Fig. 1
Scaphoid fracture. 18-year-old soccer player with chronic wrist pain since falling on an outstretched hand 1 year earlier. Wrist radiographs at that time were interpreted as normal (not shown). Coronal CT shows nonunion of a proximal pole scaphoid fracture (arrow)
With CT and MRI, the assessment of scaphoid fractures should include evaluation for apex dorsal angulation at the scaphoid waist (“humpback deformity”, diagnosed when the intrascaphoid angle is >45°) and ad latus (sideways) displacement >1 mm (especially with longitudinally-oriented fractures in the proximal scaphoid).
Follow-up Imaging. With normal healing, the fracture line may widen during the first 4 weeks, and periosteal callus should not be expected. Of note, some proximal pole osteosclerosis is a common finding during the healing process. By week 6–12, cancellous bone bridging usually should be evident (e.g., >8 oblique-sagittal CT slices of 0.5-mm thickness) [7]. Even after fracture healing, a peripheral radiolucent cleft may remain; patients with more than 50% union are generally cleared to resume normal activities.
Delayed union of a scaphoid fracture may be diagnosed on CT scans after 3 months if there is <25% union, cystic change, and resorption along the fracture.
Non-union may be diagnosed after 6 months in the presence of a pseudarthrosis (prevalence, 5–10%), with or without complications of periscaphoid osteoarthritis (e.g., scaphoid nonunion advanced collapse or “SNAC” wrist) and proximal pole AVN.
AVN on MRI is diagnosed in the proximal pole when there is decreased signal on T1-weighted images and contrast enhancement is less than the distal pole [10].
AVN—Lunate
The lunate resembles the shape of a crescent moon, and is the “keystone” intercalated segment withstanding high loads in the central column of the proximal carpal row. AVN of the lunate, commonly known as Kienböck disease, is the topic of abundant recent literature [11] summarized here.
Clinical. Clinically, the stereotypical patient is 20–40 years old. Less commonly, adolescent and elderly patients also can be seen. Patients typically present with non-specific dorsal pain aggravated by wrist use (especially in extension), limited wrist motion, and reduced grip strength.
Pathogenesis. The etiology of Kienböck disease is considered multifactorial. Causative factors may include both vascular factors that compromise bone perfusion (e.g., variations in arterial supply or venous drainage, such as single vessel arterial supply) and biomechanical factors that can concentrate loads at the proximal-radial aspect of the lunate. Specific anatomic features with a possible association with Kienböck disease development or progression include negative ulnar variance, decreased radial inclination, and type I lunate morphology. Knowledge of these anatomic features may improve diagnostic accuracy and affect therapeutic decisions (e.g., negative ulnar variance may be treated with a radial shortening osteotomy).
Imaging. After XR findings are visible, XRs can show progression along a spectrum from osteosclerosis, to bone collapse, malalignment, and premature osteoarthritis. Although the traditional Lichtman staging system was developed based on XR findings, CT can be helpful for early diagnosis and shows a higher stage than XR in two-thirds of cases. MRI also helps with diagnosis of early (XR-occult) Kienböck disease, and can be used to diagnose “nonfunctional articular surfaces” caused by bone collapse or arthritis (e.g., criteria used in the Bain and Begg classification system).
With MRI, T1 images show decreased signal intensity in the bone marrow for all stages of Kienböck disease (Fig. 2). On fat-sat T2 images, the signal intensity can be variable; it is generally hyperintense in areas of ischemic (viable) bone marrow containing edema and hypointense in areas that are necrotic. Early stress reaction may be seen at the proximal-radial lunate; later, a coronally-oriented fracture may propagate across the lunate.
Fig. 2
Kienböck disease. 16-year-old girl with wrist pain for 6 months and history of negative radiographs. Coronal T1-weighted (a) and fat-suppressed intermediate-weighted (b) MR images show abnormal signal (arrow) in the lunate (with relative sparing of the proximal-ulnar corner) characteristic of Kienböck disease
After contrast administration, MRI enhancement patterns have been described that may correlate with the potential for lunate revascularization and therefore prognosis (A, normal homogeneous bone enhancement, associated with a good prognosis; B, inhomogeneous enhancement, with viable distal lunate and necrotic proximal lunate, associated with an intermediate prognosis; C, no enhancement owing to complete necrosis, with a poor prognosis).
Differential Diagnosis. The MRI differential diagnosis for focal signal alteration in the lunate may include bone edema from other causes, such as cartilage loss (e.g., chondrosis/arthritis) and macrotrauma (e.g., contusion, fracture). Lunate AVN is usually easy to distinguish from ulnar (ulnocarpal) impaction syndrome, which is characterized by a triad of findings: positive ulnar variance, TFCC perforation, and chondrosis with subchondral reactive changes at the ulnar head and proximal-ulnar aspect of the lunate (Fig. 3). With end stage (stage IV) Kienböck disease, the pattern of malalignment and OA can resemble scapholunate dissociation with advanced collapse (“SLAC” wrist).
Fig. 3
Ulnar impaction syndrome. 54-year-old woman with ulnar-sided wrist pain and “osteosclerosis” reported on radiographs. Coronal T1-weighted (a) and fat-suppressed intermediate-weighted (b) MR images demonstrate abnormal signal (arrow) centered in the subchondral bone at the proximal-ulnar margin of the lunate. This appearance is accompanied by characteristic findings of overlying lunate chondrosis, mild ulnar positive positioning, and a tiny full-thickness perforation in the triangular fibrocartilage
Ligamentous Structures
A fundamental objective of wrist imaging is the diagnosis of injuries to wrist ligaments. Wrist ligaments are categorized as extrinsic (attaching to carpal bones and adjacent structures) or intrinsic (attaching only to carpal bones). In patients with acute wrist trauma and bone injury on MRI, there are high rates of injury in both the extrinsic (85%) and intrinsic (67%) ligaments [12]. Highlights from several recent reports [12–17] on this topic are summarized below.
Extrinsic Ligaments
The extrinsic ligaments are considered important “secondary stabilizers”. Indeed, if the extrinsic ligaments are intact, even a complete intrinsic ligament tear may not result in carpal instability.
Extrinsic ligaments are named logically according to the bones to which they attach [16]. Although there are numerous extrinsic ligaments, there are arguably four that should be evaluated routinely on MRI or US.
Volarly, the two most important extrinsic ligaments are the radioscaphocapitate and long radiolunate (also known as the radiolunotriquetral) ligaments.
Dorsally, the two most important extrinsic ligaments are the dorsal radiocarpal ligament (also known as the dorsal radiotriquetral ligament) and the dorsal intercarpal ligament (also known as the dorsal scaphotriquetral ligament).
Intrinsic Ligaments
Of the intrinsic ligaments, the two most important “primary stabilizers” are the scapholunate (SL) ligament and the lunotriquetral (LT) ligament. These two ligaments transfer opposing flexion and extension moments to the lunate, which keeps the lunate in neutral alignment.
Carpal instability varies in severity from static (severe, non-reducible), to dynamic (visible only with clenched fist or ulnar deviation), to pre-dynamic (early, normal imaging). SL ligament insufficiency is associated with dorsal lunate tilt (“DISI”); this condition is much more common than LT ligament insufficiency, which is associated with volar lunate tilt (“VISI”).
Anatomy. Both the SL and LT ligaments are “C-shaped” structures with three segments. While the central “membranous” segment is composed of fibrocartilage that commonly perforates incidentally with advancing age, the dorsal and volar segments are composed of biomechanically important collagen. Biomechanically, the dorsal segment is most important for SL stability, while the volar segment is most important for LT stability.
Imaging. The imaging diagnosis of SL instability is characterized by malalignment, generally defined by a wide SL space (>3 mm) or wide scapholunate angle (>60°). LT ligament insufficiency may be associated with abnormal volar flexion of the lunate (scapholunate angle <30° and capitolunate angle >30°). The SL angle measurements are generally similar on XR, CT, and MRI [18].
Normally, with MRI, ligaments appear as linear, hypointense structures. MRI diagnosis of a tear is made by observing hyperintense T2 signal, attenuation, or discontinuity in a ligament (Fig. 4). Injuries are commonly graded according to severity:
- 1.
Mild sprain (periligamentous edema and/or increased intrasubstance signal),
- 2.
Partial-thickness tear (focal fluid-like signal intensity involving a portion of the cross section of the ligament; or abnormal morphologic features such as fraying, irregularity, indistinctness, or abnormal caliber), or
- 3.
Full-thickness tear (focal fluid-like signal or discontinuity extending across the ligament cross section).
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