← Part 11 · Femoral reconstructionPART 12 / COMBINED EXTENSION

Same extension. Different surface heights.

Preparing anatomy and motion…

Native knee · 0°

0°Current flexion

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Flexion 0°

Both sides of the joint.

0°Extension limit

Illustrative extension response

Distal femoral resection Native

Less resectionMore resection

Tibial resection Native

Less resectionMore resection

Both surfaces at their reference positions.

Show both native surfaces

Green surfaces preserve the original articular references on each bone.

Bearing thickness, tibial slope, femoral valgus and rotation stay fixed.

About this illustration

Positive values mean more resection. More distal femur moves the femoral component proximally relative to the femur; more tibia lowers the tray and unchanged bearing. Equal and opposite resection changes can offset the extension-space change while shifting the reconstructed surfaces.

The illustrative extension limit is derived from the sum of resection offsets: net 4 mm less stops at 10°; net zero reaches 0°; net 4 mm more reaches −5°. These are authored teaching values, not a measured millimeter-to-degree conversion or a prediction of ligament balance. This section explores extension from its selected limit to 30°; it does not model the resulting flexion-gap changes.

The native references use the approved cartilage geometry; the femoral overlay is limited to the distal region for clarity. The Persona component moves rigidly and preparation follows the CAD. Contact is checked against the triangulated bearing; the femur is translated vertically to avoid sampled penetration. Ligament attachments follow the bones; their forces are not calculated. Equal extension does not establish equivalent stability or clinical outcomes.

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