Baseplate Fixation Research Articles

The modern use of the extended humeral head (cuff tear arthropathy) hemiarthroplasty.

Today, the treatment of osteoarthritis in the rotator cuff–deficient population is largely dominated by reverse shoulder arthroplasty (RSA). Despite the popularity of and increased familiarity with this procedure, the complication rate of RSA remains significant. An extended humeral head hemiarthroplasty may provide a less invasive alternative for select patients with cuff tear arthropathy (CTA) and preserved glenohumeral active elevation. With the indications for reverse arthroplasty expanding to younger patients, there are concerns about the longevity of this implant, as well as the associated revision burden. In the setting of failed RSA, the bone stock available for glenosphere baseplate fixation can be inadequate for reimplantation. The treatment strategies for complex shoulder deformities and failed RSA are limited by patient-specific issues, such as anatomy and risk factors. In this review, we discuss the potential role of extended humeral head hemiarthroplasty (CTA hemiarthroplasty) as a primary surgical option in select patients (1) who have preserved elevation > 90°, (2) who have maintained stability (intact coracoacromial ligament), and (3) who desire to circumvent the complications associated with RSA. Furthermore, CTA hemiarthroplasty may be used for severe glenoid erosion, for a fragmented acromion, and in the revision setting for failed RSA aimed at a reliable salvage procedure.

Intraoperative navigation and preoperative templating software are associated with increased glenoid baseplate screw length and use of augmented baseplates in reverse total shoulder arthroplasty.

BackgroundPreoperative templating software and intraoperative navigation have the potential to impact baseplate augmentation utilization and increase screw length for baseplate fixation in reverse total shoulder arthroplasty (rTSA). We aimed to assess their impact on the (1) baseplate screw length, (2) number of screws used, and (3) frequency of augmented baseplate use in navigated rTSA.MethodsWe compared 51 patients who underwent navigated rTSA with 63 controls who underwent conventional rTSA at a single institution. Primary outcomes included the screw length, composite screw length, number of screws used, percentage of patients in whom 2 screws in total were used, and use of augmented baseplates.ResultsNavigation resulted in the use of significantly longer individual screws (36.7 mm vs. 30 mm, P < .0001), greater composite screw length (84 mm vs. 76 mm, P = .048), and fewer screws (2.5 ± 0.7 vs. 2.8 ± 1, P = .047), as well as an increased frequency of using 2 screws in total (35 of 51 patients [68.6%] vs. 32 of 63 controls [50.8%], P = .047). Preoperative templating resulted in more frequent augmented baseplate utilization (76.5% vs. 19.1%, P < .0001).ConclusionThe difference in the screw length, number of screws used, and augmented baseplate use demonstrates the evolving role that computer navigation and preoperative templating play in surgical planning and the intraoperative technique for rTSA.

Mid-term outcomes of reverse shoulder arthroplasty using the alternate scapular line baseplate orientation for glenoid bone loss

BackgroundGlenoid-sided bone loss poses a challenge when performing reverse shoulder arthroplasty. Placing the baseplate in an anteverted position along the alternate scapular line is an option when dealing with glenoid erosion or cavitary defects. Although this allows for stable initial baseplate fixation, questions remain about the effects of placing the baseplate in a more anteverted position relative to the standard glenoid center line. The purpose of this study was to evaluate the mid-term outcomes of patients treated with reverse shoulder arthroplasty using an alternate scapular line baseplate orientation in the setting of glenoid bone loss. Materials and methodsFrom September 2007 to March 2014, 71 patients underwent reverse shoulder arthroplasty using the alternate scapular line baseplate orientation and had a minimum of 5 years of follow up. Patients with no prior surgery, prior nonarthroplasty surgery, and prior arthroplasty surgery were included in this analysis. Patients were followed clinically (American Shoulder and Elbow Surgeons score, Simple Shoulder Test score, range of motion analysis, patient satisfaction) as well as radiographically, with data recorded at the 2-year point and their last recorded follow-up after a minimum of 60 months. ResultsAt the final follow-up point (average 78 months) patients had maintained their improvement in American Shoulder and Elbow Surgeons score (75 [P<.0001]), Simple Shoulder Test score (7.8 [P < .0001]), forward elevation (1300 [P < .0001]), external rotation (310 [P < .0001]) with no change in internal rotation (62% with full IR [P = 1.0]). No significant deterioration in outcome scores or motion was noted between the 2-year and final follow-up time point. At final follow-up, 92% remained satisfied with their outcome. There was a 7% complication rate (3 acromial fractures, 1 hematoma, 1 dislocation), with 1 patient requiring revision surgery secondary to instability. ConclusionUtilizing the alternate scapular line baseplate orientation in cases with glenoid bone loss resulted in clinical improvements with no deterioration in outcome scores, range of motion or patient satisfaction at a minimum of 5 years of follow-up. Anteverting the baseplate in this position allowed for stable glenoid-sided fixation with no mechanical failures of the baseplate and did not appear to compromise the patient's functional outcomes. In patients with significant glenoid bone loss, where adequate bone stock along the standard glenoid line may be in question, use of the alternate scapular line for baseplate orientation is an effective option yielding sustained clinical improvements and a low rate of complications. Level of evidenceLevel IV; Case Series; Treatment Study

Baseplate Options for Reverse Total Shoulder Arthroplasty.

Baseplate fixation has been known to be the weak link in reverse total shoulder arthroplasty (RTSA). A wide variety of different baseplates options are currently available. This review investigates the recent literature to present the reader with an overview of the currently available baseplate options and modes of fixation. The main elements that differentiate baseplates are the central fixation element, the size of the baseplate, the shape, the backside geometry, whether or not an offset central fixation exists, the number of peripheral screws, and the availability of peripheral augmentation. The wide array of baseplate options indicates that no particular design has proven superiority. As such, surgeons should be aware of their options and choose an implant that the surgeon is comfortable with and one that best suits the individual patient anatomy. With the growing number of RTSA procedures and registries with long-term follow-up, future investigations will hopefully delineate the ideal baseplate design to optimize survivorship.

Pre-Operative CT-Based Planning Integrated With Intra-Operative Navigation in Reverse Shoulder Arthroplasty: Data Acquisition and Analysis Protocol, and Preliminary Results of Navigated Versus Conventional Surgery.

Reverse total shoulder arthroplasty (RSA) successfully restores shoulder function in different conditions. Glenoid baseplate fixation and positioning seem to be the most important factors influencing RSA survival. When scapular anatomy is distorted (eccentric osteoarthrirtis, rotator cuff arthropathy), optimal baseplate positioning and secure screw purchase can be challenging. The aim of this study was to evaluate whether CT-based pre-operative planning, integrated with intra-operative navigation could improve glenoid baseplate fixation and positioning by increasing screw length, reducing number of screws required to obtain fixation and increasing the use of augmented baseplate to gain the desired positioning. Twenty patients who underwent navigated RSA were compared retrospectively with 20 patients operated on with a conventional technique. All the procedures were performed by the same surgeon, using the same implant. Mean screw length was significantly longer in the navigation group (35.5 ± 4.4 mm vs 29.9 ± 3.6 mm; p = .001). Significant higher rate of optimal fixation using 2 screws only (17 vs 3 cases, p = .019) and higher rate of augmented baseplate usage (13 vs 4 cases, p = .009) was also present in the navigation group. Pre-operative CT-based planning integrated with intra-operative navigation can improve glenoid component positioning and fixation, possibly leading to an improvement of RSA survival.

Effect of RSA glenoid baseplate central fixation on micromotion and bone stress

BackgroundIn reverse shoulder arthroplasties (RSA), osseous in-growth is promoted if glenoid micromotion does not exceed 150 μm. The purpose of this study was to determine whether the configuration of central fixation for RSA glenoid baseplates reduces implant micromotion or changes scapula bone stresses.MethodsUsing finite element analysis, glenoid baseplate fixation was tested in a cohort of 3 male and 2 female patients who were to undergo RSA. Computer models were created for 3 different RSA glenoid baseplate and 84 glenosphere designs, a central threaded peg (1 variant, D-TP), a central unthreaded peg (2 variants, I- 85 P(15) and I-P(25)), and a central peg with a screw (2 variants, A-PS and I-PS). A compressive and shear force of 756 N was distributed across the glenosphere with the scapula anchored.ResultsDisplacement was within 20-130 μm at the glenosphere baseplate-bone interface for all baseplates. The glenospheres with unthreaded pegs had intermediate displacement values (I-P(15): median, 89 μm; range, 32-112 μm; and I-P(25): median, 93 μm; range, 31-109 μm). The von Mises stresses were 1.8-7.0 MPa within cortical bone and 0.6-1.6 MPa within trabecular bone. Cortical bone stresses were similar with unthreaded pegs (I-P(15): median, 4.2 MPa; range, 1.8-6.0 MPa; and I-P(25): median, 4.2 MPa; range, 1.8-6.1 MPa), whereas mean trabecular stresses were similar for all configurations.ConclusionsAll configurations yielded adequate stability, with micromotions being below 150 μm. The unthreaded pegged designs provided a valid alternative to the stable threaded pegged convex baseplates in terms of micromotions and bone stresses.

Risk of suprascapular nerve injury during glenoid baseplate fixation for reverse total shoulder arthroplasty: a cadaveric study

Reverse total shoulder arthroplasty (rTSA) is an effective treatment for patients with advanced rotator cuff arthropathy. During implantation of the glenoid baseplate, screws are inserted through the glenoid face into the scapular body to achieve adequate fixation. Placement of peripheral baseplate screws in the superior and posterior glenoid may increase the risk of injury to the suprascapular nerve (SSN). The purpose of this cadaveric study was to evaluate the risk of SSN injury with placement of baseplate screws in the superior and posterior direction. Twelve cadaveric shoulders were implanted with glenoid baseplates. A bicortical 44-mm screw was placed in both the superior and posterior glenoid baseplate screw holes. Following implantation, the SSN was dissected and visualized through a posterior shoulder approach. The distance from the tip of the screws to the SSN and the distance from the screw's scapular exiting hole to the SSN was recorded. Average distances were calculated for each measurement. The superior screw contacted the SSN in 8 of the 12 specimens (66%). For the superior screw, the average distance from the exiting point in the scapula to the SSN was 9.2 ± 6.3 mm, with the shortest distance being 3.9 mm. The posterior screw contacted the SSN in 6 of 12 specimens (50%). For the posterior screw, the average distance from the exiting point to the SSN was 8.9 ± 3.8 mm, with the shortest distance to the nerve being 2.2 mm. Placement of the superior and posterior screws in the glenoid baseplate during rTSA risks injury to the SSN. The safe zone for superior- and posterior-directed baseplate screw is <2 mm from its exiting point on the scapula. Therefore, precise measurements of screw lengths in this area is important in avoiding injury to the SSN.

First Place Award: A quantitative analysis of the effect of glenoid bone volume on baseplate failure in reverse total shoulder arthroplasty in patients with inflammatory arthritis: a retrospective case control study

Background: The purpose of this study was to determine and compare the glenoid vault bone volumes in patients undergoing reverse total shoulder arthroplasty (RTSA) for inflammatory arthritis to determine if a threshold exists where baseplate fixation is at risk for failure. Methods: Fourteen patients who had primary RTSA for inflammatory arthritis were included in this study; 10 had humeral head autografting to augment glenoid deficiency. Four patients experienced baseplate failure with component pull-out from the glenoid. Preoperative glenoid vault volume was measured on CT images. Results: The average glenoid vault bone volumes were significantly different between failures and nonfailures for both men and women. The average volume in women with baseplate failure was 3.5 cm3, while the average nonfailure volume in women was 8.6 cm3 (P=0.03). The average glenoid volume in men with baseplate failure was 11.8 cm3, while the average volume in men without failure was 18.3 cm3 (P=0.02). There were no baseplate failures in men with glenoid vault volumes greater than 14 cm3 or in women with volumes greater than 5 cm3. Conclusions: Patients with baseplate failure after RTSA for inflammatory arthritis had significantly lower average glenoid vault volumes than their gender-specific counterparts without failure. These findings suggest a level of glenoid volume below which baseplate fixation is potentially compromised: 14 cm3 in men and 5 cm3 in women. Level of Evidence: Level III.

Mid-term outcomes of reverse shoulder arthroplasty using the alternative center line for glenoid baseplate fixation: a case-controlled study

A critical step in reverse shoulder arthroplasty (RSA) is glenoid baseplate fixation. In cases of glenoid bone loss, use of the anatomic glenoid center line may not provide sufficient bone support for fixation. Anteversion along the alternative center line is a described method for achieving baseplate fixation in these cases. However, concern remains regarding negative consequences in functional outcomes and complications. The purpose of this study was to compare the outcomes of RSA using the anatomic or alternative center line. We performed a retrospective case-controlled study of patients who underwent RSA between November 2006 and August 2017, performed by a single surgeon, with a minimum of 2 years' follow-up. Patients treated with the anatomic center-line technique for baseplate fixation were matched 3:1 based on sex, indication for surgery, and age with patients treated with the alternative center-line technique. Patient-reported outcome measures (PROMs), active range of motion, and the ability to perform functional tasks of internal rotation were compared. Evaluations of the most recently obtained radiographs focused on acromial fractures, scapular notching, and glenoid loosening. A total of 88 patients (66 in anatomic center-line group and 22 in alternative group) participated in the matched analysis, with a mean age of 74.2 years (range, 58-89 years) and mean follow-up period of 53 months (range, 24-130 months). At the final follow-up, we found no significant differences in PROMs, including the Simple Shoulder Test score (P = .829), American Shoulder and Elbow Surgeons score (P = .601), visual analog scale pain score (P = .068), and Single Assessment Numeric Evaluation score (P = .674). Moreover, both the overall improvements in these PROMs and all active motions and functional tasks of internal rotation were not different. No radiographic evidence of glenoid loosening was found in either group, and 2 patients in each cohort (3% of the anatomic group and 9% of the alternative group) experienced an acromial fracture. Low-grade scapular notching developed in 15.2% of the anatomic group and 18.2% of the alternative center line group (P = .736). The alternative center line can be used for baseplate fixation in the settingof glenoid bone loss and leads to similar patient outcomes and functional tasks of internal rotation, as well as a low rate of complications, compared with the anatomic center line following RSA.

Mid-Term Outcomes of Reverse Shoulder Arthroplasty Using the Alternate Scapular Line Baseplate Orientation for Glenoid Bone Loss

Glenoid sided bone loss poses a challenge when performing reverse shoulder arthroplasty. Achieving stable baseplate fixation is paramount in cases where glenoid bone is deficient. Placing the baseplate in an anteverted position along the alternate scapular line, in order to engage the dense pillar of bone where the scapular spine meets the scapular body, is an option when dealing with glenoid erosion or cavitary defects. Although this allows for stable initial baseplate fixation, questions remain about the effects of placing the baseplate in a more anteverted position relative to the standard glenoid center line. The purpose of this study was to evaluate the mid-term outcomes of patients treated with reverse shoulder arthroplasty (RSA) using an alternate scapular line baseplate orientation in the setting of glenoid bone loss with a minimum of five years of follow up.

Relationship Between Insertion Torque and Compression Strength in the Reverse Total Shoulder Arthroplasty Baseplate.

Reverse shoulder arthroplasty is a well-established procedure, however, there is limited data in the literature regarding adequate insertion torque and the resulting compression for glenoid baseplate fixation. In this biomechanical study, we evaluated the relationship between insertion torque and baseplate compression by simultaneously measuring the insertion torque and axial compressive forces generated by two reverse shoulder arthroplasty baseplates with central screw design. Three different bone surrogates were chosen to mimic clinical scenarios where differences in compression achieved during baseplate insertion may exist due to varying bone quality. Epoxy resin sheets were combined with the bone surrogates to simulate the glenoid vault. A digital torque gauge was used to measure insertion torque applied to the baseplate, while compression data were collected continuously from a load cell. A strong positive correlation was found between baseplate compression and insertion torque. Among the lower density bone surrogates, neither baseplate design reached maximum insertion torque (6.8 Nm) due to material strip-out. This phenomenon did not occur in denser bone surrogates. Both baseplate designs experienced a significant increase in mean baseplate compression as insertion torque increased and were found to behave similar in the denser bone surrogates. The results presented here suggest that larger compressive forces can be achieved with an increase in insertion torque in denser bone surrogates, but caution must be used when trying to achieve fixation in poor-quality bone. Clinically, this could be useful preoperatively to minimize baseplate failure, and in further studies regarding baseplate design for improved initial fixation and stability. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:871-879, 2020.

Early radiographic failure of reverse total shoulder arthroplasty with structural bone graft for glenoid bone loss

Structural glenoid bone grafting in reverse total shoulder arthroplasty (RSA) has previously been reported to have good functional outcomes and low complication rates. We have observed different complication rates and hypothesized that baseplate fixation and severity of deformity may be predictors of early failure. We retrospectively identified 44 patients who underwent RSA with structural bone grafting for glenoid bone defects. All patients had preoperativeand postoperative (Grashey and axillary) radiographs at a minimum of 1 year after surgery and within 3 months of surgery for evaluation of implant and graft positioning. Clinical data and outcome scores were collected at the same intervals. There were 61% females and 39% males, with an average age of 74 ± 8 years at the time of surgery. The median final radiographic follow-up was 20 months, with 37 primary RSA and 7 revision RSA. Graft resorption was found in 11 of 44 patients (25%), and radiographic failure was found in 11 of 44 patients (25%) at a median of 8 months (range 3-51 months). Forward elevation, American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form, Single Assessment Numeric Evaluation (SANE), and Simple Shoulder Test (SST) scores all significantly improved postoperatively (P < .0001). Radiographic baseplate failure was associated with graft resorption (P = .002), more retroversion correction (P = .02), and worse SANE scores at final follow-up (P = .01). RSA with structural bone graft improved range of motion and function, but there was a larger than previously reported baseplate loosening rate. This early radiographic loosening appeared to be associated with graft resorption, retroversion correction, and worse outcome scores.

Central screw use delays implant dislodgement in osteopenic bone but not synthetic surrogates: A comparison of reverse total shoulder models

Adequate glenoid baseplate fixation in reverse total shoulder arthroplasty (rTSA) is important to achieve, but may prove challenging in the context of glenoid bone loss or osteopenia. Current rTSA testing standards rely upon synthetic bone surrogates, but it is unclear if these models accurately recapitulate the mechanics of osteoporotic bone. Additionally, it also unknown if the use of a central screw effectively provides resistance to micromotion in the milieu of poor quality bone. The purpose of this experiment was to create a novel cyclic load test protocol that elicited clinically relevant failures, so that comparisons of relative motion between baseplates and bones could be made with: (1) synthetic bones and poor quality cadaveric bones, and (2) the use or omission of a central screw. rTSA components were implanted into cadaveric and synthetic bones with and without a central screw. To model a range of loads that may be experienced during abduction, increasing cyclic loads were applied to shoulder joints in 30° of humeral abduction. Cycles and loads prior to permanent deformation exceeding 150 µm, 1 mm, and joint failure were determined using measurements from the test frame and from 3-D motion analysis. Synthetic bones demonstrated significantly more resistance to micromotion in comparison to cadaveric bones. Use of the central screw improved resistance to dislodgement, which was only observed in the cadaveric specimens. This study highlights the need for biomechanical testing with cadaveric specimens, especially when assessing osteopenic or osteoporotic populations.

Rationale for Small Glenoid Baseplate: Position of Central Cage within Glenoid Vault (Exactech® Equinoxe® Reverse System)

BackgroundGlenoid baseplate location is important to good clinical outcomes of reverse total shoulder arthroplasty (RTSA). The glenoid vault is the determining factor for glenoid baseplate location, but, to date, there are no reports on the effect of central cage location within the glenoid vault on RTSA outcomes when using the Exactech® Equinoxe® Reverse System. The purpose of this study was to determine the appropriate cage location in relation to the glenoid vault and monitor for vault and/or cortex penetration by the cage.MethodsData were retrospectively collected from the Samsung Medical Center (SMC) and Seoul National University Bundang Hospital (SNUBH). Patients who underwent RTSA between November 2016 and February 2018 were enrolled. Glenoid vault depth, central cage location within the vault were examined. Inferior glenoid rim–center distance, inferior glenoid rim–cage distance, and center–cage center distances were collected.ResultsTwenty-two patients were enrolled. Three SNUBH patients had inappropriate central cage fixation (33.3%) versus 4 SMC patients (30.8%). All cage exposures were superior and posterior to the glenoid vault. Mean center–cage distance was 5.0 mm in the SNUBH group and 5.21 mm in the SMC group. Center–prosthesis distance was significantly longer in the inappropriate fixation group than in the appropriate fixation group (p<0.024).ConclusionsTo ensure appropriate glenoid baseplate fixation within the glenoid vault, especially in a small glenoid, the surgeon should place the cage lower than usually targeted, and it should overhang the inferior glenoid rim.

Factors contributing to glenoid baseplate micromotion in reverse shoulder arthroplasty: a biomechanical study

Reverse shoulder arthroplasty (RSA) is typically performed in patients with cuff tear arthropathy. A common type of RSA baseplate has a central peg and 4 peripheral screws inserting into the glenoid surface. Baseplate failure is a significant postoperative complication that reduces prosthetic longevity and usually requires revision surgery. This study evaluated the contribution of mechanical factors on initial baseplate fixation. This study simulated glenoid baseplate loading in a RSA. A half-fractional factorial design was used to test 5 factors: bone density (160 or 400 kg/m3), screw length (18 or 36 mm), number of screws (2 or 4), screw angle (neutral or diverging), and central peg length (13.5 or 23.5 mm). Trials were cyclically loaded at a 60° angle with 500 N for 1000 cycles. Micromotion at 4 peripheral screw positions was analyzed using a multifactorial analysis of variance (P < .05). We found an increase in micromotion with 3 scenarios: (1) lower bone density at all screw positions; (2) shorter central peg length at the inferior, superior and anterior screws; and (3) shorter screw length at the inferior and anterior screws. There were interactions between bone density and screw length at the inferior and anterior screws and between bone density and central peg length at the inferior, superior, and anterior screws. Greater bone density, a longer central peg, and longer screws provide improved initial glenoid fixation in an RSA, whereas the number of screws, and the angle of screw insertion do not. These findings may help minimize baseplate failure and revision operations.

Stay Out of Trouble in Reverse Shoulder Arthroplasty - Award Winner

This video discusses the key steps a surgeon should follow to perform safe and successful primary reverse shoulder arthroplasty. The first step is to select the appropriate candidate for reverse shoulder arthroplasty and to ensure adequate preoperative preparation. CT is necessary to evaluate glenoid version, identify possible glenoid bone defects, and determine the eventual need for patient-specific instrumentation. Proper patient positioning is essential to avoid intraoperative patient shifting and neck stretching and to allow free range of shoulder motion. The deltopectoral or anterolateral approach can be used, and the surgeon should understand the advantages and disadvantages of both approaches. Retractors should be placed to obtain optimal joint visualization with caution exercised to avoid neurovascular structures. During preparation of the humeral head, the surgeon must be mindful of possible proximal migration of the humerus, the subjective variability of humeral version, and the patient's expectations for range of motion. Glenoid exposure is critical and must be performed meticulously. The use of appropriate instruments, release of the long head of the triceps, release of the posterior capsule and eventual revision of the humeral osteotomy allow adequate visualization of the glenoid surface and neck. Drawing the anatomic axes of the glenoid aids in placement of the guidewire in the glenoid, which should be inserted in the center of the neck slightly inferiorly and with some inferior tilt. To achieve optimal baseplate fixation, the screws should be directed toward the three columns of the scapula. The use of baseplates with variable-angle locking screws should be considered to freely orientate the screws. The suprascapular nerve must be avoided during posterior screw insertion. Finally, implant stability is assessed by evaluating shoulder range of motion and tension of the deltoid and conjoint tendons. Watch the video trailer: https://links.lww.com/JAAOS/A158.

Incidence and risk factors for aseptic baseplate loosening of reverse total shoulder arthroplasty

Aseptic glenoid baseplate loosening (AGBL) is a catastrophic complication after reverse total shoulder arthroplasty (RTSA). Our goals were to determine the incidence of AGBL in patients who underwent RTSA and identify risk factors for AGBL after RTSA. We analyzed 202 shoulders that underwent primary or revision RTSA using 1 implant system and evaluated baseplate loosening at a minimum 2-year follow-up. The associations between AGBL and the following variables were investigated: patient age, sex, primary vs. revision RTSA, scapular notching, use of bone graft, and type of baseplate screw fixation. AGBL occurred in 6 shoulders (3.0%). The incidence of AGBL after revision RTSA (10%) was significantly higher than that after primary RTSA (1.2%; P = .014). There were significant associations between AGBL and the use of bone graft and the use of nonlocking screws. Scapular notching, glenosphere center-of-rotation offset, patient age, and sex were not associated with AGBL. Multiple logistic regression analysis showed that the use of all peripheral nonlocking 3.5-mm screws (odds ratio, 10.6; 95% confidence interval, 1.1- 39) and the use of bone graft (odds ratio, 7.5; 95% confidence interval, 1.9-30) were independent risk factors for AGBL. The rate of baseplate failure after primary RTSA is low (1.2%) but is significantly higher after revision RTSA (10%). Major risk factors for baseplate failure are the use of all 3.5-mm nonlocking screws for peripheral baseplate fixation and the use of a bone graft to address deficiencies in bony support beneath the baseplate.

Reverse total shoulder arthroplasty using helical blade to optimize glenoid fixation and bone preservation: preliminary results in thirty five patients with minimum twoyear follow-up.

Glenoid loosening is a common cause of reverse total shoulder arthroplasty (RTSA) failure, and grafting of the glenoid is often required for revision due to bone loss due to the central peg in most glenoid baseplates. Helical blades have been used in the hip to optimize bone fixation in proximal femoral fracture. This study presents the initial results of specifically designed helical blade in the shoulder to optimize glenoid bone fixation and preservation as part of RTSA. Thirty-five patients underwent RTSA with glenoid helical blade fixation. An uncemented glenoid baseplate was used with a central helical blade partially coated with hydroxyapatite and two or three screws. Outcome analysis was performed pre-operatively and at twoyears. All patients were satisfied with the results and significant improvement was observed in functional outcome scores between baseline and final follow-up. There was a single intra-operative undisplaced glenoid fracture which did not compromise the baseplate fixation. There was no radiographic evidence of loosening or radiolucencies around the helical blade. The helical blade provides a satisfactory primary fixation. Because of its length (21mm), care should be taken in cases of pre-existing bone loss or sclerotic bone to avoid glenoid fracture or anterior cortical perforation. Helical blade has the potential to facilitate glenoid implant revision by preserving the glenoid bone stock.

Glenoid morphology and the safe zone for protecting the suprascapular nerve during baseplate fixation in reverse shoulder arthroplasty.

The purpose of this study was to investigate glenoid morphology and define the safe zone for protecting the suprascapular nerve baseplate screw during baseplate fixation in reverse shoulder arthroplasty (RSA) in a Chinese population. Shoulder computed tomography (CT) scans from 56 subjects were retrospectively reviewed. Three-dimensional (3D) reconstruction was performed using Mimics software, and corresponding bony references were used to evaluate glenoid morphology. To standardize evaluation, the coronal scapular plane was defined. Safe fixation distances and screw placements were investigated by constructing a simulated cutting plane of the baseplate during RSA. Mean glenoid height was 35.83±2.95mm, and width was 27.32±2.78mm, with significant sexual dimorphism (p<0.01). According to the cutting plane morphology, the average baseplate radius was 13.84±1.34mm. The distances from the suprascapular notch and from two bony reference points at the base of the scapular spine to the cutting plane were 30.27±2.77mm, 18.39±1.67mm and 16.52±1.52mm, respectively, with a gender-related difference. Based on the clock face indication system, the danger zone caused by the suprascapular nerve projection was oriented between the two o'clock and eight o'clock positions in reference to the right shoulder. Glenoid size and the safe zone for screw fixation during RSA were characterized in a Chinese population. Careful consideration of baseplate fixation and avoidance of suprascapular nerve injury are important for improved clinical outcome.

Reverse total shoulder glenoid baseplate stability with superior glenoid bone loss

Superior wear of the glenoid bone is common in patients with rotator cuff arthropathy. This can become a treatment challenge for patients who require shoulder arthroplasty. In reverse shoulder arthroplasty (RSA), glenoid bone loss may affect the stability of baseplate fixation. The primary purpose of this biomechanical laboratory study was to assess the initial fixation stability of RSA glenosphere baseplates in the presence of variable amounts of superior glenoid bone loss. High-density solid rigid polyurethane foam (30 pounds/cubic foot) was machined to model the glenoid with variable superior defects that provided different levels of support (100%, 90%, 75%, and 50%) for the glenosphere baseplate. The samples were cyclically loaded (0-750 N at 1 Hz for 5000 cycles) at a 60° glenohumeral angle. The micromotion and migration of the baseplate were calculated from displacement data captured during the loading tests with an array of 3 linear variable differential transformers mounted around the baseplate. Micromotion was significantly greater in samples with 50% defects compared with those with smaller defects. Migration was significantly greater after testing for all defect sizes. Initial fixation of RSA glenosphere baseplates was significantly reduced in models with 50% bone loss on the superior edge compared with models with less bone loss in this high-density bone foam model.