Biomechanical study of isolated radial head dislocation

Abstract

Background: Isolated radial head dislocation is a rare injury with an unclear pathomechanism, and the treatment is controversial. The purpose of the present study was to investigate the biomechanical contributions of the annular ligament, quadrate ligament, interosseous membrane, and annular ligament reconstructions to proximal radioulnar joint stability.

Methods: Five fresh frozen cadaveric upper extremities were amputated above the elbow and solidly fixed on a customized jig. Radial head dislocation was reproduced by sequential sectioning of ligamentous structures and passive mobility testing. Radial head displacement during mobility testing was measured with an electromagnetic tracking device in three forearm rotation positions. The data were compared among different sectioning stages and between two types of simulated ligamentous reconstruction.

Results: Lateral displacement of the radial head significantly increased in the neutral forearm rotation after annular ligament sectioning (46 ± 10%, p < 0.05). After quadrate ligament sectioning, we found significant posterior (67 ± 36%, p < 0.05) and lateral (74 ± 24%, p < 0.01) displacement in neutral forearm rotation and pronation. Significant radial head displacement was found in all directions and in all forearm positions after sequential sectioning of the proximal half of the interosseous membrane. Anatomical annular ligament reconstruction stabilized the proximal radioulnar joint except for anterior laxity in neutral forearm rotation (15 ± 6%, p < 0.05). The radial head with Bell Tawse procedure was significantly displaced in all directions.

Conclusion: The direction of radial head instability varied depending on the degree of soft tissue sectioning and specific forearm rotation. Anterior radial head dislocation may involve more severe ligament damage than other types of dislocation. Anatomical annular ligament reconstruction provided multidirectional radial head stability.

Keywords: Annular ligament; Biomechanical study; Interosseous membrane; Ligament reconstruction; Quadrate ligament; Radial head dislocation.

Fig. 1

Experimental setup. The humerus and ulna were solidly fixed on a customized wooden jig with the elbow flexed at 90°. The humerus was set horizontally and ulna was set perpendicularly to the ground. The radius was kept in one of three forearm positions (full pronation, neutral rotation, or full supination) with a 2.0-mm K-wire inserted in the distal radius only to keep forearm rotation. The displacement of the radial head relative to the proximal ulna was measured by an electromagnetic tracking device (trak STAR™; Ascension Technology Corporation, Shelburne, VT, USA). Sensors were inserted into the radial head and the proximal ulna. A cord was positioned around the neck of the radial head to apply load for passive mobility testing

Fig. 2

Sectioning stages of radial head stabilizers. a Stage 0: elbow with anterior joint capsule sectioned. b Stage 1: elbow with annular ligament sectioned. c Stage 2: elbow with annular and quadrate ligaments sectioned. d Stage 3: elbow with annular and quadrate ligaments and proximal half of the IOM sectioned

Fig. 3

Incidence of radial head dislocation. According to ligament sectioning, the incidence of radial head dislocation increased. Radial head began to dislocate laterally after annular ligament sectioned. And next, posterior radial head dislocation was observed after quadrate ligament sectioned especially in neutral position. Anterior radial head dislocation was occurred after proximal half of IOM sectioned

Fig. 4

Schema of annular ligament reconstructions. a Stage R1: Bell Tawse procedure reduced anterior radial head dislocation; however, it was difficult to stabilize the radial head in the posterolateral direction with this technique because of the non-anatomical nature of the procedure. b Stage R2: Anatomical reconstruction stabilized the radial head in all directions