Using Fluoroscopy to Measure Distal Radius Articular Step-Off

By: Peter Pollack

Study suggests methods to optimize imaging in the absence of CT

“Computed tomography [CT] scans offer the most accurate measurements of intra-articular fracture displacement,” explained Steven Beldner, MD, “but they are frequently unavailable in the office setting or operating room, forcing clinicians to rely on less accurate radiographs or fluoroscan images to assess minute displacements.”

Dr. Beldner and his colleagues sought to evaluate the accuracy of fluoroscopy to determine intra-articular displacement of a die punch fracture and to develop a technique to optimize the accuracy of such measurements with variable angular deformities of the distal radius on lateral view. Their findings are presented in Scientific Poster P230, “Measurement of Distal Radius Articular Step-Off Utilizing Fluoroscopy,” on display in Academy Hall.

“Intra-articular distal radius fractures frequently have two components,” noted Dr. Beldner. “The first is an intra-articular step-off between the scaphoid and lunate facet. The second is an angular component through the metaphyseal region appreciated on the lateral plane in either a volar or dorsal direction.”

Cadaveric study
The research team performed osteotomy with varying amounts of articular step-off (0 mm, 2 mm, and 4 mm) on human cadaveric forearms between the lunate and scaphoid fossas. They obtained fluoroscopic images in the posteroanterior (PA) plane, without magnification, at varying angles by tilting the X-ray beam 25° volar to 20° dorsal in 5° increments. This was performed with a 5° distal radius volar tilt and then repeated while changing the lateral tilt through a proximal osteotomy from 15° volar to 15° dorsal in 10° increments.

Printed fluoroscopic images were then randomly evaluated for intra-articular step-off by three board-certified hand surgeons, with the results recorded in a blinded fashion. The research team used chi-square analysis to compare nominal data between the tilted PA view that was tangential to the distal radius tilt and the remaining PA views not tangential to the distal radial tilt for each of the four distal radius lateral tilt positions. They performed a separate statistical analysis to determine if the accuracy estimating actual step-off diminished with increasing tilt of the PA fluoroscopic beam from tangential to the distal radial tilt.

For all four configurations of distal radius lateral tilt, the researchers found that the accuracy between the estimated and actual step-off was improved when the tilted PA view was tangential to the distal radius lateral tilt (P < 0.001). An identical subanalysis of the data pertaining to the distal radius with 0 mm of intra-articular step-off found that the tilted PA view, parallel to the distal radial tilt, was not superior to tilted radiographs not parallel to the lateral tilt of the distal radius (P > 0.05).

“This confirmed that when achieving anatomic reduction, virtually any fluoroscopic image exhibits good alignment,” said Dr. Beldner.

The researchers also observed that, when the fluoroscan beam in the PA view was tilted in angles farther away from the angle of distal radial tilt, the estimated step-off measurements were observed to be more variable from the average estimated step-off measurement as the tilt of the X-ray beam ventured farther away from the distal radial tilt (P > 0.05).

Improving accuracy
“Targeting the X-ray beam in the PA plane parallel with the lateral tilt of the distal radius produced the most accurate measurements,” Dr. Beldner observed. “When the plane of the X-ray diverged from the lateral tilt, the measurements became less reliable. This was independent of intra-articular step-off except when the fracture was anatomically reduced.

“We also found that, when the articular surface was reduced to an anatomic position, the measurements were equally accurate both in- and out-of-plane of the articular surface measured on lateral,” he continued. “This suggests that anatomic fracture reduction looks good in any plane, but nonanatomic fracture measurements have a higher chance of being inaccurately measured when the beam is not parallel with the articular surface.”

Dr. Beldner concludes that, when assessing intra-articular step-off on the PA plane, clinicians should first obtain a lateral radiograph to determine the lateral tilt of the distal radius articular surface. The X-ray beam should then be adjusted on the PA view to match the measurement of the lateral tilt, placing the X-ray beam parallel with the articular surface on the PA plane to obtain the most accurate measurement of the articular step-off between the scaphoid and lunate facet.          

Dr. Beldner’s coauthors are Remy V. Rabinovich, MD, and Daniel B. Polatsch, MD.

Details of the authors’ disclosure as submitted to the Orthopaedic Disclosure Program can be found in the Final Program; the most current disclosure information may be accessed electronically at www.aaos.org/disclosure  

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