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Several muscles potentially meet the criteria for
FMMT. The most commonly used muscles include the gracilis, latissimus, rectus
femoris, and the tensor fascia lata (TFL) muscles. The muscle selected should
offer the strength required to restore a desired function and a contractile
excursion longer than that of the muscle or muscles it is replacing.21,22
The gracilis and latissimus muscles are strap muscles meaning that their muscle
fibers are arranged longitudinal to their direction of contraction. These
muscles usually shorten between 40 to 60% of their stretched length. In the case
of a 30 cm gracilis muscle, that would be at least 12 cm of excursion. Finger
range of motion requires 6-7 cm of excursion. The rectus femoris and TFL muscles
are bipennate muscles meaning that their fibers are oriented at an angle to the
direction of muscle contraction. They shorten 40% of their average fascicule
length. Because of their fascicular orientation and the fact that they are
shorter, maximum excursion is limited to about 3cm. Muscle strength is
proportional to the cross sectional area of the muscle. Therefore, the bipennate
transplants provide increased strength but sacrifice excursion or range of
motion.
The gracilis muscle is most often used as a FMMT.
Its size, length, and shape most closely approximates that of the muscles, which
provide flexion and extension in the hand, flexion at the elbow, as well as,
dorsiflexion at the ankle. The latissimus muscle is an excellent alternative to the gracilis. It has
excellent excursion and strength. However, it is bulkier than the gracilis
muscle, fans out at its distal insertion, and does not have a distal tendon for
weave or repair making it technically more difficult to apply to the forearm and
lower leg. However, we prefer its use in restoration of function in the anterior
and posterior compartments of the thigh for restoration of function at the knee.
Even when care is taken to follow a specific
algorithm functional muscle transplanted for traumatic injuries is less
reliable. The poor quality of the recipient bed and motor nerve are believed to
be responsible. Techniques to optimize the wound bed and motor nerve are being
employed with success in our clinic.
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