- See:
Biomechanics Menu:
- Anatomy of the ACL:
- Biomechanics:
-
ultimate tensile load: 2160 ± 157 N
-
stiffness: 242 ± 28 N/mm;
- passive knee extension produces forces along ACL only during last 10 degrees of knee extension;
-
hyper-extension:
- the posterolateral bundle of the ACL is tight in extension;
- at 5 degrees of hyperextension, anterior cruciate ligament forces range between 50 and 240 newtons;
- hyperextension of the knee develops much higher forces in ACL than in the PCL;
-
flexion:
- the anteromedial bundle of the ACL is tight in flexion;
- during isometric quadriceps contraction, ACL strain at 30 deg of knee flexion are significantly higher than
at 90 deg where ligament remain unstrained with isometric quadriceps activity;
- active extension of knee between the limits of 50 and 110 degrees does not strain the anterior cruciate;
- at 90 deg of knee flexion:
- ACL accounts for approx 85% of resistance to anteior drawer test
- ref:
Tensile properties of the human femur-anterior cruciate ligament-tibia complex. The effects of specimen age and orientation
- Sectioning of ACL:
- in unsectioned ACL's in neutral rotation, application of 100 newtons of anterior force produces:
- 2-5 mm of anterior translation at full extension;
- 5-8 mm of translation at 30 deg of flexion;
- as flexion angle increases further, anterior translation decreases;
- sectioning of ACL results in increased laxity at all flexion angles;
- 20-30 deg of flexion:
- maximum anterior translation occurs w/ 100-newton anterior force, 7-9 mm of increased translation is seen;
- clinically, combined ACL and
MCL tears result in large increases in anterior translation;
- following sectioning of the ACL: anterior restraint derives from:
- iliotibial band:
24%
- mid medial capsule:
22%
- mid lateral capsule:
20%
-
MCL:
16%
-
LCL:
12%
- Functional Role:
- ACL is the predominant restraint to anterior tibial displacement;
- ligament accepts 75 % of anterior force at full extension & approx 85 % at 30 and 90 degrees of flexion;
- deep MCL is a major secondary restraint to anterior translation;
-
role in gait:
- ACL is taut in full knee extension, and tends to externally rotate tibia;
- tension in ACL is least at 40 to 50 deg of knee flexion;
- as knee moves from flexion to extension, shorter, more highly curved lateral condyle exhausts its articular surface & is checked by ACL;
- larger and less curved medial condyle continues its forward roll and skids backward, assisted by tightening of PCL;
- towards full extension there is lateral rotation of tibia & joint is "screwed home;"
- Isometry:
- anterior cruciate ligament does not remain an isometric, or constant length, structure as the knee is flexed and extended;
- ligament increases in strain magnitude as the lower leg is passively extended, with the femur in a horizontal plane;
- reconstruction of the
ACL should not strive to achieve an isometric placement of the graft,
but rather reproduce strain behavior of the normal anterior cruciate ligament;
Biomechanics of intra-articular and extra-articular reconstruction of the anterior cruciate ligament.
Biomechanics of the knee-extension exercise. Effect of cutting the anterior cruciate ligament.
Functional properties of knee ligaments and alterations induced by immobilization:
a correlative biomechanical and histological study in primates.
Biomechanical analysis of human ligament grafts used in knee-ligament repairs and reconstructions.
The role of the posterolateral and cruciate ligaments in the stability of the human knee. A biomechanical study.
Effect of intra-articular corticosteroids on ligament properties: a biomechanical and histological study in rhesus knees.
Direct in vitro measurement of forces in the cruciate ligaments. Part II: The effect of section of the posterolateral structures.
Direct in vitro measurement of forces in the cruciate ligaments. Part I: The effect of multiplane loading in the intact knee.
Biomechanics of intra-articular and extra-articular reconstruction of the anterior cruciate ligament.
Biomechanical consequences of replacement of the anterior cruciate ligament with a patellar ligament allograft.
Markolf et al.
JBJS. Vol 78-A. No 11. Nov 1996. p 1720-1734.
In Vivo Elongation of the Anterior Cruciate Ligament and Posterior Cruciate Ligament During Knee Flexion
Anatomy of the Anterior Cruciate Ligament with Regard to Its Two Bundles.
