American Society for Peripheral Nerve

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Osseous Anatomy of the Distal Radioulnar Joint: An Assessment Using Three Dimensional Modeling
Parham Daneshvar, MD1; Ryan Willing, PhD2; Ryan Willing, Phd3; Graham King, MD4
1Orthopedic Surgery, St. Paul's Hospital, University of British Columbia, Vancouver, ON, Canada; 2Musculoskeletal Health Research, Hand and Upper Limb Centre, St. Joseph's Health Centre, London, ON, Canada; 3Hand and Upper Limb Centre, Western University, London, ON, Canada; 4Hand and Upper Limb Center, University of Western Ontario, London, ON, Canada

Introduction: DRUJ osseous anatomy is important for prosthesis design and understanding joint function, however its anatomy has not been well characterized. Our hypothesis is that the anatomy of the distal radioulnar joint is quite variable and mid-coronal reverse obliquity alignment is associated with ulnar positive variance.

Materials & Methods: Computed tomography images of seventy(38 right, 32 left) cadaveric forearms were obtained. Specimens with significant arthritic changes or previous bony injury were excluded. Using MIMICS(Materialise), three dimensional models of the radius and ulna were obtained. Paraview(Kitware) was used to obtain the appropriate sections for evaluation and quantification. Measurements of the radius of curvature of the sigmoid notch(SN) and ulnar head(UH), as well as the length of the SN, volar and dorsal lips were performed in the axial plane. Similar measurements were taken in the mid coronal and at one-third and two-thirds in the volar and dorsal coronal sequences. In addition, mid coronal plane angular measurements were made of the SN and UH.

Results: The average ulnar variance was -0.90 ±1.8 mm. At the level of the wrist joint, the radius of curvature of the SN, and UH were 18.2 ± 8.5mm, and 8.2 ± 1.3mm respectively. The volar and dorsal lip lengths measured at 1.9 ± 1.2mm and 1.4 ± 0.8mm. The mean mid-coronal length of the SN was 8.4 ± 1.7mm. The coronal length of the SN measured 7.3 ± 1.7mm at one-third volar compared to 9.2 ± 2.1mm at one-third dorsal coronal planes, and 6.0 ± 1.6mm at two-third volar compared to 9.8 ± 2.2mm at two-third dorsal coronal planes with statistical significance of p<0.001. The mid coronal angle of the SN and UH was 6.0 ± 9.9° and 18.0 ± 9.9°.

Conclusions: The osseous anatomy of the DRUJ varies considerably. There is a strong correlation between ulnar variance and SN and UH angle. Reverse oblique UH/SN is present in many ulnar positive wrists. There is a mismatch between the radii of curvature of the UH and SN. The majority of the sigmoid notches in our series were cup shaped with variable depths and angles. Only a small minority(4 of 70) were flat. SN shape should be taken into account when designing prostheses and considering altering ulnar variance. Sagittal anatomy of the SN demonstrates increasing dorsal size which may give insight into increased risk of dorsal subluxation/dislocation of the ulnar head after ligamentous injury or distal radius malunion.

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