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.
DJO Stemless Reverse Arthroplasty (left) vs. Long Stem Arthroplasty (right)
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.
In addition, Dr. Spencer has also been heavily involved with the development of a product known as an augmented baseplate. This product, shown below, comes in varying sizes to specifically match the specific anatomy of each patient. Rather than a standard “one size fits all” approach, these baseplates are designed to fit the exact contour of all different anatomic shapes, sizes and orientations, increasing patient satisfaction and functional outcomes.
In-op photo of an augmented baseplate used in reverse shoulder arthroplasty
This component allows for greater customization in reverse shoulder arthroplasty to address cases with greater amounts of bone loss to the back side of the glenoid or “cup” of the shoulder joint. This specific type of bone loss is known as a B3 glenoid, and poses a unique difficulty in surgery due to the lack of bone available to place screws in for the glenoid component, or baseplate. In the image shown below, notice the differences between the structures highlighted by the 2 arrows. The back side has a very thin piece of bone while the front side has a healthy, thick stock of bone into which screws can be placed. In this case, the augmented baseplate can provide a wedge to replace the missing bone.
In addition to the components mentioned above. Dr. Spencer has also been involed in the design and development of a component known as a modular baseplate. This component allows for the use of a variety of implants that can be custom-fit to the patient’s specific anatomy during the time of surgery. With this system, each arthroplasty is tailored to exact specifications needed for each patient, reducing the need of a “one size fits all” approach or the use of generic components that can be “close enough”, but may not be an exact fit. The x-ray below highlights the use of this component and shows how these implants can fit exactly to the needs of each patient.
