- See:
Role of Knee Joint in Gait:
- Discussion:
- for reason of contour of femoral & tibial condyles, flexion & extension
of knee joint are not simple hinge movements that occur at the elbow joint.
- flexion & extension do not occur about a fixed transverse axis of
rotation but rather about a constantly changing center of rotation,
that is, polycentric rotation.
- when plotted, path of this changing center of rotation describes
J shaped curve about the femoral condyles;
- in full flexion, posterior portions of femoral condyles are in contact w/ posterior
portions of the tibial condyles.
- knee is extended, femoral condyles roll on tibial condyles &
meniscii,
movement resembling that of a rocking chair.
- Extension of Knee Joint:
- moving from flexion to extension, shorter, more highly curved lateral condyle
exhausts its articular surface & is checked by
ACL, whereas larger &
less curved medial condyle continues its forward roll &
skids backward,
assisted by tightening of
PCL;
- because medial femoral condyle is larger than lateral fem condyle, distance
from
extreme flexion contact point to extreme extension contact point of
medial femoral condyle is about 17 mm > that of lateral femoral condyle;
- as tibia travels from flexion to extension the medial tibial plataeu
must cover a greater distance;
- result is
external rotation of tibia that tightens collateral ligaments, and
joint is "screwed home;"
-
ratio of rolling to gluiding:
- ratio 1:2 in early flexion & to increase to one to four by end of flexion;
- Flexion of Knee Joint:
- flexion of extended knee is preceded by
internal rotation of the tibia,
produced by
Popliteus muscle;
- this rotation relaxes tension of collateral ligaments suffic to permit flexion.
-
ratio of rolling to gluiding:
- ratio 1:2 in early flexion & to increase to one to four by end of flexion;
- Rotation:
- during nl gait, tibia undergoes
Internal Rotation during swing phase and
external rotation during stance phase;
