NMBL - Neuromuscular Biomechanics Lab

Related Topics

Dynamic Simulation
Medical Imaging
Motion Analysis
Surgical Simulation

Movement Abnormalities - Stiff-Knee Gait Many individuals with cerebral palsy walk with insufficient flexion of the knee during the swing phase, or stiff-knee gait. This disabling gait pattern is often attributed to abnormal activity of the rectus femoris muscle, one of the quadriceps that generates both hip flexion and knee extension moments. Stiff-knee gait is commonly treated by rectus femoris transfer, a surgical procedure in which the distal tendon of the muscle is detached from the patella and reattached to one of several sites posterior to the knee. This surgery is thought to convert the rectus femoris from a knee extensor to a knee flexor. However, the surgical outcomes are inconsistent and sometimes unsatisfactory, in part because the biomechanical factors that contribute to stiff-knee gait have not been adequately characterized, and because the in vivo function of the rectus femoris after transfer is not known. Indeed, swing phase knee flexion improves significantly in some patients but changes very little in others. We are using forward dynamics simulations, MR imaging techniques, and experimental measurements on human subjects to determine the factors that contribute to stiff-knee gait and to characterize the function of the rectus femoris after transfer surgery.
		We have used cine phase-contrast magnetic resonance imaging (left) to quantify the relative motion of the rectus femoris and underlying vasti muscles in unimpaired adults and in subjects who have undergone rectus femoris transfer surgery. We found that, following surgery, the rectus femoris moved in the direction of the knee extensors, despite its attached posterior to the knee (right). The motion of the transferred rectus femoris was smaller (relative to the vasti) than in unimpaired controls. This indicates that the muscle does not act as a knee flexor following surgery, but its potential to extend the knee has been diminished by the surgery.
		We are also using dynamic simulations to understand the factors that contribute to normal swing dynamics as well as the dynamics of stiff-knee gait. Our hope is to use subject-specific simulations of stiff-knee gait to identify the biomechanical factors that contribute to stiff-knee gait and explain the functional consequences of rectus femoris transfer surgery.
Associated Publications Higginson, Zajac, Neptune, Kautz, Burgar, and Delp. Effect of equinus foot placement and intrinsic muscle response on knee extension during stance. Gait and Posture, 2006. (Download PDF) Goldberg, Ounpuu, Arnold, Gage, and Delp. Kinematic and kinetic factors that correlate with improved knee flexion following treatment for stiff-knee gait.Journal of Biomechanics, 2006. (Download PDF) Goldberg, Anderson, Pandy, and Delp. Muscles that influence knee flexion velocity in double support: implications for stiff-knee gait. Journal of Biomechanics, 2004. (Download PDF) Goldberg, Ounpuu, and Delp. The importance of swing-phase initial conditions in stiff-knee gait. Journal of Biomechanics, 2003. (Download PDF) Asakawa, Blemker, Gold, and Delp. In vivo motion of the rectus femoris muscle after tendon transfer surgery. Journal of Biomechanics, 2002. (Download PDF) Riewald and Delp. The action of the rectus femoris muscle following distal tendon transfer: Does it generate a knee flexion moment?Developmental Medicine and Child Neurology, 1997. (Download PDF) Piazza and Delp. Influence of muscles on knee flexion during the swing phase of normal gait. Journal of Biomechanics, 1996. (Download PDF file) Delp, Ringwelski, and Carroll. Transfer of the rectus femoris: effects of transfer site on moment arms about the knee and hip.Journal of Biomechanics, 1994. (Download PDF)