Ultrasound of the Calf, Ankle, and Foot

Chapter 125 discusses US examination of the calf, ankle, and foot, which is frequently performed to evaluate for muscle, tendon, and ligamentous injuries; joint effusions and synovitis; bursitis; plantar fasciitis; and Morton neuroma. US measurements of Achilles tendon ruptures in different ankle positions may help in guiding treatment selection. Dynamic US evaluation is the imaging study of choice to evaluate for peroneal tendon dislocation and intrasheath subluxation. The posterior tibial tendon (PTT) is the most commonly injured tendon at the medial aspect of the ankle which can be readily evaluated with US. US scanning may be comprehensive or focused to the region of interest.

An Introduction to Musculoskeletal Ultrasound

Musculoskeletal ultrasound is incredibly helpful in the assessment of musculoskeletal conditions, particularly those of soft tissue and joint. It very much helps to compliment other imaging modalities such as radiographs, CT and MRI. This chapter introduces the benefits and practicalities of musculoskeletal ultrasound as well as outlining the ultrasound appearances of commonly encountered normal structures and common pathological entities.

Medication-Induced Musculoskeletal Changes

Chapter 117 discusses common medication-induced changes of the musculoskeletal system. The effect of corticosteroids on the musculoskeletal system, including osteoporosis and osteonecrosis, is discussed. Corticosteroids decrease osteoblastic activity, stimulate bone resorption, and decrease intestinal absorption of calcium. Complications of bisphosphonate therapy such as atypical femoral fractures and osteonecrosis of the jaw are reviewed. Myopathies and tendon pathologies are briefly discussed, as well as bony changes potentially seen with long-term voriconazole treatment. For osteoporosis, DXA scan is the gold standard, whereas radiography is usually the first imaging modality performed in patients on voriconazole therapy who present with pain.

Developmental Hip Dysplasia

Chapter 112 focuses on developmental dysplasia of the hip, which includes a spectrum of abnormalities ranging from a stable hip with a mildly dysplastic acetabulum to complete hip dislocation. Pathophysiology, clinical findings, and screening studies are explored. The pathophysiology is multifactorial including mechanical, genetic and hormonal factors. Imaging strategies, findings, and treatment options are also discussed. Screening US, which is the imaging modality of choice, is performed on infants with predisposing risk factors. Outcome is quite variable with many cases resolving spontaneously without treatment whereas others stabilize with acetabular dysplasia. Treatment options include immobilization and surgery. MRI is used for problem solving in postoperative patients.

Internal Derangement of the Knee

Chapter 108 focuses on knee MRI, first discussing some general technical considerations of musculoskeletal MRI, and then discussing individual components, including the menisci, cruciate and collateral ligaments and articular cartilage, which often contribute to knee pathology. After initial radiographic assessment, MRI is the most helpful imaging modality to detect internal derangement of the knee, and the knee is the most commonly ordered extremity MRI examination. MRI is an extremely powerful tool for determining the source of the patient’s symptoms and directing future treatment, and it is the most sensitive imaging study to evaluate the menisci, ligaments, tendons, and muscles in the setting of knee pain or instability. Additionally, MRI is also an excellent tool to evaluate the bones and articular cartilage.

Internal Derangement of the Hip

Chapter 107 discusses the hip and its component tissues, including the bones, labrum, synovial tissues, muscles, and tendons, and covers the MRI appearances of many of the most common pathologies that occur in and around the hip joint. The hip is a ball-and-socket joint consisting of the femoral head and the cup-shaped acetabulum. Because of its shape, the hip allows multi-axial movements, including flexion/extension, abduction/adduction, and internal/external rotation. A number of supporting structures, including the acetabular labrum and joint capsule, surrounding muscles and tendons, and bursae, help stabilize the hip and allow for a smooth range of motion. Injuries to any of these structures can result in hip pain and loss of function. MRI has become the test of choice to assess hip internal derangement because of its superior assessment of soft tissues and bone marrow and its contrast resolution, which improves conspicuity of pathologic conditions.

Knee Arthrography

Chapter 102 describes indications, technique, and imaging findings of knee arthrography. Knee arthrography is selectively performed in clinical practice for MRA, typically in younger patients. Indications include evaluation for meniscal re-tear after prior repair, osteochondral injuries, and therapeutic injections (most commonly steroid). Extension of intraarticular contrast into the meniscal substance indicates a tear or re-tear. Abnormal course of the cruciate ligament fibers indicates a tear. Contrast undermines unstable osteochondral lesions and extends into the hyaline cartilage defects. Complications are rare but include infection and bleeding.

Wrist Arthrography

Chapter 100 describes the indications, the technique, and the imaging findings of wrist arthrography. Wrist arthrography is selectively performed in routine clinical practice for MR arthrography (MRA), typically in younger patients. The main indications include evaluation of the intrinsic interosseous wrist ligaments (scapholunate and lunotriquetral) and triangular fibrocartilage complex (TFCC) injuries. Contrast should easily inject and disperse throughout the radiocarpal joint space. Complications from contrast injection are rare and include infection and bleeding. Full-thickness tearing of any of the 3 components of the scapholunate and/or lunotriquetral ligament allows abnormal communication with the midcarpal joint. Central tearing of the triangular fibrocartilage disc allows abnormal communication with the distal radioulnar joint.

Soft Tissue Infections

Chapter 88 outlines the key radiologic features of soft tissue infections and the diagnostic value of the different imaging modalities such as conventional radiography, US, CT, and MRI. Soft tissue infections present in various forms that involve varying depths from skin to deeper tissues. Early diagnosis may be challenging because of nonspecific clinical presentations, resulting in delay in management. The advent of cross-sectional imaging has improved diagnostic capabilities dramatically, with US, CT, and particularly MRI being the pillars of evaluation. Prompt and appropriate imaging workup of the various MSK soft tissue infections aids early diagnosis and in demonstrating the extent of the disease process, as treatment delay significantly reduces the cure rate and increases the risk of complications.

Osteomyelitis of the Long and Flat Bones

Chapter 86 highlights the imaging manifestations of osteomyelitis (OM) involving the long and flat bones. OM refers to inflammation of the bone and bone marrow caused by underlying infection, classically bacterial. Long and flat bone OM can occur either because of hematogenous spread, direct inoculation or from a contiguous source of infection. The severity depends on the factors such as organism isolated, pathogenesis, extent of bone involvement, duration of infection, and host factors such as age and immune status. Imaging plays a crucial role in the early diagnosis of OM with MRI being the modality of choice. Both acute and chronic forms of OM are still a big challenge to treat, even in the era of advanced antibiotics and new surgical techniques. Imaging helps in early diagnosis, which in turn helps to initiate early treatment.