Knee prosthesis: operation, material and duration

The procedure for a full denture of the knee joint is an operation in which the knee joint is replaced by an artificial joint.

The knee is a joint that connects the femur (femur) to the tibia (shin) and allows the movement of flexion and extension.

Diseases that can be treated by the intervention of a knee prosthesis:

    1. Severe osteoarthritis of the knee joint
  1. Infection that can lead to severe osteoarthritis
  2. Severe cartilage injuries to the knee
  3. Rheumatoid arthritis
  4. Hemophilia (hemophilia)
  5. Gout and pseudogout
  6. Vascular necrosis (death of the bone)
  7. Malposition (heavy X-leg or O-leg)

Contents

Classifications of prostheses

There are 3 types of implants, depending on the wear and tear of the joint:

Unicompartmental prosthesis
If the joint between the shin and thigh is damaged on only one side (inside or outside), the smallest prostheses (called unicompartmental) can be used to replace the damaged part.
Recovery is the fastest and takes about 3 months after the procedure, if there are no complications.

Bicompartmental prosthesis
In this type of procedure, the following joint areas are replaced:

  1. one side of the joint between the femur and the tibia (central or lateral);
  2. Area between femur and kneecap.

Recovery takes longer than the unicompartmental approach, about 5-6 months.

Tricompartmental prosthesis
If magnetic resonance imaging shows that the entire joint is severely damaged, the surgeon may recommend a tricompartmental knee prosthesis. In this procedure, all joint surfaces between the femur, shin and kneecap are replaced.
This operation has the greatest risks and the recovery time is much longer, patients report slow improvement over 6-12 months.

When to operate?

If the joint is heavily worn, various therapies are available for pain relief:

  1. Magnetotherapy
  2. Tecar Therapy
  3. Infiltrations with hyaluronic acid or cortisone
  4. Nonsteroidal anti-inflammatory drugs

If all these treatments do not have sufficient success and the patient continues to experience constant pain (even at night), surgical intervention may be considered.

Contraindications

Contraindications to knee replacement surgery are:

  • serious heart disease,
  • respiratory insufficiency,
  • uncontrolled diabetes,
  • Renal failure
  • weakened immune system,
  • septic arthritis of the knee joint,
  • severe osteoporosis.

The components of an implant

Up to three bone surfaces can be replaced in a knee joint prosthesis:

  1. The lower end of the femur. The femoral component is made of metal and is inserted into the lower end of the bone. This metal has a shaped groove for the kneecap (patella).
  2. The upper surface of the tibia. The tibial component is a platform made of thin metal with a layer of durable plastic and durable polyethylene. Some models do not have a metal part and the polyethylene lies directly on the bone. To achieve maximum stability, the metal part of the prosthesis may have an extension that inserts into the bone canal of the tibia.
  3. The posterior surface of the patella. The patella component consists of a dome-shaped piece of polyethylene that simulates the shape of the patella (kneecap) and adjusts to the femoral part.

All components are designed so that the metal is bonded to the plastic and allows a flowing movement with minimal wear.Models with rear anti-roll bar

In these models, the thickness of the tibial component is a raised surface with an inner bollard.
The latter is inserted in a corresponding splint of the femoral component.
The posterior cruciate ligament is removed to mount the components on the bone. The pieces work together to replace the work of the posterior cruciate ligament and prevent the femur on the shin from sliding too far forward when the knee is bent.

Models with retained posterior cruciate ligament

As the name suggests, in this prosthetic model, the posterior cruciate ligament remains in place. These implants do not have a bollard or a splint like the previous ones. This surgery is suitable for patients with healthy and functioning posterior cruciate ligament, which continues to stabilize the knee joint.
If the knee joint does not have good stability, the surgeon can implant a guided prosthesis, that is, with a pen that guides the movement. This is indicated in case of sagging or rupture of the cruciate ligaments.

Materials used in knee prosthesis surgery

The use of metal and polyethylene components provides excellent articulation (joint movement) between surfaces with low wear.

Cobalt-chromium alloys
Cobalt-chromium alloys are hard, corrosion resistant and biocompatible. Together with titanium, cobalt-chromium is one of the most widely used metals in knee prostheses.

Titanium and titanium alloys
Pure titanium is mainly used in prostheses where high resistance is not required. This allows the bone to grow in the prosthesis or bond to the “cement” for better anchoring.

Titanium alloys
Titanium alloys are inherently biocompatible. Usually, in addition to titanium, they contain a lot of vanadium and aluminum
The titanium alloy used in most knee prostheses is Ti6Al4V. Pure titanium and titanium alloys have high corrosion resistance and make the biomaterial inert (it practically does not change when implanted in the body).

Non-cemented implants
Knee prostheses can be “cemented” or “non-cemented”, depending on the type of attachment method used to hold the implant in its position. Most prostheses are cemented.
There are also prostheses designed to be attached directly to the bone without the use of cement.
The latter are based on bone growth above the prosthesis surface for anchoring.

Tantalum
Tantalum is a pure metal with excellent biological and physical properties. It is flexible, corrosion resistant and biocompatible.
Recently, a new porous substance based on porous tantalum was produced.
It contains numerous pores, so this material is very suitable for bone growth inside.

Zirconium
A zirconium alloy is used in the new ceramic knee joint prostheses. This zirconium-based alloy is combined with a shin component made of pure plastic.
The prostheses made of zirconium nitride are anti-allergic, so they can be implanted in patients who are allergic to metals (for example, nickel).
These new knee joints are believed to last 20-25 years. This is considerably longer than the 15-20 years of the cobalt-chromium alloy and polyethylene prostheses.

Room ® Gender Solutions™ for the kneecap joint
Zimmer ® Gender Solutions® for the patellofemoral joint is a system designed for early intervention in patients with unresolved patellofemoral pain.
Zimmer was the first orthopedic company to determine the anatomical differences between male and female knee joints.
Zimmer Gender Solutions prostheses are revolutionary in the way they compensate for the key differences between men and women. It’s a question of shape, not size.

Before surgery

Two weeks before the procedure:

  • Two weeks before the procedure, therapy with blood-thinning drugs must be discontinued.
    These drugs include aspirin, ibuprofen, ketoprofen, naproxen (Aleve), and other pharmaceuticals.
  • Medications that increase the risk of infection should also be discontinued.
    These include: methotrexate, Enbrel or other drugs that suppress the immune system.
  • In case of diabetes, heart disease or other pathologies, the surgeon must be informed.
  • It is recommended to stop smoking, because smoking prolongs the recovery time of wounds and bones.
  • The doctor must be informed about the state of health on the days before the procedure (fever, influenza, herpes or other diseases).
  • Consult the physiotherapist for preoperative gymnastics so that the knee is prepared for the procedure.

The day of the surgical intervention

  1. One should normally stay fasted (do not eat or drink anything) for 6-12 hours before surgery.
  2. Take necessary medication only with a small amount of liquid.

During the operation, damaged cartilage and bone parts of the joint are removed.
The removed parts are replaced by artificial parts called prostheses.
During the operation, thanks to the effect of anesthesia, there is no pain whatsoever. There are basically two types of anesthesia:

  1. The whole body is put to sleep, you do not feel any pain.
  2. Local anesthesia (spinal or epidural). The drug is injected into the back so that only one half of the body “falls asleep”, from the waist down. In addition, a drug with a sedative effect is administered, which allows the patient to fall asleep and whose active ingredient helps to ensure that he does not remember the operation afterwards.

After anesthesia is administered, the surgeon begins the operation by cutting the skin above the knee to open it.
This cut is about 8-10 cm long. Then proceed in the following way:

  • The kneecap is pushed aside to access the femur and tibia. After that, the surgeon removes the two bone ends to attach the prostheses.
  • The back part of the kneecap is separated to adapt it to the new pieces.
  • The prostheses are attached to the ends of the tibia and femur.
  • Both implants are attached to the back of the kneecap. To connect the three components, the surgeon uses a special bone cement.
  • The muscles and ligaments around the joint are sutured and the skin incision is provided with a suture point.

Duration of the procedure and hospitalization

The procedure takes about 2 hours.
After surgery, the knee is covered with a bandage; excess fluid is drained through a small plastic tube, which is inserted directly at the joint.
After surgery, antibiotics are given to reduce the risk of infection and blood thinning medications to reduce the risk of blood clots.
In case of severe pain, painkillers can be given either in drop form or epidural.
On the second postoperative day, the patient can eat again without restrictions.
It is important to move your knee, leg and foot immediately to prevent blood clots from forming.
You should start walking on the second day after surgery.
The procedure for the replacement of the knee joint provides for a hospital stay of seven to ten days, if there are no complications.
The stitches are removed after about ten days after the operation.

After surgery

Before the operation, postoperative rehabilitation must be planned.
It is required to walk with crutches or walker for a few weeks after the procedure.
Transports from the apartment to the hospital and back must be planned in advance.
With the daily activities such as cooking, taking a bath and doing laundry, you have to get help.
You should set up your apartment accordingly handicapped accessible and modify something.
Above all, you have to bring all the necessary items to the same floor (preferably to the ground floor or to a floor accessible by elevator), because climbing or descending stairs can be difficult.
Safety handles should be installed in the shower or bathtub.
Attach railings along the stairs.
If the toilet bowl is very low, you should use a suitable attachment.
To shower, possibly use a bench or a sturdy chair.
Remove any carpets or loose wires that are in the house.

Risks and complications of knee prosthesis

Knee replacement surgery may involve the following risks:

  • Infection
  • Blood clots in the leg or lungs
  • Heart attack
  • Stroke
  • Hematoma and joint effusion
  • Deep vein thrombosis
  • Pulmonary embolism
  • Nerve damage
  • Vascular damage
  • Keloid scarring
  • Leg length difference (one leg is longer than the other)

The risk of infection is low, but the following symptoms require immediate medical attention:

  • Fever above 37.8 °C
  • Ague
  • Pain in the drainage area
  • Redness, stiffness, knee swelling and pain

An infected knee implant is treated by surgery to remove the artificial body parts and perform antibiotic therapy to kill the bacteria.
After treatment of the infection, the revision is carried out with a new implant.
The prostheses can wear out.
If the new joints wear out a lot, another surgical intervention is needed to replace them.
Under daily stress, the prostheses wear out, even if they are made of metal or resistant plastic. Artificial parts wear out faster when activities with great stress and strain on the joints are practiced.

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