Provisionof Skin Cover
In the combined injury of skin and skeleton, skin damage can vary from minimal up to extensive degloving.
Where skin loss has been minor, but closure by direct suture can only be achieved under tension, a ‘relaxation incision’ is often recommended. The idea is that by making such an incision, tension will be reduced, and skin closure will be easier. The method sounds safe enough in theory, but it is less so in practice.
‘relaxing’ incision really creates a bipedicled flap which moves across to allow closure of the original wound. It is a well-recognised fact that even in optimal circumstances a bipedicled flap transferred in this way is an unsafe procedure and is liable to necrose. Used in a mixed skin and skeletal injury it is even more hazardous, for soft tissue damage and degloving have so often added their quota to the local devitalisation of skin.
The presence of degloving is a virtual contraindication to its use, and even in the absence of degloving the method should be used with the greatest of care. It is likely to be safest and most effective when closure is difficult because of local swelling of the limb from oedema and haemorrhage, rather than because of skin loss. The incision itself should be straight, placed at a considerable distance from the wound, and run in the long axis of the limb.
Undermining of the skin should be avoided.
When skin loss is more extensive, the replacement methods available are free skin graft, skin or fasciocutaneous flap, muscle or myocutaneous flap, and free flap -usually used individually, occasionally in combination.
Despite the alternative reconstructive methods
available today, split skin grafting should be the first choice if the raw surface is suitable.
In determining which surfaces are suitable for grafting, the key role of the periosteum has already been stressed. Excision of avascular tissue, fixation of the fracture, conservation of periosteum, closure of joint by suture of the capsule when possible, or cover with a muscle flap to create a graftable surface -all combine to give a graft the best chance to take.
The split skin graft has the great virtue also of being able on occasion to stabilise a clinical situation at minimal cost to the patient. It gives the surgeon a breathing space, and even if the graft is unsuitable as definitive cover it is possible to replace it at leisure once the patient’s condition has become stable.
Split skin grafting can be used in conjunction with other techniques.
A muscle flap, for example, may be needed to cover the bare bone element of a composite injury, but the graft can still be applied all around the area covered by the muscle as well as providing cover for the muscle itself.
Skin and fasciocutaneous flaps, rotation or
transposed, raised locally, have little if any place in acute injuries of this sort. Although safer when they include the fascia! layer, they have not been assessed objectively in the context of acute skin-bone trauma.
Before contemplating the use of a flap of this type, it would be essential to gauge the damage to the overall vascularity of the skin which it is proposed to use as the flap, particularly when an element of degloving is
involved. In any case the size and shape of the typical defect and the state of the surrounding skin would preclude its use.
The cross-leg flap may have been increased in safety by incorporating the fascial layer, but for the surgeon with little experience in its use (and such experience is becoming rarer as the method is losing popularity in other contexts) it must be regarded as distinctly hazardous. Such flaps have also to be used with particular circumspection, even as elective procedures in older patients, because of peripheral vascular problems in the ageing limb, and problems of joint stiffness.
These considerations would apply with redoubled force in an emergency situation, especially in the lower limb where the problem really arises. In a lower limb injury a cross-leg fasciocutaneous flap can be contemplated only by an experienced operator, in the young patient with unimpaired peripheral circulation and joints capable of tolerating the immobilisation -a combination of limitations likely to restrict its usage to near zero.
Local fasciocutaneous flaps being generally unsuitable for use at the acute stage of a combined skin-bone injury, the question arises whether the skin-fascia combination is capable of recovering sufficiently to be safe to use at a later date, and if so when. It is difficult to believe that degloved skin can recover to total circulatory normality, though it has been reported as being successfully used for subsequent reconstruction, which would suggest that at least a degree of recovery can take place.
The cautious surgeon is unlikely to accept this as a blanket finding. Reasoning from other clinical contexts, such observations as the amount of superficial scarring of the skin, its degree of comparative mobility, and the thickness of the layer of superficial fascia, would all play a part in decision making.
The use of muscle and myocutaneous flaps
raised locally would be confined to defects of the knee and upper half of the anterior tibia.
The medial head of gastrocnerhius is capable of covering the medial aspect of the knee joint and the upper third of the tibia.
Transfer is probably better carried out as a
muscle flap rather than as a myocutaneous flap when the option is present. Even used in late reconstruction the virtues of a muscle flap with grafting of its exposed surface, as compared with grafting of the secondary defect left by the transfer of the corresponding myocutaneous flap, have been recognised.
The potential hazard of the presence of muscle damage in assessing its usage in muscle transfer has already been discussed, and its unexpected tolerance of transfer as a flap even when showing signs of injury.
Where the necessary facilities and micro-vascular expertise have been available, free flaps, (fasciocutaneous, muscle and myocutane-ous), have been increasingly used in managing the more severe mixed injuries of skin and bone.
The techniques involved may be demanding, but the results, judged in terms of healing time, time to fracture union and time in hospital, are all better. Muscle, transferred as a flap, appears also to bring with it a degree of vascularity which, used to cover a surface which shows damage, prevents the damage progressing to necrosis, and it seems to retain these virtues even when it is part of a free flap.
In a situation where periosteal stripping and continuing exposure of bare cortical bone is so often followed by sequestration of its outer layer, this is a particularly valuable attribute. The muscle is also able to fill any bony defect which may have resulted from the removal of comminuted bony fragments judged to be avascular, and in this way eliminate dead space.
A free flap frequently used is the latissimus
Its long pedicle and reliable vessels of a good calibre make it among the less technically demanding transfers. The large area of muscle which can be transferred also makes it possible to cope with the more extensive defects successfully so that, even if part of the area of skin loss is graftable, it may still be convenient to cover the entire area with the flap. The rectus abdominis flap has become a popular, and equally suitable, alternative.
Both flaps tend to be used as muscle rather than as myocutaneous flaps, leaving skin cover to be provided by grafting.
For the smaller defect, alternatives are the radial forearm, the lateral upper arm flap and the
scapular flap. The comparative virtues of the three are discussed in Chapter 4.
The vessels at the fracture site chosen for anastomosis will depend on the site of injury and the extent of vascular involvement. They must be examined with extreme care for signs of damage, and interpositional vein grafts may be needed if it proves necessary to reach a healthy vessel wall which can be used for anastomosis. Immediately post-traumatic, reliable criteria of total normality of the vessel wall present a problem.
Seven to 10 days later, signs of damage to vessels are more obvious, with oedema and thickening of the wall.
The state of the other main arteries of the limb may also need to be assessed to ascertain to what extent the artery chosen for anastomosis is sustaining the limb alone or with minimal assistance from the other main arteries.
The findings may preclude the use of end-to-end anastomosis to the flap artery, and even in the absence of damage to other vessels end-to-side anastomosis may be preferable. The information provided by arteriography is, as already stressed (p. 102), only partial and must be matched against the findings at operation.