Bicortical fixation is a specialized technique in orthopedic surgery used to stabilize bones. This method involves securing a bone by inserting a screw or pin through both of its outer layers, providing a strong anchor. It is commonly employed when strong stability is required for bone healing, particularly in cases of fractures or other bone-related injuries. This approach helps create a rigid structure, supporting the bone as it recovers.
Defining Bicortical Fixation
The term “bicortical” combines “bi,” meaning two, and “cortex,” referring to the outer layer of a bone. Bones have a dense, hard outer shell known as cortical bone. Inside this shell lies cancellous bone, a spongy, less dense tissue that contains bone marrow.
Bicortical fixation describes a surgical technique where a screw, pin, or other implant passes completely through the first cortical layer, then through the cancellous bone, and finally engages the second, opposite cortical layer. This dual-cortex engagement creates a secure purchase, akin to anchoring into both sides of a wall rather than just one.
The Purpose of Bicortical Fixation
Bicortical fixation is chosen for the mechanical advantages it provides, offering enhanced stability and greater resistance to various forces acting on the bone. By engaging both cortical layers, the screw creates a more rigid and durable construct. This dual engagement is particularly beneficial for resisting pull-out forces, preventing the implant from dislodging prematurely.
The technique also provides superior resistance to rotational and bending forces. This added rigidity is important for proper bone healing, as excessive movement at the fracture site can impede the natural repair process. This robust stabilization helps prevent implant failure and promotes a more predictable healing environment for the fractured bone.
Where Bicortical Fixation is Used
Bicortical fixation is commonly applied where strong, stable bone fixation is needed. It is frequently used in treating certain types of long bone fractures, such as those in the femur, tibia, or humerus, where significant loads are anticipated during the healing process. For example, it has been described for medial malleolar fractures, particularly in patients with osteopenia or poor bone quality where screw purchase might otherwise be compromised.
The choice to use bicortical fixation depends on factors such as the specific bone involved, the pattern of the fracture, and the quality of the patient’s bone. In some cases, it is employed during osteotomies, which are surgical procedures that involve cutting and reshaping bones, or in joint fusion procedures where permanent stability is desired. For instance, in proximal tibia locking plates, bicortical screw placement may offer a mechanically superior construct for stabilizing unstable fractures.
Bicortical Versus Monocortical Fixation
The distinction between bicortical and monocortical fixation lies in the number of cortical layers engaged by the implant. In monocortical fixation, the screw or pin only passes through one outer cortical layer of the bone. While bicortical fixation offers superior stability and strength, monocortical fixation has specific applications where it is preferred.
Monocortical fixation might be used in areas with thinner bone, such as some rib fractures, where bicortical penetration could risk injuring nearby anatomical structures like the pleura or lung parenchyma. It is also considered when avoiding neurovascular structures on the far side of the bone is a concern. In pediatric cases, monocortical screws may be chosen to preserve growth plates. However, in many situations, particularly in osteoporotic bone or for diaphyseal fractures, bicortical screws are often preferred due to their enhanced pull-out resistance and overall mechanical superiority.