129. PROXIMAL ULNAR ANATOMY: IMPORTANCE OF THE DORSAL ANGULATION (PUDA)

Abstract

Purpose: Recognition of the proximal ulna dorsal angulation (PUDA) is important for anatomic reduction of proximal ulnar fractures or osteotomies, especially when using newer straight precontoured proximal ulnar plates. The purpose of this study was to characterize the PUDA in 50 patients with bilateral elbow radiographs.

Method: Bilateral elbow radiographs (100 radiographs) were magnified four times using commercial software. The PUDA was measured from the intersection of lines tangent to the subcutaneous border of the olecranon and the proximal ulnar shaft. The olecranon tip-to-apex distance of the PUDA was also measured. Three orthopaedic surgeons independently examined the radiographs and intra/inter-observer reliability was calculated using Intra-Class-Correlation (ICC).

Results: A PUDA was present in 96% of radiographs. The average PUDA was 5.7° (range, 0°to14°). The Pearson Correlation coefficient for a side-to-side comparison was 0.86(p< 0.001). The average tip-to-apex distance was 47 mm (34 mm–78mm). No correlation was identified with sex or age. Intra-observer reliability was excellent for the PUDA (ICC 0.892 and 0.863) and good for tip-to-apex distance (ICC 0.762 and 0.827). Inter-observer reliability was good for PUDA (ICC 0.784 and 0.925) and for tip-to-apex distance (ICC 0.711 and 0.769).

Conclusion: A mean proximal ulna dorsal angulation of 5.7° is present in 96% of patients at an average of 47 mm distal to the olecranon tip. Measurement of the PUDA has good/excellent inter/intra-observer reliability. Recognition of the PUDA may be helpful in anatomic plating of the ulna. Contralateral PUDA measurements are useful for surgical planning in cases with comminution or distorted anatomy.