Review Question - QID 217899

Similar to total hip and knee arthroplasty procedures, revision reverse total shoulder arthroplasty (rTSA) places the patient at a significantly greater risk of complications than the indexed procedure. The repeated disruption to the soft tissue envelope can compromise stability resulting in dislocation, as seen in this patient.

The initial rTSA implants were fraught with high complication rates until Dr. Grammont introduced his revolutionary design focusing on changing the shoulder’s center of rotation (COR) to a more medial and distal location. This functionally lengthens the deltoid muscle and allows it to have an increased moment arm and serve as the primary muscle for shoulder movement (rather than the deficient rotator cuff musculature). Improvements have been made in prosthesis placement and design (i.e. introducing inferior tilt to prevent scapular notching), however, some notable complications remain. Postoperative instability remains the most commonly reported cause of early failure in rTSA and it behooves surgeons to minimize its risk. Commonly reported risk factors include male sex, obesity, Grammont-style implant, loss of humeral tuberosities, and revision surgery. In this patient, open revision surgery would be considered the most significant risk factor for dislocation.

Hagen et al. performed a randomized control trial comparing early range of motion versus six weeks of immobilization as rTSA post-operative protocols. They reported no difference in overall functional outcomes nor complications at one-year follow-up. They concluded both early and delayed rehabilitation protocols are appropriate with similar outcomes, however, early rehabilitation may be beneficial for the elderly population to avoid limitations of prolonged immobility.

Clouthier et al. performed a saw-bones biomechanical study to determine rTSA implant variables in overall stability. They report that the models utilizing an inferior-offset glenosphere or increased humeral socket depth were significantly more stable and should be utilized in implant designs. Further, active glenohumeral abduction significantly increased shoulder stability, highlighting the importance of deltoid tensioning. The authors concluded that utilizing active exercises during postoperative rehabilitation may decrease the risk of dislocation.

Cheung et al. performed a retrospective case-control study comparing 119 patients with and without a dislocation event after rTSA surgery. They report that all dislocations (n=11) occurred within 2 months after surgery and were atraumatic in nature. All dislocated patients underwent revision surgery with a high failure rate if treated with thicker polyethylene alone (54%). The authors conclude that instability after rTSA should be treated with a larger polyethylene with concomitant increasing the size of the humeral insert and/or placement of a larger glenosphere.

Figure A includes AP and scapular Y radiographic images of a right-sided four-part proximal humerus fracture. Figure B includes AP and scapular Y radiographic images of a dislocated, right-sided reverse total shoulder arthroplasty.

Incorrect Answer Choices:
Answer 1: Early range of motion protocols have not shown to impart higher dislocation rates when compared to six weeks of immobilization.
Answer 2: Male gender, as opposed to this female patient, has been shown to increase the risk for rTSA post-operative instability.
Answer 3: While prior surgery is associated with higher dislocation rates, arthroscopic and mini-open procedures do not pose the same risk for instability as more extensive open procedures requiring significant capsulotomies.
Answer 4: Four-part humerus fractures that result in failed healing of the tuberosities do have an increased risk for dislocation after rTSA, however, the question states she healed well and did not indicate malunion/nonunion.