Unicompartmental Knee Replacement

Unicompartmental Knee Replacement

Unicompartmental 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: compartment in front of the knee between the kneecap and thighbone
  • medial compartment: inside portion of the knee
  • lateral compartment: 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

Arthritis is the 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, the articular cartilage allows for smooth movement within the joint, where as in an arthritic knee, the cartilage becomes thin or wears-off completely. In addition, the bones become thicker around the edges of the joint and may form bony spurs. These factors can cause pain and restricted range-of-motion in the joint.


The exact cause is unknown, however there are several 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


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.


Your doctor will diagnose osteoarthritis based on your medical history, a thorough physical examination and X-rays.

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


Treatment may include conservative measures such as medications, injections and physiotherapy. However, your doctor may recommend surgery if nonsurgical treatment options have failed to relieve the symptoms.

During the surgery, a small incision is made over the knee to expose the knee joint. Your surgeon will remove only the damaged part of the meniscus and place the implant into the bone by slightly shaping the shinbone and thighbone. The plastic component is placed into the newly prepared area and is secured with bone cement. Now, the damaged part of the femur or thighbone is removed to accommodate the new metal component, which is fixed in place using bone cement. Once the femoral and tibial components are fixed, the knee is taken through a range of movements. The muscles and tendons are then repaired, and the incision is closed.

Postoperative care

You may walk with the help of a walker or cane for the first 1-2 weeks after surgery.  A 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.

Risks and complications

Possible risks and complications associated with unicompartmental knee replacement include:

  • Knee stiffness
  • Knee stiffness
  • Infection
  • Blood clots (deep vein thrombosis)
  • Nerve and blood vessel damage
  • Ligament injuries
  • Patella (kneecap) dislocation
  • Wearing of the plastic liner
  • Loosening of the implant


The advantages of unicompartmental knee replacement over total knee replacement include:

  • Smaller incision
  • Less blood loss
  • Quick recovery
  • Less postoperative pain
  • Better overall range of motion
  • Feels more like a natural knee
Luton and Dunstable University Hospital
  • Spire Healthcare
  • OSD Healthcare
  • The London Clini
  • One Hatfield Hospital
  • The Royal College of Surgeons of Edinburgh