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. 2020 Oct;12(5):362-367.
doi: 10.1177/1758573219831285. Epub 2019 Mar 4.

Positioning of longest axis of the radial head in neutral forearm rotation

Miguel Deschrijver  1 , Simon Lamquet  1 , Guillaume Planckaert  1 , Hannes Vermue  1 , Lieven De Wilde  1 , Alexander Van Tongel  1
Affiliations

Positioning of longest axis of the radial head in neutral forearm rotation

Miguel Deschrijver et al. Shoulder Elbow. 2020 Oct.

Abstract

Introduction: The radial head has an ellipsoid shape so that a longest and a shortest axis can be defined. The aim of this study is to evaluate the position of the longest axis of the radial head (LARH) in relation to proximal radioulnar joint (PRUJ) and to the forearm in neutral position using 3D computed tomography (CT).

Materials and methods: 3D CT reconstructions of the distal humerus, the radius and the ulna of 27 healthy volunteers (average age 27.65 ± 9.25; 24 males, 3 females) were created. First an evaluation of the elliptic form of the radial head and the location of its longest axis was performed. Next, three planes were defined: the PRUJ plane, the forearm plane and a neutral plane. Based on the angle between the forearm plane and the neutral plane, the rotation of the scanned forearm was measured. Taking this rotation into account, the position of the LARH compared to PRUJ plane and forearm plane in neutral position is recalculated.

Results: The shape of the radial head is determined to be non-circular based on this study population (p < .001). In neutral position, the angle between the LARH and the forearm plane is 5.28° (SD: 15.09) and between the LARH and the PRUJ is 33.46° (SD: 13.91).

Conclusions: The position of the LARH is found to be approximately perpendicular to the forearm plane when the forearm is in neutral position and perpendicular to the PRUJ plane when the forearm is on average in 30° of pronation.

Keywords: 3D reconstructed; CT; Radial head; neutral rotation; non-circular; proximal radioulnar joint.

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Figures

Figure 1.
Figure 1.
Definition of the longest axis and the short axis (perpendicular to the longest axis).
Figure 2.
Figure 2.
PRUJ plane: (a) the two outermost points of the radial notch are indicated (pu1, pu2) with an x–y reference system. (b) 3D visualization of the PRUJ plane.
Figure 3.
Figure 3.
Humeral plane. (a) The centre of capitellum (b) the centre of the best fitting circle at the medial border of the trochlea (c) the upper most smallest point.
Figure 4.
Figure 4.
Pronation-supination axis defined by the center of the best fitting sphere of the capitellum and the center of the best fitting sphere of the distal ulna.
Figure 5.
Figure 5.
Measurement of the pronation-supination angle in the distal forearm as the angle between the forearm plane and the neutral plane.
Figure 6.
Figure 6.
Measurement of angleLA in the proximal forearm as the angle between the longest axis and the neutral plane.
Figure 7.
Figure 7.
The length of the long axis of the radial head compared to the length of the short axis.
See this image and copyright information in PMC

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