Introduction. Initial fixation of noncemented implants is critical to achieve a stable bone/implant interface during the first few months after surgery to potentiate bone in-growth and avoid aseptic loosening. Numerous reverse shoulder glenoid implant designs have been conceived in an attempt to improve implant performance and decrease the rate of aseptic glenoid loosening, commonly reported to be 5%. Design variations include: baseplate profile, baseplate size, backside geometry, center of rotation, surface finish and coatings, fixation screw diameters, number of fixation screw options, and type of screw fixation. However, little comparative biomechanical data exist to substantiate one design consideration over another. To that end, this study quantified glenoid fixation before and after cyclic loading of simulated abduction of 6 different reverse shoulder glenoid designs when secured to a low density polyurethane bone substitute block. Methods. A displacement test quantified fixation of 6 different reverse shoulder designs: 38 mm Equinoxe standard offset (EQ), 38 mm Equinoxe lateral offset (EQL), 36 mm Depuy Delta III (DRS), 36 mm Zimmer, (ZRS), 32 mm neutral DJO RSP (DJO), and a 36 mm Tornier BIO-RSA (BIO), secured to a 0.24 g/cm. 3. polyurethane block as a shear (357 N) and compressive (50 N) load was applied before and after cyclic loading. (Figure 1) Glenoid displacement was measured relative to the block using dial indicators in the directions of the applied loads along the superior/inferior axis. A cyclic test rotated each glenosphere (n = 7 for each design) about a 55° arc of abduction at 0.5 Hz for 10k cycles as 750N was constantly applied. (Figure 2) Each implant was cycled using a 145° humeral liner of the appropriate diameter to ensure each device is subjected to the same shear load. A two-tailed unpaired student's t-test was used to compare pre- and post-cyclic mean displacements between designs; p < 0.05 denotes significance. Results. The average pre-cyclic displacement of the EQ, EQL, DRS, ZRS, DJO, and BIO devices was 181, 137, 186, 381, 238, 232 microns, respectively. The average post-cyclic displacement of the EQ, EQL, DRS, DJO, and BIO devices was 186, 129, 189, 368, 249 microns, respectively. During the cyclic test, 6 of 7 ZRS devices failed at an average of 2603 cycles, 1 of 7 DJO failed at 7342 cycles, and 4 of 7 BIO devices failed at an average of 2926 cycles. All 7 of the EQ, EQL, and DRS devices remained well fixed throughout cyclic loading. Discussion and Conclusions. The results of this study demonstrate significant difference in fixation associated 6 different reverse shoulder designs. Despite many similarities in geometry between these designs, significant differences in fixation were observed between nearly every implant design tested. This suggests that subtle changes in glenoid baseplate design can dramatically impact fixation, particularly in low density bone substitutes which are intended to simulate the bone quality of the recipient population for reverse shoulders. Future work should attempt to isolate which design parameters are the most critical contributors for initial fixation and ultimately, long-term stability

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. Shoulder joint prostheses have become the most commonly replaced after knee and hip artificial implants. Reverse shoulder arthroplasty (RSA) is the treatment option for patients with severe osteoarthritis, rotator cuff arthropathy or a massive rotator cuff tear with pseudoparalysis. Though successful, the long-term survival of such implants are limited by wear of the materials in contact [1, 2]. The aim of this study was to investigate RSA wear in vitro using a clinically relevant activities of daily living (ADLs). MATERIALS AND METHODS. Four new JRI Orthopaedics Reverse Shoulder 42 mm diameter VAIOS with cobalt-chromium (CoCr) glenospheres and ultra-high molecular weight polyethylene (UHMWPE) humeral components were tested. A five million cycles wear test was undertaken using the unique Newcastle Shoulder Wear Simulator with dilute bovine serum as a lubricant. “Mug to mouth” was performed as the ADL to the test prostheses in intervals of 100 cycles, following by 5 seconds of high load (450N) with no motion simulating an ADL such as “lifting an object”. This combined load cycle was then repeated. A fifth reverse shoulder prosthesis was subject to dynamic loading only in a soak control station. Wear was assessed gravimetrically and roughness (Sa) of the articulating surfaces was measured with a non-contacting profilometer. RESULTS AND DISCUSSION. The mean wear rate and standard deviation of the UHMWPE components was 11.4±3.7 mm. 3. /million cycles, while the CoCr components showed minimal wear over the test duration of 0.01± 0.02 mm. 3. /million cycles (Fig.1). Wear rates are comparable with Kohut et al. (14.1 mm. 3. /million cycles) [3] and Smith et al. (14.3±1.6 mm. 3. /million cycles) [4]. The CoCr glenospheres roughness was unchanged, from 32±8 nm Sa to 28±8 nm Sa over the 5 million cycles of the test (p=0.017), while the UHMWPE humeral components became smoother, from 692±123 nm Sa to 42±29 nm Sa (Fig.2), showing a statically significant change (p<0.001). CONCLUSION. The present study is the first wear test of artificial shoulder joints using a Motion-Load-Motion configuration as a clinically relevant physiological pattern of motion and load. Results are comparable with those found in the literature for in vitro testing of reverse shoulder replacements. For any figures or tables, please contact the authors directly

Background

Locked anterior shoulders (LAS) with static instability and anterior glenoid bone loss are challenging in the elderly population. Reverse shoulder arthroplasty (RSA) has been employed in treating these patients. No study has compared RSA for LAS to classically indicated RSA.

Aim. A significant number of patients undergoing shoulder arthroplasty surgery have C acnes contamination at the end of the primary surgery. The objective of this study is to determine whether patients with C acnes contamination at the end of their primary shoulder surgery have a worse prognosis than those who end up without C. acnes contamination. Method. Prospective study including all patients who underwent a reverse shoulder prosthesis from January 2015 to December 2018. In all of them, 5 to 12 cultures were performed during primary surgery. The patients underwent surgery for shoulder arthritis secondary to rotator cuff tears, acute fracture of the proximal humerus, and sequelae of fracture of the proximal humerus. Exclusion criteria included the existence of previous surgeries on the affected shoulder, the presence of signs of infection, having received infiltrations and / or complementary invasive examinations (Arthro-MRI and Arthro-CT). Follow-up from 2 to 5 years. Functional assessment according to the Constant Functional Scale. All complications were also recorded. Results. 162 patients were included. Of these, 25 had positive cultures for C. acnes at the end of primary shoulder surgery. Average age of 74.8 years. 136 women and 26 men. 75.9% Shoulder arthritis secondary to rotator cuff tears, 13.6% acute fractures and 10.5% sequelae of fractures. There were no differences between patients with C. acnes and those without C. acnes regarding age and indication for surgery. Predominance of men in the group with positive C. acnes (p <0.001). No differences at 2 and 5 years in the Constant functional scale between the two groups (2 years, 59.6 vs 59.2 p 0.870) (5 years, 62.4 vs 59.5 p 0.360). Significant differences regarding the number of complications (p 0.001). Patients without C. acnes had 1 aseptic loosening of the metaglene and patients with C. acnes had 2 infections, 1 dislocation, and 1 revision surgery. Patients with contamination by C. acnes had more comorbidities (p 0.035) than patients without contamination. Conclusions. Patients with C acnes contamination at the end of primary surgery do not have functional differences when compared with patients without contamination at 2 and 5 years, but they have a higher number of complications in the medium term

Introduction. Reverse Total Shoulder Arthroplasty (rTSA) is currently advised against in patient populations with movement disorders, due to potential premature failure of the implants from the use of walking assistive devices. The objective of this study is to measure the amount of displacement induced by the simulated loading of axillary crutches on a rTSA assembly in a laboratory mimicking immediate postoperative conditions. Methods. 8 reverse shoulder baseplate/glenosphere assemblies (Equinoxe, Exactech, Inc) were fixated to 15 lb/ft3 density rigid polyurethane bone substitute blocks. Displacement of the assemblies in the A/P and S/I axes was measured using digital displacement indicators by applying a physiologically relevant 357N shear load parallel to the face of the glenosphere, and a nominal 50N compressive axial load perpendicular to the glenosphere. Westerhoff et al. reported in vivo shoulder loads while ambulating with axillary crutches had a maximum resultant force of 170% times the patient's bodyweight with the arm at 45.25° of abduction1. This was recreated by applying a 1435.4N compressive load (Average bodyweight of 86.1kg*170%) to a humeral liner and reverse shoulder assembly in an Instron testing apparatus at 45.25° of abduction as shown in Figure 1. The glenosphere was rotated about the humeral component through the arc of the axillary crutch swing, from −5° of extension to 30° of flexion as shown in Figure 2 for 183,876 cycles2. The number of cycles was based on number of steps taken in a day from pedometer data reported by Tudor Locke et al. for patients with movement disorders, extrapolated out to a 6 week postoperative recovery period3. A Student's one-tailed, paired t-test was used to identify whether or not significant displacement occurred, where p<0.05 denoted a significant difference. Results. Displacement in the A/P and S/I axes before and after cyclic loading are presented in Table 1. The S/I direction showed no significant difference in displacement (p≤.0801), whereas the A/P direction showed significant increase in displacement (p≤.0340). The average increase in displacement in the A/P and S/I directions was 43.5 and 35.8 microns, respectively. Discussion and Conclusions. This study was designed to represent a worst case scenario, as a patient is unlikely to bear full bodyweight on crutches immediately postoperatively, and is also unlikely to take as many steps as a healthy individual until full recovery occurs. For these reasons, early results indicate statistically significant displacement could occur if a patient bears full bodyweight on axillary crutches immediately postoperatively. This risk could be lowered after the postoperative recovery period in combination with non-full weight bearing devices such as a cane or a walker. To view tables/figures, please contact authors directly

Background. One of the main concern about reverse shoulder arthoplasty for the treatment of rotator cuff deficiency is scapular notching that is still an unsolved issue for this particular prosthesis. The purpose of this multicentric retrospective study is to compare two different concept of reverse prosthesis, one with a concentric glenoshere and the other one with a new eccentric glenoshere design that aim to minimize scapular notching. Methods. From 2004 to 2009 67 patients were treated with a SMR reverse shoulder prosthesis (LIMA) with either concentric (figure 2) or eccentric glenosphere (figure 1). We selected for the study patients with criteria as much homogeneous as possible by the age and pathology. We then included for the study 25 patients (Group 1) with a concentric glenosphere and 21 (Group 2) with a eccentric glenosphere. All baseplates of concentric glenospheres were implanted with the most inferior aspect of baseplate that matched with the inferior glenoid ream, so that the glenosphere extended 4 mm beyond the glenoid inferiorly in order to minimize scapular notching. Every patient were followed clinically (Constant and Murley Score [C.S.] and Simple Shuolder test [S.S.T.]) and radiographically (notching, loosening and mechanical failure) with a minimum follow-up of 24 months. We also evaluated at the final follow-up psna (prosthesis-scapular neck angle), pgrd (peg glenoid rim distance) and DBSNG (distance between scapular neck and glenosfere). Results. At two years of follow up R.O.M. increased significantly in both groups especially in those with a eccentric glenosphere. Notably in patients with an eccentric glenosphere elevation improved from 66° to 148° and abduction from 60° to 115° while in those with a concentric glenosphere improved from 78° to 122° and 71° to 98° respectively for elevation and abduction. Outcomes for external-rotation and internal-rotation were very similar in both groups. 14 (56%) patients among those with a concentric glenosphere had scapular notching while we didn't have any notch in those with eccentric glenosphere even though we didn't find any significant different between the two groups in term of clinical outcomes and patient's satisfaction. The average C.S. increased from 38% to 69% in those with concentric SMR and from 30% to 74% in the other group. At the final follow-up PSNA, DBSNG and PGRD were respectively 88°, 3,2mm and 18,2 mm in group 1, while they were 92°, 4,3 mm and 21,2 mm in the group 2. Conclusions. Putting concentric glenosphere more inferiorly reduce the incidence of scapular notching but it doesn't solve the problem whereas, at medium follow-up, the new eccentric design seems to solved completely this issue. This study sustains PSNA, DBSNG, PGRD as reliable measures to predict scapular notching. Besides eccentric SMR glenosphere seems to increase R.O.M. mostly in flexion, abduction and adduction

Introduction. Aseptic glenoid loosening is a common failure mode of reverse shoulder arthroplasty (rTSA). Achieving initial glenoid fixation can be a challenge for the orthopedic surgeon since rTSA is commonly used in elderly osteoporotic patients and is increasingly used in scapula with significant boney defects. Multiple rTSA baseplate designs are available in the marketplace, these prostheses offer between 2 and 6 screw options, with each screw hole accepting a locking and/or compression screw of varying lengths (between 15 to 50mm). Despite these multiple implant offerings, little guidance exists regarding the minimal screw length and/or minimum screw number necessary to achieve fixation. To this end, this study analyzes the effect of multiple screw lengths and multiple screw numbers on rTSA initial glenoid fixation when tested in a low density (15pcf) polyurethane bone substitute model. Methods. This rTSA glenoid loosening test was conducted according to ASTM F 2028–17; we quantified glenoid fixation of a 38mm reverse shoulder (Equinoxe, Exactech, Inc) in a 15 pcf low density polyurethane block (Pacific Research, Inc) before and after cyclic testing of 750N for 10k cycles. To evaluate the effect of both screw fixation and screw number, glenoid baseplates were constructed using 2 and 4, 4.5×18mm diameter poly-axial locking compression screws (both n = 5) and 2 and 4, 4.5×46mm diameter poly-axial locking compression screws (both n = 5). A two-tailed unpaired student's t-test (p < 0.05) compared prosthesis displacements to evaluate each screw length (18 vs 46mm) and each screw number (2 vs 4). Results. All glenoid baseplates remained well-fixed after cyclic loading in the low density bone substitute block, regardless of screw length or screw number. As described in Table 1, the average pre- and post-cyclic displacement for baseplates with 18mm long screws was significantly greater than that of baseplates with 46mm long screws in both the A/P and S/I directions, with exception of displacements for 4 screws S/I-pre cyclic and 2 screws A/P-post cyclic loading. As described in Table 2, the average pre- and post-cyclic displacement for all baseplates with 2 screws was significantly greater than that of all baseplates with 4 screws, regardless of screw length in the A/P and S/I directions. Discussion and Conclusions. These results of this study demonstrate that rTSA glenoid baseplate fixation is impacted by both the number of screws and by the length of screws, with longer screws and more screws associated with significantly better initial fixation. However, it should be noted that none of the tested devices catastrophically failed in this non-defect/low-density model, demonstrating that adequate fixation can be achieved with as little as 2×18mm screws for some baseplate types. Care should be made when extrapolating these results to that of other designs. This study is limited by its use of only one implant design and by its use of a polyurethane substrate without any defect; future work should evaluate the effect of screw length and screw number in with multiple different prostheses in different densities of bone with and without defects

Introduction. The General Social Survey estimates that 19 million Americans shoot firearms, with 10% of this population being over the age of 65. More reverse total shoulder arthroplasty (rTSA) are seeking to return to physical activity after surgery, but the effects of shooting a firearm on the fixation of a rTSA implant are unknown. This study will seek to examine the recoil effect of a firearm on a rTSA baseplate fixation, by recording the forces absorbed by a shooter and applying these forces to a rTSA implant assembly in laboratory conditions. Methods. A total of 5 shooters over a range of heights and bodyweights fired a single action 12 gauge shotgun with 3 ounce slugs 5 times each. An accelerometer was rigidly fixated to the barrel of the firearm to record impulse values upon firing. 8 reverse shoulder baseplate/glenosphere assemblies (Equinoxe, Exactech, Inc) were fixated to 15 lb/ft3 density rigid polyurethane bone substitute blocks for drop tower testing. Displacement was measured before and after testing using digital displacement indicators by applying a physiologically relevant 357N shear load parallel to the face of the glenosphere, and a nominal 50N compressive axial load perpendicular to the glenosphere as shown in Figure 1. Measurements were taken for the S/I axis, and the sample was rotated 90 degrees for the A/P axis. The glenosphere/baseplate assemblies were loaded in a drop tower apparatus at 0° of abduction and 90° flexion to replicate the orientation of the joint seen while shooting. The drop tower utilized a 1.079kg weight set at 8” with a rubber impulse specific materil between the weight and impactor to reproduce the highest average impulse seen in shooting. A total of 50 drops were performed, to simulate two rounds of trap shooting at 25 shots each. A Student's one-tailed, paired t-test was used to identify whether or not significant loosening occurred, where p<0.05 denoted a significant difference. Results. The average shooting values for each shooter are presented in Table 1. Displacement measurements in the A/P and S/I axes before and after drop tower testing are presented in Table 2. All 8 samples remained well fixed after drop tower testing, and neither A/P nor S/I directions showed significant difference in displacement (p≤.279, p≤.158) with an average displacement of 4 and 10 microns, respectively. Discussion and Conclusions. This testing replicates a worst case scenario, as the combination of both round size and number of shots taken is not likely to be paired together while shooting recreationally. Additionally, the foam block used mimics an immediate postoperative scenario, where in reality a patient is unlikely to shoot again until recovering from the procedure. Shooting form also seemed to play a role, as shots that were considered “poor form” recorded up to 30% higher recoil values than those with “good form”. For these reasons, early results indicate chance of implant loosening due to the forces from shooting firearms is low, especially if the patient is a former experienced shooter who wishes to return to the sport. To view tables/figures, please contact authors directly

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

Purpose. Reverse shoulder prosthesis may lead to scapular notching, caused by attrition of the upper humeral component with scapular neck. We compared the clinical and radiographic results obtained with a SMR prosthesis, which allows a concentric or an eccentric glenosphere to be applied. Patients and methods. 67 patients, mean age 73 years, were treated with reverse prosthesis using concentric and eccentric glenosphere. In patients with concentric glenosphere, the glenosphere extended about 4 mm below the glenoid. The eccentric glenosphere protected the upper glenoid neck by its inferior prolongment. Patients were followed for a mean of 33 months. At final F-U the Constant Score (C.S.) and the score with the Simple Shoulder test (S.S.T.) were calculated. Radiographs were obtained to evaluate the presence of scapular notching, psna (prosthesis-scapular neck angle), pgrd (peg- glenoid rim distance) and DBSNG (distance between scapular neck and glenosfere). Included in this study were patients, as much homogeneous as possible by age and pathology, 25 with concentric (Group I) and 30 with eccentric (Group II) glenosphere, who had a minimum F-U of 24 months. Statistical analysis was performed with a paired test. Results. 25 patients of group I and 26 in group II were available for the study. In Group I mean elevation improved from 78° to 122° and mean abduction from 71° to 98°; in Group II from 66° to 148° and 60° to 115°. External and internal rotations were similar in both groups. 14 (56%) patients of Group I, and none of Group II had scapular notching (p<0.001). CS increased from 38 pt to 69 pt in Group I and from 30 pt to 74 pt in Group II. Conclusions. Low implantation of glenosphere did not eliminate scapular notching. Instead, no notching was detected with eccentric glenosphere, which also increased the ROM. The PSNA, DBSNG, PGRD are reliable measures to predict scapular notching

Introduction. A common phenomenon occurring as a result of reverse total shoulder arthroplasties (RSA) is scapular notching. While bone loss of the scapula may be quantified using radiographic techniques,[1] the material loss on the humeral bearing has not been quantified. Depending on their functional biological activity, a high volume of polyethylene wear particles has been shown to be related to osteolysis, bone loss and ultimately, loosening of implants in other joints.[2] In order to understand the threshold for osteolysis in the shoulder, it is important to have a method that can accurately quantify the amount of material loss. The aim of this research was to (I) create and validate a method for quantifying material loss from a single humeral implant design which can then (II) be used to measure retrieved devices. Methods. Measurement of the surface topography of the implant was completed using coordinate measurement machine (CMM). The resulting point cloud was then imported into MATLAB and run through a custom algorithm to determine the volumetric wear of the humeral liner. Two never implanted humeral liners with an artificially damaged material loss were used for validation purposes. Each component was scanned three times, analyzed using the custom MATLAB program, and compared to gravimetric analysis (Figure 1). Following validation, an IRB-approved database was queried to identify 10 retrieved components of the same design which were then analyzed using the validated method. Results. All average measurements of the never implanted components were within +/- 5 mm. 3. of the gravimetrically determined values, providing a reasonable estimate of the volumetric wear (Figure 1). Ten retrieved components of a single design were analyzed using the same method and material loss ranged from immeasurable (within the accuracy limits) to approximately 90 mm. 3. (Figure 3). One short term duration implant (1.8 mos) exhibited approximately 78 mm. 3. of wear, resulting in a polyethylene dosage of more than 500 mm. 3. /yr. Discussion. The posterior-inferior wear pattern on the rim of these reverse shoulders appears consistent with repetitive scapular impingement. The significant wear of short duration implants indicates that wear associated with scapular notching may progress very quickly, resulting in large dose rates of debris in the joint space. However, the impingement may result in a more abrasive wear mechanism as opposed to an adhesive wear mechanism as seen in other joint wear environments. This may result in different size and shaped polyethylene particles with different biological activity. The algorithms presented in this work can be used to establish a dose-response relationship for scapular notching in RSA

Introduction

Loosening of the baseplate is one of the most common causes of failure in Reverse Shoulder Arthroplasty. To allow osteo-integration to occur and thus provide long-term stability, initial screws fixation plays a pivotal role. In particular, tightening torque and force of nonlocking screws are two parameters that are considered to have a clear impact on implant stability, yet the relation is not fully understood. For this reason, this study aims to define an experimental set-up, to measure force and torque in artificial bone samples of different quality, in order to estimate ranges of optimal surgical values and give guidelines to maximize screw fixation and therefore initial implant stability.

Purpose

With growing attention being paid to quality and cost effectiveness in healthcare, outcome evaluations are becoming increasingly important. This determination can be especially difficult in reverse shoulder arthroplasty (RSA) given the complex pathology and extensive disabilities in this patient population. Several different scoring systems have been developed and validated for use in various shoulder pathologies. The purpose of this study was to assess the use three outcome scores in a population of patients undergoing RSA. We aim to demonstrate the validity of three outcome scores in patients undergoing RSA, and to determine if one score or a combination of scores is superior to others.

Background

There has been increased focus on understanding the risk factors associated with scapular notching in reverse shoulder arthroplasty (RSA). The purpose of this study is to evaluate the effect of scapular morphology and surgical technique on the occurrence of scapular notching using the notching index as a comprehensive predictive tool.

Before reverse shoulder replacement was an option for rotator cuff tear arthropathy the treatment modalities were limited to injections and physical therapy for pain control, arthroscopic debridement with or without biceps tenodesis/tenotomy and hemiarthroplasty. Functional improvement was limited with these treatment options and success for pain control was moderate at best. The destructive nature of the rotator cuff deficient shoulder continued with medialization of the glenoid and erosion of the acromion seen even after replacement with hemiarthroplasty. The end result usually left the patient with a pseudo paralysis of the shoulder region functionally and uncontrolled pain that made later revision with a reverse implant difficult or impossible.

Reverse arthroplasty was released for use in United States in 2004 for rotator cuff tear arthropathy. This initial procedure had a number of related complications that have been improved on over time with changes in implant design and better operative techniques. The long term results with reverse total shoulder arthroplasty have made this the procedure of choice for contained cuff tear arthropathy.

Rotator cuff arthropathy is a challenging problem to treat in many patients whose function remains intact despite pain from arthritis. In recent years, the introduction of reverse shoulder arthroplasty has improved the function and pain in pseudoparalytic shoulders with rotator cuff deficiency. However, significant evidence exists to support the use of alternative surgical and non-surgical treatments for those patients who suffer from the pain of arthritis while maintaining an intact force-couple of the rotator cuff and relatively well preserved function.

Background:. Little is known about scapular kinematics in patients with reverse total shoulder arthroplasty (RTSA). Understanding how RTSA affects shoulder function may help refine its design, use, and rehabilitation strategies. The purpose of this study was to quantify motion in the reverse shoulder. The scapulohumeral rhythm (SHR) of the RTSA shoulder was calculated using 3d-2d image registration techniques. SHR was compared to normal subjects in literature to asses kinematic changes post RTSA. Methods:. 26 subjects were recruited for an institutional review board approved study. Subjects who were ≥ 6 months post unilateral RTSA. Subjects were prompted to do abduction in the coronal plane with and without a 3 lb. weight. Three dimensional to two dimensional image registration techniques were used to derive orientation and position measurements for the humerus and scapula from dynamic x-ray. Tukey Honest differences statistics were used to assess significance differences between groups. Conclusion:. SHR in RTSA subjects was found to be significantly lower than normal subjects found in the literature. Below 30° of abduction RTSA SHR was found to be highly variable from 17: 1–2: 1. Due to the variability results were represented with the range of 30° to max elevation. Above 30° RTSA SHR was found to average to be 1.8: 1 for un-weighted abduction and 1.2 for weighted abduction (Figures 1, 2). RTSA max range of motion (ROM) during weighted trials was significantly lower than un-weighted trials. RTSA SHR standard deviation decreased with increasing elevation. Discussion:. RTSA subjects have significantly modified kinematics from normal subjects. In general RTSA SHR (1.8: 1) was significantly lower than normal (4: 1) subjects found in literature. In mid-range the normal and RTSA SHR is the same (Figure 1). The RTSA SHR is significantly different in lower and higher angles (Figures 1, 2). There is more glenohumeral rhythm in the normal group versus the RTSA group. More scapulothoracic motion was observed in the RTSA group at high levels and low levels of arm elevation. With this understanding of the motion of the reverse shoulder improvements can be made to the design and configuration of the implant to optimize RTSA outcomes

BACKGROUND:

Bony increased-offset reverse shoulder arthroplasty (BIO-RSA) creates a long-necked scapula, providing the benefits of lateralization. Experience with allogenic bone grafting of the glenoid in shoulder arthroplasty is mainly based on its use with total shoulder arthroplasty (TSA). Therefore, our study objectives were: 1) verify if the use of BIO-RSA together with glenoid surface grafting with allogenic bone would provide similar benefits (clinical and functional) as found with autologous bone, 2) determine if allograft could be a good alternative in the absence of (good quality) autograft bone, and 3) to see if the allograft would incorporate with the native glenoid bone.

Despite the high success rates of Reverse Shoulder replacements, complications of instability & scapular notching are a concern. Factors reducing relative motion of implant to underlying bone which include lateral offset to centre of rotation, screw & central peg insertion angle and early osteo-integration are maximized in the Trabecular Metal Reverse total shoulder system. We present clinico-radiological outcomes over 72 months. Analysis of a single surgeon series of 140 Reverse total shoulder replacements in 135 patients was done. Mean age was 72(range 58– 87 yrs); 81 females: 54 males. Indications were Rotator cuff arthropathy {n= 88} (63%); Osteo-arthritis with dysfunctional cuff {n= 22}(15%); post-trauma{n=23} (15%); revision from hemiarthroplasty {n=3} (2.4%) and from surface replacement {n=4} (2.8%). All patients were assessed using pre-operative Constants and Oxford scores and clinical & radiographic reviews with standard X-Rays at 6 weeks, 3, 6,12 months and yearly thereafter. X rays included an AP view in 45 degrees of external rotation and modified axillary view. Inferior Scapular notching using the Nerot-Sirveaux grades and Peg Glenoid Rim Distance were looked into by a consultant musculoskeletal radiologist/ Orthopaedic surgeon/ Senior Fellow (post CCT) or a specialist Trainee (ST4 and above). Pain on the visual analogue scale decreased by 98% (9.1 to 0.8) (p<0.01). Constant score improved by 81.8% (12.4 to 68.1) (p<0.05), Oxford shoulder score by 76.7% (56 to 13) (p<0.05). 95.6% of Humeral stems had no radiolucent lines and 4.4% had < 2mm of lucency. Scapular notching was calculated using Sirveaux grades with Peg scapular base angle distance (PSBA) measurements on PACS with Siemens calibration (grade 1= 4 (2.8%); grade 2 =1; grade 3 =0; grade 4=0). 3.57% showed radiographic signs of scapular notching at 72 months. Range of Peg Glenoid Rim Distance was 1.66 to 2.31 cm. Power analysis showed 65 patients were needed to have an 80% power to detect relation of Peg Glenoid Rim Distance to Scapular notching. A likelihood ratio test from Logistic regression model to check correlation of Peg Glenoid Rim Distance to Scapular notching gave a p value of 0.0005. A likelihood ratio from Logistic regression gave a p value of 0.0004 for Infraglenoid Scapular spurs. Highest incidence of spurring was seen in Reverse Total Shoulder Replacements done for Trauma and lowest in patients who got the procedure for Osteoarthritis. Complications included two glenosphere revisions; two stitch abscesses and two Acromial fractures in patients who had a fall two years after the procedure. Improved surgical outcomes can be attributed to surgical technique and implant characteristics. Trabacular metal promotes early osteointegration which resists shearing action of Deltoid on Glenoid component. This allows early mobilisation. Deltoid split approach preserves integrity of Subscapularis and Acromial osteotomy and lateral clavicle excision improve exposure and prevent Acromion fracture. Positioning the Glenoid component inferiorly on the Glenoid decreases incidence of Scapular notching. Our mid-term validated outcomes are promising with only 3.57% Grade I/II radiographic signs of scapular notching. Long term studies (10 year follow ups) are necessary to confirm its efficacy