Mechanics of the Knee

Abstract

The load moment of force about the knee joint during machine milking and when lifting a 12.8 kg box was quantified using a computerized static sagittal plane body model. Surface electromyography of quadriceps and hamstrings muscles was normalized and expressed as a percentage of an isometric maximum voluntary test contraction. Working with straight knees and the trunk flexed forwards induced extending knee load moments of maximum 55 Nm. Lifting the box with flexed knees gave flexing moments of 50 Nm at the beginning of the lift, irrespective of whether the burden was between or in front of the feet. During machine milking, a level difference between operator and cow of 0.70 m-1.0 m significantly lowered the knee extending moments. To quantify the force magnitudes acting in the tibio-femoral and patello-femoral joints, a local biomechanical model of the knee was developed using a combination of cadaver knee dissections and lateral knee radiographs of healthy subjects. The moment arm of the knee extensor was significantly shorter for women than for men, which resulted in higher knee joint forces in women if the same moment was produced. A diagram for quantifying patellar forces was worked out. The force magnitudes given by the knee joint biomechanical model correlated well with experimentally forces measured by others. During the parallel squat in powerlifting, the maximum flexing knee load moment was estimated to 335-550 Nm when carrying a 382.5 kg burden and the in vivo force of a complete quadriceps tendon-muscle rupture to between 10,900 and 18,300 N. During isokinetic knee extension, the tibio-femoral compressive force reached peak magnitudes of 9 times body weight and the anteroposterior shear force was close to 1 body weight at knee angles straighter than 60 degrees, indicating that high forces stress the anterior cruciate ligament. A proximal resistance pad position decreased the shear force considerably, and this position is recommended in early rehabilitation after anterior cruciate ligament repairs or reconstructions. The methods presented quantify muscle activity, sagittal ynee joint moments and forces, enabling assessments to be made of different work postures, training exercises and joint derangements. This thesis is based on the following papers which will be referred to in the text by their Roman numerals I-VI. I.

Moment arm of the patellar tendon in the human knee

“…The moment arms obtained by Nisell (1985), Herzog and Read (1993), Kellis and Baltzopoulos (1999) and Wrentenberg et al (1996) are all referenced to the contact point between the femur and tibia. Using the tibiofemoral contact point may not be meaningful because this point is itself rotating about the screw axis.…”

“…Smidt (1973) and Wretenberg et al (1996) measured the moment arm of the patellar tendon with respect to the center of rotation of the knee in the sagittal plane. Nisell (1985), Herzog and Read (1993), and Kellis and Baltzopoulos (1999) also measured the moment arm of the patellar tendon in the sagittal plane, however, their values were based on the perpendicular distance between the line of action of the patellar tendon and the contact point between the femur and tibia. Buford et al (1997) and Delp et al (1994) used the tendon excursion method to measure the moment arm in three dimensions, but their results are related to the action of the quadriceps rather than the patellar tendon.…”

Quadriceps force during knee extension after non-hinged and hinged TKA: An in vitro study

“…Generally, the lever arm changes during extension of the knee because of the translating tibiofemoral and patellofemoral contact points, which results in a changing quadriceps force during extension (Nisell andEkholm 1985, Ostermeier et al 2004). This in vitro test only simulated one constant moment during the whole extension cycle, which contrasts with the varying peak extension moments over an isokinetic extension cycle in vivo (Berman et al 1991, Fuchs et al 1998.…”

Patellar Tendon Straps Decrease Pain and May Alter Lower Extremity Kinetics in Those With Patellar Tendinopathy During Jump Landing

“…Hypothetically, if assumed all else equal (which may or not occur), then patellar tendon force could then be estimated by dividing the knee joint moment by the patellar tendon arm. 32 The estimated patellar tendon moment arm at 30° of knee flexion is approximately 4.5 cm. 32 Then, if the strap pulled the tendon posteriorly 1 cm, the patellar tendon forces would correspondingly increase by approximately 20%.…”

“…32 The estimated patellar tendon moment arm at 30° of knee flexion is approximately 4.5 cm. 32 Then, if the strap pulled the tendon posteriorly 1 cm, the patellar tendon forces would correspondingly increase by approximately 20%.…”