Aims. The aim of this study was to compare the clinical and radiological outcomes of reverse shoulder arthroplasty (RSA) using small and standard baseplates in Asian patients, and to investigate the impact of a mismatch in the sizes of the glenoid and the baseplate on the outcomes. Methods. This was retrospective analysis of 50 and 33 RSAs using a standard (33.8 mm, ST group) and a small (29.5 mm, SM group) baseplate of the Equinoxe reverse shoulder system, which were undertaken between January 2017 and March 2021. Radiological evaluations included the size of the glenoid, the β-angle, the inclination of the glenoid component, inferior overhang, scapular notching, the location of the central cage in the baseplate within the vault and the mismatch in size between the glenoid and baseplate. Clinical evaluations included the range of motion (ROM) and functional scores. In subgroup analysis, comparisons were performed between those in whom the vault of the glenoid was perforated (VP group) and those in whom it was not perforated (VNP group). Results. Perforation of the vault of the glenoid (p = 0.018) and size mismatch in height (p < 0.001) and width (p = 0.013) were significantly more frequent in the ST group than in the SM group. There was no significant difference in the clinical scores and ROM in the two groups, two years postoperatively (all p > 0.05). In subgroup analysis, the VP group had significantly less inferior overhang (p = 0.009), more scapular notching (p = 0.018), and more size mismatch in height (p < 0.001) and width (p = 0.025) than the VNP group. Conclusion. In Asian patients with a small glenoid, using a 29.5 mm small baseplate at the time of RSA was more effective in reducing size mismatch between the glenoid and the baseplate, decreasing the incidence of perforation of the glenoid vault, and achieving optimal positioning of the baseplate compared with the use of a 33.8 mm standard baseplate. However, longer follow-up is required to assess the impact of these findings on the clinical outcomes. Cite this article: Bone Joint J 2023;105-B(11):1189–1195

Osteochondral glenoid loss is associated with recurrent shoulder instability. The critical threshold for surgical stabilization is multidimensional and conclusively unknown. The aim of this work was to provide a well- measurable surrogate parameter of an unstable shoulder joint for the frequent anterior-inferior dislocation direction. The shoulder stability ratio (SSR) of 10 paired human cadaveric glenoids was determined in anterior-inferior dislocation direction. Osteochondral defects were simulated by gradually removing osteochondral structures in 5%-stages up to 20% of the intact diameter. The glenoid morphological parameters glenoid depth, concavity gradient, and defect radius were measured at each stage by means of optical motion tracking. Based on these parameters, the osteochondral stability ratio (OSSR) was calculated. Correlation analyses between SSR and all morphological parameters, as well as OSSR were performed. The loss of SSR, concavity gradient, depth and OSSR with increasing defect size was significant (all p<0.001). The loss of SSR strongly correlated with the losses of concavity gradient (PCC = 0.918), of depth (PCC = 0.899), and of OSSR (PCC = 0.949). In contrast, the percentage loss based on intact diameter (defect size) correlated weaker with SSR (PCC=0.687). Small osteochondral defects (≤10%) led to significantly higher SSR decrease in small glenoids (diameter <25mm) compared to large (≥ 25mm) ones (p ≤ 0.009). From a biomechanical perspective, the losses of concavity gradient, glenoid depth and OSSR correlate strong with the loss of SSR. Therefore, especially the loss of glenoidal depth may be considered as a valid and reliable alternative parameter to describe shoulder instability. Furthermore, smaller glenoids are more vulnerable to become unstable in case of small osteochondral loosening. On the other hand, the standardly used percentage defect size based on intact diameter correlates weaker with the magnitude of instability and may therefore not be a valid parameter for judgement of shoulder instability

Background. Use of a baseplate with a smaller diameter in reverse shoulder arthroplasty has been recommended, especially in patients with a small glenoid or insufficient bony stock due to severe glenoid wear. However, effect of a smaller baseplate on stability of the glenoid component has not been evaluated. The purpose of this study was to determine whether a smaller baseplate (25 mm) is beneficial to the initial primary stability of the glenoid component compared to that with a baseplate of a commonly used size (29 mm) by finite element analysis. Methods. Computed tomography (CT) scans of fourteen scapulae were acquired from cadavers with no apparent deformity or degenerative change. Glenoid diameter corresponding to the diameter of the inferior circle of glenoid was measured using a caliper and classified into the small and large glenoid groups based on 25mm diameter. CT slices were used to construct 3-dimensional models with Mimics (Materialise, Leuven, Belgium). A corresponding 3D Tornier Aequalis® Reversed Shoulder prosthesis model was generated by laser scanning (Rexcan 3D Laser Scanner, Solutionix, Seoul, Korea). Glenoid components with 25mm and 28mm diameter of the baseplate were implanted into the scapular of small and large glenoid group, respectively. Finite element models were constructed using Hypermesh 11.0 (Altair Engineering, Troy, MI, USA) and a reverse engineering program (Rapidform 3D Systems, Inc., Rock Hill, SC, USA). Abaqus 6.10 (Dassault Systemes, Waltham, MA) was used to simulate 30. o. , 60. o. , and 90. o. glenohumeral abduction in the scapular plane. Single axial loads of 686N (1 BW) at angles of 30. o. , 60. o. , and 90. o. abduction were applied to the center of the glenosphere parallel to the long axis of the humeral stem. Relative micromotion at the middle and inferior thirds bone–glenoid component interface, and distribution of bone stress under the glenoid component and around the screws were analyzed. Wilcoxon's rank-sum test was used for statistical comparison and p < 0.05 was considered as a minimum level of statistical significance. Results. In small glenoid group, micromotion at the middle and inferior thirds of the glenoid-glenosphere interface at angles of 30. o. and 60. o. abduction were significantly greater in the 29mm baseplate than in the 25mm baseplate. There was no significant difference in micromotion at angle of 90. o. abduction between 25mm and 29mm baseplate. In large glenoid group, there was no statistically significant difference in micromotion between 25mm and 29mm baseplate at all angles of abduction. In small glenoid group, maximum bone stress was measured at the point of cortical engagement of the inferior screw and was statistically greater in the 29mm baseplate than in the 25mm baseplate. In large glenoid group, there was no statistically significant difference of maximum bone stress around the inferior screw between 25mm and 29mm baseplates. Conclusions. Use of a baseplate with a smaller diameter (25 mm) in reverse shoulder arthroplasty is suitable for improving the primary stability of the glenoid component, especially in small glenoid

This study examined the regional variations of cortical and cancellous bone density present in superiorly eroded glenoids. It is hypothesized that eroded regions will contain denser bone in response to localized stress. The shift in natural joint articulation may also cause bone resorption in areas opposite the erosion site. Clinical CT scans were obtained for 32 shoulders (10m/22f, mean age 72.9yrs, 56–88yrs) classified as having E2-type glenoid erosion. The glenoid was divided into four measurement regions - anterior, inferior, posterior, and superior - as well as five depth regions. Depth regions were segmented in two-millimeter increments from zero to 10 millimeters, beginning at the center of the glenoid surface. A repeated-measures multiple analysis of variance (RM-MANOVA) was performed using SPSS statistical software to look for differences and interactions between mean densities in each depth, quadrant, and between genders. A second RM-MANOVA was performed to examine effects of gender and quadrant on cortical to cancellous bone volume ratios. Significance was set at p < 0 .05. Quadrant and depth variables showed significant multivariate main effects (p 0.147 respectively). Quadrant, depth, and their interaction showed significant univariate main effects for cortical bone (p≤0.001) and cancellous bone (p < 0 .001). The lowest bone density was found to be in the inferior quadrant for cancellous bone (307±50 HU, p < 0 .001). The superior quadrant contained the highest mean density for cortical bone (895±97 HU), however it was only significantly different than in the posterior quadrant (865±97 HU, p=0.022). As for depth, it was found that cortical bone is most dense at the glenoid surface (zero to two millimeters, 892±91 HU) when compared to bone at two to eight millimeters in depth (p < 0 .02). Cancellous bone was also most dense at the surface (352±51 HU), but only compared to the eight to 10 millimeters depth (p=0.005). Cancellous bone density was found to decrease with increasing depth. For cortical-to-cancellous bone volume ratios, the inferior quadrant (0.37±0.28) had a significantly lower ratio than all other quadrants (p < 0 .001). The superoposterior region of the glenoid was found to have denser cancellous bone and a high ratio of cortical to cancellous bone, likely due to decreased formation of cancellous bone and increased formation of cortical bone, in response to localized stresses. The inferior quadrant was found to have the least dense cortical and cancellous bone, and the lowest volume of cortical bone relative to cancellous bone. Once again, this is likely due to reduction in microstrain responsible for bone adaptation via Wolff's law. The density values found in this study generally agree with the range of values found in previous studies of normal and arthritic glenoids. An important limitation of this study is the sizing of measurement regions. For a patient with a smaller glenoid, a depth measurement of two millimeters may represent a larger portion of the overall glenoid vault. Segments could be scaled for each patient based on a percentage of each individual's glenoid size

Contracture of the anterior musculature causes posterior humeral head subluxation and results in a posterior load concentration on the glenoid. This reduced contact area causes glenoid wear, humeral medialisation and eventually posterior instability. After arthroplasty that does not correct for this, posterior wear stress increases in the implant, across the cement mantle and bone thus increasing the risk of aseptic loosening over time. Correction of the posterior wear pattern at the time of arthroplasty of the shoulder is recommended. Asymmetric reaming of the glenoid has been recommended as a means to correct this deformity but leads to producing a smaller glenoid which is medialised. This shortening of the glenoid causes the stabilising muscle envelope to shorten and the glenoid vault to become much smaller in volume. These potential changes may have a destabilising effect on the implant leading to early loosening and secondary failure of the prosthetic implant. Other options include using an implant to make the correction of the deformity such as augmented glenoid components. Early uses of these implants were not successful mainly due to the design flaws of the early implants. Newer implants have made design changes to overcome these early failures. CT scan evaluation is important to determine the degree of correction that is needed to balance the glenohumeral joint. Correcting the deformity and keeping the muscle envelope at the appropriate tension may lead to better long term outcomes. These implants are currently in use but long term outcome studies are not yet available to determine their ultimate values to the patients

Aims

Optimal glenoid positioning in reverse shoulder arthroplasty (RSA) is crucial to provide impingement-free range of motion (ROM). Lateralization and inclination correction are not yet systematically used. Using planning software, we simulated the most used glenoid implant positions. The primary goal was to determine the configuration that delivers the best theoretical impingement-free ROM.

Introduction. Reverse total shoulder replacement is performed for the treatment of rotator cuff arthropathy, massive irreparable cuff tears and failed shoulder hemiarthroplasty with irreparable rotator cuff tears. The aim of this study was to assess the clinical and radiological outcome of single surgeon series of Equinoxe® reverse total shoulder replacement at a district general hospital. Materials/Methods. Consecutive patients who underwent Equinoxe® reverse total shoulder replacement at our unit from Jun 2008 to Dec 2010 were retrospectively reviewed. Indications for surgery, complications and radiological outcomes were assessed. Oxford shoulder score was used to assess the functional outcome. Results. Between Jun 2008 and Dec 2012, forty-one reverse total shoulder replacements were performed by the senior author in 37 patients. Of these, Equinoxe® prostheses were used in 27 operations (26 patients). These included 22 female and 4 male patients. Cuff arthropathy was the commonest preoperative diagnosis (23 patients), followed by proximal humeral fracture non-union (2 patients), failed hemiarthroplasty (one patient) and failed resurfacing (one patient). The mean follow up was 10 months (3 to 17 months). At the time of the study, three patients had died due to unrelated causes, two were not contactable and the remaining 21 patients were analysed. The mean oxford shoulder score was 35.8 (21–48). Nineteen patients (90.5%) graded their outcome a good to excellent while 2 patients (9.5%) graded as poor. Seventeen patients (81%) expressed that they would recommend this operation. One patient (4.7%) had infection and another had dislocation. Overall, there were 3 reoperations (14.3%); first washout, second change of humeral tray and third excision of lateral end of clavicle and reattachment of deltoid. Two patients (9.5%) had small glenoid notching. There was no loosening, neurovascular injury or postoperative haematoma. Conclusion. Early outcome of Equinoxe reverse shoulder replacement is promising. Longer follow-up is required to further assess the outcome

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

Aims

Recurrent dislocation is both a cause and consequence of glenoid bone loss, and the extent of the bony defect is an indicator guiding operative intervention. Literature suggests that loss greater than 25% requires glenoid reconstruction. Measuring bone loss is controversial; studies use different methods to determine this, with no clear evidence of reproducibility. A systematic review was performed to identify existing CT-based methods of quantifying glenoid bone loss and establish their reliability and reproducibility

Aims

Scapular notching is a frequently observed radiographic phenomenon in reverse shoulder arthroplasty (RSA), signifying impingement of components. The purposes of this study were to evaluate the effect of glenoid component size and glenosphere type on impingement-free range of movement (ROM) for extension and internal and external rotation in a virtual RSA model, and to determine the optimal configuration to reduce the incidence of friction-type scapular notching.

We evaluated results at one year after surgical correction of internal rotation deformities in the shoulders of 270 patients with obstetric brachial plexus palsy. The mean age at surgery was 6.2 years (0.6 to 35). Two techniques were used: open subscapularis elongation and latissimus dorsi to infraspinatus transfer. In addition, open relocation was performed or attempted in all patients with subluxed or dislocated joints. A mixed effects model approach was used to evaluate the effects of surgery on internal and external rotation, abduction, flexion and Mallet score. Independent factors included operative status (pre- or post-operative), gender, age, the condition of the joint, and whether or not transfer was performed. The overall mean improvement in external rotation following surgery was 84.6° (95% confidence interval (CI) 80.2 to 89.1) and the mean Mallet score improved by 4.0 (95% CI 3.7 to 4.2). There was a mean decrease in internal rotation of between 27.6° and 34.4° in the relocated joint groups and 8.6° (95% CI 5.2 to 12.0) in the normal joint group. Abduction and flexion were unchanged following surgery. Adding a latissimus dorsi transfer did not result in greater improvement in the mean external rotation compared with elongation of the subscapularis alone.

Cite this article: Bone Joint J 2013;95-B:1432–8.

Total shoulder replacement is a successful procedure for degenerative or some inflammatory diseases of the shoulder. However, fixation of the glenoid seems to be the main weakness with a high rate of loosening. The results using all-polyethylene components have been better than those using metal-backed components. We describe our experience with 35 consecutive total shoulder replacements using a new metal-backed glenoid component with a mean follow-up of 75.4 months (48 to 154).

Our implant differs from others because of its mechanism of fixation. It has a convex metal-backed bone interface and the main stabilising factor is a large hollow central peg. The patients were evaulated with standard radiographs and with the Constant Score, the Simple Shoulder Test and a visual analogue scale. All the scores improved and there was no loosening, no polyethylene-glenoid disassembly and no other implant-related complications.

We conclude that a metal-backed glenoid component is a good option in total shoulder replacement with no worse results than of those using a cemented all-polyethylene prosthesis.

The generally-accepted treatment for large, displaced fractures of the glenoid associated with traumatic anterior dislocation of the shoulder is operative repair. In this study, 14 consecutive patients with large (> 5 mm), displaced (> 2 mm) anteroinferior glenoid rim fractures were treated non-operatively if post-reduction radiographs showed a centred glenohumeral joint.

After a mean follow-up of 5.6 years (2.8 to 8.4), the mean Constant score and subjective shoulder value were 98% (90% to 100%) and 97% (90% to 100%), respectively. There were no redislocations or subluxations, and the apprehension test was negative. All fragments healed with an average intra-articular step of 3.0 mm (0.5 to 11). No patient had symptoms of osteoarthritis, which was mild in two shoulders and moderate in one.

Traumatic anterior dislocation of the shoulder, associated with a large displaced glenoid rim fracture can be successfully treated non-operatively, providing the glenohumeral joint is concentrically reduced on the anteroposterior radiograph.

While the evolution of the bony skeleton of the shoulder girdle is well described, there is little information regarding the soft tissues, in particular of the rotator cuff. We dissected the shoulders of 23 different species and compared the anatomical features of the tendons of the rotator cuff. The alignment and orientation of the collagen fibres of some of the tendons were also examined histologically. The behaviour of the relevant species was studied, with particular reference to the extent and frequency of forward-reaching and overhead activity of the forelimb.

In quadrupedal species, the tendons of supraspinatus, infraspinatus and teres minor were seen to insert into the greater tuberosity of the humerus separately. They therefore did not form a true rotator cuff with blending of the tendons. This was only found in advanced primates and in one unusual species, the tree kangaroo. These findings support the suggestion that the appearance of the rotator cuff in the evolutionary process parallels anatomical adaptation to regular overhead activity and the increased use of the arm away from the sagittal plane.