[Knee endoprosthesis: biomechanical requirements and consequences].

Area of Science:

• Orthopedic surgery
• Biomechanical engineering
• Musculoskeletal research

Background:

• Total knee arthroplasty (TKA) aims to restore knee function and reduce pain.
• Understanding the biomechanical impact of different TKA designs, specifically inlay types, is crucial for improving patient outcomes.
• Assessing the mechanical efficiency of the quadriceps muscle post-TKA provides insight into functional recovery.

Purpose of the Study:

• To dynamically measure the in vitro mechanical efficiency of the quadriceps muscle before and after total knee arthroplasty (TKA).
• To evaluate tibiofemoral pressure and inlay movement in both fixed and mobile polyethylene inlays within a TKA system.
• To compare the biomechanical performance of a mobile inlay TKA system against a fixed inlay system.

Main Methods:

• Utilized 8 fresh frozen knee cadavers implanted with the Interax TKA system.
• Mounted specimens on a knee-simulating machine to perform isokinetic extension under a constant torque (31 Nm).
• Measured quadriceps muscle force, tibiofemoral pressure on fixed and mobile inlays, and inlay migration patterns.

Main Results:

• Quadriceps muscle force did not significantly increase after TKA prosthesis implantation.
• Mobile inlays experienced 60% lower pressure compared to fixed inlays.
• The mobile inlay demonstrated a 4-mm posterior migration on the tibial base plate, with its contact area remaining centered during motion, unlike the fixed inlay.

Conclusions:

• The Interax mobile inlay TKA system demonstrates favorable biomechanical properties, including reduced pressure and stable contact area.
• The findings suggest that mobile inlays may offer improved load distribution and joint congruence compared to fixed inlays.
• Further research is warranted to correlate these in vitro findings with long-term clinical efficacy and patient-reported outcomes in TKA.