Determining proper joint tension in reverse total shoulder arthroplasty (rTSA) can be a challenging task for shoulder surgeons. Often, this is a subjective metric learned by feel during fellowship training with no real quantitative measures of what proper tension encompasses. Tension too high can potentially lead to scapular stress fractures and limitation of range of motion (ROM), whereas tension too low may lead to instability. New technologies that detect joint load intraoperatively create the opportunity to observe rTSA joint reaction forces in a clinical setting for the first time. The purpose of this study was to observe the differences in rTSA loads in cases that utilized two different humeral liner sizes. Ten different surgeons performed a total of 37 rTSA cases with the same implant system. During the procedure, each surgeon reconstructed the rTSA implants to his or her own preferred tension. A wireless load sensing humeral liner trial (VERASENSE for Equinoxe, OrthoSensor, Dania Beach, FL) was used in lieu of a traditional plastic humeral liner trial to provide real-time load data to the operating surgeon during the procedure. Two humeral liner trial sizes were offered in 38mm and 42mm curvatures and were selected each case based on surgeon preference. To ensure consistent measurements between surgeons, a standardized ROM assessment consisting of four dynamic maneuvers (maximum internal to external rotation at 0°, 45°, and 90° of abduction, and a maximum flexion/extension maneuver) and three static maneuvers (arm overhead, across the body, and behind the back) was completed in each case. Deidentified load data in lbf was collected and sorted based on which size liner was selected. Differences in means for minimum and maximum load values for the four dynamic maneuvers and differences in means for the three static maneuvers were calculated using 2-tailed unpaired t-tests.INTRODUCTION
METHODS
Acromial and scapular fractures are a rare but difficult complication with reverse total shoulder arthroplasty (rTSA), with an incidence rate reported from 1–10%. The risk factors associated with these fractures types is largely unknown. The goal of this study is to analyze the clinical outcomes, demographic and comorbidity data, and implant sizing and surgical technique information from 4125 patients who received a primary rTSA with one specific prosthesis (Equinoxe, Exactech, Inc) and were sorted based on the radiographic documentation of an acromial and/or scapula fracture (ASF) to identify factors associated with this complication. 4125 patients (2652F/1441M/32 unspecified; mean age: 72.5yrs) were treated with primary rTSA by 23 orthopaedic surgeons. Revision and fracture reverse arthroplasty cases were excluded. The radiographic presence of each fracture was documented and classified using the Levy classification method. 61 patients were identified as having ASF, 10 patients had fractures of the Type 1, 32 patients had Type 2, and 18 patients had Type 3 fractures according to Levy's classification. One fracture was not classifiable. Pre-op and post-op outcome scoring, ROM as well as demographic, comorbidity, implant, and surgical technique information were evaluated for these 61 patients and compared to the larger cohort of patients to identify any associations. A two-tailed, unpaired t-test identified differences (p<0.05).Introduction
Methods
Machine learning is a relatively novel method to orthopaedics which can be used to evaluate complex associations and patterns in outcomes and healthcare data. The purpose of this study is to utilize 3 different supervised machine learning algorithms to evaluate outcomes from a multi-center international database of a single shoulder prosthesis to evaluate the accuracy of each model to predict post-operative outcomes of both aTSA and rTSA. Data from a multi-center international database consisting of 6485 patients who received primary total shoulder arthroplasty using a single shoulder prosthesis (Equinoxe, Exactech, Inc) were analyzed from 19,796 patient visits in this study. Specifically, demographic, comorbidity, implant type and implant size, surgical technique, pre-operative PROMs and ROM measures, post-operative PROMs and ROM measures, pre-operative and post-operative radiographic data, and also adverse event and complication data were obtained for 2367 primary aTSA patients from 8042 visits at an average follow-up of 22 months and 4118 primary rTSA from 11,754 visits at an average follow-up of 16 months were analyzed to create a predictive model using 3 different supervised machine learning techniques: 1) linear regression, 2) random forest, and 3) XGBoost. Each of these 3 different machine learning techniques evaluated the pre-operative parameters and created a predictive model which targeted the post-operative composite score, which was a 100 point score consisting of 50% post-operative composite outcome score (calculated from 33.3% ASES + 33.3% UCLA + 33.3% Constant) and 50% post-operative composite ROM score (calculated from S curves weighted by 70% active forward flexion + 15% internal rotation score + 15% active external rotation). 3 additional predictive models were created to control for the time required for patient improvement after surgery, to do this, each primary aTSA and primary rTSA cohort was subdivided to only include patient data follow-up visits >20 months after surgery, this yielded 1317 primary aTSA patients from 2962 visits at an average follow-up of 50 months and 1593 primary rTSA from 3144 visits at an average follow-up of 42 months. Each of these 6 predictive models were trained using a random selection of 80% of each cohort, then each model predicted the outcomes of the remaining 20% of the data based upon the demographic, comorbidity, implant type and implant size, surgical technique, pre-operative PROMs and ROM measures inputs of each 20% cohort. The error of all 6 predictive models was calculated from the root mean square error (RMSE) between the actual and predicted post-op composite score. The accuracy of each model was determined by subtracting the percent difference of each RMSE value from the average composite score associated with each cohort.Introduction
Methods
3D preoperative planning software for anatomic and reverse total shoulder arthroplasty (ATSA and RTSA) provides additional insight for surgeons regarding implant selection and placement. Interestingly, the advent of such software has brought previously unconsidered questions to light on the optimal way to plan a case. In this study, a survey of shoulder specialists from the American Shoulder and Elbow Society (ASES) was conducted to examine thought patterns in current glenoid implant selection and placement. 172 ASES members completed an 18-question survey on their thought process for how they select and place a glenoid implant for both ATSA and RTSA procedures. Data was collected using a custom online Survey Monkey survey. Surgeon answers were split into three cohorts based on their responses to usage of 3D preoperative planning software: high users, seldom users, and non-users. Data was analyzed for each cohort to examine differences in thought patterns, implant selection, and implant placement.INTRODUCTION
METHODS
The advent of CT based 3D preoperative planning software for reverse total shoulder arthroplasty (RTSA) provides surgeons with more data than ever before to prepare for a case. Interestingly, as the usage of such software has increased, further questions have appeared over the optimal way to plan and place a glenoid implant for RTSA. In this study, a survey of shoulder specialists from the American Shoulder and Elbow Society (ASES) was conducted to examine thought patterns in current RTSA implant selection and placement. 172 ASES members completed an 18-question survey on their thought process for how they select and place a RTSA glenoid implant. Data was collected using a custom online Survey Monkey survey. Surgeon answers were split into two cohorts based on number of arthroplasties performed per year: between 0–75 was considered low volume (LV), and between 75–200+ was considered high volume (HV). Data was analyzed for each cohort to examine differences in thought patterns, implant selection, and implant placement.INTRODUCTION
METHODS
3D preoperative planning software for anatomic total shoulder arthroplasty (ATSA) provides surgeons with increased ability to visualize complex joint relationships and deformities. Interestingly, the advent of such software has seemed to create less of a consensus on the optimal way to plan an ATSA rather than more. In this study, a survey of shoulder specialists from the American Shoulder and Elbow Society (ASES) was conducted to examine thought patterns in current ATSA implant selection and placement. 172 ASES members completed an 18-question survey on their thought process for how they select and place an ATSA glenoid implant. Data was collected using a custom online Survey Monkey survey. Surgeon answers were split into two cohorts based on number of arthroplasties performed per year: between 0–75 was considered low volume (LV), and between 75–200+ was considered high volume (HV). Data was analyzed for each cohort to examine differences in thought patterns, implant selection, and implant placement.INTRODUCTION
METHODS
Over the last decade, sensor technology has proven its benefits in total knee arthroplasty, allowing the quantitative assessment of tension in the medial and lateral compartment of the tibiofemoral joint through the range of motion (VERASENSE, OrthoSensor Inc, FL, USA). In reversal total shoulder arthroplasty, it is well understood that stability is primarily controlled by the active and passive structures surrounding the articulating surfaces. At current, assessing the tension in these stabilizing structures remains however highly subjective and relies on the surgeons’ feel and experience. In an attempt to quantify this feel and address instability as a dominant cause for revision surgery, this paper introduces an intra-articular load sensor for reverse total shoulder arthroplasty (RTSA). Using the capacitive load sensing technology embedded in instrumented tibial trays, a wireless, instrumented humeral trial has been developed. The wireless communication enables real-time display of the three-dimensional load vector and load magnitude in the glenohumeral joint during component trialing in RTSA. In an in-vitro setting, this sensor was used in two reverse total shoulder arthroplasties. The resulting load vectors were captured through the range of motion while the joint was artificially tightened by adding shims to the humeral tray.Introduction & Aims
Method
Preoperative planning software for anatomic total shoulder arthroplasty (ATSA) allows surgeons to virtually perform a reconstruction based off 3D models generated from CT scans of the glenohumeral joint. The purpose of this study was to examine the distribution of chosen glenoid implant as a function of glenoid wear severity, and to evaluate the inter-surgeon variability of optimal glenoid component placement in ATSA. CT scans from 45 patients with glenohumeral arthritis were planned by 8 fellowship trained shoulder arthroplasty specialists using a 3D preoperative planning software, planning each case for optimal implant selection and placement. The software provided three implant types: a standard non-augmented glenoid component, and an 8° and 16° posterior augment wedge glenoid component. The software interface allowed the surgeons to control version, inclination, rotation, depth, anterior- posterior and superior-inferior position of the glenoid components in 1mm and 1° increments, which were recorded and compared for final implant position in each case.INTRODUCTION
METHODS
Preoperative planning software for reverse total shoulder arthroplasty (RTSA) allows surgeons to virtually perform a reconstruction based off 3D models generated from CT scans of the glenohumeral joint. While anatomical studies have defined the range of normal values for glenoid version and inclination, there is no clear consensus on glenoid component selection and position for RTSA. The purpose of this study was to examine the distribution of chosen glenoid implant as a function of glenoid wear severity, and to evaluate the inter-surgeon variability of optimal glenoid component placement in RTSA. CT scans from 45 patients with glenohumeral arthritis were planned by 8 fellowship trained shoulder arthroplasty specialists using a 3D preoperative planning software, planning each case for optimal implant selection and placement. The software provided four glenoid baseplate implant types: a standard non-augmented component, an 8° posterior augment wedged component, a 10° superior augment wedged component, and a combined 8° posterior and 10° superior wedged augment component. The software interface allowed the surgeons to control version, inclination, rotation, depth, anterior-posterior and superior-inferior position of the glenoid components in 1mm and 1° increments, which were recorded and compared for final implant position in each case.INTRODUCTION
METHODS
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. 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).Introduction
Methods
The clinical impact of radiolucent glenoid lines is controversial, where the presence of a radiolucent glenoid lines has been suggested to be an indicator of clinical glenoid loosening. The goal of this database analysis is to quantify and compare the pre- and post-operative outcomes of 427 patients who received a primary aTSA with one specific prosthesis and were sorted based upon the radiographic presence of a radiolucent glenoid line at latest clinical followup. 427 patients (mean age: 67.0yrs) with an average follow-up of 49.4 months was treated with aTSA for OA by 14 fellowship trained orthopaedic surgeons. Of these 427 patients, 293 had a cemented keel glenoids (avg follow-up = 50.8 months) and 134 had a cemented pegged glenoids (avg follow-up = 48.7 months). Cemented peg and keel glenoid patients were analyzed separately and also combined into 1 cohort: 288 patients (158 female, avg: 68.7 yrs; 130 male, avg: 64.9 yrs) did not have a radiolucent glenoid line (avg follow-up = 46.9 months); whereas, 139 patients (83 female, avg: 68.5 yrs; 56 male, avg: 64.6 yrs) had a radiolucent glenoid line (avg follow-up = 54.4 months). Outcomes were scored using SST, UCLA, ASES, Constant, and SPADI metrics; active ROM also measured. A two-tailed, unpaired t-test identified differences (p<0.05) in pre-operative, post-operative, and pre-to-post improvements.Introduction
Methods
Humeral radiolucent lines after anatomic TSA (aTSA) have been well described; however, little clinical consequences have been attributed to them. The recent emergence of shorter humeral stems has demonstrated higher incidences of humeral radiolucencies than has been reported historically with standard length components. This large scale database analysis quantifies and compares the clinical outcomes of aTSAs with and without radiolucent humeral lines using one specific prosthesis to determine their impact on clinical outcomes. This is a multicenter, retrospective, case controlled radiographic and clinical review. Preoperative and postoperative data was analyzed from 671 aTSA patients with a minimum of 2 years followup. 538 of these 671 aTSA patients had full radiographic followup (80.2%) and were included in this study; these patients had an average followup of 45.3 months). 459 patients had noncemented humeral stems; whereas, 79 patients had cemented humeral stems. Radiographs were reviewed at latest follow up for humeral radiolucent lines based on the technique described by Gruen et al. Patients were evaluated and scored pre-operatively and at latest follow-up using the SST, UCLA, ASES, Constant, and SPADI scoring metrics; ROM was also recorded. A Student's two-tailed, unpaired t-test was used to identify differences in pre-operative, post-operative, and improvement in results, where p<0.05 denoted a significant difference.Introduction
Methodology
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. 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).Introduction
Methods
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. 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 Introduction
Methods
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. 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.Introduction
Methods
Posterior glenoid wear is common with glenohumeral osteoarthritis. To correct posterior wear, surgeons may eccentrically ream the anterior glenoid to restore version. However, eccentric reaming undermines prosthesis support by removing unworn anterior glenoid bone, compromises cement fixation by increasing the likelihood of peg perforation, and medializes the joint line which has implications on joint stability. To conserve bone and preserve the joint line when correcting glenoid version, manufacturers have developed posterior augment glenoids for aTSA and rTSA applications. This clinical study quantifies outcomes achieved using posteriorly augmented aTSA/rTSA glenoid implants in patients with severe posterior glenoid wear at 2 years minimum follow-up. 47 patients (mean age: 68.7yrs) with 2 years minimum follow-up were treated by 5 fellowship trained orthopaedic surgeons using either 8° posteriorly augmented aTSA/rTSA glenoid components in patients with severe posterior glenoid wear. 24 aTSA patients received posteriorly augmented glenoids (65.8 yrs; 7F/17M) for OA and 23 rTSA patients received posteriorly augmented glenoids (71.8 yrs; 9F/14M) for treatment of CTA and OA. Outcomes were scored using SST, UCLA, ASES, Constant, and SPADI metrics; active abduction, forward flexion, and external rotation were also measured to quantify function. Average follow-up was 27.5 months (aTSA 29.4; rTSA 25.5). A two-tailed, unpaired t-test identified differences (p<0.05) in pre-operative, post-operative, and pre-to-post improvements.Introduction
Methods
A better understanding of the rate of improvement associated with aTSA and rTSA is critical to establish accurate patient expectations for treatment to reduce pain and restore function; more realistic patient expectations pre-operatively may lead to greater patient satisfaction post-operatively. To this end, this study quantifies the rate of improvement in outcomes of aTSA and rTSA using 5 different scoring metrics for 1641 patients with one platform shoulder arthroplasty system. 1641 patients (mean age: 69.3yrs) were treated by 14 orthopaedic surgeons using one platform shoulder system (Exactech, Inc). 729 patients received aTSA (65.3yrs; 384F/345M) for treatment of degenerative arthritis and 912 patients received rTSA (72.5yrs; 593F/319M) for treatment of CTA/RCT/OA. Each patient was scored pre-operatively and at various follow-up intervals (3 months, 6months, annually, etc) using the SST, UCLA, ASES, Constant, and SPADI metrics; active abduction, active forward flexion, and active/passive external rotation were also measured. 4439 total follow-up reports were analyzed (1851 and 2588 rTSA). Improvements in outcome using each metric score were calculated and normalized on a 100 point scale. The rate of improvement was analyzed using a 40 point moving filter treadline and with a 3rd order polynomial treadline over the entire range of follow-up.Introduction
Methods
The clinical impact of scapular notching is controversial. Some reports suggest it has no impact while others have demonstrated it does negatively impact clinical outcomes. The goal of this clinical study is to analyze the pre- and post-operative outcomes of 415 patients who received rTSA with one specific prosthesis (Equinoxe; Exactech, Inc). 415 patients (mean age: 72.2yrs) with 2 years minimum follow-up were treated with rTSA for CTA, RCT, and OA by 8 fellowship trained orthopaedic surgeons. 363 patients were deemed to not have a scapular notch by the implanting surgeon at latest follow-up (72.1 yrs; 221F/131M) whereas 52 patients were deemed to have a scapular notch at latest follow-up (73.3 yrs; 33F/19M). Outcomes were scored using SST, UCLA, ASES, Constant, and SPADI metrics; active abduction, forward flexion, and internal/external rotation were also measured to quantify function. Average follow-up was 38.1 months (No Notch: 37.2; Notch: 44.4). A two-tailed, unpaired t-test identified differences (p<0.05) in pre-operative, post-operative, and pre-to-post improvements.Introduction
Methods
Due to the predictability of outcomes achieved with reverse shoulder arthroplasty (rTSA), rTSA is increasingly being used in patients where glenoid fixation is compromised due to presence of glenoid wear. There are various methods to achieve glenoid fixation in patients with glenoid wear, including the use of bone grafting behind the glenoid baseplate or the use of augmented glenoid baseplates. This clinical study quantifies clinical outcomes achieved using both techniques in patients with severe glenoid wear at 2 years minimum follow-up. 80 patients (mean age: 71.6yrs) with 2 years minimum follow-up were treated by 7 fellowship trained orthopaedic surgeons using rTSA with bone graft behind the baseplate or rTSA with an augmented glenoid baseplate in patients with severe posterior glenoid wear. 39 rTSA patients (14 female, avg: 73.1 yrs; 25 male, avg: 71.5 yrs) received an augmented glenoid (cohort composed of 24 patients with an 8° posterior augment baseplate and 15 patients with a 10° superior augment baseplate) for treatment of CTA, RCT, and OA with a medially eroded scapula. 41 rTSA patients (27 female, avg: 73.0 yrs; 14 male, avg: 66.9 yrs) received glenoid bone graft (cohort composed of 5 patients with allograft and 36 patients with autograft) for treatment of CTA, RCT, and OA with a medially eroded scapula. Outcomes were scored using SST, UCLA, ASES, Constant, and SPADI metrics; active abduction, forward flexion, and internal/external rotation were also measured to quantify function. Average follow-up was 31.2 months (augment 28.3; graft 34.1). A two-tailed, unpaired t-test identified differences (p<0.05) in pre-operative, post-operative, and pre-to-post improvements.Introduction
Methods
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. 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/cm3 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.Introduction
Methods
