The role of pectoralis major and latissimus dorsi muscles in a biomechanical model of massive rotator cuff tear

Middle trapezius tendon transfer using Achilles allograft for irreparable isolated supraspinatus tendon tears effectively restores the superior stability of the humeral head without restricting range of motion: a biomechanical study

BACKGROUND

Middle trapezius tendon (MTT) transfer has been suggested for promising treatment of irreparable isolated supraspinatus tendon tears (IISTTs). However, there have been no attempts to assess the biomechanical efficacy of MTT transfer. This study aims to evaluate the biomechanical efficacy of MTT transfer in the setting of IISTTs.

METHODS

Eight fresh frozen cadaveric shoulders were tested in 3 conditions: (1) intact rotator cuff, (2) IISTT, and (3) MTT transfer using Achilles allograft for IISTTs. Total humeral rotational range of motion (ROM), superior translation of the humeral head, and subacromial contact characteristics were measured at 0°, 20°, and 40° glenohumeral abduction (representing 0°, 30°, and 60° shoulder abduction). Superior translation and subacromial contact pressures were measured at 0°, 30°, 60°, and 90° external rotation (ER). Two different MTT muscle loading conditions were investigated. A linear mixed effects model and Tukey post hoc test were used for statistical analysis.

RESULTS

Total ROM was significantly increased after IISTT at 20° abduction (P = .037). There were no changes in total ROM following MTT transfer compared to the IISTT condition (P > .625 for all comparisons). The IISTT condition significantly increased superior translation compared to the intact rotator cuff condition in 0° and 20° abduction with all ER angles (P < .001), 40° abduction-30° ER (P = .016), and 40° abduction-60° ER (P = .002). MTT transfer significantly decreased superior translation of the humeral head at all abduction angles compared to the IISTT condition (P < .026). MTT transfer significantly decreased peak contact pressure by 638.7 kPa (normal loading) and 726.8 kPa (double loading) at 0° abduction-30° ER compared to the IISTT condition (P < .001). Mean contact pressure was decreased by 102.8 kPa (normal loading) and 118.0 kPa (double loading) at 0° abduction-30° ER (P < .001) and 101.0 kPa (normal loading) and 99.2 kPa (double loading) at 0° abduction-60° ER (P < .001). MTT transfer at 20° abduction-30° ER with 24 N loading significantly decreased contact pressure by 91.2 kPa (P = .035).

CONCLUSIONS

The MTT transfer biomechanically restored the superior humeral head translation and reduced the subacromial contact pressure in a cadaveric model of IISTT, while not restricting total ROM. These findings suggest that MTT transfer may have potential as a surgical treatment for IISTTs.

Neuromuscular electrical stimulation of humeral adductors in subjects with rotator cuff tear

INTRODUCTION

In symptomatic patients with rotator cuff tear, MRI and radiographic studies have ascribed the pain symptom to insufficient humeral head depression during arm elevations. The arm adductors such as the teres major and pectoralis major may contribute to depression of the humerus head during arm elevations. Researchers have demonstrated that neuromuscular electrical stimulation (NMES) of the serratus anterior and lower trapezius can control scapular motions and improve acromiohumeral distance. It is unknown, however, if adductor neuromuscular training could help patients with rotator cuff tear.

MATERIALS AND METHODS

A cross-sectional study of NMES of the teres major and pectoralis major was conducted on 30 symptomatic subjects with rotator cuff tear. We measured the acromiohumeral distance by ultrasonography and scapular kinematics during arm elevation with a three-dimensional motion tracking system.

RESULTS

The acromiohumeral distance significantly increased during NMES of the teres major (0.73 mm, p < 0.001). However, the distance significantly decreased with NMES of the pectoralis major (0.78 mm, p < 0.001). Additionally, scapular upward rotation was greater during NMES of the teres major than during NMES of the pectoralis major (3.4°, p < 0.001). Scapular external rotation decreased significantly more during NMES of the pectoralis major than during NMES of the teres major (1.6°, p = 0.003).

CONCLUSIONS

NMES of the teres major can increase acromiohumeral distance and scapular upward rotation during arm elevation. However, the decreased upward and external rotation of the scapula during arm elevation with NMES of the pectoralis major may be associated with subacromial impingement.

Biomechanical analysis of progressive rotator cuff tendon tears on superior stability of the shoulder

BACKGROUND

The biomechanical relationship between irreparable rotator cuff tear size and glenohumeral joint stability in the setting of superiorly directed forces has not been characterized. The purpose of this study was to quantify kinematic alterations of the glenohumeral joint in response to superiorly directed forces in a progressive posterosuperior rotator cuff tear model.

METHODS

Nine fresh-frozen cadaveric shoulders (mean age; 58 years) were tested with a custom shoulder testing system. Three conditions were tested: intact, stage II (supraspinatus) tear, stage III (supraspinatus + anterior half of infraspinatus) tear. At each condition, range of motion and humeral head positions were measured with a "balanced" loading condition, and with a superiorly directed force ("unbalanced loading condition"). At each of the 0°, 20°, and 40° of glenohumeral abduction positions, all measurements were made at 0°, 30°, 60°, and 90° of external rotation (ER). Two-way repeated measures analysis of variance with Tukey post hoc tests were performed for statistical analyses.

RESULTS

With the balanced load, no significant change in superior humeral head position was observed in stage II tears. Stage III tears significantly changed the humeral head position superiorly at 30° and 60° ER at each abduction angle compared with the intact condition (P ≤ .028). With superiorly directed load, stage II and stage III tears both showed statistically significant increases in superior translation at all degrees of ER for all degrees of abduction (P ≤ .035), except stage II tears at 0° ER and 40° abduction (P = .185) compared with the intact condition. Stage II tears showed posterior translations with 30° and 60° ER, both at 20° and 40° of abduction. Stage III tears also showed posterior translations with 90° ER for all abduction angles (P ≤ .039).

CONCLUSION

With superiorly directed loads, complete supraspinatus tendon tears created superior translations at all abduction angles, and posterior instability in the middle ranges of rotation for 20° and 40° of abduction. Larger tears involving the anterior half of the infraspinatus tendon caused significant superior and posterior translations within the middle ranges of ER for all abduction angles. In addition to superior instability, posterior translation should be considered when selecting or developing surgical techniques for large posterosuperior rotator cuff tears.

Superior capsule reconstruction using a single 6-mm-thick acellular dermal allograft for massive rotator cuff tears: a biomechanical cadaveric comparison to fascia lata allograft

BACKGROUND

Success of superior capsule reconstruction (SCR) using both fascia lata (FL) and human acellular dermal (ACD) allografts have been reported. One possible explanation for a discrepancy in outcomes may be attributed to graft thickness. SCR with commercially available 3-mm-thick ACD allograft is not biomechanically equivalent to FL. Our hypothesis was that SCR with a single 6-mm-thick ACD allograft will restore the subacromial space distance (SubDist) and peak subacromial contact pressures (PSCPs) to intact shoulder and will be comparable to SCR with an 8-mm FL allograft.

METHODS

Eight cadaveric shoulders were tested in 4 conditions: intact, irreparable supraspinatus tear (SST), SCR FL allograft (8-mm-thick), and SCR single ACD allograft (6-mm-thick). SubDist and PSCP were measured at 0°, 30°, and 60° of glenohumeral abduction in the scapular plane. Parameters were compared using a repeated measures analysis of variance with Tukey post hoc test, and graft dimensions were compared using a Student t test.

RESULTS

SST had decreased SubDist (P < .05) and increased PSCP (P < .05) compared with the intact state. At all angles, the SCR ACD allograft demonstrated increased SubDist compared with the tear condition (P < .001), with no difference between grafts. Furthermore, there was decreased PSCP after both ACD and FL SCR compared with the intact condition, with no difference between grafts at 0° (P = .006, P = .028) and 60° abduction (P = .026, P = .013). Both ACD and FL grafts elongated during testing.

CONCLUSIONS

Our results suggest SCR with a single 6-mm-thick ACD allograft is noninferior to FL regarding SubDist and PSCP while completely restoring the superior stability of the glenohumeral joint compared with the intact state.

Investigation of the range of motion of the shoulder joint in subjects with rotator cuff arthropathy while performing daily activities

Background

Patients who have rotator cuff arthropathy experience a limited range of motion (ROM) of the shoulder joint and experience problems in performing their daily activities; however, no evidence is available to suggest the exact ROM of the shoulder joint in this population. Therefore, this study sought to determine the degree of motion of the shoulder joint in three planes during different activities.

Methods

Five subjects with rotator cuff injuries participated in this study. The motion of the shoulder joints on both the involved and normal sides was assessed by a motion analysis system while performing forward abduction (task 1), flexion (task 2), and forward flexion (task 3). The OpenSIM software program was used to determine the ROM of the shoulder joints on both sides. The difference between the ranges of motion was determined using a two-sample t-test.

Results

The ROMs of the shoulder joint in task 1 were 93.5°±16.5°, 72.1°±2.6°, and 103.9°±25.7° for flexion, abduction, and rotation, respectively, on the normal side and 28°±19.8°, 31°±31.56°, and 48°±33.5° on the involved side (p<0.05). There was no significant difference between the flexion/extension and rotation movements of the shoulder joint when performing task 1. However, the difference between flexion and rotation movements of the shoulder joints for the second task was significant (p>0.05).

Conclusions

Those with rotator cuff arthropathy have functional limitations due to muscle weakness and paralysis, especially during the vertical reaching task. However, although these individuals have decreased ROM for transverse reaching tasks, the reduction was not significant.

Superior Capsule Reconstruction Using Fascia Lata Allograft Compared With Double- and Single-Layer Dermal Allograft: A Biomechanical Study

PURPOSE

To biomechanically characterize superior capsule reconstruction (SCR) using fascia lata allograft, double-layer dermal allograft, and single-layer dermal allograft for a clinically relevant massive irreparable rotator cuff tear involving the entire supraspinatus and 50% of the infraspinatus tendons.

METHODS

Eight cadaveric specimens were tested in 0°, 30°, and 60° abduction for (1) intact, (2) massive rotator cuff tear, (3) SCR using fascia lata, (4) SCR using double-layer dermis, and (5) SCR using single-layer dermis. Superior translation and subacromial contact pressure were measured. Statistical analysis was conducted using repeated measures ANOVA or paired t test with P < .05.

RESULTS

Massive rotator cuff tear significantly increased superior translation of the humeral head at all abduction angles (P < .05). At 0° abduction, all SCR conditions significantly decreased superior translation compared with the massive tear but did not restore translation (P < .05) to intact. Fascia lata and double-layer dermis SCR restored superior translation to intact at 30° and 60° of abduction, but single-layer dermis did not. Subacromial contact pressure at 0° of abduction significantly decreased with SCR with fascia lata and double-layer dermis compared with tear. At 30°, all SCR conditions significantly decreased subacromial contact pressure. Single-layer dermis graft thickness significantly decreased more than fascia lata during testing (P = .02).

CONCLUSION

For SCR tensioned at 20° glenohumeral abduction, all 3 graft types may restore superior translation and subacromial contact pressure depending on the glenohumeral abduction angle; fascia lata and double-layer dermis may be more effective than single-layer dermis.

CLINICAL RELEVANCE

If a dermal graft is to be used for SCR, consideration should be given to doubling the graft for increased thickness and better restorative biomechanical properties, which may improve clinical outcomes following SCR.

Estimating Muscle Forces for Breast Cancer Survivors During Functional Tasks

Breast cancer survivors have known scapular kinematic alterations that may be related to the development of secondary morbidities. A measure of muscle activation would help understand the mechanisms behind potential harmful kinematics. The purpose of this study was to define muscle force strategies in breast cancer survivors. Shoulder muscle forces during 6 functional tasks were predicted for 25 breast cancer survivors (divided by impingement pain) and 25 controls using a modified Shoulder Loading Analysis Module. Maximum forces for each muscle were calculated, and 1-way analysis of variance (P < .05) was used to identify group differences. The differences between maximum predicted forces and maximum electromyography were compared with repeated-measures analysis of variance (P < .05) to evaluate the success of the model predictions. Average differences between force predictions and electromyography ranged from 7.3% to 31.6% but were within the range of previously accepted differences. Impingement related pain in breast cancer survivors is associated with increased force of select shoulder muscles. Both pectoralis major heads, upper trapezius, and supraspinatus peak forces were higher in the pain group across all tasks. These force prediction differences are also associated with potentially harmful kinematic strategies, providing a direction for possible rehabilitation strategies.

The pathogenesis and management of cuff tear arthropathy

Massive rotator cuff tears may lead to the development of cuff tear arthropathy (CTA). Although this pathology has been recognized for more than 150 years, treatment strategies have continued to evolve. During the last decade, there has been increased understanding of the molecular and cellular changes that govern rotator cuff tear outcomes and development of new treatment strategies to repair or reconstruct the rotator cuff. These have included an expansion of the use of arthroscopic double-row transosseous-equivalent repairs and the development of superior capsule reconstruction. However, the greatest change in the management of CTA has been the expansion of the use of reverse total shoulder arthroplasty, which has become the standard of care for patients who do not have a repair option and when nonoperative management has failed. This review article summarizes the current literature on the management of CTA, including nonoperative, repair, reconstruction, and replacement options, with a focus on literature in the last 5 years.

Biomechanical Effect of Thickness and Tension of Fascia Lata Graft on Glenohumeral Stability for Superior Capsule Reconstruction in Irreparable Supraspinatus Tears

PURPOSE

To investigate the effects of graft length and thickness on shoulder biomechanics after superior capsule reconstruction.

METHODS

Subacromial peak contact pressure and glenohumeral superior translation were measured at 0°, 30°, and 60° of glenohumeral abduction in 8 fresh-frozen cadaveric shoulders under 5 conditions: (1) intact shoulder; (2) irreparable supraspinatus tendon tear, (3) superior capsule reconstruction with a fascia lata allograft 4-mm thick and 15 mm longer than the distance from the superior glenoid to the lateral edge of the greater tuberosity, as determined during placement at 30° of glenohumeral abduction; (4) superior capsule reconstruction with a fascia lata allograft 8-mm thick and with the same 15 mm relative length determined at 10° of glenohumeral abduction, and (5) superior capsule reconstruction with a fascia lata allograft 8-mm thick and with the 15-mm relative length determined at 30° of glenohumeral abduction. To investigate the effect of graft thickness, we compared the data from conditions 1, 2, 3, and 5. To assess the effect of graft length, we compared conditions 1, 2, 4, and 5.

RESULTS

With superior capsule reconstruction using a 4-mm graft, subacromial peak contact pressure (but not superior translation) was significantly lower than with irreparable supraspinatus tears (at 0° abduction: 259% decrease; P = .0002; at 30° abduction: 113% decrease; P = .01). The superior capsule reconstruction using an 8-mm graft significantly decreased both subacromial peak contact pressure (at 0° abduction: 246% decrease, P = .0002; at 30° abduction: 158% decrease; P = .0008; at 60° abduction: 57% decrease; P = .04) and superior translation (at 0° abduction: 135% decrease; P = .02; at 30° abduction; 130% decrease; P = .004). Graft length with placement at 10° glenohumeral abduction was 5 mm greater than that at 30° abduction. The 8-mm superior capsule reconstruction performed at 10° or 30° of glenohumeral abduction significantly decreased subacromial peak contact pressure (placement at 10° and 30°: 0° abduction, P = .0002 and .0002, respectively; 30° abduction, P = .0004 and .0005, respectively; 60° abduction, P = .04 and .04, respectively) and superior translation (placement at 10° and 30°; 0° abduction, P =.04 and .02, respectively; 30° abduction, P = .02 and .004, respectively) compared with irreparable supraspinatus tears.

CONCLUSIONS

Superior capsule reconstruction normalized the superior stability of the shoulder joint when the graft was attached at 10° or 30° of glenohumeral abduction. An 8-mm-thick graft of fascia lata had greater stability than did a 4-mm-thick graft.

CLINICAL RELEVANCE

Grafts 8-mm thick and attached at 15° to 45° of shoulder abduction (equal to 10° to 30° of glenohumeral abduction) biomechanically restore shoulder stability during superior capsule reconstruction using fascia lata.

Posterior Capsular Plication Constrains the Glenohumeral Joint by Drawing the Humeral Head Closer to the Glenoid and Resisting Abduction

BACKGROUND

Shoulder pain is a common problem, with 30% to 50% of the American population affected annually. While the majority of these shoulder problems improve, there is a high rate of recurrence, as 54% of patients experience persistent symptoms 3 years after onset.

PURPOSE

Posterior shoulder tightness has been shown to alter glenohumeral (GH) kinematics. Clinically, posterior shoulder contractures result in a significant loss of internal rotation and abduction (ABD). In this study, the effect of a posterior capsular contracture on GH kinematics was investigated using an intact cadaveric shoulder without violating the joint capsule or the rotator cuff.

STUDY DESIGN

Controlled laboratory study.

METHODS

Glenohumeral motion, humeral load, and subacromial contact pressure were measured in 6 fresh-frozen left shoulders during passive ABD from 60° to 100° using an automated robotic upper extremity testing system. Baseline values were compared with the experimental condition in which the full thickness of posterior tissues was plicated without decompressing the joint capsule.

RESULTS

Posterior soft tissue plication resulted in increased compression between the humeral head and the glenoid (axial load) at 90° of ABD. Throughout ABD, the posterior contracture increased the anterior and superior moment on the humeral head, but it did not change the GH kinematics in this intact model. As a result, there was no increase in the subacromial contact pressure during ABD with posterior plication.

CONCLUSION

In an intact cadaveric shoulder, posterior contracture does not alter GH motion or subacromial contact pressure during passive ABD. By tightening the soft tissue envelope posteriorly, there is an increase in compressive load on the articular cartilage and anterior/superior force on the humeral head. These findings suggest that subacromial impingement in the setting of a posterior soft tissue contracture may result from alterations in scapulothoracic motion, not changes in GH kinematics.

CLINICAL RELEVANCE

This investigation demonstrates that posterior capsular plication increases the axial load on the shoulder joint during ABD. While a significant difference from baseline was observed in the plicated condition, posterior capsular plication did not change GH motion or subacromial contact pressure significantly.