The effect of in vivo rotator cuff muscle contraction on glenohumeral joint translation: An ultrasonographic and electromyographic study

Managing Subscapularis in Shoulder arthroplasty

Managing subscapularis forms an integral part of shoulder arthroplasty and the ideal technique for subscapularis release and repair during shoulder arthroplasty is still under debate. The three common techniques are tenotomy, peel and lesser tuberosity osteotomy (LTO). Current literature from clinical studies does not show any difference in the outcome between the 3 techniques. However biomechanical studies favour LTO. Subscapularis sparing approach can be an alternative solution allowing early rehabilitation but needs further clinical studies to assess its longterm benefits. Failure of subscapularis repair in anatomical shoulder replacement can lead to pain, loss of movements, instability and loosening of implants. Treatment options include revision repair, tendon transfer, reconstruction with allograft tendon and revision to reverse shoulder arthroplasty (RSA). Repairing subscapularis in RSA can improve rotations and stability, however it also has adverse biomechanical effects on deltoid. Absence of subscapularis repair is seen to affect stability only in medialised implant designs, while no such effects are seen in lateralised design implants.

Stabilizing Mechanisms in Patients Treated Using Hill-Sachs Remplissage With Bankart Repair in Abduction-External Rotation Position

BACKGROUND

Hill-Sachs lesion (HSL) remplissage with Bankart repair (RMBR) provides a minimally invasive solution for treating HSLs and glenoid bone defects of <25%. The infraspinatus tendon is inserted into the HSL during the remplissage process, causing the infraspinatus to shift medially, leading to an unknown effect on glenohumeral alignment during the resting abduction-external rotation (ABER) and muscle-active states.

PURPOSE/HYPOTHESIS

The purpose of this study was to evaluate the possible check-rein effect and muscle-active control in stabilizing the glenohumeral joint after RMBR in vivo. We hypothesized that the check-rein effect and active control would stabilize the glenohumeral joint in the ABER position in patients after RMBR.

STUDY DESIGN

Controlled laboratory study.

METHODS

We included 42 participants-22 patients in group A who met the inclusion criteria after RMBR and 20 healthy participants in group B without shoulder laxity. Three-dimensional magnetic resonance imaging was performed to analyze the alignment relationship of the glenohumeral joint with and without muscular activity. Ultrasonic shear wave elastography was used to evaluate the elastic properties of the anterior capsule covered with the anterior bands of the inferior glenohumeral ligament.

RESULTS

Patients who underwent RMBR demonstrated more posterior (-1.81 ± 1.19 mm vs -0.76 ± 1.25 mm; P = .008) and inferior (-1.05 ± 0.62 mm vs -0.45 ± 0.48 mm; P = .001) shifts of the humeral head rotation center and less anterior capsular elasticity (70.07 ± 22.60 kPa vs 84.01 ± 14.08 kPa; P = .023) than healthy participants in the resting ABER state. More posterior (-3.17 ± 0.84 mm vs -1.81 ± 1.19 mm; P < .001) and less-inferior (-0.34 ± 0.56 mm vs -1.05 ± 0.62 mm; P < .001) shifts of the humeral head rotation center and less anterior capsular elasticity (36.57 ± 13.89 kPa vs 70.07 ± 22.60 kPa; P < .001) were observed in the operative shoulder during muscle-active ABER than in resting ABER states.

CONCLUSION

The check-rein effect and muscle-active control act as stabilizing mechanisms in RMBR during the ABER position.

CLINICAL RELEVANCE

Stabilizing mechanisms in RMBR during the ABER position include the check-rein effect and muscle-active control.

Load-induced increase in muscle activity during 30° abduction in patients with rotator cuff tears and control subjects

BACKGROUND

Rotator cuff muscles stabilise the glenohumeral joint and contribute to the initial abduction phase with other shoulder muscles. This study aimed to determine if the load-induced increase in shoulder muscle activity during a 30° abduction test is influenced by asymptomatic or symptomatic rotator cuff pathologies.

MATERIALS AND METHODS

Twenty-five patients with unilateral rotator cuff tears (age, 64.3 ± 10.2 years), 25 older control subjects (55.4 ± 8.2 years) and 25 younger control subjects (26.1 ± 2.3 years) participated in this study. Participants performed a bilateral 30° arm abduction and adduction movement in the scapular plane with handheld weights (0-4 kg). Activity of the deltoid, infraspinatus, biceps brachii, pectoralis major, latissimus dorsi and upper trapezius muscles was analysed at maximum abduction angle after normalisation to maximum voluntary contraction. Shoulders were classified into rotator cuff tendinopathy, asymptomatic and symptomatic rotator cuff tears, and healthy based on magnetic resonance images. A linear mixed model (loads, shoulder types) with random effects (shoulder identification) was applied to the log-transformed muscle activities.

RESULTS

Muscle activity increased with increasing load in all muscles and shoulder types (P < 0.001), and 1-kg increments in additional weights were significant (P < 0.001). Significant effects of rotator cuff pathologies were found for all muscles analysed (P < 0.05). In all muscles, activity was at least 20% higher in symptomatic rotator cuff tears than in healthy shoulders (P < 0.001). Symptomatic rotator cuff tears showed 20-32% higher posterior deltoid (P < 0.05) and 19-25% higher pectoralis major (P < 0.01) activity when compared with asymptomatic tears.

CONCLUSIONS

Rotator cuff pathologies are associated with greater relative activity of shoulder muscles, even with low levels of additional load. Therefore, the inclusion of loaded shoulder tests in the diagnosis and rehabilitation of rotator cuff pathologies can provide important insight into the functional status of shoulders and can be used to guide treatment decisions.

LEVEL OF EVIDENCE

Level 2.

TRIAL REGISTRATION

Ethical approval was obtained from the regional ethics committee (Ethics Committee Northwest Switzerland EKNZ 2021-00182), and the study was registered at clinicaltrials.gov on 29 March 2021 (trial registration number NCT04819724, https://clinicaltrials.gov/ct2/show/NCT04819724 ).

Are Previous Joint Injuries Associated with Muscle Performance in Volleyball Athletes?

Objective  The aim of the present study is to determine whether previous shoulder and knee injuries were associated with isokinetic fatigue index and agonist/antagonist ratio of shoulder internal/external rotators and knee flexors/extensors in male volleyball athletes. Methods  The current study is a cross-sectional investigation of 49 male elite volleyball players competing at a high level in Brazil. Isokinetic fatigue index and agonist/antagonist profiles were assessed during the preseason. Additionally, in order to record previous injuries, the athletes answered a standardized questionnaire. We conducted a receiver operating characteristic (ROC) curve analysis to determine the association strength and the clinically relevant cut-off point for variables presenting statistical significance for the area under the curve (AUC) (α = 0.05). An independent t-test was used to compare isokinetic variables between athletes with and without previous injury (α = 0.05). Results  The results of the ROC curve analysis indicated that hamstring fatigue index values at 300 o /s were associated with the presence of previous knee injury (area under the curve [AUC] = 73%, p  = 0.004), and shoulder external rotators fatigue index values at 360°/s were not associated with the presence of previous shoulder injury (AUC = 68%, p  = 0.053). Conclusions  Elite volleyball athletes who reported previous knee injuries were prone to a higher fatigue index than those reporting no injuries. Knee flexor resistance training might be useful for those athletes who reported knee injuries in the previous season.

Ultrasound Assessment of Anterior Humeral Head Translation in Patients With Anterior Shoulder Instability: Correlation With Demographic, Radiographic, and Clinical Data

Background:

Ultrasonography can be used to quantitatively assess anterior humeral head translation (AHHT) at different degrees of shoulder abduction. Risk factors for recurrent shoulder instability have been identified.

Hypothesis:

It was hypothesized that the number of dislocations or glenoid or humeral bone loss would be associated with more AHHT as measured using ultrasound.

Study Design:

Cross-sectional study; Level of evidence, 3.

Methods:

A total of 39 patients who underwent surgery for anterior shoulder instability were prospectively studied. Ultrasound assessment of AHHT was performed immediately after general anesthesia was induced. The upper arm was placed at 0°, 45°, and 90° of abduction, and a 40-N anterior force was applied to the proximal third of the arm. The distance from the posterior edge of the glenoid to that of the humeral head was measured at each abduction angle using ultrasound with and without a 40-N anterior force, and the AHHT was calculated. The differences in translation at each shoulder angle were compared. Additionally, the authors investigated the association between AHHT and demographic, radiographic, and clinical data.

Results:

Compared with the AHHT at 0° of abduction (5.29 mm), translation was significantly larger at 45° of abduction (8.90 mm; P < .01) and 90° of abduction (9.46 mm; P < .01). The mean translation was significantly larger in female patients than in male patients at all degrees of abduction (P ≤ .036 for all). There was no correlation between AHHT at any abduction angle and number of dislocations, clinical data, or radiographic data (including bone loss).

Conclusion:

Ultrasound assessment of AHHT showed larger amounts of laxity at 45° and 90° than at 0° of abduction. Anterior glenohumeral laxity was greater in female than male patients. Glenoid or humeral bone loss did not correlate with AHHT, thereby clarifying that bone loss has no direct effect on measurements of capsular laxity in neutral rotation.

EURO-MUSCULUS/USPRM Dynamic Ultrasound Protocols for Shoulder

ABSTRACT

In this dynamic protocol, ultrasound examination of the shoulder using different maneuvers is described for several/relevant shoulder problems. Scanning videos are coupled with real-time patient examination videos for better understanding. The authors believe that this practical guide prepared by an international consensus of several experts (EURO-MUSCULUS: European Musculoskeletal Ultrasound Study Group and USPRM: Ultrasound Study Group of ISPRM [International Society of Physical and Rehabilitation Medicine]) will help musculoskeletal physicians perform a better and uniform/standard approach.

The Subscapularis Muscle: A Proposed Classification System

Background

On the basis of the available literature, we proposed the hypothesis that the number of muscle bellies is morphologically constant. The main purpose of this study was to examine the morphological variability of the SM and to create a new classification of it based on number of muscle bellies.

Methods

Sixty-six adult cadavers of Central European population (45 females, 21 males) were obtained and fixed in 10% formalin before examination.

Results

The SM was found in all 66 specimens (45 females, 21 males, 31 left and 35 right sides). After meticulous dissection, we distinguished nine types on the basis of number of bellies. Type I was characterized by single belly and occurred in 1.5%. Type II had a double belly and was present in 3%. Type III, the most common type, occurring in almost 32% of the studied population, had three bellies. The frequency of type IV, characterized by four bellies, was also high, just over 30%. The following types were less frequent: type V with five bellies (18.2%), type VI with six bellies (7.6%), type VII with seven bellies (3%), type VIII with eight bellies (1.5%), and type IX with nine bellies (3%). All of the types had origin on the anterior surface of the scapula.

Conclusions

The SM is morphologically variable in the number of its bellies. Evolutionary changes are probably the reason. The most common type was the SM with three bellies, in line with Larson's model of the division of the SM into three parts. Subsequent studies should be carried out based on MRI or ultrasonography examination to confirm if it is possible to show all types (presented in this study) among group of patients during MRI.

Clinical outcomes and temporal changes in the range of motion following superior capsular reconstruction for irreparable rotator cuff tears: comparison based on the Hamada classification, presence or absence of shoulder pseudoparalysis, and status of the subscapularis tendon

BACKGROUND

Superior capsular reconstruction (SCR) has recently gained popularity as a surgical solution for patients with massive rotator cuff tears or shoulder pseudoparalysis (PPS). Good clinical outcomes have been reported after SCR; however, the factors that influence its clinical outcomes remain unclear. Therefore, in this study, we aimed to clarify the factors influencing postoperative outcomes after SCR using tensor fascia lata graft, for which we evaluated the Hamada grade, patients with or without PPS, and the status of the subscapularis tendon (SSC).

METHODS

In total, 54 consecutive patients with irreparable rotator cuff tears or PPS who underwent SCR between June 2014 and October 2018 were included. The enrolled patients were grouped and compared as follows: (1) Hamada grade 2 (11 patients) and Hamada grade 3 (43 patients) and (2) non-PPS (22 patients), moderate PPS (16 patients), and severe PPS (16 patients). For subanalysis, the 32 PPS patients were divided into 3 groups: intact SSC (11 patients), repairable SSC (16 patients), and irreparable SSC (5 patients). To assess shoulder function, the American Shoulder and Elbow Surgeons (ASES) score was evaluated before surgery and at 24 months postoperatively; shoulder range of motion was evaluated at 2, 3, 4, 5, 6, 8, 10, 12, and 24 months postoperatively.

RESULTS

No significant differences in postoperative ASES scores and shoulder range of motion were observed between the Hamada grade 2 and grade 3 groups or between the non-PPS, moderate PPS, and severe PPS groups. However, significant differences in postoperative shoulder elevation and ASES scores were observed between the intact SSC and irreparable SSC groups (P = .006) and between the repairable SSC and irreparable SSC groups (P = .003).

CONCLUSIONS

This study demonstrated that the status of the SSC, rather than the Hamada grade or the presence or absence of PPS, influences the clinical outcomes after SCR. Therefore, reparability or intactness of the SSC is an important factor in considering the surgical indication for SCR.

Muscle Contraction Has a Reduced Effect on Increasing Glenohumeral Stability in the Apprehension Position

PURPOSE

Glenohumeral instability accounts for 23% of all shoulder injuries among collegiate athletes. The apprehension position-combined shoulder abduction and external rotation-commonly reproduces symptoms in athletes with instability. Rehabilitation aims to increase glenohumeral stability by strengthening functional positions. However, it is unclear how much glenohumeral stability increases with muscle contraction in the apprehension position. The purpose of this study was to determine whether the ability to increase translational glenohumeral stiffness, a quantitative measure of glenohumeral stability, with muscle contraction is reduced in the apprehension position.

METHODS

Seventeen asymptomatic adults participated. A precision-instrumented robotic system applied pseudorandom, anterior-posterior displacements to translate the humeral head within the glenoid fossa and measured the resultant forces as participants produced isometric shoulder torques. Measurements were made in neutral abduction (90° abduction/0° external rotation) and apprehension (90° abduction/90° external rotation) positions. Glenohumeral stiffness was estimated from the relationship between applied displacements and resultant forces. The ability to increase glenohumeral stiffness with increasing torque magnitude was compared between positions.

RESULTS

On average, participants increased glenohumeral stiffness from passive levels by 91% in the neutral abduction position and only 64% in the apprehension position while producing 10% of maximum torque production. The biggest decrease in the ability to modulate glenohumeral stiffness in the apprehension position was observed for torques generated in abduction (49% lower, P < 0.001) and horizontal abduction (25% lower, P < 0.001).

CONCLUSION

Our results demonstrate that individuals are less able to increase glenohumeral stiffness with muscle contraction in the apprehension position compared with a neutral shoulder position. These results may help explain why individuals with shoulder instability more frequently experience symptoms in the apprehension position compared with neutral shoulder positions.

An improved quantitative ultrasonographic technique could assess anterior translation of the glenohumeral joint accurately and reliably

PURPOSE

Since poor repeatability of the load and shift test using a grading scale has been reported, an objective and quantitative method to assess anterior translation should be established to assess glenohumeral joint function. The purpose of this study was to assess the accuracy and repeatability of the ultrasonographic techniques to quantify anterior translation of the glenohumeral joint.

METHODS

Eight fresh-frozen cadaveric shoulders were used. For the standard technique, the ultrasound transducer was positioned on the anterolateral aspect of the shoulder viewing the coracoid process, glenoid, and humeral head. For the revised technique, the transducer was positioned on the anterior aspect of the shoulder, perpendicular to the scapular plane, viewing the conjoint tendon, glenoid, and humeral head. During the load and shift test, the distance between anterior edges of the glenoid and the humeral head was measured. The difference between distances before and after applying an anterior load was calculated as an anterior translation and compared with the anterior translation assessed using a motion tracking system. The repeatability and accuracy of both techniques were analyzed statistically.

RESULTS

Intra- and inter-observer repeatability was good-excellent for both ultrasonographic techniques (ICC, 0.889-0.998). The revised technique achieved a stronger correlation to the anterior translations obtained using the motion tracking system (R = 0.810-0.913, p < 0.001) than the standard technique (R = 0.619-0.806, p < 0.001).

CONCLUSION

Better accuracy and repeatability was found in the revised technique than the standard technique. The revised technique will be useful to determine the individual laxity and modify the treatment plan and return-to-sports protocol.

LEVEL OF EVIDENCE

III.

Biomechanical comparison of zoned-conformity glenoid versus standard glenoid in total shoulder arthroplasty: impact on rotator cuff strain and glenohumeral translation

BACKGROUND

Current standard total shoulder arthroplasty glenoid implants allow for high levels of glenohumeral mismatch and associated high levels of humeral head translation to improve range of motion and reduce rim stresses on the glenoid. However, high levels of glenohumeral mismatch could also increase glenoid edge loading, eccentric wear, and rotator cuff strain. A zoned-conformity glenoid may be able to reduce the forces on the rotator cuff and glenoid. We compared rotator cuff strain and glenohumeral translation between a standard glenoid (SG) with moderate glenohumeral mismatch and a zoned-conformity glenoid (conforming glenoid [CG]) that limits mismatch. We hypothesized that the CG would have lower levels of strain on the rotator cuff and lower levels of humeral head translation compared with the SG.

METHODS

Eight fresh frozen cadaveric shoulders, aged 72 years (range, 67-76 years), were used in this biomechanical study. The specimens were first tested in the intact state. We cycled them 3 times from 0° to 60° of abduction and measured the superiorly-inferiorly and anteriorly-posteriorly directed forces at the joint, compressive forces applied to the glenoid, and humeral head translation. The specimens were then implanted with a standard press-fit humeral component and a polyethylene glenoid with 3 peripherally cemented pegs and a central press-fit peg. Testing was repeated. Finally, the SG was removed, the CG was implanted, and each specimen was tested a third time.

RESULTS

The average superiorly directed force at the glenohumeral joint was significantly lower in the intact and CG groups (18.1 ± 18.6 N and 19.8 ± 16.2 N, respectively) than in the SG group (29.3 ± 21.9 N, P = .024). The maximum force directed against the glenoid was also significantly lower in the CG group (87.6 ± 11.7 N) than in the SG (96.0 ± 7.3 N) and intact (98.9 ± 16.5 N) groups (P = .035). No difference was observed in humeral head translation in the anterior-posterior plane from 0° to 60° of abduction (P = .998) or in the superior-inferior plane (P = .999).

CONCLUSION

A zoned-conformity glenoid was associated with similar humeral head translation but significantly lower superior forces against the rotator cuff and a significantly lower maximum force against the glenoid compared with an SG implant. These biomechanical findings suggest that a zoned-conformity implant warrants further study in the effort to maintain humeral head translation while reducing rotator cuff and glenoid forces for successful outcomes of total shoulder arthroplasty.

Line Hops and Side Hold Rotation Tests Load Both Anterior and Posterior Shoulder: A Biomechanical Study

BACKGROUND

Clinical tests should replicate the stressful positions encountered during sport participation. Evaluating the kinetic and electromyographical demands of clinical tests enables clinicians to choose appropriate tests for specific sports.

PURPOSE

To describe the shoulder forces and muscle activation levels during closed chain functional tests of Line Hops (LH) and Side Hold Rotation (SHR).

STUDY DESIGN

Descriptive biomechanical study.

METHODS

Ten asymptomatic participants were examined in a university laboratory. Two functional tests were evaluated using three-dimensional video analysis and electromyography to measure shoulder forces, moments, and muscular activity levels.

RESULTS

SHR produced a peak average posterior translation force of 4.84 N/kg (CI95 4.32-5.36N/kg) and a peak average anterior translational force of 1.57 N/kg (CI95 1.10-2.01N/kg). High levels of serratus anterior (98% maximum voluntary isometric contraction (MVIC) and infraspinatus (52 %MVIC) were recorded during SHR. LH produced a posterior translational force of 4.25 N/kg (CI95 3.44-5.06N/kg). High levels of serratus anterior (105 %MVIC) and infraspinatus (87 %MVIC) were recorded during the push off phase of this activity.

CONCLUSIONS

LH and SHR placed large posterior translational forces that approached half of a person's bodyweight on shoulder structures. SHR produced an anterior translation force at extremes of horizontal abduction placing approximately 18% of bodyweight on shoulder structures. The LH test required the serratus anterior to provide power to push the upper torso of the ground while both the serratus and the infraspinatus provides scapular and humeral stability, respectively.

LEVEL OF EVIDENCE

4: Case series.

Compensatory Movement Patterns Are Based on Abnormal Activity of the Biceps Brachii and Posterior Deltoid Muscles in Patients with Symptomatic Rotator Cuff Tears

BACKGROUND

Abnormal movement patterns due to compensatory mechanisms have been reported in patients with rotator cuff tears. The long head of the biceps tendon may especially be overactive and a source of pain and could induce abnormal muscle activation in these patients. It is still unknown why some patients with a rotator cuff tear develop complaints and others do not.

QUESTIONS/PURPOSES

(1) Which shoulder muscles show a different activation pattern on electromyography (EMG) while performing the Functional Impairment Test-Hand and Neck/Shoulder/Arm (FIT-HaNSA) in patients with a symptomatic rotator cuff tear compared with age-matched controls with an intact rotator cuff? (2) Which shoulder muscles are coactivated on EMG while performing the FIT-HaNSA?

METHODS

This comparative study included two groups of people aged 50 years and older: a group of patients with chronic symptomatic rotator cuff tears (confirmed by MRI or ultrasound with the exclusion of Patte stage 3 and massive rotator cuff tears) and a control group of volunteers without shoulder conditions. Starting January 2019, 12 patients with a chronic rotator cuff tear were consecutively recruited at the outpatient orthopaedic clinic. Eleven age-matched controls (randomly recruited by posters in the hospital) were included after assuring the absence of shoulder complaints and an intact rotator cuff on ultrasound imaging. The upper limb was examined using the FIT-HaNSA (score: 0 [worst] to 300 seconds [best]), shoulder-specific instruments, health-related quality of life, and EMG recordings of 10 shoulder girdle muscles while performing a tailored FIT-HaNSA.

RESULTS

EMG (normalized root mean square amplitudes) revealed hyperactivity of the posterior deltoid and biceps brachii muscles during the upward phase in patients with rotator cuff tears compared with controls (posterior deltoid: 111% ± 6% versus 102% ± 10%, mean difference -9 [95% confidence interval -17 to -1]; p = 0.03; biceps brachii: 118% ± 7% versus 111% ± 6%, mean difference -7 [95% CI -13 to 0]; p = 0.04), and there was decreased activity during the downward phase in patients with rotator cuff tears compared with controls (posterior deltoid: 89% ± 6% versus 98% ± 10%, mean difference 9 [95% CI 1 to 17]; p = 0.03; biceps brachii: 82% ± 7% versus 89% ± 6%, mean difference 7 [95% CI 0 to 14]; p = 0.03). The posterior deltoid functioned less in conjunction with the other deltoid muscles, and lower coactivation was seen in the remaining intact rotator cuff muscles in the rotator cuff tear group than in the control group.

CONCLUSION

Patients with a symptomatic rotator cuff tear show compensatory movement patterns based on abnormal activity of the biceps brachii and posterior deltoid muscles when compared with age-matched controls. The posterior deltoid functions less in conjunction with the other deltoid muscles, and lower coactivation was seen in the remaining intact rotator cuff muscles in the rotator cuff tear group than the control group.

CLINICAL RELEVANCE

This study supports the potential benefit of addressing the long head biceps tendon in the treatment of patients with a symptomatic rotator cuff tear. Moreover, clinicians might use these findings for conservative treatment; the posterior deltoid can be specifically trained to help compensate for the deficient rotator cuff.

Changes in glenohumeral translation, electromyographic activity, and pressure-pain thresholds following sustained or oscillatory mobilizations in stiff and healthy shoulders: Results of a randomized, controlled laboratory trial

STUDY DESIGN

Randomized Controlled Laboratory Study.

BACKGROUND

Posterior glide glenohumeral (GH) mobilizations are utilized to improve motion and decrease pain in patients with shoulder pathologies, thought to be due to capsular stretch and neurophysiologic effects. However, it remains unclear how different GH mobilizations influence mobility, rotator cuff (RC) activity, and pain processing, or if effects are different in stiff (≥15-degree loss of passive motion in any plane) rather than healthy shoulders.

OBJECTIVES

To compare the effects of oscillatory and sustained posterior GH mobilizations on translation, RC activity, and pressure pain threshold (PPT) in stiff and healthy shoulders.

METHODS

Eighty-eight participants, (44 control, 44 stiff shoulders) were randomly assigned to one of two mobilization conditions. Pre-post intervention measurements of PPT, GH translation via ultrasound imaging, and RC activity assessed via electromyography were performed. Sustained or oscillatory grade III posterior GH mobilizations were then provided to all participants. Data were analyzed using tests of difference and regression modeling.

RESULTS

Sustained glides (2.8 ± 3.3 mm) demonstrated significantly greater changes in translation compared to oscillatory glides (1.1 ± 3.9 mm), p = .028. Stiff shoulders demonstrated higher total RC activity than controls both pre (+24.51%, p = .004) and post-intervention (+23.10%, p = .01). Small changes in PPT occurred across all conditions, none reaching clinically meaningful levels.

CONCLUSION

Sustained mobilizations resulted in greater changes in GH translation. RC activity was higher in the stiff shoulder group, and remained higher post-intervention despite gains in GH translation, suggesting a mechanical rather than neurophysiologic effect. There was no meaningful difference in PPT between modes of mobilization.

LEVEL OF EVIDENCE

Therapy, Randomized Controlled Laboratory Study, Level 1b.

Association Between the Postoperative Condition of the Subscapularis Tendon and Clinical Outcomes After Superior Capsular Reconstruction Using Autologous Tensor Fascia Lata in Patients With Pseudoparalytic Shoulder

BACKGROUND

Superior capsular reconstruction (SCR) has been performed for irreparable rotator cuff tear and pseudoparalytic shoulder (PPS); however, poor clinical outcomes have occasionally been reported. Previous studies have shown that the cause of poor clinical results was mainly graft rupture; however, poor clinical outcomes have also been observed in some cases even though the graft was not ruptured.

HYPOTHESIS/PURPOSE

We hypothesized that the subscapularis (SSC) tendon would be an important factor affecting clinical outcomes after SCR. The purpose was to clarify the correlation between the condition of the SSC tendon and clinical outcomes after SCR in patients with PPS.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

This retrospective cohort study included 27 patients who had undergone SCR for PPS performed by 1 surgeon between June 2014 and July 2017. The 27 patients were divided into 3 groups for evaluation: group A (n = 12), irreparable supraspinatus (SSP) and infraspinatus (ISP) tears but intact SSC tendon; group B (n = 11), irreparable SSP and ISP tears and repairable SSC tear; and group C (n = 4), irreparable SSP, ISP, and SSC tears. We evaluated the preoperative and postoperative ranges of motion (ROMs; active flexion, abduction, external rotation, and internal rotation), the American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form score, and graft condition on magnetic resonance imaging at 12 months postoperatively. All data were analyzed using the Mann-Whitney U, Wilcoxon signed-rank test, and Fisher exact tests, and P < .05 was considered significant.

RESULTS

Postoperative flexion, abduction, and internal rotation ROMs were significantly lower in group C than in groups A and B (flexion: 70.0° ± 17.8° vs 153.3° ± 14.3° and 154.5° ± 14.3°, P = .003 and P = .003, respectively; abduction: 67.5° ± 15° vs 148.3° ± 22.5° and 140° ± 29.3°, P = .003 and P = .004, respectively; internal rotation: L4 vs Th10 and Th11, P = .005 and P = .008, respectively). All 23 patients in groups A and B were able to recover from PPS; however, no patient recovered from PPS in group C.

CONCLUSION

The present study suggests that the SSC tendon is the important factor for achieving good clinical outcomes after SCR in patients with PPS. When the SSC tendon was irreparable, SCR was not an effective treatment for patients with PPS.

Effect of rotator cuff muscle activation on glenohumeral kinematics: A cadaveric study

Healthy shoulder function requires the coordination of the rotator cuff muscles to maintain the humeral head's position in the glenoid. While glenohumeral stability has been studied in various settings, few studies have characterized the effect of dynamic rotator cuff muscle loading on glenohumeral translation during shoulder motion. We hypothesize that dynamic rotator cuff muscle activation decreases joint translation during continuous passive abduction of the humerus in a cadaveric model of scapular plane glenohumeral abduction. The effect of different rotator cuff muscle activity on glenohumeral translation was assessed using a validated shoulder testing system. The Dynamic Load profile is a novel approach, based on musculoskeletal modeling of human subject motion. Passive humeral elevation in the scapular plane was applied via the testing system arm, while the rotator cuff muscles were activated according to the specified force profiles using stepper motors and a proportional control feedback loop. Glenohumeral translation was defined according to the International Society of Biomechanics. The Dynamic load profile minimized superior translation of the humeral head relative to the conventional loading profiles. The total magnitude of translation was not significantly different (0.805) among the loading profiles suggesting that the compressive forces from the rotator cuff primarily alter the direction of humeral head translation, not the magnitude. Rotator cuff muscle loading is an important element of cadaveric shoulder studies that must be considered to accurately simulate glenohumeral motion. A rotator cuff muscle activity profile based on human subject muscle activity reduces superior glenohumeral translation when compared to previous RC loading profiles.

Anatomy of the Subscapularis: A Review

The subscapularis is the largest and most powerful muscle of the rotator cuff. Occupying the vast majority of the subscapular fossa, it is the only internal rotator of the rotator cuff. The subscapularis innervation is classically taught as a dual innervation of 1 upper subscapular and 1 lower subscapular nerve arising from the posterior cord of the brachial plexus. However, there is a large amount of research that suggests there is significant variance in the innervation of the muscle from multiple upper subscapular nerves to multiple lower subscapular nerves arising from various portions of the plexus. Although one of the main functions of the subscapularis is to internally rotate the humerus, there is substantial evidence that displays its importance in glenohumeral stability as well. The insertion of the subscapularis is both tendinous as well as muscular. The more superior tendinous portion inserts on the lesser tuberosity while the more muscular portion inserts inferior to the less tuberosity. The medial to lateral spread of the insertion is quite variable ranging from only on the lesser tuberosity to merging with fibers from the supraspinatus. Understanding the anatomy of the subscapularis improves subscapularis management during shoulder arthroplasty including techniques for takedown, release, and repair.

A comparison of glenohumeral joint translation between young and older asymptomatic adults using ultrasonography: a secondary analysis

Background: The rotator cuff muscles are subject to age-related changes, but the effect of aging on glenohumeral joint stability is poorly understood. Objectives: This study aimed to compare glenohumeral joint translation in asymptomatic young and older people. Methods: Twenty young (23.6 ± 5.3 years) and twenty older (66.5 ± 7.8 years) participants with no symptomatic shoulder pathology were recruited. Anterior and posterior glenohumeral joint translations were measured using real-time ultrasound in two positions: (1) shoulder neutral; and (2) shoulder at 90 degrees' abduction and four testing conditions: (1) rest; (2) passive accessory motion testing (PAMT) force alone; (3) PAMT with isometric internal rotation contraction; and (4) PAMT with external rotation contraction. Results: In both groups, there were significant differences between the amount of translation limited by anterior and posterior rotator cuff muscles in response to anterior and posterior PAMT force (p < 0.03), indicating rotator cuff activity-limited translation in a direction-specific manner. Young participants demonstrated increased passive posterior glenohumeral joint translation in the neutral shoulder position (p < 0.001) and their rotator cuff muscle contraction led to greater reductions in glenohumeral joint translation in the neutral shoulder position (p < 0.001), as compared with older participants. Conclusions: Rotator cuff contraction limits glenohumeral joint translation in a direction-specific manner in both young and older participants. However, younger age is associated with increased passive translation but greater ability to reduce glenohumeral joint translation with rotator cuff muscle contraction. Age-related changes should be considered when assessing and treating glenohumeral joint stability.

The upper and lower segments of subscapularis muscle have different roles in glenohumeral joint functioning

Subscapularis muscle is divided into two independent segments, upper and lower (USUB and LSUB), but the role of each segment in glenohumeral functioning is unclear. We compared the electromyographic (EMG) activity of USUB and LSUB during a variety of shoulder movements, with and without an external translation force. Intramuscular electrodes were inserted in USUB and LSUB segments of 20 adults without pathology and EMG activity was measured in stabilization trials (with and without an anterior or posterior directed force at the humerus and isometric rotations) and two shoulder positions (shoulder neutral, abduction). Maximal voluntary isometric contraction (MVIC) trials were performed in abduction, internal and external rotation of the shoulder. In MVIC trials, USUB showed higher activity during internal rotation (p=0.03), whereas LSUB showed higher activity during external rotation (p<0.01). In stabilization trials, the interaction effects were significant for muscle segment×condition (p<0.01), and approached significance for muscle segment×position (p=0.06). In the neutral position, the pattern of activity for LSUB was similar to USUB. In the abducted position the LSUB, unlike USUB, was more active during external rotation (p=0.06) and also showed increased activity in response to the posterior directed force at the humerus (p=0.04). Our results suggest that USUB primarily acts asan agonist for internal rotation. In contrast LSUB was particularly active in external rotation in the abducted position and demonstrated increased EMG activity in response to the posteriorly directed force at the humerus in that position, suggesting more of a role in glenohumeral stabilization.

Muscle recruitment patterns of the subscapularis, serratus anterior and other shoulder girdle muscles during isokinetic internal and external rotations

The aims of this study were to investigate the differences in peak muscle activity and recruitment patterns during high- and low-velocity, concentric and eccentric, internal and external isokinetic shoulder rotations. Electromyographic activity of the rotator cuff and eight superficial muscles of the shoulder girdle was recorded on 25 healthy adults during isokinetic internal and external shoulder rotation at 60°/s and 240°/s. Peak muscle activity, electromyographic envelopes and peak isokinetic moments were analyzed using three-factor ANOVA and statistical parametric mapping. The subscapularis and serratus anterior showed moderate to high peak activity levels during each conditions, while the middle and posterior deltoids, upper, middle and lower trapezius, infraspinatus and supraspinatus showed higher peak activity levels during external rotations (+36.5% of maximum voluntary activation (MVA)). The pectoralis major and latissimus dorsi were more active during internal rotations (+40% of MVA). Only middle trapezius and pectoralis major electromyographic activity decreased with increasing velocity. Peak muscle activity was similar or lower during eccentric contractions, although the peak isokinetic moment increased by 35% on average. The subscapularis and serratus anterior appear to be important stabilizers of the glenohumeral joint and scapula. Isokinetic eccentric training at high velocities may allow for faster recruitment of the shoulder girdle muscles, which could improve joint stability during shoulder internal and external rotations.