Close this search box.

Unicompartmental Knee Replacement


Knee Arthroplasty, also known as Knee Replacement, is a surgical procedure that replaces an arthritic knee joint or its part with an artificial joint. The primary goals of this surgery are to alleviate pain, restore function, and preserve knee anatomy.

Depending on the extent of the joint destruction it can involve replacing the whole knee joint, total knee replacement, or only its part, unicompartmental knee replacement.

With a Unicompartmental Knee Replacement, only the affected portion of the knee joint is replaced, hence it is a less invasive procedure than would normally be used for a total knee replacement. As a result, most patients resume their daily activities more quickly than those who undergo a total knee replacement.

Please find below more detailed information on the unicompartmental knee arthroplasty procedure, which includes what to expect before, during, and after the surgery, as well as information on the recovery period.

Indications and Contraindications

Suitable candidates for Unicompartmental Knee Replacement:
  • Patients with Arthritis limited to only one compartment of the knee, which is confirmed by an x-ray.
  • Ideally, patients should be over 60 years of age.
  • Patients should have a BMI (body mass index) of less than 30.


Unsuitable candidates for Unicompartmental Knee Replacement:
  • Patients with arthritis affecting more than one compartment of the knee
  • Patients with severe angular deformities in the knee
  • Patients with an unstable knee
  • Patients who have undergone a previous osteotomy (surgical procedure to realign bones)
  • Patients who are involved in heavy physical work or contact sports

Benefits and Risks


You can find about general benefits of knee replacement here. There are also some specific benefits related particularly to Unicompartmental Knee Replacement:

  • Smaller operation with a smaller incision.
  • Removal of a smaller amount of bone.
  • Shorter hospital stay.
  • Quicker recovery.
  • Less pain after surgery.
  • Reduced blood loss, with blood transfusions rarely required.
  • Greater range of motion in the knee.
  • A more ‘natural’-feeling knee post-surgery, as the bone, cartilage, and ligaments in the healthy parts of the knee remain untouched.
  • Requires a smaller amount of post-surgery physiotherapy.
  • Patients can be more active after the surgery compared to a Total Knee Replacement.
  • In the event of failure or complications of the unicompartmental replacement in the future, revision to a Total Knee Replacement is relatively easy and straightforward.


  • A Unicompartmental Knee Replacement is not as reliable or predictable in completely alleviating all the pain associated with osteoarthritis compared to a Total Knee Replacement.
  • There may be a need for more surgery in the future, and a Total Knee Replacement may be required if arthritis develops in the parts of the knee that have not been replaced.

Surgical Approach

The approach to unicompartmental knee replacement involves surgically replacing only the damaged or arthritic part of the knee joint, preserving the healthy areas. With such an approach knee function can be restored with less surgical damage to the knee tissues and preserving more of the natural patient’s tissues. In a UKR, only the damaged compartment is replaced with metal and plastic components. The remaining healthy cartilage and bone in the rest of the knee are left untouched.   

Pre-Surgery Information

Prior to unicompartmental knee replacement surgery, the following procedures and preparations will take place:

  1. Patient Evaluation: A thorough assessment of the patient’s overall health, medical history, and orthopaedic condition. When necessary, your health might need optimisation and we may refer you to another specialist.
  2. Medications: Inform your healthcare provider about any medications you’re taking, as some may need to be adjusted before surgery. You should stop taking aspirin or anti-inflammatory medications 10 days prior to the surgery. Also, you should discontinue any naturopathic or herbal medications during this period.
  3. Imaging: X-rays, CT scans, and MRIs are used to evaluate the extent of damage and plan the surgery. CT scans are especially helpful in planning the surgical steps.  
  4. Skin preparation: The night before and on the morning of the operation, you will be asked to wash the leg with a sponge provided at the pre-admission clinic. If there is any suspicion of an iodine allergy, a Betadine Skin test might be used.
  5. Bowel Prep: Glycerin suppositories will be provided at the pre-admission clinic, and you will need to administer them the evening prior to the surgery. An instruction leaflet will be given to guide them.
  6. Patient education: During a physiotherapy assessment, a qualified physical therapist will provide you with personalised instructions on gait training, the use of crutches, and pre- and postoperative exercises. You will be fitted with crutches to take home and practise before the surgery.

On the day of the Surgery

  • Surgical paperwork will be administered by the nurses, and the anaesthetist will meet with the patient to ask a few questions.
  • A hospital gown will be given, and the operation site will be shaved and cleaned.
  • Betadine skin prep will be applied to the area above the operation site and wrapped.
  • All x-rays are to be sent with the patient to the theatre.

Surgical Procedure

Unicompartmental Knee Replacement surgery is performed under spinal or general anaesthesia. The entire procedure typically takes one to two hours.

Step 1: Bone Preparation

An incision of about 7cm is made to expose the bones of the knee joint. The damaged cartilage surfaces at the ends of the femur (thigh bone) and tibia (shin bone) are carefully removed.

Step 2: Implant Positioning

Specialised jigs are used to precisely cut the femur and tibia at the appropriate angles. Test components are then inserted to check the accuracy of the cuts and determine the thickness of plastic required to be placed between the two components.

Each knee is unique to the patient, and the knee replacement implants come in various sizes to cater to individual needs. If there is more than the standard amount of bone loss, additional pieces of metal or bone may be added.

Step 3: Implant Insertion and Spacer Placement

The surgeon replaces the damaged cartilage and bone with permanent implants that closely resemble the former structure of the joint. Implants can be fixed in place with medical-grade cement or a press-fit technique that encourages bone growth onto the implant.

To create a smooth, gliding surface within the knee joint, a medical-grade plastic spacer is inserted between the metal components. This spacer enhances the knee’s mobility and helps prevent friction, providing a more comfortable experience.


Post-Procedure Care:

After these steps are completed, the knee is thoroughly checked to ensure that all components are correctly positioned and working as intended. The knee is then meticulously closed, then a dressing and drains are applied.

Post-Surgery Information

Immediate Post-Surgery:

Following the surgery, patients will be taken to the recovery room for monitoring. Once their condition stabilises, they will be transferred to the ward.

The patient will be set up with a button for self-administered pain relief through a machine called a PCA machine (Patient-Controlled Analgesia). It is crucial for patients to use the PCA machine as prescribed by their healthcare provider to avoid overmedication.

Patients will be encouraged to start moving their knee and walking within a day or two of the surgery. The surgical wound dressing will usually be reduced on the second day post-op to make movement easier. A physiotherapist will be available to guide them through exercises and assist with rehabilitation and mobility.

Discharge: The expected hospital stay after the surgery is approximately three to five days. Depending on individual needs and situations, patients may be discharged home or transferred to a rehabilitation hospital. It is essential to continue with the prescribed physiotherapy exercises for a successful recovery.

The Recovery Process:

Following discharge, patients may require a walker or crutches for about six weeks. As their leg gains strength and control, they can transition to using a walking stick under the guidance of a healthcare provider. Patients may resume driving around the six-week mark, but only when they feel confident that they’ve regained leg control.

The degree of knee flexion will vary from patient to patient, but ideally, the goal is to achieve at least 120 degrees of movement. 

Upon returning home, an occupational therapist will assess the patient’s living space and provide necessary precautions. This may include installing rails in the bathroom or adjusting sleeping arrangements if there are stairs in their home.

Patients typically experience a reasonable level of comfort while walking within six weeks after the procedure. Engaging in more physically demanding activities, such as sports, may require up to three months to achieve a comfortable level of performance.


If patients are worried about their level of pain, experience significant bleeding, or notice fever or redness around the surgical site, they should contact the office immediately. If assistance is needed after hours, patients can contact the hospital where the surgery was performed, and they will contact Professor Al Muderis on their behalf.

Norwest Private Hospital: (02) 8882 8882

Macquarie University Hospital: (02) 9812 3000

This treatment could be eligible for our No 'Out-of-Pocket' Expenses Program

For further information, click here or to check your eligibility, please contact our team.