1. Amy Meyers DO – Ascension Genesys Hospital
2. Andrew Ames DO – Ascension Genesys Hospital
3. Curtis Barnes DO – Ascension Genesys Hospital
4. Garrett Gilbert DO – Ascension Genesys Hospital
5. James Heming DO – Ascension Genesys Hospital
6. Jake Stahnke DO – Ascension Genesys Hospital

Abstract
Reverse total shoulder arthroplasty is a commonly performed surgery in elderly patients who may have osteopenic and osteoporotic bone. During glenoid preparation and component implantation, retractors are often used to retract the proximal humerus posterior to the glenoid. This places the proximal humeral metaphyseal bone at increased risk for fracture intraoperatively. We present a technique for glenosphere insertion with inlay design reverse total shoulder arthroplasty utilizing a lateralized glenoid component which reduces risk of intraoperative fracture to the proximal humerus. We utilize a “sphere-in-socket” technique to employ the reamed out proximal humeral metaphysis to increase available space to insert the glenosphere on the baseplate and then dislocate the humerus anteriorly for later humeral preparation. Our technique shows the potential to improve outcomes in reverse total shoulder arthroplasty by reducing the risk of iatrogenic intraoperative fracture.

Keywords: Reverse total shoulder, reverse shoulder arthroplasty, iatrogenic fracture, glenosphere, reverse total shoulder reduction, intraoperative fracture

Introduction  
Reverse total shoulder arthroplasty is commonly performed in elderly patients with rotator cuff arthropathy.(1, 4, 9, 11, 13) This procedure has undergone rapid technological evolution during the past two decades.(5, 7) It has been established that patients with osteoporosis are at increased risk of periprosthetic fracture.(3) In addition to the risk of periprosthetic fracture, the incidence of intraoperative humerus fracture during shoulder arthroplasty procedures has been reported between 0.6% to 3%.(6, 14) The use of good surgical technique for reverse shoulder arthroplasty is important for successful intraoperative placement of components and reducing incidence of intraoperative fracture. Surgeons may prefer to prepare and implant the glenoid implants after the humeral head cut, but prior to humerus preparation with a protective cap on the cut humerus. This sequence of preparation can place increased strain on the glenoid and underlying scapula, as well as the proximal humeral metaphysis as it is retracted posteriorly to allow exposure for preparation of the glenoid for baseplate insertion and impaction of the glenosphere. Substantial forces can be required to mobilize the humerus anteriorly after glenoid component placement to facilitate exposure for humeral preparation. The soft bone of proximal humeral metaphysis can be fractured during these stages of the procedure.(14) We describe a unique approach to glenosphere insertion with inlay design reverse total shoulder arthroplasty utilizing a lateralized glenoid component which limits risk of iatrogenic damage and intraoperative fracture to the proximal humerus. This procedure utilizes a “sphere-in-socket” technique to employ the reamed out proximal humeral metaphysis to increase available joint space to place the glenosphere on the baseplate and dislocate the humerus anteriorly for later humeral preparation. 

Surgical Technique 
Preoperatively, the patient has a single injection interscalene block performed by the anesthesia department. The patient is then brought to the operative suite, undergoes induction and intubation under general anesthesia. The patient is then positioned in semi-Fowler’s position with the knees bent about 30 degrees on a standard OR table. The patient’s eyes are padded with a clean ABD dressing, and the head is secured in place with an ace bandage wrapped gently across the forehead, around the upper part of the operating table and tied off to the accessory rails on each side of the table. The operative extremity from the lateral neck distal is prepped and draped. We utilize plastic U drapes, first from the cranial side, and then under the axilla. This is followed by paper U drapes, again draping the cranial aspect first, followed by the axillary side. The operative hand and forearm are wrapped with Coban self-adherent wrap. We do not employ use of an arm holder. The intended incision is marked with a surgical marker, and the remaining exposed skin is covered with Ioban wrap. A deltopectoral approach through an 8-centimeter incision beginning at the inferior margin of the clavicle is utilized to access the shoulder joint to allow for bone preparation to receive implants.  

The proximal humerus resection is made free hand with an oscillating saw along a plane established by utilizing the trial implant as a guide and placed in 0 degrees of retroversion. The humeral protective cap is then placed, and attention is turned to glenoid preparation which proceeds in typical fashion with placement of a central Steinmann pin over which the glenoid is reamed to the appropriate version. Caution is required to prevent damage to the proximal humerus from vigorous retraction during glenoid preparation, reaming, and baseplate implantation. The appropriately sized glenoid baseplate is impacted and fixated to the prepared glenoid with screws. 

The proximal humerus is then brought anterior, and the humeral metaphysis is reamed for the inlay implant. (Figure 1) The bony concavity created during reaming of the proximal humeral metaphysis is then used to facilitate glenosphere placement and reduction. The humerus is internally rotated to the plane of the glenoid baseplate and subluxed posteriorly to allow visualization of the baseplate for glenosphere implantation. The lateralized glenosphere partially rests inside the space of the reamed out proximal humerus until appropriately aligned over the glenoid baseplate, and it is subsequently impacted into place to obtain secure fit.(Figure 2)

Attention is then turned back to the humerus for final component implantation and a “push-pull technique” is utilized to aid with humeral canal exposure. To perform the “push-pull technique” after glenosphere implantation, the surgeon applies direct axial pressure to the glenosphere with one thumb while carefully rotating and applying lateral and distal oriented forces to the humerus with the other hand. (Figure 3) Occasionally, a bone hook may be used to aid with applying traction and distraction to the prepared proximal humerus in especially tight shoulders to facilitate exposure. The final humeral implant is selected and impacted into place, and the shoulder is reduced and trialed until satisfactory fit and stability are obtained. The final polyethylene liner is impacted into place and the incision is closed in layered fashion.  

Discussion 
Reverse total shoulder is increasingly in popularity and has seen expansion of surgical indications year after year to include patients with cuff tear arthropathy, fracture, and failed anatomic shoulder arthroplasty.(10) Shoulder arthroplasty implants have evolved since the device’s introduction, and consideration for proximal humeral bone conservation continues to drive new shoulder implant designs to market.(8) Inherent to increasing humeral bone conservation with newer designs such as stemless or short stem options is less space within the shoulder joint to operate. We feel that this can lead to increased risk for glenoid fracture, humerus fracture or subsidence, malposition, and failure. The technique described in this paper provides for greater access to the glenoid baseplate by utilizing the proximal humerus reaming to increase available space for glenosphere implantation. This helps decrease the amount of retractor force required to sublux the proximal humerus sufficiently to gain exposure for glenosphere implantation, as is described in many surgical technique guides. 

This technique has anecdotally reduced intraoperative proximal humerus injury, iatrogenic fracture, and provided for increased glenoid exposure and access. This is especially important with the newest generation of implants which strive to conserve proximal humeral bone stock.(12) Intraoperative fracture during stemmed versus stemless implants is approximately 2.3% and 0.9%, respectively.(2)

While our technique strives to limit these complications, the reamed out proximal metaphyseal shell is more susceptible to crushing and/or fracture and care is required to place the glenosphere into the reamed out “socket” without levering against the metaphyseal shell. Should the cortical rim be damaged during glenosphere insertion, salvage option to a longer stemmed humeral implant will provide necessary stability to the humeral component. Rarely, destruction of the metaphyseal shell could produce rotational instability of the humeral implant. This may be overcome by converting to cemented humeral fixation. Traction neuropraxia from aggressive retraction or extreme external rotation during glenoid or humeral preparation, respectively are other potential complications. Care must be taken to avoid these maneuvers as axillary nerve function is critical to successful reverse total shoulder arthroplasty function. This technique strives to limit these complications while adhering to evolving concepts regarding bone preserving arthroplasty. 

Conclusion 
We have presented a unique “sphere-in-socket” technique to potentially lead to a reduction of iatrogenic fracture during reverse total shoulder arthroplasty. This technique has shown improved outcomes in our patient population and has allowed us to safely and successfully treat many patients with osteoporotic bone. 

Acknowledgment 
Voluntary informed consent was obtained prior to collection of clinical photographs. 

Figure 1 | Figure 2 | Figure 3

References                

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Figure captions 

• Figure 1
  After right glenosphere implantation, push-pull technique with bone hook in humerus and thumb on glenosphere is demonstrated to facilitate humeral exposure for final implant placement.
• Figure 2
  “Sphere-in-socket” technique. Right glenosphere resting in reamed out proximal humeral metaphysis to increase effective working space. 
• Figure 3
  Prepared right proximal humerus with reaming for inlay implant completed.

Required Disclosures and Declaration

• IRB Approval Information: Not applicable
• Disclosure Information: No known conflicts of interest