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Hypothesis: The three-dimensional anatomy of the proximal ulna can be difficult to interpret with two-dimensional imagery techniques, especially standard intraoperative fluoroscopy.  The purpose of this study is to delineate the borders of the trochlear ridge, and the medial and lateral facets, and provide identifying measurements to assist surgeons intraoperatively. 

Methods: Ten fresh-frozen cadaveric elbows were analyzed:  five female and five male specimens with an average age of 62 years.  Female height ranged from 5’0”- 5’2” and male height ranged from 6’0”-6’2”. True lateral static fluoroscopic images were obtained of each specimen with a custom radiographic scale to allow assessments of true measurements.  Radiographic markers were placed intra-articularly onto the trochlear ridge and the floor of the medial fossa. The specimens were imaged again and measurements taken using the custom scale.

Results: In the small specimen group, the average distance to the trochlear ridge, the medial facet, and lateral facet from the center of the trochlea were 10.2mm (95% CI 9.7 to10.6mm), 13.6mm (95% CI 12.4 to 14.8mm), and 11.2mm (95% CI 10.9 to 11.5mm) respectively.  The large specimens had average distances of 11.9mm (95% CI 11.3 to 12.4 mm), 16.6mm (95% CI 15.8 to 17.4mm), and 14mm (95% CI 13.3 to14.7mm) respectively.  Interobserver and intraobserver reliabilities were good to excellent (.85 to .98 for all measurements).

Conclusion:  When viewing a true lateral of the elbow by intraoperative fluoroscopic imagery, the lateral facet may be easily visualized and resides 11-14mm from the center of the trochlea in most patients.  The trochlear ridge and medial facet are not readily seen on standard fluoroscopy.  The trochlear ridge in most patients may be identified by measuring 10-12mm from the center of the trochlea.  The medial facet in most patients may be identified by measuring 13.5-16.5mm from the center of the trochlea.  These measurements are reliably reproducible.