A Review on Reading Wrist X-rays
Wrist injuries are a common part of an orthopedic practice. Patients frequently present for evaluation after a slip and fall injury and the development of acute wrist pain. Radiographs are part of the initial evaluation for all acute wrist injuries. When interpreting wrist x-rays, radiologists will discuss multiple different angles and measurements that correlate with various clinical conditions. Many of these angles and measurements remain foreign to clinical providers. What we hope to do in this review is help clarify what some of these more common measurements are and to go through some common fracture patterns.
Measurements and angles
Dating back to 1979, a review published in the American Journal of Roentgenology looked at three different arcs to help predict fracture patterns in the wrist carpal bones (Gilula, 1979). Arc I was defined as the proximal portion of the scaphoid, lunate, and triquetrum; Arc II was the distal portion of Arc I; and Arc III includes the proximal portions of the capitate and hamate (Gilula, 1979). The arcs should be smooth and any step off or disruption may indicate carpal injury (Davies, 2013).
Then, in 1985 an article published in Skeletal Radiology discussed the role for assessing the greater and lesser arc when evaluating traumatic wrist injuries (Bradford Yeager MD, 1985). They classified the wrist into injury patterns where the lesser arc is a pure dislocation pattern and the greater arc is a fracture dislocation pattern (Bradford Yeager MD, 1985).
Radiologists will also attempt to measure certain angles to evaluate for radius shortening (Jack Porrino, 2014). Ulnar variance should be evaluated in all wrist x-rays, because an increased ulnar variance is associated with multiple wrist pathologies. These can include TFFC tears, Kienbock disease, and DRUJ instability (Derek Bernstein, 2018). Ulnar variance is measured by drawing a straight line across the distal ulna, drawing another straight line across the distal radius, and then measuring the length between them (Andrew Parker, 2014). A positive ulnar variance is when the ulna surface is higher than the radial surface. A negative ulnar variance is when the ulna surface is shorter than the radial surface and a neutral variance is when the radius and ulna surfaces are at the same height (Luis Cerezal, 2002). Posteroanterior radiographs of the wrist are the best projection to measure ulnar variance (Judy Squires, 2014). In an article published in the Journal of Hand Surgery, they evaluated the use of the lateral radiograph in measuring ulnar variance. However, they found that the lateral radiographs were not more accurate than the PA radiographs (Derek Bernstein, 2018).
In a study published in 2012 in Clinical Orthopaedics and Related Research, they evaluated factors on radiographs that suggest distal radioulnar joint instability (Bong Cheol Kwon, 2012). What they found was that in those wrists where there was >6mm ulnar variance, there was an increased probability of the patient having DRUJ instability (Bong Cheol Kwon, 2012).
There is also the angle of radial inclination, which is measured as a horizontal line from the distal tip of the radial styloid, an angled line through the distal tip of the radial styloid, and the portion of the distal radius that articulates with the distal ulna (Kimia Khalatbari Kani, 2016). The average angle is 23 degrees and any shortening of the angle could represent DRUJ instability (Wolfe, 2017). An abnormal radial inclination can also be consistent with radius fracture (Jack Porrino, 2014).
Carpal Bone Fractures
The most common carpal bone fracture is the scaphoid, which amounts for 70% of all carpal fractures (Rodney Welling, 2008). When evaluating scaphoid fractures, you have to consider the blood supply to the scaphoid which originates at the distal pole of the scaphoid (Charles Goldfarb MD, 2001). This places fractures at the waist and proximal pole at risk for avascular necrosis (Charles Goldfarb MD, 2001). X-ray views when evaluating the scaphoid include not only the PA and lateral wrist x-ray, but also an external oblique view and a dedicated scaphoid view (Charles Goldfarb MD, 2001). Multiple views are required as a PA wrist may not detect scaphoid waist fractures (Davies, 2013). A dedicated scaphoid view is a posteroanterior x-ray placed over the scaphoid and having the wrist in ulnar deviation (Charles Goldfarb MD, 2001). The lateral x-ray can also be used to evaluate for dorsal and distal scaphoid fractures and a diagram of the lateral x-ray is seen below (Davies, 2013).
Scaphoid fractures are classified by the Herbert classification see Figure 6.
Also, when evaluating for a scaphoid injury you must also consider a scapholunate ligament tear. This can lead to scapholunate widening which can be seen on a PA x-ray with the patient clenching the first (Charles Goldfarb MD, 2001).
The second most common carpal fracture is the triquetrum (Ekaterina Urch, 2015). The most common mechanism of injury is a fall on an outstretched hand. When the patient hits the ground, the ulnar styloid will articulate with the triquetrum and cause an avulsion off the dorsal portion of the triquetrum (Nisha Rao, 2015). The dorsal avulsion can be best seen on the lateral radiograph. There are other fracture patterns, which include the body of the triquetrum and the volar cortex (Ekaterina Urch, 2015). Typically, triquetrum body fractures are associated with perilunate dislocation (Heras-Palou, 2019).
Fractures of the lunate are considered rare (Heras-Palou, 2019). However, we wanted to highlight the positioning of the lunate in relation to the radius on a lateral radiograph. The lateral x-ray of the wrist is often difficult to interpret due to the anatomy of the carpal bones. Figure 9 shows the proper positioning of the lunate and its rounded surface sitting on the distal portion of the radius.
The other carpal fractures are rare and we will not cover them in this review.
Radius and Ulna fractures
Distal radius fractures account for 17% of the acute injuries seen in the ER (Charles Goldfarb MD, 2001). An initial series of radiographs includes an AP, lateral, and oblique. The best view to visualize a distal radius or ulna fracture is the PA projection (Davies, 2013). Physicians should look for any cortical disruption that would indicate a fracture (Davies, 2013).
There are different types of distal radius fractures. In order to assist physicians in detecting distal radius fractures, a Teardrop angle should be calculated. A normal lateral radiograph of the wrist shows slight volar tilt of the radius (Jack Porrino, 2014). In order to assess for pathologic tilt, a vertical line is drawn through the radius and then a perpendicular line is drawn through the lunate facet (Jack Porrino, 2014). This angle typically measures at 70 degrees and larger angles suggest radius fracture (Jack Porrino, 2014).
The most common fracture pattern of the distal radius is the Colles Fracture. The Colles fracture is characterized by a fracture within 2cm of the articular surface and dorsal angulation of the distal fracture segment (Davies, 2013). These are classified using the Frykman classification found in Figure 14 (Nisha Rao, 2015)
The dorsal Barton, another variant of a distal radius fracture, is considered an intra-articular fracture and involves the ulna surface of the distal radius (Nisha Rao, 2015).
This is contrasted with a Chauffer fracture (also known as Hutchinson fracture), which includes the distal portion of the radial styloid (Nisha Rao, 2015).
There is also the Smith fracture, which is a distal radius fracture with volar angulation (Nisha Rao, 2015).
Finally, there are the Colles fractures, which are classified by the Frykman classification (Nisha Rao, 2015).
It is also the job of the physician to assess for DRUJ instability in the setting of distal radius fractures (Shohei Omokawa, 2014). A study published in the Journal of Wrist Surgery in 2014 looked at radiographic predictors of DRUJ instability in patients with distal radius fractures (Shohei Omokawa, 2014). What they found was that widening of the DRUJ gap distance on a PA x-ray was found to be predictive of an unstable distal radius fracture (Shohei Omokawa, 2014). Another indicator on radiographs of an unstable fracture was an ulnar styloid fracture (Shohei Omokawa, 2014). They found that fractures that involves the base of the ulnar styloid with displacement of the fracture increased the chances for DRUJ instability (Shohei Omokawa, 2014).
In summary, reporting the results of wrist radiographs involve both evaluation of the carpal bones and distal radius and ulna. For the purpose of this review, we did not go in to carpal instability patterns. Wrist factors are difficult to analyze due to the complexity of interactions between the multiple joint surfaces and soft tissue structures present. Also difficult for the provider are the multiple measurements used by radiologists to help predict radius fractures that are not easily done at the bedside with patients. Ultimately, we hope that this helps the physician create an algorithm for evaluating wrist radiographs that works for them and catches most of the common conditions seen in a Sports Medicine practice.
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