Personalizing Revision Tibial Baseplate Position and Stem Trajectory With Custom Implants Using 3D Modeling to...

Area of Science:

• Orthopedic Surgery
• Biomedical Engineering
• Implant Design

Background:

• Revision total knee arthroplasty (TKA) commonly uses press-fit stems engaging the diaphysis.
• Tibial canal bowing frequently necessitates compromises in implant selection for optimal patient anatomy fit.
• Current stemmed implants may not adequately address anatomical variations, potentially limiting fixation.

Purpose of the Study:

• To evaluate, using 3D modeling, if current press-fit tibial stem options fit patient anatomy.
• To determine if an alternative stem-to-baseplate angle can enhance cortical engagement for long press-fit tibial stems.

Main Methods:

• 3D models were created from preoperative CT scans of 100 TKA patients.
• Tibial stems were modeled at both a fixed perpendicular angle and a custom angle to the revision baseplate.
• Measurements included stem diameter, depth, offset, and contact surface area for comparative analysis.

Main Results:

• Custom free-angle stem placement resulted in significantly greater cortical contact and larger stem diameter compared to fixed 90-degree placement (P < .001).
• Custom placement was associated with a smaller offset of the stem from the baseplate center.
• Significant demographic differences influenced these outcomes.

Conclusions:

• Custom free-angle stem placement enhances press-fit tibial stem fixation by increasing cortical contact and stem diameter.
• Existing revision tibia implants with fixed 90-degree interfaces can mismatch patient anatomy, limiting fixation.
• Alternative custom keel angles may offer improved solutions for patients with significant anatomical mismatches.