IX. Mechanical Failure After Reverse Shoulder Arthroplasty
T. Bradley Edwards, MD
Although reverse shoulder arthroplasty has been associated with many postoperative complications, mechanical failure of either the glenoid or humeral component is rare. In the absence of precedent trauma, infection must be considered first in all cases of mechanical failure of the reverse prosthesis.
Evaluation of a Failed Reverse Shoulder Arthroplasty
All patients are evaluated initially with fluoroscopically controlled radiography including anteroposterior, axillary, and outlet views that diagnose mechanical failure of the implant. Secondary evaluation consists of computed tomography to evaluate residual bone stock and predict the need for bone graft at the time of revision arthroplasty. Fluoroscopically guided aspiration of the glenohumeral joint and serology including a white blood cell count with differential, a c-reactive protein, and a sedimentation rate is performed to evaluate for infection. Patients should not be taking any antibiotics in the two weeks before the aspiration and the anaerobic culture should be maintained for at least three weeks to observe for p. acnes. Even in the presence of a negative culture, if any of the serological markers is suggestive of infection, then frozen sections should be performed at the time of revision arthroplasty before proceeding with implantation.1
Glenoid failure following reverse shoulder arthroplasty is rare. Multiple factors can contribute including patient related issues and technical issues. Severe osteopenia like that observed commonly in inflammatory arthropathy can compromise support of the glenoid component and lead to failure.2 Technical factors contributing to glenoid component failure usually involve errors in initial component placement.
If the glenoid is inserted in a superiorly oriented direction, forces generated by the deltoid can act to drive the glenoid component out of the glenoid bone (Figure 1). Use of the Deltopectoral approach instead of a superior approach may mitigate this technical error.
|Figure 1. Failure of a reverse glenoid component inserted in superior tilt through a superior approach (Courtesy of Gilles Walch, MD).|
Another cause is implantation of the glenoid component in the setting of intra-operative glenoid fracture resulting in an unstable component. Fracturing of the glenoid can best be avoided by adequate capsular release, starting the reamer off of glenoid bone and less aggressive reaming. If a glenoid fracture occurs and the surgeon is able to implant the central post of the baseplate into the native glenoid, a stable construct may be obtainable allowing completion of the procedure. If the glenoid component does not seem stable or if the majority of the central post of the baseplate cannot be placed within the intact native glenoid, a staged replacement delaying implantation of the humeral component six months is indicated.
The glenoid component is also susceptible to trauma. A careful history should reveal any recent falls or traumatic events. Although a well-placed glenoid can fail as a result of trauma, avoiding the pitfalls described above will minimize the chances of implant failure. Mechanical problems related to implant design, such as dissociation of the glenosphere from the baseplate, have also been observed. Fortunately, advances in implant design have made these failures increasingly rare.
Scapular notching is a radiographic finding that occurs in over half of patients within the first 2 years after reverse shoulder arthroplasty. It is thought to be the result of mechanical impingement of the humeral component on the inferior border of scapula. To date there has been no conclusive evidence that it contributes to failure of the glenoid component.
Aseptic loosening of the humeral component is also rare and occurs in less than 1% of cases.3 The most common risk factor for aseptic loosening of the humeral component is proximal humeral bone loss. Many reverse shoulder arthroplasties are for fracture sequelae and revision, which may present with proximal humeral bone loss. Patients with proximal humeral bone loss are more susceptible to traumatic humeral loosening. A fall onto an outstretched hand or onto a flexed elbow may traumatically loosen the humeral component. Loosening of the humeral component requires revision, possibly with the addition of a proximal humeral structural allograft to address bone loss (Figure 2).
|Figure 2. Radiographs of a patient with proximal humeral bone loss and an initially successful reverse shoulder arthroplasty. The patient fell onto a flexed elbow and traumatically subsided the humeral component. Revision arthroplasty was accomplished using a proximal humeral allograft.|
The polyethylene liner can also be another place for failure. The polyethylene can dissociate from the stem, which is likely due to incomplete seating during initial implantation. The polyethylene is also susceptible to wear which can lead to failure (Figure 3). Mechanical problems related to implant design, such as dissociation of the diaphyseal portion of the implant from the metaphyseal portion of the implant, have also been observed. Fortunately, advances in implant design have made these failures increasingly rare.
|Figure 3. Severe medial polyethylene wear.|
Certainly, reverse arthroplasties are no less susceptible to periprosthetic humeral fracture than conventional arthroplasty. These fractures are treated the same as with fractures occurring in the setting of periprosthetic fractures in conventional arthroplasty. Most of these fractures can be managed nonoperatively with fracture bracing, activity modification and frequent radiographic monitoring. If not healed by 3 months, then an external bone stimulator may be incorporated. Indications for operative management include complete displacement, angulation greater than 30 degrees and loosening or dislocation.
1. Gartsman GM, Edwards TB. Preoperative Planning, Imaging, and Special Tests. In: Shoulder Arthroplasty, edited by GM Gartsman and TB Edwards. Saunders Elsevier, Philadelphia, 2008, pp 375-84.
2. Rittmeister M, Kerschbaumer F. Grammont reverse total shoulder arthroplasty in patients with rheumatoid arthritis and nonreconstructible rotator cuff lesions. J Shoulder Elbow Surg 2001;10:17-22.
3. Wall B, Nové-Josserand L, O’Connor D, Edwards TB, Walch G. Reverse total shoulder arthroplasty: a review of results by etiology. J Bone Joint Surg 2007;89-A:1476-85.