Date Published: July 31, 2017
Author(s): Juan M. Giugale, Mitchell S. Fourman, Deidre L. Bielicka, John R. Fowler.
The dorsal tangential (DT) view has been shown to improve the detection of dorsal screw perforation during volar distal radius fracture fixation. Here we performed a cadaveric imaging survey study to evaluate if the DT view was uniformly beneficial for all screws.
Standardized placement of fixed-angle volar distal radius plates was performed on two cadavers. Fluoroscopic images depicting variable screw perforation of each of the four screw holes on the plate were generated. A 46-image survey was distributed at a large academic medical center. Respondents were asked to answer if the screw was perforating through the dorsal cortex in each image. Statistical analysis was performed using Fisher’s exact test. A p value < .05 was considered significant. The DT view offered a significantly more reliable determination of dorsal screw penetration than traditional lateral imaging for the radial-most screw at all degrees of perforation and the middle two screws at 2 mm of perforation. Residents and attendings had more accurate screw readings overall using the DT view. The DT view is superior to traditional lateral imaging in the detection of small amounts of dorsal perforation of the radial-most three screws of a fixed-angle volar plate.
Although volar plate fixation has become the gold standard in the treatment of unstable distal radius fractures, extensor tendon irritation and rupture are known complications of this procedure. The etiology of extensor rupture is believed to relate to dorsal screw prominence in the majority of cases [1, 2]. Intraoperative lateral fluoroscopic films are typically used to assess screw depth after insertion. However, the presence of Lister’s tubercle makes the distal radial cortex convex, not flat. A previous anatomic study showed that the height of Lister’s tubercle ranges from 1.4 to 6.6 mm in relation to the radial border of the radius . This implies that the screws radial and ulnar to Lister’s tubercle can be proud several millimeters and still appear to be within the dorsal cortex on lateral fluoroscopic films. Prior work also examined the third extensor compartment floor through a limited dorsal approach after volar fixation and found that 12.5% of patients had dorsal screw prominence not identified on lateral fluoroscopic films .
All protocol elements were approved by the Committee for Oversight of Research and Clinical Training Involving Descents (CORID #587) at our institution. All procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and with the Helsinki Declaration of 1975, as revised in 2008. A traditional volar approach to the wrist was performed on two fresh-frozen cadaveric forearms, permitting the placement of a fixed-angle distal radius plate (Stryker, Kalamazoo, MI) with 4 distal screw holes. Screws were inserted into each of the distal holes with their tips flush with the dorsal cortex, confirmed by visual inspection through a separate dorsal incision. Plate positioning and placement were performed by the senior investigator (JRF). A screw from a single hole was then removed and replaced with a longer screw, producing a collection of images with standardized single screw prominences of 0, 2, 4, or 6 mm. Lateral and DT fluoroscopic radiographs were obtained after each screw exchange (Figures 1(a) and 1(b)). A true lateral was obtained by rotating the image until the pisiform overlapped the distal pole of the scaphoid. To produce the DT view, the wrist was maximally flexed and the forearm was placed at a 15° inclination in relation to the axis of the mini-C arm radiographic beam.
Completed responses were logged from a total of 18 respondents (7 faculty, 7 residents, and 4 fellows) out of a total of 52 faculty, fellows, and residents surveyed. A response was considered complete if it included answers to all questions. An additional five responses that failed to meet this criterion were removed from our sample size.
Extensor tendon rupture after volar plate fixation of distal radius fractures may occur secondary to screw prominence. The protuberance of Lister’s tubercle can mask dorsal screw penetration on lateral fluoroscopic views. The dorsal tangential (DT) view has been proposed as a method that can more sensitively detect dorsal screw prominence compared to standard lateral radiographs. Our work suggests that the primary advantage of the DT view compared to traditional lateral fluoroscopic views is in the evaluation of small degrees (2 mm) of screw protrusion on the radial three screws on a fixed-angle volar plate. Larger magnitudes of screw protrusion further limit the benefit of the DT view to the single most-radial screw on the plate. Overall, the DT view was found to be more reliable than the lateral view by all experience cohorts but active clinical fellows. However, the sensitivity and specificity of both techniques were still equivocal.
In a survey study based on measurements made using a cadaveric model, we found that the DT view is superior to the lateral view of the wrist in the identification of any degree of dorsal cortex perforation of the radial-most screw in a volar locking plate. Further, the DT view may also be superior to the lateral view in the detection of 2 mm screw prominence in central plate holes. Further work that utilizes an increased sample size and image quantity and considers additional plate types and hole configurations is required to validate the findings of this pilot work.