Reverse total shoulder
A glenohumeral joint replacement used to manage complex shoulder problems with instability and weakness. With this prosthesis the glenoid socket is replaced with a metal ball secured to the scapula and the humeral articular surface is replaced with a cup attached to a stem.
When a shoulder lacks the stabilizing effect of the intact rotator cuff, the humeral head moves upward resulting in slack of the deltoid and weakness of elevation (below left); pseudoparalysis (inability to raise the arm even though the deltoid muscle is healthy) may result.
When an anatomic arthroplasty is used for a rotator cuff deficient shoulder, superior instability may prevent function and increase the risk of glenoid component failure.
The special feature of the reverse total shoulder is its intrinsic stability that is not dependent on a functioning rotator cuff. This stability enables the deltoid to function in raising the arm even though the rotator cuff is compromised.
A reverse total should can be used in a wide variety of conditions in which shoulder instability prevents use of the arm and cannot be managed in more conservative ways. The classical indication is rotator cuff tear arthropathy. Other indications include failed unstable anatomic shoulder arthroplasty, severe fractures of the proximal humerus in which the rotator cuff and tuberosities cannot be securely reconstructed, irreparable rotator cuff defects with pseudoparalysis, arthritis coupled with a compromised rotator cuff, and severe glenohumeral deformities that cannot be reconstructed otherwise. These varied pathologies make the application of this arthroplasty challenging. An additional major challenge is that many of the candidates for this procedure have had prior surgery and / or injuries, are elderly, have fragile bone and soft issues, have medical issues and are at risk for falls. Some individuals whose shoulders appear to be candidates for a reverse total shoulder may not themselves be candidates for the procedure.
There are a number of different prosthesis types available, each with their advantages, advocates, and challenges. We have no financial ties to any manufacturer. We use a prosthesis that has the following features:
- *excellent initial fixation of the glenoid sphere by a screw that obtains purchase in the cortex of the scapular neck - the best available bone, and does not require bone ingrowth for stability
- *a neck on the glenoid sphere enabling 'east-west' tensioning and reducing the risk of notching as opposed to the original Grammont design in which the glenosphere center of rotation is on the glenoid surface.
- *a monobock option that enables consideration of fixation using impaction grafting without diaphyseal cementation.
Deltopectoral with careful attention to protect the deltoid and the axillary nerve. Care is taken to identify, preserve and reconstruct the subscapularis. In that anterior instability is a relatively common complication, it is important to perform sufficient posterior soft tissue releases to accommodate the prosthesis and prevent unwanted anterior pressure on the back of the humeral component. This can be a particular challenge in revision of anteriorly unstable anatomic prostheses and in small individuals.
Three competing priorities exist here:
- leaving as much of the tuberosities as possible for rotational control of the prosthesis,
- resecting enough bone so that the glenoid arthroplasty can be done well, and
- enabling reconstruction at the proper length.
We begin with a very conservative cut to keep options open. Osteophytes and other unwanted bony prominences are removed. Further humeral preparation is delayed until after the glenoid arthroplasty to avoid weakening the humerus and risking fracture during the glenoid part of the arthroplasty.
We strive to retain as much glenoid bone as possible. The inferior lip of the glenoid is conservatively removed to leave a flat glenoid bone surface. The hole for the central screw is drilled a distance equal to half the diameter of the baseplate up from the inferior extent of the glenoid bone.
The glenoid bone surface is reamed by hand only to the point where the surface is flat, minimizing the removal of the important subchondral cortex.
The glenoid baseplate is inserted. The central screw compresses the baseplate firmly on the prepared glenoid surface.
It is critical to remove all bone from around the periphery of the base plate once it is inserted.
Special reamers may be helpful in this regard, but it is still essential to check that the entire baseplate is clear.
Our default glenosphere is the 36 neutral and it is usually inserted at this point of the procedure.
The canal is gently reamed, preserving the endosteal bone. Progressively large broaches are used to find the best fit in the canal and the appropriate height without removing excessive bone. Great care is taken here in that preservation of the proximal humeral bone is important for fixation.
Impaction grafting is used to achieve a good diaphyseal fit of the selected broach.
The sizes of the humeral metaphyseal component and polyethylene liner are selected by trialing. Usually the humeral prosthesis is inserted in 20 degrees of retroversion; however, if there is a concern about anterior instability, the degree of anteversion can be increased. The ideal height if the humeral component results in mild tension in the deltoid when the arm is adducted. Again care is taken to assure adequate posterior soft tissue release. The motion of the shoulder is examined with the trial humeral component in place. Particular attention is directed to avoiding unwanted contact between the humeral component and the scapula in all arm position. Drill holes are placed in the lesser tuberosity area for later reattachment of the subscapularis. The definitive humeral component is fixed in place using proximal cement if necessary to control height and rotation. Distal cement to a cement restrictor is avoided if possible to minimize the risk of fracture should the patient fall on the arm after surgery.
The subscapularis is securely repaired to sutures previously placed in the lesser tuberosity area. The wound is thoroughly irrigated. the deltopectoral interval is carefully closed. The skin is closed with staples. No drain is used.
The arm is protected in a sling for six weeks and the hand used only for gentle 'hand to mouth' activities. From this point the patient is encouraged to gently and progressively increase the use of the arm, avoiding heavy or sudden activities and avoiding extreme positions of the arm and falls.
Reverse total shoulder arthroplasty can dramatically increase the function of the arm. The quality of the result in each patient is variable, depending in large part on the pathology treated.
Rhe complication rate of reverse total shoulder arthroplasty can be high, especially when it is used to revise a failed prior arthroplasty. Complications include instability, infection, fracture of the humerus, fracture of the acromion, and neurologic problems. The risk of the latter two is increased if the arm is substantially lengthened by the procedure.