|Microsurgery: Transplantation and Replantation by Harry J. Buncke, MD, et al.|
| Secondary bone healing occurs when there is motion or inadequate bony contact at the fracture zone. Bony gaps stimulate fibrous ingrowth and the production of callus as a temporary internal splint, allowing capillary growth into the area of bony instability. Osteogenesis occurs, and the fibrous bed becomes calcified with membranous bone that must undergo later remodeling. Surrounding soft tissue structures may undergo calcification during this process, and local scarring and fibrosis may occur.
X-ray analysis of the initial injury yields key information: location of fractures, pattern, displacement, comminution, joint involvement, skeletal age, density, and absolute bone loss.' Bony fixation is likely to be difficult with extensive, high-energy injuries and may require a combination of fixation methods to reduce bone gaps and limit motion. By careful analysis of the injury and the x ray, the fixation requirements and the expected course of soft and hard tissue healing can be anticipated and postoperative splinting and therapy can be planned.
Before discussing methods of bony fixation, some biomechanical concepts and definitions applicable to all fractures must be emphasized. Internal fixation implies only some degree of immobilization by the internal splinting provided by implant placement. Rigid fixation, however, implies that the fracture segments are secured by a means so strong that there is essentially no motion at the fracture site. Compression indicates not only that the fracture is held rigid, but that there is a net compressive or impacting force between fracture fragments. This force can be applied in either a static or dynamic fashion, as described in the following section.
STATIC AND DYNAMIC COMPRESSION
With the skeletal system at rest, an implant can be placed across the fracture so that interfragment compression will occur. The implant accepts a static load applied as a net impacting force based on the stable nature of the bone/implant interface. For hand fractures, the screws and plates of the mini-fragment set are a typical static compression device, with the implant itself providing compression and stabilization. If the implant has significant stability, advantage can be taken of the dynamic forces at work on the fracture during postoperative motion. Dynamic compression is particularly important during rehabilitation after digit replantation, although the general principles of anatomic reduction, stabilization, and compression are important at all replantation sites.
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