Ulnar trochlear notch articular surface has three morphological patterns: a neglected major anatomical feature

Abstract

Purpose

The typical anatomical illustration of the trochlear notch articular surface includes a transverse rough non-articular ridge which separates the olecranon and coronoid part of the joint. This transverse ridge, the “bare area”, is not covered by cartilage and represents the optimal entry point for olecranon osteotomies. Aim of the present study was to encounter the anatomical variations in the morphology of the trochlear notch articular surface.

Methods

Two-hundred seventy-three dried ulnae were inspected and a qualitative classification of the variations of the trochlear notch articular surface was done. Correlation to gender and side was examined.

Results

Three distinct morphological patterns were observed. Separate olecranon and coronoid facets (Type I) were the most common pattern (165/273, 60.4%). Partial fusion of olecranon and coronoid facets (Type II) was observed in 75 out of 273 bones (27.5%), while a single olecranon and coronoid facet (Type III) was present in 33 out of 273 bones (12.1%). The occurrence of Type II and III was significantly more common in females (p < 0.001).

Conclusions

The most common morphological pattern of the proximal ulna articular surface was the olecranon and coronoid facets separated by the transverse ridge, which is considered as the typical anatomical pattern. The partial fusion of olecranon and coronoid facets was the second most common pattern (27.5%) and the single olecranon and coronoid facet with no transverse ridge present was the rarest one (12.1%). These variations affect the area covered by cartilage. They are noticeable in an elbow MRI and they may have implications on olecranon osteotomy. Absence of the transverse ridge may confuse the surgeon during elbow arthroscopy.