Similar to a Total Shoulder Arthroplasty, a reverse total shoulder arthroplasty involves replacing the natural surfaces of the arm bone (humerus) and cup side of the shoulder (glenoid). However, excessive wear of the bony surfaces or deficiency of the rotator cuff muscles can lead to a painful, dysfunctional shoulder that cannot be repaired using components that restore natural anatomic position. In these cases, a reverse shoulder replacement can be used, placing a ball on the cup side of the joint and a cup on the ball side of the joint. See the video below to watch the surgical procedure.
Watch a Reverse Shoulder Replacement
The ball placed on the cup side requires far less bone to achieve adequate fixation than an anatomic shoulder replacement, so it can be used in cases of more severe bone loss or deformity of the glenoid.
Reverse shoulder replacement also allows the shoulder to function using the deltoid instead of the rotator cuff. The altered biomechanics of the shoulder joint with this type of arthroplasty allows the humeral component to be stabilized against the ball on the glenoid surface (called a “glenosphere”) without any additional need for stabilization by the rotator cuff muscles. Classified as a “semi-constrained arthroplasty”, these components restore stability to the shoulder without sacrificing a significant amount of functional motion. While some patients may have some persistent stiffness with raising the arm out towards the side, but this is generally tolerated fairly well and does not seem to impede function. This allows patients with irreperable rotator cuff tears or rotator cuff atrophy to regain a considerable amount of motion.
Updates in Reverse Shoulder Arthroplasty
As shown above, it is not out of the ordinary for surgical components to be modified by the operating physician to perfectly fit their patient’s pathology. Often, these modifications can be implemented in the manufacturing process to create specialized components.
The component above was originally a long stem component, shown in the picture below on the right. Rather than cutting the stems off of long-stemmed components, DJO manufactures what is known as a short stem arthroplasty that doesn’t require removing any part of the components. This is the component seen in the second picture.
Removing this stem allows for much more freedom when placing the component in the humerus. Rather than the components position being dictated by the angle of the stem, the stemless arthroplasty can be placed with much more ease and freedom. This makes perfect alignment of the components much easier to achieve, and eliminates the need for drilling down into the medullary canal.