A partial knee replacement, also known as a unicompartmental knee replacement, is a minimally invasive solution for unilateral osteoarthritis of the knee joint. It replaces only the damaged part of the knee, preserving healthy structures such as ligaments, the kneecap, and cartilage. While this method offers many advantages, there are also clear limitations and situations in which a partial knee replacement is not recommended.

Limits of indication for partial knee replacement

Partial knee replacements are only suitable for patients whose knee osteoarthritis is limited to a single compartment, usually the medial side. However, if there is advanced cartilage wear in multiple areas of the knee, a total knee replacement (total endoprosthesis) is more appropriate. Furthermore, the cruciate ligaments must be functional, as they ensure the stability of the knee. Partial knee replacements are not recommended in cases of ligament instability or knee misalignment that cannot be corrected.

Risks and disadvantages of partial knee replacement

• Higher revision rate: Studies show that partial knee replacements require revision more frequently than total knee replacements. This is often due to an inadequate indication or problems with the remaining natural knee joint, which can continue to wear down.

• Limitations for later operations: Even though a partial denture can generally be converted into a total denture more easily, such revision procedures are more demanding if the implantation was not performed precisely.

• Increased demands on the surgeon's experience: Successful implantation of a partial knee replacement requires a high level of surgical expertise. In experienced hands, the result can be very good, but with inexperienced surgeons, the risk of complications such as malposition and instability increases.

Long-term durability

While modern partial knee replacements are comparable to total knee replacements in terms of durability, this depends heavily on precise implantation and the selection of the correct indication. Errors can lead to premature failure of the prosthesis, necessitating further surgery

When is a partial knee replacement not worthwhile?

• Generalized disease pattern: Patients with advanced or generalized osteoarthritis in all compartments of the knee do not benefit from partial joint replacement.
• Knee instability: If the knee is unstable due to damage to the ligaments, a unicompartmental knee replacement will not result in satisfactory stability.
• Severe deformities: In cases of pronounced deformities such as bowlegs or knock-knees, correction with a unicompartmental knee replacement may be difficult or insufficient.

Conclusion

Partial knee replacement offers a minimally invasive option for selectively replacing damaged areas of the knee while largely preserving natural joint function. However, it should only be used when appropriate and by experienced surgeons. In cases of generalized osteoarthritis, instability, or complex malalignment, total knee replacement is a better choice, as it provides a more comprehensive solution for the entire knee joint.

With careful consideration of the advantages and disadvantages and an accurate diagnosis, a partial knee replacement can be an excellent solution for selected patients.