Download Evaluation of Rectus Femoris Transfer Surgery using Cine

Evaluation of Rectus Femoris Transfer Surgery using Cine-PC MRI
S. Blemker', D. A s a k a ~ a ' , ~S., Delp', and G.
Stanford University Depts. of 'Mechanical Engineering, and 'Radiology,
and the 'Palo Alto VA Health Care System, Palo Alto, California, USA
Abstract
Persons with cerebral palsy often walk with stiff-knee gait. To improve
knee motion in these subjects, surgeons transfer the tendon of the rectus
femoris muscle to the posterior side of the knee. This surgery is
intended to convert the muscle from a knee extensor to a knee flexor.
Using cine phase-contrast magnetic resonance imaging, we measured the
velocity of the rectus femoris during passive knee extension in six
subjects who had undergone rectus femoris transfer surgery. In all
subjects, the rectus femoris moved superiorly with knee extension,
indicating that this surgery does not convert the muscle to a knee flexor.
Introduction
The goal of the rectus femoris transfer surgery is to increase knee
flexion during walking in persons with cerebral palsy who walk
with troublesome stiff-knee gait. In this procedure, the rectus
femoris muscle is detached from the patella and reattached to a
tendon posterior to the knee in an effort to convert the muscle
from a knee extensor to a knee flexor [2]. However, the surgery
is sometimes unsuccessful, and the in vivo action of the muscle
after surgery is not known. One previous study showed that the
transferred rectus femoris generated a knee extension moment
[3]. However, few other studies have been able to characterize
the in vivo action of the rectus femoris after surgery because
existing techniques are invasive. In this study, we show how
dynamic imaging can be used to non-invasively assess the action
of the rectus femoris muscle after tendon transfer surgery.
Cine phase-contrast magnetic resonance imaging (cine-PC MRI)
has been shown to produce reliable estimates of muscle tissue
velocities during dynamic joint motion [l]. The direction of the
muscle tissue velocity indicates the muscle's action (i.e., as the
knee extends, the knee extensors move superiorly and the knee
flexors move inferiorly). We used cine-PC MRI to test the
hypothesis that the transferred rectus femoris acts as a knee
flexor and therefore moves inferiorly with knee extension. We
measured the velocities in the rectus femoris and surrounding
muscles during passive knee extension motion in control subjects
and in subjects with cerebral palsy who had undergone rectus
femoris transfer surgery.
Methods
We acquired axial plane cine-PC MR images in the proximal
thigh in five control subjects (age = 23-29 yrs) and six rectus
femoris transfer subjects who have cerebral palsy (age = 8-16
yrs). Each subject was positioned supine in the 1.5T GE Signa
scanner with a flexible radiofrequency coil on each side of the
thigh. The subject's leg was attached to a motion device that
enabled the investigator to move the leg through a forty degree
range of knee flexion/extension (requiring no effort from the
subject) and ensured repeatable knee motion of 35 cycles/min.
We acquired anatomical and velocity images throughout the
motion cycle (TR = 17ms, slice thickness = lOmm, encoding
velocity = 20 c d s , FOV = 21x28 - 27x36 cm). The images were
interpolated into 24 evenly spaced time frames that represented
the entire motion cycle. Using MATLAB, one cm square regions
of interest were defined in the tissue of the rectus femoris, vastus
intermedius, and semitendinosus muscles. For each time frame,
the average and standard deviation of the superior-inferior
velocity in each region were calculated (Fig. 1).
Results
In the control subjects, the rectus femoris and the vastus
intermedius moved superiorly and the semitendinosus moved
inferiorly during knee extension, as expected. The maximum
rectus femoris velocity was greater than the maximum vastus
intermedius velocity by 35%-100% (e.g., Fig.lC). In all the
post-rectus femoris transfer subjects, the rectus femoris moved
superiorly with knee extension. The maximum velocity of the
transferred rectus femoris was less than vastus intermedius
velocity by 35%-75% (e.g., Fig. 1F). These results suggest that
the transferred rectus femoris does not act as a knee flexor. Scar
tissue, which was evident in static M R images of some subjects,
may restrict the motion of the transferred muscle.
Control Subject
Post-Transfer Subject
anatomy
anatomy
st.per'or-'nferior ve oc iy
%per or-'nferor velocity
-20 rl? b
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I:
1
9
5
time (frames)
10
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vastus intermedius
1
>
5
time (frames)
10
L
Figure 1. Anatomy images (A-Control, D-Post-transfer) at one time
frame during knee extension show the regions of interest for each
muscle. Velocity images (B-Control, E-Post-transfer) are shown at the
same time frame, where dark (light) pixels indicate superior (inferior)
velocity. The velocity profiles indicate that, for the control (C) and posttransfer (F) subjects, the rectus femoris and vastus intermedius move
superiorly and the semitendinosus moves inferiorly with knee extension.
Discussion
Cine-PC MRI is a powerful non-invasive tool for evaluating
muscle function after surgery. In this study, we characterized the
motion of the rectus femoris after tendon transfer; our results
indicate that the surgery does not convert the muscle to a knee
flexor. These data dramatically increase our understanding of the
rectus femoris function after surgery and will help provide a
scientific basis for treating stiff-knee gait.
References
1. Drace, J.E. andPelc, N.J. J. Magn. Reson., 4, 157-163, 1994.
2. Perry, J. Dev Med ChildNeurol, 29, 153-8, 1987.
3. Riewald and Delp. Dev Med ChildNeurol. 39,99-105, 1997.
Acknowledgements
We are thankful to A. Bagley, G. Rah, D. Schwandt. G. Pappas, and J. Drace.
Support was provided by the Dept. of Veterans Affairs, the Whitaker Foundation,
and NIH Grants HD38962 and T32 GM63495.
© Proc. Intl. Soc. Mag. Reson. Med. 10 (2002)