Microsurgery: Transplantation and Replantation by Harry J. Buncke, MD, et al.
  Table of Contents / Chapter 32:
Bony Fixation in Replantation
  With movement, the bones of the longitudinal arches of the hand have unequal forces acting upon them. Functionally, the palmar flexor forces are relatively greater than their extensor counterparts, particularly for the metacarpal fracture. This imbalance of forces creates a net compressive force or the volar cortex, with distraction or tension occurring at the dorsal cortex. This inequality is responsible for the loss of reduction and motion at the fracture site, but can be used to advantage with proper placement of a stabilizing fixation device. If the distracting force on the cortex under tension can be neutralized by a dorsal plate or "tension band" wire, fracture motion can be markedly reduced. With increasing flexion and subsequent dynamic volar cortex compression, the implant accepts the tension load without allowing distraction. An ideal healing environment is thus created with limited motion and bony compression, permitting motion of the structures distal to the fracture without disrupting the fracture interface. This system of dynamic compression and tension banding assumes the presence of a complete volar cortex accepting the compressive load. Without this cortex, forces created by motion must be carried solely by the implant, increasing the risk of failure and eliminating the stress-sharing capacity of bone. Bone shortening or contouring is often required to provide sufficient bony contact.



The forces acting on proximal phalanx fractures are somewhat different. The tension side is the volar cortex because of three forces: flexor, extensor, and lumbrical. The lumbrical pull is directly on the dorsal hood. The flexor acts through the A-2 pulley, pulling the proximal fracture fragment volarly, while the extensors act by pullthrough to the insertion on the middle phalanx. These forces together tend to collapse the proximal phalanx fracture into an apex-volar angulation (Fig. 32-1). These forces have been demonstrated in the laboratory with videofluoroscopy in a cadaver fracture model, and remain under investigation.23

Fixation Techniques


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