Does the type of tibial component affect mechanical alignment in unicompartmental knee replacement?

Area of Science:

• Orthopedic surgery
• Biomaterials science
• Biomechanics

Background:

• Unicompartmental knee replacement (UKR) longevity depends on factors like postoperative alignment and material type.
• The influence of component design and material on UKR postoperative alignment remains underexplored.

Purpose of the Study:

• To investigate the impact of different unicompartmental knee replacement (UKR) component designs on postoperative mechanical alignment.
• To compare the alignment outcomes between all-polyethylene inlay and metal-backed onlay tibial components in UKR.

Main Methods:

• Retrospective review of 89 patients undergoing robot-assisted UKR.
• Patients were categorized into two groups: all-polyethylene inlay and metal-backed onlay components.
• Analysis focused on the degree of mechanical alignment correction achieved in each group.

Main Results:

• The metal-backed onlay group achieved significantly better postoperative mechanical alignment (mean 2.8°) compared to the all-polyethylene inlay group (mean 3.9°).
• Tibial polyethylene insert thickness was identified as a significant factor influencing postoperative alignment.
• Results were adjusted for patient demographics and preoperative alignment.

Conclusions:

• Metal-backed onlay tibial components result in superior postoperative mechanical alignment in UKR compared to all-polyethylene inlay prostheses.
• The thicker construction of onlay components is a key factor in achieving optimal alignment.
• Onlay prostheses are recommended as the primary choice for medial UKR due to improved alignment and higher survivorship rates.