American Association for Hand Surgery
Theme: Beyond Innovation

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Characterization of the Dorsal Ulnar Corner in Distal Radius Fractures: Implications for Surgical Decision Making
Danielle Nichole Atwood, MD, PhD1; Joseph Zimmer, BS1; Andrew J Lovy, MD2; Jay Bridgeman, MD1; Alexander Y. Shin, MD3; David M Brogan, MD, MSc4
1University of Missouri, Columbia, MO, 2Mayo Clinic, Rochester, MN, 3Division of Hand Surgery, Department of Orthopedic Surgery, Mayo Clinic, Rochester, MN, 4Washington University in St. Louis, St. Louis, MO

HYPOTHESIS
The dorsal ulnar corner (DUC) of intra-articular distal radius fractures constitutes a small, but important, component of the sigmoid notch and radiocarpal articular surface that may not be adequately captured with volar only surgical techniques.
METHODS
A multicenter retrospective review identified post-menopausal female patients with surgically treated low-energy intra-articular distal radius fractures. Patients with low-energy injuries (defined as a fall from standing height or < five feet) with pre-operative CT scans were included. High-energy trauma or extra-articular fractures were excluded. DICOM data from each CT scan was analyzed using Amira 5.0 3D reconstruction software to visualize intra-articular fracture patterns and isolate the DUC fragment. The fragment was measured (dorsal surface radio-ulnar and proximal-distal dimensions; articular surface radio-ulnar and anterior-posterior dimensions). Articular surface measurement (dorsal to volar) was divided by each specimen's lunate depth (dorsal-volar, measured horn to horn) to normalize and control for distal radius size variabilityand is reported as percentage of lunate depth.
RESULTS
80 patients met inclusion criteria. Mean dimension measurements of the DUC: dorsal surface proximal-distal dimension: 9.82 5.02 mm, 95% confidence interval [8.72, 10.92]; dorsal surface radio-ulnar dimension: 9.07 3.72 mm, 95% CI [8.25, 9.88]; articular surface radio-ulnar dimension: 7.44 3.92 mm, 95% CI [6.58, 8.30]; articular surface anterior-posterior dimension: 4.14 2.39 mm, 95% CI [3.62, 4.67]. Individual lunate depth measurement was used to normalize articular surface depth. On average, the DUC comprises 23.6% of the articular surface 13.6% with a 95% CI [20.7, 26.6].
SUMMARY
Biomechanical studies of extra-articular fracture models suggest volar plate distal locking screws extending 75% of the articular surface depth are sufficient for fixation; however, our modeling suggests that, on average, this will not capture the DUC in intra-articular fractures. Mean DUC fragment articular surface depth in this study is < 5 mm and articular surface width is < 8 mm wide. This accounts for approximately 24% of the volar-dorsal width of the distal radius at the lunate facet indicating that use of screws extending across the distal radius 75% would most likely not capture this fragment. These findings expand current understanding of the morphology and size of the DUC fracture fragment and provide serious implications critical to understanding optimal operative fixation methods, which may include utilizing longer screws or performing fragment specific fixation. Additionally, this information can also be used to develop more accurate distal radius intra-articular fracture models for biomechanical studies.


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