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

Preoperative planning and inferior glenosphere overhang increases the odds of achieving high internal rotation after Univers reverse total shoulder arthroplasty

BACKGROUND

Despite advances in surgical technique and implant design, internal rotation (IR) after reverse total shoulder arthroplasty (rTSA) continues to be relatively unpredictable. The purpose of this study was to compare patient characteristics, use of 3-dimensional computed tomography (3D CT)-based preoperative planning, and postoperative implant position between patients with high or low IR after rTSA.

METHODS

A retrospective review was performed of a multicenter prospectively collected database on patients who underwent primary rTSA (Univers Revers; Arthrex, Inc.) from 2016-2021 with a minimum 2-year follow-up. Patients were selected for a comparative analysis who either achieved high IR (T12 or better) or low IR (below the hip) postoperatively. Baseline demographics and postoperative radiographs were evaluated for association with IR. Implant position was assessed on radiographs for lateralization shoulder angle (LSA), distalization shoulder angle (DSA), inferior glenosphere overhang, and coracoid-to-glenosphere distance. Regression analyses were performed on component and clinical variables to assess for factors predictive of high vs. low IR.

RESULTS

A total of 344 rTSAs were eligible, of which 98 patients met criteria for the high-IR group and 50 met criteria for the low-IR group. Decreased body mass index (BMI) (odds ratio [OR] 1.14, 95% confidence interval [CI] 1.01-1.30, P = .044), high preoperative IR (OR 1.30, 95% CI 1.02-1.66, P = .034), and surgery on the dominant arm (OR 5.38, 95% CI 1.31-22.1, P = .019) correlated with an increased odds of high IR. The use of 3D CT-based preoperative planning was associated with having high IR (OR 9.69, 95% CI 1.83-51.3, P = .008). Radiographically, increased DSA (OR 1.09, 95% CI 1.02-1.16, P = .012) and increased inferior glenoid overhang (OR 1.39, 95% CI 1.07-1.80, P = .013) were associated with a greater chance of being in the high-IR group.

CONCLUSION

Although specific baseline patient characteristics influence the ability to obtain high IR after rTSA including increased preoperative IR, decreased BMI, and surgery on the dominant arm, there are several factors within the surgeon's control. The use of 3D CT-based preoperative planning greatly increases the odds of obtaining increased postoperative IR. More precisely, mindful implant positioning including inferior glenosphere overhang and slight distalization increased postoperative IR. Therefore, the use of 3D CT-based preoperative planning may be considered in order to carefully and consciously position the glenosphere to slightly increase distalization and inferior overhang in order to optimize IR. However, further evaluation with regard to 3D planned position and postoperative outcomes are required.

Dialing the glenosphere eccentricity posteriorly to optimize range of motion in reverse shoulder arthroplasty

Background

Friction is the primary cause of notching in reverse shoulder arthroplasty during internal, external rotation (IR/ER), and extension (EXT). To address notching, glenosphere eccentricity (ECC) was introduced. The primary objective of this study was to investigate different positions of glenosphere ECC to determine whether there is an optimal position for impingement-free range of motion.

Methods

In this computer model study, 10 female CTs were analyzed and EXT, ER, IR, and adduction simulated (18 models.) A 135° stem with a +10° liner (145°) was combined with a 25-mm standard/or +3-mm lateralized baseplate (BP) and a 36-mm +2-mm eccentric glenosphere in 4 ECC positions (50° posterior; 30° posterior; 30° anterior; 50° anterior) from the reference position 0° neutral (10 models). Additionally, a concentric 39-mm glenosphere was tested (+2 models). A 0° insert, 135° neck shaft angle (NSA), was tested with a 25-mm standard/or +3-mm BP for 3 configurations (30° posterior; neutral; 39 mm; +6 models).

Results

Compared to the 0° neutral reference position, 30° posterior dialing improved the mean ER (group 145°: 40° vs. 38°, group 145° + 3: 51° vs. 49°, both P < .0001), and EXT (group 145°: 35° vs. 34°, P = .029, group 145° + 3: 57° vs. 47°, P = .046, but at the expense of IR (group 145°: 83° vs. 87°, group 145° + 3: 87° vs. 91°, both P < .0001). The position 30° anterior increased IR (group 145°: 90° vs. 87°, group 145° + 3: 94° vs. 91°, both P < .0001) at the expense of ER (group 145°: 33° vs. 38°, group 145° + 3: 44° vs. 49°, both P < .0001) and EXT (group 145°: 24° vs. 34°, P = .055, group 145° +3 mm: 39° vs. 47°, P = .0042). For group 145°, 0° neutral was the best position for combined EXT + IR (121°) compared to 30° posterior/30° anterior/39 mm/50° posterior/50° anterior (118°/113°/118°/113°/110°, P < .0001/P = .15/P = .076/P < .0001/P = .074, respectively) and IR + ER (125° vs. 122°/123°/123°/118°/119°/, P < .001/P = .0028/P = .7/P < .0001/P = .0001, respectively). Lateralization, but most effectively a 135° NSA improved combined EXT + IR + ER + adduction (group 145°: 179° vs. group 135°: 243°, group 145° + 3: 215° vs. group 135° + 3: 276°, P = .0019/P = .00019, respectively). The influence of position 0°neutral or 30°posterior became marginal with a 135°NSA.

Conclusion

Posterior dialing of the ECC increases EXT and ER but at the expense of IR. Lateralization, but most effectively a 135° NSA, increase impingement-free motion. A larger noneccentric glenosphere on the same BP is a safe all-round solution to prevent ECC positioning outliers.

Predictors of Internal Rotation-Dependent Activities of Daily Living Performance and Favorable Satisfaction Despite Loss of Objective Internal Rotation After Reverse Shoulder Arthroplasty

INTRODUCTION

Previous research has determined that objective and subjective internal rotation (IR) may be discordant. The purpose of this study was to identify predictors of patient-reported ability to perform IR-dependent activities of daily living (IRADLs) and favorable patient satisfaction after reverse shoulder arthroplasty (RSA) despite the loss of objective IR.

METHODS

A single, institutional, shoulder arthroplasty database was queried for patients undergoing primary RSA with a minimum 2-year follow-up. Patients who were wheelchair bound or had a preoperative diagnosis of infection, fracture, or tumor were excluded. We first identified patients in the overall cohort that lost objective IR from pre- to postoperative assessment, defined as a one-point reduction in the eight-point Flurin scale. In this cohort, we identified patient characteristics that were predictive of patient-reported ability to perform IRADLs and overall patient satisfaction and thresholds in postoperative objective IR.

RESULTS

Out of 599 RSAs initially identified, 107 RSAs lost objective IR (45% female, mean age 70 years). On average, patients lost 1.7 IR score points pre- to postoperatively. Greater preoperative IR and lesser loss of objective IR pre- to postoperatively were associated with greater patient-reported ability to perform all 4 IRADLs (odds ratio 1.54 to 2.5), whereas female sex was associated with worse patient-reported ability to perform 3 IRADLs (odds ratio 0.26 to 0.36). We identified that patients with postoperative IR below the sacrum were unlikely to be able to perform IRADLs and those with postoperative IR at or above L4-L5 were likely to be satisfied.

CONCLUSION

Despite losing objectively assessed IR after RSA, many patients are still able to perform IRADLs and report favorable satisfaction as long as objective IR reaches L4/5. Female sex and postoperative IR below the sacrum were associated with the inability to perform IRADLs, whereas postoperative IR to or above L4-L5 was associated with subjective ratings of satisfaction.

Internal rotation limitation is prevalent following modern reverse shoulder arthroplasty and negatively affects patients' subjective rating of the procedure

BACKGROUND

Although forward elevation, abduction, and external rotation are often successfully restored, internal rotation (IR) is frequently not satisfactorily recovered following reverse shoulder arthroplasty (RSA), affecting patients' ability to perform certain daily activities. This study examined the prevalence of limited IR in patients receiving modern RSA and its impact on clinical outcomes and patient satisfaction with their RSA.

METHODS

A cross-sectional study was conducted on patients who had undergone primary RSA using a modern RSA prosthesis with a minimum 1-year follow-up. Patients returned for a research visit where they were examined for range of motion and surveyed for patient-reported outcome measures (PROMs) and subjective rating of the success level of their RSA. Postoperative range of motion data were compared with the preoperative data. The relationship of postoperative IR with PROMs and patients' subjective rating of RSA was analyzed. Logistic regression was performed to identify factors affecting patients' subjective rating of RSA.

RESULTS

A total of 78 patients met the criteria and completed the study. A significant portion (59%) reported subjective IR limitations, and 41% had objective IR limitations. Comparison of preoperative and postoperative IR showed that 24% had worsened IR, whereas 33% improved. Limited IR was associated with lower patients' subjective rating of RSA and negatively affected PROMs, especially when the dominant side was operated on. Regression analysis showed that limited IR was the only independent determining factor that was significantly associated with a lower subjective rating of RSA.

DISCUSSION

Despite advancements in RSA design, limited IR remains a prevalent issue, significantly affecting patients' satisfaction and clinical outcomes. This study underscores the need for setting appropriate expectations regarding IR through patient education and focused efforts to improve IR limitations in RSA patients, particularly on the dominant side.

Optimizing range of motion in reverse shoulder arthroplasty

Aims

Optimal glenoid positioning in reverse shoulder arthroplasty (RSA) is crucial to provide impingement-free range of motion (ROM). Lateralization and inclination correction are not yet systematically used. Using planning software, we simulated the most used glenoid implant positions. The primary goal was to determine the configuration that delivers the best theoretical impingement-free ROM.

Methods

With the use of a 3D planning software (Blueprint) for RSA, 41 shoulders in 41 consecutive patients (17 males and 24 females; means age 73 years (SD 7)) undergoing RSA were planned. For the same anteroposterior positioning and retroversion of the glenoid implant, four different glenoid baseplate configurations were used on each shoulder to compare ROM: 1) no correction of the RSA angle and no lateralization (C-L-); 2) correction of the RSA angle with medialization by inferior reaming (C+M+); 3) correction of the RSA angle without lateralization by superior compensation (C+L-); and 4) correction of the RSA angle and additional lateralization (C+L+). The same humeral inlay implant and positioning were used on the humeral side for the four different glenoid configurations with a 3 mm symmetric 135° inclined polyethylene liner.

Results

The configuration with lateralization and correction of the RSA angle (C+L+) led to better ROM in flexion, extension, adduction, and external rotation (p ≤ 0.001). Only internal rotation was not significantly different between groups (p = 0.388). The configuration where correction of the inclination was done by medialization (C+M+) led to the worst ROM in adduction, extension, abduction, flexion, and external rotation of the shoulder.

Conclusion

Our software study shows that, when using a 135° inlay reversed humeral implant, correcting glenoid inclination (RSA angle 0°) and lateralizing the glenoid component by using an angled bony or metallic augment of 8 to 10 mm provides optimal impingement-free ROM.

Optimizing stability and motion in reverse shoulder arthroplasty with a 135° neck-shaft-angle: a computer model study of standard versus retentive humeral inserts

Background

There has been a trend to shift from a 155° and 145° neck-shaft-angle (NSA) to a more "anatomical" reverse shoulder arthroplasty with less distalization and a 135° NSA. Multiple studies have shown that a 135° NSA is beneficial for motion. There are some concerns about primary implant stability with a 135° NSA. When instability is detected, increasing the tension with thicker inlays or changing the NSA to 145° are possible solutions. A retentive 135° (Ret135) inlay may be an alternative to avoiding increased distalization; however, retentive liners are widely regarded as salvage options reducing range of motion (ROM) and avoided by most surgeons. The hypothesis of this study was that a retentive 135° insert of the tested implant system may not have drawbacks for impingement-free ROM compared to a standard 145° insert (Sta145).

Methods

In this computer model study, 22 computed tomographic scans (11 males/11 females) were used to create models with a constant humeral stem (Perform/Stryker) and +3 mm lateralized baseplate +36 mm glenosphere for females and +6 mm lateralized baseplate +39 mm glenosphere for males using Blueprint software (Imascap, Brest, France). A Ret135, standard 135° (Sta135), and Sta145 (+10°) insert were compared for adduction (ADD), extension (EXT), external rotation (ER), and internal rotation (IR) all with the arm at the side as well as for combined IR (CIR = EXT + IR) and combined notching relevant (CNR) ROM (EXT + ER + IR + ADD).

Results

Sta135 showed significantly better ROM for ER, IR, ADD, EXT, CNR ROM, and CIR compared to Ret135 (P < .05) and significantly better EXT and ADD compared to Sta145 (P < .0001). Comparison of Ret135 and Sta145 showed equivalent ROM performance, which was slightly better but nonsignificant for ADD (P = .16), EXT (P = .31), CNR ROM (P = .7), and CIR (P = .54) in favor of Ret135. Isolated IR (P = .39) and ER (P = .32) were slightly better but nonsignificant in favor of a Sta145.

Conclusion

For this implant system tested in a computer model, a 135° standard liner offers the best ROM. A 135° retentive liner maintains at least equivalent CIR and motion to prevent notching compared to a standard 145° liner. 135° retentive liners are more than salvage options and may help to prevent distalization and overtensioning by increased liner thickness.

Predictive factors influencing internal rotation following reverse total shoulder arthroplasty

BACKGROUND

Reverse total shoulder arthroplasty (RTSA) is increasingly used as a treatment modality for various pathologies. The purpose of this review is to identify preoperative risk factors associated with loss of internal rotation (IR) after RTSA.

METHODS

A systematic review was conducted using Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Ovid MEDLINE, Ovid Embase, and Scopus were queried. The inclusion criteria were as follows: articles in English language, minimum 1-year follow-up postoperatively, study published after 2012, a minimum of 10 patients in a series, RTSA surgery for any indication, and explicitly reported IR. The exclusion criteria were as follows: articles whose full text was unavailable or that were unable to be translated to English language, a follow-up of less than 1 year, case reports or series of less than 10 cases, review articles, studies in which tendon transfers were performed at the time of surgery, procedures that were not RTSA, and studies in which the range of motion in IR was not reported.

RESULTS

The search yielded 3792 titles, and 1497 duplicate records were removed before screening. Ultimately, 16 studies met the inclusion criteria with a total of 5124 patients who underwent RTSA. Three studies found that poor preoperative functional IR served as a significant risk factor for poor postoperative IR. Eight studies addressed the impact of subscapularis, with 4 reporting no difference in IR based on subscapularis repair and 4 reporting significant improvements with subscapularis repair. Among studies with sufficient power, BMI was found to be inversely correlated with degree of IR after RTSA. Preoperative opioid use was found to negatively affect IR. Other studies showed that glenoid retroversion, component lateralization, and individualized component positioning affected postoperative IR.

CONCLUSIONS

This study found that preoperative IR, individualized implant version, preoperative opioid use, increased body mass index and increased glenoid lateralization were all found to have a significant impact on IR after RTSA. Studies that analyzed the impact of subscapularis repair reported conflicting results.

Lateralising reverse shoulder arthroplasty using bony increased offset (BIO-RSA) or increasing glenoid component diameter: comparison of clinical, radiographic and patient reported outcomes in a matched cohort

BACKGROUND

This study aims to compare the range of motion (ROM) of reverse shoulder arthroplasty lateralised by bony increased offset (BIO-RSA) using a standard 38-mm (mm) component to regular reverse shoulder arthroplasty (RSA) lateralised by using a 42-mm glenoid component. The secondary aims are to compare patient-reported and radiographic outcomes between the two groups.

MATERIALS AND METHODS

All patients with a BIO-RSA and size 38 glenosphere were retrospectively identified and matched to patients with a regular RSA and size 42 glenosphere. Matched patients were invited for a follow-up visit. ROM was assessed as well as radiographic outcomes (lateralisation, distalisation, inferior overhang, scapular notching, heterotopic bone formation, radiolucency, stress shielding, bone graft healing and viability and complications) and patient-reported outcomes (subjective shoulder value, Constant score, American Shoulder and Elbow Surgeons, activities of daily living which require internal rotation, activities of daily living which require external rotation and a visual analogue scale for pain). Outcomes were compared between the two groups.

RESULTS

In total, 38 BIO-RSAs with a size 38 glenosphere were matched to 38 regular RSAs with a size 42 glenosphere. Of the 76 matched patients, 74 could be contacted and 70 (95%) were included. At the final follow-up, there were no differences between the two groups in ROM, patient-reported outcomes or radiographic outcomes (p > 0.485).

CONCLUSIONS

Using a larger glenosphere is a feasible alternative to BIO-RSA for lateralising RSA, providing comparable ROM, patient-reported and radiographic results, while potentially decreasing costs, operative time and complication rates.

LEVEL OF EVIDENCE III

Scapular motion during shoulder joint extension movement

A few reports on scapular motion during shoulder joint extension exist. Understanding the normal motion of shoulder joint extension may be useful in evaluating and treating patients with diminished or minimal shoulder joint extension. Therefore, this study aimed to identify scapular motion during shoulder joint extension movement in a sitting position. Shoulder joint extension movement in the sitting position were measured in 22 healthy adults (age, 25.8 ± 2.7 years). Shoulder joint extension, scapular upward rotation, anterior tilt, external rotation angles, and the acromion position were investigated using a three-dimensional motion analyzer. The difference from each value of 10° to 50° shoulder joint extension to each value of 0° shoulder joint extension were checked. The results were compared using multiple comparison method. In most participants, the scapula tilted posteriorly up to 30° of the shoulder joint extension and anteriorly after 30°. Scapular upward and external rotation continued to increase with shoulder extension. Furthermore, the acromion was displaced upward and backward. Thus, scapular posterior tilt is necessary for shoulder joint extension during the initial movement, followed by anterior tilt. The acromion may have been displaced posteriorly because of clavicular retraction, causing the scapula to tilt posteriorly. After 30° of shoulder joint extension, the scapular anterior tilt may have prevailed over the scapular posterior tilt.

Reverse shoulder arthroplasty with a 155° neck-shaft angle inlay implant design without reattachment of the subscapularis tendon results in satisfactory functional internal rotation and no instability: a cohort study

BACKGROUND

The aim of this study was to use the Activities of Daily Living which require Internal Rotation (ADLIR) questionnaire to assess the functional internal rotation in patients who had undergone reverse shoulder arthroplasty (RSA) without reattachment of the subscapularis (SSc) tendon at a minimum follow-up of 2 years. The secondary aim was to report the objective range of motion (ROM) and the rate of postoperative instability.

MATERIALS AND METHODS

All consecutive primary RSA procedures without reattachment of the SSc tendon that were performed using a Delta Xtend prosthesis (an inlay system with a 155° neck-shaft angle) between January 2015 and December 2020 were identified to ensure a minimum follow-up of 2 years. Patients were contacted and requested to fill in several questionnaires, including the ADLIR and Auto-Constant scores.

RESULTS

In total, 210 patients met the inclusion criteria; among those patients, 187 could be contacted and 151 completed questionnaires (response rate: 81%). The SSc tendon was fully detached without repair in all cases, and a superolateral approach was used in 130 (86%) cases. The median follow-up was 4.5 years (range: 2.0-7.6). At final follow-up, the mean ADLIR score was 88/100 (interquartile range (IQR): 81-96). The median level reached in internal rotation was the 3rd lumbar vertebra (IQR: lumbosacral region-12th thoracic vertebra). Of the 210 eligible patients, one required a revision for a dislocation within the first month after primary surgery. With regards to regression analysis with ADLIR score as the outcome, none of the factors were associated with the ADLIR score, although age and smoking approached significance (0.0677 and 0.0594, respectively). None of the explanatory variables were associated with ROM in internal rotation (p > 0.05).

CONCLUSIONS

This study demonstrates that satisfactory ADLIR scores and internal rotation ROM were obtained at mid-term follow-up after RSA leaving the SSc detached. Leaving the SSc detached also did not lead to high instability rates; only one out of 210 prostheses was revised for dislocation within the first month after primary surgery.

LEVEL OF EVIDENCE III

High and low performers in internal rotation after reverse total shoulder arthroplasty: a biplane fluoroscopic study

BACKGROUND

Internal rotation in adduction is often limited after reverse total shoulder arthroplasty (rTSA), but the origins of this functional deficit are unclear. Few studies have directly compared individuals who can and cannot perform internal rotation in adduction. Little data on underlying 3D humerothoracic, scapulothoracic, and glenohumeral joint relationships in these patients are available.

METHODS

Individuals >1-year postoperative to rTSA were imaged with biplane fluoroscopy in resting neutral and internal rotation in adduction poses. Subjects could either perform internal rotation in adduction with their hand at T12 or higher (high, N = 7), or below the hip pocket (low, N = 8). Demographics, the American Shoulder and Elbow Surgeons score, Simple Shoulder Test, and scapular notching grade were recorded. Joint orientation angles were derived from model-based markerless tracking of the scapula and humerus relative to the torso. The 3D implant models were aligned to preoperative computed tomography models to evaluate bone-implant impingement.

RESULTS

The Simple Shoulder Test was highest in the high group (11 ± 1 vs. 9 ± 2, P = .019). Two subjects per group had scapular notching (grades 1 and 2), and 3 high group and 4 low group subjects had impingement below the glenoid. In the neutral pose, the scapula had 7° more upward rotation in the high group (P = .100), and the low group demonstrated 9° more posterior tilt (P = .017) and 14° more glenohumeral elevation (P = .047). In the internal rotation pose, axial rotation was >45° higher in the high group (P ≤ .008) and the low group again had 11° more glenohumeral elevation (P = .058). Large rotational differences within subject groups arose from a combination of differences in the resting neutral and maximum internal rotation in adduction poses, not only the terminal arm position.

CONCLUSIONS

Individuals who were able to perform high internal rotation in adduction after rTSA demonstrated differences in joint orientation and anatomic biases versus patients with low internal rotation. The high rotation group had 7° more resting scapular upward rotation and used a 15°-30° change in scapular tilt to perform internal rotation in adduction versus patients in the low group. The combination of altered resting scapular posture and restricted scapulothoracic range of motion could prohibit glenohumeral rotation required to reach internal rotation in adduction. In addition, inter-patient variation in humeral torsion may contribute substantially to postoperative internal rotation differences. These data point toward modifiable implant design and placement factors, as well as foci for physical therapy to strengthen and mobilize the scapula and glenohumeral joint in response to rTSA surgery.

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.

Challenges for Optimization of Reverse Shoulder Arthroplasty Part I: External Rotation, Extension and Internal Rotation

A detailed overview of the basic science and clinical literature reporting on the challenges for the optimization of reverse shoulder arthroplasty (RSA) is presented in two review articles. Part I looks at (I) external rotation and extension, (II) internal rotation and the analysis and discussion of the interplay of different factors influencing these challenges. In part II, we focus on (III) the conservation of sufficient subacromial and coracohumeral space, (IV) scapular posture and (V) moment arms and muscle tensioning. There is a need to define the criteria and algorithms for planning and execution of optimized, balanced RSA to improve the range of motion, function and longevity whilst minimizing complications. For an optimized RSA with the highest function, it is important not to overlook any of these challenges. This summary may be used as an aide memoire for RSA planning.