420 - Anatomical Versus Reverse Shoulder Arthroplasty

In the case of a large, irreparable rotator cuff tear a reverse shoulder comes into play. If a patient with a torn rotator cuff receives an anatomic total shoulder, they would still have to rely on their damaged rotator cuff muscles to move their arm. In addition, the rotator cuff is a humeral head suppressor, which prevents the head from riding up the glenoid. With a damaged rotator cuff, the ball would not sit in the socket. This constant striking of the top of the glenoid by the head could cause loosen- ing of the glenoid component. By performing a reverse shoulder, the patient now relies on their deltoid muscle to power and position their arm because the role of the humeral head and glenoid are reversed. The surgical technologist needs to keep in mind the differences between anatomical and reverse arthroplasty procedures when setting up. As mentioned previously, the stem may be the same for either type of shoulder, thus those trays also will be the same. However, the trays for the glenoid and humeral head will be different. Instru- ments and trials that allow for a head component to be placed on the stem are needed for an anatomic total shoulder, whereas a socket component will be placed on the stem on a reverse arthroplasty. Trays will be needed for a glenoid component to be placed in the socket on a regular total shoulder versus ones for a head component on a reverse arthroplasty. The use of cement also varies. On either type of shoul- der replacement, the stem typically will be press fit unless there is a fracture to the humerus or it is osteoporotic and therefore requires the stem to be cemented. For an anatomic total shoulder, typically one bag of cement with a mixing bowl and a Toomey syringe will be used for the glenoid. This is because there is either a keel, pegs or a post on the back side of the implant that is cemented into holes that were created in the glenoid during the procedure. For a reverse shoulder arthroplasty, cement is usually not needed (unless it is going to be used on the stem). The baseplate for the head, which is now located in the glenoid cavity on a reverse shoulder arthroplasty, will be inserted with screws into the socket instead of cement. P R O C E D U R E After a timeout is performed, the surgeon starts by dis- secting through the soft tissue down to the bone, where the humeral canal is addressed first. A smaller diam- eter starter reamer, usually 4- or 5-mm, is placed on a T-handle and given to the surgeon. Unlike other total joint procedures, power equipment is not necessary for reaming. The reamer is placed through the humeral head and into the canal. This process of reaming continues in increments of 1-2 mm until cortical contact or “bite” is achieved. The surgical technologist will need to have all reamers close at hand to switch out on the T-handle because this process goes quickly. Once the surgeon is finished reaming, they will remove the T-handle, leaving the reamer in the canal to be used for the attachment of the intramedullary (IM) cutting guide. This is the most common method of cutting off the humeral head. The cutting guide and associated boom will attach to the shaft of the reamer that is in the canal. Two pins on power will be placed through holes in the cutting guide and into the humer- us. Once the cutting guide is pinned to the bone, the reamer along with the boom will be removed. The surgeon will then cut off the head of the humerus with a saw placed through the cutting guide. The surgical technolo- gist will need to compare the patient’s humeral head to the tri- als in the tray. Since the trials come in an assortment of sizes, they will need to grab the head trial that most closely matches that of the patient’s bone and have it ready for the surgeon when they do a trial reduction. The surgical technologist also INSTRUMENTS Ortho tray Open shoulder tray Total shoulder retractor tray Osteotomes tray Power drill Power saw Cement gun (available) Vendor trays EQUIPMENT Beach chair positioner Arm positioner (surgeon preference) Bair hugger Bovie machine Suction SCD pump Space suits (surgeon preference) Nitrogen hose for cement (hospital preference) DECEMBER 2018 | The Surgical Technologist | 549