Translations and Rotations Across the Knee Under Isometric Quadriceps Contraction

The suggested mechanism of failure of the anterior cruciate ligament (ACL) through quadriceps contraction motivated the research discussed in this paper. The three components of translation and rotation of the tibia relative to the femur, produced under isometric quadriceps contraction in vivo, were measured with a six degree of freedom acoustic transducer. Tests on six subjects were conducted at 30° and 90° knee flexions. The principal component responses across the knee under isometric quadriceps contraction are internal rotation, anterior translation, and proximal translation. The average anterior displacement under a 24 Nm isometric quadriceps contraction was significantly greater (P < 0.001) at knee flexion 30° than at 90° (1.8 mm vs. -0.4 mm). From the data and analyses here, there is no support for the hypothesis that isometric quadriceps contraction alone can produce sufficient anterior displacement of the tibia relative to the femur to rupture the ACL.