|Microsurgery: Transplantation and Replantation by Harry J. Buncke, MD, et al.|
Although successful replantation and revascularization procedures involve a series of complex steps, bony stabilization is the foundation of the repair. The benefits of adequate osteosynthesis are two fold. One, it provides intra-operative stability to protect tension on multiple micro-anastomoses. Two, during the postoperative period, it allows early mobility to reduce stiffness while protecting bony healing. To limit ischemia time in replantation, fixation methods must be rapid and relatively easy to apply, and minimize additional soft tissue injury.
Currently, a number of techniques available for small bone fracture repair are applicable to replantation: miniature screws 4,11,15 and plates, 15-17 various tension band techniques, 13,15,17,22 intraosseous wires, 2,3,5,8 mini-external fixators,10,12,21 intramedullary bone pegs and devices, 6-14,18 and Kirschner wires. 6,7,9,19,20 Fundamental to the selection and application of these techniques is an understanding of the mechanism of bone and soft tissue healing, as well as the biomechanics of the hand.
The skeletal fixation requirements of the replantation injury can be categorized as anatomic or physiologic. Anatomic goals are those related to obtaining and maintaining adequate reduction and preventing unacceptable rotation or instability. If joint fusion is required, a functional position should be carefully selected so that late corrective osteotomies are not needed. Physiologic parameters include choosing a fixation method that does not increase tissue damage by dissection or by impingement on gliding structures, that limits ischemia by rapid application, and that allows early protective motion. Healing by end-to-end contact or primary intention should be encouraged by some degree of rigidity in the method selected. In the case of multiple fractures or prolonged transportation time, the critical factor remains the ischemia time. The viability of the tissue block is of primary importance, with bony fixation coming second. The fastest method of osteosynthesis should be selected. Postoperative care must then be tailored with this compromise to stability in mind. With more proximal amputation of the extremities, additional time for bony fixation can be gained with the use of temporary arterial shunts that immediately reperfuse the devascularized part during plate or external fixation of the proximal fractures. Although not ideal, delaying proper bony stabilization may be necessary to ensure the survival of the revascularized tissue, despite a poor functional position or malunion that may occur. Deviations from normal healing can often be corrected later with osteotomies or bone grafting in a viable replant.
SOFT AND HARD TISSUE HEALING
Trauma to the extremities resulting in amputation or devascularization can vary greatly with respect to the amount of energy imparted to the tissues and the size of the zone of injury. A clean, guillotine type of amputation has markedly less tissue destruction than a crushing avulsive injury. Theoretically, fractures heal by a mechanism similar to that of soft tissue, with a continuum of fibrosis and inflammatory reaction that will be influenced by the extent of injury.
Primary bone healing, as with soft tissue, occurs only under ideal circumstances. These require a lack of motion at the fracture site and close apposition of bone ends, which allow primary membranous bone regeneration with minimal fibrosis or callus formation. With primary healing, there is limited involvement of surrounding soft tissue. If compressive forces can be applied across the fracture, union can occur by direct lamellar growth of osteoblasts into the fracture defect without a fibrous intermediary.
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