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Timing of the functional muscle microvascular
transplantation depends on the circumstance for
which reconstruction is being undertaken. The functional muscle can be transplanted acutely for
non-traumatic muscle deficits after Volkmann’s ischemic contracture11,12
and compartmental surgical resection for malignant tumors.13-14 In
these situations, the zone of injury is limited. However, functional muscle
transplantation must typically be staged in situations where patients have sustained
traumatic loss. These include muscle compartment destruction after limb
amputation, mechanical crush/avulsion, and major nerve avulsion. In these
situations, the wound is dynamic and can be often be characterized by infection or
ongoing muscle and nerve demarcation. Because of this, intervention is usually
separated into acute, sub acute, and late reconstruction - each with specific goals.
Acute period
The acute period can be defined as the time of
injury until the initial effects of the trauma such as limb compromise and open
wounds with exposure of vital structures have been addressed. The goal in this
period is to revascularize the limb, provide stabilization or skeletal support,
and provide stable coverage of the wounds. Of course the first priority is
saving the patient’s life. Only after that has been addressed should attention
be directed towards salvage of a limb.
Limb salvage can begin with either
revascularization or bony stabilization. Despite advances in microsurgical
technique, prolonged tissue ischemia is a contraindication to replantation and a
concern in revascularization. Upon return of blood flow, ischemic tissue
generates toxins, which can threaten the replanted or revascularized tissue and
even the patient. This is referred to as “re-perfusion syndrome”.15,16 The
duration of ischemia that tissue will tolerate is dependent on the amount of
muscle present. Muscle has a much higher metabolic requirement and is therefore
much more sensitive to ischemia. Multiple studies have shown that lowering the
metabolic requirement by hypothermic ischemia protects it from enzyme leakage,
histologic changes, and adverse re-flow patterns. This protection is limited to
4-5 hours if ischemia is normothermic (body temperature) and 8-10 hours if
hypothermic. Surviving muscle will have greater return of function the shorter
the ischemic period. Tissues close to their ischemic limit can have vascular
shunts placed initially so that the limb can perfuse while time consuming
procedures such as bony reduction and stabilization are being undertaken.
Thereafter, vein grafts to the inflow artery and outflow vein can be done.
Testing the venous blood prior to vein repair has been reported as a way to
reduce or prevent reperfusion syndrome.17 An implantable doppler is then placed
to monitor the patency of this vascular circuit.
Once blood flow has been reestablished all tissues
are inspected for reperfusion injury or non-viable elements. Compartments can be
opened (fasciotomy) to allow for muscle swelling and decrease progressive muscle
loss. Serial debridements continue until the wound is clean. Vascular tissue
such as muscle can be transplanted to close the wound, cover vital structures
and decrease infection risk.18 Grafts to damaged structures such as nerve, bone,
and tendon should be deferred until control of the wound is achieved.
Sub-Acute Period
The sub acute period begins after limb salvage,
stable cover has been provided, and there is no evidence of infection. At that
point, the patient can be returned to the operating room where structures not
repaired acutely can be addressed. In certain injuries, there is loss of bone
from comminution, and nerve, or muscle from crush/avulsion. In these situations,
nerve gaps can be grafted to restore sensation/motor function or offer a target
for muscle transplantation, and stabilized bone defects can be grafted. If the
bone has been shortened, the Ilizarov distraction technique can be employed to
lengthen the residual bone. Ulnar or median nerve grafting should be performed
as early as possible (usually within 3 weeks) to restore sensation and salvage
the intrinsic muscles of the hand.
Late Period
After the sub-acute period, a rehabilitation
protocol is instituted to optimize return of function. This can require up to
one year. Regular exams through this period identify what function has returned
and what is lost. Only with this understanding can the appropriate strategy for
reconstruction be formulated. After conservative approaches have been exhausted
and functional deficiencies persist, a FMMT can be considered. One or more FMMTs
can be transplanted to restore function. Each requires a nutrient vessel and a
healthy motor nerve. An angiogram can be used to determine the adequacy of the
target vessel. Assessment of the adequacy of the motor nerve target is difficult
prior to surgical exploration. Fascicles usually sprout from the proximal nerve
stump to form a neuroma by the third week after nerve injury. At this time
exploration can reveal a neuroma and help define the appropriate nerve level.19,20
The vessel and nerve, which supplied the original muscle group, should be used
preferentially. If the original vessel cannot be utilized, vein can be harvested
and grafted to supply blood flow to the transplant. If the original nerve cannot
be utilized, a nerve can be borrowed from another muscle group. The nerve
selected should not result in significant disability and must have a similar
function to that which it is replacing or be under voluntary control such that
the patient can relearn and control that function.
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