Partial or Unicondylar Knee Replacement

What is unicondylar knee replacement?

Unicondylar knee replacement, is a minimally invasive surgery in which only the damaged compartment of the knee is replaced with an implant. It is also called a partial knee replacement. The knee can be divided into three compartments: patellofemoral, the compartment in front of the knee between the knee cap and thigh bone, medial compartment, on the inside portion of the knee, and lateral compartment which is the area on the outside portion of the knee joint.

Traditionally, total knee replacement was commonly indicated for severe osteoarthritis of the knee. In total knee replacement, all worn out or damaged surfaces of the knee joint are removed and replaced with new artificial parts. Partial knee replacement is a surgical option if your arthritis is confined to a single compartment of your knee.

Disease Overview

What is arthritis?

Arthritis is inflammation of a joint causing pain, swelling (inflammation), and stiffness.

Osteoarthritis is the most common form of knee arthritis in which the joint cartilage gradually wears away. It most often affects older people. In a normal joint, articular cartilage allows for smooth movement within the joint, where as 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.

What are the causes of arthritis?

The exact cause is unknown, however there are a number of factors that are commonly associated with the onset of arthritis and may include:

  • Injury or trauma to the joint
  • Fractures of the knee joint
  • Increased body weight
  • Repetitive overuse
  • Joint infection
  • Inflammation of the joint
  • Connective tissue disorders

What are the symptoms of arthritis?

Arthritis of the knees can cause knee pain, which may increase after activities such as walking, stair climbing, or kneeling.

The joint may become stiff and swollen, limiting the range of motion. Knee deformities such as knock-knees and bow-legs may also occur.

How is arthritis diagnosed?

I will diagnose osteoarthritis based on your medical history, physical examination, and X-rays.

X-rays typically show a narrowing of joint space in the arthritic knee.

How is the surgical procedure performed?

I will discuss surgery if non-surgical treatment options such as medications, injections, and physical therapy have failed to relieve the symptoms and is tests (including previous arthroscopy, X-ray and bone scan confirm that the arthritis is localized to only one compartment (usually the medial) of the knee.

During the surgery, a small incision is made over the knee to expose the knee joint. I will remove only the damaged part of the joint and place the implant into the bone by slightly shaping the tibia bone and the thigh bone. The metal backed plastic component is placed into the new prepared area and is secured with bone cement. Now the damaged part of the femur is removed to accommodate the new metal component which is fixed in place using bone cement. Once the femoral and tibial components are fixed in proper place the knee is taken through a range of movements and ligament balance and alignment checked. The muscles and tendons are then repaired and the incision is closed.

There is no Joint Registry evidence anywhere in the world confirming the Robotic or Computer Assisted Partial Knee Replacement gives better results that non- robotic and non-computer assisted. I was involved with the development of Computer Assisted Partial Knee Replacement technology (precursor of Robotic Surgery) with the leading German company BrainLab some years ago. I will explain to you personally why this experience has not convinced me to use Robotic Surgery today.

What post-operative care may be necessary following the procedure?

You may walk with the help of a stick/cane for the first 1-2 weeks after surgery. Our hospital physiotherapist will advise you on an exercise program to follow for 4 to 6 months to help maintain range of motion and restore your strength. You may perform exercises such as walking, swimming and biking but high impact activities such as jogging should be avoided to minimize wear of the plastic component.

What are the risks and complications associated with unicompartmental knee replacement?

Possible risks and complications associated with unicompartmental knee replacement include:

  • Knee stiffness
  • Infection
  • Blood clots (Deep vein thrombosis)
  • Nerve and blood vessel damage
  • Ligament injuries
  • Patella (kneecap) dislocation
  • Plastic liner wears out
  • Loosening of the implant

What are the advantages of unicompartmental knee replacement?

The advantages of Unicompartmental Knee Replacement over Total Knee Replacement include:

  • Smaller incision
  • Less blood loss
  • Quick recovery
  • Less post-operative pain
  • Better overall range of motion
  • Feels more like a natural knee

However, Joint Registry and other data strongly suggests that surgeons must do 30 cases per year to do this tricky, difficult operation well. It is a much harder operation than a Total Knee Replacement.

I have been on design teams for 2 different partial knee replacements (Preservation and subsequently the Sigma HP). The Sigma HP Partial Knee Replacement has the second lowest 5-year Revision Rate in the 2017 AOANJRR annual report and lower than the 2 other prostheses with more frequent use in 2016. This prosthesis is for medial or lateral unicompartmental disease.

Partial Knee Replacement is one of my 2 VERY special interests and I have done far more of these procedures than any surgeon in SA.

I also perform a partial replacement confined to the patella-femoral joint (kneecap) and perform about 15 of these per year There are only 230 performed nationally per year. My revision rate for these cases is a third (1/3) the national average. I use the Zimmer Gender Solutions prosthesis which is selected nationally 3 times more often than any of its competitors.

Many of the lectures that I have given overseas and in Australia have been on this topic of Partial (Unicompartmental) Knee Replacement


I or my family receive no incentives of any kind for my selection of joint prosthesis. I select only the best performing prostheses

Make sure you ask this question of any other joint replacement surgeon you may see for your knee.