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Danger Zones For Flexor Tendons In Volar Plating Of Distal Radius Fractures
Jerry I. Huang, MD; Sonya Agnew, MD; Karin Ljungquist, MD
Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, WA

Introduction: Flexor tendon rupture is a well-recognized complication after volar plating of distal radius fractures, with an incidence as high as 12%. Cadaver studies investigating the location of flexor tendons with respect to plate position are inherently flawed by the distortion of the position of the tendons after dissection. This study was undertaken using MR imaging to analyze the position of the flexor tendons "at risk" for rupture in a zone around the watershed line, and to define a 'danger zone' for flexor tendons in the region of volar plates.

Material and Methods: With institutional research board approval, we analyzed 40 MRIs of the wrist without distal radius pathology. The location of the FPL and index FDP (FDPi) tendons was recorded at 3mm and 6mm proximal to the watershed line of the distal radius. The distance between the volar margin and the FPL and FDPi tendons as well as the radial to ulnar position of the tendons with respect to proximity from the sigmoid notch were analyzed.

Results: At a point 3mm proximal to the watershed line, FPL and FDPi were located on average 2.6mm (+/-1.0mm) and 2.2mm (+/-1.1mm) anterior to the volar margin of the distal radius. This distance increased to 4.7mm (+/-1.4mm) and 5.3mm (+/-1.7mm) at a level 6mm proximal to the watershed line. FPL and FDPi were located 57% (+/-8%) and 42% (+/-8%) of the total width of the distal radius from the sigmoid notch at 3mm from the watershed, and 66% (+/- 8%) and 46% (+/- 10%) at 6mm from the watershed. This corresponds to a high risk zone for FPL and FDPi ruptures (Figure 1).

Conclusions: Surgeons should be aware that the flexor tendons are at risk for rupture with volar plate placement within a zone that is more proximal and ulnar than previously appreciated. At a position 3 mm proximal to the watershed line, plate placement more than 2 mm anterior to the volar cortex or use of plates thicker than 2mm pose a high risk for directly contacting, irritating or causing attritional rupture. This distance nearly doubles at a point 6mm proximal to the watershed line.
Figure 1 Red zone represents the watershed line; the yellow and green zones represent the area where FPL and FDPi tendons are on average approximately 2.5 and 5mm volar to the distal radius, respectively.

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