Effective stretching position for the posterior deltoid muscle evaluated by shear wave elastography.

BACKGROUND: Deteriorated extensibility of the posterior deltoid muscle is one of the factors of posterior shoulder tightness, and improvement in its extensibility is needed. However, no study has investigated which shoulder positions effectively stretch the posterior deltoid muscle in vivo. The aim of this study was to verify the effective stretching position of the posterior deltoid muscle in vivo by shear wave elastography. METHODS: Fifteen healthy men participated in this study. The shear modulus of the posterior deltoid was measured at resting and 13 stretching positions: 60°, 90°, and 120° shoulder flexion; maximum shoulder flexion, horizontal adductions at 60°, 90°, and 120° shoulder flexion; internal rotations at 60°, 90°, and 120° shoulder flexion; and combinations of horizontal adduction with internal rotation at 60°, 90°, and 120° shoulder flexion. The shear moduli of each stretching position were compared to those of the rest. Then, among the stretching positions for which the shear modulus was significantly different from the rest, the shear moduli were compared using a three-way analysis of variance with repeated measures of the 3 factors-flexion, horizontal adduction, and internal rotation. RESULTS: The shear moduli in all stretching positions were significantly higher than those of the rest, except for maximum shoulder flexion. The three-way analysis of variance with repeated measures revealed significant main effects in flexion and horizontal adduction. Comparing the flexion angles, the shear modulus was significantly higher at 90° than that at 60° and 120°. The shear modulus with horizontal adduction was significantly higher than that without horizontal adduction. Moreover, a significant two-way interaction was found only at flexion and horizontal adduction. The shear modulus with horizontal adduction was significantly higher at all angles than that without horizontal adduction at each flexion angle. Comparing the flexion angles with horizontal adduction, the shear modulus was significantly higher at 90° than that at 60° and 120°. No significant three-way interactions were found. CONCLUSION: Shoulder flexion and horizontal adduction affected the extensibility of the posterior deltoid muscle, whereas the effect of shoulder internal rotation was limited. More precisely, maximal horizontal adduction at 90° shoulder flexion was the most effective stretching position for the posterior deltoid muscle.

The Effect of Glenohumeral Fixation Angle on Deltoid Function During Superior Capsule Reconstruction: A Biomechanical Investigation.

PURPOSE: To evaluate the effect of dermal allograft fixation at different angles of glenohumeral abduction on deltoid forces during superior capsule reconstruction (SCR). METHODS: Fifteen cadaveric specimens were tested using a dynamic shoulder simulator. Following testing in the native state, shoulders underwent SCR in 2 of 5 possible fixation angles; 0°, 15°, 30°, 45°, or 60° of glenohumeral abduction, allowing for 6 specimens per group. Angles were measured radiographically with the glenoid fixed perpendicular to the floor. Maximum mean deltoid abduction force was compared among 5 separate conditions within each angle group: (1) native shoulder, (2) complete supraspinatus (SSP) and superior capsule tear, (3) SCR alone, (4) SCR with posterior margin sutured, and (5) SCR with anterior and posterior margins sutured. RESULTS: SSP tears significantly increased the maximum deltoid forces for all 5 fixation angles compared with the native state (P < .05). Specimens repaired at 0°, 30°, and 45° were unable to restore deltoid forces compared with the native state in any condition (P < .05). SCR at 15° with anterior and posterior margin convergence showed similar abduction forces compared with the native state (P = .19). When fixed at 60° abduction, SCR alone significantly reduced deltoid forces compared to SSP (Δ143N, P < .001) and native (Δ48N, P < .001). No significant differences were found between the 3 repair subtypes (SCR ± anterior/posterior margin repair) in the 60° group. CONCLUSIONS: SCR with anterior and posterior margin convergence tensioned at 15° of glenohumeral abduction showed similar deltoid abduction force requirements compared with the native state, whereas graft fixation in 60° significantly reduced deltoid force in all SCR conditions. CLINICAL RELEVANCE: Increased graft tension with a greater abduction angle may provide greater functional outcome by placing less load on the deltoid. In contrast, graft fixation in lower abduction angles may require additional margin convergence to reproduce native forces.

Increasing the deltoid muscle volume positively affects functional outcomes after arthroscopic rotator cuff repair.

PURPOSE: The aim of this study was to determine the effect of changes in deltoid muscle volume (DMV) on the clinical outcomes of patients who underwent arthroscopic repair due to chronic rotator cuff rupture. METHODS: A total of 54 patients (35 females, 19 males) between 40 and 70 years of age who underwent single-row arthroscopic repair due to chronic rotator cuff tears were compared via preoperative (preop) and postoperative (postop) (6-12 months) magnetic resonance imaging (MRI) to determine the total DMV (tDMV). A clinical evaluation was performed with American Shoulder and Elbow Surgeons (ASES) and Constant scores in both the preop and postop groups. tDMV values were also measured in a randomly selected control group (50 patients). A standardized rehabilitation program was recommended for all patients. RESULTS: Positive correlations were found between the change in tDMV (ΔtDMV) and ASES and Constant scores (p < 0.03 and p < 0.032, respectively). The preop tDMV value was significantly lower in the patient group than in the control group (p < 0.02). Significantly lower ΔtDMV and body mass index (BMI)-adjusted tDMV values [Δ(tDMV/BMI)] were observed in patients who had rerupture at the postop MRI. CONCLUSIONS: According to the present study, changes in DMV impact clinical outcomes after rotator cuff repair. Rehabilitation of the DMV or increasing the preop DMV values positively affects postop clinical outcomes. In addition, if the DMV is below the cutoff value during the preop period, there is insufficient improvement in clinical scores. The clinical relevance of this study is the finding that in patients with a chronic rotator cuff tear and a hypotrophic deltoid muscle, increasing the preop DMV could help achieve better functional outcomes. LEVEL OF EVIDENCE: Prognostic, Level 3, case-control study.

Effects of Exergaming in Cancer Related Fatigue in the Quality of Life and Electromyography of the Middle Deltoid of People with Cancer in Treatment: A Controlled Trial

Objective: In the present study, we aimed to evaluate the effects an exergaming protocol for cancer patients who undergo or have already undergone cancer treatment. We sought to evaluate changes in cancer-related fatigue, function, and ability to perform daily activities, in addition to changes in the electromyographic pattern of the middle deltoid muscle. Methods: We conducted a controlled trial. Nineteen volunteers in the cancer group (aged 61 ± 9 years; body mass index28 ± 5) and 19 in the control group (aged 58 ± 8 years); body mass index 28 ± 4) participated in the study. They were evaluated by means of a sociodemographic and clinical questionnaire, the Functional Assessment of Chronic Therapy-Fatigue (FACIT-F) questionnaire, and surface electromyography in the deltoid muscle at three moments: before the beginning of the exergaming protocol, after 10 training sessions, and after 20 sessions. The protocol consisted of practicing exergaming using Xbox 360® (Microsoft, Redmond, USA) with Kinect®. The game "Your Shape Fitness Evolved" (Ubisoft, Rennes, France) was used. Results: Total FACIT-F scores, fatigue subscale scores, and median frequency values observed in the cancer group were lower than those in the control group. These values improved in relation to the initial evaluation in the cancer group after the practice of the exergaming protocol. Conclusion: The exergaming protocol used in this study was effective for reducing reported symptoms of fatigue, increasing perceived quality of life, and improving the pattern of deltoid muscle contraction in cancer patients.

Scapular kinematic and shoulder muscle activity alterations after serratus anterior muscle fatigue.

BACKGROUND: Although the serratus anterior muscle has an important role in scapular movement, no study to date has investigated the effect of serratus anterior fatigue on scapular kinematics and shoulder muscle activity. The purpose of this study was to clarify the effect of serratus anterior fatigue on scapular movement and shoulder muscle activity. METHODS: The study participants were 16 healthy men. Electrical muscle stimulation was used to fatigue the serratus anterior muscle. Shoulder muscle strength and endurance, scapular movement, and muscle activity were measured before and after the fatigue task. The muscle activity of the serratus anterior, upper and lower trapezius, anterior and middle deltoid, and infraspinatus muscles was recorded, and the median power frequency of these muscles was calculated to examine the degree of muscle fatigue. RESULTS: The muscle endurance and median power frequency of the serratus anterior muscle decreased after the fatigue tasks, whereas the muscle activities of the serratus anterior, upper trapezius, and infraspinatus muscles increased. External rotation of the scapula at the shoulder elevated position increased after the fatigue task. CONCLUSION: Selective serratus anterior fatigue due to electric muscle stimulation decreased the serratus anterior endurance at the flexed shoulder position. Furthermore, the muscle activities of the serratus anterior, upper trapezius, and infraspinatus increased and the scapular external rotation was greater after serratus anterior fatigue. These results suggest that the rotator cuff and scapular muscle compensated to avoid the increase in internal rotation of the scapula caused by the dysfunction of the serratus anterior muscle.

Anterior deltoid reeducation for irreparable rotator cuff tears revisited.

BACKGROUND: A previous study introduced a method of conservative treatment of irreparable rotator cuff tears (RCTs) using a rehabilitation program (anterior deltoid reeducation [ADR]). The purposes of this study were to present our experience with ADR and to compare our results with those of the previous study. METHODS: Thirty consecutive elderly patients with irreparable RCTs were prospectively enrolled and taught how to perform the home-based ADR program for a period of 3 months. Clinical and radiographic evaluations were determined at the first visit. Clinical follow-up was available after 9 and 24 months. Failure of the ADR program was defined as abandonment of the ADR program because of pain and/or a patient's decision to undergo surgery at any time or a less than 20-point improvement in the American Shoulder and Elbow Surgeons score at last follow-up. RESULTS: Of the 30 patients, 9 did not complete the 3-month ADR program because of pain. Of the 21 patients who completed the ADR program, 3 were not satisfied with the outcome and went on to undergo surgery. Eighteen of the 30 patients completed the program and had a follow-up at 24 months. Among these 18 cases, there were significant mean improvements between pre-ADR and follow-up outcome scores among all variables (P < .005). However, 6 of these 18 patients did not have an improvement in the American Shoulder and Elbow Surgeons score by at least 20 points. Overall, the ADR program had a success rate of only 40%. CONCLUSION: A 3-month ADR program had limited success to treat irreparable RCTs. We could not reproduce the high rate of satisfactory results of 82% found in a previous study.

Impact of Arthroscopic Lateral Acromioplasty on the Mechanical and Structural Integrity of the Lateral Deltoid Origin: A Cadaveric Study.

PURPOSE: To determine whether a 5-mm and/or 10-mm arthroscopic lateral acromioplasty (ALA) would weaken the structural and mechanical integrity of the lateral deltoid. METHODS: The acromion and lateral deltoid origin were harvested from 15 pairs (n = 30) of fresh-frozen human cadaveric shoulder specimens. One side of each specimen pair (left or right) was randomly assigned to either a 5-mm (n = 7) or 10-mm (n = 8) ALA group, and the contralateral sides (n = 15) were used as matched controls. Acromion thickness and width were measured pre- and postoperatively. After ALA, specimens were inspected for damage to the lateral deltoid origin. Each specimen was secured within a dynamic testing machine, and the deltoid muscle was pulled to failure. Statistical analysis was performed to determine whether ALA reduced the lateral deltoid's failure load. RESULTS: There was no significant difference in failure load between the 5-mm ALA group (661 ± 207 N) and its matched control group (744 ± 212 N; mean difference = 83 N; 95% confidence interval [CI], -91 to 258; P = .285) nor between the 10-mm ALA group (544 ± 210 N) and its matched control group (598 ± 157 N; mean difference = 54 N; 95% CI, -141 to 250; P = .532). There was no correlation found between the amount of bone resected (measured by percent thickness and width of the acromion after ALA) and the failure load of the deltoid. Visual evaluation of the acromion after ALA revealed the lateral deltoid origin had no damage in any case. CONCLUSIONS: ALA did not weaken the structural or mechanical integrity of the lateral deltoid origin. Neither a 5-mm nor a 10-mm ALA significantly reduced the deltoid's failure load. The lateral deltoid origin was not macroscopically damaged in any case. CLINICAL RELEVANCE: ALA can be performed without the potential risk of macroscopically damaging the lateral deltoid origin or reducing its failure load.

Rehabilitation After Posterior Deltoid to Triceps Transfer in Tetraplegia.

OBJECTIVE: To describe and evaluate the rehabilitation concept after posterior deltoid to triceps transfer in patients with tetraplegia. DESIGN: Retrospective observational study. SETTING: Rehabilitation units. PARTICIPANTS: Patients with tetraplegia who had posterior deltoid to triceps tendon transfer and had muscle strength measurements 1 year postsurgery from 2009 to 2013 (N=44). INTERVENTIONS: Posterior deltoid to triceps tendon transfer to restore elbow extension and postoperative rehabilitation. MAIN OUTCOME MEASURES: Elbow extension range of motion and muscle strength and the modified Canadian Occupational Performance Measure (COPM). RESULTS: Surgery was performed on 53 arms. No major complications (eg tendon rupture, lengthening) were reported. Muscle strength measured 1 year after surgery was on average grade 3 (out of 5) in the 53 operated arms. The ability to extend the elbow against gravity was achieved in 62% of the arms (muscle strength of grade ≥3). In patients with a preoperative elbow extension deficit (n=14), the deficit was reduced on average from 16° to 9°. The performance of the prioritized activities as measured with the COPM improved on average 2.6 scale steps, from 3.3 to 5.9. Satisfaction with the performance improved on average 3.2 scale steps, from 2.8 to 6.0. CONCLUSIONS: The posterior deltoid to triceps tendon transfer with the applied rehabilitation protocol is a safe and effective procedure. There were no tendon ruptures, and all patients were able to complete the rehabilitation protocol. The shorter restriction time after surgery allows the patient to be independent at an earlier stage of the rehabilitation and reduces hospitalization or care burden.

The champagne toast position isolates the supraspinatus better than the Jobe test: an electromyographic study of shoulder physical examination tests.

BACKGROUND: While Jobe's test is widely used, it does not isolate supraspinatus activity. Our purpose was to examine the electromyographic (EMG) activity within the supraspinatus and deltoid with resisted abduction to determine the shoulder position that best isolates the activity of the supraspinatus. METHODS: We performed EMG analysis of the supraspinatus, anterior head of the deltoid, and middle head of the deltoid in 10 normal volunteers. We measured EMG activity during resisted shoulder abduction in the scapular plane to both manual resistance and a standardized load in varying degrees of abduction and rotation. To determine which position best isolates supraspinatus activity, the ratio of supraspinatus to deltoid activity (S:D) was calculated for each position. Results were analyzed with a repeated-measures analysis of variance with Bonferroni correction. The posterior deltoid was excluded as it serves mostly to extend and externally rotate. RESULTS: Our study confirmed Jobe's findings of maximal supraspinatus activity at 90° of abduction. However, decreasing abduction significantly increased S:D for both resisted manual testing and testing against a standardized load (P = .002 and .001, respectively). The greatest S:D ratio (4.6 ± 3.4 for standardized load testing) was seen at the "champagne toast" position, i.e., 30° of abduction, mild external rotation, 30° of flexion, and 90° of elbow flexion. The smallest ratio (0.8 ± 0.6) was seen at Jobe's position. CONCLUSIONS: Testing of abduction strength in the champagne toast position, i.e., 30° of abduction, mild external rotation, and 30° of flexion, better isolates the activity of the supraspinatus from the deltoid than Jobe's "empty can" position.

Once an arthrodesis, always an arthrodesis?

BACKGROUND: An arthrodesis of the shoulder is historically a solution for severe shoulder joint problems, for which no prosthetic solution is deemed possible. With the introduction of the reverse shoulder arthroplasty (RSA), which is intrinsically stable at the glenohumeral joint, it seems logical to consider conversion of a painful arthrodesis into a RSA, provided that the deltoid was not destroyed during the arthrodesis. METHODS: Four patients (2 men, 2 women; age 46-66 years) with a longstanding arthrodesis (5-11 years) visited our clinic with a painful shoulder (mainly around the scapula) with the request to provide more mobility. In all, the shoulder was fused in 60° to 80° of abduction, 20° to 40° of flexion, and 40° to 50° of internal rotation. All patients refused an osteotomy as treatment for the pain. A preoperative electromyelogram showed activity in at least the posterior or middle parts of the deltoid, or both. They were offered revision of arthrodesis to a reverse prosthesis. All complications, especially instability, were discussed. Surgery was performed through the previous deltopectoral scar. In 3 cases, the osteotomy was lateral to the original joint line, providing some lateralization. RESULTS: Follow-up was 22 to 60 months. The Constant-Murley score improved from 15-21 to 30-60. No dislocations occurred. All patients were satisfied, especially with the increased, although not impressive, rotations. Pain did not disappear but decreased considerably, from visual analog scale 8-10 to 0-4. CONCLUSION: Conversion into a RSA is a safe procedure in patients with a painful arthrodesis and grossly intact deltoid, providing better glenohumeral mobility (especially rotations), leading to improved patient satisfaction.

Age-related structural changes in upper extremity muscle tissue in a nonhuman primate model.

BACKGROUND: Longitudinal studies of upper extremity aging in humans include logistical concerns that animal models can overcome. The vervet is a promising species with which to study aging-related processes. However, age-related changes in upper extremity muscle structure have not been quantified in this species. This study measured age-related changes to muscle structure, examined relationships between muscle structure and measures of physical performance, and evaluated the presence of rotator cuff tears. METHODS: Muscle structure (volume, optimal fiber length, and physiologic cross-sectional area (PCSA)) of 10 upper extremity muscles was quantified from the right upper limb of 5 middle-aged and 6 older adult female vervets. RESULTS: Total measured PCSA was smaller (P = .001) in the older adult vervets than in the middle-aged vervets. Muscle volume reduction predominate the age-related reductions in PCSA. Total measured PCSA was not correlated to any measures of physical performance. No rotator cuff tears were observed. Supraspinatus volume was relatively larger and deltoid volume relatively smaller in the vervet compared with a human. CONCLUSIONS: The vervet is an appropriate translational model for age-related upper extremity muscle volume loss. Functional measures were not correlated to PCSA, suggesting the vervets may have enough strength for normal function despite loss of muscle tissue. Reduced relative demand on the supraspinatus may be responsible for the lack of naturally occurring rotator cuff tears.

The effects of progressive lateralization of the joint center of rotation of reverse total shoulder implants.

BACKGROUND: There has been a renewed interest in lateralizing the center of rotation (CoR) in implants used in reverse shoulder arthroplasty. The aim of this study was to determine the sensitivity of lateralization of the CoR on the glenohumeral joint contact forces, muscle moment arms, torque across the bone-implant interface, and the stability of the implant. METHODS: A 3-dimensional virtual model was used to investigate how lateralization affects deltoid muscle moment arm and glenohumeral joint contact forces. This model was virtually implanted with 5 progressively lateralized reverse shoulder prostheses. The joint contact loads and deltoid moment arms were calculated for each lateralization over the course of 3 simulated standard humerothoracic motions. RESULTS: Lateralization of the CoR leads to an increase in the overall joint contact forces across the glenosphere. Most of this increased loading occurred through compression, although increases in anterior/posterior and superior/inferior shear were also observed. Moment arms of the deltoid consistently decreased with lateralization. Bending moments at the implant interface increased with lateralization. Progressive lateralization resulted in improved stability ratios. CONCLUSIONS: Lateralization results in increased joint loading. Most of that loading occurs through compression, although there were also increases in shear forces. Anterior/posterior shear is currently not accounted for in implant fixation studies, leaving its effect on implant fixation unknown. Future studies should incorporate shear forces into their models to more accurately assess fixation methods.

Reverse total shoulder arthroplasty: a biomechanical evaluation of humeral and glenosphere hardware configuration.

BACKGROUND: Various reverse total shoulder arthroplasty (rTSA) implant options are available for the humeral and glenosphere components. This study used a cadaveric biomechanical shoulder simulator to evaluate how hardware configurations in 2 common rTSA systems affect (1) abduction/adduction range of motion (ROM), (2) rotational ROM, and (3) forces to elevate the arm. METHODS: Seven pairs of shoulders were tested on a biomechanical shoulder simulator before and after rTSA implantation. The Aequalis Reverse Shoulder (Tornier, Edina, MN, USA) and the Reverse Shoulder Prosthesis (RSP; DJO Surgical, Austin, TX, USA) were implanted in opposing shoulders. Aequalis implant options included humeral polymer insert thickness and eccentricity and glenosphere tilt. RSP implant options included glenosphere diameter and lateralization, humeral shell offset, and polymer insert depth. RESULTS: Both the RSP and Aequalis shifted the center of rotation inferior and medially compared with native shoulders (P < .001). Increased Aequalis insert thickness reduced adduction (P < .003) and internal/external (P < .028) passive ROM. The 10° inferiorly tilted glenosphere increased deltoid abduction forces (P < .032). In the RSP, smaller glenosphere diameter (P < .012), a semiconstrained humeral insert (P < .023), and a neutral humeral shell offset (P < .002) all decreased adduction deficit, whereas lateral glenosphere offset increased passive abduction ROM (P < .028). Increased humeral shell offset decreased passive internal/external rotation ROM (P < .050). DISCUSSION: Hardware configurations in rTSA have different effects on passive ROM and deltoid forces required for abduction. Identifying these changes may guide surgical decision making during rTSA placement.

Deltoid muscle pressures during arthroscopic rotator cuff repair.

The purpose of this study was to investigate deltoid compartment pressures during arthroscopic rotator cuff repair using modern pressure pumps to achieve visualization. Twelve patients undergoing arthroscopic rotator cuff repairs were monitored for deltoid compartment pressure changes intraoperatively. Pre-, intra-, and postoperative intramuscular pressures were recorded. All patients demonstrated varying degrees of swelling due to fluid extravasation. Swelling was qualified as mild, moderate, or severe by clinical assessment and quantified objectively using a pressure monitor to record deltoid compartment pressures. Clinically, severe swelling occurred in 4 patients, all of whom underwent procedures lasting longer than 90 minutes. Objectively, no patient had evidence of dangerously elevated pressure measurements. The mean increase in compartment pressures was 9 mm Hg. All patients were treated and discharged as outpatients. No patient required more than oral narcotic analgesics for postoperative pain control beyond the postanesthesia care unit stay. Arthroscopic rotator cuff repair may lead to clinically impressive swelling, but within the current study group, no evidence existed of clinically significant, persistent elevation of deltoid compartment measures using current arthroscopic techniques and arthroscopic pump systems. However, caution should be observed with regard to extended operative times and elevation of pump pressures.

Glenohumeral contact pressure in a simulated active compression test using cadaveric shoulders.

BACKGROUND: The active compression test has been described to detect superior labrum anterior and posterior (SLAP) lesions. Some have speculated that contact between the lesser tuberosity and the superior glenoid in the testing position causes a positive test. This study evaluated the location of peak glenohumeral contact pressures during a simulated active compression test in a cadaveric model with and without SLAP lesions. MATERIALS AND METHODS: Six specimens were tested. A pressure sensor was used to record glenohumeral contact, and a motion analysis system was used to measure humeral head translation. Contact pressures and translations were measured during serial deltoid and biceps loads. These were repeated for small and large SLAP lesions. RESULTS: There was a notable shift in the location of peak contact pressure from the anterior-inferior glenoid to the anterior-superior glenoid with increasing deltoid load. Deltoid loading translated the humeral head posteriorly relative to the glenoid. Conversely, biceps loads countered the pull of the deltoid only when the biceps load was greater than the deltoid load. The SLAP tears did not significantly alter the degree of humeral head translation or location of the contact pressures. CONCLUSIONS: In the active compression test, the posterior capsule is taut and the anterior capsule is lax, which permits the deltoid to translate the humeral head posteriorly. This shift in the peak contact pressure to the superior glenoid may elicit a positive active compression test. LEVEL OF EVIDENCE: Basic Science Study, Biomechanics, Cadaver Model.

The anterior deltoid's importance in reverse shoulder arthroplasty: a cadaveric biomechanical study.

BACKGROUND: Frequently, patients who are candidates for reverse shoulder arthroplasty have had prior surgery that may compromise the anterior deltoid muscle. There have been conflicting reports on the necessity of the anterior deltoid thus it is unclear whether a dysfunctional anterior deltoid muscle is a contraindication to reverse shoulder arthroplasty. The purpose of this study was to determine the 3-dimensional (3D) moment arms for all 6 deltoid segments, and determine the biomechanical significance of the anterior deltoid before and after reverse shoulder arthroplasty. METHODS: Eight cadaveric shoulders were evaluated with a 6-axis force/torque sensor to assess the direction of rotation and 3D moment arms for all 6 segments of the deltoid both before and after placement of a reverse shoulder prosthesis. The 2 segments of anterior deltoid were unloaded sequentially to determine their functional role. RESULTS: The 3D moment arms of the deltoid were significantly altered by placement of the reverse shoulder prosthesis. The anterior and middle deltoid abduction moment arms significantly increased after placement of the reverse prosthesis (P < .05). Furthermore, the loss of the anterior deltoid resulted in a significant decrease in both abduction and flexion moments (P < .05). CONCLUSION: The anterior deltoid is important biomechanically for balanced function after a reverse total shoulder arthroplasty. Losing 1 segment of the anterior deltoid may still allow abduction; however, losing both segments of the anterior deltoid may disrupt balanced abduction. Surgeons should be cautious about performing reverse shoulder arthroplasty in patients who do not have a functioning anterior deltoid muscle.

Muscle fatigue in fibromyalgia is in the brain, not in the muscles: a case-control study of perceived versus objective muscle fatigue.

OBJECTIVE: To investigate relationships between perceived and objectively measured muscle fatigue during exhausting muscle contractions in women with fibromyalgia (FM) compared with healthy controls (HC). METHODS: Women with FM and HC completed an isometric muscle exhaustion task at 90° shoulder abduction. Surface electromyographic (EMG) activity in the deltoid muscle was recorded together with self-reported level of muscle fatigue. RESULTS: 25 participants with FM and 23 HC were included. Average time to exhaustion was 254 s shorter in participants with FM than in HC. Participants with FM did not exhibit the same level of objective signs of muscle fatigue, seen as fewer changes in the EMG activity, as the HC during the exhaustion task. The task did not provoke pain in the HC, while participants with FM reported a doubling of pain. CONCLUSIONS: Women with FM had shorter exhaustion times and showed fewer objective signs of muscle fatigue during an exhausting isometric shoulder abduction compared with younger HC. This indicates that perceived muscle fatigue may be of central origin and supports the notion of central nervous dysfunction as basic pathological changes in FM.

Infraspinatus fatigue during resisted arm elevation with isometric contraction: an electromyographic study.

BACKGROUND: Various forms of resistance are used in rotator cuff training programs. However, the muscular activity of the infraspinatus during arm elevation has not been clarified in detail. We aimed to evaluate infraspinatus fatigue during resisted arm elevation in various positions. METHODS: The dominant (right) shoulders of 39 healthy subjects were examined. Average mean power frequency shifts of the infraspinatus and deltoid were evaluated electromyographically when the subjects performed isometric contractions equivalent to 30% of the maximal voluntary isometric contraction force for 60 s during 90° arm elevation in the sagittal and scapular planes, prone and side-lying external rotations, and repeated side-lying external rotation exercise. Further, the arm-elevation force was measured before and after the repeated external rotation exercise. Analysis of variance and paired t tests were used for statistical analyses; differences at P < .05 were considered significant. RESULTS: The infraspinatus was fatigued easily during resisted arm elevation in the sagittal plane compared with the scapular plane (P < .01). Comparisons of sagittal-plane elevation with side-lying and prone external rotations revealed no significant differences in the fatigue levels. The arm-elevation force after the repeated external rotations was significantly decreased in the sagittal plane compared with the scapular plane (P < .01). CONCLUSION: In clinical settings, this data may be helpful in knowing how to helpful to protect the infraspinatus after surgical repair. Therefore, therapeutic exercise regimes with resisted arm elevation should avoid infraspinatus overfatigue in the sagittal plane in the early postoperative period.

Thin-filament length correlates with fiber type in human skeletal muscle.

Force production in skeletal muscle is proportional to the amount of overlap between the thin and thick filaments, which, in turn, depends on their lengths. Both thin- and thick-filament lengths are precisely regulated and uniform within a myofibril. While thick-filament lengths are essentially constant across muscles and species (∼1.65 µm), thin-filament lengths are highly variable both across species and across muscles of a single species. Here, we used a high-resolution immunofluorescence and image analysis technique (distributed deconvolution) to directly test the hypothesis that thin-filament lengths vary across human muscles. Using deltoid and pectoralis major muscle biopsies, we identified thin-filament lengths that ranged from 1.19 ± 0.08 to 1.37 ± 0.04 µm, based on tropomodulin localization with respect to the Z-line. Tropomodulin localized from 0.28 to 0.47 µm further from the Z-line than the NH(2)-terminus of nebulin in the various biopsies, indicating that human thin filaments have nebulin-free, pointed-end extensions that comprise up to 34% of total thin-filament length. Furthermore, thin-filament length was negatively correlated with the percentage of type 2X myosin heavy chain within the biopsy and shorter in type 2X myosin heavy chain-positive fibers, establishing the existence of a relationship between thin-filament lengths and fiber types in human muscle. Together, these data challenge the widely held assumption that human thin-filament lengths are constant. Our results also have broad relevance to musculoskeletal modeling, surgical reattachment of muscles, and orthopedic rehabilitation.

Electromyographic validation of the deltoid (anterior portion) and pectoralis major (clavicular portion) in military press exercises with open and middle grips

The deltoid (anterior portion) and pectoralis major (clavicular portion) were evaluated in several execution ways of military press exercises with open and middle grips in order to know their behavior pattern. It was analyzed 24 male volunteers, using a 2-channel TECA TE4 electromyograph and Hewllet Packard surface electrodes. It was observed that the execution variation with open and middle grips does not present any significant difference as for the demanding level neither for the pectoralis major muscle nor the deltoid muscle.