knee

Joints are the areas where 2 or more bones meet. Most joints are mobile, allowing the bones to move. Basically, the knee is 2 long leg bones held together by muscles, ligaments, and tendons. Each bone end is covered with a layer of cartilage that absorbs shock and protects the knee.

There are 2 groups of muscles involved in the knee, including the quadriceps muscles (located on the front of the thighs), which straighten the legs, and the hamstring muscles (located on the back of the thighs), which bend the leg at the knee.

Tendons are tough cords of connective tissue that connect muscles to bones. Ligaments are elastic bands of tissue that connect bone to bone. Some ligaments of the knee provide stability and protection of the joints, while other ligaments limit forward and backward movement of the tibia (shin bone).

The knee consists of the following:

Tibia. This is the shin bone or larger bone of the lower leg.

Femur. This is the thighbone or upper leg bone.

Patella. This is the kneecap.

Cartilage.  A type of tissue that covers the surface of a bone at a joint. Cartilage helps reduce the friction of movement within a joint.

Synovial membrane. A tissue that lines the joint and seals it into a joint capsule. The synovial membrane secretes synovial fluid (a clear, sticky fluid) around the joint to lubricate it.

Ligament. A type of tough, elastic connective tissue that surrounds the joint to give support and limits the joint's movement.

Tendon. A type of tough connective tissue that connects muscles to bones and helps to control movement of the joint.

Meniscus. A curved part of cartilage in the knees and other joints that acts as a shock absorber, increases contact area, and deepens the knee joint.

Types of surgery

There are two main types of surgery, depending on the condition of the knee:

• total knee replacement (TKR) – both sides of your knee joint are replaced

• partial (half) knee replacement (PKR) – only one side of your joint is replaced in a smaller operation with a shorter hospital stay and recovery period

Why is knee replacement surgery needed?

The most common reason for knee replacement surgery is osteoarthritis. Other conditions that cause knee damage include:

• rheumatoid arthritis
• haemophilia
• gout
• knee injury

A knee replacement is major surgery, so is normally only recommended if other treatments, such as physiotherapy or steroid injections, haven't helped reduce pain or improve mobility.

You may be offered knee replacement surgery if:

• you have severe pain, swelling and stiffness in your knee joint and your mobility is reduced
• your knee pain is so severe that it interferes with your quality of life and sleep
• everyday tasks, such as shopping or getting out of the bath, are difficult or impossible
• you cannot work or have a normal social life

Before the procedure

• Your doctor will explain the procedure to you and offer you the opportunity to ask any questions that you might have about the procedure.

• You will be asked to sign a consent form that gives your permission to do the procedure. Read the form carefully and ask questions if something is not clear.

• In addition to a complete medical history, your doctor may perform a complete physical examination to ensure you are in good health before undergoing the procedure. You may undergo blood tests or other diagnostic tests.

• Notify your doctor if you are sensitive to or are allergic to any medications, latex, tape, and anesthetic agents (local and general).

• Notify your doctor of all medications (prescribed and over-the-counter) and herbal supplements that you are taking.

• Notify your doctor if you have a history of bleeding disorders or if you are taking any anticoagulant (blood-thinning) medications, aspirin, or other medications that affect blood clotting. It may be necessary for you to stop these medications prior to the procedure.

• If you are pregnant or suspect that you are pregnant, you should notify your doctor.

• You will be asked to fast for eight hours before the procedure, generally after midnight.

• You may receive a sedative prior to the procedure to help you relax.

• You may meet with a physical therapist prior to your surgery to discuss rehabilitation.

• Arrange for someone to help around the house for a week or two after you are discharged from the hospital.

• Based on your medical condition, your doctor may request other specific preparation.

What happens during knee replacement surgery?

• A knee replacement is normally performed under general anaesthetic
• During the operation your whole existing knee joint is replaced with a new prosthetic knee joint
• This takes between one and two hours
• Your surgeon will make an incision (cut) at the front of your knee where the replacement will be inserted
• Usually, you will stay in hospital for 2-4  days, but you may have to stay longer if necessary.

Most total knee replacement operations involve replacing the joint surfaces at the end of your thigh bone (femur) and at the top of your shin bone (tibia).

A total knee replacement may also involve replacing the under-surface of your kneecap (patella) with a smooth plastic dome. Some surgeons prefer to preserve the natural patella if possible, but sometimes the decision will need to be made during the operation.

If you’ve had a previous operation to remove the patella altogether (patellectomy), this won’t stop you having a knee replacement, but it may affect the type of replacement part (prosthesis) your surgeon uses.

The new parts are normally cemented in place. If cement is not used then the surface of the component facing the bone is textured or coated to encourage bone to grow onto it, forming a natural bond.

Exercises after knee replacement : 

The following exercises should be performed three times per day for at least 12 weeks and supervision by a therapist may be useful. These exercises will help knee range and strength and should be performed pre and post-operatively.

Please note: these exercises may worsen your pain initially.

Pain following a knee replacement remains for many weeks and is normal for everyone. Take pain killers before you exercise to try and reduce the after-effects.

Sit on a chair with a towel under one foot. Slide the foot under the chair as far as you can. Move your knee forward keeping the sole of your foot in contact with the floor. Hold for approximately 10 seconds.

Repeat 10 times.

Sit on the floor with your legs straight out in front of you. Put a band around your foot. Bend your knee as far as possible. Gently pull the band to bend your knee a little more. Hold for approximately 10 seconds.

Repeat 10 times.

Sitting on a chair, with the leg to be exercised supported on a chair as shown, let your leg straighten in this position. Hold for approximately 15 seconds.

Repeat 10 times, three times per day.

Sit on a chair with one leg straight in front of you. Place your hand on your thigh just above the knee cap. Lean forward keeping your back straight. Straighten your knee, assisting the stretch with your hands. Hold for approximately 15 seconds.

Repeat three times, three times per day.

Sit on a chair. Pull your toes up, tighten your thigh muscle and straighten your knee. Hold for approximately five seconds and slowly relax your leg.

Repeat 10 times.

Lie on your back. Bend your leg, place a cushion under your knee and keep your other leg straight on the bed. Exercise your straight leg by pulling your foot and toes up, tightening your thigh muscle and straightening the knee (keep your knee on the cushion). Hold for approximately five seconds and slowly relax. To make the exercise harder, put a small weight around your ankle.

Repeat 10 times.

Risks specific to knee replacement surgery are:

Knee replacement surgery is a common operation and most people do not experience complications. However, as with any operation, there are risks as well as benefits.

Complications are rare but can include:

• stiffness of the knee
• infection of the wound
• deep infection of the joint replacement, needing further surgery
• unexpected bleeding into the knee joint
• ligament, artery or nerve damage in the area around the knee joint
• blood clots or deep vein thrombosis (DVT)
• persistent pain the in the knee

In some cases, the new knee joint may not be completely stable and further surgery may be needed to correct it.

More information

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