Electromyographic analysis of shoulder joint function of the biceps brachii muscle during isometric contraction

The long head of biceps at the shoulder: a scoping review

BACKGROUND

This review aimed to explore the available literature to update our understanding of the long head of biceps (LHB) at the shoulder. Synthesise our findings to identify emergent themes and knowledge gaps to inform future research and management directions.

METHODS

PubMed, Embase, Cinahl, SportDiscus, CENTRAL, and Web of Science were searched from inception to 31st December 2021. Articles were included if they referenced adult participants > 18 years of age and were written in English.

RESULTS

214 articles were included in the final analysis, and results were categorised into six emergent themes: (1) Anatomy - Normal anatomical variation of the biceps from aberrant origins, third and fourth accessory heads, and an absence of the LHB tendon (LHBT) are not necessarily benign, with shoulder pain and instability a commonly reported theme. (2) Function - Bicep's role in glenohumeral elevation and stability in healthy shoulders is minimal. In contrast, LHB has a more significant role in shoulder stability and humeral head depression in subjects with rotator cuff failure or an absent LHBT. (3) Pathology - There is an association between LHB tendinopathy, rotator cuff disease, LHBT instability and occult rotator cuff tears. Early recruitment and hyperactivity of the LHB in subjects with symptomatic rotator cuff tears and instability suggest a potential compensatory role. (4) Assessment - The limited diagnostic utility of special orthopaedic tests in assessing LHBT pathology was a consistent theme. The utility of magnetic resonance imaging and ultrasound to identify full-thickness tendon tears and instability of the LHBT was moderate to high. However, the utility of clinical tests and imaging may be underestimated due to arthroscopy's limitations in fully visualising the proximal LHBT. (5) Non-Surgical Management - Ultrasound-guided injections into the biceps sheath show greater accuracy and patient outcomes than blinded injections; however, the entry of injectate into the intraarticular glenohumeral joint may have unwanted complications. (6) Surgical management - For the surgical management of biceps pathology with or without rotator cuff pathology, both biceps tenodesis and tenotomy report similar improvements in pain without any significant adverse effect on strength or function. Tenodesis favoured higher overall constant scores and a lower incidence of Popeye deformity and cramping arm pain, with tenotomy trending to be more cost and time effective. For patients with a healthy LHBT, rotator cuff repair with adjunctive tenodesis or tenotomy fails to provide additional clinical improvements compared to rotator cuff repair in isolation.

CONCLUSIONS

The scoping review highlights the variability of biceps anatomy, which is not necessarily benign and suggests a minimal role of the LHB in shoulder elevation and stability in healthy individuals. In contrast, individuals with rotator cuff tears experience proximal humeral migration and demonstrate hyperactivity of the LHB, suggesting a potential compensation role. The observed prevalence of LHBT pathology with rotator cuff tears is well established; however, the cause-and-effect relationship between LHBT pathology and rotator cuff disease is undetermined. The diagnostic utility of clinical tests and imaging to exclude LHBT pathology may be understated due to the limitations of arthroscopy to visualise the proximal LHBT fully. Rehabilitation programs for the LHB are understudied. Similar post-surgical clinical outcomes are observed for tenodesis and tenotomy for biceps and rotator cuff-related shoulder pain. Subjects undergoing biceps tenodesis are less likely to have cramping arm pain and a Popeye deformity than patients undergoing biceps tenotomy. The significance of routine surgical removal of the LHBT and sequelae on rotator cuff tear progression to failure and long-term shoulder function is unknown, and further research is required.

PRE-REGISTRATION

OSF: https://osf.io/erh9m.

Upper extremity muscle activity when vacuuming floors with cordless stick vacuum cleaners

Upright vacuum cleaners for home use have been replaced with lightweight cordless stick vacuum cleaners, specifically those with the center of mass (CoM) near the handle. The current study evaluated upper extremity muscular loads associated with household floor vacuuming with the high CoM stick vacuum cleaners. Twenty participants conducted vacuuming on tiled and carpeted floors with straight and curved back-and-forth motions using medium (2.92 kg) and heavier weight (3.56 kg) cordless stick vacuums. The myoelectric signals of their upper extremity muscles were quantified during vacuuming. Mean normalized activity ranged from 8.2% to 20.2% of the maximum contraction capacity, with greater activity when vacuuming carpeted floors with a heavier vacuum cleaner. Study findings indicate that floor vacuuming with a cordless stick vacuum may not be as ergonomically efficient as assumed by their lighter weight. Instead, it is a physically demanding housekeeping activity that needs ergonomic attention.

A biomechanical study on the effect of long head of biceps tenotomy on supraspinatus load and humeral head position during shoulder abduction

INTRODUCTION

The purpose of this study was to determine the effect of biceps tendon tenotomy on the load of the supraspinatus tendon/muscle complex during abduction of the arm from 0° to 15°.

METHODS

Eleven fresh frozen human cadaver shoulders (6 males, 5 females, age ranged 44-88 years, mean upper extremity weight 2.96 ± 0.56 kg) were included. The specimens were sequentially mounted onto a custom-made fixture attached to a pulley system and load cell. The pulley system was used to pull the supraspinatus tendon/muscle complex along its fiber directions to abduct the arm to 15°. Abduction angles were recorded with a digital inclinometer. Two conditions were tested: (1) long head biceps tendon (LHBT) intact and in normal anatomical position; (2) LHBT cut within the bicipital groove. Qualitative visual inspection of humeral head displacement during abduction was also included. Descriptive statistics were calculated. The Shapiro-Wilk test was used to establish normal data distribution, and the paired t-test was used to compare the 2 conditions.

RESULTS

For the intact condition (LHBT intact), the mean load was 45.71 ± 21.04 N. For the biceps tenotomy test, the load measured 41.37 ± 23.43 N. These differences were not significant (P = .1480). In the tenotomy condition, the humeral head initially displaced inferior, and with initiation of abduction, the humeral head translated superior to its normal position.

CONCLUSION

The results suggest that the LHBT has no critical role with initial abduction of the arm. Furthermore, the LHBT does not appear to increase loads required for the supraspinatus muscle/tendon complex to perform the same action of abduction.

Clinical implications of the distinct anatomy and innervation of the long head biceps tendon

The proximal long head of the biceps tendon (LHBT) has been recognized as a well-known cause of anterior shoulder pain. Previous studies have identified a heterogeneous distribution of nerve fibers in the tendon, with a higher abundance of fibers in the proximal and distal thirds of the tendon. This suggests that the proximal portion of the long head biceps tendon may have a different source of innervation than the distal portion. The purpose of this study was to review the innervation of the superior shoulder and identify the proximal source of sensory innervation of the LHBT. The relevant hypothesis was that the suprascapular nerve (SSN) was the proximal source of sensory innervation to the LHBT. Gross and microdissection of eight fresh human cadaver shoulders were performed, with a focus on the distal articular branches of suprascapular nerve (SSN). Utilizing 3.5× magnification loupes, the medial subacromial branch (MSAb), lateral subacromial branch (LSAb), and posterior glenohumeral branch (PGHb) were identified and followed distally to their terminal branches. In all specimens, terminal branches of the lateral subacromial branch supplied the proximal LHBT and the superior labrum. Terminal branches of the posterior glenohumeral branch supplied the posterosuperior labrum and, to a lesser extent, the labral attachment of the LHBT. These findings confirm branches of the suprascapular nerve as the proximal source of sensory innervation to the LHBT. Identification of the suprascapular nerve as a source of proximal innervation of the LHBT may influence clinical decisions related to nonsurgical and surgical intervention, nerve blocks, and nerve ablation procedures.

Disabled Throwing Shoulder 2021 Update: Part 1-Anatomy and Mechanics

The purpose of this article is to provide updated information for sports health care specialists regarding the Disabled Throwing Shoulder (DTS). A panel of experts, recognized for their experience and expertise in this field, was assembled to address and provide updated information on several topics that have been identified as key areas in creating the DTS spectrum. Each panel member submitted a concise presentation on one of the topics within these areas, each of which were then edited and sent back to the group for their comments and consensus agreement in each area. Part 1 presents the following consensus conclusions and summary findings regarding anatomy and mechanics, including: 1) The current understanding of the DTS identifies internal impingement, resulting from a combination of causative factors, as the final common pathway for the great majority of the labral pathoanatomy; 2) intact labral anatomy is pivotal for glenohumeral stability, but its structure does not control or adapt well to shear or translational loads; 3) the biceps plays an active role in dynamic glenohumeral stability by potentiating "concavity compression" of the glenohumeral joint; 4) the ultimate function of the kinetic chain is to optimize the launch window, the precise biomechanical time, and position for ball release to most effectively allow the ball to be thrown with maximum speed and accuracy, and kinetic chain function is most efficient when stride length is optimized; 5) overhead throwing athletes demonstrate adaptive bony, capsular, and muscular changes in the shoulder with repetitive throwing, and precise measurement of shoulder range of motion in internal rotation, external rotation, and external rotation with forearm pronation is essential to identify harmful and/or progressive deficits. LEVEL OF EVIDENCE: Level V, expert opinion.

Biceps, Brachialis, and Triceps

Tendon injuries at the elbow affect mostly the distal biceps and can progressively degenerate over time or rupture in an acute event. The degree of retraction may depend on the integrity of the lacertus fibrosus, a fibrous expansion that merges with the forearm flexor fascia. Biceps disorders are frequently associated with fluid or synovitis of the adjacent bicipital bursa; primary bursal disorders (primary inflammatory synovitis) can also be observed. Distal triceps is less frequently injured than the distal biceps, and tears usually manifest as distal ruptures with avulsion of a small flake of bone from the tip of the olecranon. Brachialis injuries are uncommon and the consequence of sudden muscle stretching during forced elbow hyperextension, as in posterior elbow luxation.

Long Head of the Biceps Tendon Ruptures: Biomechanics, Clinical Ramifications, and Management

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Pathology of the long head of the biceps tendon is a common source of shoulder pain and often occurs in combination with other shoulder disorders.

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Nonsurgical management, including rest and activity modification, use of nonsteroidal anti-inflammatory drugs, physical therapy, and corticosteroid injections, is usually the first line of treatment.

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Patients with symptoms that are refractory to nonsurgical management are indicated for biceps tenotomy or various tenodesis procedures.

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Although several studies have reported a higher incidence of "Popeye" deformity, muscle cramping, and pain in the bicipital groove postoperatively with tenotomy compared with tenodesis, there are no substantial differences in functional scores or patient satisfaction between the 2 techniques.

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To date, both tenotomy and tenodesis have been shown to be effective options in the management of long head of the biceps tendinopathy, and there are advantages to each procedure.

Comparison of the clinical results of isolated Bankart and SLAP 5 lesions after arthroscopic repair

OBJECTIVES

This study aims to compare the clinical results of patients with traumatic isolated Bankart lesions and type V superior labrum anterior to posterior (SLAP) lesions after arthroscopic repair.

PATIENTS AND METHODS

Patients who underwent arthroscopic repair for traumatic anterior glenohumeral instability were evaluated retrospectively between December 2014 and January 2019. Fifty-one patients (49 males, 2 females; mean age 25 years; range, 18 to 36 years) without bone defects affecting >20% of the glenoid fossa, off-track engaging Hills-Sachs lesions, multidirectional instability, or ligamentous laxity were included in the study. Group 1 had 31 patients with isolated Bankart lesions and group 2 had 20 patients with type V SLAP lesions. There were only two female patients in group 1 and all patients were male in group 2. The mean age was 25 years (range, 18 to 36 years) in group 1 and 25 years (range, 19 to 35 years) in group 2. Rowe, Constant, and Western Ontario Shoulder Instability (WOSI) scoring systems were used to evaluate the clinical outcomes of the patients preoperatively and at the last follow-up.

RESULTS

The mean follow-up time was 32 months (range, 12 to 48 months) in group 1 and 28.5 months (range, 12 to 42 months) in group 2. There were no statistically significant differences between the two groups in terms of the number of shoulder dislocations before the surgery, mean age at the time of surgery, and the mean time from the first dislocation to surgical treatment. When the Rowe, Constant, and WOSI scores were evaluated preoperatively and at the last follow-up, there were statistically significant changes within, but not between, the two groups.

CONCLUSION

In type V SLAP lesions, the affected and repaired labrum surface area is larger than isolated Bankart lesions. However, as a result of appropriate surgical treatment, the affected surface area does not have a negative effect on clinical outcomes, and similar clinical results can be obtained in patients with type V SLAP lesions compared to patients with isolated Bankart lesions.

Posture-dependent neuromuscular contributions to three-dimensional isometric shoulder torque generation

This study is the first to identify the muscle synergies underlying three-dimensional isometric shoulder torque generation. Although the overall structure of these synergies was unaffected by arm posture, the weighted contributions of several muscles composing two synergy patterns changed as a function of the elevation or plane of elevation of the shoulder. Our findings provide valuable insight for the development of targeted interventions for the restoration of shoulder function after neuromuscular or orthopedic pathologies.

The effect of long and short head biceps loading on glenohumeral joint rotational range of motion and humeral head position

PURPOSE

To evaluate the effect of loading the long and short heads of the biceps on glenohumeral range of motion and humeral head position.

METHODS

Eight cadaveric shoulders were tested in 60° abduction in the scapula and coronal plane. Muscle loading was applied based on cross-sectional area ratios. The short and long head of the biceps were loaded individually followed by combined loading. Range of motion was measured with 2.2 Nm torque, and the humeral head apex position was measured using a MicroScribe. A paired t test with Bonferroni correction was used for statistics.

RESULTS

Long head loading decreased internal rotation in both the scapular (17.9 %) and coronal planes (5.7 %) and external rotation in the scapular plane (2.6 %) (P < 0.04). With only short head loading, maximum internal rotation was significantly increased in the scapular and coronal plane. Long head and short head loading shifted the humeral head apex posteriorly in maximum internal rotation in both planes with the long head shift being significantly greater than the short head. Long head loading also shifted the humeral apex inferiorly in internal rotation and inferiorly posteriorly in neutral rotation in the scapular plane. With the long head unloaded, there was a significant superior shift with short head loading in both planes.

CONCLUSION

Loading the long head of the biceps had a much greater effect on glenohumeral range of motion and humeral head shift than the short head of the biceps; however, in the absence of long head loading, with the short head loaded, maximum internal rotation increases and the humeral head shifts superiorly, which may contribute to impingement following tenodesis of the long head of the biceps. These small changes in rotational range of motion and humeral head position with biceps tenodesis may not lead to pathologic conditions in low-demand patients; however, in throwers, biceps tenodesis may lead to increased contact pressures in late-cocking and deceleration that will likely translate to decreased performance therefore every effort should be made to preserve the biceps-labral complex.

Feasibility of ultrasound-guided percutaneous tenotomy of the long head of the biceps tendon--A pilot cadaveric study

OBJECTIVE

To describe an ultrasound-guided proximal percutaneous tenotomy technique of long head of the biceps tendon (LHBT).

METHODS

Three fresh cadavers with no prior shoulder surgery or LHBT tears were included in the study. A single experienced musculoskeletal radiologist completed six ultrasound-guided proximal percutaneous tenotomies of LHBT. A superficial to deep approach was performed on four shoulders using an arthroscopic banana blade or retractable blade. A deep to superficial approach was performed on two shoulders using an arthroscopic hook blade. A blinded anatomist dissected each specimen and graded the tenotomy, length of proximal LHBT stump, and evidence of iatrogenic injuries.

RESULTS

Four of the six cadaveric LHBTs were fully transected. The two partially transected tenotomies were performed using the arthroscopic banana and retractable serrated blades (63% and 80% transections, respectively). The proximal LHBT stump mean length was 2.6 cm (95% CI, 1.8-3.4). There was no evidence of iatrogenic lesions.

CONCLUSIONS

This cadaveric study showed that the ultrasound-guided percutaneous tenotomy of the LHBT is a feasible procedure. The deep to superficial approach using an arthroscopic hook blade resulted in complete transection. Further cadaveric studies with larger numbers are warranted to confirm this novel technique's applicability in clinical practice.

Characteristics of stabilizer muscles: a systematic review

PURPOSE

To identify the main characteristics, based on available evidence, of stabilizer muscles to inform the development of a definition of stabilizer muscles.

METHODS

Electronic databases were systematically searched for relevant literature from the databases' inception to June 2013 using keywords related to stability, muscles, and characteristics of stabilizer muscles. Studies that provided at least one characteristic of a stabilizer muscle were included. For the quality assessment, all included articles were categorized as either experimental or opinion-based studies. Methodological quality was assessed using a customized checklist, and data were analyzed with a narrative synthesis involving content analysis. The number of articles providing either direct evidence supporting a link between the characteristic and joint stability or indirect evidence that a muscle considered to be a stabilizer has that characteristic determined the level of significance of that characteristic for stabilizer muscles.

RESULTS

A total of 77 studies met the inclusion criteria. The highest number of articles providing supporting evidence that a particular muscle characteristic plays a stabilizing role related to biomechanical characteristics (27 articles), followed by neurological characteristics (22 articles) and anatomical/physiological characteristics (4 articles).

CONCLUSION

Based on a synthesis of supporting evidence from the literature, stabilizer muscles can be defined as muscles that contribute to joint stiffness by co-contraction and show an early onset of activation in response to perturbation via either a feed-forward or a feedback control mechanism. These results may guide researchers to investigate which muscles exhibit these characteristics to determine whether particular muscles have a stabilizer rather than a prime mover role during normal functioning.

Decision-making in massive rotator cuff tear

Treatment of massive rotator cuff tears has developed over many years ranging from conservative treatment to open and arthroscopic repair, muscle transfers and reversed arthroplasty. The evolution of more advanced techniques in arthroscopic repair has changed the treatment approach and improved the prognosis for functional outcome despite low healing rates. Due to this rapid development, our evidence-based knowledge today is mainly founded in Level 3 and Level 4 studies. Based on the literature, the current knowledge on treatment of symptomatic massive rotator cuff tears is proposed in an algorithm. Level of evidence V.

Postoperative restoration of upper extremity motion and neuromuscular control during the overhand pitch: evaluation of tenodesis and repair for superior labral anterior-posterior tears

BACKGROUND

Superior labral anterior-posterior (SLAP) tears are a common cause of shoulder pain and dysfunction in overhand throwers. Treatment outcomes remain unpredictable, with a large percentage of athletes unable to return to sport. There is considerable debate about the optimal treatment between debridement, repair, and tenodesis.

HYPOTHESIS

Labral repair more closely restores neuromuscular control and motion during the overhand pitch than tenodesis of the long head of the biceps.

STUDY DESIGN

Controlled laboratory study.

METHODS

Eighteen pitchers, including 7 uninjured controls, 6 players pitching after SLAP repair, and 5 players pitching after subpectoral biceps tenodesis (BT), underwent simultaneous surface electromyographic measurement at 1500 Hz and motion analysis at 120 Hz with a 14-camera markerless motion analysis system and high-speed video (120 Hz) to confirm accurate motion tracking. Patients had undergone surgery at least 1 year previously and had returned to pitching with a painless shoulder.

RESULTS

No significant differences were observed in the long head of the biceps muscle, short head of the biceps muscle, deltoid, infraspinatus, or latissimus activity between controls, patients after SLAP repair, and patients after BT. The variability from pitch to pitch for each study participant was similar between groups. Based on visual inspection of the activity time plots, BT appeared to more closely restore the normal pattern of muscular activation within the long head of the biceps muscle than did SLAP repair. There were no significant differences between controls and postoperative patients in the majority of pitching kinematics; however, pitchers after SLAP repair showed significantly altered patterns of thoracic rotation (P = .034) compared with controls and were significantly less likely to fall into previously published normal values for lead knee flexion at front foot contact (P = .019).

CONCLUSION

While both BT and SLAP repair can restore physiologic neuromuscular control, pitchers who undergo SLAP repair may exhibit altered patterns of thoracic rotation when compared with controls and pitchers who undergo BT.

CLINICAL RELEVANCE

While both tenodesis and SLAP repair can restore physiologic neuromuscular control, SLAP repair may alter pitching biomechanics.

Arthroscopic tenodesis of the long head of the biceps

The long head of the biceps (LHB) is commonly implicated in shoulder pathology due to its anatomic course and intimacy with the rotator cuff and superior labrum of the glenoid. Treatment of tendinosis of the LHB may be required secondary to partial thickness tears, instability/subluxation, associated rotator cuff tears, or SLAP (superior labrum, anterior to posterior) lesions. Treatment options include open or arthroscopic techniques for tenodesis vs tenotomy. Controversy exists in the orthopedic literature regarding the preferred procedure. The all-arthroscopic biceps tenodesis technique is a viable and reproducible option for treatment. This article provides a review of the all-arthroscopic biceps tenodesis technique using proximal interference screw fixation and its subsequent postoperative regimen. All-arthroscopic biceps tenodesis maintains elbow flexion and supination power, minimizes cosmetic deformities, and leads to less fatigue soreness after active flexion. Thus, arthroscopic biceps tenodesis should be offered and encouraged as a treatment option for younger, active patients.

Glenohumeral Function of the Long Head of the Biceps Muscle: An Electromyographic Analysis

Background:

Optimal treatment of superior labral anterior-posterior (SLAP) tears is controversial, in part because the dynamic role of the long head of the biceps muscle (LHBM) in the glenohumeral joint is unclear. The aim of this study was to determine dynamic LHBM behavior during shoulder activity by studying (1) the electromyographic activity of the LHBM during shoulder motion, (2) the effect of elbow immobilization on this activity, and (3) the effect of a load applied to the distal humerus on this activity.

Hypothesis:

The LHBM would not play a significant role in active glenohumeral range of motion.

Study Design:

Controlled laboratory study.

Methods:

Thirteen normal volunteers underwent surface electromyography (EMG) measurement of the LHBM, short head biceps muscle (SHBM), deltoid, infraspinatus, and brachioradialis during shoulder motion from the neutral position (0° of rotation, flexion, and abduction) to 45° of flexion, 90° of flexion, 45° of abduction, and 90° of abduction. These motions were repeated both with and without splint immobilization of the forearm and elbow at 100° of flexion and neutral rotation and with and without a 1-kg weight placed on the lateral distal humerus.

Results:

Mean EMG activity within the LHBM and the SHBM was low (≤11.6% ± 9.1%). LHBM activity was significant increased by flexion and abduction (P < .049 in all cases), while SHBM activity was not. EMG activity from the middle head of the deltoid was significantly increased by loading with the shoulder positioned away from the body (ie, in abduction or flexion). When compared with the unloaded state, the addition of a distal humeral load significantly increased LHBM activity in 45° of abduction (P = .028) and 90° of flexion (P = .033) despite forearm and elbow immobilization. The SHBM showed similar trends.

Conclusion:

In normal volunteers with forearm and elbow immobilization and application of a load to the distal humerus, LHBM EMG activity is increased by both glenohumeral flexion and abduction, suggesting that this muscle plays a dynamic role in glenohumeral motion with higher demand activities.

Clinical Relevance:

Biceps tenodesis may result in dynamic change within the glenohumeral joint with higher demand activities.

The management of type II superior labral anterior to posterior injuries

Arthroscopic repair of type II superior labral anterior to posterior (SLAP) tears is currently the standard of care, with most patients obtaining good to excellent surgical results. However, overhead athletes and older patients have inferior outcomes. Recent clinical studies and biomechanical data suggest that a biceps tenodesis is a suitable alternative in select patients. This article reviews the literature to identify the biomechanical and clinical indications for performing a biceps tenodesis for type II SLAP lesions.

Electromyographic study in 5 muscles during an isometric fatiguing protocol

In this study, 12 healthy men aging 22.8 ± 2.2 years old were submitted to a protocol of isometric resistance to fatigue contemplating elbow flexion on three different angles: 45°, 90° and 135°. The objective was to study electromyographic median frequency (MDF) in the following muscles: i) Biceps Brachialis Long Head (BBL), Brachioradialis (BRD), Flexor Digitorum Superficialis (FDS), Triceps Brachialis Long Head (TBL), and Extensor Digitorum (ED). It was verified that, for all muscles, including the muscles that act in opposition to the contraction, fatigue presence was verified by the decrease of MDF value.

Lesions of the biceps pulley as cause of anterosuperior impingement of the shoulder in the athlete: potentials and limits of MR arthrography compared with arthroscopy

PURPOSE

This study aimed to evaluate the diagnostic possibilities of MR arthrography in the correct identification of complex tears of the biceps pulley and their possible correlation with anterosuperior impingement (ASI) development.

MATERIALS AND METHODS

MR arthrography examinations of 23 athletes with clinical suspicion of ASI were reviewed. All examinations were obtained with a 1.5-T unit (Signa Horizon, GE Healthcare). The shoulders were studied with a dedicated surface coil with the patient's arm in the neutral position and in internal and external rotation. In five patients, images in abduction-external rotation (ABER) were obtained. Within 2 month after MR arthrography, the athletes underwent arthroscopic surgery.

RESULTS

MR arthrography images showed a spectrum of tears that, according to the Habermeyer classification, were subdivided into four groups: type 1 in three patients; type 2 in five; type 3 in seven; type 4 in eight. At arthroscopic evaluation, one patient presented type 1 lesion, five type 2, five type 3 and ten type 4. During arthroscopic dynamic manoeuvres, ASI signs were observed in three patients with type 3 lesion and in ten with type 4 lesion.

CONCLUSIONS

MR arthrography is the imaging modality of choice for evaluating lesions of the rotator interval structures, and only complex lesions of the biceps pulley are related to the development of ASI.

Evaluation of muscle fatigue of wheelchair basketball players with spinal cord injury using recurrence quantification analysis of surface EMG

Wheelchair basketball is the most popular exercise activity among individuals with spinal cord injury (SCI). The purpose of this study was to investigate muscular endurance and fatigue in wheelchair basketball athletes with SCI using surface electromyography (SEMG) and maximal torque values. SEMG characteristics of 10 wheelchair basketball players (WBP) were compared to 13 able-bodied basketball players and 12 sedentary able-bodied subjects. Participants performed sustained isometric elbow flexion at 50% maximal voluntary contraction until exhaustion. Elbow flexion torque and SEMG signals were recorded from three elbow flexor muscles: biceps brachii longus, biceps brachii brevis and brachioradialis. SEMG signals were clustered into 0.5-s epochs with 50% overlap. Root mean square (RMS) and median frequency (MDF) of SEMG signals were calculated for each muscle and epoch as traditional fatigue monitoring. Recurrence quantification analysis was used to extract the percentage of determinism (%DET) of SEMG signals. The slope of the %DET for basketball players and WBP showed slower increase with time than the sedentary able-bodied control group for three different elbow flexor muscles, while no difference was observed for the slope of the %DET between basketball and WBP. This result indicated that the athletes are less fatigable during the task effort than the nonathletes. Normalized MDF slope decay exhibited similar results between the groups as %DET, while the slope of the normalized RMS failed to show any significant differences among the groups (p > 0.05). MDF and %DET could be useful for the evaluation of muscle fatigue in wheelchair basketball training. No conclusions about special training for WBP could be determined.

Biceps brachii long head overactivity associated with elbow flexion contracture in brachial plexus birth palsy

BACKGROUND

The etiology of elbow flexion contracture in children with brachial plexus birth palsy remains unclear. We hypothesized that the long head of the biceps brachii muscle assists with shoulder stabilization in children with brachial plexus birth palsy and that overactivity of the long head during elbow and shoulder activity is associated with an elbow flexion contracture.

METHODS

Twenty-one patients with brachial plexus birth palsy-associated elbow flexion contracture underwent testing with surface electromyography. Twelve patients underwent repeat testing with fine-wire electromyography. Surface electrodes were placed on the muscle belly, and fine-wire electrodes were inserted bilaterally into the long and short heads of the biceps brachii. Patients were asked to perform four upper extremity tasks: elbow flexion-extension, hand to head, high reach, and overhead ball throw. The mean duration of muscle activity in the affected limb was compared with that in the contralateral, unaffected limb, which was used as a control. Three-dimensional motion analysis, surface dynamometry, and validated function measures were used to evaluate upper extremity kinematics, elbow flexor-extensor muscle imbalance, and function.

RESULTS

The mean activity duration of the long head of the biceps brachii muscle was significantly higher in the affected limb as compared with the contralateral, unaffected limb during hand-to-head tasks (p = 0.02) and high-reach tasks (p = 0.03). No significant differences in mean activity duration were observed for the short head of the biceps brachii muscle between the affected and unaffected limbs. Isometric strength of elbow flexion was not significantly higher than that of elbow extension in the affected limb (p = 0.11).

CONCLUSIONS

Overactivity of the long head of the biceps brachii muscle is associated with and may contribute to the development of elbow flexion contracture in children with brachial plexus birth palsy. Elbow flexion contracture may not be associated with an elbow flexor-extensor muscle imbalance, as previously hypothesized. The negative impact of elbow flexion contracture on upper extremity function warrants future research in the development of preventive and therapeutic techniques to address elbow flexion contractures in children with brachial plexus birth palsy.

Non-uniform muscle adaptations to eccentric exercise and the implications for training and sport

Due to the variations in morphological and architectural characteristics of fibers within a skeletal muscle, regions of a muscle may be differently affected by eccentric exercise. Although eccentric exercise may be beneficial for increasing muscle mass and can be beneficial for the treatment of tendinopathies, the non-uniform effect of eccentric exercise results in regional muscle damage and as a consequence, non-uniform changes in muscle activation. This regional muscle weakness can contribute to muscle strength imbalances and may potentially alter the load distribution on joint structures, increasing the risk of injury. In this brief review, the non-uniform effects of eccentric exercise are reviewed and their implications for training and sport are considered.

Muscle soreness and delayed-onset muscle soreness

Immediate and delayed-onset muscle soreness differ mainly in chronology of presentation. Both conditions share the same quality of pain, eliciting and relieving activities and a varying degree of functional deficits. There is no single mechanism for muscle soreness; instead, it is a culmination of 6 different mechanisms. The developing pathway of DOMS begins with microtrauma to muscles and then surrounding connective tissues. Microtrauma is then followed by an inflammatory process and subsequent shifts of fluid and electrolytes. Throughout the progression of these events, muscle spasms may be present, exacerbating the overall condition. There are a multitude of modalities to manage the associated symptoms of immediate soreness and DOMS. Outcomes of each modality seem to be as diverse as the modalities themselves. The judicious use of NSAIDs and continued exercise are suggested to be the most reliable methods and recommended. This review article and each study cited, however, represent just one part of the clinician's decisionmaking process. Careful affirmation of temporary deficits from muscle soreness is not to be taken lightly, nor is the advisement and medical management of muscle soreness prescribed by the clinician.

Role of the long head of the biceps brachii muscle in axial humeral rotation control

This anatomical and biomechanical study focuses on the specific influence of the long head of biceps brachii muscle in controlling axial humeral rotation. The tendon of the long head of the biceps brachii (biceps tendon) is shown to either facilitate or restrict axial humeral rotation. Its effect on axial humeral rotation is strongly related to firstly the amount of biceps tendon load, secondly glenohumeral scapular plane elevation, and thirdly the rotatory position of the humerus. At 0° glenohumeral elevation, biceps tendon load caused an increase of internal humeral rotation, from 0° at 2.25 N biceps tendon load to 23° at 82.25 N. Under 45° glenohumeral elevation, biceps tendon load can restrict and facilitate as well internal and external axial humeral rotation, increasing the rotatory range of motion. Above 45° glenohumeral elevation biceps tendon load restricts internal and external axial humeral rotation, increasing actively joint stability by increasing torsional rigidity. These findings on the function of the biceps tendon could have consequences for the clinical interpretation. In the elevated arm position, extreme rotation loads the long head of the biceps tendon and may turn out to biceps or bicepslabrum complex injuries.

Intrasubstance ruptures of the biceps brachii: diagnosis and management

Traumatic intrasubstance ruptures of the biceps brachii are rare and historically specific to military static line parachute jumps; however, these injuries have recently been reported in the civilian literature. Diagnosis is made by history, clinical weakness in supination and elbow flexion, extensive ecchymosis and edema, and a palpable defect. Ultrasound and magnetic resonance imaging are useful to confirm the diagnosis and injury severity. Nonoperative treatment involves splinting in acute flexion. Percutaneous hematoma aspiration has been described. Early surgical intervention with primary repair has been shown to be more successful than late reconstruction. Studies comparing operative and nonoperative treatment are lacking.

Variation of tension in the long head of the biceps tendon as a function of limb position with simulated biceps contraction

Purpose:

This study was designed to quantify tensile forces within the intra-articular long head of the bicep tendon (LHBT) under conditions of passive limb positioning and physiologic load, which simulate contraction of the LHBT.

Materials and Methods:

A force probe was inserted into the intra-articular LHBT, just distal to its supra-glenoid origin, in six fresh-frozen cadaveric specimens. Initially, specimens were manually manipulated through 30 glenohumeral joint positions, combining humeral rotation and elbow/forearm position. In the second phase, a 55 N tensile load was applied through the LHBT in 18 limb positions. Intra-tendinous tension was recorded in all positions under both conditions.

Results:

External humeral rotation significantly increased tension with glenohumeral forward flexion (P<0.0001). Conversely, internal humeral rotation significantly increased tension with glenohumeral abduction and extension (P<0.0001). A position of glenohumeral extension and internal rotation, with the elbow extended and forearm pronated, produced the highest tension in the intra-articular LHBT (P<0.0001). Under applied load conditions, observed LHTB tension was not statistically different in any glenohumeral position (P=0.1468, power = 88%). The greater tuberosity was noted to impinge on the force probe in forward flexion and internal rotation in two specimens.

Conclusions:

Variable tensile forces are seen in the intra-articular LHBT as a function of both limb position and simulated biceps contraction. Our findings provide a thorough data set that may be used to help substantiate or refute current or future hypotheses regarding LHBT function, pathology, and clinical tests.

Clinical Relevance:

Identifying positions of glenohumeral motion, which affect LHBT tension will provide an anatomic basis for clinical tests proposed to be for diagnosing LHBT lesions, including superior labral anterior and posterior tears.

Anatomy, function, injuries, and treatment of the long head of the biceps brachii tendon

Lesions of the long head biceps tendon (LHB) are frequent causes of shoulder pain and disability. Biceps tenotomy and tenodesis have gained widespread acceptance as effective procedures to manage both isolated LHB pathology and combined lesions of the rotator cuff and biceps-labral complex. The function of the LHB tendon and its role in glenohumeral kinematics presently remain only partially understood because of the difficulty of cadaveric and in vivo biomechanical studies. The purpose of this article is to offer an up-to-date review of the anatomy and biomechanical properties of the LHB and to provide an evidence-based approach to current treatment strategies for LHB disorders.

Long head of the biceps tendinopathy: diagnosis and management

Tendinopathy of the long head of the biceps brachii encompasses a spectrum of pathology ranging from inflammatory tendinitis to degenerative tendinosis. Disorders of the long head of the biceps often occur in conjunction with other shoulder pathology. A thorough patient history, physical examination, and radiographic evaluation are necessary for diagnosis. Nonsurgical management, including rest, nonsteroidal anti-inflammatory drugs, physical therapy, and injections, is attempted first in patients with mild disease. Surgical management is indicated for refractory or severe disease. In addition to simple biceps tenotomy, a variety of tenodesis techniques has been described. Open biceps tenodesis has been used historically. However, promising results have recently been reported with arthroscopic tenodesis.

The effect of posterosuperior rotator cuff tears and biceps loading on glenohumeral translation

PURPOSE

To investigate the biomechanical effects of posterosuperior rotator cuff tear (RCT) size and of loading the long biceps tendon in the presence of various-sized RCTs.

METHODS

Ten cadaveric shoulders were subjected to loading in the superior and anterosuperior directions in the intact state and with sequentially larger RCTs. Glenohumeral translation was measured with and without biceps tendon loading.

RESULTS

As long as the inferior infraspinatus remained intact, there was no significant difference in glenohumeral translation for any load studied. Once the supraspinatus and the entire infraspinatus were released, 50 N of load led to significantly increased translation in both directions. When we compare the results of this study with those of a previous study, the subscapularis appears to be more effective than the infraspinatus in constraining both anterosuperior and superior translation. For the intact specimens and for all sizes of RCTs, biceps loading led to a significant decrease in both anterosuperior and superior glenohumeral translation. Depending on the size of the RCT and the direction of loading, this decrease in glenohumeral translation varied from 19% to 53%.

CONCLUSIONS

Tears of the subscapularis have greater biomechanical consequences than do tears of the infraspinatus. Loading the long biceps tendon led to a significant decrease in anterosuperior and superior glenohumeral translation for all sizes of RCTs, with a greater decrease in the percentage of glenohumeral translation noted for larger tears.

CLINICAL RELEVANCE

Knowledge of the biomechanics of posterosuperior RCTs enhances our ability to treat them. Surgeons should be aware that, although biceps tenotomy or tenodesis may provide pain relief in shoulders with RCTs, there are biomechanical consequences to these procedures.

Electromyographic evaluation of upper limb muscles involved in armwrestling sport simulation during dynamic and static conditions

OBJECTIVE

To evaluate the electromyographic activity of the Pectoralis Major (PM), Biceps Brachii (BB), Pronator Teres (PT) and Flexor Carpi Ulnaris (FCU) muscles involved in simulated armwrestling.

METHODS

Ten trained volunteers were selected to perform the armwrestling movement, during dynamic tests with 40% and 80% of maximum voluntary load (MVL) and static tests in the initial, intermediary and final positions. Electromyographic and force data were normalized for analyses.

RESULTS

In dynamic tests with 40% MVL, electric activity of the PT muscle was greater than FCU (p<0.01) and BB (p<0.05) muscles, and with 80% MVL, PM and PT muscles were the most active. In static tests, electric activity increased from the initial to final positions for the PM muscle (p<0.05), while it decreased for the BB and PT muscles (p<0.001 and p<0.05, respectively). No significant changes were observed for force and no correlation was found with the simultaneous electric activity.

CONCLUSIONS

It can be concluded that the PM and FCU muscles participate as agonists in the simulated armwrestling whereas the BB and PT muscles seem to perform secondary functions. Electric activity showed to be dependent on the load and on the position of the upper limb, but not on the force produced during the movement.

The effect of the long head of the biceps on glenohumeral kinematics

The long head of the biceps has been described as a stabilizing force in the setting of glenohumeral instability. However, data are lacking on the effect of loading the long head of the biceps on glenohumeral kinematics. Six cadaveric shoulders were tested for glenohumeral rotational range of motion and translation using a custom shoulder testing system and the Microscribe 3DLX (Immersion, San Jose, CA). The path of glenohumeral articulation (PGA) was measured by calculating the humeral head center with respect to the glenoid articular surface at maximal internal rotation, 30 degrees, 60 degrees, 90 degrees, and maximal external rotation. Significant decreases in glenohumeral rotational range of motion and translation were found with 22-N biceps loading vs the unloaded group. With respect to the PGA, the humeral rotation center was shifted posterior with biceps loading at maximal internal rotation, 30 degrees, and 60 degrees of external rotation. Loading the long head of the biceps significantly affects glenohumeral rotational range of motion, translations, and kinematics.

Evaluation of three methods for determining EMG-muscle force parameter estimates for the shoulder muscles

BACKGROUND

Accurate prediction of in vivo muscle forces is essential for relevant analyses of musculoskeletal biomechanics. The purpose of this study was to evaluate three methods for predicting muscle forces of the shoulder by comparing calculated muscle parameters, which relate electromyographic activity to muscle forces.

METHODS

Thirteen subjects performed sub-maximal, isometric contractions consisting of six actions about the shoulder and two actions about the elbow. Electromyography from 12 shoulder muscles and internal shoulder moments were used to determine muscle parameters using traditional multiple linear regression, principal-components regression, and a sequential muscle parameter determination process using principal-components regression. Muscle parameters were evaluated based on their sign (positive or negative), standard deviations, and error between the measured and predicted internal shoulder moments.

FINDINGS

It was found that no method was superior with respect to all evaluation criteria. The sequential principal-components regression method most frequently produced muscle parameters that could be used to estimate muscle forces, multiple regression best predicted the measured internal shoulder moments, and the results of principal-components regression fell between those of sequential principal-components regression and multiple regression.

INTERPRETATION

The selection of a muscle parameter estimation method should be based on the importance of the evaluation criteria. Sequential principal-components regression should be used if a greater number of physiologically accurate muscle forces are desired, while multiple regression should be used for a more accurate prediction of measured internal shoulder moments. However, all methods produced muscle parameters which can be used to predict in vivo muscle forces of the shoulder.

Multijoint reflexes of the stroke arm: neural coupling of the elbow and shoulder

The reflex torque responses of the elbow and shoulder to constant velocity angular extensions of the full comfortable range of the spastic elbow were measured in 16 people with unilateral stroke and 6 neurologically intact controls in order to identify the interjoint reflex coupling that occurs after stroke. The resulting responses showed a substantial reflex torque at the elbow and shoulder in subjects with stroke, with 12 of the 16 subjects producing adduction of the shoulder in response to passive extension of the elbow. The presence of simultaneous shoulder flexion torque with elbow flexion torque and with an identical waveform indicated an active role of biarticular elbow/shoulder flexors, such as the biceps. As the biceps muscle produces a shoulder abduction moment, shoulder adduction produced during elbow extension was thought to be associated with neural rather than biomechanical coupling. These results suggest that spasticity in people with stroke is more complex than its traditional perception as a hyperexcitable stretch reflex, and includes potent heteronymous reflex pathways. The reflex coupling observed between the shoulder and elbow should be considered in the diagnosis and clinical management of spasticity. The potential impact of this reflex on the coordination of volitional arm movements will be examined in future studies.

Impact of gravity loading on post-stroke reaching and its relationship to weakness

The ability to extend the elbow following stroke depends on the magnitude and direction of torques acting at the shoulder. The mechanisms underlying this link remain unclear. The purpose of this study was to evaluate whether the effects of shoulder loading on elbow function were related to weakness or its distribution in the paretic limb. Ten subjects with longstanding hemiparesis performed movements with the arm either passively supported against gravity by an air bearing, or by activation of shoulder muscles. Isometric maximum voluntary torques at the elbow and shoulder were measured using a load cell. The speed and range of elbow extension movements were negatively impacted by actively supporting the paretic limb against gravity. However, the effects of gravity loading were not related to proximal weakness or abnormalities in the elbow flexor-extensor strength balance. The findings support the existence of abnormal descending motor commands that constrain the ability of stroke survivors to generate elbow extension torque in combination with abduction torque at the shoulder.

Time to failure of a sustained contraction is predicted by target torque and initial electromyographic bursts in elbow flexor muscles

The purpose of the study was to identify factors that could predict differences among individuals in the time to failure of a submaximal contraction. Twenty subjects (10 men, 25+/-6 years) supported an inertial load equivalent to 20% of the maximal voluntary contraction (MVC) force with the elbow flexor muscles for as long as possible. The time to failure was predicted by the frequency of electromyographic bursts in the long head of biceps brachii during the first 20% of the contraction, the amplitude of bursts in the brachioradialis during the first 20% of the contraction, and the target torque. Subjects who could sustain the task longer exhibited greater initial (first 20% of contraction) electromyographic burst frequency in the long head of biceps brachii, lower initial burst amplitudes in the brachioradialis muscle, and lower target torque. Knowing the main predictors of a submaximal fatiguing contraction with the elbow flexor muscles may assist clinicians in personalizing therapeutic interventions.

SLAP tears of the glenoid labrum in contact athletes

OBJECTIVE

To describe the distribution and clinical presentation of labral injuries in rugby players and the time taken for them to return to sports.

DESIGN

Retrospective cohort study.

SETTING

Busy shoulder practice in the North West of England, treating a large number of professional athletes.

PATIENTS

A review of 51 shoulder arthroscopies performed on professional rugby players over a 35 month period. All patients diagnosed with a SLAP lesion at arthroscopy were identified. Eighteen patients had a documented SLAP tear; this group represented our study population.

INTERVENTIONS

Arthroscopic debridement and/or stabilization was carried out for all labral injuries using Panaloc anchors and No. 2 PDS via a 2 portal technique.

MAIN OUTCOME MEASUREMENTS

Classification of injury, Satisfaction, Time to return to play.

RESULTS

The incidence of SLAP tears in our study population was 35%. There were 11 isolated SLAP tears (61%), 3 SLAP tears associated with a Bankart lesion (17%), 2 SLAP tears associated with a posterior labral lesion (11%), and 2 SLAP tears associated with an anterior and posterior labral injuries (11%). Of the 18 SLAP tears, 14 (78%) were type 2, 3 (17%) were type 3, and 1 (5%) was type 4. None of the patients with a SLAP tear presented with symptoms of instability. MR Arthrogram had a 76% sensitivity for detecting SLAP tears. By 6 months postsurgery, 89% of patients were satisfied. Patients with isolated SLAP tears were the quickest to return to sports, at an average of 2.6 months postsurgery.

CONCLUSIONS

SLAP tears are a common injury in rugby players. These can often be diagnosed with MR arthrography. Arthroscopic repair is associated with excellent results and early return to sports.

Electromyographic analysis of physical examination tests for type II superior labrum anterior-posterior lesions

Physical examination tests that place tension on the long head of the biceps may best reproduce symptoms in patients with type II superior labrum anterior-posterior (SLAP) lesions. The objective of this study is to compare the normalized electromyographic signal of the long head of the biceps for SLAP lesion physical examination tests. The active compression test, anterior-superior SLAP test, biceps load test II, biceps tension test, and pain provocation test were performed on 13 subjects while biceps electromyographic data were recorded. The active compression test and biceps tension test had significantly higher electromyographic signals than the other tests. We found no significant differences when comparing forearm supination and pronation within individual tests. Because the active compression and biceps tension tests maximize muscle activation on the long head of the biceps, they may be the best physical examination tests by which to identify type II SLAP lesions.

Effect of experimental suprascapular nerve block on active glenohumeral translations in vivo

Static superior shoulder instability is associated with long-standing rotator cuff tears. Factors or mechanisms which can prevent superior migration of the humeral head, and therefore allow preservation or restoration of shoulder function despite nonanatomical cuff repair, are poorly understood. The question has therefore arisen, whether centering of the humeral head was the result of active shoulder muscle function. It was the goal of this experimental investigation to (1) determine the pattern of glenohumeral translations during active shoulder abduction measured by open-magnetic resonance imaging (MRI) techniques, and to (2) determine the influence of experimental paralysis of the infra- and supraspinatus muscles on these translations. In contrast to prior experimental investigations, the humeral head remained always centered in the glenoid fossa during active abduction. No superior migration of the humeral head could be provoked with experimental paralysis of the supra- and/or infraspinatus muscles. The hypothesis that static or dynamic superior humeral head displacement is prevented by active-supra- and/or infraspinatus muscle function must therefore be rejected, for the shoulder with a structurally intact muscle-tendon-bone unit.