Effect of the neck-shaft angle on stability in the onlay type of reverse shoulder arthroplasty: a cadaveric study

BackgroundAlthough reverse shoulder arthroplasty (RSA) has been indicated for treating patients suffering from cuff tear arthropathy, instability is a severe complication. The relationship between the humeral neck-shaft angle and joint stability in RSA as well as the clinical effect of subscapularis tendon repair on postoperative stability after RSA remain controversial. This study is primarily aimed to investigate the relationship between humeral neck-shaft angle and stability using the onlay type of RSA with preserved shoulder girdle muscles using fresh frozen cadavers. Moreover, we aimed to investigate the effect of subscapularis tendon repair after RSA placement.MethodsAn onlay type RSA of not-lateralized glenosphere in a massive rotator cuff tear model with preserved shoulder component muscles was placed on 7 fresh frozen cadavers, and traction tests were performed to dislocate by changing the neck-shaft angle of the stem to 135°, 145°, and 155°. The anterior dislocation force (DF) was evaluated in 6 patterns as follows: 2 patterns at 30° and 60° of abduction and 3 patterns at 30° of internal rotation, in neutral rotation, and 30° of external rotation. DF was recorded at neck-shaft angles of 135°, 145°, and 155° and with and without subscapularis tendon repair.ResultsAt 30° abduction, DF was significantly higher at a neck-shaft angle of 155° regardless of the rotational position (P < .05), and at abduction 60°, there was no difference in DF according to any rotational position and any neck-shaft angle. Regardless of the neck-shaft angle, the DF was significantly higher at 60° abduction than at 30° abduction (P < .05). Furthermore, the DF was significantly higher with subscapularis tendon repair (P < .01).ConclusionOur results showed some relationship between humeral neck-shaft angle and stability in the onlay type of RSA with preserved shoulder component muscles using fresh frozen cadavers. Moreover, a neck-shaft angle of 155° showed the highest anterior DF among neck-shaft angles of 135° and 145° at 30° abduction, and there was no difference at abduction 60° among any neck-shaft angle. Furthermore, subscapularis tendon repair also contributed to anterior stability.     

Biomechanical analysis of the subscapularis,infraspinatus and teres minor length and moment arm after reverse shoulder arthroplasty: a cadaveric study

BackgroundReverse shoulder arthroplasty (RSA) affects the length and moment arm of the deltoid and rotator cuff. Currently, RSA is commonly considered for cuff-intact conditions, such as primary glenohumeral osteoarthritis. As such, understanding the effect of contemporary lateralized designs on the rotator cuff is paramount. The purpose of this study was to determine changes in length and moment arm of the subscapularis, infraspinatus and teres minor with implantation of one of 3 RSA designs.MethodsA previously validated model was used in 6 hemi-toraces with the shoulder attached. Suture lines were run through pneumatic cylinders from the insertion to the origin of 10 muscles to apply a constant, stabilizing load. Electromagnetic tracking sensors were fixed to the thorax, scapula, and humerus to record 3-dimensional kinematics. Coordinate systems were established according to ISB recommendations. The origin and insertion of the subscapularis, infraspinatus and teres minor were digitized and tracked. Testing consisted of manually rotating the humerus through 5 cycles of its internal-external rotation arc. Kinematic data was collected at 120 Hz. Testing was performed in 3 positions of abduction: 0°, 30°, and 60°. After testing the intact shoulder, RSA was performed using 3 different configurations: an onlay 135-degree humeral component matched with a 2-mm lateralized glenosphere, the same humeral component with a 6-mm lateralized glenosphere, and an inlay 135-degree humeral component matched with a 10 mm lateralized glenosphere. Minimal muscle operative lengths, maximal muscle operative lengths, and muscle moment arms were computed.ResultsWhen compared with the native shoulder, all 3 configurations of RSA resulted in statistically significant increases in both the minimal and maximal operative lengths of the subscapularis in all abduction positions. The teres minor only showed a statistically significant increase in minimal and maximal length at 60° of abduction. The infraspinatus showed a statistically significant increase in tendon excursion at 0° and 30° of abduction. In 40° of abduction and 40° of internal rotation, all RSA configurations translated in a decreased subscapularis internal rotation moment arm. On the contrary, RSA increased the external rotation moment arm of the infraspinatus in neutral rotation and 0° of abduction.ConclusionImplantation of contemporary lateralized RSA implants led to increased length of the subscapularis to a greater extent than the increased length experienced by the infraspinatus and teres minor. The moment arm of the subscapularis decreased, whereas the moment arm of the teres minor in neutral rotation with the arm in abduction increased.Level of EvidenceLevel III; Basic Science, Biomechanics Study     

Reverse Total Shoulder Arthroplasty for the Treatment of Defect Arthropathy

Abstract Objective: Total shoulder replacement for restoration of function and for pain relief of damaged glenohumeral joint accompanied by extensive irreparable cuff defect. Indications: Any painful shoulder arthropathy with insufficient and irreparable rotator cuff, especially primary defect arthropathy, rheumatoid arthritis with extensive rotator cuff defect, arthropathy after reconstruction of rotator cuff, mutilating rheumatoid arthritis, and crystal-induced arthropathy. Relative: failure of primary shoulder replacement in the presence of an irreparable cuff defect. Contraindications: Structural or neurogenic lesion of deltoid muscle. Advanced glenoid destruction. Relative: age < 65 years. Surgical Technique: Anterosuperior or deltopectoral approach. Exposure of glenoid. Resection of humeral head at epi-metaphyseal junction. Complete detachment of anterior, inferior, and posterior capsule from glenoid neck. Preparation of glenoid for cement-free fixation of glenoid base plate (metaglène). Preparation of humeral shaft for implantation of humeral component in 0–10° of retroversion. Screwing of glenosphere to base plate. Insertion of cemented or cement-free modular humeral component. Results: Between 10/1997 and 03/2001, a reverse total shoulder arthroplasty was done in 57 patients (14 men, 43 women; average age 70.1 years). Average follow-up time was 18.2 months. 98% of patients would agree to repeat surgery. Average Constant Score adjusted to age and gender was 94%, 97% for patients not having undergone previous surgery. All patients reported complete or almost complete freedom of pain. On the condition that the deltoid muscle was not damaged during previous surgery, a good improvement of power and function could be obtained. All functional parameters were normal for the patient’s age with the exception of a slight limitation of internal rotation (average L5). The power of maintained abduction also corresponded in general to age-specific values. Only grade 1 or 2 inferior glenoid notching was observed but never reaching or surpassing the inferior screw (grade 3 or 4); no glenoid base plate loosening. The following is a reprint from Operat Orthop Traumatol 2005;17:1–24 and continues the new series of articles at providing continuing education on operative techniques to the European trauma community. Reprint from: Operat Orthop Traumatol 2005;17:1–24. DOI 10.1007/s00064-005-1119-1     

Clinical results of humeral stem lateralization in reverse shoulder arthroplasty: Comparative study of 145° onlay curved stem vs 155° inlay straight stem

BackgroundThe main limits of Grammont's reverse shoulder arthroplasty (RSA) design are loss of external rotation and scapular notching. These limits can be addressed with glenoid and/or humeral lateralization. Currently, there is no uniformity in the literature regarding the best option to improves these outcomes. Lateralization of the humeral side should be an option. The aim of the present study was to compare outcomes of a 145 degree onlay curved stem vs a 155 degree inlay straight stem.MethodsA retrospective analysis of 96 consecutive patients undergoing RSA (98 shoulders) was performed. Of these, 47 patients (48 shoulders) underwent RSA with a Aequalis Reversed II Stem (Group A) and 49 (50 shoulders) with a lateralized humeral stem (Ascend Flex©) (Group B). The exclusion criteria included any relevant glenoid bone loss in the horizontal plane or vertical plane and patients with post-traumatic conditions including humeral head necrosis. Patient with teres minor fatty infiltration superior to grade 2 according to Goutallier's classification were also excluded. Constant score, muscular strength and range of motion (ROM), were evaluated preoperatively and for 2 years postoperatively. Radiographs were examined for scapular notching.ResultsComparing clinical outcomes, there were significant improvements with active ROM using lateralized shoulder stem (Group B) in flexion, abduction and external rotation (P > .05). However, while evaluating the Constant score and muscular strength, no important difference emerged between the two groups. Scapular notching was observed in 29.17% of cases (24 shoulders) of Group A and in 12% of cases (6 shoulders) of Group B. Moreover, the average degree of notching was reduced in Group B in which the grade 1 was observed in 4 shoulders out of 50. Grade 2 was observed in 7 shoulders in Group A and in 2 shoulders in Group B. Grade 3 and grade 4 were observed only in 1 patient in Group A, and no one in Group B.ConclusionsThe lateralized humeral stem (145°, onlay, curved stem) in RSA improves ROM, particularly external rotation and abduction compared to Aequalis Reversed II Stem. No significant difference was found between the two groups regarding muscular strength. Both designs provide an overall improvement on function and pain relief. Moreover, the incidence of scapular notching is lower in a lateralized humeral stem implant (12% of cases) compared to traditional reverse prostheses with an Aequalis Reversed II Stem (29.17% of cases).Level of EvidenceIII     

Die inverse Schulterendoprothese zur Behandlung der Defektarthropathie

OBJECTIVE: Total shoulder replacement for restoration of function and for pain relief of damaged glenohumeral joint accompanied by extensive irreparable cuff defect. INDICATIONS: Any painful shoulder arthropathy with insufficient and irreparable rotator cuff, especially primary defect arthropathy, rheumatoid arthritis with extensive rotator cuff defect, arthropathy after reconstruction of rotator cuff, mutilating rheumatoid arthritis, and crystal-induced arthropathy. Relative: failure of primary shoulder replacement in the presence of an irreparable cuff defect. CONTRAINDICATIONS: Structural or neurogenic lesion of deltoid muscle. Advanced glenoid destruction. Relative: age < 65 years. SURGICAL TECHNIQUE: Anterosuperior or deltopectoral approach. Exposure of glenoid. Resection of humeral head at epi-metaphyseal junction. Complete detachment of anterior, inferior, and posterior capsule from glenoid neck. Preparation of glenoid for cement-free fixation of glenoid base plate (metaglène). Preparation of humeral shaft for implantation of humeral component in 0-10 degrees of retroversion. Screwing of glenosphere to base plate. Insertion of cemented or cement-free modular humeral component. RESULTS: Between 10/1997 and 03/2001, a reverse total shoulder arthroplasty was done in 57 patients (14 men, 43 women; average age 70.1 years). Average follow-up time was 18.2 months. 98% of patients would agree to repeat surgery. Average Constant Score adjusted to age and gender was 94%, 97% for patients not having undergone previous surgery. All patients reported complete or almost complete freedom of pain. On the condition that the deltoid muscle was not damaged during previous surgery, a good improvement of power and function could be obtained. All functional parameters were normal for the patient's age with the exception of a slight limitation of internal rotation (average L5). The power of maintained abduction also corresponded in general to age-specific values. Only grade 1 or 2 inferior glenoid notching was observed but never reaching or surpassing the inferior screw (grade 3 or 4); no glenoid base plate loosening.     

Does critical shoulder angle predict abduction motion and acromion-tuberosity impingement in reverse shoulder arthroplasty?

BackgroundVirtual planning software for reverse shoulder arthroplasty (RSA) has introduced the ability to optimize implant position in an effort to maximize bony impingement–free motion. Abduction impingement typically occurs between the glenoid and polyethylene or between the tuberosities and the acromion or coracoid. Acromion-tuberosity impingement has been considered less desirable, as it may create additional stress on the acromion. Patients with a large acromion overhang may have higher rates of acromion-tuberosity impingement. As the critical shoulder angle (CSA) represents a larger distance from the glenoid face to the acromion, the purpose of this study was to evaluate the impact of implant selection and position on abduction motion and acromion-tuberosity impingement, with a focus on the association to CSA. We hypothesize that a larger CSA will be associated with less abduction motion and an increase in acromion-tuberosity impingement.MethodsThis is a retrospective cohort case series of 85 consecutive patients who underwent RSA from June 2020 to January 2021. Humeral and glenoid components were implanted virtually (SurgiCase) using a standard protocol for a single implant system (DJO AltiVate Short Stem Reverse) with an inset humeral component. Implant variables analyzed included baseplate location (central vs. inferior glenoid), glenosphere lateralization (10 mm vs. 6 mm), and humeral shell (standard vs. semiconstrained). The maximal degree of abduction and location of impingement were recorded at external rotation of 0°, 45°, and 90°. Implant combinations that resulted in no impingement and no motion were recorded.ResultsIncrease in CSA was associated with acromion-tuberosity impingement for nearly every combination at 0° and 45° external rotation; however, there were no significant associations between CSA and maximum abduction motion. Acromion-tuberosity impingement was associated with central glenosphere placement in all degrees of external rotation (P < .001), use of a 10 mm lateralized glenosphere for 0° (P < .001) and 45° (P = .076), and using a standard polyethylene shell for 0° (P = .032) and 45° external rotation (P = .007). Maximal abduction motion was associated with inferior placement (P < .001), and use of a 10 mm lateralized glenosphere (P < .001) in all positions of external rotation but was not influenced by the polyethylene type.ConclusionIncreased CSA is associated with acromion-tuberosity impingement and can be used to screen for patients at risk for bony impingement in abduction. Placement of the glenosphere centrally and use of a 10 mm lateralized glenosphere were associated with higher rates of acromion-tuberosity impingement. Maximal abduction can be achieved using a 10 mm lateralized glenosphere and inferior placement.     

Glenoid baseplate migration with subsequent stabilization after reverse shoulder arthroplasty using a through-growth cage: a matched cohort study

BackgroundFew studies have evaluated the outcomes of glenoid baseplate migration after reverse shoulder arthroplasty (RSA). The question is whether an ingrowth central cage implant that has undergone early migration can restabilize due to cage ingrowth. The primary purpose of this study is to evaluate the radiographic factors associated with glenoid baseplate migration after RSA using a through-growth cage implant and secondarily evaluate their clinical outcomes with nonoperative management.MethodsA retrospective review of a single institution database was performed from January 1,2008 to June 30, 2017 for all shoulders using a single implant system (Equinoxe, Exactech, Inc., Gainesville, FL, USA). All RSAs with a documented complication of glenoid loosening were evaluated. Chart and radiograph review was performed to identify shoulders with confirmed glenoid loosening undergoing revision (revision group, n = 10) and those with migration that stabilized over time and avoided revision surgery (stable migration group, n = 10). The stable migration group was matched to an age-, sex-, and follow-up matched control group (1:3) (control group, n = 30). Demographic factors, preoperative and immediate postoperative radiographic factors, active range of motion (ROM), and patient-reported outcomes (PROMs) were compared. Radiographic factors evaluated included preoperative alpha/beta angles, humeral lengthening, glenosphere overhang, prosthesis-scapular neck angle, glenosphere inclination, and postoperative alpha/beta angles.ResultsA total of 50 RSA patients were evaluated at a mean follow-up of 38 months. Immediate postoperative inferior glenoid overhang was significantly less in the stable migration group compared to the control group (6.2 vs. 8.6 mm, P = .03). Preoperative ROM and PROMs were similar amongst all 3 groups. The stable migration group demonstrated improved ROM and PROMs compared preoperatively with all ROM and PROM values exceeding the minimally clinically important difference (MCID). The control group demonstrated greater improvements in ROM and PROMs compared to the stable migration group, with a majority exceeding the MCID. When compared to the revision group, the stable migration group had significantly greater improvements in forward flexion, ASES score, and Constant score as well as improvements above the MCID in abduction, external rotation, and SST score.ConclusionRSA patients with glenoid migration and secondary stabilization still achieve improved ROM above the MCID, but the results are inferior to those RSA patients without glenoid migration. Approximately half of the shoulders with baseplate loosening using a through-growth cage implant will restabilize and have better ROM and function compared to those that are ultimately revised.Level of EvidenceLevel III; Treatment Study     

The entire rotator cuff contributes to elevation of the arm

The function of the infraspinatus, teres minor, and subscapularis during elevation of the arm remains poorly defined. These muscles may generate moments that contribute to abduction of the arm, although they frequently are classified as humeral depressors. The purposes of this study were to measure the contributions to abduction made by the more inferiorly positioned rotator cuff muscles relative to the contributions of the supraspinatus and to determine the range of motion at which the muscles are most effective. Five fresh cadaveric shoulder girdles were mounted in an apparatus designed to simulate contraction of the deltoid and rotator cuff while maintaining the normal relationship between glenohumeral and scapulothoracic motions. The deltoid force required for elevation was measured without simulated contraction of the rotator cuff and with simulated contraction of the entire rotator cuff, of the supraspinatus only, and of the infraspinatus-teres minor and subscapularis only. A significant reduction in deltoid force when other muscle activity was added indicated that the additions contributed significantly to abduction. The deltoid force required with concurrent contraction of the entire rotator cuff averaged 41% less than with the deltoid alone but was not significantly different than with the deltoid and supraspinatus or with the deltoid, infraspinatus-teres minor, and subscapularis. Concurrent application of forces to the supraspinatus or the infraspinatusteres minro and subscapularis significantly reduced the required deltoid force over the range of motion studied by an average of 28 and 36%, respectively. The contributions of the rotator cuff muscles to abduction of the arm were greatest at low abduction angles (30 and 60°) and were insignificant by 120°. The infraspinatus-teres minor and subscapularis contribute significantly to abduction: their contibution was equal to that of the supraspinatus and, like the supraspinatus, they are most effective during the first 90° of abduction.     

Postimpingement instability following reverse shoulder arthroplasty: a parametric finite element analysis

BackgroundInstability following reverse shoulder arthroplasty is influenced by various factors such as component design, component positioning, and soft tissue tensioning. Patients may achieve glenohumeral motion beyond initial scapular impingement during activities of daily living which could further compound instability. However, instability/subluxation risk postscapular impingement is not well documented. Conventional range of motion analysis tools cannot account for the restraining effect of soft tissues or subluxation risk after impingement. Using a previously validated finite element analysis approach, the purpose of this study was to investigate the effects of glenoid component lateralization and humeral component angle of inclination (AOI), with or without simulated subscapularis repair, on postimpingement subluxation. We hypothesized that lack of subscapularis repair, a valgus humeral component AOI, and glenoid medialization would all result in greater postimpingement instability.MethodsA FE model of the shoulder including the subscapularis tendon and middle deltoid was created, incorporating a general representation of a commercial reverse shoulder arthroplasty implant placed under the direction of a fellowship-trained shoulder surgeon. The deltoid and subscapularis were tensioned and wrapped around the reconstructed glenohumeral joint prior to simulating motion. Humeral rotations were then prescribed to simulate external rotation (neutral to 50°), extension (neutral to 50°), adduction (neutral to 30°), and abduction (neutral to 90°). The effects of three glenosphere lateralization offsets (2, 4, and 10 mm) and 2 humeral liner angles of inclination (varus-150° and valgus-155°) on subluxation propensities were investigated with and without the subscapularis tendon present.ResultsSimulated subscapularis repair resulted in 21%-34% less postimpingement subluxation. Presence of the subscapularis provided stability over a greater range of abduction. Impingement-free range of motion was similar regardless of the presence or absence of the subscapularis. The valgus AOI resulted in 23% less subluxation during abduction. During other motions however, the valgus AOI resulted in 67%-110% greater postimpingement subluxation (subscapularis present), which further worsened without the subscapularis.ConclusionImplant design modifications to improve stability may not be beneficial for all motions, highlighting the importance of directionality when investigating instability. Liner-bone impingement appears to compound instability/subluxation and the subscapularis appears to restrain postimpingement instability.Level of evidenceBasic Science Study; Computer Modeling     

Radiographic evaluation of glenohumeral kinematics: a muscle fatigue model

The purpose of this study was to document the effect of muscle fatigue on glenohumeral kinematics. Twelve male volunteers without shoulder disease and with an average age of 27 years were studied. Glenohumeral anteroposterior radiographs were taken at 45 degrees intervals as the arm was abducted in the plane of the scapula from 0 degree to 135 degrees. This series of radiographs was performed both before and immediately after the subject performed a series of deltoid and rotator cuff fatiguing exercises. The average humeral head position or translation before and after muscle fatigue for each arm angle was compared. For all subjects, before fatigue, the position of the humeral head was below the center of the glenoid for all angles of abduction. There was essentially no change in position of the humeral head in the prefatigue state, as the arm was abducted from 0 degree to 135 degrees with no more than an average 0.3 mm of total humeral head excursion. After fatigue, excursion of the humeral head increased to an average of 2.5 mm between the tested positions. The position of the humeral head with the arm at 0 degree of abduction was lower or had migrated inferiorly compared with the rested state, with an average 1.2 mm significant increase in inferior translation. With the initiation of abduction, the humeral head demonstrated significant superior migration or translation in all positions tested. This result has important implications for conservative treatment of shoulder impingement and underscores the importance of rehabilitation to maximize the endurance and strength of the rotator cuff musculature.     

Comparing bone resorption after anatomical shoulder arthroplasty between various surgical procedures using a single-stem model

BackgroundIn shoulder arthroplasty, bone resorption around the stem can lead to stem loosening and makes surgery difficult at the time of revision. Proximal bone resorption after reverse shoulder arthroplasty can cause instability because of a decrease of deltoid wrapping effect. As factors of the stem itself, such as stem coating, shape, length, and use of bone cement, may also affect bone resorption, a single-stem model should be used to compare bone resorptions between different pathologies and surgical procedures. However, to date, a few reports have compared these differences in detail using a single-stem model. Therefore, we investigated the prevalence and location of humeral bone resorption in a single-stem model.MethodsThe study included 100 shoulders that underwent anatomical total shoulder arthroplasty (TSA) or humeral head replacement (HHR) with a single uncemented humeral stem from 2008 to 2018. The patients were 31 men and 69 women. The mean age at surgery was 72.9 years (range, 41-86 years). The patients were divided into three groups: especially, 25, 61, and 14 shoulders received TSA for primary osteoarthritis without rotator cuff tears (TSA group), HHR using an anatomical head with rotator cuff repair for cuff tear arthropathy (CTA) (HHR group), and HHR using a CTA head without rotator cuff repair (CTA group), respectively. Patients were monitored for a mean of 56 months (range, 12-98 months). The location of bone resorption was divided into seven zones as follows: zone 1, greater tuberosity; zone 2, lateral diaphysis; zone 3, lateral diaphysis beyond the deltoid tuberosity; zone 4, tip of the stem; zone 5, medial diaphysis beyond the deltoid tuberosity; zone 6, medial diaphysis; and zone 7, calcar region. The degree of bone resorption was classified from grade 0 to 4.ResultsBone resorption of grade 3 or higher was significantly more frequent at the greater tuberosity in the HHR and CTA groups (P < .001 and P < .001, respectively) than that in the TSA group. Grade 4 bone resorption was significantly more frequent in the CTA than that in the TSA and HHR groups in zone 1 (P = .016 and P = .041, respectively).ConclusionThe state of attachment of the rotator cuff to the greater tuberosity might affect bone resorption at the greater tuberosity, such as the greater tuberosity after shoulder arthroplasty. In cases of shoulder arthroplasty for arthropathy with rotator cuff tear, performing rotator cuff repair might prevent bone resorption.Level of evidenceLevel IV; Prognosis Study     

Biomechanical benefits of anterior offsetting of humeral head component in posteriorly unstable total shoulder arthroplasty: A cadaveric study

Restoration of joint stability during total shoulder arthroplasty can be challenging in the face of severe glenoid retroversion. A novel technique of humeral head component anterior‐offsetting has been proposed to address posterior instability. We evaluated the biomechanical benefits of this technique in cadaveric specimens. Total shoulder arthroplasty was performed in 14 cadaveric shoulders from 7 donors. Complementary shoulders were assigned to either 10° or 20° glenoid retroversion, with retroversion created by eccentric reaming. Two humeral head component offset positions were tested in each specimen: The anatomic (posterior) and anterior (reverse). With loads applied to the rotator cuff and deltoid, joint contact pressures and the force and energy required for posterior humeral head translation were measured. The force and energy required to displace the humeral head posteriorly increased significantly with the anterior offset position compared to the anatomic offset position. The joint contact pressures were significantly shifted anteriorly, and the joint contact area significantly increased with the anterior offset position. Anterior offsetting of the humeral head component increased the resistance to posterior humeral head translation, shifted joint contact pressures anteriorly, and increased joint contact area, thus, potentially increasing the joint stability in total shoulder arthroplasty with simulated glenoid retroversion. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:666–674, 2016.     

Adjusting Implant Size and Position Can Improve Internal Rotation After Reverse Total Shoulder Arthroplasty in a Three-dimensional Computational Model

BackgroundEfforts during reverse total shoulder arthroplasty (RSA) have typically focused on maximizing ROM in elevation and external rotation and avoiding scapular notching. Improving internal rotation (IR) is often overlooked, despite its importance for functional outcomes in terms of patient self-care and hygiene. Although determinants of IR are multifactorial, it is unable to surpass limits of bony impingement of the implant. Identifying implant configurations that can reduce bony impingement in a computer model will help surgeons during preoperative planning and also direct implant design and clinical research going forward.Questions/purposesIn a CT-modeling study, we asked: What reverse total shoulder arthroplasty implant position improves the range of impingement free internal rotation without compromising other motions (external rotation and extension)?MethodsCT images stored in a deidentified teaching database from 25 consecutive patients with Walch A1 glenoids underwent three-dimensional templating for RSA. Each template used the same implant and configuration, which consisted of an onlay humeral design and a 36-mm standard glenosphere. The resulting constructs were virtually taken through ROM until bony impingement was found. Variations were made in the RSA parameters of baseplate lateralization, glenosphere size, glenosphere overhang, humeral version, and humeral neck-shaft angle. Simulated ROM was repeated after each parameter was changed individually and then again after combining multiple changes into a single configuration. The impingement-free IR was calculated and compared between groups. We also evaluated the effect on other ROM including external rotation and extension to ensure that configurations with improvements in IR were not associated with losses in other areas.ResultsCombining lateralization, inferiorization, varus neck-shaft angle, increased glenosphere size, and increased humeral anteversion resulted in a greater improvement in internal rotation than any single parameter change did (median baseline IR: 85° [interquartile range 73° to 90°]; combined changes: 119° [IQR 113° to 121°], median difference: 37° [IQR 32° to 43°]; p < 0.001).ConclusionIncreased glenosphere overhang, varus neck-shaft angle, and humeral anteversion improved internal rotation in a computational model, while glenoid lateralization alone did not. Combining these techniques led to the greatest improvement in IR.Clinical RelevanceThis computer model study showed that various implant changes including inferiorization, varus neck-shaft angle, increased glenosphere size, and increased humeral anteversion can be combined to increase impingement-free IR. Surgeons can employ these currently available implant configurations to improve IR when planning and performing RSA. These findings support the need for further clinical studies validating the effect of implant configuration on resultant IR.     

Why a surgically treated humeral shaft fracture became a nonunion: review of 11 years in two trauma centers

Purpose

To report the outcomes and complications of reverse shoulder arthroplasty (RSA) in massive irreparable rotator cuff tears (MIRCT) and cuff tear arthropathy (CTA).

Methods

A systematic review of the literature contained in Medline, Cochrane, EMBASE, Google Scholar and Ovid databases was conducted on May 1, 2016, according to PRISMA guidelines. The key words “reverse total shoulder arthroplasty” or “reverse total shoulder prostheses” with “rotator cuff tears”; “failed rotator cuff surgery”; “massive rotator cuff tears”; “irreparable rotator cuff tears”; “cuff tear arthropathy”; “outcomes”; “complications” were matched. All articles reporting outcomes and complications of RSA for the management of MIRCT or CTA were included. The comparison between preoperative and postoperative clinical scores, as well as range of motion (ROM), was performed using the Wilcoxon–Mann–Whitney test. P values lower than 0.05 were considered statistically significant.

Results

Seven articles were included in our qualitative synthesis. A statistically significant improvement in all clinical scores and ROM was found comparing the preoperative value with the postoperative value. The degrees of retroversion of the humeral stem of the RSA do not influence the functional outcomes in a statistically significant fashion. There were 17.4% of complications. The most frequent was heterotopic ossification, occurring in 6.6% of patients. Revision surgery was necessary in 7.3% of patients.

Conclusions

RSA restores pain-free ROM and improves function of the shoulder in patients with MIRCT or CTA. However, complications occur in a high percentage of patients. The lack of level I studies limits the real understanding of the potentials and limitations of RSA for the management of MIRCT and CTA.

     

Contemporary use of reverse total shoulder arthroplasty

Reverse total shoulder arthroplasty (RTSA) has evolved as the treatment for glenohumeral joint disease in patients with rotator cuff pathology because it allows for the deltoid to be further recruited during abduction. Surgical procedure for an RTSA can be done via two approaches, deltopectoral and superolateral. The most commonly reported complications include infection, dislocation, humeral fracture, glenoid fracture, hematoma, neurological damage, implant loosening, and scapular notching. The RTSA has become prominent in the treatment of shoulder pathology due to its ability to treat a gamut of complex disorders, while awarding pain relief and enhanced functional range of motion.     

Biomechanische Evaluation der glenohumeralen Stabilität durch Muskelkraftvektoranalyse

OBJECTIVES: The aim of the study was to quantify the decrease in glenohumeral stability following a global rotator cuff tear and to evaluate the effect of a decreased glenoid inclination angle through analysis of muscle force vectors in a computer model. MATERIAL AND METHODS: The lines of action of eight shoulder muscles were integrated into a standard geometric model. Muscle force magnitudes were estimated based on physiological cross-sectional area and normalized electromyographic activity. The magnitude and elevation angle of the resultant force vector was calculated at 0, 30, 60, and 90 degrees of abduction. A rotator cuff tear was simulated by reduction of the corresponding muscle force vectors. RESULTS: At 0 and 30 degrees of glenohumeral abduction a global rotator cuff tear showed a resultant force vector pointing outside the glenoid. In the computer model, decreasing the inclination angle of the glenoid by 30 degrees increased the stability in rotator cuff-deficient shoulders. CONCLUSIONS: The results of this study provide a biomechanical rationale for clinical complications of global rotator cuff tear such as superior humeral head translation. The decreased glenoid inclination simulated in the computer model may represent a biomechanical basis for the development of new operative techniques to treat global rotator cuff tears.     

Does Humeral Component Lateralization in Reverse Shoulder Arthroplasty Affect Rotator Cuff Torque? Evaluation in a Cadaver Model

Background

Humeral component lateralization in reverse total shoulder arthroplasty (RTSA) may improve the biomechanical advantage of the rotator cuff, which could improve the torque generated by the rotator cuff and increase internal and external rotation of the shoulder.

Purpose

The purpose of this in vitro biomechanical study was to evaluate the effect of humeral component lateralization (or lateral offset) on the torque of the anterior and posterior rotator cuff.

Methods

Eight fresh-frozen cadaveric shoulders from eight separate donors (74 ± 8 years; six males, two females) were tested using an in vitro simulator. All shoulders were prescreened for soft tissue deficit and/or deformity before testing. A custom RTSA prosthesis was implanted that allowed five levels of humeral component lateralization (15, 20, 25, 30, 35 mm), which avoided restrictions imposed by commercially available designs. The torques exerted by the anterior and posterior rotator cuff were measured three times and then averaged for varying humeral lateralization, abduction angle (0°, 45°, 90°), and internal and external rotation (−60°, −30°, 0°, 30°, 60°). A three-way repeated measures ANOVA (abduction angle, humeral lateralization, internal rotation and external rotation angles) with a significance level of α = 0.05 was used for statistical analysis.

Results

Humeral lateralization only affected posterior rotator cuff torque at 0° abduction, where increasing humeral lateralization from 15 to 35 mm at 60° internal rotation decreased external rotation torque by 1.6 ± 0.4 Nm (95% CI, −0.07 −1.56 Nm; p = 0.06) from 4.0 ± 0.3 Nm to 2.4 ± 0.6 Nm, respectively, but at 60° external rotation increased external rotation torque by 2.2 ± 0.5 Nm (95% CI, −4.2 to −0.2 Nm; p = 0.029) from 6.2 ± 0.5 Nm to 8.3 ± 0.5 Nm, respectively. Anterior cuff torque was affected by humeral lateralization in more arm positions than the posterior cuff, where increasing humeral lateralization from 15 to 35 mm when at 60° internal rotation increased internal rotation torque at 0°, 45°, and 90° abduction by 3.2 ± 0.5 Nm (95% CI, 1.1–5.2 Nm; p = 0.004) from 6.6 ± 0.6 Nm to 9.7 ± 0.6 Nm, 4.0 ± 0.3 Nm (95% CI, 2.8-5.0 Nm; p < 0.001) from 1.7 ± 1.0 Nm to 5.6 ± 0.9 Nm, and 2.2 ± 0.2 Nm (95% CI, 1.4–2.9 Nm; p < 0.001) from 0.6 ± 0.6 Nm to 2.8 ± 0.6 Nm, respectively. In neutral internal and external rotation, increasing humeral lateral offset from 15 to 35 mm increased the internal rotation torque at 45˚ and 90˚ abduction by 1.5 ± 0.3 Nm (95% CI, 0.2–2.7 Nm; p = 0.02) and 1.3 ± 0.2 Nm (95% CI, 0.4–2.3 Nm; p < 0.001), respectively.

Conclusions

Humeral component lateralization improves rotator cuff torque.

Clinical Relevance

The results of this preliminary in vitro cadaveric study suggest that the lateral offset of the RTSA humeral component plays an important role in the torque generated by the anterior and posterior rotator cuff. However, further studies are needed before clinical application of these results. Increasing humeral offset may have adverse effects, such as the increased risk of implant modularity, increasing tension of the cuff and soft tissues, increased costs often associated with design modifications, and other possible as yet unforeseen negative consequences.

     

Experimental investigation of reaction forces at the glenohumeral joint during active abduction

Reaction forces at the glenohumeral joint counterbalance the mass moment of the upper extremity during shoulder motion and are directly related to the activity of muscles across the joint. Because stability of the glenohumeral joint depends on compression of the humeral head into the glenoid, reaction forces constitute an important aspect of shoulder biomechanics. The objective of this study was to measure reaction forces at the glenohumeral joint during active scapula plane abduction. Furthermore, to clarify the relationship between the deltoid and supraspinatus muscles throughout abduction, this study investigated the effect of 4 variations of applied muscle forces on the magnitude and direction of glenohumeral reaction forces. We used a dynamic shoulder testing apparatus equipped with a force-moment sensor to directly measure reaction forces. Joint reaction forces increased throughout abduction and peaked at approximately 90 degrees for all testing conditions. The largest reaction forces occurred when the ratio of applied forces favored the supraspinatus tendon, whereas simulated paralysis of the supraspinatus resulted in a significant decrease in joint compression. There were no differences in direction of the reaction force between testing conditions. The results of this study indicate that the magnitude of glenohumeral joint reaction forces varies according to the ratio of forces between the supraspinatus and deltoid muscles. Thus, conditions characterized by either deltoid or supraspinatus dysfunction may result in abnormal loading mechanics at the glenohumeral joint. Understanding the relationship between rotator cuff function and glenohumeral reaction forces will aid in clarifying the importance of muscular activity to shoulder stability and strength as it relates to compression of the humeral head.     

Primary reverse shoulder arthroplasty did not result in increased blood metal ion levels regardless of glenosphere size: A randomized controlled trial

BackgroundThe utilization of reverse shoulder arthroplasty (RSA) has increased over time. Toxic increases of metal ion levels have been reported selectively after hip arthroplasty. However, studies evaluating the effect of RSA on in vivo metal ion levels have not been evaluated. Therefore, the purposes of this study were (1) to determine in vivo levels of cobalt, chromium, and nickel in a randomized controlled trial of patients undergoing reverse total shoulder arthroplasty (RSA) with one of four glenosphere sizes, and (2) to identify possible factors affecting changes in metal ion levels.MethodsBetween May 2016 and September 2018, 72 shoulders with cuff tear arthropathy, massive irreparable cuff tears, or glenohumeral osteoarthritis with posterior subluxation were randomized to undergo RSA using a single implant system and four possible glenosphere options based on size (36 or 40 mm) and offset (+2 mm, +6 mm). In vivo metal ion levels (cobalt, chromium, nickel) and complete blood count (CBC) were assessed preoperatively, 3-months, and 1-year after surgery. Clinical evaluation included pain, motion, Subjective Shoulder Value, ASES scores, and Oxford Shoulder Scores.ResultsReverse shoulder arthroplasty led to statistically significant improvements in all outcome measures considered (p < 0.001). Changes in nickel, cobalt or chromium blood levels did not reach statistical significance at 3 months (p = 0.87, 0.86, 0.85, respectively) or 1 year (p = 0.88, 0.38, 0.98, respectively). There was no difference in any of these metal ion levels when assessed by (1) glenosphere size, or (2) offset at 3 months or 1 year. This was also true when each of the four groups were assessed individually at 3 months and 1 year.ConclusionIn this randomized controlled trial of patients undergoing reverse total shoulder arthroplasty with a single design, in vivo levels of cobalt, chromium, and nickel remained reassuringly low. In addition, increase in glenosphere size, offset, or both, did not appear to affect in vivo metal ion levels over the short-term. Longer term studies are needed to further assess the effects of implant modularity on metal ion levels and their potential adverse effects in patients undergoing reverse shoulder arthroplasty.Level of evidenceLevel I; Randomized Controlled Trial     

Biomechanical relevance of glenoid component positioning in the reverse Delta III total shoulder prosthesis

The presence of a notch at the inferior part of the scapular neck is a common radiographic finding in patients treated with a reverse Delta III shoulder prosthesis. It is thought that this notch is a result of mechanical contact between the polyethylene cup of the humeral implant and the inferior glenoid pole during adduction of the arm. This in vitro study assessed the effect of glenoid component positioning on glenohumeral range of motion in 8 shoulder specimens. Four different positions of the glenosphere were tested: glenosphere centered on the glenoid, leaving the inferior glenoid rim uncovered (configuration A); glenosphere flush with the inferior glenoid rim (configuration B); glenosphere extending beyond the inferior glenoid rim (configuration C); and glenosphere tilted downward 15 degrees (configuration D). The respective mean adduction and abduction angles in the scapular plane were -25 degrees and 67 degrees for configuration A, -14 degrees and 68 degrees for configuration B, -1 degrees and 81 degrees for configuration C, and -9 degrees and 75 degrees for configuration D. Placing the glenosphere distally (test configuration C) significantly improved adduction and abduction angles compared with all other test configurations (P < .001).