This study extends the functional knee phenotype concept beyond the coronal plane by adding the posterior condylar angle and anterior trochlear angle. It asks whether patients with the same coronal alignment have predictable rotational alignment, and how often all four knee joint lines are congruent. It then simulates how mechanical, anatomical, and kinematic concepts affect the trochlea and flexion gap.
The clinical rule: coronal alignment does not predict femoral rotation, so you cannot infer trochlear or posterior condylar orientation from a standing alignment film. This paper extends the functional knee phenotype framework into the axial plane, adding the posterior condylar angle and anterior trochlear angle to the coronal femoral and tibial angles.
The key teaching point is the trade-off built into off-the-shelf implants. Because the trochlea and posterior condyles sit at a fixed angle on the implant, any rotation you pick to balance the flexion gap simultaneously sets patellar tracking. With only 2.3% of knees having all four joint lines congruent, most patients force you to compromise either the flexion gap or the 'third space' of the patellofemoral joint.
For boards, connect this to the alignment-concept debate: mechanical, anatomical, restricted kinematic, and kinematic alignment each shift the joint lines differently, and none restores all four. Preoperative CT planning should therefore assess the anterior and posterior femoral joint lines, not just the coronal lines. This remains an emerging concept, not settled practice.
This study extends the functional knee phenotype concept beyond the coronal plane by adding the posterior condylar angle and anterior trochlear angle. It asks whether patients with the same coronal alignment have predictable rotational alignment, and how often all four knee joint lines are congruent. It then simulates how mechanical, anatomical, and kinematic concepts affect the trochlea and flexion gap.
The clinical rule: coronal alignment does not predict femoral rotation, so you cannot infer trochlear or posterior condylar orientation from a standing alignment film. This paper extends the functional knee phenotype framework into the axial plane, adding the posterior condylar angle and anterior trochlear angle to the coronal femoral and tibial angles.
The key teaching point is the trade-off built into off-the-shelf implants. Because the trochlea and posterior condyles sit at a fixed angle on the implant, any rotation you pick to balance the flexion gap simultaneously sets patellar tracking. With only 2.3% of knees having all four joint lines congruent, most patients force you to compromise either the flexion gap or the 'third space' of the patellofemoral joint.
For boards, connect this to the alignment-concept debate: mechanical, anatomical, restricted kinematic, and kinematic alignment each shift the joint lines differently, and none restores all four. Preoperative CT planning should therefore assess the anterior and posterior femoral joint lines, not just the coronal lines. This remains an emerging concept, not settled practice.