Friday, December 29, 2017

Reverse total shoulder - from the top or from the front?

Assessing glenosphere position: superior approach versus deltopectoral for reverse shoulder arthroplasty

The senior author of this paper has has used the anterosuperior deltoid-splitting approach for reverse total shoulder arthroplasty in 87 shoulders. This was his preferred approach unless there had been a previous deltopectoral approach contralaterally or unless there was the possibility of performing an anatomic total shoulder, in which cases the deltopectoral approach was used (22 cases during the period of this report). The indication for surgery with either approach was cuff tear arthropathy or osteoarthritis with cuff tearing.

Both approaches produced acceptable baseplate position, clinical outcomes, and rates of scapular notching when they are used for RTSA. 

Comment: The authors point out that the anterior superior approach for reverse total shoulder arthroplasty requires splitting between the anterior and middle heads of the deltoid, placing the axillary nerve at risk at the distal aspect of the exposure. Trauma to the nerve and potential disruption of the deltoid origin from the acromion from retraction may lead to postoperative deltoid dysfunction and affect patient outcomes. Another potential disadvantage of the anterior superior approach is glenoid baseplate malposition, scapular notching and implant loosening.

There is no question that some experienced shoulder surgeons (as the senior author of this paper) have developed expertise with the anterior superior approach for the implant system they use. However, in that most surgeons are familiar with the anterior deltopectoral approach for shoulder arthroplasty, fracture fixation and instability surgery, that approach may be a reasonable 'workhorse' for reverse shoulder arthroplasty as well.

Our approach to reverse total shoulder is shown here.
The surgical keys to a successful reverse total shoulder arthroplasty are (1) immediate secure glenoid and humeral component fixation, (2) absence of unwanted contact between the medial proximal humeral component and the scapula, (3) preservation of humeral and glenoid bone stock, (4) stability throughout the range of motion using East-West tensioning, and (5) a functional range of motion.

The patient positioning, anesthetic, prophylactic antibiotics, skin preparation, and skin and subscapularis incision are identical to those for an anatomic arthroplasty. A deltopectoral approach is used with careful attention to protect the deltoid and the axillary nerve. Care is taken to identify, preserve and protect the subscapularis. The intrinsic stability of the reverse arthroplasty allows the adhesions and scar tissue to be completely removed. In that anterior instability can be a 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. It is also important to release the contracted inferior capsule, which is frequently present when the humerus has been chronically displaced upwards.

In performing the humeral resection, three priorities exist: (1) leaving as much of the tuberosities as possible for rotational control of the prosthesis, (2) resecting enough bone so that the glenoid arthroplasty can be done well, and (3) enabling reconstruction at the proper length. We begin with a very conservative cut to keep our 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.

A complete circumferential release of the soft tissues from around the glenoid allows excellent visualization. The glenoid is curetted free of cartilage and the inferior lip of the glenoid fossa is smoothed so that it is flush with the glenoid face. The starting point for the glenoid drill is selected so that the base plate will cover the inferior glenoid where the best bone support exists. Excessive inferior positioning of the glenosphere is avoided. While some advocate an inferior inclination of the glenoid, we prefer to orient the baseplate squarely on the face of the glenoid to optimize the quality and quantity of the bone supporting the baseplate; minimal glenoid reaming allows for the preservation of the denser bone at the glenoid surface.

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 baseplate is fixed securely using the central screw that engages the strong bone of the subscapularis fossa.

After the peripheral screws are inserted, 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 verify that the entire baseplate is clear.

Our default glenosphere is the 36 neutral and it is usually inserted at this point of the procedure.

Once the glenosphere is inserted and vigorously impacted into place, traction and rotation are applied using the insertion handle to assure that the Morse taper of the glenosphere has securely engaged the baseplate.

Attention is then directed to the humerus. The goal is to achieve secure fixation without creating a stress riser at the tip of the component. Impaction grafting enables us to use a prosthetic humeral stem that is smaller in diameter than the humeral diaphysis so that diaphyseal loading is avoided. The medullary canal is conservatively reamed to remove cancellous but retain cortical bone. The humeral metaphysis is reamed to 42 mm to accommodate the metaphyseal aspect of the humeral component 

A trial component is inserted to assure that reduction can be accomplished, that the joint is stable, and that there is no unwanted contact between the prosthesis and the scapula. Impaction grafting is carried out with an impactor of the same size and shape of the monoblock humeral component.

Drill holes are placed in the lesser tuberosity for reattachment of the subscapularis if sufficient tendon is available. The wound is thoroughly irrigated. The humeral prosthesis is driven into the impaction grafted canal, assuring a snug fit and rotational stability.

The joint is reduced; range of motion and stability are again verified. The subscapularis is repaired to the previously placed sutures. A standard wound closure is followed by the application of dry sterile dressings. 

Postoperative rehabilitation consists of the use of a sling for comfort and support for 6 weeks. Gentle activities of daily living are allowed during this period. After six weeks progressive increase in active use of the shoulder is encouraged; stretching exercises are usually unnecessary.

Here are the post operative radiographs from two case examples of the technique.



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