Total knee replacement

Total Knee Replacement

What does total knee replacement / arthroplasty mean?

Knee replacement surgery is also called as arthroplasty and this procedure involves removing parts of the damaged knee and replacing them with artificial parts called prosthesis.

Your orthopedic joint replacement surgeon will remove the damaged and diseased portions at the end of the femur (thigh bone) and top of tibia (shin bone) and replace them with artificial implants made up of metal or plastic. Each bone is shaped to exactly fit the prosthesis. Components are then attached to the thigh bone, shin and knee cap, most commonly using surgical cement. The surgeon may need to resurface the back of the kneecap, known as the patella.

The artificial prostheses consist of three pieces:

Femoral component – metal piece that caps the end of the femur and has a groove, which allows the kneecap to move up and down as the knee bends and straightens

Tibial component – flat piece of a metal with a plastic plate that covers the top of the tibia.

Patellar component – dome-shaped piece of plastic that allows it to glide

Diagnosis:

Physical examination: Medical history, symptoms, and level of pain, muscle strength, joint motion, and knee alignment. Blood tests and other laboratory tests

Radiographic Evaluation: X-rays, Magnetic Resonance Imaging (MRI)

What are the goals of Total knee replacement (TKR)/ Total knee arthroplasty (TKA)?

The following are the clinical goals of a Total Knee Replacement(TKR) procedure

  • To put the implants in a correct alignment and position
  • To ensure that the remaining soft tissues are balanced
  • To ensure that the implant is well fixed to the bone
  • To ensure that the implant used is designed to offer high level of function & longevity
  • The above clinical goals translate to the following qualitative goals from a patient standpoint
  • To relieve pain
  • To restore function
  • To last as long as possible
How is knee replacement done- An Overview

When the decision is made to perform a total knee replacement, your orthopedic surgeon will require a few activities to be completed prior to knee replacement surgery that may include the following:

Complete Physical Examination: Your doctor will ask for an examination as well as some tests to be completed such as blood work, an EKG, and a chest x-ray.

Surgical Consultation: Your doctor will review the procedure with you and answer the questions if any. You will need to sign a surgical consent form. Doctor will also review the test results from your physical examination and you will notify the surgeon of any allergies or medications you currently take.

Patient preparation for Knee surgery:
  • Consumables used in this step include (but not limited to) bandage / drape for wrapping patient’s legs, leg positioning tools and anesthesia for the patient.
  • Supine positioning on the OR table
  • Pneumatic tourniquet is used (high up in the thigh) to minimize blood loss during surgery
  • Special table support may be used to allow the knee to be flexed and extended several times during the procedure
  • Required levels of anesthesia (general anesthesia) are given to the patient
A Step-by-step guide on preparation before knee surgery.

Alignment of the axes

In a normal knee, there are two axes:

Mechanical axis: this is a straight line that connects the femoral head, passes through the knee and the center of the ankle joint.

Anatomical axis: this is a straight line that passes through the bone shaft of the femur as well as the tibia

On the femoral side, there is 5-7 degrees of angular difference between the anatomical axis and the mechanical axis, whereas the axes are parallel on the tibial side.

In a deformed knee these angles deviate from the nominal values and hence bone cuts have to be made at specific angles in order to achieve appropriate alignments on the femoral as well as tibial side.

This is one of the critical goals of the Total Knee replacement procedure and hence several precision instruments are provided that produce artificial prostheses in order to enable the surgeons to measure the deviations and plan for appropriate cuts to achieve alignment between the axes and the components.

Overview of femoral and tibial cuts in Total Knee Replacement-

The surgeon goes through the following bone cuts on the distal femoral end and proximal tibial side once the appropriate plan is made based on the axes alignments.

  • Transverse distal femoral cut
  • Medial/lateral femoral jig location
  • Anterior femoral cut
  • Posterior femoral cut
  • Anterior and posterior femoral chamfer cuts
  • Transverse proximal tibial cut
  • Overview of Femoral & tibial cuts

Note: All surgeons do not follow the exact sequence of cuts listed above. They differ based on their preferences and surgical training.

There are 2 surgical techniques which the surgeons follow
  • Posterior referencing
  • Anterior referencing

and based on these techniques, the instrumentation is used.

Overview of implanting of prosthesis in Total Knee Replacement

Once the satisfactory cuts are made and the trailing is done, the actual components (Femoral component, tibial component and poly liner) are fixed with the help of bone cement. Implanting prosthesis in Total Knee Replacement

Post-Operative Care/ rehabilitation

Once the knee surgery is completed, the patient will be transferred to a room for close observation of vital signs, circulation, and pain management. Once the patient is awake, you may notice the following:

  • A drain near incision to collect the drainage and monitor its amount
  • Elastic hose or compression stockings to help minimize the risk of blood clots
  • Bandage covering the incision area to maintain cleanliness and prevent infection
  • Pain pump to manage pain levels
  • Catheter inserted into your bladder
  • Ice packs to reduce the swelling in knee area
  • You can expect to be up on your feet within a day. That might be hard to do on your own at first. So you may need parallel bars, crutches, a walker, or a cane for a while.

Usually, you can expect a big improvement in flexibility and much less pain within a month. It is important to exercise your knee often; initially you will need help of physiotherapist to keep down swelling and to strengthen your muscles.

One of the first priorities is to get your new knee moving – to regain the range of motion.

Following total knee replacement surgery, patients are encouraged to resume an active lifestyle.