Knee

Knee

knee_mesh builds the articular cartilage, both menisci and both collateral ligaments from a humanoid's stature and sex.

extensions/humanoid/skeleton/leg/knee/{dimensions,geometry,mass}.mojo. Shared field and isosurface code lives under extensions/humanoid/skeleton/. Soft-tissue density lives in extensions/anatomy/soft_tissue.mojo, which the humanoid and the animals share. The visual look lives in look.mojo.

This is not a three.js port. See Extensions, Femur and Leg.

Call it

from extensions.humanoid.sex import MALE
from extensions.humanoid.spec import HumanoidSpec
from extensions.humanoid.skeleton.leg.knee.geometry import articular_cartilage
from units.si import FOOT, Length

var person = HumanoidSpec(Length(6.0, FOOT), MALE)
var cartilage = articular_cartilage(person)

Named wrappers build each solid: articular_cartilage, medial_meniscus, lateral_meniscus, medial_collateral and lateral_collateral. side picks RIGHT or LEFT. A right knee is the default.

detail sets the marching-tetrahedra grid. Twenty-four is the default. Eight is the least. Sixty-four is the most.

The solids live in the leg frame. The origin is the tibiofemoral joint line. Plus y is proximal. Plus x is body-right. Plus z is anterior.

KneePart names the five solids. A bare integer is a compile error.

Cartilage thickness

Thickness at the six foot male template uses Shepherd and Seedhom 1999 as named adult means.

Surface	Six foot male mean	Role
Femoral condyles	2.2 mm	Shepherd and Seedhom 1999
Tibial plateau	2.5 mm	Shepherd and Seedhom 1999
Patella	3.3 mm	Shepherd and Seedhom 1999

Other statures scale those thicknesses in proportion to stature. That scale is an authored template rule. It is not a cited stature regression. The female template uses slightly smaller ratios of stature.

The solid uses a thin patch on each femoral condyle, the trochlea, each tibial plateau and the posterior patella. Thickness uses Shepherd and Seedhom 1999. Each patch footprint is an authored template.

knee_dimensions(stature, sex, side) returns the lengths and landmarks without building a mesh.

The accepted stature interval is 1.2 m through 2.5 m. That is the software range.

Menisci and collaterals

Meniscus size and collateral size are authored sex-specific ratios of stature. They are template parameters. They are not a cited osteometric table.

The medial meniscus is a C-shaped ring on the medial plateau. The posterior horn is the thicker end. The lateral meniscus is more circular. The opening of each C faces the intercondylar notch.

The MCL is a capsule from the medial femoral epicondyle to the medial tibia. The LCL is a capsule from the lateral femoral epicondyle to the fibular head.

KneeDimensions is editable. Editing a length does not rebuild landmarks. Call knee_dimensions to resolve a template. Call validate before a field, mesh or mass consumes an edited copy.

Soft tissue

cartilage_tissue(), meniscus_tissue() and ligament_tissue() hold wet density, water fraction and a compressive modulus.

Cartilage water fraction 0.75 is the middle of the 60% to 85% range in Mow, Kuei, Lai and Armstrong 1980. Wet density 1.12 g/cm³ is a named adult template inside the published 1.06 to 1.16 g/cm³ range. It is not a cited table cell.

Meniscus water fraction 0.70 follows Fithian, Kelly and Mow 1990. Wet density 1.10 g/cm³ is a named template.

Ligament wet density 1.12 g/cm³ and water fraction 0.65 are named adult templates.

Water fraction is metadata. Wet density already describes the hydrated tissue. Mass uses wet density times envelope volume. Do not scale by one minus water fraction again.

These values are sourced or named research metadata. This extension does not implement a constitutive model.

SoftTissueKind is CARTILAGE, LIGAMENT or MENISCUS. SoftOccupancy is SOFT_EMPTY or SOFT_FILL. A bare integer is a compile error.

Mass and weight

articular_cartilage_mass(spec) samples the field. Each cell is empty or filled. The default step is 2 mm.

from extensions.humanoid.skeleton.leg.knee.mass import articular_cartilage_mass
from units.si import GRAM, NEWTON, POUND_FORCE

var report = articular_cartilage_mass(person)
report.mass.to(GRAM)
report.weight().to(NEWTON)
report.weight().to(POUND_FORCE)

report.envelope is the volume inside the surface. report.mass is wet-tissue mass. Each patch overlaps the adjacent bone enough to prevent a rendering gap. The value is a grid-sampled estimate. It is not a proven upper bound.

Named mass wrappers exist for each of the five solids.

Look

cartilage_phong is opaque warm ivory. meniscus_phong is natural off-white fibrocartilage. ligament_phong is pale fibrous tissue. All three are visual approximations. cartilage_physical and ligament_physical are the physical looks. See Leg.

Limits

Stature must lie in 1.2 m through 2.5 m. Sex must be MALE or FEMALE. BodySide must be RIGHT or LEFT. KneePart must name one of the five solids. Edited zero or non-finite dimensions fail at validate.

Example

examples/knee.mojo draws a close view of one six foot male right knee and writes out/knee.png. Run it with:

.venv/bin/mojo run -I . examples/knee.mojo out/knee.png

The connected-leg figures live on Leg.