When the plastic surgeon is asked to help in managing a problem arising from infection occurring in a bone, the bone involved is nearly always the tibia. The pathology is usually one of periodic flare-ups of chronic osteitis, with the background either an old infected fracture or the residuum of acute osteitis, the latter less frequently today with more effective control of the initial episode, possibly with the background of a sequestrum.
The problem relates either to the skin overlying the subcutaneous border of the bone and /or the bone itself.
There are several reasons why the tibia should
be the bone so often involved. Apart from being the long bone whose shaft is probably most frequently fractured, it has a larger subcutaneous surface than any of the others. Less obviously significant, but probably just as important, a much smaller area of its total surface is covered with attached muscle.
The cover provided by the extensive muscle attachments to the other long bones distances them from the surface, and eliminates to a large extent the problem of providing effective skin cover after surgery. In this they provide a sharp contrast to the problems created by the long subcutaneous surface of the tibia, particularly if the injury has involved skin damage, or there is the deep skin fixation which so often follows previous surgery in the area.
The muscles attached to a bone are also
important providers of blood supply to the cortex to which they are attached. The lower half of the tibia, the segment of the shaft most at risk from fracture, has virtually no muscles attached to it, and this leaves perfusion of the bone largely reliant on its nutrient artery.
In a comminuted fracture, bony fragments which appear on X-ray to be detached from the main tibial shaft cannot rely on the perfusion source which the presence of a muscle attachment would provide, increasing the likelihood of sequestration.
This explanation of the reasons why the
problems exist provides at the same time some clues to their solution.
At a clinical level one of the problems concerns the most effective way of replacing the scarred and deeply adherent skin overlying the tibial shaft. When chronic infection of the bone with periodic flare-ups is an additional problem, avascularity and sclerosis are added to the pattern.
The objectives then become ones of providing stable skin cover for
the subcutaneous surface, trying to add to the blood supply of the sclerotic bone, and filling any defect in the bone which may result from the activities of the orthopaedic surgeon, if he has to carry out a sequestrectomy or remove sclerotic bone.
In managing the acute combined skin-bone injury, vascularised muscle used to cover the defect and fill any gaps in bony continuity has been found to have a beneficial effect in salvaging damaged tissues, and it has proved equally useful in these subsequent problems.
The form which soft tissue replacement should
take, whether by fasciocutaneous or myocu-taneous flap, will depend on the local cir-cumstances, but it should be generous in area, and planned with enough reserve to cope with any minor infection which might arise from the bone subsequently. At which precise point the bony problem should be tackled in relation to the timing of the flap transfer is a matter for discussion with the orthopaedic surgeon but, in general, operation on the diseased bone should be undertaken only when it can be immediately and completely covered by the flap.
The extent of the typical area of pretibial scarring is likely to make the possibility of using local tissues to reconstruct the defect a remote one. The use of a distant flap is unavoidable, and the demands of time and patient comfort and convenience are strong arguments in favour of a free flap. The form it should take will depend on the details of the local problem. If skin replace-ment alone is required a fasciocutaneous flap would be adequate.
If surgery of the bone will be required, and particularly if there is the possibility of dead space after its completion, or surgery of sclerotic, relatively avascular bone is involved, a flap which includes muscle is likely to be pre-ferable, bringing a more effective blood supply to the site, and capable of filling dead space.
Safe use of a free flap in this context requires as
much knowledge as possible of any changes in the major vessels which may have resulted from the original injury. Caveats regarding the use of vessels which are already damaged, and the use of end-to-side rather than end-to-end anastomosis, have already been discussed in relation to the acute skin-bone injury.