Glenohumeral stabilizing roles of the scapulohumeral muscles: Implications of muscle geometry

Latissimus Dorsi and Teres major tendon transfer increases internal rotation torque following lateralized reverse shoulder arthroplasty with subscapularis insufficiency

INTRODUCTION

Limitation of active Internal Rotation (IR) following Reverse Shoulder Arthroplasty (RSA) in patients with massive Rotator Cuff Tears (mRCTs) with subscapularis insufficiency remains a challenge. Recently, RSA with Latissimus dorsi and Teres major (LDTM) transfer in patients with limited active IR has been demonstrated as a reliable treatment option. The purpose of this study was to biomechanically compare the IR torque following LDTM transfer with RSA in mRCT with subscapularis insufficiency to RSA without tendon transfer.

METHODS

Eight cadaveric shoulders were tested (mean age: 64.5 ± 1.9 years) using a custom shoulder testing system that permits loading conditions of mRCT with subscapularis insufficiency. Two conditions were tested and compared. The first condition was RSA alone and the second condition was RSA with LDTM transfer. RSA with a medialized glenoid and lateralized humerus design was used for all specimens. The specimens were tested at 0°, 20° and 40° abduction at three different muscle loads: baseline, double, and triple, while the Teres minor and deltoid loads were kept constant. IR torque was measured with a torque wrench at 0°, 20°, and 40° abduction and 60° and 45° IR positions. Force required for anterior dislocation was measured at 20° abduction and 10° IR position.

RESULTS

RSA with LDTM transfer had significantly higher IR torque at all abductions and muscle loading compared with RSA without transfer (average at all positions; RSA without transfer: 0.80 ± 0.02 Nm, LDTM transfer for all loads: 1.43 ± 0.10 Nm). RSA with LDTM transfer (91.4 ± 3.9 N) needed higher force for anterior dislocation compared to RSA alone (89.4 ± 4.1 N), but there was no significant difference.

CONCLUSION

LDTM transfer with RSA increases IR torque compared to RSA without tendon transfer in a cadaveric model. LDTM transfer with RSA may be a reliable treatment option for patients with mRCT and subscapularis insufficiency who are expected to have limited active IR following RSA.

Neuromuscular control: from a biomechanist's perspective

Understanding neural control of movement necessitates a collaborative approach between many disciplines, including biomechanics, neuroscience, and motor control. Biomechanics grounds us to the laws of physics that our musculoskeletal system must obey. Neuroscience reveals the inner workings of our nervous system that functions to control our body. Motor control investigates the coordinated motor behaviours we display when interacting with our environment. The combined efforts across the many disciplines aimed at understanding human movement has resulted in a rich and rapidly growing body of literature overflowing with theories, models, and experimental paradigms. As a result, gathering knowledge and drawing connections between the overlapping but seemingly disparate fields can be an overwhelming endeavour. This review paper evolved as a need for us to learn of the diverse perspectives underlying current understanding of neuromuscular control. The purpose of our review paper is to integrate ideas from biomechanics, neuroscience, and motor control to better understand how we voluntarily control our muscles. As biomechanists, we approach this paper starting from a biomechanical modelling framework. We first define the theoretical solutions (i.e., muscle activity patterns) that an individual could feasibly use to complete a motor task. The theoretical solutions will be compared to experimental findings and reveal that individuals display structured muscle activity patterns that do not span the entire theoretical solution space. Prevalent neuromuscular control theories will be discussed in length, highlighting optimality, probabilistic principles, and neuromechanical constraints, that may guide individuals to families of muscle activity solutions within what is theoretically possible. Our intention is for this paper to serve as a primer for the neuromuscular control scientific community by introducing and integrating many of the ideas common across disciplines today, as well as inspire future work to improve the representation of neural control in biomechanical models.

Biomechanical comparison of combined latissimus dorsi and teres major tendon transfer vs. latissimus dorsi tendon transfer in shoulders with irreparable anterosuperior rotator cuff tears

BACKGROUND

Irreparable anterosuperior rotator cuff tears (IASRCTs) can result in a gradual loss of active elevation and internal rotation, superior and anterior translation of the humeral head, and cuff tear arthropathy. Joint-preserving treatment options for IASRCTs in young and high-demand elderly patients remain a subject of ongoing debate. The aim of the study was to evaluate the biomechanical efficacy of the combined latissimus dorsi and teres major tendon (LDTM) transfer and compare it to an isolated latissimus dorsi (LD) transfer in a cadaveric IASRCT model.

METHODS

Eight cadaveric shoulders (mean age, 68.3 ± 5.2 years; range 58-71) were tested with a custom shoulder testing system. All specimens were tested at 0°, 30°, and 60° of glenohumeral abduction in the scapular plane under 4 conditions: (1) intact, (2) IASRCT, (3) combined LDTM transfer, and (4) isolated LD transfer. The superior and anteroinferior translation and subacromial contact pressure were measured. The effects of 3 different LD and LDTM muscle loading conditions were investigated to determine the effectiveness of the muscle transfer conditions. A linear mixed effect model was used for statistical analysis, followed by a Tukey post hoc test.

RESULTS

IASRCTs significantly increased superior translation, anteroinferior translation, and subacromial peak contact pressure. Combined LDTM transfer significantly decreased superior and anteroinferior translation compared with IASRCTs in all positions and muscle loadings. Isolated LD transfer did not significantly decrease superior (P > .115) and anteroinferior translation (P > .151) compared to IASRCT at any abduction and muscle loads except superior translation at 60° abduction and 90° of external rotation (ER) (P < .036). LDTM transfer also significantly decreased peak contact pressure from the IASRCT condition at every abduction angle (P < .046). However, isolated LD transfer significantly decreased subacromial peak contact pressure only at 30° abduction and 0° and 30° of ER with triple loading (P < .048), as well as at 60° abduction and 90° of ER (P < .003).

CONCLUSIONS

Combined LDTM transfer decreased superior translation, anteroinferior translation, and subacromial contact pressure compared with the IASRCT condition. Isolated LD transfer did not improve glenohumeral translation and subacromial contact pressure. Combined LDTM transfer may be a more reliable treatment option than isolated LD transfer in patients with an IASRCT.

Latissimus dorsi and teres major tendon transfer for irreparable anterosuperior rotator cuff tear improves kinematics and internal rotation compared to latissimus dorsi tendon transfer

INTRODUCTION

Latissimus dorsi and teres major (LDTM) tendon transfer has demonstrated better clinical outcomes compared to Latissimus dorsi (LD) transfer for irreparable anterosuperior cuff (subscapularis/supraspinatus) tears; however, the biomechanical effects of these procedures are unknown. Therefore, the objective of this study was to compare kinematics and internal rotation of LDTM transfer to LD transfer for anterosuperior cuff tear.

METHODS

Eight cadaveric shoulders were tested in four conditions; (1) intact, (2) anterosuperior rotator cuff tear, (3) LDTM transfer, and (4) LD transfer. Glenohumeral kinematics and internal rotation at 0°, 30°, and 60° of glenohumeral abduction in the scapular plane were measured. Muscle loading was applied based on physiological cross-sectional area ratios with three muscle loading conditions to simulate potentially increased tension due to the advanced insertion site of the transferred tendons.

RESULTS

The anterosuperior rotator cuff tear leads to a significant superior shift of the humeral head compared to intact at 0° and 30° abduction (p < 0.039). Both the LDTM (p < 0.047) and LD transfers (p < 0.032) significantly shifted the humeral head inferiorly compared to the tear condition.; however, the LDTM transfer shifted the head in the anteroinferior direction compared to the LD transfer at 60° abduction and 30° ER (p < 0.045). Both LDTM and LD transfer significantly increased internal resting rotation (p < 0.008) and maximum internal rotation (p < 0.008) compared to anterosuperior rotator cuff tear and intact at 30° and 60° abduction. LDTM transfer resulted in a significant internal resting rotation compared with the LD transfer at 30° abduction with double muscle loading (p = 0.02). At 0° abduction, the LDTM transfer (p < 0.027) significantly increased maximum internal rotation compared to anterosuperior rotator cuff tear and intact.

CONCLUSION

Although both LDTM and LD tendon transfer improved the abnormal humeral head apex position and internal rotation compared with the tear condition, the LDTM transfer was biomechanically superior to the LD transfer in a cadaveric model.

Outcomes of combined anterior latissimus dorsi and teres major tendon transfer for irreparable anterosuperior rotator cuff tears

BACKGROUND

Irreparable anterosuperior rotator cuff tears (IASRCTs) can result in loss of active elevation, loss of internal rotation, and pseudoparalysis. Joint-preserving treatment options for IASRCTs in young and high-demand elderly patients are limited. The purpose of this study was to evaluate the clinical and radiologic outcomes of combined anterior latissimus dorsi and teres major (aLDTM) tendon transfer in patients with IASRCTs without reconstruction of the superior rotator cuff and capsular portion.

METHODS

This retrospective study was conducted between 2015 and 2018. We included patients who underwent combined aLDTM tendon transfer for IASRCTs. Clinical outcomes included visual analog scale for pain, Constant score, American Shoulder and Elbow Surgeons score, University of California Los Angeles shoulder scores, activities of daily living requiring active internal rotation score, active range of motion, subscapularis-specific physical examination, and rate of return to work. Radiographic analyses included the assessment of acromiohumeral distance, Hamada grade for cuff tear arthropathy, rate of anterior glenohumeral subluxation reduction, and transferred tendon integrity at 2 years postoperatively.

RESULTS

The mean follow-up period was 38.1 ± 13.7 (range: 24-63) months. Of the patients, 30 (mean age: 64.1 years) met the study criteria. Postoperatively, mean Constant, American Shoulder and Elbow Surgeons, University of California Los Angeles, and activities of daily living requiring active internal rotation scores improved from 47.4 to 69.9 (P < .001), 44.9 to 79.2 (P < .001), 20.0 to 28.7 (P < .001), and 13.2 to 26.9 (P < .001), respectively. The mean active range of motion was significantly increased postoperatively for both forward elevation (P < .001) and internal rotation at the back (P < .001). Of the patients, 24 (83%) returned to their previous work. No significant progression of cuff tear arthropathy was observed at final follow-up (Hamada grade: preoperative 1.3 ± 0.5 to postoperative 1.5 ± 0.7; p=0.155). Fifteen of 30 patients (50%) restored the anterior glenohumeral subluxation that was apparent preoperatively. One patient presented with transient axillary nerve palsy after surgery. Two patients presented with partial nonretracted tears of the transferred tendon.

CONCLUSION

This minimum 2-year follow-up study demonstrated that combined aLDTM tendon transfer without reconstruction of the superior rotator cuff and capsular portion was a viable treatment option with favorable clinical and radiologic outcomes for patients with IASRCTs.

Analysis of Rotator Cuff Muscle Injury on the Drawing Side of the Recurve Bow: A Finite Element Method

Background

This study establishes the shoulder model on the drawing side of recurve archers by the finite element method and finds out the stress changes on the rotator cuff muscles in the position of the humerus and scapula under different stages of special techniques. The aim of this study is to investigate the mechanism of rotator cuff damage on a recurve archer's drawing arm.

Methods

A 22-year-old healthy male's shoulder CT and MRI data were collected, and the drawing side shoulder joint finite element model was constructed, which contains the structure of the shoulder blades, clavicle, humerus, supraspinatus, infraspinatus, teres minor, and subscapularis. The humerus on the drawing arm was simulated to raising the bow, drawing, holding, and releasing on the scapula plane, and stress changes in rotator cuff muscles are analyzed.

Results

The peak stress on the infraspinatus increased slowly, and from the start of raising the bow to hold and release, the stress peak increased from 0.007 MPa to 0.009 MPa. The peak stress on teres minor rises slowly from 0.003 MPa at the start of raising the bow to 0.010 MPa at the moment of releasing. The peak stress in the subscapularis increased from 0.096 MPa to 0.163 MPa between the start of raising the bow and releasing. The peak stress on the supraspinatus varied greatly, and from the start of raising the bow to the start of drawing, the stress peak increased markedly from 1.159 MPa to 1.395 MPa. Subsequently, the stress peak immediately decreased to 1.257 MPa at the start of holding and then increased to 1.532 MPa at releasing.

Conclusion

The position of the humerus and scapula would change with the different stages of special techniques. It causes stress changes in the rotator cuff muscles, and when the stress accumulates over time, the shoulder 5on the drawing side will gradually become injured and dysfunctional. In combination with the depth of the structural site and the surrounding structural features, corrective exercises can be used to prevent injury to the rotator cuff muscles.

Relevance between Proximal Humeral Migration and Rotator Cuff Tears

Background

Proximal humeral migration is common in patients with rotator cuff tears. In this study, we aimed to evaluate the relevance between proximal humeral migration and some rotator cuff tear-related factors.

Methods

A total of 75 patients with unilateral rotator cuff tears were retrospectively included from August 2016 to January 2018 who underwent magnetic resonance imaging and X-ray examinations before enrollment. We introduced the upward migration index (UMI) to stratify the patients into three groups, Group A: 1 &lt; UMI ≤ 1.3; Group B: 1.3 &lt; UMI ≤ 1.4; and Group C: UMI &gt; 1.4. Pearson correlation analysis and logistic regression analysis were used to evaluate the relationship between UMI and age, sex, body mass index, pain, fatty degeneration grade, tear size, and thickness of ruptured tendon. Then, the χ2 test and receiver operator characteristic curve were applied to measure the diagnostic value of UMI.

Results

The average UMI was 1.34 ± 0.07, ranging from 1.16 to 1.48. For the Pearson correlation analysis, there was a negative correlation between UMI and tear size (R = −0.68, p &lt; 0.01), and also, there was a negative correlation between UMI and the visual analogue scale score (R = 0.342, p &lt; 0.01). What is more, there was a negative correlation between UMI and the fatty degeneration grade (R = −0.373, p &lt; 0.01). Ordinal multinomial logistic regression analysis indicated that tear size (β = −1.825, p &lt; 0.001) was the independent predictor of UMI, which was a risk factor for humeral upward migration. The cutoff points of UMI were 1.38 and 1.3 to determine tears and distinguish large tears from small ones.

Conclusions

UMI is a good predictor for humeral upward migration, which is related to the tear size of posterosuperior cuff tears. When the UMI is &lt;1.3, a large tear should be alerted. Combining physical examination and X-ray is helpful for evaluating rotator cuff tears.