Shoulder arthroplasty humeral stem design has evolved to accommodate patient anatomy characteristics. As a result, stems are available in numerous shapes, coatings, lengths, sizes, and vary by fixation method. This abundance of stem options creates a surgical paradox of choice. Metrics describing stem stability, including a stem's resistance to subsidence and micromotion, are important factors that should influence stem selection, but have yet to be assessed in response to the diametral (i.e., thickness) sizing of short stem humeral implants. Eight paired cadaveric humeri (age = 75±15 years) were reconstructed with surgeon selected ‘standard’ sized short-stemmed humeral implants, as well as 2mm ‘oversized’ implants. Stem sizing conditions were randomized to left and right humeral pairs. Following implantation, an anteroposterior radiograph was taken of each stem and the metaphyseal and diaphyseal fill ratios were quantified. Each humerus was then potted in polymethyl methacrylate bone cement and subjected to 2000 cycles of 90º forward flexion loading. At regular intervals during loading, stem subsidence and micromotion were assessed using a validated system of two optical markers attached to the stem and humeral pot (accuracy of <15µm). The metaphyseal fill ratio did not differ significantly between the oversized and standard stems (0.50±0.06 vs 0.50±0.10; P = 0.997, Power = 0.05); however, the diaphyseal fill ratio did (0.52±0.06 vs 0.45±0.07; P < 0.001, Power = 1.0). Neither fill ratio correlated significantly with stem subsidence or micromotion. Stem subsidence and micromotion were found to plateau following 400 cycles of loading. Oversizing stem thickness prevented implant head-back contact in all but one specimen with the least dense metaphyseal bone, while standard sizing only yielded incomplete head-back contact in the two subjects with the densest bone. Oversized stems subsided significantly less than their standard counterparts (standard: 1.4±0.6mm, oversized: 0.5±0.5mm; P = 0.018, Power = 0.748;), and resulted in slightly more micromotion (standard: 169±59µm, oversized: 187±52µm, P = 0.506, Power = 0.094,). Short stem diametral sizing (i.e., thickness) has an impact on stem subsidence and micromotion following humeral arthroplasty. In both cases, the resulting three-dimensional stem micromotion exceeded, the 150µm limit suggested for bone ingrowth, although that limit was derived from a uniaxial assessment. Though not statistically significant, the increased stem micromotion associated with stem oversizing may in-part be attributed to over-compacting the cancellous bed during broaching, which creates a denser, potentially smoother, interface, though this influence requires further assessment. The findings of the present investigation highlight the importance of proper short stem diametral sizing, as even a relatively small, 2mm, increase can negatively impact the subsidence and micromotion of the stem-bone construct. Future work should focus on developing tools and methods to support surgeons in what is currently a subjective process of stem selection.
Shoulder arthroplasty is effective at restoring function and relieving pain in patients suffering from glenohumeral arthritis; however, cortex thinning has been significantly associated with larger press-fit stems (fill ratio = 0.57 vs 0.48; P = 0.013)1. Additionally, excessively stiff implant-bone constructs are considered undesirable, as high initial stiffness of rigid fracture fixation implants has been related to premature loosening and an ultimate failure of the implant-bone interface2. Consequently, one objective which has driven the evolution of humeral stem design has been the reduction of stress-shielding induced bone resorption; this in-part has led to the introduction of short stems, which rely on metaphyseal fixation. However, the selection of short stem diametral (i.e., thickness) sizing remains subjective, and its impact on the resulting stem-bone construct stiffness has yet to be quantified. Eight paired cadaveric humeri (age = 75±15 years) were reconstructed with surgeon selected ‘standard’ sized and 2mm ‘oversized’ short-stemmed implants. Standard stem sizing was based on a haptic assessment of stem and broach stability per typical surgical practice. Anteroposterior radiographs were taken, and the metaphyseal and diaphyseal fill ratios were quantified. Each humerus was then potted in polymethyl methacrylate bone cement and subjected to 2000 cycles of compressive loading representing 90º forward flexion to simulate postoperative seating. Following this, a custom 3D printed metal implant adapter was affixed to the stem, which allowed for compressive loading in-line with the stem axis (Fig.1). Each stem was then forced to subside by 5mm at a rate of 1mm/min, from which the compressive stiffness of the stem-bone construct was assessed. The bone-implant construct stiffness was quantified as the slope of the linear portion of the resulting force-displacement curves. The metaphyseal and diaphyseal fill ratios were 0.50±0.10 and 0.45±0.07 for the standard sized stems and 0.50±0.06 and 0.52±0.06 for the oversized stems, respectively. Neither was found to correlate significantly with the stem-bone construct stiffness measure (metaphysis: P = 0.259, diaphysis: P = 0.529); however, the diaphyseal fill ratio was significantly different between standard and oversized stems (P < 0.001, Power = 1.0). Increasing the stem size by 2mm had a significant impact on the stiffness of the stem-bone construct (P = 0.003, Power = 0.971; Fig.2). Stem oversizing yielded a construct stiffness of −741±243N/mm; more than double that of the standard stems, which was −334±120N/mm. The fill ratios reported in the present investigation match well with those of a finite element assessment of oversizing short humeral stems3. This work complements that investigation's conclusion, that small reductions in diaphyseal fill ratio may reduce the likelihood of stress shielding, by also demonstrating that oversizing stems by 2mm dramatically increases the stiffness of the resulting implant-bone construct, as stiffer implants have been associated with decreased bone stimulus4 and premature loosening2. The present findings suggest that even a small, 2mm, variation in the thickness of short stem humeral components can have a marked influence on the resulting stiffness of the implant-bone construct. This highlights the need for more objective intraoperative methods for selecting stem size to provide guidelines for appropriate diametral sizing. For any figures or tables, please contact the authors directly.
Clinical decision support tools are software that match the input characteristics of an individual patient to an established knowledge base to create patient-specific assessments that support and better inform individualized healthcare decisions. Clinical decision support tools can facilitate better evidence-based care and offer the potential for improved treatment quality and selection, shared decision making, while also standardizing patient expectations. Predict+ is a novel, clinical decision support tool that leverages clinical data from the Exactech Equinoxe shoulder clinical outcomes database, which is composed of >11,000 shoulder arthroplasty patients using one specific implant type from more than 30 different clinical sites using standardized forms. Predict+ utilizes multiple coordinated and locked supervised machine learning algorithms to make patient-specific predictions of 7 outcome measures at multiple postoperative timepoints (from 3 months to 7 years after surgery) using as few as 19 preoperative inputs. Predict+ algorithms predictive accuracy for the 7 clinical outcome measures for each of aTSA and rTSA were quantified using the mean absolute error and the area under the receiver operating curve (AUROC).Introduction
Methods
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
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. 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.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
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
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
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
Reverse shoulder design philosophy can impact external rotation moment arms. Lateralizing the humerus can increase the external rotator moment arms relative to normal anatomy. The design of reverse shoulders continues to evolve. These devices are unique in that they are not meant to reproduce the healthy anatomy. The reversal of the fulcurm in these devices impacts every muscle that surrounds the joint. This study is focused on analyzing the moment arms for the rotator cuff muscles involved in internal and external rotation for a number of reverse shoulder design philosophies.Summary Statement
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. 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
Both anatomic (aTSA) and reverse (rTSA) total shoulder arthroplasty are the standard of care for various end-stage degenerative conditions of the glenohumeral joint. Osteoarthritis (OA) is the most common indication for aTSA while Rotator Cuff Tear Arthropathy (CTA) is the most common indication for rTSA. Worldwide, the usage of both aTSA and rTSA has increased significantly due in part, to the predictability of acceptable outcomes achieved with each prosthesis type. The aim of this study is to quantify outcomes using 5 different metrics and compare results achieved for each indication using one platform total shoulder arthroplasty system which utilizes the same humeral component and instrumentation to perform both aTSA or rTSA. 200 patients (70.9 ± 7.3 yrs) were treated by two orthopaedic surgeons using either aTSA or rTSA. 73 patients received aTSA (67.4 ± 8.0 yrs) for treatment of OA (PHF: 64 patients; YM: 9 patients) and 127 patients received a rTSA (72.9 ± 6.1 yrs) for treatment of CTA (PHF: 53 patients; YM: 74 patients). These patients were scored pre-operatively and at latest follow-up using the SST, UCLA, ASES, Constant, and SPADI metrics; active abduction, forward flexion, and external rotation were also measured. The average follow-up for all patients was 31.4 ± 9.7 months (aTSA: 32.5 ± 12.1 months; rTSA: 30.8 ± 8.0 months). A Student's two-tailed, unpaired t-test was used to identify differences in pre-operative, post-operative, and pre-to-post-operative improvements in results, where p < 0.05 denoted a significant difference.Introduction
Methods
Reverse shoulder arthroplasty (rTSA) increases the deltoid abductor moment arm length to facilitate the restoration of arm elevation; however, rTSA is less effective at restoring external rotation. This analysis compares the muscle moment arms associated with two designs of rTSA humeral trays during two motions: abduction and internal/external rotation to evaluate the null hypothesis that offsetting the humerus in the posterior/superior direction will not impact muscle moment arms. A 3-D computer model simulated abduction and internal/external rotation for the normal shoulder, the non-offset reverse shoulder, and the posterior/superior offset reverse shoulder. Four muscles were modeled as 3 lines from origin to insertion. Both offset and non-offset reverse shoulders were implanted at the same location along the inferior glenoid rim of the scapula in 20° of humeral retroversion. Abductor moment arms were calculated for each muscle from 0° to 140° humeral abduction in the scapular plan using a 1.8: 1 scapular rhythm. Rotation moment arms were calculated for each muscle from 30° internal to 60° external rotation with the arm in 30° abduction.Introduction
Methods
