Prosthesis design and placement in reverse total shoulder arthroplasty

Reverse total shoulder replacement for patients with "weight-bearing" shoulders

BACKGROUND

Reverse total shoulder arthroplasty (rTSA) has gained popularity in recent years and is indicated for a wide variety of shoulder pathologies. However, use of rTSA in patients with "weight-bearing" shoulders that support wheelchair use or crutches has higher risk. The aim of this study was to assess the results of rTSA in such patients.

METHODS

Between 2005 and 2014, 24 patients (30 shoulders) with weight-bearing shoulders were treated with rTSA at our unit. Patients had cuff arthropathy (n=21), rheumatoid arthritis (n=3), osteoarthritis (n=1), acute fracture (n=3), or fracture sequela (n=2). Postoperatively, patients were advised not to push themselves up and out of their wheelchair for 6 weeks. This study was performed in 2016, and 21 patients (27 shoulders) were available for a mean follow-up of 5.6 years (range, 2-10 years). The mean age at surgery was 78 years (range, 54-90 years).

RESULTS

Constant-Murley score improved from 9.4 preoperatively to 59.8 at the final follow-up (P=0.001). Pain score improved from 2/15 to 13.8/15 (P=0.001). Patient satisfaction (Subjective Shoulder Value) improved from 0.6/10 to 8.7/10 (P=0.001). Significant improvement in mean range of motion from 46° to 130° of elevation, 14° to 35° of external rotation, and 29° to 78° internal rotation was recorded (P=0.001). Final mean Activities of Daily Living External and Internal Rotation was 32.4/36. Only three patients showed Sirveaux-Nerot grade-1 (10%) glenoid notching and three grade 2 (10%).

CONCLUSIONS

rTSA can be used for treatment of patients with weight-bearing shoulders. Such patients reported pain free movement, resumed daily activities, and high satisfaction rates. Level of evidence: IV.

The Influence of Component Design and Positioning on Soft-Tissue Tensioning and Complications in Reverse Total Shoulder Arthroplasty: A Review

» Reverse total shoulder arthroplasty was designed to function in the rotator cuff deficient shoulder by adjusting the glenohumeral center of rotation (COR) to maximize deltoid function.» Adjustments in the COR ultimately lead to changes in resting tension of the deltoid and remaining rotator cuff, which can affect implant stability and risk of stress fracture.» Soft-tissue balance and complication profiles can be affected by humeral component (version, neck shaft angle, and inlay vs. onlay) and glenoid component (sagittal placement, version, inclination, and lateralization) design and application.» A good understanding of the effects on soft-tissue balance and complication profile is critical for surgeons to best provide optimal patient outcomes.

Scapular morphology variation affects reverse total shoulder arthroplasty biomechanics. A predictive simulation study using statistical and musculoskeletal shoulder models

Reverse total shoulder arthroplasty (RTSA) accounts for over half of shoulder replacement surgeries. At present, the optimal position of RTSA components is unknown. Previous biomechanical studies have investigated the effect of construct placement to quantify mobility, stability and functionality postoperatively. While studies have provided valuable information on construct design and surgical placement, they have not systematically evaluated the importance of scapular morphology on biomechanical outcomes. The aim of this study was to assess the influence of scapular morphology variation on RTSA biomechanics using statistical models, musculoskeletal modeling and predictive simulation. The scapular geometry of a musculoskeletal model was altered across six modes of variation at four levels (±1 and ±3 SD) from a clinically derived statistical shape model. For each model, a standardized virtual surgery was performed to place RTSA components in the same relative position on each model then implemented in 50 predictive simulations of upward and lateral reaching tasks. Results showed morphology affected functional changes in the deltoid moment arms and recruitment for the two tasks. Variation of the anatomy that reduced the efficiency of the deltoids showed increased levels of muscle force production, joint load magnitude and shear. These findings suggest that scapular morphology plays an important role in postoperative biomechanical function of the shoulder with an implanted RTSA. Furthermore a "one-size-fits-all" approach for construct surgical placement may lead to suboptimal patient outcomes across a clinical population. Patient glenoid as well as scapular anatomy may need to be carefully considered when planning RTSA to optimize postoperative success.

Three-Dimensional Finite Element Analysis of a Notched Insert Design for Reverse Total Shoulder Arthroplasty to Prevent Scapular Notching

Purpose

Reverse total shoulder arthroplasty (RSA) is an effective treatment option for rotator cuff arthropathy. Scapular notching following RSA remains a major complication and has a high incidence. This finite element analysis (FEA) study provides a future reference for the optimal design of the insert component of RSA. This study aims to clarify the effect of a new design RSA with a notched insert on the range of adduction, scapular notching, and stress variation of its insert component using three-dimensional (3D) FEA.

Methods

3D nominal Grammont-type monobloc RSA implant components are modeled on the sawbones glenohumeral joint. The polyethylene insert is redesigned with notching of the inferior part. The comparison of standard and notched designs was performed by FEA for stress pressure of scapular notching and the degree of adduction. 3D mesh models are created for stress analysis to compare the results between standard and notched inserts for the adduction.

Results

The redesigned notched inserts had an additional ~ 11.2° on adduction and prevented scapular notching. The stress analysis results for the notched insert design were lower than the standard ones (4.7 vs 22.4 Kpa).

Conclusions

Notched insert design of Grammont-type RSA could provide additional adduction with lower stress on the glenoid, leading to less scapular notching. Further experimental and clinical studies on different RSA types are needed to verify this effect.

Study Design

Basic Science Study; Biomechanics and Computer Modeling.

Influence of sportive activity on functional and radiographic outcomes following reverse total shoulder arthroplasty: a comparative study

BACKGROUND

The purpose of the present study was to compare the functional and radiographic outcomes following reverse total shoulder arthroplasty (RTSA) in a senior athletic and non-athletic population.

MATERIAL AND METHODS

In this retrospective cohort study, patients who underwent RTSA between 06/2013 and 04/2018 at a single institution were included. Minimum follow-up was 2 years. A standardized questionnaire was utilized for assessment of patients' pre- and postoperative physical fitness and sportive activity. Patients who resumed at least one sport were assigned to the athletic group, while patients who ceased participating in sports were assigned to the non-athletic group. Postoperative clinical outcome measures included the Constant score (CS), American Shoulder and Elbow Surgeons (ASES) score, Simple Shoulder Test (SST), and visual analog scale (VAS) for pain. Active shoulder range of motion (ROM) and abduction strength were assessed. Radiographic evaluation was based on a standardized core set of parameters for radiographic monitoring of patients following shoulder arthroplasty.

RESULTS

Sixty-one of 71 patients (85.9%; mean age: 72.1 ± 6.6 years) were available for clinical and radiographic follow-up at a mean of 47.1 ± 18.1 months. Thirty-four patients (55.7%) were assigned to the athletic group and 27 patients (44.3%) to the non-athletic group. The athletic group demonstrated significantly better results for CS (P = 0.002), ASES score (P = 0.001), SST (P = 0.001), VAS (P = 0.022), active external rotation (P = 0.045) and abduction strength (P = 0.016) compared to the non-athletic group. The overall rate of return to sport was 78.0% at an average of 5.3 ± 3.6 months postoperatively. Incomplete radiolucent lines (RLL) around the humeral component were found significantly more frequently in the athletic group compared to the non-athletic group (P = 0.019), whereas the occurrence of complete RLLs around the implant components was similar (P = 0.382). Scapular notching was observed in 18 patients (52.9%) of the athletic group and 12 patients (44.9%) of the non-athletic group (P = 0.51). The overall rate for revision surgery was 8.2%, while postoperative complications were encountered in 3.3% of cases.

CONCLUSION

At mid-term follow-up, the athletic population demonstrated significantly better clinical results following RTSA without a higher rate of implant loosening and scapular notching when compared to non-athletic patients. However, incomplete radiolucency around the humeral component was observed significantly more often in the athletic group.

LEVEL OF EVIDENCE

III.

Strength Assessment After Reverse Shoulder Arthroplasty

Objective

The main objective was to evaluate the anterior flexion force (AFF) and the lateral abduction force (LAF) of patients who underwent reverse shoulder arthroplasty (RSA) and to compare the measured force with that in a similar-age control group. The secondary objective was to identify prognostic factors for muscle strength recovery.

Methods

Forty-two shoulders that underwent primary RSA between September 2009 and April 2020 met the inclusion criteria and were called the arthroplasty group (AG). The control group (CG) consisted of 36 patients. The mean AFF and the mean LAF were evaluated with a digital isokinetic traction dynamometer.

Results

The average AFF found in the AG was 15 N, while in the CG, the average AFF was 21 N (P < .001). The average LAF in the AG was 14 N (standard deviation [SD] 8 N), while in the CG the average LAF was of 19 N (SD 6 N) (P = .002). All prognostic factors studied in the AG showed no statistical significance: dominance (AFF 0.697/LAF 0.883), previous rotator cuff repair surgery (AFF 0.786/LAF 0.821), Hamada radiological classification (AFF 0.343/LAF 0.857), magnetic resonance imaging (MRI) pre-operative evaluation of the quality of the teres minor (AFF 0.131/LAF 0.229), suture of the subscapularis at the end of the arthroplasty procedure (AFF 0.961/LAF 0.325) and postoperative complications (AFF 0.600/LAF 0.960).

Conclusion

The mean AFF was 15 N, and the mean LAF was 14 N. The comparison of AFF and LAF with a CG showed a 25% reduction in muscle strength. It was not possible to demonstrate prognostic factors for muscle strength recovery after RSA.

Management of Proximal Humeral Oncologic Lesions

The proximal humerus is a common location for primary tumors, benign lesions, and metastatic disease. Advances in neoadjuvant and adjuvant therapy have allowed for limb-salvage surgery in most of the cases. There are numerous of options for surgical management of proximal humerus lesions and the decision to pursue one over another depends on factors such as age, comorbidities, pathology, location within the proximal humerus, planned resection margins/size of defect, and bone quality. Long-term outcomes for these techniques tend to be retrospective comparative studies, with recent studies highlighting the improved outcomes of reverse total shoulders.

Cause analysis of the liner dissociation of a customized reverse shoulder prosthesis based on finite element analysis

Background: Dissociation of the polyethylene liner after reverse shoulder arthroplasty could cause shoulder dislocation that could not achieve closed reduction. The cause of liner dissociation is currently unclear.

Method: Non-homogeneous model of the bone was constructed and dynamic finite element analysis was utilized to simulate the impingement of the polyethylene liner and scapula during humeral adduction. The stress distribution of the fixation claws, their degree of deformation (DOD), and the stress of the impingement sites in three initial humeral postures (neutral, 30° flexion, and 30° extension) were measured and analyzed. The influence of the liner material stiffness was also investigated.

Result: The impingement stress on the liner and scapula was 100–200 MPa, and different humeral postures caused different locations of impingement points. The fixation claws’ maximum principal stress (MPS) results were below 5 MPa. In the connection area between some fixation claws and the liner, compressive stresses on the inside and tensile stresses on the outside were observed, which showed that the fixation claws were prone to deform toward the center direction. The maximum DOD results of three initial humeral postures (neutral, 30° flexion, and 30° extension) were 3.6%, 2.8%, and 3.5%, respectively. The maximum DOD results of neutral initial humeral posture were 0.51% and 11.4% when the elastic modulus of the liner was increased and decreased by a factor of 10, respectively.

Conclusion: The humeral adduction impingement could lead to the deformation of the claw-shaped liner fixation structure, which might be one of the reasons for the liner dissociation. The increased stiffness of the liner material helped to reduce the deformation of the fixation structure.

Assessment of glenoid baseplate initial micromotion and fixation strength in reverse total shoulder arthroplasty designs using a direct shear force methodology

Background

In a reverse total shoulder arthroplasty, the altered glenohumeral joint center of rotation subjects the glenoid baseplate to increased shear forces and potential loosening.

Methods

This study examined glenoid baseplate micromotion and initial fixation strength with the application of direct shear force in a Sawbone model. The reverse total shoulder arthroplasty systems examined were the DJO Reverse® Shoulder Prosthesis, the Exactech Equinoxe® Reverse System, and the Tornier AequalisTM Reverse Shoulder Prosthesis. Specimens were cyclically tested with increasing shear loads until 150 µm of displacement between the implant and glenoid was achieved, and subsequently until failure, classified as either 1 cm of implant/glenoid displacement or fracture.

Results

The average load withstood for the 150 µm threshold for DJO, Tornier, and Exactech was 460 ± 88 N, 525 ± 100 N, and 585 ± 160 N, respectively. The average total load at device failure for DJO, Tornier, and Exactech was 980 ± 260 N, 1260 ± 120 N, and 1350 ± 230 N, respectively.

Discussion

The Exactech implant design trended toward requiring more load to induce micromotion at each threshold and to induce device failure, most commonly seen as inferior screw pull out. This study proposes design features that may enhance fixation and suggests little risk of initial micromotion or failure during initial post-operative recovery.

Accuracy of an Apparatus for Measuring Glenoid Baseplate Micromotion in Reverse Shoulder Arthroplasty

Reverse shoulder arthroplasty (RSA) is used to treat patients with cuff tear arthropathy. Loosening remains one of the principal modes of implant failure and the main complication leading to revision. Excess micromotion contributes to glenoid loosening. This study assessed the predictive accuracy of an experimental system designed to assess factors contributing to RSA glenoid baseplate micromotion. A half-fractional factorial experiment was designed to assess 4 factors: central element type (screw vs. peg), central element length (13.5 vs. 23.5 mm), anterior posterior peripheral screw type (locking vs. nonlocking) and cancellous bone density (10 vs. 25 pounds per cubic foot [pcf]). Four linear variable differential transducers (LVDTs) recorded micromotion from a stainless-steel disc surrounding a modified glenosphere. The displacements were used to interpolate micromotion at each of the respective peripheral screw positions. The mean absolute percentage error (MAPE) was used to determine the predictive accuracy and error range of the system. The MAPE for each condition ranged from 6.8% to 12.9% for an overall MAPE of (9.5&amp;#177;0.9)%. The system had an error range of 2.7 &amp;#181;m to 20.1 &amp;#181;m, which was lower than those reported by prior studies using optical systems. One of the eight conditions had micromotion that exceeded 150 &amp;#181;m. These findings support the use of displacement transducers, specifically LVDTs, as an accurate system for determining RSA baseplate micromotion in rigid polyurethane foam bone surrogates.

Three dimensional patient-specific guides for guide pin positioning in reverse shoulder arthroplasty: An experimental study on different glenoid types

INTRODUCTION

Incorrect positioning is one of the main factors for glenoid component loosening in reverse shoulder arthroplasty and component placement can be challenging. This study aimed to assess whether Patient-Specific Instrumentation (PSI) provides better guide pin positioning accuracy and is superior to standard guided and freehand instrumentation methods in cases of glenoid bone deformity.

MATERIALS AND METHODS

Based on the Walch classification, five different scapula types were acquired by computed tomography (CT). For each type, two different surgeons placed a guide pin into the scapula using three different methods: freehand method, conventional non-patient-specific guide, and PSI guide. Each method was repeated five times by both surgeons. In these experiments, a total of 150 samples of scapula models were used (5 × 2 × 3 × 5 = 150). Post-operative CT scans of the samples with the guide pin were digitally assessed and the accuracy of the pin placement was determined by comparison to the preoperative planning on a three-dimensional (3D) model.

RESULTS

The PSI method showed accuracies to the preoperative plan of 2.68 (SD 2.10) degrees for version angle (p < .05), 2.59 (SD 2.68) degrees for inclination angle (p < .05), and 1.55 (SD 1.26) mm for entry point offset (p < .05). The mean and standard deviation errors compared to planned values of version angle, inclination angle, and entry point offset were statistically significant for the PSI method for the type C defected glenoid and non-arthritic glenoid.

CONCLUSION

Using the PSI guide created by an image processing software tool for guide pin positioning showed advantages in glenoid component positioning over other methods, for defected and intact glenoid types, but correlation with clinical outcomes should be examined.

Bony increased-offset reverse shoulder arthroplasty (BIO-RSA) associated with eccentric glenosphere and an onlay 135° humeral component : Clinical and Radiological Outcomes at a minimum 2 year follow-up

Background

Various implant designs have been proposed to increase active range of motion (ROM) and avoid notching in patients treated by reverse total shoulder arthroplasty (RSA). The purpose of this study was to investigate the efficacy and safety of an onlay prosthesis design combining a 135° humeral neck-shaft angle with the glenoid component lateralized and inferiorized.

Methods

A retrospective descriptive study was conducted of the clinical and radiological outcomes at the final follow-up (≥24 months) of all RSAs performed by the same surgeon between September 2015 and December 2016 in the study center. At the last follow-up, patients were clinically assessed for ROM, Constant score, and subjective shoulder value and radiologically for scapular notching and glenoid radiolucent lines. Patients were followed up radiographically at 1 month and clinically at between 6 and 12 months (midterm) and again at between 24 and 48 months (final follow-up). Scapular notching was graded as per the Sirveaux classification at the last follow-up on anterior-posterior radiographs.

Results

Seventy-nine RSAs were included with a mean follow-up time of 31 months. The mean Constant score at the final follow-up was 42 points higher than before surgery (69 vs. 27, P < .001). There were also significant postoperative improvements in ROM (active anterior elevation, active external rotation, and active internal rotation). The final means for motions were 133° for active anterior elevation, 32° active external rotation, and level 7 for active internal rotation. The overall notching rate was 3% (2/67), and there were no cases of severe notching. Radiolucent lines were observed in 8 of 70 prostheses (11.5%) around the peg, and they were observed in 9 prostheses (13%) around the screws. Among the 79 RSAs included, there were 11 complications (13.9%) (two infections, two fractures, four cases of glenoid component loosening, and three cases of instability), 2 reoperations, and 4 prosthesis revisions.

Conclusion

This study shows that an RSA design with a 135° humeral neck-shaft angle and an inferiorized and lateralized glenoid component is associated with significant improvements in active ROM, especially in rotation, and a low notching rate. However, rates of 3.8% for dislocation and 5% for glenoid loosening are certainly a concern at such a short follow-up of two years. Future studies with a larger population are needed to confirm these rates.

Micromachined Tactile Sensor Array for RTSA

This work presents a polymer-based tactile capacitive sensor capable of measuring joint reaction forces of reverse total shoulder arthroplasty (RTSA). The capacitive sensor contains a polydimethylsiloxane (PDMS) dielectric layer with an array of electrodes. The sensor was designed in such a way that four components of glenohumeral contact forces can be quantified to help ensure proper soft tissue tensioning during the procedure. Fabricated using soft lithography, the sensor has a loading time of approximately 400 ms when a 14.13 kPa load is applied and has a sensitivity of 1.24 × 10-3 pF/kPa at a load of 1649 kPa. A replica RTSA prothesis was 3D printed, and the sensor was mounted inside the humeral cap. Four static right shoulder positions were tested, and the results provided an intuitive graphical description of the pressure distribution across four quadrants of the glenohumeral joint contact surface. It may help clinicians choose a right implant size and offset that best fit a patient's anatomy and reduce postoperative biomechanical complications such as dislocation and stress fracture of the scapula.

Complications of Reverse Total Shoulder Arthroplasty: A Computational Modelling Perspective

Reverse total shoulder arthroplasty (RTSA) is an established treatment for elderly patients with irreparable rotator cuff tears, complex proximal humerus fractures, and revision arthroplasty; however, with the increasing indications for RTSA over the last decade and younger implant recipients, post-operative complications have become more frequent, which has driven advances in computational modeling and simulation of reverse shoulder biomechanics. The objective of this study was to provide a review of previously published studies that employed computational modeling to investigate complications associated with RTSA. Models and applications were reviewed and categorized into four possible complications that included scapular notching, component loosening, glenohumeral joint instability, and acromial and scapular spine fracture, all of which remain a common cause of significant functional impairment and revision surgery. The computational shoulder modeling studies reviewed were primarily used to investigate the effects of implant design, intraoperative component placement, and surgical technique on postoperative shoulder biomechanics after RTSA, with the findings ultimately used to elucidate and mitigate complications. The most significant challenge associated with the development of computational models is in the encapsulation of patient-specific anatomy and surgical planning. The findings of this review provide a basis for future direction in computational modeling of the reverse shoulder.

Concept and simulation of an alternative design for an orthopaedic shoulder implant

For a first-time glenohumeral arthritis patient, total shoulder arthroplasty (TSA) is an option where the shoulder joint is replaced with an artificial humeral head that articulates against a cup attached to the glenoid. A patient with rotator cuff deficiency can undergo reverse total shoulder arthroplasty (RTSA) where the components are switched. Presented here is a concept design at simulation stage which offers a platform-based implant where either a system can be assembled and implanted for TSA or a reverse system for RTSA. Platform components and the glenoid baseplate have been designed as part of this concept stage. Modular components are also described as part of the concept, which can influence a patient's range of motion (ROM), as well as the effect of implant positioning within the patient. A 42 mm hemisphere is used as the articulating component providing a good balance between ROM, joint load and deltoid force. The most suitable material concluded for the concept design TSA was as follows: grade 5 Ti-6Al-4V for the humeral stem and baseplate and CoCrMo with cross-linked polyethylene (XLPE) for the metal-on-polymer bearing surface. Finite element analysis concluded that the concept prosthesis is able to withstand an impact force of six times bodyweight from a forward fall. A dynamic fatigue test concluded that the expected lifetime of the concept polymer bearing surface is 33 years.

The Schulthess local Shoulder Arthroplasty Registry (SAR): cohort profile

PURPOSE

Clinical registries are essential for evaluation of surgical outcomes. The Schulthess Shoulder Arthroplasty Registry (SAR) was established in 2006 to evaluate safety, function, quality-of-life and patient satisfaction in patients undergoing shoulder arthroplasty.

PARTICIPANTS

Adult patients undergoing anatomic or reverse shoulder joint replacement at the Schulthess Klinik, a high-volume, leading orthopaedic surgery centre in Zürich, Switzerland.

FINDINGS TO DATE

Between March 2006 and December 2019, the registry covered 98% of eligible operations. Overall, 2332 patients were enrolled with a total of 2796 operations and 11 147 person-years of follow-up. Mean age at baseline was 71 (range: 20-95), 65% were women. Most common indication was rotator cuff tears with osteoarthritis (42%) and the mean preoperative Constant Score was 31 (±15). The most frequent arthroplasty type was reverse, increasing from 61% in 2006-2010 to 86% in 2015-2019. Functional recovery peaked at 12-month postoperatively and did not show a clinically relevant deterioration during the first ten follow-up years. Since its establishment, the registry was used to address multiple pertinent clinical and methodological questions. Primary focus was on comparing different implant configurations (eg, glenosphere diameter) and surgical techniques (eg, latissimus dorsi transfer) to maximise functional recovery. Additionally, the cohort contributed to the determination of the clinical relevance and validity of radiological monitoring of cortical bone resorption and scapular notching. Finally, SAR data helped to demonstrate that returning to sports was among key patient expectations after reverse shoulder arthroplasty.

FUTURE PLANS

As first patients are approaching the 15 years follow-up landmark, the registry will continue providing essential data on long-term functional outcomes, implant stability, revision rates and aetiologies as well as patient satisfaction and quality-of-life. In addition to research and quality-control, the cohort data will be brought back to the patients by bolstering real-time clinical decision support.

Short-term safety, function, and quality of life in patients treated with Univers Revers prosthesis: a multicenter 2-year follow-up case series

BACKGROUND

The use of reverse total shoulder arthroplasty (RTSA) has dramatically increased in recent years with the advent of new prosthesis designs regularly entering the market. We define the rate of local complications during the first 2 years after RTSA with the Univers Revers prosthesis and describe the changes in radiologic outcomes, as well as function, pain, satisfaction, and quality of life.

METHODS

This multicenter, prospective case series included rotator cuff tear arthropathy patients who underwent RTSA with the Univers Revers. Incidence percentages of complications and pathologic radiographic changes were documented. Mixed-model linear regression was used to examine changes in range of motion, shoulder function (Constant score, Shoulder Pain and Disability Index, Subjective Shoulder Value), and quality of life (EQ-5D-5L [European Quality of Life 5 Dimensions 5 Level] and EQ-VAS [EuroQol Visual Analog Scale]).

RESULTS

Of 187 patients, 59.4% were women, and the mean age was 75.3 years (range, 56-91 years). Twenty-five percent of patients had a postoperative complication; 5 complications were severe (2.7%, 5 of 187), whereby 2 were implant related (1.1%; 95% confidence interval [CI], 0.1%-3.8%). The incidence of scapular notching was 10.6% (95% CI, 6.5%-16%). After 2 years, abduction, flexion, and abduction strength improved by 54° (95% CI, 50°-58°), 57° (95% CI, 53°-60°), and 5 kg (95% CI, 4-5 kg), respectively (P < .001), whereas external rotation at 0° (1°; 95% CI, -1° to 3°) did not improve (P = .4). The Constant score improved by 39 (95% CI, 38-41); Shoulder Pain and Disability Index, by 50 (95% CI, 47-52); and Subjective Shoulder Value, by 43 (95% CI, 41-45) (P < .001). Furthermore, the EQ-5D-5L index value improved by 0.31 (95% CI, 0.30-0.33), and the EQ-VAS score improved by 16 (95% CI, 14-18) (P < .001).

CONCLUSION

Our case series showed a low complication rate with a consistent clinically relevant and statistically significant improvement across most clinical and patient-reported outcomes for the Univers Revers. Long-term safety requires further investigation.

Effect of Reverse Shoulder Arthroplasty Lateralization Design on Scapular Notching: A Single-Surgeon Experience

Scapular notching remains a concern with both medialized and lateralized reverse shoulder arthroplasty (RSA) designs. Few studies have directly compared the rate of notching among various designs. The purpose of this study was to compare a single surgeon's rate of scapular notching in relation to RSA design. A total of 156 primary RSAs were performed for cuff tear arthropathy or osteo-arthritis with rotator cuff insufficiency by a single surgeon. Follow-up was controlled to between 3 and 5 years. Shoulders were grouped according to implant design: medialized center of rotation (CoR; n=17), lateralized CoR (n=14), and lateralized humerus (n=125). Objective clinical outcomes, patient-reported outcomes, and radiographic outcomes were compared. Scapular notching occurred more frequently with medialized CoR (82%) and lateralized CoR (57%) designs compared with a lateralized humerus design (22%; P<.001). Mean notching grade was also lower in the lateralized humerus design (0.2) compared with the medialized CoR (2.1; P<.001) and lateralized CoR (1.1; P=.01) designs. Postoperative pain, range of motion, and patient-reported outcomes were not significantly different among groups. A low rate of reoperation was seen in all groups. The lateralized humeral RSA design showed less frequent and less severe scapular notching compared with medialized CoR and lateralized CoR designs. There were no observed differences in range of motion or patient-reported outcomes between different implant designs. [Orthopedics. 2020;43(6):e585-e591.].

Clinical implications of scapular notching at 2 and 5-year follow-up after reverse total shoulder arthroplasty

Objective

Scapular notching is a unique radiographic sequela of reverse total shoulder arthroplasty (rTSA) with unclear long-term clinical consequences.

Methods

Our retrospective review of a single surgeon, single implant, primary rTSA database investigates the incidence of scapular notching at 2 and 5-year follow-up. Various patient outcome scores were also obtained.

Results

Of 158 primary rTSAs performed, 82 (52%) patients completed 2-year and subsequent 5-year follow-up. The incidence of scapular notching at 2 and 5-years was 11.9% and 19.5%, respectively.

Conclusion

Scapular notching negatively affects validated post-operative outcome scores, active range of motion and total complications, and furthermore increases with time.

Influence of reverse total shoulder arthroplasty baseplate design on torque and compression relationship

Background

A linear relationship between baseplate insertion torque and compression force in reverse shoulder arthroplasty (RSA) baseplates with central screw design has been recently established. In this study, we evaluated 3 different baseplate designs and their influence on the torque-compression relationship.

Methods

Three different RSA baseplate designs were evaluated through biomechanical testing using a glenoid vault, bone surrogate model. A digital torque gauge was used to measure insertion torque applied to the baseplate, whereas compression data were collected continuously from a load cell. Additionally, 2 predictive models were developed to predict the compression forces of each baseplate design at varying levels of torque.

Results

A linear relationship was found between baseplate compression and insertion torque for all 3 baseplate designs. Both the monoblock and 2-piece locking designs achieved the goal torque of 6.8 Nm, whereas the 2-piece nonlocking design did not due to material strip-out. No significant difference in maximum compression was found between the monoblock and 2-piece locking designs. However, the 2-piece nonlocking design achieved significantly higher compression. Both predictive models were shown to adequately predict compressive forces at different torque inputs for the monoblock and 2-piece locking designs but not the 2-piece nonlocking design.

Conclusion

The torque-compression relationship of a central screw baseplate is significantly affected by baseplate design. A 2-piece nonlocking baseplate reaches higher compression levels and risks material strip-out at lower insertional torques compared with a monoblock and 2-piece locking design. This has implications both on component design and on surgeon tactile feedback during surgery.

Reverse total shoulder arthroplasty: an imaging overview

Although not as common as hip or knee arthroplasty, shoulder arthroplasty is becoming a more common procedure. Reverse total shoulder arthroplasty (RTSA) is known to be an effective surgical procedure for massive irreparable rotator cuff tears, comminuted proximal humerus fractures, and revision shoulder arthroplasty. The utilization of RTSA has been increasing, and although complications following reverse arthroplasty have been reported, there are few reports in the literature that focus on the imaging features of RTSA. Herein, we demonstrate the biomechanics of RTSA, prosthesis components, indications, and imaging features of the normal postoperative appearance and various complications after RTSA. Familiarization with the normal and abnormal imaging appearances after RTSA can be helpful for appropriate management of patients.

The Personalized Shoulder Reconstruction Assisted by 3D Printing Technology After Resection of the Proximal Humerus Tumours

Background

The reverse shoulder arthroplasty (RSA) may be a promising alternative for proximal humerus tumours because of good postoperative shoulder function. However, the conventional reverse shoulder prosthesis can not meet individual needs and RSA has been associated with a relatively high complication rate. Therefore, implant design and surgical reconstruction technique warrant further study.

Methods

Between September 2015 and May 2018, 7 patients were treated via RSA after en-bloc resection of the proximal humerus tumours. A 3D-printed guiding baseplate was used to assist the implant of the 3D-printed glenoid prosthesis; a personalized humerus prosthesis was used to reconstruct the proximal humerus. The functional outcomes were assessed by range of motion (ROM) of the shoulder joint, Musculoskeletal Tumour Society (MSTS) functional score, and Toronto Extremity Salvage Score (TESS). We also analyzed tumour recurrence, metastases, and complications associated with the reconstruction procedure.

Results

All patients were observed for 14 to 36 months, with an average of 23.6 months. At the final follow-up, the mean MSTS score was 85.7% (range, 73.3–93.3%), and the mean TESS score was 90.0% (range, 84.1–95.9%). No instability, infection, scapular notching, loosening or fracture were observed in this series. One patient with GCT suffered from pulmonary metastasis, while one with osteosarcoma died because of pulmonary metastasis.

Conclusion

The 3D-printed guiding baseplate facilitated the accurate implantation of the glenoid prosthesis. The RSA based on a 3D-printed glenoid prosthesis and a personalized custom-made humerus prosthesis significantly improved the shoulder function and decreased the complication rate. Further studies of a larger scale with longer follow-up are required to validate this technology.

Effect of critical shoulder angle, glenoid lateralization, and humeral inclination on range of movement in reverse shoulder arthroplasty

Objectives

To date, no study has considered the impact of acromial morphology on shoulder range of movement (ROM). The purpose of our study was to evaluate the effects of lateralization of the centre of rotation (COR) and neck-shaft angle (NSA) on shoulder ROM after reverse shoulder arthroplasty (RSA) in patients with different scapular morphologies.

Methods

3D computer models were constructed from CT scans of 12 patients with a critical shoulder angle (CSA) of 25°, 30°, 35°, and 40°. For each model, shoulder ROM was evaluated at a NSA of 135° and 145°, and lateralization of 0 mm, 5 mm, and 10 mm for seven standardized movements: glenohumeral abduction, adduction, forward flexion, extension, internal rotation with the arm at 90° of abduction, as well as external rotation with the arm at 10° and 90° of abduction.

Results

CSA did not seem to influence ROM in any of the models, but greater lateralization achieved greater ROM for all movements in all configurations. Internal and external rotation at 90° of abduction were impossible in most configurations, except in models with a CSA of 25°.

Conclusion

Postoperative ROM following RSA depends on multiple patient and surgical factors. This study, based on computer simulation, suggests that CSA has no influence on ROM after RSA, while lateralization increases ROM in all configurations. Furthermore, increasing subacromial space is important to grant sufficient rotation at 90° of abduction. In summary, increased lateralization of the COR and increased subacromial space improve ROM in all CSA configurations.Cite this article: A. Lädermann, E. Tay, P. Collin, S. Piotton, C-H Chiu, A. Michelet, C. Charbonnier. Effect of critical shoulder angle, glenoid lateralization, and humeral inclination on range of movement in reverse shoulder arthroplasty. Bone Joint Res 2019;8:378-386. DOI: 10.1302/2046-3758.88.BJR-2018-0293.R1.

Muscle and Joint Function After Anatomic and Reverse Total Shoulder Arthroplasty Using a Modular Shoulder Prosthesis

Changes in joint architecture and muscle loading resulting from total shoulder arthroplasty (TSA) and reverse total shoulder arthroplasty (RSA) are known to influence joint stability and prosthesis survivorship. This study aimed to measure changes in muscle moment arms, muscle lines of action, as well as muscle and joint loading following TSA and RSA using a metal-backed uncemented modular shoulder prosthesis. Eight cadaveric upper extremities were assessed using a customized testing rig. Abduction, flexion, and axial rotation muscle moment arms were quantified using the tendon-excursion method, and muscle line-of-force directions evaluated radiographically pre-operatively, and after TSA and revision RSA. Specimen-specific musculoskeletal models were used to estimate muscle and joint loading pre- and post-operatively. TSA lateralized the glenohumeral joint center by 4.3 ± 3.2 mm, resulting in small but significant increases in middle deltoid force (2.0%BW) and joint compression during flexion (2.1%BW) (p < 0.05). Revision RSA significantly increased the moment arms of the major abductors, flexors, adductors, and extensors, and reduced their peak forces (p < 0.05). The superior inclination of the deltoid significantly increased while the inferior inclination of the rotator cuff muscles decreased (p < 0.05). TSA using an uncemented metal-backed modular shoulder prosthesis effectively restores native joint function; however, lateralization of the glenoid component should be minimized intra-operatively to mitigate increased glenohumeral joint loading and polyethylene liner contact stresses. Revision RSA reduces muscle forces required during shoulder function but produces greater superior joint shear force and less joint compression. The findings may help to guide component selection and placement to mitigate joint instability after arthroplasty. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1988-2003, 2019.

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

BACKGROUND

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.

MATERIALS AND METHODS

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).

RESULTS

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.

DISCUSSION

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.

The influence of rotator cuff tears on muscle and joint-contact loading after reverse total shoulder arthroplasty

Rotator cuff tears are known to affect clinical outcome of reverse total shoulder arthroplasty (RSA). This study aimed to use computational modelling to quantify the effect of rotator cuff tear severity on muscle and joint forces after RSA, as well as stresses at the glenosphere, base-plate, fixation screws, scapula, and humeral components. A multi-body musculoskeletal model of the glenohumeral joint was developed comprising the scapula, humerus and nine major upper limb muscles. Simulations of abduction and flexion after RSA were performed in the case of the intact rotator cuff and tears to (i) supraspinatus; (ii) supraspinatus and infraspinatus, and (iii) supraspinatus, infraspinatus and subscapularis. The intact and supraspinatus deficient rotator cuff resulted in the largest calculated muscle forces, glenohumeral joint contact forces and implant stresses. Peak glenohumeral joint forces during flexion were lower than those during abduction in all cases; however, substantially more posterior joint shear force was generated during flexion than abduction. A tear involving the supraspinatus and infraspinatus reduced glenohumeral joint forces by a factor of 8.7 during abduction (603.1 N) and 7.1 during flexion (520.7 N) compared to those in the supraspinatus deficient shoulder. RSA with an intact or supraspinatus deficient rotator cuff produces large glenohumeral joint forces that may increase base-plate failure risk, particularly during flexion when posterior shear forces are largest. Infraspinatus tears after RSA greatly reduce glenohumeral joint compression and may ultimately reduce joint stability. Future research ought to focus on experimental validation of subject-specific muscle recruitment strategies and joint loading after RSA. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Analysis of impingement-free range of motion of the glenohumeral joint after reverse total shoulder arthroplasty using three different implant models

BACKGROUND

This study aimed to investigate impingement-free range of motion (ROM) of the glenohumeral joint following reverse total shoulder arthroplasty (RTSA) with three types of implant models using computational motion analysis.

METHODS

Three-dimensional (3D) scapulohumeral models were created from preoperative computed tomography (CT) images of seven patients by using visualization and computer-aided design software. Three types of implant designs, namely, typical medialization, in between, and lateralization implants, were used for the reconstruction of 3D model; each design was designated as group I, II, and III, respectively. All possible combinations of virtual surgeries were evaluated for impingement-free ROM in all three groups. Maximal ROMs were compared. The effect of implant positions on ROM of the shoulder joints were investigated in each group.

RESULTS

The all lateralization group (group III) showed significantly greatest maximal adduction, abduction and external rotation (ER). Adduction and abduction were significantly increased by the glenoid component inferior translation in all three groups. (In group I, p < 0.001 for adduction, p = 0.002 for abduction, respectively; in group II, p = 0.025, p < 0.001, respectively; in group III, p = 0.038, p = 0.011, respectively). Increasing humerus retroversion might have some effect on increasing abduction. In group II and III, internal rotation (IR) and ER were significantly affected by the humerus retroversion (in group II, p = 0.033 for IR, p = 0.007 for ER, respectively; in group III, p = 0.004, p < 0.001, respectively). In group III, ER was also significantly affected by the glenoid component inferior translation (p = 0.003).

CONCLUSIONS

Lateralization design model showed greatest ROM of the shoulder joint. The effects of implant positions on impingement-free ROM exhibited different tendencies between medialization and lateralization implant models. Humerus retroversion affected both IR and ER, especially in lateralization design. Increasing glenoid inferior translation increases both adduction and abduction regardless of implant designs.

Instability in Reverse Total Shoulder Arthroplasty

Recently, indications for reverse total shoulder arthroplasty have expanded to include glenohumeral arthritis, rotator cuff arthropathy, irreparable rotator cuff tears, complex proximal humerus fractures, sequelae of trauma, and failed shoulder prostheses. Dislocation is a common complication, with rates ranging from 1.5% to 31%. The literature pertaining to management of instability in reverse total shoulder arthroplasty is scanty. Assessment of the patient and biomechanical and surgical factors is critical in determining the best course of treatment. Future studies involving patient selection, prosthetic design, surgical technique, and biomechanics may help reduce the rate of instability.

Design and clinical outcome of a novel 3D-printed prosthetic joint replacement for the human temporomandibular joint

BACKGROUND

Stock prosthetic temporomandibular joint replacements come in limited sizes, and do not always encompass the joint anatomy that presents clinically. The aims of this study were twofold. Firstly, to design a personalized prosthetic total joint replacement for the treatment of a patient's end-stage temporomandibular joint osteoarthritis, to implant the prosthesis into the patient, and assess clinical outcome 12-months post-operatively; and secondly, to evaluate the influence of changes in prosthetic condyle geometry on implant load response during mastication.

METHODS

A 48-year-old female patient with Grade-5 osteoarthritis to the left temporomandibular joint was recruited, and a prosthesis developed to match the native temporomandibular joint anatomy. The prosthesis was 3D printed, sterilized and implanted into the patient, and pain and function measured 12-months post-operatively. The prosthesis load response during a chewing-bite and maximum-force bite was evaluated using a personalized multi-body musculoskeletal model. Simulations were performed after perturbing condyle thickness, neck length and head sphericity.

FINDINGS

Increases in prosthetic condyle neck length malaligned the mandible and perturbed temporomandibular joint force. Changes in condylar component thickness greatly influenced fixation screw stress response, while a more eccentric condylar head increased prosthetic joint-contact loading. Post-operatively, the prosthetic temporomandibular joint surgery reduced patient pain from 7/10 to 1/10 on a visual analog scale, and increased intercisal opening distance from 22 mm to 38 mm.

INTERPRETATION

This study demonstrates effectiveness of a personalized prosthesis that may ultimately be adapted to treat a wide-range of end-stage temporomandibular joint conditions, and highlights sensitivity of prosthesis load response to changes in condylar geometry.

Imaging of Shoulder Arthroplasties

OBJECTIVE

In this article, we review the preoperative imaging features used for planning shoulder arthroplasty as well as review the various shoulder arthroplasty component types, discussing the expected normal imaging features and specific complications to look for with each.

CONCLUSION

Given the increasing use of shoulder arthroplasty, it is important to understand the imaging features of the various shoulder arthroplasty complications.

3D image-based morphometric analysis of the scapular neck length in subjects undergoing reverse shoulder arthroplasty

Scapular notching after RSA may, in part, be related to a patient's scapular morphology. The purpose of this study was to develop a novel 3 D measurement technique to describe infraglenoid tubercle morphometry. We hypothesize that the parameters describing infraglenoid tubercle would be normally distributed and would correlate with individual's demographics and glenoid morphometry. A group of 110 subjects treated with RSA were evaluated. Scapular geometry was obtained from pre-operative CT scans. The scapular neck length was defined in anterior and posterior view as the orthogonal distance between the glenoid surface and (a) the point of most significant change of curvature on lateral pillar; (b) the most lateral portion of the infraglenoid tubercle. Scapular neck angle, maximum anatomical adduction angle, glenoid width, height and version were also measured. Scapular neck length measured in the anterior and posterior view were normally distributed with mean values of 17.6 ± 2.8 mm and 7.9 ± 2.5 mm, respectively. Scapular neck angle was on average 112.4 ± 10.6° and maximal adduction angle was 17.6 ± 2.8°. No significant associations between infraglenoid tubercle morphometric parameters, demographic, glenoid size or version were identified. Improved understanding of the patient-specific risk factors for scapular notching will help surgeons with pre-surgical planning and implant selection. Parametrization of the infraglenoid tubercle presented in this study showed normal distribution in the population unrelated to gender, side or demographics. The size of the infraglenoid tubercle is a unique trait, pre-operative evaluation of the scapular neck should be always warranted to decrease the incidence of post-operative notching. Clin. Anat. 31:43-55, 2018. © 2017 Wiley Periodicals, Inc.

Optimizing baseplate position in reverse total shoulder arthroplasty in small-sized Japanese females: technical notes and literature review

The management of cuff tear arthropathy (CTA) has always been a challenge for shoulder surgeons. Introduction of reverse total shoulder arthroplasty (RTSA) helped in providing pain relief and improved shoulder function in patients with CTA. In this study, we aimed to evaluate the short-term clinical results and some clinical details regarding the types of available prosthesis, positioning, and size of the components for RTSA in a population of short-stature female Japanese. In our seven cases, the average glenoid size was 23.9 mm in width and 34.2 mm in height. The average width was smaller than the size of all available baseplates. We implanted reverse shoulder prostheses with baseplate that measured 28 mm in diameter and two locking screws. The center of the baseplate was shifted to allow slight anterior overhang relative to the anatomical center to avoid breakage of the posterior cortex and to achieve firm fixation. One case of humeral shaft fracture occurred while inserting the humeral stem and required encircling wiring. In our experience, the short term clinical results of RTSA were excellent, but a new prosthesis that is designed to fit the short stature of Asians with smaller glenoid and humerus should be considered.