Locked Plating: Biomechanics and Biology

Since the early ideas of internal fixation, many different concepts and techniques have been developed for the use in fracture surgery. Each technique has been welcomed by many with excitement while others have suggested caution, locked plating is no exception. Since its advent over 15 years ago many have viewed this as a violation of the strict AO principles of anatomic reduction and rigid fixation. Others have looked at it as an extension of the blade plate (single locked plate), that is, an “internal external fixator.” This initial paper will deal with the biomechanics and biology of locked plating as compared with conventional plating. The following paper will suggest some of the clinical indications and the rationale for use of locked plating. In reviewing biomechanical studies, the surgeon must be clear on the model that is used including the number of screws on each side of the fracture, how close the screws are to the fracture site, the length of the plate, how close the plate is to the bone, the material of the plate and the screws, unicortical or bicortical screws, the density of the bone, and the stability of the fracture. Furthermore, the surgeon must understand that more stability does not always equal better healing. Although fractures require a 2% to 10% strain rate to heal, the optimal biomechanics for fracture healing is unknown. Too rigid of fixation can delay healing. A strain rate of >10% may not allow bone to form at the fracture site. Locked plating has different biomechanics in axial loading, bending, and torsion. Biologically, locked plating preserves the blood supply by preventing necrosis under the plate (no compression between the plate and the bone) and allows a more percutaneous insertion. Although locked plating is a useful tool, indiscriminate use will cause the surgeon to lose the fracture-healing race and cause construct failure.