Rocking-horse phenomenon

Last revised by Domenico Nicoletti on 1 Feb 2023

Rocking-horse phenomenon occurs in total shoulder arthroplasty when there is an abnormal glenoid version angle positioning that causes glenoid component failure.

The glenoid component is stable when the load applied by the humeral head is centered, whereas anterior or posterior translation of the head of the glenoid causes eccentric loading and lifting of the opposite, unloaded glenoid rim. Massive rotator cuff tear is another important cause of eccentric loading creating the risk of rocking-horse phenomenon loosening of the glenoid component with superior subluxation of the humeral component.

Abnormal glenoid version angle can result from fracture, dysplasia, instability, or asymmetrical wear and is associated with an increased rate of glenoid component failure.

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