Hip Fracture

A simple classification of hip fractures can direct surgical management and indicate prognosis. In general, hip fractures can be divided into two types: intracapsular fractures and extracapsular fractures (see Diagram 1). The reason for this dichotomy concerns the blood supply to the femoral head. Blood flow arises chiefly from branches of the medial circumflex femoral artery that runs along the posterior superior aspect of the femoral neck with the capsule (fibrous covering of the joint that maintains the joint's synovial fluid and with the hip joint maintains it's blood supply) to form a ring of blood vessels around the femoral head. Therefore, if the fracture is intracapsular and the femoral head is displaced it can tear or disrupt the blood supply. This gives rise to a condition known as avascular necrosis. In addition, a displaced fracture gets bathed in the synovial fluid capsule of the hip joint. This does not lead to an optimal healing environment. The fracture, therefore, is at a greater risk for nonunion.

Diagram 1 Anatomy of the Proximal Femur SOURCE: Author

Displaced intracapsular fractures have, at least, a one in three risk of avascular necrosis and an additional one in three risk of nonunion. Therefore, in an elderly person, management usually consists of prosthetic replacement of the hip joint. By contrast, undisplaced hip fractures have much lower rates of avascular necrosis and nonunion and are usually treated with multiple screw fixations.

Extracapsular fractures consist of intertrochanteric fractures and subtrochanteric fractures. These can be further classified as stable or unstable. Unstable fractures have loss of bone continuity posteromedially along the proximal femur, which is where most weight bearing occurs. If there is significant disruption of bone here these fractures are inherently unstable. In general these require anatomic reduction and fixation.

Subtrochanteric fractures comprise approximately 15 percent of hip fractures. In the elderly population there are two groups of patients who sustain this injury. The first includes those whose femurs are quite osteoporotic and break from a minor fall. The second group may have pathologic lesions in the proximal femur, and a fracture may occur to the weakened pathologic bone. Special care needs to be taken in evaluating these patients clinically and radiographically. These fractures, because of the high biomechanical stresses in this region of the femur, tend to be unstable and often require intramedullary fixation. Figure 1. Multiple screw fixation in situ compressing fracture fragments (AO cannulated screws synthesis). (X-ray provided by P. Rockwood.) Displaced pathologic fractures may require prosthetic replacement.