Introduction. Achieving prosthesis fixation in patients with glenoid defects can be challenging, particularly when the bony defects are large. To that end, this study quantifies the impact of 2 different sizes of large anterior glenoid defects on reverse shoulder glenoid fixation in a composite scapula model using the recently approved ASTM F 2028–14 reverse shoulder glenoid loosening test method. Methods. This rTSA glenoid loosening test was conducted according to ASTM F 2028–14; we quantified glenoid fixation of a 38mm reverse shoulder (Equinoxe, Exactech, Inc) in composite/dual density scapulae (Pacific Research, Inc) before and after cyclic testing of 750N for 10k cycles. Anterior defects of 8.5mm (31% of glenoid width and 21% of glenoid height; n=7) and 12.5mm (46% of glenoid width and 30% of glenoid height; n=7) were milled into the composite scapula along the S/I glenoid axis with the aid of a custom jig. The baseplate fixation in scapula with anterior glenoid defects was compared to that of scapula without an anterior glenoid defect (n = 7). For the non-defect scapula, initial fixation of the glenoid baseplates were achieved using 4, 4.5×30mm diameter poly-axial locking compression screws. To simulate a worst case condition in each anterior defect scapulae, no 4.5×30mm compression screw were used anteriorly, instead fixation was achieved with only 3 screws (one superior, one inferior, and one posterior). A one-tailed unpaired student's t-test (p < 0.05) compared prosthesis displacements relative to each scapula (anterior defect vs no-anterior defect). Results. All glenoid baseplates remained well-fixed after cyclic loading in composite scapula without a defect and those with an 8.5mm anterior glenoid defect. However, only 6 of the 7 glenoid baseplates remained well-fixed after cyclic loading in scapula with a 12.5mm anterior glenoid defect, where 1 device failed catastrophically at 5000 cycles by loosening from the substrate. As described in Table 1, the average pre- and post-cyclic glenoid baseplate displacement in scapula with 8.5mm and 12.5mm anterior glenoid defects was significantly greater than that of baseplates in scapula without an anterior glenoid defect in both the A/P and S/I directions. Similarly, the average pre- and post-cyclic glenoid baseplate displacement in scapula with 12.5mm anterior glenoid defects was significantly greater than that of baseplates in scapula with 8.5mm anterior glenoid defects in the both the A/P and S/I directions. Discussion and Conclusions. These results demonstrate that reverse shoulder glenoid baseplate fixation was achievable in scapula with an 8.5mm anterior glenoid defect. Given that one sample catastrophically loosened in the 12.5mm anterior defect model, supplemental bone grafting may be required to achieve fixation in 12.5mm anterior glenoid defects with reverse shoulder arthroplasty. Future work should evaluate whether adding additional screws mitigates the increased displacement observed in this anterior glenoid defect scenario. This study is limited by its use of polyurethane dual-density composite scapula

Introduction. Posterior glenoid wear is common in glenohumeral osteoarthritis. Tightening of the subscapularis causes posterior humeral head subluxation and a posterior load concentration on the glenoid. The reduced contact area causes glenoid wear and potentially posterior instability. To correct posterior wear and restore glenoid version, surgeons may eccentrically ream the anterior glenoid to re-center the humeral head. However, eccentric reaming undermines prosthesis support by removing unworn anterior glenoid bone, compromises cement fixation by increasing the likelihood of peg perforation, and medializes the joint line which has implications on joint stability. To conserve bone and preserve the joint line when correcting glenoid version, manufacturers have developed posterior augment glenoids. This study quantifies the change in rotator cuff muscle length (relative to a nonworn/normal shoulder) resulting from three sizes of posterior glenoid defects using 2 different glenoids/reaming methods: 1) eccentric reaming using a standard (nonaugmented) glenoid and 2) off-axis reaming using an 8, 12, and 16° posterior augment glenoid. Methods. A 3-D computer model was developed in Unigraphics (Siemens, Inc) to simulate internal/external rotation and quantify rotator cuff muscle length when correcting glenoid version in three sizes of posterior glenoid defects using posterior augmented and non-augmented glenoid implants. Each glenoid was implanted in a 3-D digitized scapula and humerus (Pacific Research, Inc); 3 sizes (small, medium, and large) of posterior glenoid defects were created in the scapula by posteriorly shifting the humeral head and medially translating the humeral head into the scapula in 1.5 mm increments. Five muscles were simulated as three lines from origin to insertion except for the subscapularis which was wrapped. After simulated implantation in each size glenoid defect, the humerus was internally/externally rotated from 0 to 40° with the humerus at the side. Muscle lengths were measured as the average length of the three lines simulating each muscle at each degree of rotation and compared to that at the corresponding arm position for the normal shoulder without defect to quantify the percentage change in muscle length for each configuration. Results. As depicted in Figures 1–3, muscle shortening was observed for each muscle for each size defect. For each size uncorrected defect, the subscapularis was observed to wrap around the anterior glenoid rim during internal rotation and with the arm at neutral; both eccentric successfully re-centered the humeral head and eliminate subscapularis wrapping around the anterior glenoid rim. However, eccentric reaming was also found to medialize the joint line and resulted in approximately 1.5, 2.5, and 3.5% additional muscle shortening for each muscle relative to the augmented glenoid in each size defect, respectively. Discussion and Conclusions. This study demonstrates that posterior glenoid wear medializes the joint line and results in rotator cuff muscle shortening. Augmented glenoids offer the potential to better restore the joint line and minimize muscle shortening, particularly when used in large glenoid defects. Future work should investigate the clinical significance of 1.5–3.5% of muscle shortening and evaluate the functional impact of subscapularis wrapping around the anterior glenoid rim

Anatomic studies have demonstrated that bipolar glenoid and humeral bone loss have a cumulative impact on shoulder instability, and that these defects may engage in functional positions depending on their size, location, and orientation, potentially resulting in failure of stabilisation procedures. Determining which lesions pose a risk for engagement remains a challenge, with Itoi's 3DCT based glenoid track method and arthroscopic assessment being the accepted approaches at this time. The purpose of this study was to investigate the interaction of humeral and glenoid bone defects on shoulder engagement in a cadaveric model. Two alternative approaches to predicting engagement were evaluated; 1) CT scanning the shoulder in abduction and external rotation 2) measurement of Bankart lesion width and a novel parameter, the intact anterior articular angle (IAAA), on conventional 2D multi-plane reformats. Hill-Sachs and Bony Bankart defects of varying size were created in 12 cadaveric upper limbs, producing 45 bipolar defect combinations. The shoulders were assessed for engagement using cone beam CT in various positions of function, from 30 to 90 degrees of both abduction and external rotation. The humeral and glenoid defects were characterised by measurement of their size, location, and orientation. The abduction external rotation scan and 2D IAAA approaches were compared to the glenoid track method for predicting engagement. Engagement was predicted by Itoi's glenoid track method in 24 of 45 specimens (53%). The abduction external rotation CT scan performed at 60 degrees of glenohumeral abduction (corresponding to 90 degrees of abduction relative to the trunk) and 90 degrees of external rotation predicted engagement accurately in 43 of 45 specimens (96%), with sensitivity and specificity of 92% and 100% respectively. A logistic model based on Bankart width and IAAA provided a prediction accuracy of 89% with sensitivity and specificity of 91% and 87%. Inter-rater agreement was excellent (Kappa = 1) for classification of engagement on the abduction external rotation CT, and good (intraclass correlation = 0.73) for measurement of IAAA. Bipolar lesions at risk for engagement can be identified using an abduction external rotation CT scan at 60 degrees of glenohumeral abduction and 90 degrees of external rotation, or by performing 2D measurements of Bankart width and IAAA on conventional CT multi-plane reformats. This information will be useful for peri-operative decision making around surgical techniques for shoulder stabilisation in the setting of bipolar bone defects

Massive uncontained glenoid defects are a difficult surgical problem requiring reconstruction in the setting of either primary or revision total shoulder arthroplasty. Our aim is to present a new one-stage technique that has been developed in our institution for glenoid reconstruction in the setting of massive uncontained glenoid bone loss. We utilise a modified delto-pectoral approach to perform our dual biology allograft autograft glenoid reconstruction. The native glenoid and proximal femoral allograft are prepared and shaped to create a precisely matched contact surface, which permits axial compression to secure fixation. The surface of the glenoid is lateralised to at least the level of the coracoid. The central cancellous femoral allograft is removed and impaction autografting is performed prior to implantation of a glenoid base plate with 25-mm long centre peg. Two screws are inserted into the best quality native scapular bone available to ensure compression. A reverse shoulder arthroplasty is implanted. We have performed our dual-biology reconstruction of the glenoid in combination with reverse total shoulder arthroplasty in 8 patients to date. The technique has been performed in the setting of massive uncontained glenoid defects without prostheses as well as in revisions from failed hemiarthroplasties and total shoulder arthroplasties. Our post-operative follow-up is now up to 32 months. CT scanning as early as 6 months demonstrates incorporation of the graft. There has been no evidence of loosening. None of our cases have been complicated by infection or peri-prosthetic fracture and there have been no dislocations. One patient sustained an acromial stress fracture at 9 months post-operatively after lifting a 100-pound gas cylinder. This was diagnosed on bone scan, had no impact on the construct and was managed in a sling for comfort. Another patient has developed Nerot grade I notching which substantially in all patients, with an average improvement of 6.6 on a 10-point scale. Our dual biology allograft-autograft reconstruction is a useful and elegant technique in the setting of massive uncontained defects of the glenoid, which permits the implantation of a reverse total shoulder arthroplasty. We believe this technique to be reproducible and uses materials that are both readily available and familiar

Superiorly eroded glenoids in cuff tear arthropathy represent a surgical challenge for reconstruction. The bone loss orientation and severity may influence glenoid component fixation. This computed-tomography study quantifies both the degree of erosion and orientation in superiorly eroded Favard E2 glenoids. We hypothesized that the erosion in E2 glenoids does not occur purely superiorly, rather, it is oriented in a predictable posterosuperior orientation with a largely semicircular line of erosion. Three-dimensional reconstructions of 40 shoulders with E2 glenoids (28 female, 12 male patients) at a mean age of 74 years (range, 56–88 years) were created from computed-tomography images. Point coordinates were extracted from each construct to analyze the morphologic structure. The anatomical location of the supra- and infraglenoid tubercle guided the creation of a superoinferior axis, against which the orientation angle of the erosion was measured. The direction and, thus, orientation of erosion was calculated as a vector. By placing ten point coordinates along the line of erosion and creating a circle of best fit, the radius of the circle was placed orthogonally against a chord that resulted by connecting the two outermost points along the line of erosion. To quantify the extent of curvature of the line of erosion between the paleo- and neoglenoid, the length of the radius of the circle of best fit was calculated. Individual values were compared against the mean of circle radii. The area of bony erosion (neoglenoid), was calculated as a percentage of the total glenoid area (neoglenoid + paleoglenoid). The severity of the erosion was categorized as mild (0% to 33%), moderate (34% to 66%), and severe erosion (>66%). The mean orientation angle between the vector of bony erosion and the superoinferior axis of the glenoid was 47° ± 17° (range, 14° – 74°) located in the posterosuperior quadrant of the glenoid, resulting in the average erosion being directed between the 10 and 11 o'clock position (right shoulder). In 63% of E2 cases, the line of erosion separating the paleo- and neoglenoids was more curved than the average of all bony erosions in the cohort. The mean surface area of the neoglenoid was 636 ± 247 mm2(range, 233 – 1,333 mm2) and of the paleoglenoid 311 ± 165 mm2(range, 123 – 820 mm2), revealing that, on average, the neoglenoids consume 67% of the total glenoid surface. The extent of erosion of the total cohort was subdivided into one mild (2%), 14 moderate (35%) and 25 severe (62%) cases. Using a clock-face for orientation, the average orientation of type E2 glenoid defects was directed between the 10 and 11 o'clock position in a right shoulder, corresponding to the posterosuperior glenoid quadrant. Surgeons managing patients with E2 type glenoids should be aware that a superiorly described glenoid erosion is oriented in the posterosuperior quadrant on the glenoid clock-face when viewed intra-operatively. Additionally, the line of erosion in 63% of E2 glenoids is substantially curved, having a significant effect on bone removal techniques when using commercially available augments for defect reconstruction

Introduction. Little guidance exists regarding the minimum screw length and number necessary to achieve fixation with reverse shoulder arthroplasty (rTSA). The goal of this study is to quantify the pre- and post-cyclic baseplate displacements associated with two baseplate designs of different sizes using multiple screw lengths and numbers in a low density polyurethane bone substitute model. Methods. The test was conducted according to ASTM F 2028–17. The baseplate displacements of standard and small reverse shoulder constructs (Equinoxe, Exactech, Inc.) were quantified in a 15pcf polyurethane block (Pacific Research, Inc.) before and after cyclic testing with an applied load of 750N for 10,000 cycles. Baseplates were constructed using 2 or 4 screws with 3 different poly-axial locking compression screw lengths: 4.5×18mm, 4.5×30mm, and 4.5×46mm. Five of each configuration were tested for a total of 30 specimens for each baseplate. A two-tailed, unpaired student's t-test (p<0.05) compared baseplate displacements before and after cyclic loading in both the superior-inferior (S/I) and anterior-posterior (A/P) directions. The standard and small results were then compared. Results. All standard and small reverse glenoid baseplates remained well-fixed after cyclic loading in the low-density bone substitute model regardless of screw length or number. The average pre- and post-cyclic displacement for baseplates with 2 screws was significantly greater than that of baseplates with 4 screws in both the A/P and S/I directions. The average pre- and post-cyclic displacements for baseplates with 18mm screws were significantly greater than baseplates with 46mm screws in the A/P and S/I directions, post-cyclic displacement with 18mm screws was significantly greater than with 30mm screws in the A/P and S/I directions, and post-cyclic displacement with 30mm screws was significantly greater than with 46mm screws in the S/I direction only. Few differences in fixation were observed between baseplate sizes. Statistically significant difference was reached for post cyclic S/I displacement for 30mm (small baseplate superior) and 46mm screws (standard baseplate superior). Discussion and Conclusions. The results demonstrate that rTSA glenoid displacement is impacted by both the number and length of screws for both standard and small baseplate sizes. Regardless of the number of screws, the use of longer screws was associated with significantly better initial fixation. Additionally, the use of more screws was associated with significantly better fixation irrespective of screw length in the A/P direction. None of the tested devices catastrophically failed, demonstrating that adequate fixation can be achieved with as little as two 18mm screws for the baseplates utilized. However, this screw configuration was associated with the largest pre- and post-cyclic displacements, so it is assumed to be at a greater risk for aseptic loosening. If using 4 screws is not feasible in a given case, the results suggest that using longer screws can be used to improve fixation. The results of the small and standard baseplates were comparable for the given lengths and quantities of screws, suggesting that the reduced surface area of the small baseplate has no detrimental impact on fixation. Care should be made when extrapolating these results to glenoid defects. For any figures or tables, please contact authors directly

Reverse total shoulder arthroplasty (RTSA) has improved the lives of many patients with complex shoulder pathology including rotator cuff arthropathy, glenoid bone defects, post-traumatic arthritis and failed non-constrained total shoulder arthroplasty. However, this non-anatomic replacement has a very different complication profile than has been observed with non-constrained shoulder arthroplasty and the revision of RTSA can be extremely challenging. The purpose of this talk is to review some of the typical complications observed in RTSA including instability, infection, stress fractures, peri-prosthetic fractures and glenoid failures, and discuss the treatment options for dealing with these difficult problems

The classic Hill-Sachs lesion is a compression or impression fracture of the humeral head in occurrence with anterior glenohumeral instability. The true incidence is unknown but clearly increases with recurrent instability episodes. Recent peer-reviewed literature has highlighted the importance of addressing “significant” humeral and glenoid bone defects in the management of glenohumeral instability. Quantification of the “significance” of a Hill-Sachs lesion with regard to location, size, and depth in relation to the glenoid has helped guide indications for surgical management. Options for managing Hill-Sachs lesions include both humeral-sided techniques (soft tissue, bone, and/or prosthetic techniques) and also glenoid-sided techniques (bone transfers to increase glenoid width). The majority of significant acute or chronic Hill-Sachs lesions can be effectively managed without prosthetic replacement. Is a prosthetic surface replacement ever indicated for the management of Hill-Sachs lesions? The peer-reviewed literature is sparse with the outcomes of this treatment, and significant consideration must be given to both the age of the patient and the need for such management when other effective non-prosthetic options exist. In a patient with more than half of the humeral head involved after instability episodes (perhaps seizure or polytrauma patients), metallic surface replacement arthroplasty may be an option that could require less involved post-operative care while restoring range of motion and stability

Acute Hill-Sachs (HS) reduction represents a potential alternative method to remplissage for the treatment of an engaging HS lesion. The purpose of this study is to biomechanically compare the stabilising effects of a acute HS reduction technique and remplissage in a complex instability model. This was a comparative cadaveric study of 6 shoulders. For the acute HS lesion, a unique model was used to create a 30% defect, compressing the subchondral bone while preserving the articular surface in a more anatomic fashion. In addition, a 15% glenoid defect was made in all specimens. The HS lesion was reduced through a lateral cortical window with a bone tamp, and the subchondral void was filled with Quickset (Arthrex) bone cement to prevent plastic deformation. Five scenarios were tested; intact specimen, bipolar lesion, Bankart repair, remplissage with Bankart repair and HS reduction technique with Bankart repair. Translation, kinematics and dislocation events were recorded. For all 6 specimens no dislocations occurred after either remplissage or the reduction technique. At 90 degrees of abduction and external rotation (ABER), anterior-inferior translation was 11.1 mm (SD 0.9) for the bipolar lesion. This was significantly reduced following both remplissage (5.1±0.7mm; p<0.001) and HS reduction (4.4±0.3mm; p<0.001). For anterior-inferior translation there was no significant difference in translation between the reduction technique and remplissage (p=0.91). At 90 degrees of ABER, the intact specimens average joint stiffness was 7.0±1.0N/mm, which was not significantly different from the remplissage (7.8±0.9 N/mm; p=0.9) and reduction technique (9.1±0.6 N/mm; p=0.50). Compared with an isolated Bankart repair, the average external rotation loss after also performing a remplissage procedure was 4.3±3.5 deg (p=0.65), while average ER loss following HS reduction was 1.1±3.3 deg (p=0.99). There was no significant difference in external rotation between remplissage and the reduction technique (p=0.83). Similar joint stability was conferred following both procedures, though remplissage had 3.2-degree loss of ER in comparison. While not statistically significant, even slight ER loss may be clinically detrimental in overhead athletes. Overall, the acute reduction technique is a more anatomic alternative to the remplissage procedure with similar ability to prevent dislocation in a biomechanical model, making it a viable treatment option for engaging Hill-Sachs lesions

To evaluate the efficacy of using a novel button-suture construct in place of traditional screws to provide bone block fixation for the Latarjet procedure. Four paired cadaveric shoulders (n=8) were denuded, with the exception of the conjoint tendon on the coracoid, and were potted. A 15% anterior glenoid bone defect was simulated. Right and left specimens were randomised into two groups: double-screw versus quadruple-button Latarjet reconstruction techniques. A uniaxial mechanical actuator loaded the Latarjet reconstructed glenoid articular surface via a 47mm diameter metallic hemisphere. Cyclic loading between 50–200N was applied to the glenoid at a rate of 1Hz for 1000 cycles. Testing was repeated three times for conjoint tendon loads of 0N, 10N and 20N. The relative positions of three points on the inferior, central and superior edges of the coracoid bone fragment were optically tracked with respect to a glenoid coordinate system throughout testing. Screw and button constructs were compared on the basis of maximum relative displacement at these points (RINF, RCENT, RSUP). Statistical significance was assessed using a paired-samples t-test in SPSS. When conjoint tendon loading was not present the double screw and quadruple button constructs were not significantly (P>0.779) different (0N: RINF: 0.11 (0.05)mm vs. 0.12 (0.03)mm, RCENT: 0.12 (0.04)mm vs. 0.12 (0.03)mm, RSUP: 0.13 (0.04)mm vs. 0.12 (0.03)mm). Additionally, the double screw construct was not found to differ (P>0.062) from the quadruple button in terms of resultant coracoid displacement for all central and superior points, regardless of conjoint loading (10N: RCENT: 0.11 (0.03)mm vs. 0.19 (0.05)mm, RSUP: 0.11 (0.01)mm vs. 0.18 (0.04)mm; 20N: RCENT: 0.13 (0.01)mm vs. 0.30 (0.13)mm, RSUP: 0.13 (0.03)mm vs. 0.26 (0.14)mm). It was only for the inferior point with conjoint loading of 10N and 20N that the double screw construct began to produce significantly lower displacements than the quadruple button (10N: RINF: 0.11 (0.03)mm vs. 0.23 (0.05)mm, P=0.047; 20N: RINF: 0.12 (0.02)mm vs. 0.39 (0.15)mm, P=0.026). The results of the screw and button constructs when conjoint tendon loading was absent suggest that the button may be a suitable substitute to the screw when the coracoid is used as a bone block. Due to the small resultant displacements (max: screw = 0.19mm, button = 0.52mm), it is suggested that buttons may also act as a substitute to screws for Latarjet procedures, provided conjoint tendon overloading is minimised during the post-operative graft healing period. These in-vitro results support the in-vivo results of Boileau et al (2015) that demonstrated the suture-button technique to be an excellent alternative to screw fixation Latarjet, with graft healing in 91% of their subjects