Approach to Pediatric Musculoskeletal System

Radiography

Although there have been great advances in imaging technology, radiographs (i.e., x-rays or plain films) remain the most important imaging test in most circumstances of suspected musculoskeletal pathology. Most studies will require 2-3 views to adequately image the site of interest. Each of these views is typically obtained with different patient positioning &/or projection of the x-ray beam to analyze different components of the anatomy of interest on each view. With appropriate techniques, the associated radiation exposure is usually minimal, & radiography is less expensive than other more advanced imaging modalities. Most cases of trauma require no imaging beyond radiographs.

Specific circumstances

• Joint effusions: Radiographs show high sensitivity for abnormal volumes of joint fluid at some sites (such as the elbow & the knee). However, the sensitivity is very low at other sites, including the hip & the shoulder; high clinical suspicion of joint effusion at these sites will require further imaging with ultrasound or MR. It should also be noted that radiographs are not specific for the various processes that can cause joint capsule distention, including hemarthrosis, septic arthritis, transient synovitis, & synovitis secondary to juvenile idiopathic arthritis, among others.

• Infection: The earliest radiographic findings of osteomyelitis actually relate to the overlying soft tissues rather than the bones. Thickening & edema of the surrounding soft tissues (with blurring of the normal fat-muscle interfaces) will manifest long before bone findings (which often require 10-14 days to become visible on radiographs).

• Occult fractures: Some particular clinical scenarios are notorious for producing false-negative radiographs in the setting of a fracture, requiring a low threshold for temporary immobilization until confirmatory findings manifest radiographically. Two classic examples include the spiral toddler's fracture of the mid to distal tibial diaphysis & the nondisplaced supracondylar fracture of the distal humerus.

• Nonaccidental trauma: When there is clinical suspicion for child abuse, a full skeletal survey must be obtained. While each institution will differ slightly in exactly how it performs this exam, most will follow a similar protocol of obtaining at least 1 targeted view of every body part. The radiologist involved in the case will then help decide what additional images will be required before the patient leaves the department. In some cases, a follow-up skeletal survey should be performed in 2-3 weeks, mainly to search for healing fractures that were occult on the initial survey.

• Foreign bodies: Some foreign bodies (such as glass & metal) are easily demonstrated by radiographs. Other foreign bodies (such as wood) will typically require ultrasound for detection.

• Tumors: Some bone neoplasms, especially focal lesions involving the cortex, will be easily detected & characterized by radiographs, with the classic example being osteosarcoma. Other lesions, particularly systemic processes involving the marrow (such as leukemia or metastatic neuroblastoma) may only show subtle alterations of mineralization & periosteal reaction, potentially going undetected until an MR or nuclear medicine bone scan is obtained.