X-ray diagnostics of the musculoskeletal system is usually the first diagnostic measure when a pathological (disease-related) change in bone elements and joints of the skeletal system is suspected. In addition to computed tomography (CT) and magnetic resonance imaging (MRI), projection radiography (normal X-ray) is the basis of diagnostic imaging. Conventional X-ray technology refers to the film-slide technique, i.e. the X-ray images are developed, while digital X-ray technology represents the modern variant, which is currently undergoing rapid development. An X-ray image is the two-dimensional projection of the three-dimensional tissue in the form of a summation image. The structures of the skeletal system appear as shadows and overlap, so that multiple acquisition angles are advantageous. Generally, radiographs are taken in 2 perpendicular planes, with the radiographic area selected according to clinical indication. There are also oblique exposures, which are used, for example, to visualize the spine or first allow the assessment of a fracture (e.g., at the head of the radius – radius). Overview images provide an overall impression, while target images are used for special questions or complex anatomical conditions. Functional images (e.g. in various postures when assessing the spine) or side comparison images of the extremities are also used for diagnostics. In principle, countless variants are possible, which are used depending on the indication and preference, so that a detailed description of every possible, diagnostically valuable X-ray exposure would lead too far. The following text provides an overview of the basic imaging of bones, joints and soft tissues in conventional radiography.
Indications (areas of application)
- The follow-up of fractures (bone fractures).
- The follow-up of dislocations and ligament ruptures
- Suspicion of sclerosis – hardening remodeling of the bone marrow, for example, in osteomyelofibrosis.
- Degenerative diseases of the musculoskeletal system – eg osteoporosis (bone loss).
- Inflammatory diseases of the musculoskeletal system – e.g. arthritides (inflammation of the joints), which can have bone changes as a result.
- Metabolic changes of the musculoskeletal system – e.g. hyperparathyroidism (parathyroid hyperfunction) with increased bone loss as a result.
- Tumorous changes of the musculoskeletal system – e.g., bone metastases that are osteolytic or osteoplastic. The word “lysis” stands for dissolution and means that dissolving processes take place due to the influence of tumor cells on the bone, resulting in bone defects and consequently bone instability. In osteoplastic metastases, there is compaction of the bone, which reduces the biomechanical load-bearing capacity of the bone. As a result, fractures (bone fractures) may occur spontaneously or due to minor trauma.
- Congenital malformations of the skeletal system
The procedure
Radiographic imaging of the bone system (skeletal images: Skull, spine, shoulder girdle, upper extremities, thorax, pelvis and lower extremities) provides valuable information about the condition and any change: a healthy bone presents with a clear smooth boundary by the bone cortex, while inside the cancellous bone (woven bone) and the bone marrow are of honeycomb structure. The radiological criteria for a pathological process are derived from this knowledge: Degenerative or inflammatory diseases destroy the healthy architecture, as do aggressive metastases (daughter tumors). In addition, fractures with dislocated bone fragments or joint involvement as well as axial misalignments of the bones become visible in the radiograph. However, not all pathological changes are detected in the X-ray image, so that this diagnostic method is primarily used to confirm the diagnosis. Sometimes subtle findings are superimposed by soft tissues (muscles, tendons, fatty tissue, nervous tissue, connective tissue as well as vessels) or by intestinal gases. The joints can only be partially visualized in the X-ray image because they consist of various soft tissue components (cartilage, ligaments, tendons, joint capsule with synovia and synovial fluid) in addition to the bony silhouette.For this reason, the anatomical position of the joint-forming bones in relation to each other is usually assessed. Visible pathological changes of the joints are:
- Narrowed joint space
- Displacement of the joint axes – e.g., dislocation of the humerus (upper arm bone) in a dislocated shoulder joint
- Osteophyte attachments – reactively newly formed bone protrusions.
- Subchondral cyst formation – formation of cavities below the cartilage.
- Free calcium particles in the synovial fluid – e.g. in inflammatory processes.
- Joint effusions – this is visible in the X-ray image by displacement of the surrounding tissue.
The representation of the soft tissues in the X-ray is rather unsatisfactory, so that magnetic resonance imaging is used here. The image quality here is considerably better.
