Carpal Ligament Instability Workup
- Author: Sunjay Berdia, MD; Chief Editor: Harris Gellman, MD more...
Standard radiographic examination of the wrist should include a posteroanterior (PA) view in neutral rotation, as well as lateral views. Both the symptomatic and the asymptomatic wrist should be evaluated. Static instability patterns can be seen with these radiographs. Additional radiographs (eg, PA grip, PA maximum radial deviation, PA maximum ulnar deviation, lateral maximum flexion, and lateral maximum extension views) can also be obtained and can help diagnose dynamic instability.
To determine scapholunate dissociation, the scapholunate gap can be measured on PA and PA grip radiographs. However, obtaining a PA view that clearly shows the scapholunate gap without some bony overlap can be difficult. Findings should always be compared side to side. Kindynis et al suggested angling the x-ray tube to obtain a clearer view of the scapholunate joint and to measure the space at the level of the midportion of the flat ulnar facet of the scaphoid.
The amount of gap that is diagnostic of scapholunate dissociation is not agreed upon. Many authors define the gap to be pathologic if it is greater than 3 mm.[26, 30] In 1991, Cautilli and Wehbe measured the gap on 100 normal radiographs and found a mean distance of 3.7 mm (range, 2.5-5 mm). Given the wide range, comparing the injured wrist with the contralateral uninjured wrist is crucial before scapholunate dissociation is diagnosed.
If the lunate is dorsiflexed more than 15º than the capitate on lateral radiography, a diagnosis of a dorsal intercalated-segment instability (DISI) deformity is confirmed. Conversely, a volar intercalated-segment instability (VISI) deformity is defined if the lunate if volarly flexed more than 15º. A DISI deformity is associated with scapholunate instability, whereas a VISI deformity is associated with lunotriquetral instability.
In addition, the scapholunate angle can be measured on lateral radiography. In scapholunate instability, the scaphoid tends to assume a volarly flexed posture. As such, the scapholunate angle, which normally measures 30-60º (average, 46º), increases to more than 70º. Conversely, in lunotriquetral instability, the lunate is usually palmarly flexed, and the scapholunate angle can be less than 30º.
McMurty et al defined a method to determine ulnar translocation on PA radiography (see the image below). The distance between the center of the capitate and a line extending from the intermedullary axis of the ulna is divided by the length of the third metacarpal. McMurty et al found that this ratio was 0.30±0.03 in normal wrists but was smaller in patients with ulnar translocation.
Other imaging modalities
Other diagnostic imaging studies that may be considered in this setting include the following :
Computed tomography (CT)
Magnetic resonance imaging (MRI)
Because the false-positive rate is relatively high for arthrography (especially in those >40 years), some have suggested comparing images of the injured wrist with images in the contralateral uninjured wrist. Communication between the different compartments of the wrist may not be a result of trauma but, rather, may be a result of age-related degenerative changes.
Arthroscopy remains the criterion standard for diagnosing specific ligament injuries in the wrist.[35, 36, 37, 38] Both radiocarpal and midcarpal joints should be evaluated. More important, surgical management can take place in the same setting.
Leng et al studied a proposed dynamic four-dimensional (4D) CT imaging technique that generated images with high spatial and temporal resolution without requiring periodic joint motion. Preliminary results from this cadaveric study demonstrate the feasibility of detecting joint instability using this technique.
Many schemes have been described to classify the different degrees of carpal instability. The one described by Linscheid et al is one of the earliest and probably the easiest to use.[27, 1]
Linscheid et al separated most instabilities into two groups on the basis of the orientation of the proximal row relative to the distal row. They used the lunate to define the orientation of the proximal row, and they used the capitate to define the orientation of the distal row because it is most easily seen on lateral radiography. In their system, if the lunate is dorsally flexed relative to the distal row (capitate) on lateral radiography, the instability is considered a DISI. The proximal row is the intercalated segment because no tendons directly insert on it. Similarly, if the lunate is palmarly flexed relative to the distal row, the instability is defined as a VISI.
These two patterns have been further subclassified into dissociative and nondissociative types. The dissociative type occurs when the injury results in instability between adjacent carpal bones within a row. For example, scapholunate instability is most commonly associated with a dorsiflexed lunate; this pattern is called a DISI deformity, dissociative type. A nondissociative type occurs when the DISI or VISI pattern is secondary to an injury that results in instability between rows. This nondissociative pattern has also been called midcarpal instability.
Two patterns that do not fit this classification are ulnar translocation and dorsal subluxation of the carpus. Ulnar translocation is defined as an ulnar shift of the entire carpus relative to the radius. This type of instability is seen in wrists with rheumatoid arthritis after chronic attrition of radial-side extrinsic ligaments and bony changes. Dorsal subluxation describes a dorsal shift of the entire carpus relative to the radius. This pattern, also called adaptive carpal instability, is often seen after malunion of distal radius fractures where the radius has lost its normal volar tilt.
Two other adjectives commonly used in classifying carpal instabilities are static and dynamic. A static instability is one that can be clearly recognized on routine radiography by a loss of the normal alignment. A dynamic instability is any instability that requires external forces placed on the carpus to elicit an instability pattern. Therefore, the diagnosis of dynamic instability relies on other means, such as dynamic radiography, physical examination with provocative maneuvers, or arthroscopic evaluation.
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