Guidelines for Instrumentation for Total Knee Replacement Based on Frontal Plane Radiographs

Area of Science:

• Orthopedic Surgery
• Biomechanical Engineering
• Medical Imaging

Background:

• Osteoarthritis significantly impacts knee joint biomechanics.
• Accurate pre-operative assessment is crucial for successful total knee arthroplasty (TKA).
• Current surgical instrumentation may not fully account for anatomical variations in arthritic knees.

Purpose of the Study:

• To quantify femur and tibia dimensions and angulations in knees scheduled for TKA.
• To inform the design of patient-specific surgical instruments, including 3D-printed cutting guides.
• To provide data for optimizing implant alignment and surgical technique.

Main Methods:

• EOS radiographs of 66 osteoarthritic knees were analyzed using CAD software.
• Anatomic and mechanical axes, joint lines, and key dimensions were measured for femur and tibia.
• Angulations between axes and joint lines, and femoral canal diameter were determined.

Main Results:

• The angle between anatomic and mechanical axes was 5.5° ± 1.4°.
• Femoral and tibial joint lines showed slopes of 2.2° and 4.3° to the mechanical axes, respectively.
• Femoral canal diameter at 150 mm from distal averaged 19 ± 5 mm, with a notable tibial slope increase compared to non-arthritic knees.

Conclusions:

• Aligning perpendicular to the mechanical axis in TKA results in approximately 2° valgus and 2-3° joint line tilt.
• Surgical instruments should be calibrated for individual patient anatomy, recognizing potential variations.
• A multi-diameter femoral intramedullary rod system is recommended to minimize alignment errors to 1° or less.