Follow-up radiographs to detect callus formation after fractures.

Follow-up radiographs are important to assess proper alignment and adequate healing of a fracture. The formation of a callus is one characteristic used to follow these features, but the timing and size of its appearance is variable. Therefore, when to expect to see a callus on radiographs requires a general understanding of the fracture healing process and the many variables that can affect callus formation. The callus, or immature bone, results from a precise chronological process. Many factors can alter the sequence of events that result in the delay or even absence of callus formation. The fracture healing process begins immediately after the fracture with the inflammatory phase. In this phase, damage to the surrounding blood vessels and tissue lead to the formation of a hematoma. Inflammatory mediators are released causing inflammatory cells to migrate to the region. These cells are involved in producing the framework in which the callus forms. This stage lasts 5 to 7 days, with some overlap into the next phase. The next stage, the reparative phase, is when the callus develops. This stage lasts from 4 to 40 days, composing about 40% of the healing process time with overlap into the final phase. The hematoma formed in the initial phase serves as a structure in which the callus forms into mature bone. Through the action of growth factors and other proteins, granulation tissue is converted to radiolucent cartilaginous callus. Eventually, this is mineralized by the deposition of calcium salts. Once the calcification occurs, the callus becomes evident radiographically. This woven bone, or periosteal callus, creates an irregular radiographic appearance that is fluffy, amorphous, and biologically plastic. If not properly protected, this immature bone can be disrupted, resulting in prolongation of the fracture’s healing process and the development of bone deformities. Endosteal callus or intramedually callus also develops as part of the healing process. This type of callus is usually not visible on x-ray film. Fractures of short or irregular bones, such as the scaphoid or calcaneus, primarily heal internally and rely chiefly on endosteal callus formation for repair. This is because these types of bone have little cortex to produce radiodense callus. The last stage of repair is the remodeling phase. This composes about 70% of the healing time and can last for well over 1 year. This phase is characterized by conversion of periosteal callus into lamellar or mature bone. Unnecessary callus is resorbed and trabecular bone produced. The final product is a mechanically stable bone similar to its original state in form and function. Thefracture’shealingprocess, includingtheformation of the callus, is influenced by the patient, tissue, and treatment variables. Subsequently, these factors can influence the time when one would expect to see a callus on a follow-up radiograph. Age is one of the most important variables that influences fracture healing, although the influence of aging on fractures has undergone little investigation. The younger the individual, the faster a break tends to heal. For example, the healing period of a femur fracture can be 3 to 5 weeks in an 8-year-old, 12 to 14 weeks in a 12-yearold, and 20 to 24 weeks in an adult. This may be related to the increased vascularity and ability of the cells to differentiate in the younger individual’s periosteum. Other patient factors that influence healing include nutritional deficiencies (ie, calcium and phosphorus) and concurrent medical illnesses, such as diabetes mellitus, hormonal deficiencies, and iron deficiency anemia. Certain tissue variables can also affect the development of callus formation. Radiographic evidence of callus is dependent on the type of bone involved, as well as the nature of the fracture. Fractures, particularly in the diaphyseal region, develop more callus than metaphyseal fractures and those of smaller, irregular bones. This difference is related to the amount of periosteum enveloping the bone. Fractures of the phalanxes, scaphoid, calcaneous, skull, and those of intraarticular surfaces develop minimal to no callus that is evident on radiography. In these cases, clinical parameters, such as lack of pain with movement or tenderness to palpation, are used to assess fracture healing. This is also true for impacted fractures, but is not the case for comminuted fractures or those with wider gaps between the bony fragments. Other tissue factors, such as bone cancer, can adversely affect the healing process. SOLUTIONS TO OFTEN-ASKED PROBLEMS