A novel 3D MRI-based approach for assessing supraspinatus muscle length.

Rotator cuff (RC) tears are a common source of pain and decreased shoulder strength. Muscle length is known to affect muscle strength, and therefore evaluating changes in supraspinatus muscle length associated with RC pathology, surgical repair, and post-operative recovery may provide insights into functional deficits. Our objective was to develop a reliable MRI-based approach for assessing supraspinatus muscle length. Using a new semi-automated approach for identifying 3D location of the muscle-tendon junction (MTJ), supraspinatus muscle length was calculated as the sum of MTJ distance (distance between 3D MTJ position and glenoid plane) and supraspinatus fossa length (distance between root of the scapular spine and glenoid plane). Inter- and intra-operator reliability of this technique were assessed with intraclass correlation coefficient (ICC) and found to be excellent (ICCs > 0.96). Muscle lengths of 6 patients were determined before RC repair surgery and at 3- and 12-months post-surgery. Changes in normalized muscle length (muscle length as a percentage of pre-surgical muscle length) at 3 months post-surgery varied considerably across patients (16.1 % increase to 7.0 % decrease) but decreased in all patients from 3- to 12-months post-surgery (0.3 % to 17.2 %). This study developed a novel and reliable approach for quantifying supraspinatus muscle length and provided preliminary demonstration of its utility by assessing muscle length changes associated with RC pathology and surgical repair. Future studies can use this technique to evaluate changes over time in supraspinatus muscle length in response to clinical intervention, and associations between muscle length and shoulder function.

The Long Head of the Biceps Has a Stabilizing Effect on the Glenohumeral Joint in Simulated Infraspinatus or Subscapularis but Not Supraspinatus Rotator Cuff Deficiency: A Biomechanical Study.

PURPOSE: To investigate the stabilizing role of the long head of the biceps (LHB) for different simulated rotator cuff (RC) tears. METHODS: Human cadaveric specimens (n = 8) were fixed in a robotic-based experimental setup with a static loading of the RC, deltoid, and the LHB. RC tears were simulated by unloading of the corresponding muscles. A throwing motion and an anterior load-and-shift test were simulated under different RC conditions by unloading the supraspinatus (SS), subscapularis (SSc), infraspinatus (IS), and combinations (SS + SSc, SS + IS, SS + SSc + IS). The LHB was tested in 3 conditions: unloaded, loaded, and tenotomy. Translation of the humeral head and anterior forces depending on loading of the RC and the LHB was captured. RESULTS: Loading of LHB produced no significant changes in anterior force or glenohumeral translation for the intact RC or a simulated SS tear. However, if SSc or IS were unloaded, LHB loading resulted in a significant increase of anterior force ranging from 3.9 N (P = .013, SSc unloaded) to 5.2 N (P = .001, simulated massive tear) and glenohumeral translation ranging from 2.4 mm (P = .0078, SSc unloaded) to 7.4 mm (P = .0078, simulated massive tear) compared to the unloaded LHB. Tenotomy of the LHB led to a significant increase in glenohumeral translation compared to the unloaded LHB in case of combined SS + SSc (2.6 mm, P = .0391) and simulated massive tears of all SS + SSc + IS (4.6 mm, P = .0078). Highest translation was observed in simulated massive tears between loaded LHB and tenotomy (8.1 mm, P = .0078). CONCLUSIONS: Once SSc or IS is simulated to be torn, the LHB has a stabilizing effect for the glenohumeral joint and counteracts humeral translation. With a fully loaded RC, LHB loading has no influence. CLINICAL RELEVANCE: With an intact RC, the condition of the LHB showed no biomechanical effect on the joint stability. Therefore, from a biomechanical point of view, the LHB could be removed from the joint when the RC is intact or reconstructable. However, since there was a positive effect even of the unloaded LHB in this study when SSc or IS is deficient, techniques with preservation of the supraglenoid LHB origin may be of benefit in such cases.

Individuals with rotator cuff tears unsuccessfully treated with exercise therapy have less inferiorly oriented net muscle forces during scapular plane abduction.

Exercise therapy for individuals with rotator cuff tears fails in approximately 25.0 % of cases. One reason for failure of exercise therapy may be the inability to strengthen and balance the muscle forces crossing the glenohumeral joint that act to center the humeral head on the glenoid. The objective of the current study was to compare the magnitude and orientation of the net muscle force pre- and post-exercise therapy between subjects successfully and unsuccessfully (e.g. eventually underwent surgery) treated with a 12-week individualized exercise therapy program. Twelve computational musculoskeletal models (n = 6 successful, n = 6 unsuccessful) were developed in OpenSim (v4.0) that incorporated subject specific tear characteristics, muscle peak isometric force, in-vivo kinematics and bony morphology. The models were driven with experimental kinematics and the magnitude and orientation of the net muscle force was determined during scapular plane abduction at pre- and post-exercise therapy timepoints. Subjects unsuccessfully treated had less inferiorly oriented net muscle forces pre- and post-exercise therapy compared to subjects successfully treated (p = 0.039 & 0.045, respectively). No differences were observed in the magnitude of the net muscle force (p > 0.05). The current study developed novel computational musculoskeletal models with subject specific inputs capable of distinguishing between subjects successfully and unsuccessfully treated with exercise therapy. A less inferiorly oriented net muscle force in subjects unsuccessfully treated may increase the risk of superior migration leading to impingement. Adjustments to exercise therapy programs may be warranted to avoid surgery in subjects at risk of unsuccessful treatment.

Mechanical characteristic of supraspinatus muscle changes independent of its size and intramuscular fat in patient with rotator cuff repair.

PURPOSE: This study aimed i) to investigate the mechanical, morphological, and compositional characteristics of the supraspinatus muscle after rotator cuff repair by using ultrasound shear wave elastography (SWE) and B-mode imaging, and ii) to determine whether the morphological or compositional characteristics are associated with the mechanical characteristic of the supraspinatus during contraction. METHODS: Using SWE and B-mode imaging, active and passive shear moduli, muscle thickness, and echo intensity of the supraspinatus were measured from the repaired and contralateral control shoulders of 22 patients with rotator cuff repair. The shear modulus, muscle thickness, and echo intensity were compared between the repaired and control shoulders. The association between the active shear modulus and the other variables was determined. RESULTS: While the active and passive shear moduli were lower in the repaired shoulder compared to the control, the muscle thickness and echo intensity did not vary between them. Interestingly, the passive shear modulus was positively correlated with the active shear modulus only in the control shoulder. CONCLUSION: The mechanical characteristic of supraspinatus remains impaired, even without degenerative changes in the morphological and compositional characteristics after rotator cuff repair. Furthermore, the association between contractile and elastic characteristics in the supraspinatus was deteriorated in control shoulder.

Editorial Commentary: A Biphasic (Calcified and Demineralized), Cancellous, Interpositional Allograft Augmenting Rotator Cuff Repair in an Ovine Model Does Not Show Harmful Inflammation or Foreign Body Reaction.

To improve the outcomes of arthroscopic rotator cuff (RC) repair, it is important to achieve tendon-to-bone healing at the repair site. Healed repairs are more likely to restore shoulder strength and lead to higher magnitudes of satisfaction. Patches or grafts that can be either secured to the bursal surface of the RC or interposed between the RC tendon and greater tuberosity at the time of repair have been described as adjuncts to RC repair. A cancellous, biphasic allograft tissue composed of 2 layers (calcified to promote osseointegration and demineralized to support soft-tissue ingrowth) has been shown to be safe in an ovine model, without a harmful inflammatory or foreign body response. Human trials may be a reasonable next step.

Test-retest reliability of isometric shoulder muscle strength during abduction and rotation tasks measured using the Biodex dynamometer.

BACKGROUND: The Constant score (CS) is often used clinically to assess shoulder function and includes a muscle strength assessment only for abduction. The aim of this study was to evaluate the test-retest reliability of isometric shoulder muscle strength during various positions of abduction and rotation with the Biodex dynamometer and to determine their correlation with the strength assessment of the CS. METHODS: Ten young healthy subjects participated in this study. Isometric shoulder muscle strength was measured during 3 repetitions for abduction at 10° and 30° abduction in the scapular plane (with extended elbow and hand in neutral position) and for internal and external rotation (with the arm at 15° abduction in the scapular plane and elbow flexed at 90°). Muscle strength tests with the Biodex dynamometer were measured in 2 different sessions. The CS was acquired only in the first session. Intraclass correlation coefficients (ICCs) with 95% confidence interval, limits of agreement, and paired t tests for repeated tests of each abduction and rotation task were calculated. Pearson's correlation between the strength parameter of the CS and isometric muscle strength was investigated. RESULTS: Muscle strength did not differ between tests (P > .05) with good to very good reliabilities for abduction at 10° and 30°, external rotation and internal rotation (ICC >0.7 for all). A moderate correlation of the strength parameter of the CS with all isometric shoulder strength parameters was observed (r > 0.5 for all). CONCLUSION: Shoulder muscle strength for abduction and rotation measured with the Biodex dynamometer are reproducible and correlate with the strength assessment of the CS. Therefore, these isometric muscle strength tests can be further employed to investigate the effect of different shoulder joint pathology on muscle strength. These measurements consider a more comprehensive functionality of the rotator cuff than the single strength evaluation in abduction within the CS as both abduction and rotation are assessed. Potentially, this would allow for a more precise differentiation between the various outcomes of rotator cuff tears.

The Effect of Vitamin C and N-Acetylcysteine on Tendon-to-Bone Healing in a Rodent Model of Rotator Cuff Repair.

BACKGROUND: Oxidative stress inhibits tendon-to-bone healing after rotator cuff repair. Regulation of oxidative stress has the potential to accelerate this healing, but its mechanism remains unclear. PURPOSE: To investigate the effects of reducing oxidative stress by applying antioxidants, such as N-acetylcysteine (NAC) and vitamin C (VC), on rotator cuff repair in a rat rotator cuff repair model. STUDY DESIGN: Controlled laboratory study. METHODS: A total of 48 Sprague Dawley rats underwent bilateral surgery to repair the infraspinatus tendon to its insertion site 1 week after detachment. Rats were assigned to either the NAC group, the VC group, or a control group. Histological evaluation was performed via hematoxylin-eosin or toluidine blue staining, and oxidative stress was assessed via dihydroethidium intensity and protein carbonyl concentration at 3 and 6 weeks. Superoxide dismutase 1 (SOD1), SOD2, SOD3, peroxiredoxin 5, collagen type I (COL1), COL3, matrix metalloproteinase 1 (MMP-1), MMP-3, and MMP-13 expression and SOD activity were determined at 3 and 6 weeks. Biomechanical tests were performed at 6 and 12 weeks. RESULTS: Histological evaluation showed that the number of chondrocytes in the NAC group at 6 weeks and in the VC group at 3 and 6 weeks, the area of fibrocartilage at 6 weeks in the VC group, and collagen fibers at 6 weeks in the NAC and VC groups were significantly increased compared with those in the control group. Dihydroethidium intensity at 3 and 6 weeks and protein carbonyls at 6 weeks in the NAC and VC groups were significantly decreased. SOD1 expression and SOD activity at 3 weeks in the VC group and peroxiredoxin 5 expression at 6 weeks in the NAC group were significantly upregulated compared with that in the control group. COL3 expression was significantly upregulated at 6 weeks in the VC group, and MMP-13 expression was significantly decreased at 6 weeks in the NAC and VC groups. The biomechanical strength showed no significant difference. CONCLUSION: Antioxidant treatment, via NAC or VC administration, reduced oxidative stress in the rotator cuff repair site and accelerated healing. CLINICAL RELEVANCE: These findings provide essential indications to develop clinical strategies for improved healing after rotator cuff surgical repair in patients.

Rotator cuff training with upper extremity blood flow restriction produces favorable adaptations in division IA collegiate pitchers: a randomized trial.

BACKGROUND: Recent evidence indicates that combined upper extremity blood flow restriction (BFR, applied distally to the shoulder) and low-load resistance exercise (LIX) augments clinically meaningful responses in shoulder region tissues proximal to the occlusion site. The purpose of this investigation was to determine the efficacy of BFR-LIX for the shoulder when added to standard offseason training in Division IA collegiate baseball pitchers. We hypothesized that BFR-LIX would augment training-induced increases in shoulder-region lean mass, rotator cuff strength, and endurance. As secondary outcomes, we sought to explore the impact of BFR-LIX rotator cuff training on pitching mechanics. METHODS: Twenty-eight collegiate baseball pitchers were randomized into 2 groups (BFRN = 15 and non-BFR [NOBFR]N = 13) that, in conjunction with offseason training, performed 8 weeks of shoulder LIX (Throwing arm only; 2/week, 4 sets [30/15/15/fatigue], 20% isometric max) using 4 exercises (cable external and internal rotation [ER/IR], dumbbell scaption, and side-lying dumbbell ER). The BFR group also trained with an automated tourniquet on the proximal arm (50% occlusion). Regional lean mass (dual-energy x-ray absorptiometry), rotator cuff strength (dynamometry: IR 0 & 90, ° ER 0 & 90, ° Scaption, Flexion), and fastball biomechanics were assessed pre and post-training. Achievable workload (sets × reps × resistance) was also recorded. An ANCOVA (covaried on baseline measures) repeated on training timepoint was used to detect within-group and between-group differences in outcome measures (α = 0.05). For significant pairwise comparisons, effect size (ES) was calculated using a Cohen's d statistic and interpreted as: 0-0.1, negligible; 0.1-0.3, small; 0.3-0.5, moderate; 0.5-0.7, large; >0.7, and very large (VL). RESULTS: Following training, the BFR group experienced greater increases in shoulder-region lean mass (BFR: ↑ 227 ± 60g, NOBFR: ↑ 75 ± 37g, P = .018, ES = 1.0 VL) and isometric strength for IR 90 ° (↑ 2.4 ± 2.3 kg, P = .041, ES = 0.9VL). The NOBFR group experienced decreased shoulder flexion ↓ 1.6 ± 0.8 kg, P = .007, ES = 1.4VL) and IR at 0 ° ↓ 2.9 ± 1.5 kg, P = .004, ES = 1.1VL). The BFR group had a greater increase in achievable workload for the scaption exercise (BFR: ↑ 190 ± 3.2 kg, NOBFR: ↑ 90 ± 3.3 kg, P = .005, ES = 0.8VL). Only the NOBFR group was observed to experience changes in pitching mechanics following training with increased shoulder external rotation at lead foot contact (↑ 9.0° ± 7.9, P = .028, ES = 0.8VL) as well as reduced forward ↓ 3.6° ± 2.1, P = .001, ES = 1.2VL) and lateral ↓ 4.6° ± 3.4, P = .007, ES = 1.0VL) trunk tilt at ball release. CONCLUSION: BFR-LIX rotator cuff training performed in conjunction with a collegiate offseason program augments increases in shoulder lean mass as well as muscular endurance while maintaining rotator cuff strength and possibly pitching mechanics in a manner that may contribute to favorable outcomes and injury prevention in baseball pitching athletes.

Effect of CCR2 Knockout on Tendon Biomechanical Properties in a Mouse Model of Delayed Rotator Cuff Repair.

BACKGROUND: The high incidence of incomplete or failed healing after rotator cuff repair (RCR) has led to an increased focus on the biologic factors that affect tendon-to-bone healing. Inflammation plays a critical role in the initial tendon-healing response. C-C chemokine receptor type 2 (CCR2) is a chemokine receptor linked to the recruitment of monocytes in early inflammatory stages and is associated with an increase in pro-inflammatory macrophages. The purpose of this study was to evaluate the role of CCR2 in tendon healing following RCR in C57BL/6J wildtype (WT) and CCR2-/- knockout (CCR2KO) mice in a delayed RCR model. METHODS: Fifty-two 12-week-old, male mice were allocated to 2 groups (WT and CCR2KO). All mice underwent unilateral supraspinatus tendon (SST) detachment at the initial surgical procedure, followed by a delayed repair 2 weeks later. The primary outcome measure was biomechanical testing. Secondary measures included histology, gene expression analysis, flow cytometry, and gait analysis. RESULTS: The mean load-to-failure was 1.64 ± 0.41 N in the WT group and 2.50 ± 0.42 N in the CCR2KO group (p = 0.030). The mean stiffness was 1.43 ± 0.66 N/mm in the WT group and 3.00 ± 0.95 N/mm in the CCR2KO group (p = 0.008). Transcriptional profiling demonstrated 7 differentially expressed genes (DEGs) when comparing the CCR2KO and WT groups (p < 0.05) and significant differences in Type-I and Type-II interferon pathway scores (p < 0.01). Flow cytometry demonstrated significant differences between groups for the percentage of macrophages present (8.1% for the WT group compared with 5.8% for the CCR2KO group; p = 0.035). Gait analysis demonstrated no significant differences between groups. CONCLUSIONS: CCR2KO may potentially improve tendon biomechanical properties by decreasing macrophage infiltration and/or by suppressing inflammatory mediator pathways in the setting of delayed RCR. CLINICAL RELEVANCE: CCR2 may be a promising target for novel therapeutics that aim to decrease failure rates following RCR.

Determination of the reference range for semi-quantified elasticity of healthy supraspinatus muscles using real-time tissue elastography and its clinical use in patients after rotator cuff repair.

BACKGROUND: The quantitative assessment of healthy supraspinatus muscle elasticity may provide clinically useful preliminary information after rotator cuff repairs. We aimed to determine the reference range for supraspinatus muscle semi-quantified elasticity and describe how it can be used clinically after rotator cuff repair. METHODS: The elasticity of healthy bilateral supraspinatus muscles in 43 participants aged between 24 and 75 years (categorized into two subgroups: <50 and ≥ 50 years) was measured as a strain ratio at 0° and 60° of shoulder abduction using real-time tissue elastography. The reference and modified reference ranges calculated by excluding outliers for elasticity were determined using normal distribution methods for logarithmically transformed data. The modified reference range was applied to eight cases of rotator cuff repair. FINDINGS: Strain ratios under and over 50 years of age were 1.63 vs. 2.21 at 0° of shoulder abduction (P = 0.028) and 0.92 vs. 1.29 at 60° of shoulder abduction (P = 0.002), respectively. Modified reference ranges for under and over 50 years of age were 0.72-4.17 and 0.98-4.50 at 0° of shoulder abduction and 0.38-1.95 and 0.56-2.76 at 60° of shoulder abduction, respectively. Among eight cases, two showed strain ratios above the reference range at 1 month postoperatively, and rehabilitation protocols were adjusted. INTERPRETATION: A strain ratio above the reference range, especially above the upper limit at 0° of shoulder abduction, may indicate increased passive stiffness of the musculotendinous unit. Clinically, the reference range has the potential to be used as a baseline after rotator cuff repairs.

Decreased muscle strength and scapular muscle endurance associated with shoulder function after neck dissection.

BACKGROUND: Shoulder disability is a common problem following neck dissection. Even if nerve structures are preserved, this may occur after the surgery. OBJECTIVE: The primary aim was to research changes in rotator cuff and scapular muscles strength, and scapular muscle endurance after neck dissection in patients with head and neck cancer. The secondary aim was to investigate the relationship between these changes and postoperative shoulder function. METHODS: This cross-sectional and prospective follow-up study included 14 patients who underwent neck dissection (9 unilateral and 5 bilateral). Evaluations were performed preoperatively and at 3 months postoperatively. Muscle strength measurements, including trapezius, serratus anterior, and rotator cuff muscles, were obtained using a handheld dynamometer. The scapular muscle endurance test was used for muscle endurance assessment. Postoperative shoulder function was evaluated using Constant-Murley shoulder score. RESULTS: A decrease in muscle strength and the scapular muscle endurance test was found at 3 months postoperatively, except for the subscapularis muscle strength (p< 0.05). There were moderate to strong correlations between Constant-Murley shoulder score and percentage changes in muscle strength and the scapular muscle endurance test, except for the upper trapezius muscle strength (p< 0.05). CONCLUSIONS: Muscle strength and scapular muscle endurance may reduce following neck dissection. These reductions are associated with postoperative shoulder function. Thus, muscle strength and endurance training may be beneficial for early postoperative rehabilitation in patients with head and neck cancer.

Excessively High Repair Tension Decreases Microvascular Blood Flow Within the Rotator Cuff.

BACKGROUND: Repair tension and microvascular blood flow within the rotator cuff has a critical impact on tendon healing after rotator cuff repair. However, the relationship between repair tension and microvascular blood flow within the rotator cuff remains unclear. PURPOSE/HYPOTHESIS: The purpose of this study was to determine how much tension adversely affects microvascular blood flow within the rotator cuff. The hypothesis was that as the repair tension increases, the microvascular blood flow within the rotator cuff decreases. STUDY DESIGN: Controlled laboratory study. METHODS: Repair tension and microvascular blood flow within the rotator cuff of 30 patients with full-thickness rotator cuff tears were simultaneously measured using a digital tension meter and a contact-type laser Doppler flowmeter, respectively. Microvascular blood flow was measured under 4 levels of tension (0, 10, 20, and 30 N) at 5 points on the rotator cuff. The obtained values were statistically analyzed by a linear mixed-effects model to clarify the effect of tension on microvascular blood flow within the rotator cuff. RESULTS: There was no statistically significant difference in microvascular blood flow (mL/min/100 g) within the rotator cuff between 0 N (mean, 3.51; 95% CI, 3.0-4.0) and 10 N (mean, 3.74; 95% CI, 3.2-4.3) of tension (P = .716). However, there were statistically significant differences in microvascular blood flow within the rotator cuff between 0 and 20 N of tension (mean, 2.84; 95% CI, 2.3-3.4) (P = .002) and between 0 and 30 N of tension (mean, 2.45; 95% CI, 1.9-3.0) (P < .001). CONCLUSION/CLINICAL RELEVANCE: Our findings indicate that tension of ≥10 N during rotator cuff repair significantly decreases the microvascular blood flow within the rotator cuff. These data will contribute to determining the optimal repair tension during rotator cuff repair.

Review of human supraspinatus tendon mechanics. Part I: fatigue damage accumulation and failure.

Repetitive stress injuries to the rotator cuff, and particularly the supraspinatus tendon (SST), are highly prevalent and debilitating. These injuries typically occur through the application of cyclic load below the threshold necessary to cause acute tears, leading to accumulation of incremental damage that exceeds the body's ability to heal, resulting in decreased mechanical strength and increased risk of frank rupture at lower loads. Consistent progression of fatigue damage across multiple model systems suggests a generalized tendon response to overuse. This finding may allow for interventions before gross injury of the SST occurs. Further research into the human SST response to fatigue loading is necessary to characterize the fatigue life of the tendon, which will help determine the frequency, duration, and magnitude of load spectra the SST may experience before injury. Future studies may allow in vivo SST strain analysis during specific activities, generation of a human SST stress-cycle curve, and characterization of damage and repair related to repetitive tasks.

Does the osteoarthritic shoulder have altered rotator cuff vectors with increasing glenoid deformity? An in silico analysis.

BACKGROUND: A transverse force couple (TFC) functional imbalance has been demonstrated in osteoarthritic shoulders by recent 3-dimensional (3D) muscle volumetric studies. Altered rotator cuff vectors may be an additional factor contributing to a muscle imbalance and the propagation of glenoid deformity. METHODS: Computed tomography images of 33 Walch type A and 60 Walch type B shoulders were evaluated. The 3D volumes of the entire subscapularis, supraspinatus, and infraspinatus-teres minor (ISP-Tm) and scapula were manually segmented. The volume masks and scapular landmarks were imported into MATLAB to create a coordinate system, enabling calculation of muscle force vectors. The direction of each muscle force vector was described in the transverse and vertical plane, calculated with respect to the glenoid. Each muscle vector was then resolved into compression and shear force across the glenoid face. The relationship between muscle force vectors, glenoid retroversion or inclination, compression/shear forces on the glenoid, and Walch type was determined using linear regression. RESULTS: In the transverse plane with all rotator cuff muscles combined, increasing retroversion was significantly associated with increasing posterior drag (P < .001). Type B glenoids had significantly more posterior drag than type A (P < .001). In the vertical plane for each individual muscle group and in combination, superior drag increases as superior inclination increases (P < .001). Analysis of individual muscle groups showed that the anterior thrust of ISP-Tm and supraspinatus switched to a posterior drag at 8° and 10° of retroversion respectively. The compression force on the glenoid face by ISP-Tm and supraspinatus did not change with increasing retroversion for type A shoulders (P = .592 and P = .715, respectively), but they did for type B shoulders (P < .001 for both). The glenoid shear force ratio in the transverse plane for the ISP-Tm and supraspinatus moved from anterior to posterior shear with increasing glenoid retroversion, crossing zero at 8° and 10° of retroversion, whereas the subscapularis exerted a posterior shear force for every retroversion angle. CONCLUSION: Increased glenoid retroversion is associated with increased posterior shear and decreased compression forces on the glenoid face, explaining some of the pathognomonic bone morphometrics that characterize the osteoarthritic shoulder. Although the subscapularis always maintains a posterior thrust, the ISP-Tm and supraspinatus together showed an inflection at 8° and 10° of retroversion, changing from an anterior thrust to a posterior drag. This finding highlights the importance that in anatomic TSA the rotator cuff functional balance might be better restored by correcting glenoid retroversion to less than 8°.

The Rotator Cable Does Not Stress Shield the Crescent Area During Shoulder Abduction.

BACKGROUND: It is accepted by the orthopaedic community that the rotator cable (RCa) acts as a suspension bridge that stress shields the crescent area (CA). The goal of this study was to determine if the RCa does stress shield the CA during shoulder abduction. METHODS: The principal strain magnitude and direction in the RCa and CA and shoulder abduction force were measured in 20 cadaveric specimens. Ten specimens underwent a release of the anterior cable insertion followed by a posterior release. In the other 10, a release of the posterior cable insertion was followed by an anterior release. Testing was performed for the native, single-release, and full-release conditions. The thicknesses of the RCa and CA were measured. RESULTS: Neither the principal strain magnitude nor the strain direction in either the RCa or the CA changed with single or full RCa release (p ≥ 0.493). There were no changes in abduction force after single or full RCa release (p ≥ 0.180). The RCa and CA thicknesses did not differ from one another at any location (p ≥ 0.195). CONCLUSIONS: The RCa does not act as a suspension bridge and does not stress shield the CA. The CA primarily transfers shoulder abduction force to the greater tuberosity. CLINICAL RELEVANCE: The CA is important in force transmission during shoulder abduction, and efforts should be made to restore its continuity with a repair or reconstruction.

Editorial Commentary: Allogenic Dermal Fibroblasts in Collagen Matrix Scaffold Enhance Rotator Cuff Repair in an Animal Model.

There has been a recent surge of interest on the use of biologic supplements to facilitate rotator cuff repair healing. Experimental evidence appears to support use of allogenic dermal fibroblasts (ADFs), either in the form of local injection or tenocytes embedded in collagen matrix scaffold, to enhance healing of a repaired rotator cuff tendon tear in an animal model. When compared with the ADFs, the platelet-rich plasma (PRP)-induced response seems to be limited in terms of the specific increases in local collagen 1 concentration, thus resulting in a bone-tendon healing response that is inferior in both biology and biomechanical behavior under the same laboratory conditions. While on the one hand, there is pilot data supporting use of dermal fibroblast in the clinical setting, thus reinforcing the animal study findings, on the other hand, we are also aware of the encouraging biologic changes that occurred in the retrieved acellular dermal matrix (ADM) allograft that was used for superior capsular reconstruction as a treatment of irreparable rotator cuff tears. In theory, ADFs locally instilled as an injection should further enhance the healing response compared to the ADM. However, this needs to be further studied to be able to be widely applicable clinically.

Moment arms of the deltoid, infraspinatus and teres minor muscles for movements with high range of motion: A cadaveric study.

BACKGROUND: Moment arms are an indicator of the role of the muscles in joint actuation. An excursion method is often used to calculate them, even though it provides 1D results. As shoulder movement occurs in three dimensions (combination of flexion, abduction and axial rotation), moment arms should be given in 3D. Our objective was to assess the 3D moment arms of the rotator cuff (infraspinatus and teres minor) and deltoid muscles for movements with high arm elevation. METHODS: The 3D moment arms (components in plane of elevation, elevation and axial rotation) were assessed using a geometric method, enabling to calculate the moment arms in 3D, on five fresh post-mortem human shoulders. Movement with high range of motion were performed (including overhead movement). The humerus was elevated until it reaches its maximal posture in different elevation plane (flexion, scaption, abduction and elevation in a plane 30° posterior to frontal plane). FINDINGS: We found that the anterior deltoid was a depressor and contributes to move the elevation plane anteriorly. The median deltoid was a great elevator and the posterior deltoid mostly acted in moving the elevation plane posteriorly. The infraspinatus and teres minor were the greatest external rotator of the shoulder. The position of the glenohumeral joint induces changes in the muscular moment arms. The maximal shoulder elevation was 144° (performed in the scapular plane). INTERPRETATION: The knowledge of 3D moment arms for different arm elevations might help surgeons in planning tendon reconstructive surgery and help validate musculoskeletal models.

Anatomic total shoulder glenoid component inclination affects glenohumeral kinetics during abduction: a cadaveric study.

BACKGROUND: Although typically favorable in outcome, anatomic total shoulder arthroplasty (aTSA) can require long-term revision. The most common cause for revision is glenoid loosening, which may result from eccentric cyclic forces and joint translations. "Rocking" of the glenoid component may be exacerbated by the joint geometry, such as glenoid inclination and version. Restoration of premorbid glenoid inclination may be preferable, although laboratory and computational models indicate that both superior inclination and inferior inclination have benefits. This discrepancy may arise because previous studies were limited by a lack of physiological conditions to test inclination. Therefore, a cadaveric shoulder simulator with 3-dimensional human motion was used to study joint contact and muscle forces with isolated changes in glenoid inclination. METHODS: Eight human cadaveric shoulders were tested before and after aTSA. Scapular-plane abduction kinematics from human subjects were used to drive a cadaveric shoulder simulator with 3-dimensional scapulothoracic and glenohumeral motion. Glenoid inclination was varied from -10° to +20°, whereas compressive, superior-inferior shear, and anterior-posterior shear forces were collected with a 6-df load cell during motion. Outputs also included muscle forces of the deltoid and rotator cuff. Data were evaluated with statistical parametric mapping repeated-measures analysis of variance and t tests. RESULTS: Inferior glenoid inclination (-10°) reduced both compressive and superior-inferior shear forces vs. neutral 0° inclination by up to 40%, and even more when compared with superior inclination (P < .001). Superior inclinations (+10° and +20°) tended to increase deltoid and rotator cuff forces vs. neutral 0° inclination or inferior inclination, on the order of 20%-40% (P ≤ .045). All force metrics except anterior-posterior shear were lowest for inferior inclination. Most aTSA muscle forces for neutral 0° inclination were not significantly different from native shoulders and decreased 45% and 15% in the posterior deltoid and supraspinatus, respectively (P ≤ .003). Joint translations were similar to prior reports in aTSA patients and did not differ between any inclinations or compared with native shoulders. Joint reaction forces were similar to those observed in human subjects with instrumented aTSA implants, providing confidence in the relative magnitude of our results. CONCLUSIONS: Inferior inclination reduces overall forces in the shoulder. Superior inclinations increase the muscle effort required for the shoulder to achieve similar motion, thus increasing the forces exerted on the glenoid component. These results suggest that a preference toward aTSA glenoid components in inferior inclination may reduce the likelihood of glenoid loosening by reducing excessive muscle and joint contact forces.

Ultrasound assessment after a subscapularis-sparing approach to total shoulder arthroplasty.

BACKGROUND: Although anatomic total shoulder arthroplasty (ATSA) has favorable outcomes, nearly all techniques involve subscapularis tendon release for shoulder joint access. Such takedown of the subscapularis may be associated with decreased function, instability, and pain. Subscapularis-sparing approaches have the theoretical benefits of improved function, decreased failure of the tendon reattachment site, and early range of motion and rehabilitation. The primary purpose of this study was to use ultrasound to assess the postoperative integrity of the subscapularis tendon and surrounding soft tissues after ATSA with a subscapularis-sparing technique through an extensile anterosuperior skin incision. Our hypothesis was that this subscapularis-sparing approach would have low rates of subscapularis disruption. METHODS: A consecutive cohort of patients who underwent subscapularis-sparing ATSA between 2014 and 2017 were included. Ultrasound was used to evaluate the rotator cuff tendons and deltoid postoperatively, and these were classified as intact, disrupted, or unable to be adequately visualized. Clinical outcome scores, range of motion, and strength measurements were also collected at 1-3 years postoperatively. RESULTS: Thirty-seven subscapularis tendons and 40 supraspinatus and infraspinatus muscles were adequately visualized and included for analysis. Of the subscapularis muscles, 32 (86%) were intact; 38 of the visualized supraspinatus muscles (95%) and 39 of the infraspinatus muscles (98%) were intact. No dehiscence or loss of integrity of the deltoid was noted. Clinical comparison between patients with disrupted subscapularis muscles and patients without such disruption demonstrated no difference in clinical outcome scores and postoperative range of motion but showed less strength in forward flexion, abduction, and external rotation. CONCLUSIONS: The rate of subscapularis disruption using a subscapularis-sparing approach for ATSA was low (14%), but the potential for tendon disruption was not eradicated. Favorable clinical outcomes support this surgical approach as a potential technique for ATSA.