In a partial, or unicompartmental, knee replacement only the damaged compartment of the knee is resurfaced. The healthy cartilage and both cruciate ligaments are preserved. For the right patient it offers a knee that feels closer to normal than a total replacement, with a smaller operation and a faster recovery.
The knee has three compartments: medial, lateral and patellofemoral. Osteoarthritis frequently begins in, and for years remains confined to, the medial compartment. A total knee replacement resurfaces all of them and removes the anterior cruciate ligament. A partial replacement resurfaces only the worn compartment through a smaller incision, removes far less bone and keeps the ligaments that give the knee its proprioception. Patients commonly describe the result as feeling like their own knee.
Suitability is decided on examination and imaging, not on age alone. The favourable pattern is arthritis limited to one compartment, an intact anterior cruciate ligament, a deformity that corrects passively, a good range of movement with less than fifteen degrees of fixed flexion, and pain localised to the affected side of the joint. Inflammatory arthritis, significant patellofemoral or lateral compartment disease, a deficient cruciate ligament or a fixed deformity point towards a total replacement instead. Final confirmation is often made intraoperatively after inspecting the other compartments.
Compared with total knee replacement, partial replacement involves less blood loss, less post-operative pain, a shorter hospital stay, better flexion and a more natural gait pattern. Complication rates including infection and thromboembolism are lower. Many patients are discharged the day after surgery.
Revision rates for partial replacement are higher than for total replacement in registry data, largely because arthritis can progress in the remaining compartments and because the threshold for revising a partial knee is lower. The counterweight is that conversion of a failed partial replacement to a total replacement is usually a straightforward procedure, close to a primary operation. Careful patient selection and accurate implant positioning — where robotic assistance is particularly valuable — are what determine long-term success.
Patients walk on the day of surgery and usually leave hospital within one to two days. Crutches are needed for one to two weeks, driving resumes at two to four weeks and desk work at three to four weeks. Cycling, swimming, golf and hiking are all realistic goals. Rehabilitation focuses on regaining full extension and quadriceps strength.
If you have been told you need a knee replacement, it is worth establishing whether your arthritis is confined to one compartment — a decision that changes the operation you are offered. A second opinion with weight-bearing radiographs is the starting point.
to guide you about your condition, to choose the best possible treatment.
