Maximizing tibial coverage is detrimental to proper rotational alignment

Area of Science:

• Orthopedic surgery
• Biomechanical engineering
• Implant design

Background:

• Traditional total knee arthroplasty (TKA) prioritizes tibial component coverage.
• The impact of maximal coverage on rotational accuracy for symmetric and asymmetric tibial components is not well-defined.
• Implant design may influence rotational placement accuracy.

Purpose of the Study:

• To quantify malrotation in tibial components placed for maximal coverage.
• To compare malrotation between symmetric and asymmetric tibial component designs.
• To evaluate rotational accuracy using a computer model with CT reconstructions.

Main Methods:

• Utilized CT reconstructions of 30 tibial specimens.
• Generated 3D tibia models, noting anatomic axis, tibial tubercle, and resected surface.
• Placed two symmetric and two asymmetric tibial components based on maximal coverage criteria.

Main Results:

• 70% of all components placed for maximal coverage exhibited internal malrotation (average 9°).
• Asymmetric designs showed significantly lower malrotation rates (28% and 52%) versus symmetric designs (100% and 96%; p < 0.001).
• Average malrotation was less with asymmetric designs (2°, 5°) compared to symmetric designs (14°; p < 0.001).

Conclusions:

• Maximizing tibial coverage frequently results in component malrotation.
• Asymmetric tibial designs are more likely to achieve correct rotational positioning.
• Further clinical research is needed to assess the impact of asymmetric designs on TKA outcomes.