Understanding the Radiographic Anatomy of the Proximal Ulna and Avoiding Inadvertent Intraarticular Screw Placement.

OBJECTIVES

To map the proximal ulnar articular margins and ensure safe extraarticular placement of implants.

METHODS

Ten fresh frozen adult elbow cadaver specimens were obtained. Radiopaque wire was applied to the articular margin of the articular facets and the central trochlear ridge of the proximal ulna. Fluoroscopic images were obtained demonstrating the articular facet margins. Radiographic measurements were performed and used to identify relative safe screw zones.

RESULTS

All specimens demonstrated marked extension of the ulnar and radial facets dorsal to the central trochlear ridge. The dorsal extent of the ulnar facets from the central trochlear ridge averaged 9.7 mm (range, 7.9-13 mm; SD, 1.5 mm) and 6.2 mm (range, 3.4-9.4 mm; SD, 1.9 mm), respectively. The average footprint of the posterior ulnar facet occupied 44% (±4.9%) of the total ulnar height from the dorsal cortex to the trochlear ridge.

CONCLUSIONS

The articular margins of the anterior and posterior facets of the proximal ulna are challenging to identify radiographically. A surgical "at-risk zone" exists within 9.7 mm from the radiographic margin of the central trochlear ridge. Implants placed within this zone have the potential to violate the articular surface.