COMPLICATIONS
Two complications developed in the group undergoing composite cage augment. One patient experienced glenoid loosening after a motor vehicle accident. Another patient sustained significant intraoperative tuberosity avulsion during implantation of the humeral component, requiring a change of implant and tuberosity fixation. Although no complications were noted in the 8° all-polyethylene group, 3 patients in the 16° augment group sustained complications. One of these patients suffered a cardiac event that was unrelated to the implant. Two complications in this group were both related to loosening of the glenoid component, requiring subsequent revision.
DISCUSSION
The first report on augmented aTSA was published in 2008, and it involved a 5° augmented, anatomic glenoid.12 One study was based on a small series of augments; the poor results led the reporting surgeons to subsequently abandon the implant.12 This early design produced a correction on the articular side of the implant rather than the pathologic bony side. By performing such correction, the component pegs remained anteriorly oriented, placing the component at risk of perforation through the anterior glenoid neck. All current augment designs feature pegs that are oriented down the glenoid vault, with corrections occurring on the bony surface. This condition requires 2 different axes for reaming the glenoid and drilling the pegs. This approach allows the pegs to be directed down the glenoid neck, and is a far superior solution to neutralizing shear forces when compared with the implants used in the 1990s.
Early to midterm results of modern aTSA augments have been extremely encouraging with low revision rates. The main concern of recurrent posterior subluxation has been rarely reported. The concerns over glenoid loosening due to high shear forces, similarly, have not been described to date. However, surgeons should remain cautious, as longer-term follow-up remains unavailable.
The main advantage of aTSA augments is their capacity to preserve bone compared with eccentric reaming and better long-term stability. Each of the augment designs requires varying amounts of bone removal. Through biomechanics and using finite element analysis, the 3 augment types act differently, with no design demonstrating remarkable biomechanical superiority.6 Favorito and colleagues16 performed a retrospective review of 22 patients who underwent aTSA using an all-polyethylene, posteriorly augmented, and stepped glenoid component for posterior bone loss. At an average follow-up of 36 months, all patients experienced improvements in active forward elevation, external rotation, visual analog scale, Short Form-36 Physical Component Summary, and Western Ontario Osteoarthritis of the Shoulder scores. The authors noted that 2 patients (9%) experienced complications: 1 with an anterior dislocation and the other with recurrent posterior instability requiring revision. Sandow and Schutz17 reported the preliminary results of 10 patients who underwent aTSA using trabecular metal augment with a minimum of 2-year follow-up. All patients received either a 15° or 30° posterior, metal-backed augment for severe glenoid bone loss (Walch grade B2 or C). At a minimum of 2-year follow-up, all patients received correction to within 10° of neutral glenoid version, without any complications nor implant failures.
Regardless of augment design, all current components restore the native glenoid version, improving the length and subsequent tension of rotator cuff musculature. Similarly, re-centering the humeral head decreases the forces on the glenoid and allows for optimal function with decreasing loss of vital subchondral bone.
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