Changes in postoperative extension angle after total knee arthroplasty: Effect of polyethylene insert thickness

Area of Science:

• Orthopedic Surgery
• Biomaterials Science

Background:

• Flexion contracture is a significant complication following total knee arthroplasty (TKA).
• Excessive polyethylene insert (PE) thickness relative to the surgical extension gap is a primary cause of flexion contracture.
• Understanding the relationship between PE thickness, extension gap, and postoperative range of motion is critical.

Purpose of the Study:

• To analyze the temporal changes in the postoperative extension angle after TKA.
• To investigate the correlation between the "gap difference" (PE thickness minus extension gap) and the extension angle over time.
• To determine if thicker PE implants contribute to persistent flexion contracture.

Main Methods:

• A retrospective analysis of 127 TKAs was conducted.
• Patients were grouped based on the "gap difference" between PE thickness and the extension gap (0-3 mm or greater).
• Postoperative extension angles were measured and correlated with the gap difference at multiple time points up to 2 years.

Main Results:

• Extension angles showed an initial worsening at 3 months post-surgery, followed by improvement up to 2 years.
• A negative correlation was observed between gap difference and extension angle at both surgery and 2-year follow-up.
• Groups with larger gap differences exhibited significantly worse 2-year extension angles, indicating persistent flexion contracture.

Conclusions:

• Postoperative extension deficits in TKA can worsen initially but may improve over time.
• A significant correlation exists between the gap difference and extension angle, persisting for at least 2 years.
• Appropriate selection of polyethylene insert thickness, considering the intraoperative extension gap, is essential to minimize the risk of flexion contracture after TKA.