The use of plates for internal fixation gains more and more importance and acceptance due to the introduction of new implants offering the possibility to lock the screw head with the plate. With this new plate generation, different fixation concepts can be considered and in addition the indication for plating is spread out to the diaphyseal segment of bone.For proper application of the implants—and to avoid technical or mechanical complications—a thorough understanding of the basic concepts of fixation, the bone biology and biomechanics, remains of outstanding importance.
Refections useful for the adapted use of plates and screws in internal fixation
More or less all implant systems used in internal fixationconsist of two main elements—a longitudinal element for the load transfer from one main fragment to the other and a transverse element to assure the coupling of the implant system to bone (Table 1). When comparing internal fixation with intramedullary nails or internal fixation with plates some major differences appear. Using an intramedullary nail for a diaphyseal fracture the mechanical concept ismore or less independent from the fracture pattern—simple fracture, wedge fracture, comminuted fracture. In addition, the position of the nail, the length and diameter of the nail as well as the position of the locking bolts are more or less given and standardised by the local anatomy of the broken bone segment as well as the implant design. In contrast to nailing, plating offers two differentfixation concepts—splinting and interfragmentary compression. Comminuted fractures are best treated using a splinting technique, because local bone and soft tissue devascularization can be minimized; while in simple fractures the application of interfragmentary compression can be considered as a stabilization tool. Plate position is chosen mainly according to the local anatomy and the surgicalapproach chosen. But, depending on mechanical demands, the plate position can be altered (tension side, compression side). In addition, the length of the plate itself, the number and the relative position of screws which need
2 | 09
to be inserted, as well as the type of screws (standard cortical screws or locking head screws, mono- or bicortical screws, self drilling or self tapping screws) remainunder debate. Thus, a lot of additional decisions have to be taken by the surgeon when planning and performing plate osteosynthesis. It is also evident that plating is intellectually and technically much more demanding than nailing (Table 2). The three following main factors influence the stability of the fixation and the loading conditions of the plate bone construct: The overall length of theplate, the overspan length of the plate, and the number, position and design of the screws.
Length of the plate
Utilizing the newer minimally invasive techniques of indirect reduction, subcutaneous or submuscular plate insertion and splinting as a stabilization concept, the plate length can be chosen to be very long without the need of additional soft tissue section and devascularization.Theoretically the plate can equal the whole length of the broken bone. But, at least the minimal length of the internal plate can be determined by means of the two factors: The plate span width and the plate screw density. Plate span width is defined as the quotient of the plate length and overall fracture length. Empirically we find that the plate length should be two to three times higher than theoverall fracture length in comminuted fractures and eight to ten times higher in simple fractures. The second factor is the
1a Fig 1a–c
Plate span ratio and plate screw density
In comminuted fracture the plate length should be 2 to 3 times higher than the overall fracture length (a). In simple fractures this ratio should be raised to a value of 8 to 10 (b)....