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

Indication limits of unicompartmental knee prosthesis

Sled prostheses are only suitable for patients whose knee arthrosis is limited to a single compartment area, 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 suitable. Additionally, the cruciate ligaments must be functional as they ensure the stability of the knee. In cases of ligament instability or knee malalignment that cannot be corrected, partial knee replacement is not recommended.

Risks and disadvantages of unicompartmental knee prosthesis

• Higher revision rate: Studies show that unicompartmental knee replacements need to be revised more frequently than total knee replacements. The reason often lies in inadequate indication or problems with the remaining natural knee joint, which can continue to wear out.

• Limitation in later surgeries: Even though a unicompartmental prosthesis can generally be converted to a total prosthesis more easily, such revision surgeries are more demanding if the implantation was not performed precisely.

• Increased demands on the surgeon's experience: The successful implantation of a unicompartmental knee prosthesis requires high surgical expertise. In experienced hands, the result can be very good, but in inexperienced hands, the risk of complications such as malpositioning and instability increases.

Long-term durability

While modern unicompartmental knee prostheses are comparable to total knee prostheses in terms of durability, this depends heavily on precise implantation and the choice of the correct indication. Errors can lead to premature failure of the prosthesis, requiring further surgery

When is a unicompartmental knee prosthesis not worth it?

• Generalized condition: Patients with advanced or generalized osteoarthritis in all compartments of the knee do not benefit from a partial joint replacement.
• Knee instability: If the knee is unstable due to ligament damage, a unicompartmental prosthesis will not result in satisfactory stability.
• Severe malalignment: In cases of pronounced malalignment, such as bowlegs or knock knees, correction with a unicompartmental prosthesis can be difficult or inadequate.

Conclusion

Sled prostheses offer a minimally invasive option to replace targeted damaged areas of the knee while largely preserving natural joint functions. Nevertheless, they should only be used with suitable indications and by experienced surgeons. In cases of generalized arthrosis, instabilities, or complex malalignments, total knee arthroplasty is a better choice as it provides a more comprehensive solution for the entire knee joint.

With careful weighing of pros and cons and accurate diagnosis, a unicompartmental knee prosthesis can be an excellent solution for selected patients.