← Part 8 · Compare motionPART 9 / TIBIAL SLOPE

Change the slope. Keep the reference.

Preparing anatomy and motion…

Native knee · 0°Drag to rotate · Scroll to zoom

Flexion 0°

Restore the native slope.

Native slope 6°Reconstructed slope 6°

Matches the 6° native reference

The green point stays fixed. The tray, bearing, and cut plane tilt together. The femur reseats against the bearing throughout flexion.

6° native reference plane Current cut plane

Geometric motion—not a calculation of ligament tension or maximum flexion.

Overlay motion at 6° native slope

Slope, flexion space, and ligaments

Part 5 used 6° as its simulated native slope and allowed exploration from 0–15°. This is a model reference, not a measurement of an individual knee.

Increasing posterior slope can increase flexion space and reduce PCL strain in cruciate-retaining TKA. That does not establish that all ligaments become looser, or that greater slope always improves flexion. The response depends on the reference point, resection, implant, and soft tissues.

Cadaveric study · posterior slope and PCL strain
Clinical study · slope and flexion gap

These studies support the teaching rationale; they do not calibrate this Persona illustration or quantify its ligament strain.

Angles are relative to this model’s tibial shaft. The green point is a medial bearing reference, not a measured anatomical landmark.

Zimmer Biomet’s MC system overview recommends 5° and permits 7°, particularly with the PCL retained. The 0–15° exploration range includes values outside that manufacturer guidance and is not a surgical prescription. The bearing remains an MC-inspired reconstruction, not manufacturer CAD.

Zimmer Biomet · MC system overview

Illustrative implant motion · contact is checked at each sampled flexion angle. This is not a prediction of ligament balance or clinical motion.

Both cruciates intact.

The ACL and PCL retain their bone attachments as the knee bends. The medial side travels less than the lateral side.

ACLPCL

See ligaments through bone Show medial and lateral menisci Show MCL and LCL Overlay intact position

Tibia held still for comparison. A posterior shift of the femur represents anterior tibial translation relative to the femur.

Illustrative motion—not a prediction of instability, ligament strain, or contact pressure.

Model and component details

Femoral component: supplied Persona CR CAD, size 11 Right. Tibial tray: supplied Persona cemented keel CAD, size E Right. Bearing: the accepted MC-inspired illustration from Part 5, not manufacturer bearing CAD. Assembly is for visual review; motion is an authored geometric illustration, with both compartments seated at sampled angles.

The intact trajectory reuses our previously refined 0–120° animation: limited early medial travel, greater lateral rollback, and coupled rotation. Its timing and excursions are authored teaching values.

The torn-ACL example adds a smooth illustrative offset strongest near extension (up to 3 mm relative translation and 2° rotation). These are not patient-specific measurements or a load/force simulation. Different tasks and loading produce different ACL-deficient motion.

Li et al. · ACL-deficient knee kinematics
ACL-deficient knee during squatting

ACL and PCL surfaces are reused from the earlier Open Knee(s) model and fitted to the approved bones. Attachments and fiber deformation need anatomical review; deformation is not calculated from ligament forces. The ACL discontinuity is schematic. Menisci are illustrative crescent wedges fitted to the approved tibial surfaces, with posterior body movement and retained horn locations. The solid wedge and smoothed tibial fit are illustrative; this is not a contact-pressure or tissue-deformation simulation. The patella is omitted. Vedi et al. · Dynamic MRI of meniscal movement.

Open Knee(s) attribution