Effect of lateralized design on muscle and joint reaction forces for reverse shoulder arthroplasty

Anatomic Versus Reverse Total Shoulder Arthroplasty for Primary Osteoarthritis With an Intact Rotator Cuff: A Midterm Comparison of Early Top Performers

BACKGROUND

Several surgeons state that their best anatomic total shoulder arthroplasty (aTSA) outperforms their best reverse total shoulder arthroplasty (rTSA) when performed for rotator cuff-intact glenohumeral osteoarthritis. We identified the top-performing aTSAs and rTSAs at short-term follow-up and compared their clinical performance at midterm follow-up to validate this common claim.

METHODS

A retrospective review of a multicenter shoulder arthroplasty database was conducted. All shoulders undergoing primary aTSA or rTSA for rotator cuff-intact glenohumeral osteoarthritis between 2007 and 2020 were reviewed. Shoulders with a follow-up clinical visit between 2 and 3 years and a clinical follow-up of minimum 5 years were included. Two separate cohorts were identified: patients with a top 20% (1) American Shoulder and Elbow Surgeons (ASES) score and (2) Shoulder Arthroplasty Smart (SAS) score at 2 to 3 years of follow-up. Clinical outcomes including range of motion, outcome scores, and rates of complications and revision surgeries were compared at minimum 5-year follow-up.

RESULTS

The ASES score cohort comprised 185 aTSAs (mean age 67 years, 42% female) and 49 rTSAs (mean age 72 years, 45% female). The SAS score cohort comprised 145 aTSAs (mean age 67 years, 59% female) and 42 rTSAs (mean age 71 years, 57% female). Active external rotation (ER) was greater after aTSA at midterm follow-up in both ASES and SAS score cohorts; however, preoperative to postoperative improvement was equivalent. Postoperative ER and SAS scores were greater after aTSA in both cohorts ( P < 0.05); however, no other significant differences in any preoperative or postoperative clinical outcomes were present ( P > 0.05), and patients achieved the minimal clinically important difference and substantial clinical benefit at similar rates for all outcomes. No difference was found in the incidence of complications and revision surgeries between top-performing aTSAs and rTSAs.

CONCLUSION

Among top-performing shoulder arthroplasties at early follow-up, aTSA does not appear to outperform rTSA, except superior ER at midterm follow-up.

LEVEL OF EVIDENCE

Retrospective comparative cohort study, Level Ⅲ.

Reverse shoulder arthroplasty design-inlay vs. onlay: does it really make a difference?

BACKGROUND

The design of reverse shoulder arthroplasty (RSA) implants has evolved significantly over the past 50 years. Today there are many options available that differ in design of the glenoid and humeral components, fixation methods, sizes, and modularity. With respect to the humeral component, the literature has generally focused on the differences between inlay and onlay designs and the potential impact on outcomes. However, inlay and onlay design represents only one factor of many.

METHODS

It is our hypothesis that separating onlay and inlay designs into 2 distinct entities is an oversimplification as there can be a wide overlap of the 2 designs, depending on surgical technique and the implant selected. As such, the differences between inlay and onlay designs should be measured in absolute terms-meaning combined distalization and lateralization.

RESULTS

By reviewing the many factors that can contribute to the glenosphere-humerus relationship, the role of inlay and onlay humeral designs as an important distinguishing feature is shown to be limited. Preliminary studies suggest that the amount of distalization and lateralization of the construct may be the most accurate method of describing the differences in the constructs.

CONCLUSIONS

Inlay and onlay humeral component design represents only one factor of many that may impact outcomes. A more accurate method of defining specific design and technique factors in RSA is the degree of lateralization and distalization.

Demographic-, Radiographic-, and Surgery-Related Factors Do Not Affect Functional Internal Rotation Following Reverse Total Shoulder Arthroplasty: A Retrospective Comparative Study

PURPOSE

This study aimed to identify the demographic-, radiographic-, and surgery-related factors influencing postoperative functional internal rotation (fIR) following reverse total shoulder arthroplasty (RTSA).

METHODS

In this retrospective cohort study, patients who underwent RTSA between June 2013 and April 2018 at a single institution were assigned to two groups ("IROgood" or "IRObad"). Patients were classified as having good fIR (≥8 points in the Constant-Murley score (CS) and fIR to the twelfth thoracic vertebra or higher) or poor fIR (≤2 points in the CS and fIR to the twelfth thoracic vertebra or lower) after RTSA with a single implant model. The minimum follow-up period was two years. Standardized shoulder-specific scores (Visual Analogue Scale (VAS), Simple Shoulder Test (SST), American Shoulder and Elbow Surgeons Score (ASES), Constant-Murley score (CS)) were used to assess the pre- and postoperative functional status of patients. Postoperative radiographic evaluation included the distalization shoulder angle (DSA), lateralization shoulder angle (LSA), critical shoulder angle (CSA), acromiohumeral distance (AHD), glenoid inclination (GI), medialization of the center of rotation (COR), lateralization of the humerus, and distalization of the greater tuberosity. Additionally, preoperative evaluation included rotator cuff arthropathy according to Hamada, glenoid version, anterior or posterior humeral head subluxation, and fatty infiltration of the rotator cuff according to Goutallier. Univariate analysis of demographic, surgical, radiographic, and implant-associated parameters was performed to identify factors associated with postoperative fIR. The Shapiro-Wilk test assessed the normal distribution of the data. Intergroup comparisons regarding demographic and surgery-related factors were conducted using the Mann-Whitney-U Test. Radiographic changes were compared using chi-square or Fisher's exact tests. The significance level was set at p < 0.05.

RESULTS

Of a total of 42 patients, 17 (age: 73.7 ± 5.0 years, follow-up (FU) 38 months [IQR 29.5-57.5]) were included in the "IRObad" group, and 25 (age: 72 ± 6.1 years, FU 47 months [IQR 30.5-65.5]) were included in the "IROgood" group. All patients were treated with the same type of implant (glenosphere size: 36 mm, 14.3%; 39 mm, 38.1%; 42 mm, 47.6%; neck-shaft angle: 135° in 68.0%; 155° in 32.0%) and had comparable indications. Univariate analysis did not reveal any of the investigated demographic, radiographic, or surgery-related parameters as risk factors for poor postoperative fIR (p > 0.05).

CONCLUSION

None of the investigated factors, including implant-associated parameters, influenced postoperative fIR after RTSA in this cohort.

The lateralization and distalization index is more reliable than angular radiographic measurements in reverse shoulder arthroplasty

BACKGROUND

The lateralization shoulder angle (LSA) and distalization shoulder angle (DSA) are used to reproducibly measure lateralization and distalization after reverse shoulder arthroplasty (RSA). However, LSA and DSA may not offer a precise measurement of humeral lateralization and distalization and this relationship has not been explored. The aim of this study was to evaluate the validity of these measurements and to propose new measurement methods to estimate implant lateralization and distalization.

METHODS

3D models were constructed from computed tomography (CT) scans of 30 patients using a software platform. For each patient 24 different RSA modifications were created, resulting in 720 different RSA configurations. For each configuration LSA and DSA angles as well as lateralization and distalization distances were measured. Moreover, for each configuration two new measurements were done: the lateralization index (LI) and distalization index (DI). Correlations of the lateralization and distalization parameters were evaluated between measurements.

RESULTS

Weak correlations were founded between LSA and lateralization (r = 0.36, p < 0.01), whereas moderate correlations were observed between LI and lateralization (r = 0.72, p < 0.01). No significant correlations were found between DSA and distalization (r = 0.17, p = 0.113). In contrast, moderate correlations were identified between DI and distalization (r = 0.69, p < 0.01).

CONCLUSION

LI and DI are more reliable methods to estimate implant lateralization and distalization compared to angular radiographic measurements. However, the prognostic significance in predicting clinical outcomes after RSA remains unknown.

High delta angle after reverse total shoulder arthroplasty increases stresses of the acromion: biomechanical study of different implant positions

BACKGROUND

Acromial fractures after reverse total shoulder arthroplasty (RTSA) are a common complication. Nevertheless, only a few studies have identified risk factors for acromial fractures after RTSA. High delta angle (combination of inferiorization and medialization of the center of rotation [COR]) after RTSA was identified as a risk factor in recent studies. The aim of this study was the biomechanical exploration of different delta angles and implant configurations with regard to the acromial stress.

METHODS

In a rigid body model of the upper extremity muscle, forces of the deltoid muscle were calculated before and after implanting RTSA in different arm and implant positions. The deltoid muscle was divided into an anterior, middle, and posterior part. Implant positions of the glenoid components were changed in the medialization, lateralization, and inferiorization of the COR as well as lateralization of the humeral component. Further, in a finite element model of the upper extremity, the stresses of the acromion in the same implant design configurations were measured.

RESULTS

Differences in acromial stress between different delta angle model configurations were observed. Lateralization (5 and 10 mm) of the glenosphere reduced the maximal acromial stress by 21% (1.5 MPa) and 31% (1.3 MPa), respectively. Inferiorization (5 and 10 mm) of the glenosphere increased the maximal acromial stress by 5% (2.0 MPa) and 15% (2.2 MPa), respectively. Changes in positioning the humeral component was found to have the highest impact in this model configuration. A 10-mm-lateralized humeral component reduced acromial stress by 37% (1.2 MPa), whereas in the 6-mm-medialized configuration, an increase in acromial stress by 83% (3.48 MPa) was observed. There was a high correlation between the delta angle and acromial stress (R2 = 0.967).

CONCLUSION

Implant design configuration has an impact on the acromial stress. High delta angles correlate with an increase in acromial stress. Both lateralization of the COR and the humerus decreased the acromial stress in our study. The lateralization of the humerus has the highest impact in influencing acromial stress. Because of contrary results in the current literature, further studies with focus on the acromial stress influenced by different anatomic variants of the shoulder and the acromion are needed before a clinical recommendation can be made.

Inlay vs. onlay humeral components in reverse total shoulder arthroplasty: a biorobotic shoulder simulator study

BACKGROUND

Both inlay and onlay humeral implants are available for reverse total shoulder arthroplasty (rTSA), but biomechanical data comparing these components remain limited. This study investigated the effects of inlay and onlay rTSA humeral components on shoulder biomechanics using a biorobotic shoulder simulator.

METHODS

Twenty fresh-frozen cadaveric shoulders were tested before and after rTSA with either an inlay or onlay humeral implant. Comparisons were performed between the most commonly implanted configurations for each implant (baseline) and with a modification to provide equivalent neck-shaft angles (NSAs) for the inlay and onlay configurations. Specimens underwent passive range-of-motion (ROM) assessment with the scapula held static, and scapular-plane abduction was performed, driven by previously collected human-subject scapulothoracic and glenohumeral kinematics. Passive ROM glenohumeral joint angles were compared using t tests, whereas muscle force and excursion data during scapular-plane elevation were evaluated with statistical parametric mapping and t tests.

RESULTS

Maximum passive elevation was reduced for the inlay vs. onlay humeral components, although both implants caused reduced passive elevation vs. the native joint. Inlay rTSA also demonstrated reduced passive internal rotation at rest and increased external rotation at 90° of humerothoracic elevation vs. the native joint. All preoperative planning estimates of ROM differed from experiments. Rotator cuff forces were elevated with an onlay vs. inlay humeral implant, but simulated muscle excursions did not differ between systems. Compared with the native joint, rotator cuff forces were increased for both inlay and onlay implants and deltoid forces were reduced for inlay implants. Muscle excursions were dramatically altered by rTSA vs. the native joint. Comparisons of inlay and onlay humeral implants with equivalent NSAs were consistent with the baseline comparisons.

CONCLUSIONS

Rotator cuff forces required to perform scapular-plane abduction increase following rTSA using both inlay and onlay implants. Rotator cuff forces are lower with inlay implants compared with onlay implants, although inlay implants also result in reduced passive-elevation ROM. Deltoid forces are lower with inlay implants in comparison to the native joint but not with onlay implants. The differences between inlay and onlay components are largely unaffected by NSA, indicating that these differences are inherent to the inlay and onlay designs. In those patients with an intact rotator cuff, decreased rotator cuff forces to perform abduction with an inlay humeral implant compared with an onlay implant may promote improved long-term outcomes owing to reduced deltoid muscle fatigue when using an inlay implant.

A two-year comparison of reverse total shoulder arthroplasty mini-humeral tray and augmented mini-glenoid baseplate implants vs. standard implants

BACKGROUND

Patients who undergo reverse total shoulder arthroplasty (RTSA) are getting younger with greater function expectations. This retrospective, longitudinal study of prospectively collected data compared perceived shoulder function and strength, active shoulder mobility, radiographic evidence of scapular notching, and implant survival over the initial 2-years post-RTSA among patient groups who received either standard central fixation point liner and glenoid baseplate implants, or lower size profile mini-humeral tray with offset trunnion options and mini-augmented glenoid baseplate implants.

MATERIALS AND METHODS

Patients who underwent primary RTSA using standard central fixation point liner and glenoid baseplate implants (Group 1, n = 180) were compared with patients who underwent primary RTSA using lower size profile mini-humeral tray with offset trunnion options and mini-augmented glenoid baseplate implants (Group 2, n = 53) for active shoulder mobility, American Shoulder and Elbow Surgeons (ASES) score, perceived ability to lift 10 lbs (4.5 kg) overhead, radiographic evidence of scapular notching, and implant survival. Data was collected pre-surgery, 6-weeks, 6-months, 1-year, and 2-years post-RTSA (p ≤ 0.05).

RESULTS

More Group 2 patients had more complex B or C Walch glenoid morphology, while Group 1 had more A1 or A2 types (p ≤ 0.001). Group 2 had greater active shoulder flexion at 6-months, 1-year, and 2-years (p ≤ 0.018) and external rotation (in adduction) at 6-months and 2-years (p ≤ 0.004) compared to Group 1, with higher ASES scores at 6-months and 2-years (p ≤ 0.026) (with small-to-medium effect sizes), and with more patients meeting or exceeding the minimal clinically important difference (MCID) at 2-years (p = 0.045) and patient acceptable symptomatic state (PASS) levels at 6-months, 1-year and 2-years (p ≤ 0.045). Scapular notching was identified in six of 53 (11.3%) Group 2 patients and in 32 of 180 (17.7%) Group 1 patients. Group 1 patients had more grade 2 or greater scapular notching grades compared to Group 2 (p = 0.04). Implant survival was comparable with Group 1 = eight of 180 (4.4%) and Group 2 = 1 of 53 (1.9%) of patients requiring removal for 95.6% and 98.1% implant survival, respectively.

CONCLUSION

Limited scapular notching and excellent implant survival was observed in both groups. Despite including individuals with more complex glenoid deficiency, patients receiving the lower size profile implants generally displayed better active shoulder mobility and perceived shoulder function compared to those who received standard implants. These patients also more frequently met or exceeded the MCID by 2-years post-RTSA and PASS levels by 6-months, 1-year, and 2-years post-RTSA, with lower scapular notching grades.

LEVEL OF EVIDENCE

Retrospective comparative study.

Mini-augmented glenoid baseplate and mini-humeral tray reverse total shoulder arthroplasty implant comparisons: two-year clinical outcomes

BACKGROUND

Augmented glenoid baseplate and offset humeral tray reverse total shoulder arthroplasty (RTSA) implants may decrease the mechanical impingement that creates scapular notching and improve shoulder function. This study evaluated the clinical efficacy of three different RTSA glenoid baseplate and offset humeral tray combinations for patient-reported shoulder function, pain and instability, radiographic imaging evidence of glenoid baseplate or humeral stem subsidence and migration, bony changes associated with implant loosening, and scapular notching over the initial 2 years post-RTSA. Primary outcomes included active shoulder mobility, perceived function, pain, instability, scapular notching, and implant survival.

METHODS

Sixty-seven patients from 6 research sites received one of three different glenoid baseplate and humeral tray combinations. Group 1 (n = 21) received a mini-augmented glenoid baseplate with a standard humeral tray; Group 2 (n = 23) received a standard glenoid baseplate and a mini-humeral tray with 3 trunnion offset options; Group 3 (n = 23) received both a mini-augmented glenoid baseplate and a mini-humeral tray with 3 trunnion offset options. Subjects underwent radiologic evaluation, completed the ASES scale, the EQ-5D-5L quality of life scale, VAS shoulder pain and instability questions, and active shoulder mobility measurements pre-operatively, and 6-weeks, 6-months, 1-2 years post-RTSA.

RESULTS

Improved active shoulder mobility, quality of life, perceived function, decreased shoulder pain and instability, excellent implant survival and minimal scapular notching were observed for all groups. Group 3 had better overall active shoulder mobility than the other groups and better perceived function than Group 1.

CONCLUSION

The group that received the mini-augmented glenoid baseplate and mini-humeral tray combination had better overall active shoulder flexion, external rotation at 90° abduction, and internal rotation. This group also had better perceived shoulder function compared to the group that received a mini-augmented glenoid baseplate with a standard humeral tray.

Total shoulder arthroplasty in patients with dementia or mild cognitive impairment

Background

Anatomic total shoulder arthroplasty (ATSA) and reverse total shoulder arthroplasty (RTSA) reliably alleviate pain and restore shoulder function for a variety of indications. However, these procedures are not well-studied in patients with neurocognitive impairment. Therefore, the purpose of this study was to investigate whether patients with dementia or mild cognitive impairment (MCI) have increased odds of surgical or medical complications following arthroplasty.

Methods

The PearlDiver database was queried from 2010 through October 2021 to identify a cohort of patients who underwent either ATSA or RTSA and had a minimum 2-year follow-up. Current Procedural Terminology and International Classification of Diseases codes were used to stratify this cohort into three groups: (1) patients with dementia, (2) patients with MCI, and (3) patients with neither condition. Surgical and medical complication rates were compared among these three groups.

Results

The overall prevalence of neurocognitive impairment among patients undergoing total shoulder arthroplasty was 3.0% in a cohort of 92,022 patients. Patients with dementia had increased odds of sustaining a periprosthetic humerus fracture (odds ratio [OR] = 1.46, P < .001), developing prosthesis instability (OR = 1.72, P < .001), and undergoing revision arthroplasty (OR = 1.55, P = .003) after RTSA compared to patients with normal cognition. ATSA patients with dementia did not have an elevated risk of surgical complications or revision. Conversely, RTSA patients with MCI did not have an elevated risk of complications or revision, although ATSA patients with MCI had greater odds of prosthesis instability (OR = 2.51, P = .008). Additionally, patients with neurocognitive impairment had elevated odds of medical complications compared to patients with normal cognition, including acute myocardial infarction and cerebrovascular accident.

Conclusion

Compared to patients with normal cognition, RTSA patients with preoperative dementia and ATSA patients with preoperative MCI are at increased risk for surgical complications. Moreover, both ATSA and RTSA patients with either preoperative MCI or dementia are at increased risk for medical complications. As the mean age in the U.S. continues to rise, special attention should be directed towards patients with neurocognitive impairment to minimize postoperative complications aftertotal shoulder arthroplasty, and the risks of this surgery more carefully discussed with patients and their families and caretakers.

Impact of reverse shoulder arthroplasty design and patient shoulder size on moment arms and muscle fiber lengths in shoulder abductors

BACKGROUND

Reverse shoulder arthroplasty (RSA) increases the moment arm of the deltoid; however, there is limited knowledge on the accompanying changes in muscle architecture that play a role in muscle force production. The purpose of this study was to use a geometric shoulder model to evaluate the anterior deltoid, middle deltoid, and supraspinatus regarding (1) the differences in moment arms and muscle-tendon lengths in small, medium, and large native shoulders and (2) the impact of 3 RSA designs on moment arms, muscle fiber lengths, and force-length (F-L) curves.

METHODS

A geometric model of the native glenohumeral joint was developed, validated, and adjusted to represent small, medium, and large shoulders. Moment arms, muscle-tendon lengths, and normalized muscle fiber lengths were assessed for the supraspinatus, anterior deltoid, and middle deltoid from 0° to 90° of abduction. RSA designs were modeled and virtually implanted, including a lateralized glenosphere with an inlay 135° humeral component (lateral glenoid-medial humerus [LGMH]), a medialized glenosphere with an onlay 145° humeral component (medial glenoid-lateral humerus [MGLH]), and a medialized glenosphere with an inlay 155° humeral component (medial glenoid-medial humerus [MGMH]). Descriptive statistics were used to compare moment arms and normalized muscle fiber lengths.

RESULTS

As shoulder size increased, the moment arms and muscle-tendon lengths for the anterior deltoid, middle deltoid, and supraspinatus increased. All RSA designs achieved greater moment arms for the anterior and middle deltoid, with the MGLH design achieving the largest increase. The resting normalized muscle fiber length of the anterior and middle deltoid was substantially increased in the MGLH (1.29) and MGMH (1.24) designs, shifting the operating ranges of these muscles to the descending portions of their F-L curves, whereas the LGMH design maintained a resting deltoid fiber length (1.14) and operating range similar to the native shoulder. All RSA designs demonstrated a decrease in the native supraspinatus moment arm in early abduction, with the largest decrease in the MGLH design (-59%) and minimal decrease in the LGMH design (-14%). The supraspinatus operated on the ascending limb of its F-L curve in the native shoulder and remained on this portion of the F-L curve for all RSA designs.

CONCLUSION

Although the MGLH design maximizes the abduction moment arm for the anterior and middle deltoid, overlengthening of the muscle may compromise deltoid muscle force production by forcing the muscle to operate on the descending portion of its F-L curve. In contrast, the LGMH design increases the abduction moment arm for the anterior and middle deltoid more modestly while allowing the muscle to operate near the plateau of its F-L curve and maximizing its force-producing potential.

The association between humeral lengthening and clinical outcomes after reverse shoulder arthroplasty: a systematic review and meta-analysis

BACKGROUND

The purpose of this study was to evaluate the relationship between humeral lengthening and clinical outcomes after reverse shoulder arthroplasty (RSA) with stratification based on measurement method and implant design.

METHODS

This systematic review was performed using PRISMA-P guidelines. PubMed/Medline, Cochrane Trials, and Embase were queried for articles evaluating the relationship between humeral lengthening and clinical outcomes inclusive of range of motion (ROM), strength, outcome scores, and pertinent complications (acromial and scapular spine fractures, nerve injury) after RSA. The relationship between humeral lengthening and clinical outcomes was reported descriptively overall and stratified by measurement method and implant design (globally medialized vs. lateralized). A positive association was defined as increased humeral lengthening being associated with greater ROM, outcome scores, or a greater incidence of complications, whereas a negative association denoted that increased humeral lengthening was associated with poorer ROM, outcome scores, or a lower incidence of complications. Meta-analysis was performed to compare humeral lengthening between patients with and without fractures of the acromion or scapular spine.

RESULTS

Twenty-two studies were included. Humeral lengthening was assessed as the acromiohumeral distance (AHD), the distance from the acromion to the greater tuberosity (AGT), the acromion to the deltoid tuberosity (ADT), and the acromion to the distal humerus (ADH). Of 11 studies that assessed forward elevation, a positive association with humeral lengthening was found in 6, a negative association was found in 1, and 4 studies reported no association. Of studies assessing internal rotation (n = 9), external rotation (n = 7), and abduction (n = 4), all either identified a positive or lack of association with humeral lengthening. Studies assessing outcome scores (n = 11) found either a positive (n = 5) or no (n = 6) association with humeral lengthening. Of the studies that assessed fractures of the acromion and/or scapular spine (n = 6), 2 identified a positive association with humeral lengthening, 1 identified a negative association, and 3 identified no association. The single study that assessed the incidence of nerve injury identified a positive association with humeral lengthening. Meta-analysis was possible for AGT (n = 2) and AHD (n = 2); greater humeral lengthening was found in patients with fractures for studies using the AGT (mean difference 4.5 mm, 95% CI 0.7-8.3) but not the AHD. Limited study inclusion and heterogeneity prohibited identification of trends based on method of measuring humeral lengthening and implant design.

CONCLUSION

The relationship between humeral lengthening and clinical outcomes after RSA remains unclear and requires future investigation using a standardized assessment method.

Latissimus Dorsi and Teres major tendon transfer increases internal rotation torque following lateralized reverse shoulder arthroplasty with subscapularis insufficiency

INTRODUCTION

Limitation of active Internal Rotation (IR) following Reverse Shoulder Arthroplasty (RSA) in patients with massive Rotator Cuff Tears (mRCTs) with subscapularis insufficiency remains a challenge. Recently, RSA with Latissimus dorsi and Teres major (LDTM) transfer in patients with limited active IR has been demonstrated as a reliable treatment option. The purpose of this study was to biomechanically compare the IR torque following LDTM transfer with RSA in mRCT with subscapularis insufficiency to RSA without tendon transfer.

METHODS

Eight cadaveric shoulders were tested (mean age: 64.5 ± 1.9 years) using a custom shoulder testing system that permits loading conditions of mRCT with subscapularis insufficiency. Two conditions were tested and compared. The first condition was RSA alone and the second condition was RSA with LDTM transfer. RSA with a medialized glenoid and lateralized humerus design was used for all specimens. The specimens were tested at 0°, 20° and 40° abduction at three different muscle loads: baseline, double, and triple, while the Teres minor and deltoid loads were kept constant. IR torque was measured with a torque wrench at 0°, 20°, and 40° abduction and 60° and 45° IR positions. Force required for anterior dislocation was measured at 20° abduction and 10° IR position.

RESULTS

RSA with LDTM transfer had significantly higher IR torque at all abductions and muscle loading compared with RSA without transfer (average at all positions; RSA without transfer: 0.80 ± 0.02 Nm, LDTM transfer for all loads: 1.43 ± 0.10 Nm). RSA with LDTM transfer (91.4 ± 3.9 N) needed higher force for anterior dislocation compared to RSA alone (89.4 ± 4.1 N), but there was no significant difference.

CONCLUSION

LDTM transfer with RSA increases IR torque compared to RSA without tendon transfer in a cadaveric model. LDTM transfer with RSA may be a reliable treatment option for patients with mRCT and subscapularis insufficiency who are expected to have limited active IR following RSA.

Subacromial notching after reverse total shoulder arthroplasty

BACKGROUND

Scapular notching is a well-known postoperative complication of reverse total shoulder arthroplasty (RTSA). However, subacromial notching (SaN), a subacromial erosion caused by repeated abduction impingement after RTSA, has not been previously reported in a clinical setting. Therefore, this study aimed to assess the risk factors and functional outcomes of SaN after RTSA.

METHODS

We retrospectively reviewed the medical records of 125 patients who underwent RTSA with the same design between March 2014 and May 2017 and had at least 2 years of follow-up. SaN was defined as subacromial erosion observed at the final follow-up but not on the X-ray 3 months after surgery. Radiologic parameters representing the patient's native anatomy and degrees of lateralization and/or distalization during surgery were evaluated using preoperative and 3 months postoperative X-rays. The visual analogue scale of pain, active range of motion, and American Shoulder and Elbow Surgeons score were assessed preoperatively and at the final follow-up to evaluate the functional outcomes of SaN.

RESULTS

SaN occurred in 12.8% (16/125) of enrolled patients during the study period. Preoperative center of rotation-acromion distance (P = .009) and postoperative humerus lateralization offset, which evaluated the degree of lateralization after RTSA (P = .003), were risk factors for SaN. The preoperative center of rotation-acromion distance and postoperative humerus lateralization cutoff values were 14.0 mm and 19.0 mm, respectively. The visual analogue scale of pain (P = .01) and American Shoulder and Elbow Surgeons score (P = .04) at the final follow-up were significantly worse in patients with SaN.

CONCLUSIONS

SaN might adversely affect postoperative clinical outcomes. As SaN correlated with patients' anatomical characteristics and degree of lateralization during RTSA, the implant's degree of lateralization should be adjusted according to the patient's own anatomical characteristics.

Computer-assisted analysis of functional internal rotation after reverse total shoulder arthroplasty: implications for component choice and orientation

PURPOSE

Functional internal rotation (IR) is a combination of extension and IR. It is clinically often limited after reverse total shoulder arthroplasty (RTSA) either due to loss of extension or IR in extension. It was the purpose of this study to determine the ideal in-vitro combination of glenoid and humeral components to achieve impingement-free functional IR.

METHODS

RTSA components were virtually implanted into a normal scapula (previously established with a statistical shape model) and into a corresponding humerus using a computer planning program (CASPA). Baseline glenoid configuration consisted of a 28 mm baseplate placed flush with the posteroinferior glenoid rim, a baseplate inclination angle of 96° (relative to the supraspinatus fossa) and a 36 mm standard glenosphere. Baseline humeral configuration consisted of a 12 mm humeral stem, a metaphysis with a neck shaft angle (NSA) of 155° (+ 6 mm medial offset), anatomic torsion of -20° and a symmetric PE inlay (36mmx0mm). Additional configurations with different humeral torsion (-20°, + 10°), NSA (135°, 145°, 155°), baseplate position, diameter, lateralization and inclination were tested. Glenohumeral extension of 5, 10, 20, and 40° was performed first, followed by IR of 20, 40, and 60° with the arm in extension of 40°-the value previously identified as necessary for satisfactory clinical functional IR. The different component combinations were taken through simulated ROM and the impingement volume (mm³) was recorded. Furthermore, the occurrence of impingement was read out in 5° motion increments.

RESULTS

In all cases where impingement occurred, it occurred between the PE inlay and the posterior glenoid rim. Only in 11 of 36 combinations full functional IR was possible without impingement. Anterosuperior baseplate positioning showed the highest impingement volume with every combination of NSA and torsion. A posteroinferiorly positioned 26 mm baseplate resulting in an additional 2 mm of inferior overhang as well as 6 mm baseplate lateralization offered the best impingement-free functional IR (5/6 combinations without impingement). Low impingement potential resulted from a combination of NSA 135° and + 10° torsion (4/6 combinations without impingement), followed by NSA 135° and -20° torsion (3/6 combinations without impingement) regardless of glenoid setup.

CONCLUSION

The largest impingement-free functional IRs resulted from combining a posteroinferior baseplate position, a greater inferior glenosphere overhang, 90° of baseplate inclination angle, 6 mm glenosphere lateralization with respect to baseline setup, a lower NSA and antetorsion of the humeral component. Surgeons can employ and combine these implant configurations to achieve and improve functional IR when planning and performing RTSA.

LEVEL OF EVIDENCE

Basic Science Study, Biomechanics.

Effects of neuromuscular electrical muscle stimulation on the deltoid for shoulder function restoration after reverse total shoulder arthroplasty in the early recovery period: a prospective randomized study

INTRODUCTION

Neuromuscular electrical stimulation (NMES) is a treatment modality that has been used to accelerate the rehabilitation of patients with neurological damage. However, it is unclear whether NMES of the deltoid can lead to the early restoration of shoulder function after reverse total shoulder arthroplasty (RSA).

MATERIALS AND METHODS

In this prospective and randomized study, 88 patients who underwent RSA with the same prosthesis design for cuff tear arthropathy or irreparable rotator cuff tear were assessed. The patients were divided into two groups (NMES group and non-NMES group, 44 patients each). For the NMES group, two pads of the NMES device were placed over the middle and posterior deltoid area, and NMES was maintained for 1 month after surgery. Shoulder functional outcomes and deltoid thickness were compared at 3, 6, and 12 months postoperatively. Shoulder functional outcomes were assessed based on the visual analog scale (VAS) for pain, American Shoulder and Elbow Surgeons (ASES), and Constant scores and the range of motion (ROM) and power of the affected shoulder. The thickness of the anterior, middle, and posterior deltoid was measured by ultrasonography.

RESULTS

A total of 76 patients (NMES group, 33 patients; non-NMES group, 43 patients) were enrolled in the final analysis. The preoperative demographics and status of the remaining rotator cuff of both groups were not significantly different. At postoperative 3 months, the ROM and power of external rotation of the NMES group were significantly greater than those of the non-NMES group (ROM, 36° ± 14° vs. 29° ± 12°; P = .003; power, 4.8 kg ± 1.8 kg vs. 3.8 kg ± 1.0 kg; P < .002). The ROM of external rotation of the NMES group at postoperative 6 months was also greater than that of the non-NMES group (41° ± 12° vs. 34° ± 11°; P = .013). However, there was no significant difference in the VAS, ASES, and Constant scores at all follow-up points despite gradual improvements until 1 year postoperatively. Serial measurements of the thickness of the anterior, middle, and posterior deltoid of both groups did not show significant differences.

CONCLUSIONS

Postoperative NMES of the deltoid after RSA contributed to significantly faster ROM restoration and considerable improvement in the power of external rotation. Therefore, NMES following RSA could lead to the early restoration of external rotation and recovery of deltoid function.

Extension of the shoulder is essential for functional internal rotation after reverse total shoulder arthroplasty

BACKGROUND

Disabling loss of functional internal rotation (fIR) after reverse total shoulder arthroplasty (RTSA) is frequent but not well understood. This study tested the hypothesis that limitation of fIR after RTSA is not primarily related to a deficit in internal rotation.

METHODS

Fifty patients (mean age at RTSA, 74 ± 11.7 years) who were consecutively seen at a yearly follow-up visit at 1-10 years (median, 4 years) after RTSA were prospectively examined with special attention to fIR. Patients with axillary nerve or deltoid dysfunction were excluded. Relative (age- and sex-adjusted) Constant-Murley scores (CSs) and Subjective Shoulder Values were assessed preoperatively and at final follow-up. In addition, active extension and 4 postoperative activities of daily living (ADLs) requiring fIR were tested at follow-up. Rotator cuff fatty infiltration and notching were evaluated radiographically. For analysis, patients were divided into a group with poor fIR (fIR-, n = 19), defined as ≤2 internal-rotation points in the CS, and a group with good fIR (fIR+, n = 31), defined as ≥4 internal-rotation points in the CS.

RESULTS

Active extension of the contralateral shoulders was comparable in the fIR- group (mean, 60.3° [standard deviation (SD), 11.2°]) and fIR+ group (66.1° [SD, 14.2°]). Postoperatively, a difference in active extension between the unaffected and operated sides was present in both groups and averaged 16° (55° [SD, 14.3°] in fIR+ group and 39.1° [SD, 10.8°] in fIR- group; P < .001). No patient in the fIR+ group had active extension < 40° (range, 40°-85°). Shoulders with extension ≥ 40° but unsatisfactory fIR had restricted passive internal rotation in extension. The ability to perform ADLs behind the back correlated better with shoulder extension than with so-called fIR measurements in the CS.

CONCLUSION

Functional internal rotation after RTSA requires at least 40° of shoulder extension. If fIR is unsatisfactory despite 40° of extension, passive restriction of internal rotation in full extension is the limiting factor. It is crucial to preserve or restore active shoulder extension to allow ADLs involving internal rotation.

Innovations in Shoulder Arthroplasty

Innovations currently available with anatomic total shoulder arthroplasty include shorter stem designs and augmented/inset/inlay glenoid components. Regarding reverse shoulder arthroplasty (RSA), metal augmentation, including custom augments, on both the glenoid and humeral side have expanded indications in cases of bone loss. In the setting of revision arthroplasty, humeral options include convertible stems and newer tools to improve humeral implant removal. New strategies for treatment and surgical techniques have been developed for recalcitrant shoulder instability, acromial fractures, and infections after RSA. Finally, computer planning, navigation, PSI, and augmented reality are imaging options now available that have redefined preoperative planning and indications as well intraoperative component placement. This review covers many of the innovations in the realm of shoulder arthroplasty.

In Vitro Simulation of Shoulder Motion Driven by Three-Dimensional Scapular and Humeral Kinematics

In vitro simulation of three-dimensional (3D) shoulder motion using in vivo kinematics obtained from human subjects allows investigation of clinical conditions in the context of physiologically relevant biomechanics. Herein, we present a framework for laboratory simulation of subject-specific kinematics that combines individual 3D scapular and humeral control in cadavers. The objectives were to: (1) robotically simulate seven healthy subject-specific 3D scapulothoracic and glenohumeral kinematic trajectories in six cadavers, (2) characterize system performance using kinematic orientation accuracy and repeatability, and muscle force repeatability metrics, and (3) analyze effects of input kinematics and cadaver specimen variability. Using an industrial robot to orient the scapula range of motion (ROM), errors with repeatability of ±0.1 mm and <0.5 deg were achieved. Using a custom robot and a trajectory prediction algorithm to orient the humerus relative to the scapula, orientation accuracy for glenohumeral elevation, plane of elevation, and axial rotation of <3 deg mean absolute error (MAE) was achieved. Kinematic accuracy was not affected by varying input kinematics or cadaver specimens. Muscle forces over five repeated setups showed variability typically <33% relative to the overall simulations. Varying cadaver specimens and subject-specific human motions showed effects on muscle forces, illustrating that the system was capable of differentiating changes in forces due to input conditions. The anterior and middle deltoid, specifically, showed notable variations in patterns across the ROM that were affected by subject-specific motion. This machine provides a platform for future laboratory studies to investigate shoulder biomechanics and consider the impacts of variable input kinematics from populations of interest, as they can significantly impact study outputs and resultant conclusions.

Effect of two types of shoulder prosthesis on the muscle forces using a generic multibody model for different arm motions

Background

This study aims to analyze the effects of a novel dual-bearing shoulder prosthesis and a conventional reverse shoulder prosthesis on the deltoid and rotator cuff muscle forces for four different arm motions. The dual-bearing prosthesis is a glenoid-sparing joint replacement with a moving center of rotation. It has been developed to treat rotator cuff arthropathy, providing an increased post-operative functionality.

Methods

A three-dimensional musculoskeletal OpenSim® model of an upper body, incorporating a natural gleno-humeral joint and a scapula-thoracic joint developed by Blana et al. (J Biomech 41: 1714-1721, 2008), was used as a reference for the natural shoulder. It was modified by integrating first a novel dual-bearing prosthesis, and second, a reverse shoulder prosthesis into the shoulder joint complex. Four different arm motions, namely abduction, scaption, internal and external rotation, were simulated using an inverse kinematics approach. For each of the three models, shoulder muscle forces and joint reaction forces were calculated with a 2 kg weight in the hand.

Results

In general, the maximal shoulder muscle force and joint reaction force values were in a similar range for both prosthesis models during all four motions. The maximal deltoid muscle forces in the model with the dual-bearing prosthesis were 18% lower for abduction and 3% higher for scaption compared to the natural shoulder. The maximal rotator cuff muscle forces in the model with the dual-bearing prosthesis were 36% lower for abduction and 1% higher for scaption compared to the natural shoulder. Although the maximal deltoid muscle forces in the model with the dual-bearing prosthesis in internal and external rotation were 52% and 64% higher, respectively, compared to the natural shoulder, the maximal rotator cuff muscle forces were 27% lower in both motions.

Conclusion

The study shows that the dual-bearing shoulder prosthesis is a feasible option for patients with rotator cuff tear and has a strong potential to be used as secondary as well as primary joint replacement. The study also demonstrates that computer simulations can help to guide the continued optimization of this particular design concept for successful clinical outcomes.

Reverse Shoulder Arthroplasty Biomechanics

The reverse total shoulder arthroplasty (rTSA) prosthesis has been demonstrated to be a viable treatment option for a variety of end-stage degenerative conditions of the shoulder. The clinical success of this prosthesis is at least partially due to its unique biomechanical advantages. As taught by Paul Grammont, the medialized center of rotation fixed-fulcrum prosthesis increases the deltoid abductor moment arm lengths and improves deltoid efficiency relative to the native shoulder. All modern reverse shoulder prostheses utilize this medialized center of rotation (CoR) design concept; however, some differences in outcomes and complications have been observed between rTSA prostheses. Such differences in outcomes can at least partially be explained by the impact of glenoid and humeral prosthesis design parameters, surgical technique, implant positioning, patient-specific bone morphology, and usage in humeral and glenoid bone loss situations on reverse shoulder biomechanics. Ultimately, a better understanding of the reverse shoulder biomechanical principles will guide future innovations and further improve clinical outcomes.

Influence of rotator cuff integrity on loading and kinematics before and after reverse shoulder arthroplasty

Reverse Shoulder Arthroplasty has become a very common procedure for shoulder joint replacement, even for scenarios where an anatomical reconstruction would traditionally be used. Our hypothesis is that implanting a reverse prosthesis with a functional rotator cuff may lead to higher joint reaction force (JRF) and have a negative impact on the prosthesis. Available motion capture data during anterior flexion was input to a finite-element musculoskeletal shoulder model, and muscle activations were computed using inverse dynamics. Simulations were carried out for the intact joint as well as for various types of rotator cuff tears: superior (supraspinatus), superior-anterior (supraspinatus and subscapularis), and superior-posterior (supraspinatus, infraspinatus and teres minor). Each rotator cuff tear condition was repeated after shifting the humerus and the glenohumeral joint center of rotation to represent the effect of a reverse prosthesis. Changes in compressive, shear, and total JRF were analyzed. The model compared favorably to in vivo JRF measurements, and existing clinical and biomechanical knowledge. Implanting a reverse prosthesis with a functional rotator cuff or with an isolated supraspinatus tear led to more than 2 times higher compressive JRF than with massive rotator cuff tears (superior-anterior or superior-posterior), while the shear force remained comparable. The total JRF increased more than 1.5 times. While a lower shear to compressive ratio may reduce the risk of glenosphere loosening, higher JRF might increase the risk for other failure modes such as fracture or polyethylene wear of the reverse prosthesis.

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.

Early restoration of shoulder function in patients with the Grammont prosthesis compared to lateralized humeral design in reverse shoulder arthroplasty

BACKGROUND

This study aimed to compare the clinical outcomes and radiographic parameters of patients after reverse shoulder arthroplasty (RSA) between the Grammont prosthesis and lateralized humeral design prosthesis.

METHODS

A total of 114 patients who underwent RSA with a lateralized humeral design (group L; 71 shoulders) and medialized humeral design (group M; 43 shoulders) prosthesis for cuff tear arthropathy or irreparable rotator cuff tear were enrolled. Clinical outcomes including visual analog scale (VAS), American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form (ASES), and Constant scores and range of motion (ROM) were serially followed up at postoperative 3, 6, 12, and 24 months. Radiographic parameters were measured to evaluate preoperative and postoperative status.

RESULTS

Both prostheses demonstrated similar clinical outcomes and shoulder function preoperatively and at postoperative 2 years (P >.05). However, patients in group M had significantly better postoperative active forward flexion (postoperative 3 months, 115° ± 12° vs. 101° ± 14°; P <.001; 6 months, 125° ± 13° vs. 118° ± 13°; P <.013) and abduction (3 months, 105° ± 12° vs. 98° ± 12°; P = .002); VAS (3 months, 3.1 ± 1.2 vs. 3.7 ± 1.4; P = .031; 6 months, 2.3 ± 1.1 vs. 2.8 ± 1.3; P = .038); ASES (3 months, 64.2 ± 7.0 vs. 60.4 ± 9.2; P = .022; 6 months, 70.6 ± 6.0 vs. 66.6 ± 8.1; P = .007); and Constant scores (6 months, 59.6 ± 6.9 vs. 55.7 ± 9.3; P = .020). Group L showed a significantly lower rate of scapular notching than group M (15.5% vs. 41.8%; P < .001). The position of the proximal humerus in group L was more lateralized and less distalized than in group M after RSA.

CONCLUSIONS

RSA with both the Grammont and lateralized humeral design prostheses provided similar shoulder ROM restoration and functional improvements at a minimum of 2 years. However, patients with a humeral lateralized prosthesis showed slower recovery of shoulder function and ROM up to postoperative 6 months despite a lower incidence of scapular notching.

Reverse shoulder arthroplasty used for revision of reverse shoulder arthroplasty: a systematic review

Background

As reverse shoulder arthroplasty (RSA) cases increase, so too will the need to revise subsequent failures. Many of the complications associated with revising anatomic total shoulder and hemiarthroplasty have been adequately addressed by RSA including glenoid bone deficiency, instability, and functional outcomes. However, the risk for complication when revising a failed reverse prosthesis may be more pronounced with increased bone and soft tissue deficiency. The ability for the reversed prosthesis to accommodate these insufficiencies following a prior reversed prosthesis is unclear.

Methods

PubMed, Embase, and Google Scholar were queried for articles which fit the inclusion criteria of a reversed prosthesis used to revise a failed primary reverse prosthesis with a minimum follow-up of 12 months and clinical outcome reporting.

Results

After exclusions, 9 studies reporting on 242 reverse shoulders with a mean follow-up of 40.29 months were analyzed. The differences between preoperative and postoperative weighted means were not significant for Constant (P = .26), American Shoulder and Elbow Surgeons Shoulder score (P = .61), SSV (P = .57), and visual analog scale for pain (P = .48). Functional improvements in elevation (74°-102°) and external rotation (18°-21°) were consistent with those reported for primary reverse procedures, although differences in preoperative and postoperative measures were not statistically significant. Patient satisfaction was 89% with a major complication rate of 25%.

Discussion

The reverse shoulder prosthesis has proven satisfactory in revising hemiarthroplasty and anatomic total shoulder arthroplasty. The current results indicate RSA is also a satisfactory treatment option when revising a prior reverse prosthesis. Inherent to revision shoulder surgery is the obstacle of humeral and glenoid bone loss, an attenuated soft-tissue envelope, and instability. The reverse prosthesis may adequately address these commonly confronted difficulties with its inherent design characteristics. RSA provides a secure glenoid fixation for bone grafting, the ability to increase construct stability with component sizing, and a reliance on the deltoid for function. As our learning about revision of RSA improves, so will our ability to preemptively address potential issues which may lead to decreased complications in these cases. Despite the 25% rate of major complication, patients reported satisfaction of 89% which demonstrates the improvements in function and pain relief that are provided by the reverse prosthesis.

Reverse shoulder arthroplasty glenoid lateralization influences scapular spine strains

BACKGROUND

Scapular spine insufficiency fractures following reverse shoulder arthroplasty are poorly understood. There exists limited literature regarding the role of reverse shoulder arthroplasty lateralization on scapular spine strains and fractures. The purpose of this cadaveric biomechanical simulator study was to evaluate the role of glenoid lateralization on scapular spine strain.

METHODS

Eight cadaveric shoulders were tested using an in-vitro simulator. A custom modular reverse shoulder arthroplasty was implanted that allowed for in-situ glenoid lateralization adjustment. Scapular spine strain was measured by strain gauges placed in clinically relevant Levy zones along the scapular spine. All specimens were tested in loaded forward elevation and abduction.

RESULTS

Glenoid lateralization from 0 to 5 mm caused negligible changes in scapular spine strains. Lateralization from 5 to 10 mm, however, caused significant increases in strain at 0° forward elevation in all strain gauges (p < 0.026). Strains measured in Levy zone 2 were significantly higher than all other locations (p < 0.039). Additionally, forward elevation resulted in significantly higher strain values than abduction (p = 0.001).

CONCLUSIONS

Glenoid lateralization is an important parameter in reverse shoulder arthroplasty; however, our results demonstrate higher degrees of lateralization may place higher strains on the scapular spine. An understanding of reverse shoulder arthroplasty lateralization and scapular spine strains is important to optimize parameters and to mitigate negative effects.

LEVEL OF EVIDENCE

Basic Sciences Study, Cadaveric Model, Biomechanics.

Biomechanics of anatomic and reverse shoulder arthroplasty

The biomechanics of the shoulder relies on careful balancing between stability and mobility. A thorough understanding of normal and degenerative shoulder anatomy is necessary, as the goal of anatomic total shoulder arthroplasty is to reproduce premorbid shoulder kinematics.With reported joint reaction forces up to 2.4 times bodyweight, failure to restore anatomy and therefore provide a stable fulcrum will result in early implant failure secondary to glenoid loosening.The high variability of proximal humeral anatomy can be addressed with modular stems or stemless humeral components. The development of three-dimensional planning has led to a better understanding of the complex nature of glenoid bone deformity in eccentric osteoarthritis.The treatment of cuff tear arthropathy patients was revolutionized by the arrival of Grammont's reverse shoulder arthroplasty. The initial design medialized the centre of rotation and distalized the humerus, allowing up to a 42% increase in the deltoid moment arm.More modern reverse designs have maintained the element of restored stability but sought a more anatomic postoperative position to minimize complications and maximize rotational range of motion. Cite this article: EFORT Open Rev 2021;6:918-931. DOI: 10.1302/2058-5241.6.210014.

Tomographic Analysis of Positioning of Reverse Baseplates Positioning

Objective

To verify whether reverse baseplate positioning without the support of intraoperative three-dimensional technology is within the acceptable parameters in the literature and whether glenoid bone deformity (GBD) compromises this positioning.

Methods

Sixty-nine reverse shoulder arthroplasties were evaluated with volumetric computed tomography (CT). Two radiologists performed blinded CT scan analysis and evaluated baseplate position within 2mm of the inferior glenoid; the inclination and version of the baseplate in relation to the Friedman line; and upper and lower screw and baseplate metallic peg end point positionings. The patients were divided according to the presence of GBD for statistical analyses.

Results

The two radiologists concurred reasonably in their interpretations of the following analyzed parameters: baseplate position within 2mm of the inferior glenoid rim (97.1% and 95.7%), baseplate inclination (82.6% and 81.2%), baseplate version (69.6% and 56.5%), the upper screw reaching the base of the coracoid process (71% and 79.7%), the inferior screw remaining inside the scapula (88.4% and 84.1%), and the metallic peg of the baseplate considered intraosseous (88.4% and 72.5%).

Conclusion

Reverse baseplate positioning without intraoperative three-dimensional technology is within the acceptable parameters of the literature, except for baseplate version and upper screw position. GBD did not interfere with baseplate positioning in reverse shoulder arthroplasty.

Scapular Notching Following Ipsilateral Traumatic Clavicle Fracture in Reverse Total Shoulder Arthroplasty: A Case Report

Introduction

Reverse total shoulder arthroplasty (RTSA) procedures are becoming increasingly more common. While the main complications are known, the management of clavicle fractures in patients with an ipsilateral RTSA is not well described. There are three case studies that document clavicular stress fractures following RTSA with an atraumatic etiology, and to our knowledge, no studies have described a traumatic clavicular fracture following RTSA.

Case

We describe the case of a 75-year-old woman with a traumatic clavicle fracture five years after RTSA for rotator cuff tear arthropathy. With minimal pain and subjective symptoms initially, the patient wished to pursue non-operative treatment. However, she eventually developed a painful non-union and pseudoparalysis of the shoulder with serial radiographs demonstrating progressive superior scapular tilting and scapular notching. Subsequent open reduction internal fixation of her clavicle fracture significantly improved her pain and function.

Conclusion

We report a traumatic clavicle fracture in the setting of RTSA that not only failed to heal but also resulted in scapular notching and shoulder pseudoparalysis that was improved with surgical stabilization of the fracture. It is possible that the setting of a semi-constrained RTSA, the resulting biomechanical imbalance may predispose to impaired fracture healing and non-union of the clavicle fracture.

Lateralized versus nonlateralized reverse total shoulder arthroplasty

Throughout the history of reverse total shoulder arthroplasty, the extent of lateral offset has changed considerably from "too lateral" to "too medial" and has been lately swinging back towards a point somewhere in between. Nonlateralized designs minimize shear forces on the glenoid and decrease force required by the deltoid. Glenoid lateralization decreases impingement and scapular notching and improves range of motion. Humeral lateralization achieves a more anatomic position of the tuberosities while maintaining a nonlateralized center of rotation. Several factors play a role in choosing the extent of lateral offset and method of lateralization.

Factors influencing functional internal rotation after reverse total shoulder arthroplasty

Background

Functional internal rotation (fIR) of the shoulder is frequently limited after reverse shoulder arthroplasty (RTSA). The objective of this study was to study a cohort of satisfied patients after RTSA who had comparable active mobility except for fIR and to identify factors associated with selective loss of fIR.

Methods

A retrospective cohort study was conducted to compare 2 patient groups with either poor (≤ 2 points in the Constant-Murley score [CS]) or excellent (≥8 points in CS) fIR after RTSA at a minimum follow-up of 2 years. Influencing factors (demographic, surgical or implant related, radiographic parameters) and clinical outcome were analyzed.

Results

Fifty-two patients with a mean age of 72.8 (±9.3) and a mean follow-up of 41 months were included in the IR≤2 group and 63 patients with a mean age of 72.1 (±8.0) and a mean follow-up of 59 months in the IR≥8 group. All patients had undergone RTSA with the same implant type and only 2 different glenosphere sizes (36 and 40) for comparable indications. A multivariate analysis identified the following significant risk factors for poor postoperative fIR: poor preoperative fIR (pts in CS: 3 [range: 2-6] vs. 6 [range: 4-8], P<.0001), smoking (17.3% vs. 6.5%, P = .004), male gender (59.6% vs. 31.7%, P = .002), less preoperative to postoperative distalization of the greater tuberosity (Δ 19.4 mm vs. 22.2 mm, P = .026), a thin humeral insert (≤3 mm: 23.1% vs. 54.8%, P = .039), and a high American Society of Anesthesiologists score (≤ III: 30.8% vs. 14.3%, P = .043). Subscapularis repair status and glenosphere size had no influence on fIR. Clinical outcome scores improved in both groups from preoperatively to last follow-up. The IR≥8 group had overall significantly better outcome scores compared to the IR≤2 group (Δ 9.3% SSV and Δ 9.5% relative CS, P < .0001). There was no difference in CS between the cohorts when the score for fIR was discarded.

Conclusion

Independent risk factors for poor postoperative fIR after RTSA are poor preoperative fIR, smoking, male gender, less preoperative to postoperative distalization of the greater tuberosity, a thin humeral insert height, and a high American Society of Anesthesiologists score. Except for male gender, these factors are modifiable. These findings may be a valuable addition to patient counselling as well as preoperative planning and preoperative and intraoperative decision-making. The relevance of fIR for overall satisfaction is substantiated by this study.

Infraspinatus or teres minor fatty infiltration does not influence patient outcomes after reverse shoulder arthroplasty with a lateralized glenoid

Background

Previous studies show that reverse shoulder arthroplasty (RSA) may improve forward elevation (FE) but external rotation may remain impaired with substantial teres minor fatty infiltration. The purpose of this study was to examine the influence of fatty infiltration on postoperative range of motion (ROM) and patient-reported outcomes (PROs) after RSA with a more lateralized center of rotation.

Methods

About 69 patients (average age 69 years; 44 women, 25 men) with preoperative MRI, 1-year postoperative ROM, 2-year Veteran's Rand Survey, American Shoulder and Elbow Surgeons subjective form, and Single Alpha-Numeric Evaluation scores who underwent RSA with a lateralized glenoid component between 2010 and 2014 were identified. Patients with Fuchs stage 3 fatty degeneration were compared with patients with Fuchs stage ≤ 2 using a one-way ANOVA.

Results

Eleven patients had Fuchs stage 3 in the teres minor and 28 with stage 3 in the infraspinatus. Charlson comorbidity indices, Veteran's Rand Survey scores, age, and BMI were not different between groups. There were no differences after one year (follow-up = 15 ± 14 months) in FE (FE = 128 ± 29) or external rotation (33 ± 13) between groups. There were no differences in two-year minimum (follow-up = 42.9 ± 17.9 months) American Shoulder and Elbow Surgeons scores between degenerated teres minor (76.4 ± 20) or infraspinatus (69.1 ± 24) groups.

Conclusion

This is the first study to assess the influence of teres minor and infraspinatus fatty infiltration on the postoperative ROM and PROs with a more lateralized glenoid RSA implant. Our results show that in a more lateralized RSA, neither teres minor nor infraspinatus fatty infiltration appear to negatively influence ROM or PROs.

In vivo reverse total shoulder arthroplasty contact mechanics

BACKGROUND

Several in vitro studies have investigated the biomechanics of reverse total shoulder arthroplasty (RTSA); however, few in vivo studies exist. The purpose of this study was to examine in vivo RTSA contact mechanics in clinically relevant arm positions. Our hypothesis was that contact would preferentially occur in the inferior region of the polyethylene liner.

METHODS

Forty patients receiving a primary RTSA were recruited for a prospective cohort study. All patients received the same implant design with a nonretentive liner. Stereo radiographs were taken at maximal active range of motion. Model-based radiostereometric analysis was used to identify implant position. Contact area between the polyethylene and glenosphere was measured as the geometric intersection of the 2 components and compared with respect to polyethylene liner size, arm position, and relative position within the liner.

RESULTS

There were no differences in the proportion of contact area in any arm position between polyethylene liner sizes, ranging from 30% ± 17% to 38% ± 23% for 36-mm liners and 32% ± 21% to 41% ± 25% for 42-mm liners. Contact was equally distributed between the superior and inferior halves of the liner at each arm position (P = .06-.79); however, greater contact area was observed in the outer radius of the liner when the arm was flexed (P = .002).

CONCLUSION

This study highlights that contact mechanics are similar between 36- and 42-mm liners. Contact area is generally equally distributed throughout the liner across the range of motion and not preferentially in the inferior region as hypothesized.

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

Background

In reverse shoulder arthroplasties (RSA), osseous in-growth is promoted if glenoid micromotion does not exceed 150 μm. The purpose of this study was to determine whether the configuration of central fixation for RSA glenoid baseplates reduces implant micromotion or changes scapula bone stresses.

Methods

Using finite element analysis, glenoid baseplate fixation was tested in a cohort of 3 male and 2 female patients who were to undergo RSA. Computer models were created for 3 different RSA glenoid baseplate and 84 glenosphere designs, a central threaded peg (1 variant, D-TP), a central unthreaded peg (2 variants, I- 85 P(15) and I-P(25)), and a central peg with a screw (2 variants, A-PS and I-PS). A compressive and shear force of 756 N was distributed across the glenosphere with the scapula anchored.

Results

Displacement was within 20-130 μm at the glenosphere baseplate-bone interface for all baseplates. The glenospheres with unthreaded pegs had intermediate displacement values (I-P(15): median, 89 μm; range, 32-112 μm; and I-P(25): median, 93 μm; range, 31-109 μm). The von Mises stresses were 1.8-7.0 MPa within cortical bone and 0.6-1.6 MPa within trabecular bone. Cortical bone stresses were similar with unthreaded pegs (I-P(15): median, 4.2 MPa; range, 1.8-6.0 MPa; and I-P(25): median, 4.2 MPa; range, 1.8-6.1 MPa), whereas mean trabecular stresses were similar for all configurations.

Conclusions

All configurations yielded adequate stability, with micromotions being below 150 μm. The unthreaded pegged designs provided a valid alternative to the stable threaded pegged convex baseplates in terms of micromotions and bone stresses.

Survivorship of a Medialized Glenoid and Lateralized Onlay Humerus Reverse Shoulder Arthroplasty Is High at Midterm Follow-up

BACKGROUND

Reverse shoulder arthroplasty (RSA) is a common treatment of a variety of disabling shoulder conditions. The purpose of this study was to determine revision-free survivorship after RSA using a medialized glenoid and lateralized onlay-type humerus implant and to identify etiologies of revision.

METHODS

All RSAs performed using the Comprehensive^® Reverse Shoulder System (Zimmer Biomet, Inc.; Warsaw, IN, USA) at one institution from 2008 to 2014 were identified through a retrospective review. Charts were reviewed to determine whether the RSA was a primary or revision surgery. Patients were contacted by telephone, and survivorship was defined as no subsequent surgery after RSA. Of the 526 RSAs performed, responses were obtained from 403 patients (77%). A Kaplan-Meier analysis was performed to determine survivorship over time. A χ ² test was used to determine differences between revision rates after RSA.

RESULTS

Minimum follow-up was 3 years, and average follow-up was 4.83 ± 1.60 years. Survivorship was 96% at 2 years and 93% at 5 years after RSA. Revisions were performed for instability (n = 8), humeral tray-taper junction failure (n = 5), acute fracture (n = 4), infection (n = 3), glenoid loosening (n = 3), osteolysis (n = 1), or notching (n = 1). Fourteen of the 151 patients (9.2%) who had surgery prior to RSA required revision after RSA. Having shoulder surgery prior to RSA was associated with higher rates of subsequent revision after RSA.

CONCLUSION

Overall, survivorship after RSA using a medialized glenoid and lateralized onlay-type humerus RSA is high, and prostheses implanted in native shoulders have lower rates of revision at midterm follow-up. Instability (1.9%) was the most common reason for revision.

Acromial and Scapular Fractures After Reverse Total Shoulder Arthroplasty with a Medialized Glenoid and Lateralized Humeral Implant: An Analysis of Outcomes and Risk Factors

This article was updated on TK because of a previous error, which was discovered after the preliminary version of the article was posted online. In Table VII, the fracture rate in the study by Walch et al. that had read "4.6% (21 of 457)" now reads "0.9% (4 of 457)."

BACKGROUND

Acromial and scapular fractures after reverse total shoulder arthroplasty (rTSA) are rare and challenging complications, and little information is available in the literature to identify patients who are at risk. This study analyzes risk factors for, and compares the outcomes of patients with and without, acromial and scapular fractures after rTSA with a medialized glenoid/lateralized humeral implant.

METHODS

Four thousand one hundred and twenty-five shoulders in 3,995 patients were treated with primary rTSA with 1 design of reverse shoulder prosthesis by 23 orthopaedic surgeons. Sixty-one of the 4,125 shoulders had radiographically identified acromial and scapular fractures. Demographic characteristics, comorbidities, implant-related data, and clinical outcomes were compared between patients with and without fractures to identify risk factors. A multivariate logistic regression, 2-tailed unpaired t test, and chi-square test or Fisher exact test identified significant differences (p < 0.05).

RESULTS

After a minimum duration of follow-up of 2 years, the rate of acromial and scapular fractures was 1.77%, with the fractures occurring at a mean (and standard deviation) of 17.7 ± 21.1 months after surgery. Ten patients had a Levy Type-1 fracture, 32 had a Type-2 fracture, 18 had a Type-3 fracture, and 1 fracture could not be classified. Patients with acromial and scapular fractures were more likely to be female (84.0% versus 64.5% [p = 0.004]; odds ratio [OR] = 2.75 [95% confidence interval (CI) = 1.45 to 5.78]), to have rheumatoid arthritis (9.8% versus 3.3% [p = 0.010]; OR = 3.14 [95% CI = 1.18 to 6.95]), to have rotator cuff tear arthropathy (54.1% versus 37.8% [p = 0.005]; OR = 2.07 [95% CI = 1.24 to 3.47]), and to have more baseplate screws (4.1 versus 3.8 screws [p = 0.017]; OR = 1.53 [95% CI = 1.08 to 2.17]) than those without fractures. No other implant-related differences were observed in the multivariate analysis. Patients with fractures had significantly worse outcomes than patients without fractures, and the difference in mean improvement between these 2 cohorts exceeded the minimum clinically important difference for the majority of measures.

CONCLUSIONS

Acromial and scapular fractures after rTSA are uncommon, and patients with these fractures have significantly worse clinical outcomes. Risk factors, including female sex, rheumatoid arthritis, cuff tear arthropathy, and usage of more baseplate screws were identified on multivariate logistic regression analysis. Consideration of these findings and patient-specific risk factors may help the orthopaedic surgeon (1) to better inform patients about this rare complication preoperatively and (2) to be more vigilant for this complication when evaluating patients postoperatively.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Preoperative external rotation deficit does not predict poor outcomes or lack of improvement after reverse total shoulder arthroplasty

INTRODUCTION

The purpose was to compare postoperative outcomes and functional improvement between patients with preoperative aER deficits vs. preserved aER function.

RESULTS

There were 115 patients in the <0° aER group and 314 in the ≥30° aER group. Preoperative patients in the <0° group were worse for all measures except subjective pain while post-operatively, they had significantly greater improvement for all measures of motion. Postoperatively, both groups achieved comparable scores for forward elevation, pain, SST and ASES.

CONCLUSION

This study demonstrates that patients with a complete aER deficit can recover substantial and comparable function after RTSA.

Clinical comparison of humeral-lateralization reverse total shoulder arthroplasty between patients with irreparable rotator cuff tear and patients with cuff tear arthropathy

Background

This study aimed to compare the clinical and radiologic outcomes between patients with irreparable cuff tears (ICTs) and those with cuff tear arthropathy (CTA) after reverse total shoulder arthroplasty (RTSA) with a humeral-lateralization prosthesis.

Methods

A total of 127 patients with ICTs and CTA who underwent RTSA were enrolled and matched at a 1:2 ratio by propensity score. Preoperative shoulder function was assessed for all patients. Radiologic parameters including the acromion-deltoid tuberosity (ADT) distance, lateral humeral offset, and scapular notching were evaluated.

Results

Thirty-four patients in the ICT group and 68 patients in the CTA group were matched for comparison. Preoperatively, mean active forward flexion in the ICT group (89.7° ± 29.4°) was significantly better than that in the CTA group (65.5° ± 24.0°, P < .001). In the CTA group, fatty infiltration of the supraspinatus was worse (3.7 ± 0.5) and the ADT distance was shorter (134.0 ± 12.0 mm) compared with the ICT group preoperatively (3.3 ± 0.8 [P = .008] and 140.7 ± 12.5 mm [P = .001], respectively). There was no significant difference in postoperative functional or radiologic outcomes between the 2 groups. However, gains in active forward flexion (37.9° in ICT group vs. 61.5° in CTA group, P < .01) and abduction (42.1° in ICT group vs. 60.6° in CTA group, P < .01) were significantly greater in the CTA group than in the ICT group.

Conclusions

Shoulder function was significantly improved after RTSA regardless of the preoperative diagnosis. Postoperatively, radiologic findings were not significantly different between the 2 groups. Due to the fact that preoperative range of motion and rotator cuff status were better in patients with ICTs, improvements in active forward flexion and abduction were significantly greater in patients with CTA.

Periprosthetic Fractures in Reverse Total Shoulder Arthroplasty: Current Concepts and Advances in Management

PURPOSE OF REVIEW

Expanded indications for reverse total shoulder arthroplasty (RSA) have raised awareness of associated complications, including periprosthetic fractures. The purpose of this article was to provide a comprehensive update on how, when, and why RSA-related periprosthetic fractures occur, as well as to describe the current treatment strategies.

RECENT FINDINGS

Periprosthetic acromial and scapular spine fractures occur in up to 4.3% of cases and periprosthetic humeral fractures occur in approximately 3.5% of RSA procedures. Fractures of the coracoid process and clavicle have also been reported. Current literature has identified several risk factors for intraoperative or postoperative fracture, including underlying osteoporosis, revision arthroplasty, use of a superiorly placed screw during metaglene fixation, and disruption of the scapular ring by transection of the coracoacromial ligament. Periprosthetic fracture associated with RSA is a clinically significant event that warrants prolonged postoperative vigilance, timely diagnosis, and shared patient decision-making regarding treatment. Further research is needed to identify optimal treatment strategies and characterize long-term clinical outcomes following RSA-related periprosthetic fracture.

Lateralization in reverse shoulder arthroplasty: A review

Reverse shoulder arthroplasty, as originally designed by Grammont, has revolutionized the treatment of rotator cuff arthropathy as well as fractures about the proximal humerus. The original design consisted of glenoid and humeral components with a medialized center or rotation compared to the native shoulder. Long term outcome studies on this design demonstrated high rates of scapular notching as well as significant loss of external rotation. To combat these flaws, prosthesis design has evolved to include the concept of lateralization whereby the center of rotation is moved laterally compared to the Grammont prosthesis via either the glenoid or humeral components. Lateralization via the glenoid component has sought to reduce scapular notching, however, concerns over early loosening have been raised secondary to increasing stress at the glenosphere/glenoid interface. Lateralization via the humeral component has been theorized to improve the mechanics of the remaining rotator cuff and deltoid musculature while avoiding the problems inherent with glenoid lateralization. While limited clinical evidence is available currently to support one design over the other, multiple biomechanical studies have shown improvements in rates of scapular notching and post-operative external rotation for lateralized humeral and glenoid components. Future research should aim to delineate advantages of one design over the other or optimal combinations of the two designs.

Development and Application of a Novel Metric to Characterize Comprehensive Range of Motion of Reverse Total Shoulder Arthroplasty

Active range of motion (ROM) of reverse total shoulder arthroplasty (rTSA) can be limited by bony impingement, muscle inability, and joint instability. The aim of this study was to develop a novel metric representative of comprehensive ROM of rTSA, which is evaluated in the context of all three factors. It was hypothesized that the metric, termed global circumduction ROM (GC-ROM), would capture differences resulting from directional changes in rTSA design parameters known to increase ROM. GC-ROM was calculated for a set of 18 rTSA configurations with humeral polyethylene cup depths of 6 and 8.1 mm, glenosphere lateralization (GLat) distances of 0, 5, and 10 mm, and neck-shaft angles (NSA) of 135°, 145°, and 155°. For any implant configuration, arm positions were defined by internal/external (IE) rotation angle and two spherical coordinates representing the elevation plane angle and elevation angle. At each IE rotation angle, incremental positions with variable elevation plane and elevation angles were checked for feasibility based on impingement, muscle ability, and risk of instability. Coordinates of feasible positions were mapped to unit spheres and connected to form regions, of which the surface area was calculated to represent allowable circumduction ROM. ROMs were averaged across all IE rotation angles to produce a single metric, GC-ROM. The results showed that decreasing cup depth and increasing GLat and NSA increased GC-ROM. In conclusion, a novel metric to characterize comprehensive ROM, evaluated based on several ROM-limiting factors, was developed as a performance metric through which rTSA designs can be compared. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:880-887, 2020.

The role of greater tuberosity healing in reverse shoulder arthroplasty: a finite element analysis

BACKGROUND

The lack of greater tuberosity (GT) healing in proximal humerus fractures has been negatively correlated with outcomes for hemiarthroplasty; however, there is still debate regarding the effects of GT healing in reverse shoulder arthroplasty (RSA). Our goal was to examine the effects of GT healing using a kinematic finite element analysis (FEA) model.

MATERIAL AND METHODS

Computer-aided design models of a medialized glenoid with a lateralized humerus (MGLH) RSA design were uploaded into an FEA shoulder model in 2 different configurations: healed greater tuberosity (HGT) and nonunion greater tuberosity (NGT). Deltoid muscle forces and joint reaction forces (JRFs) on the shoulder were calculated during abduction (ABD), forward flexion (FF), and external rotation (ER).

RESULTS

Force magnitude of the anterior, middle, and posterior deltoid muscle as well as JRFs modeled in both GT scenarios were similar for ABD (muscle forces P = .91, P = .75, P = .71, respectively; and JRF P = .93) and for FF (muscle forces P = .89, P = .83, P = .99, respectively; and JRF P = .90). For ER, the force magnitude between 2 GT settings showed statistically significant differences (HGT: 9.51 N vs. NGT: 6.13 N) (P < .001). Likewise, during ER, JRFs were different, and the NGT group showed a steep drop in JRF after 10° of ER (HGT: 28.4 N vs. NGT: 18.38 N) (P < .001).

CONCLUSION

GT healing does not seem to impact RSA biomechanics during abduction or forward flexion; however, it does affect biomechanics during external rotation. Overall orthopedic surgeons can expect good results for patients after RSA even with poor GT healing.

Toileting ability of patients after primary reverse total shoulder arthroplasty

Background

This study aimed to determine the toileting ability (TA) of patients undergoing primary reverse total shoulder arthroplasty (RTSA) and identify factors associated with TA postoperatively.

Methods

A questionnaire regarding toileting was administered to 119 patients who underwent primary RTSA with a minimum 1-year follow-up. Patients were separated into 2 groups based on whether the arm that underwent RTSA was the one used for toileting (study group, n = 74) or not (control group, n = 45). Patient-reported TA was calculated both before and after RTSA. Multivariate analysis was performed to identify factors associated with TA postoperatively.

Results

Impairment in TA before RTSA was higher in the study group and affected almost three-quarters of the patients (72%). In the study group, primary RTSA resulted in a statistically significant improvement in TA (P < .001), and no difference in TA was found between groups after RTSA (P = .076). Postoperatively, 92% of the patients in the study group were able to manage toileting with the involved extremity (54% without difficulty and 38% with some degree of difficulty). Only 1 patient (1.3%) was totally unable to manage toileting with either arm postoperatively. The patients at risk of toileting difficulties postoperatively were those who had preoperative toileting difficulties and lower postoperative internal rotation range of motion.

Conclusions

Over 90% of patients can manage toileting after primary RTSA, and total toileting inability is rare after the procedure (1.3%). Patients should be counseled that after primary RTSA, they have a high probability of being able to manage toileting with independence even if it is with some difficulty.

Numerical Study of the Biomechanical Behaviour of the Different Implantation Methods of the Reverse Shoulder Replacement

Despite the widespread use of reverse total shoulder arthroplasty, there is still a problem of conflict between the polyethylene cup of the prosthesis and the scapula, which over time causes the phenomenon of notching. In order to circumvent this problem correctly, several innovations have been proposed regard to the implementation method. In this context, the aim of this work is to study the biomechanical behavior of new implantation methods using different glenoid configurations in order to avoid the notching phenomenon between the cup and the scapula. The study was performed using virtual prototypes of the shoulder prosthesis assembly. Using CT scan images, three-dimensional models of shoulder bones were reconstructed. The implantation of the prosthesis in the three-dimensional model was performed in collaboration with an experienced surgeon from the Caduceus Clinic (Oran, Algeria). The numerical models were imported to finite element calculation software. After the validation of the numerical model using the literature results, we assessed the biomechanical behavior of four implantation methods under the same boundary conditions and abduction movements. From the obtained results, it was found that among the proposed methods, the BIO-SR lateralization method offers significant biomechanical advantages in terms of the forces applied to the glenoid during the abduction movement.

Isokinetic Evaluation of Shoulder Strength and Endurance after Reverse Shoulder Arthroplasty: A Comparative Study

OBJECTIVE

The present study aimed to compare the isometric strength and endurance of shoulder abduction and internal and external rotation between operated shoulders and nonoperated, contralateral shoulders of patients who underwent reverse shoulder replacement due to unilateral rotator cuff tear arthropathy.

PATIENTS AND METHODS

With a diagnosis of cuff tear arthropathy, 41 consecutive patients (mean age of 70.8 years; age range, 57 to 84; 36 females, 5 males) who underwent unilateral reverse shoulder arthroplasty were reviewed based on functional and radiological data. In all cases, cuff tear arthropathy was unilateral and contralateral shoulder was asymptomatic, with normal shoulder function. The average length of follow-up was 34 months (range of 12-67). To assess patients' functional level, the Constant score and the Disabilities of the Arm, Shoulder, and Hand (the Quick-DASH) outcome measure were used preoperatively and at the final examination. The primary outcomes of the present study were measurement of isokinetic strength and endurance of shoulder abduction and internal and external rotation using an isokinetic evaluator.

RESULTS

Patients exhibited marked improvement in functional level as reflected by a significant increase in the mean Constant score from 38 preoperatively to 65 at the final follow-up (p = 0.03). The functional improvement was supported by a decrease in the mean Quick-DASH from 64 preoperatively to 26 at the final follow-up (p = 0.018). In the comparison of the isokinetic strength and endurance of shoulder abduction, no statistical difference was observed between operated shoulders and contralateral shoulders (p > 0.05). However; the strength and endurance of internal and external rotation were lower in operated shoulders than in contralateral shoulders (p < 0.05). Similarly, there was no statistically significant difference in comparisons of the durability of abduction (p > 0.05); however, the durability of internal and external rotation were significantly lower in operated shoulders (p < 0.05).

CONCLUSION

In terms of durability and strength of abduction, similar results with the unaffected shoulder may be accomplished; nonetheless, the surgeon should be aware that durability and strength of rotation would be weak.

LEVEL OF EVIDENCE

Level III, Therapeutic Study.

Is subscapularis repair associated with better outcome compared to non-repair in reverse total shoulder arthroplasty? A systematic review of comparative trials

We aimed to investigate whether combined reverse total shoulder arthroplasty (RTSA) and subscapularis repair leads to improved clinical and functional outcome in comparison with RTSA alone. Two reviewers independently conducted a systematic search according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) using the MEDLINE/PubMed database and the Cochrane Database of Systematic Reviews. These databases were queried with the terms "reverse" AND "shoulder" AND "arthroplasty" AND "with" AND "subscapularis" AND "repair". From the 72 initial studies, we finally chose five studies which were eligible to our inclusion-exclusion criteria. The total mean modified Coleman methodology test was 55/100 (range: 47/100 to 60/100). The eligible studies included 1087 patients, in total. Regarding the subjective functional scores as well as range of motion (ROM), the differences amongst groups were insignificant in almost all studies. The mean complications' rate of the repair group was 10.4%, whereas the respective rate of the nonrepair group was 10.2%. All studies concluded that the repair of subscapularis did not affect the complications' rate of patients who were treated with RTSA. The mean dislocations' rates of the repair and the nonrepair group were 1.5% and 2.3%, respectively. Although subscapularis repair was proven safe and effective for the augmentation of RTSA, it did not offer any additional clinical or functional benefit in the outcome of patients treated with lateralized RTSA. Therefore, it is not supported its routine use for patients who have a preoperatively sufficient subscapularis tendon.

The effect of subscapularis repair on dislocation rates in reverse shoulder arthroplasty: a meta-analysis and systematic review

BACKGROUND

Reverse total shoulder arthroplasty is an effective treatment for patients with rotator cuff arthropathy; however, complication rates are relatively high (19%-50%), with implant instability and infection being particularly devastating to overall outcomes. The objective of this study was to analyze the highest level of data comparing dislocation rates and outcomes in reverse total shoulder arthroplasty with and without the subscapularis tendon repaired.

METHODS

The databases MEDLINE, Embase, and CINAHL were searched using a sensitive search strategy for this meta-analysis/systematic review. Eligibility included any studies in which patients were treated with a reverse total shoulder arthroplasty in which the status of the subscapularis tendon could be determined. A data extraction form was developed to collect select data from the included studies. A meta-analysis was performed on pooled data of 5 studies comparing dislocation rates and 3 studies comparing postoperative forward elevation, rate of infection, overall complication rates, and fractures.

RESULTS

Two independent researchers reviewed 1008 studies. Seven studies met inclusion criteria. A meta-analysis was performed on all level III studies, resulting in 1306 patients being analyzed. Results demonstrated lower dislocation rates in the subscapularis repair group (odds ratio, 0.19; P < .001). However, in patients without a subscapularis repair, lateralized center of rotation (COR) resulted in a significantly lower dislocation rate compared with medialized COR (odds ratio, 0.24; P < .001).

CONCLUSION

The results of our meta-analysis of the available data demonstrated a decrease in dislocation risk when the subscapularis tendon was repaired in medialized and lateralized designs. When subscapularis repair is not performed, lateralized COR, regardless of humeral socket design, may reduce the dislocation rates.

Increased scapular spine fractures after reverse shoulder arthroplasty with a humeral onlay short stem: an analysis of 485 consecutive cases

BACKGROUND

Scapular stress fractures after reverse shoulder arthroplasty (RSA) are a potentially serious complication with modern lateralized and onlay implants. The aim of this study was to report the scapular spine stress fracture rate after RSA with an onlay, 145° humeral stem, analyzing potential fracture risk factors and clinical outcomes in a large cohort of patients.

METHODS

A consecutive series of 485 RSAs were implanted with the Aequalis Ascend Flex stem. Data collection included preoperative and postoperative clinical and radiographic assessment findings (rotator cuff Goutallier grade; Hamada, Walch, and Favard classifications; range of motion; Constant score) and perioperative data. Patients with a scapular spine fracture following RSA were matched with nonfracture control patients, and preoperative variables were tested to determine whether they were predictive of a scapular spine fracture.

RESULTS

A scapular spine fracture following RSA occurred in 21 patients (4.3%), with a mean time to diagnosis of 8.6 months (range, 1-34 months). No preoperative factor was found to be a significant predictor of scapular spine fracture. Both groups showed significant improvements in active mobility measurements and Constant scores from preoperatively to final follow-up (P < .001). The control group scored significantly better than the scapular spine fracture group regarding the Constant score and forward flexion.

CONCLUSION

Scapular spine fractures have shown an increased prevalence after onlay-design RSA. This series was not able to link any clear risk factors. Functional results are limited, regardless of the fracture management.

Restoration of External Rotation Following Reverse Shoulder Arthroplasty without Latissimus Dorsi Transfer

Background

Latissimus dorsi transfers have been considered necessary to restore active external rotation following reverse shoulder arthroplasty (RSA). The purpose of this study was to assess the effectiveness of an RSA system that lateralizes the center of rotation in restoring active external rotation without a latissimus dorsi transfer in patients with a preoperative external rotation deficit (external rotation of <0°).

Methods

We retrospectively reviewed the records of patients who had undergone RSA with a lateralized center of rotation without a latissimus dorsi transfer. All patients had had a preoperative external rotation deficit (active external rotation of <0°), and all were followed for a minimum of 2 years. Patients were stratified into 2 groups on the basis of the preoperative diagnosis: (1) those with a combined loss of active elevation and external rotation as a result of rotator cuff tear arthropathy (CLEER group) and (2) those with a combined loss of active elevation and external rotation as a result of other posttraumatic etiologies (non-CLEER group). The mean improvement of external rotation was analyzed. Subgroup analysis was performed on the basis of the Goutallier classification, glenosphere lateralization, and total prosthetic lateralization.

Results

Thirty-three patients (24 in the CLEER group and 9 in the non-CLEER group) met the inclusion criteria. The average follow-up was 43.4 months (range, 24 to 77 months). External rotation improved significantly in both the CLEER group (from -21° preoperatively to 28° postoperatively; p < 0.001) and the non-CLEER group (from -19° preoperatively to 26° postoperatively; p = 0.001). Goutallier classification, glenosphere lateralization, and total prosthetic lateralization were not correlated with the degree of improvement of external rotation in either group (p > 0.05 for all).

Conclusions

RSA with a lateralized center of rotation can effectively restore external rotation without the use of a latissimus dorsi transfer in patients with a preoperative external rotation deficit as a result of rotator cuff arthropathy or other posttraumatic etiologies.

Level of Evidence

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.