Unlike a total knee replacement, a partial knee replacement involves resurfacing a part of the knee. Also known as an unicondylar knee arthroplasty or unicondylar knee replacement, this surgery is reserved for those presenting degradation of the joint in specifically one compartment of the knee such as the:

• Medial compartment (inside of the knee)
• Lateral compartment  (outside of the knee)
• Patellofemoral compartment (front of knee between thigh bone and kneecap)

Partial knee replacements are more favoured in general due to their extensive benefits.

Individuals suitable for a partial knee replacement include the following:

• Patients who present with pain localised on either the inner or outer portion of the knee
• Patients presenting signs of moderate knee deformity
• Patients with conditions such as osteoarthritis that have gradually progressed in one specific compartment
• Patients who show no signs of improvement from previous conservative or more minimally invasive procedures
• Occasionally, older patients (80 years and above) even if they do not meet suitability criteria due to its’ less invasive nature
  

Contraindications of a partial/unicompartmental knee replacement include:

• Untreated torn ACL
• Significant angular deformity
• Morbidly obese
• Rheumatoid arthritis/inflammatory arthritis

This is because treating these conditions with partial knee replacements would generally be counter-productive.

Following your orthopaedic evaluation,  imaging tests such as x-rays or magnetic resonance imaging (MRI) will be conducted. Next, your orthopaedic surgeon will confirm surgery suitability and a surgery date will be assigned. During the surgery, an incision is first made over the knee. Muscles and other soft tissues will be cut to obtain a better view of your knee’s condition.  

The analysis of knee conditions is particularly important in partial knee replacement surgeries. If injuries are more significant than the ones presented in imaging tests– damage not limited to one compartment or significant injuries of ligament, your surgeon would perform a total knee replacement instead. The possibility and mechanism behind this decision will be informed and your consent will be gathered during the consultation itself.

Following assessment and confirmation that damage is limited to one compartment, damaged cartilage and bones are removed to provide space and to address injuries. The removed compartment of bones and cartilage is then replaced with metal implants fitted into the area or by cementation. Where cementless fixation is opted, the metal parts are press-fitted instead.

A plastic spacer is then inserted between the metal to provide a smooth gliding surface. Finally, the site of surgery is cleaned with antiseptic solution to prevent infections. The incisions are then closed with sutures.

• Quicker recovery
• Lesser pain compared to a complete knee replacement
• Less blood loss
• Lower risks and complications
• Higher preservation of the knee
• Minimally invasive compared to a total knee replacement
• Improved mobility

Partial / unicompartmental knee replacement surgery can be used to treat the following conditions:

• Unicompartmental osteoarthritis
• Connective tissue disorder
• Mild obesity
• Osteonecrosis
• Post-traumatic arthritis
• Avascular necrosis
• Bone dysplasia

Typically, partial knee replacements tend to have higher satisfaction than complete knee replacements with a reported 90-95% success rate. Unicompartmental knee replacements were described as feeling “more natural” than a total knee replacement. Higher bending and flexion capabilities have also been reported post-surgery.  

One may expect to return to their usual activities within 6 weeks as pain and stiffness subside. It would take up to 6 months to completely recover from a partial knee replacement. Additionally, discipline and dedication towards physiotherapy are key in recovery. Diets, habits, and rehabilitation frequency will play a role comprehensively.

You can generally expect an improved quality of life. With positive post-surgical care and collaborative work with your orthopaedist, you can expect a satisfactory outcome.

Results will vary from person to person, depending on the severity of the issue and your overall health. Your orthopaedist can give you a better idea of what to expect based on your individual needs and circumstances.

Implants from a partial knee replacement can last up to 25 years, with a potential need for recurring surgery slightly higher than total knee replacement. Whilst capable of lasting up to 25 years, revision is particularly prone among kids, women, and patients with obesity. Recurring surgery would be required when components wear out, loosen up, and if subsequent movement from the implants causes pain.