Wednesday, August 2, 2017

Reverse total shoulder - when is a glenoid bone graft needed?

Bone Graft Augmentation for Severe Glenoid Bone Loss in Primary Reverse Total Shoulder Arthroplasty Outcomes and Evaluation of Host Bone Contact by 2D-3D Image Registration

The authors reviewed the functional outcomes for 57 patients who were treated with a primary RSA and glenoid bone-grafting for severe glenoid bone loss. Three glenoids were classified as type A2; 2, as type B2; and 2, as type C, according to the Walch classification; 16 glenoids, as grade E1; and 19, as grade E3, according to the Sirveaux classification; 9 glenoids, as grade 3, according to the Levigne classification; and 6 were unable to be classified. 

For the 44 patients with adequate preoperative computed tomographic data and postoperative radiographs, they evaluated native bone contact under the glenoid baseplate by matching the projected shape of the implant and scapula from the postoperative radiographs with a generated 3-dimensional (3D) model of the preoperative scapula. They then analyzed functional outcomes in relation to native bone support of the baseplate.

Results: At a mean of 46 months (minimum, 24 months), the patients demonstrated significant improvements in their clinical outcomes (e.g. change in SST = 5.4).  

On the basis of the generated 3D model, the baseplate contact to host bone was a mean (and standard deviation) of 17% ± 12% (range, 0% to 50%). There was no significant correlation between host bone coverage and clinical outcome.  

There were 4 major complications (7%) in the study group. One baseplate demonstrated radiolucent lines concerning for loosening.  Two shoulders underwent a single-stage revision to a long-stemmed implant for humeral loosening, and 1 was treated with open reduction and internal fixation for a periprosthetic fracture. There were 5 acromial or scapular spine fractures (9%) noted in the study group. Four patients (7%) demonstrated scapular notching; 3 had grade 1 and 1 had grade 3, according to the system described by Sirveaux et al.

Comment: As the authors point out in their introduction, the treatment of patients with severe glenoid bone loss using reverse total shoulder arthroplasty is challenging because of the difficulty in obtaining glenoid fixation. What is even more challenging is determining the need for bone grafting as opposed to inserting the glenoid baseplate on native bone, even though it may seem deficient. The key to early baseplate stability is the fixation of the baseplate to native bone. With the baseplate design used in this study, it is essential that the central compression screw achieves solid purchase in native bone, whether bone graft is used or not.

In this study the authors' indications for use of a bone graft was the inability to achieve 80% contract between the glenoid baseplate and the host bone. Here is AP x-ray of a case presented in the paper. It does not appear to show an usual amount of glenoid bone deficiency.

 A superior bone graft was used at surgery because the inferior inclination selected for the baseplate compromised the contact between the native bone and the baseplate (see below).
Thus, in this example the need for the graft arose not from apparent glenoid deficiency, but rather from the inclination selected for the baseplate.

Currently, we are leaning away from distal inclination of the base plate for a several reasons: (a) less removal of native bone from reaming, (b) better contact between the baseplate and the native bone, (c) less distalization of the humerus (less risk to the acromion and brachial plexus, more normal anatomy for the remaining cuff musculature), and (d) less risk of fracture of the scapular spine from superiorly directed screws. 

Here's an example from yesterday's OR where a reverse total shoulder was indicated by severe post fracture deformity.
With this approach, the percentage of cases that require bone grafting in our practice is low.

Here's another example:

Even though there was some glenoid deficiency, the strong purchase of the central screw provided excellent immediate fixation.
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