Functional knee brace alters predicted knee muscle and joint forces in people with ACL reconstruction during walking

Functional knee braces used during rehabilitation from injury and surgery t o the anterior cruciate ligament (ACL) have been reported to provide a stra in-shielding effect on the ACL in healthy people while standing, reduce qua driceps electromyography in ACL-deficient individuals, and alter joint torq ue patterns in people with ACL reconstruction during walking. These results led to the hypothesis that functional knee braces protect a reconstructed ACL during dynamic activity by reducing the anterior shear load applied to the knee. This hypothesis was tested by investigating the effects of a func tional knee brace on lower extremity muscle forces and the anteroposterior shear force at the knee joint during the stance phase of walking in people with ACL reconstruction. Ground reactions and sagittal plane video were rec orded from 9 ACL-reconstructed individuals as they walked with and without a functional knee brace, and from 10 healthy people without the functional knee brace. Inverse dynamics were used to calculate the net joint torques i n the lower extremity during the stance phase. Hamstrings, quadriceps, and gastrocnemius muscle and knee anteroposterior shear force were then predict ed with a sagittal-plane mathematical model. Compared to healthy individual s, those with ACL reconstruction walked with 78% more hamstrings impulse an d 19% less quadriceps impulse (both p <.05). The functional knee brace prod uced an additional 43% increase in hamstrings impulse and an additional 13% decrease in quadriceps impulse in the ACL group. Peak anterior knee shear force and anterior impulse were 41% lower and 16% lower in ACL vs. healthy individuals, respectively. The functional knee brace further reduced the pe ak knee shear force and impulse 28% and 19%, respectively, in the ACL group . It was concluded that a functional knee brace protects a reconstructed AC L during walking by altering muscle forces and reducing the anterior shear force applied to the knee joint.