Musculoskeletal Imaging

1. Musculoskeletal Imaging

3. Conventional Radiography They are chiefly useful for evaluation of the bones. Also provides useful information about the adjacent soft tissues. Gas may be seen within the soft tissues and may be a clue to an open wound, ulcer, or infection with a gas-producing organism. Calcifications within the soft tissues can indicate a tumor, myositis ossificans, or systemic disorders such as scleroderma or hyperparathyroidism.

4. Views At a minimum, two views at right angles to one another should be obtained when a fracture or dislocation is suspected�AP and Lateral views. Radiographs of the ankle, for example, usually include a straight frontal view of the ankle, a frontal view obtained with approximately 15 degrees internal rotation of the ankle (the mortise view), and a lateral view.

5. Slipped capital femoral epiphysis. AP radiograph of the pelvis.

6. Frog-leg lateral view of the left hip

7. Phalangeal fracture. AP and lateral radiographs of the hand.

8. Phalangeal fracture. AP and lateral radiographs of the hand.

9. Conventional radiograph of a normal bone will show a smooth, homogeneous cortex surrounding the medullary space. The cortex will be thicker along the shaft (diaphysis) of long bones and thinner in small, irregular bones such as the carpal and tarsal bones and at the ends of long bones. Within the medullary space of a normal bone are trabeculae. These are visible in radiographs as thin, crisp white lines that are arranged in predictable patterns that enhance the stress-bearing capability of the bone.

10. Normal metacarpals. PA radiograph of the second and third metacarpals of a 36-year-old woman. The cortex is thick and homogeneously white in the midshaft of the metacarpal. It becomes progressively thinner as it approaches the ends of the bones. At the articular surfaces the cortex has been reduced to a thin, yet distinct, white line.

11. How to identify abnormal X rays Correlation with the results of the history and physical examination may be helpful. comparison with the patient's prior plain radiographs or with a radiograph of the opposite extremity may also help.

12. Mammographic Techniques In extremity imaging, the mammographic technique is occasionally used to search for small calcifications or foreign bodies in the soft tissues.

13. Fluoroscopy Fluoroscopy plays an important role in evaluation of joint motion. It is often used by orthopedic surgeons to monitor placement of hardware.

14. Computed Tomography Tomography has two major uses in skeletal imaging. The first is evaluation of fracture fragment position. The second major use of CT is in evaluation of bone tumors or tumor-like diseases. For this purpose, MR imaging is the principal competing technique.

15. Magnetic Resonance Imaging The exquisite contrast of MR imaging makes it ideal for evaluation of soft tissues. Its most frequent use in skeletal imaging, therefore, is for diagnosis of injuries to muscles, tendons, or ligaments about joints. Also useful for evaluating disorders of the bone marrow including neoplasm, osteomyelitis, fractures that are occult on conventional radiographs, and avascular necrosis.

16. Nuclear Medicine The two most common are the technetium bone scan and the technetium- or indium-labeled white blood cell scan. One of several phosphate compounds of 99m Tc is selected for use in a bone scan. Methylene diphosphonate is used most frequently. If there is a specific anatomic area of interest, images may be acquired over that area at the time the radionuclide is injected, as well as 3 to 4 hours later. The immediate images reflect the amount of blood flow to the area; the delayed images reflect the amount of bone remodeling occurring there.

17. Bone scintigraphy is a sensitive but nonspecific technique. Most osseous abnormalities of clinical significance will cause an increase in radiolabeling. Because of their sensitivity and because they provide physiologic rather than anatomic information, bone scans can be used to find abnormalities before they are detectable by conventional radiography. In particular, they are often used for screening of bone metastases in patients with known malignancy.

18. Legg-Calv�-Perthes disease (spontaneous avascular necrosis of the capital femoral epiphysis) in children� bone scans may be more sensitive than MR imaging. Osteomyelitis�bone scan or MRI

19. Biopsy When tumor or infection is suspected, it is often useful to obtain a tissue sample for cytologic or histologic analysis or for culture. This may be accomplished by means of an "open" procedure in the operating room or a percutaneous needle puncture of the lesion to obtain a cellular aspirate or slender core of tissue. Needle biopsies of palpable lesions need no radiologic intervention. When the lesion is not palpable, however, biopsy may be accomplished under fluoroscopic, CT, or sometimes ultrasound guidance.

20. Technique Selection In general, as in most other organ systems, the radiograph is the initial imaging test after history and physical examination.

21. Trauma Rely primarily on conventional radiography. When a strongly suspected fracture is not identified, you may choose among repetition of conventional radiographs in 7 to 10 days, nuclear medicine bone scanning, and MR imaging. If a fracture is noticed and more information is needed concerning the location of fragments, CT is useful.

22. Bone or Soft-Tissue Tumors For local staging of both bone and soft-tissue neoplasms, MR imaging is the best technique. When a bone tumor is suspected but is not discovered with conventional radiographs, MR imaging is a useful secondary screening tool.

23. Metastatic Tumors Symptomatic sites suspected of being involved by metastatic neoplasm are best evaluated initially with radiographs. An overall survey for osseous metastases may be performed by nuclear medicine bone scan. Suspected soft-tissue metastases are best evaluated by MR imaging.

24. Osteomyelitis Conventional radiographs should be obtained first. If these are normal or inconclusive, MR imaging, nuclear medicine bone scan may be helpful.

25. Imaging of Joints

26. Techniques Radiography Arthrography Computed Tomography Magnetic Resonance Imaging Ultrasonography Radionuclide Imaging ("Bone Scans")

27. Radiography Conventional radiography is the most commonly used imaging technique to evaluate the joints. This technique should always be the first imaging study performed in a patient suspected of having joint problems. In all instances, when possible, two images of the joint perpendicular to each other should be performed. These are usually a frontal projection in the anteroposterior (AP) view and a lateral view.

28. In certain instances it may also be important to obtain images of the joint above and below an injury. Two examples of this scenario are in forearm and lower leg injuries (paired bones), because pathology may exist at either the proximal or distal joint. Because some ionizing radiation is present in radiography, it should be used only when absolutely necessary in pediatric patients and pregnant women.

29. Arthrography Arthrography is a technique in which contrast is injected into the joint. The joint is then imaged using radiography, CT, or MR imaging or a combination of these techniques. The injected contrast may be an iodine-containing water-soluble compound, which is then imaged with radiography or CT .

30. Computed Tomography Conventional computed tomography, a technique that makes individual axial (transverse) slices of the patient, uses the same ionizing radiation as radiography. CT technique has been vastly improved in the past few years. The recently developed "spiral" CT has major advantages over conventional CT. With the spiral CT technique, axial (transverse) images are acquired much more rapidly with dramatic decreases in radiation dose.

31. Magnetic Resonance Imaging MR imaging has revolutionized the imaging evaluation of almost all body areas but particularly those of the central nervous system and musculoskeletal system. It has tremendous advantages over other imaging modalities in the evaluation of joints because of its excellent soft-tissue contrast, high resolution, and ability to image in every plane. This technique may show pathophysiologic events even before they are seen on x-ray, such as showing the very early changes of avascular necrosis .

32. Because of its exquisite soft-tissue contrast, MR imaging allows radiologists to visualize subtle differences in soft tissues that had never before been seen with other imaging modalities. MR imaging can also depict subtle changes within the bone marrow cavity, an area difficult to evaluate with radiography or CT. Finally, this technique allows precise definition of almost each component within or surrounding the joint.

33. MR imaging of avascular changes in bone. Sagittal MR image of the knee shows an area of bone infarct in the femur just below the cortex (arrowheads). This abnormality was not seen on the radiograph. MR imaging can also show these changes in the femoral head long before conventional film shows any abnormality.

34. Posterior MR image of the knee shows the differentiation between the fat (F) and the biceps femoris muscle (arrow). MR can dramatically demonstrate small changes in density, one of its most effective advantages over other imaging techniques.

35. Therefore, MR imaging is a tremendous aid to preoperative evaluation of any person who has unexplained joint pain or who has had trauma to a joint. In fact, MR imaging should almost always be performed in patients with these symptoms before any invasive procedure is attempted. The major disadvantages of MR imaging are that some patients with claustrophobia cannot tolerate the small space of the magnet, and patients with metal in their bodies or who have certain heart valves or clips for vascular problems cannot be imaged.

36. Ultrasonography High-frequency transmission of sound can be used to evaluate the soft tissues, tendons, ligaments, and even the cartilage of the joint. The ultrasound waves cannot be transmitted through cortical bone so the intramedullary cavity cannot be imaged with this technique.

37. Radionuclide Imaging ("Bone Scans") Radionuclide imaging uses radioactive materials that are injected intravenously so they can localize in regions of abnormally increased blood flow (hyperemia) or regions of increased osteoblastic or osteolytic changes or heightened metabolic activity. The major uses of bone scanning are in patients suspected of having metastatic disease or infection. Its primary use in suspected joint disease is limited.

38. Anatomy of the Normal Joint The typical normal synovial joint consists of at least two articulating bones enclosed in a synovium-lined joint capsule. The apposing bony surfaces are covered by smooth articular cartilage (hyaline cartilage). On radiographs, the normal joint has a separation between the adjacent bones which is occupied by the hyaline or articular cartilage, meniscus, and joint fluid (the so-called "articular space") depending on which joint is imaged. However, MR imaging exquisitely shows the components of the normal joint.

39. Frontal views of 82-year-old woman showing chondrocalcinosis represented by calcification of the menisci (arrows). The menisci are not normally demonstrated on radiography unless they are calcified.

40. Coronal MR image showing the normal components of the knee joint. Note the menisci, the posterior cruciate ligament (arrow), and the medial (tibial) collateral ligament (arrowhead).

41. Joint Disease The clinical signs and symptoms of joint disease are manifestations of abnormal function such as reduced mobility, hypermobility, and pain. Altered function may be due to pain, discomfort, apprehension, or instability.

42. Radiographically, joint disease may be diagnosed by any of the following: Incongruity of the articulating bone as is seen with dislocations, e.g., traumatic dislocation or dislocations caused by arthropathies such as lupus arthritis or rheumatoid arthritis Irregularity of articulating bone ends and margins, as in erosions (e.g., in psoriasis or gout) Increased density or sclerosis of articulating bone ends (also called eburnation), as in osteoarthritis Bony outgrowth (proliferation) at bone ends, known as osteophytes

43. 5. Diffuse reduced density of bone ends, described as juxta-articular or periarticular osteopenia (e.g., rheumatoid arthritis, tuberculous arthritis) 6. Loss of articular space from articular cartilage destruction (e.g., septic arthritis, osteoarthritis) 7. Accumulation of excess joint fluid within the joint (joint effusion) (Excess joint fluid is a common manifestation of joint disorders. The fluid may be synovial fluid, blood, or even pus, depending on the etiology of the joint disease.)

44. Technique Selection

45. Radiography should always be the initial imaging test to evaluate the joints and should only be obtained after the patient has had a thorough history and physical examination and there is a clear indication to obtain the study. At least two projections perpendicular to each other should be obtained.

46. selection of the imaging techniques in a few common clinical scenarios.

47. Congenital Diseases If the clinical situation of a suspected congenital anomaly or a pediatric joint abnormality or if a limp is present in a child, an x-ray film of the suspected joint should be obtained first. Because the joint structures are not well mineralized in the child, further evaluation of the joint with ultrasonography or MR imaging will often be required to make a more definitive diagnosis because, as discussed earlier, they are the best techniques to image nonmineralized structures.

48. Acute Trauma In acute trauma, the first line of radiologic investigation is the radiograph. Generally, fractures that extend into the joint surface (intra-articular fractures) are treated very aggressively with the aim of reestablishing the integrity of the joint. Intra-articular fractures are frequently treated by operative reduction and internal fixation if the fracture fragments are severely displaced.

49. CT examination of the involved limb and joints may also be performed preoperatively in selected cases for surgical planning. Postoperative CT may also be required to assess the results of surgical intervention. The advantages of CT are that it enables precise assessment of joint reconstitution and also confirms or excludes the presence of any intra-articular fragments that may interfere with proper reduction and healing .

50. Subacute and Remote Trauma If the trauma is subacute or remote, the investigation should also begin with the radiograph. If the joint is normal and there is a strong clinical suspicion of injury, the patient may benefit from a radionuclide bone scan or more appropriately MR imaging because of its superior soft-tissue contrast and resolution. MRI is particularly suited for investigation of the intra-articular and periarticular soft-tissue structures and subchondral bone.

51. Nontraumatic Cases After an initial normal or unrevealing radiographic examination, MR imaging is the next modality of choice. If there is a joint effusion, it may be cost effective to aspirate the fluid and analyze it for metabolic or infectious causes. If there is no obvious effusion at radiography, MR imaging is usually the next best and most cost-effective imaging test to evaluate injury to the intra-articular and periarticular structures of a joint.