Humeral trochlear morphology does not influence coronoid fractures in elbow dislocation

Abstract

Purpose: Traumatic elbow dislocation is the second most frequent joint dislocation, even though the elbow is a congruent and stable joint. Individual variability in anatomical congruence of the elbow and how it relates to simple or complex instability has rarely been studied in the literature; we hypothesized that a greater articular coverage by the humeral trochlea would be more likely to result in complex dislocation. The aim of this study is to analyze trochlear morphology in simple (SED) and complex elbow dislocation (CED), to assess whether the degree of humeroulnar joint congruence influences the incidence of coronoid fractures in elbow dislocation. The secondary goal is to evaluate the association between trochlear morphology and coronoid fracture pattern.

Methods: All the elbow CT scans of the hospital server were retrospectively analyzed. 62 patients were enrolled and so divided in 2 groups: SED and CED with isolated coronoid fracture. Patients who were skeletally immature, presented with other concomitant elbow fractures, or who previously underwent elbow surgery were excluded. The CT scans were performed after closed reduction and prior to further treatment. Coronoid fracture pattern was classified on CT scan according to Regan-Morrey and O'Driscoll classifications; "grade 0" was assigned to SED. Trochlear coverage was measured and expressed as three angles (anterior, posterior, and distal) and their width/depth ratios. Measurements were taken by four different readers and the assessment was repeated after 15 days.

Results: No statistically significant difference was found between humeral trochlear morphology of SED and CED patients. There was no association between morphometric measurements and coronoid fracture pattern. The results are strengthened by a good intra- and inter-reader reproducibility of the CT analysis protocol.

Conclusions: Our study is the first to evaluate the impact of trochlear morphology on elbow instability. Considering the results, other variables may have a greater impact on coronoid bone damage, such as trauma energy or ligamentous hyperlaxity: in particular, we believe that the capsuloligamentous structures of the elbow might contribute in a preponderant way to articular stability. The CT analysis protocol gave excellent results: reproducible, accurate and easy to perform.

Level of evidence: III.

Keywords: Complex elbow dislocation; Elbow CT scan; Elbow instability; Isolated coronoid fracture; PLRI; Simple elbow dislocation; Trochlear coverage; Trochlear morphology.

Fig. 1

CT Standardization - 3D MPR. (a) Position the blue line parallel to humeral diaphysis in sagittal view and parallel to the transepicondylar axis in axial view. Locate the yellow line parallel to the trochlear axis in coronal view. Place the pink line passing through the deepest point of the trochlea in axial and coronal view. (b) Position the intersection between the blue line and the yellow one in the center of the humeral trochlea in sagittal view

Fig. 2

Trochlear angles. (a) The anterior α and the posterior γ trochlear angles – axial view. (b) The distal β angle – coronal view

Fig. 3

Trochlear ratios. (a) The anterior α and the posterior γ width/depth ratios – axial view. (b) The distal β width/depth ratio – coronal view

Fig. 4

Trochlear groove measurements. (a) Both on axial and coronal JPEGs, identify the deepest, the most lateral and most medial points of the trochlear articular surface. Measure anterior α; posterior γ and distal β angles. (b) Draw the segment connecting the most lateral and medial point. (c) Draw its perpendicular through the deepest point and mark the crossing point of these two lines. (d) Calculate the ratio between width and depth of the articular surface in the anterior, posterior, and distal portion of the trochlea in both axial and coronal view

Fig. 5

Fracture pattern distribution according to Regan-Morrey and O’Driscoll classifications