Identifying the Complications of Reverse TSA
As use of the prosthesis for reverse total shoulder arthroplasty has expanded, a number of complications associated with the procedure have been recognized. In this article, the authors familiarize surgeons with the common complications.
Lynn Crosby, MD, and John Hinson, MD
The reverse total shoulder arthroplasty (TSA) prosthesis was first approved by the U.S. Food and Drug Administration in 2004. Indications for use include:
- Rotator cuff arthropathy
- Massive rotator cuff tear
- Failed shoulder arthroplasty
- Fracture sequelae
As use of the prosthesis has expanded, a number of complications associated with the procedure have been recognized. Our goal is to familiarize surgeons with the common complications.
Hematoma formation is a widely recognized complication of reverse TSA: The dead space created is a factor in hematoma formation. Rates of hematoma formation have varied in the literature from 1-20%. [1,2,3] Meticulous hemostasis and placement of a drain are recommended to help prevent hematoma formation.
Management of hematomas is surgeon dependent:
- If the surgical wound is benign appearing and completely dry, it can be managed with observation as it is resorbed.
- If there is excessive tension on the wound or persistent drainage, irrigation and debridement is recommended.
In a review of 21 cohort studies with at least 2 years of follow up,  the overall infection rate in patients undergoing reverse TSA was 3.8%. Rheumatoid arthritis and revision surgery are recognized risk factors for infection. [2,5]
Proprionobacteria acnes has been implicated as a common pathogen in infection, and recognition of this pathogen has helped shape the prevention and treatment of infections in our institution:
- Preoperatively, patients are given intravenous cefazolin, which is repeated for two doses postoperatively.
- They are also given a single dose of vancomycin just prior to surgery.
- The skin is prepped with chlorhexadine solution, which has been shown to lower the rate of skin colonization compared to iodine-based solutions.  The chlorhexadine solution is used to prep the skin again, just prior to wound closure.
- If cultures are taken for a suspected infection, it is important to notify the lab that P. acnes is a suspected pathogen and cultures should be held a minimum of 10-14 days to ensure growth of the slow-growing organism.
- Acute infections are treated with irrigation and debridement with polyethylene exchange and retention of implants. Chronic infections are treated with two-stage revision.
In a review of multiple studies, dislocation rates following reverse TSA were noted to average 4.7%.  Dislocation is usually anterior and typically occurs in the position of adduction, extension, and internal rotation (Figures 1-2).
Joint compressive forces have been shown to be the most important factor in stability,  and appropriate soft tissue tension is the most important factor in prevention of dislocation. In the early post-operative period, patients are advised to avoid activities that would put them into the position of risk, such as pushing off from a chair.
The importance of repairing the subscaplularis tendon has been debated:
- Some studies show no difference in dislocation without an intact subscapularis,  while others show a significant increase in dislocation events without an intact subscapularis. 
- Prosthesis design appears to play a role in the importance of an intact subscapularis.
- The authors do not routinely repair the subscapularis during surgery.
In the event of a dislocation, a closed reduction should be attempted followed by a brief period of immobilization and avoidance of the provocative position. If closed reduction cannot be accomplished, dissociation of the humeral polyethylene insert should be suspected.
The position of the implants should be closely assessed if surgery is required. Surgery often necessitates placing a thicker polyethylene insert or tray to further tension the soft tissue. Surgery may also need to include placing a larger glenosphere or changing the position of the implants.
It is important to remove all soft tissue from the inferior glenoid to prevent any soft tissue impingement that can cause instability.
Figure 1. AP image of dislocated reverse TSA.
Figure 2. Axillary lateral image of dislocated reverse TSA.
Scapular notching is the most commonly noted complication after reverse TSA. Inferior notching is caused by mechanical impingement of the humeral bone or prosthesis on the neck of the scapula. Polyethylene debris can be created and osteolysis can cause further advancement of notching. Scapular notching has been classified using a system described by Sirveaux et al (Figure 3). 
Figure 3. Sirveaux scapular notching classification system
Figure 4. Grade IV scapular notching
In some studies, notching has had no clinical effect. 11 Others, though, show lower Constant scores and decreased range of motion in patients with notching. 
Prosthesis design appears to play a role in the development of notching:
- Designs that lateralize the center of rotation and lower the neck shaft angle have been shown to decrease the incidence of notching. 
- Inferior position of the glenosphere has also been shown to decrease the incidence of notching. 
- Inferior tilt of the glenosphere has not been shown to lower the incidence of notching,  but superior tilt should be avoided.
In their review of 400 patients with reverse TSA, Crosby et al  reported a 5.5 % incidence of acromial fracture. Three patterns of fracture were identified:
Avulsion fractures of the anterior acromion (type I, Figure 5) appeared to have occurred during surgery. These were treated symptomatically, with symptoms resolving without further intervention.
Figure 5. Type I acromion fracture
Fractures that occurred through the acromion just posterior to the acromioclavicular (AC) joint (type II, Figures 6a-b) presented with pain over the anterior acromion and AC joint at an average of 10.8 months postoperatively. Plain films often do not show the fracture but do demonstrate AC arthrosis; CT scan can be helpful in fracture visualization.
Patients with unstable fractures were treated with ORIF of the fracture, with resolution of symptoms. Patients with stable fractures were treated with distal clavicle excision alone with resolution of their pain.
Figures 6a-b. Type II acromial fracture
A displaced fracture at the base of the acromion (type III, Figure 7) was observed in the radiographs of four patients in the study. Type III fractures were treated with ORIF. All these patients had screws placed through the superior aspect of the baseplate that exited at the junction of the acromion and scapular spine. This superior screw is felt to be a stress riser and is no longer routinely placed.
Figure 7. Type III acromial fracture
Glenosphere fixation to the baseplate varies between implants and is accomplished by either a morse taper or central locking screw.
Early designs of the Grammont system were known to have dissociation of the morse taper of the glenosphere to the baseplate. The morse taper has since been modified, with a decrease of this complication. 
In systems that employ a central screw, the glenosphere may not be fully seated and the locking screw may cross-thread with the baseplate. If this occurs, dissociation is possible (Figure 8).
Regardless of the system used, the glenosphere should be inspected on the post-operative x-ray to be sure it is flush with the baseplate.
Figure 8. Dissociated glenosphere
The reverse TSA is being performed in growing numbers in the United States. As the procedure has become more common, we have begun to recognize its complications.
Even in the hands of experienced shoulder surgeons, there appears to be learning curve for the procedure; the number of complications goes down with experience.  Familiarity with the complications of this procedure should assist surgeons in avoiding them as they become more familiar with successfully performing this surgery.
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