Candidates for unicondylar replacement
Partial knee replacement is most appropriate when arthritis is truly limited to one compartment and the rest of the knee is functioning well enough to preserve.
Ideal Patient Characteristics
- Isolated medial compartment osteoarthritis
- Intact anterior cruciate ligament (ACL)
- Correctable varus deformity (typically <15-20°)
- Body mass index (BMI) <35-40
- Realistic expectations about recovery and potential revision
- Active lifestyle with desire to return to recreational activities
Age Considerations
Unlike earlier guidelines that restricted partial knee replacement to older patients, current evidence shows excellent outcomes across all age groups when selection criteria are met. Younger patients (<60) can benefit from partial replacement as it preserves bone stock for potential future revisions, while older patients (>75) may prefer the quicker recovery and lower complication rates compared to total knee replacement.
Patient Selection Criteria
The ideal candidate has arthritis confined to one knee compartment (most commonly the medial compartment) with intact cruciate ligaments and correctable deformity. Modern imaging techniques, including MRI and weight-bearing X-rays, help confirm isolated compartment involvement. Patients should be willing to accept the possibility of revision surgery if the partial replacement does not provide adequate relief.
Body mass index is less restrictive than previously thought, with good outcomes reported in patients with BMI up to 40. However, patients with inflammatory arthritis, severe patellofemoral disease, fixed deformities greater than 20°, or ACL deficiency are generally not candidates for partial knee replacement.
Approximately 5-10% of patients with knee osteoarthritis meet the criteria for partial knee replacement. With modern implant designs and surgical techniques, including robotic assistance, survival rates exceed 85% at 10-15 years, making it an excellent option for appropriately selected patients.