Novel Solution for Massive Glenoid Defects in Shoulder Arthroplasty: A Patient-Specific Glenoid Vault Reconstruction System
Complex glenoid deformities present the most difficult challenges in shoulder arthroplasty. These deformities may be caused by severe degenerative or congenital deformity, posttraumatic anatomy, tumor, or, in most cases, bone loss after glenoid failure in anatomical total shoulder arthroplasty. Methods of treating severe bone loss have included inlay and onlay bone-graft options with augmented fixation and, in severe cases, salvage hemiarthroplasty with limited goal expectations. Unfortunately, none of these methods has provided consistently satisfactory reproducible results. In fact, each has had high rates of failure and complications. Borrowing from hip and knee arthroplasty surgeons’ experience in using CAD/CAM (computer-aided design/computer-aided manufacturing) patient-specific implants to fill significant bony defects, Dr. D. M. Dines developed a glenoid vault reconstruction system (VRS) in conjunction with the Comprehensive Shoulder Arthroplasty System (Zimmer Biomet) to treat severe glenoid bone deficiency. The VRS is patient-specific; each case involves making a preoperative plan based on 3-dimensional reconstruction of a 2-dimensional computed tomography scan. The patient-specific implant and instrumentation that are created are used to reconstruct the deformed glenoid in an anatomical position without the need for additional bone graft. In this article, we describe the implant and its indications, technical aspects of production, and surgical technique.
Implant Positioning
With the glenoid surface properly exposed, the removable inserter handle and the built-in lip on the implant are used to position the patient-specific guide. Next, a central guide pin is placed through the inserter for temporary fixation and further instrumentation. If enough bone is present, a boss reamer can be used over the guide pin to prepare and increase the fixation surface. 
The central 6.5-mm nonlocking compression screw is placed to provide strong initial compressive fixation in best bone. 
With the patient-specific glenoid VRS implant now rigidly fixed in the glenoid, the sized and offset glenosphere is properly positioned, and the reverse SA is completed in routine fashion.
Case Examples
A 49-year-old man underwent hemiarthroplasty for osteoarthritis. The procedure failed and, 3 years later, was revised to conventional total SA. Unfortunately, the cemented all-polyethylene glenoid loosened secondary to active Propionibacterium acnes infection, which required excisional arthroplasty with antibiotic spacer. Significant cavitary bone loss was found with anterior glenoid wall bone loss compromising the glenoid vault. Given the history of bone loss and infection, patient-specific glenoid vault reconstruction was performed after infection eradication. Within 4 years after this surgery, the patient had resumed all activities. At age 57 years, he had restricted active forward elevation and abduction to 120° but was satisfied with the outcome. 
A 71-year-old man underwent reverse SA for rotator cuff-deficient osteoarthritis. After implant excision and spacer placement, he was left with severe soft-tissue deficiency and glenoid bone loss, which caused substantial disability. After treatment for infection, a work-up was performed for glenoid bone deficiency and insertion of a patient-specific glenoid VRS implant. 
Discussion
Glenoid bone deformity and deficiency are among the most difficult challenges in SA—a particularly compelling fact given the increasing number of SAs being performed in younger, more active patients. SA surgeons can now expect to be performing even more revisions with concomitant bone defects, which may be severe in some cases.
In addition to these causes of extreme bone loss, recent awareness of the importance of recognizing and treating bone deficits in osteoarthritis, rheumatoid arthritis, trauma, and instability has led to the development of patient-specific guides, instrumentation, and implants. Concepts from the use of CAD/CAM acetabular implants in total hip arthroplasty for severe acetabular bony defects were applied to the use of patient-specific glenoid reconstruction implants without bone graft augmentation.12 In different form, this idea was reported by Chammaa and colleagues13 in 30 cases, and clinical and durable results were very promising.
We have described use of this technique in 2 extreme cases of glenoid vault deficiency. In each case, short-term results were quite satisfactory. However, both patients were relatively young, and long-term clinical and radiographic follow-up is needed.
Many of the severe cases of glenoid bone loss require an implant that specifically matches the patient’s anatomy. The glenoid VRS implant described here may be of great benefit in these difficult reconstructions and is a valuable addition to the armamentarium of treatments for distorted glenoid anatomy. Eventually, the idea may become useful in treating other, less significant defects by re-creating more-normal biomechanics in SA without bone graft.
Am J Orthop. 2017;46(2):104-108. Copyright Frontline Medical Communications Inc. 2017. All rights reserved.
