Reverse shoulder arthroplasty (RSA) provides an effective alternative to anatomic shoulder replacements for individuals with cuff tear arthropathy, but certain osteoarthritic glenoid deformities make it challenging to achieve sufficient long term fixation. To compensate for bone loss, increase available bone stock, and lateralize the glenohumeral joint center of rotation, bony increased offset RSA (BIO-RSA) uses a cancellous autograft for baseplate augmentation that is harvested prior to humeral head resection. The motivations for this computational study are twofold: finite element (FE) studies of BIO-RSA are absent from the literature, and guidance in the literature on screw orientations that achieve optimal fixation varies. This study computationally evaluates how screw configuration affects BIO-RSA graft micromotion relative to the implant baseplate and glenoid. A senior shoulder specialist (GSA) selected a scapula with a Walch Type B2 deformity from patient CT scans. DICOM images were converted to a 3D model, which underwent simulated BIO-RSA with three screw configurations: 2 divergent superior & inferior locking screws with 2 convergent anterior & posterior compression screws (SILS); 2 convergent anterior & posterior locking screws and 2 superior & inferior compression screws parallel to the baseplate central peg (APLS); and 2 divergent superior & inferior locking screws and 2 divergent anterior & posterior compression screws (AD). The scapula was assigned heterogeneous bone material properties based on the DICOM images’ Hounsfield unit (HU) values, and other components were assigned homogenous properties. Models were then imported into an FE program for analysis. Anterior-posterior and superior-inferior point loads and a lateral-medial distributed load simulated physiologic loading. Micromotion data between the RSA baseplate and bone graft as well as between the bone graft and glenoid were sub-divided into four quadrants.INTRODUCTION
METHODS
In this study we evaluated whether the Instability
Severity Index Score (ISIS) and the Western Ontario Shoulder Instability
Index (WOSI) could detect those patients at risk of failure following
arthroscopic Bankart repair. Between April 2008 and June 2010, the
ISIS and WOSI were recorded pre-operatively in 110 patients (87
male, 79%) with a mean age of 25.1 years (16 to 61) who underwent
this procedure for recurrent anterior glenohumeral instability. A telephone interview was performed two-years post-operatively
to determine whether patients had experienced a recurrent dislocation
and whether they had returned to pre-injury activity levels. In
all, six (5%) patients had an ISIS >
6 points (0 to 9). Of 100 (91%)
patients available two years post-operatively, six (6%) had a recurrent dislocation,
and 28 (28%) did not return to pre-injury activity. No patient who
dislocated had an ISIS >
6 (p = 1.0). There was no difference in
the mean pre-operative WOSI in those who had a re-dislocation and
those who did not (p = 0.99). The pre-operative WOSI was significantly
lower (p = 0.02) in those who did not return to pre-injury activity, whereas
the ISIS was not associated with return to pre-injury activity (p
= 0.13). In conclusion, neither the pre-operative ISIS nor WOSI predicted
recurrent dislocation within two years of arthroscopic Bankart repair.
Patients with a lower pre-operative WOSI were less likely to return
to pre-injury activity. Cite this article:
