Search

Shoulder pain is a complex, prevalent problem that is multifactorial in nature. While there are many potential causes, one common suspect is the rotator cuff musculature. The purpose of the present study was to induce pain in the supraspinatus muscle of healthy subjects and observe the resulting changes in muscle activity. Eight muscles on 23 subjects were assessed using electromyography: anterior, middle, and posterior deltoid; pectoralis major; upper trapezius; latissimus dorsi; serratus anterior; supraspinatus; and infraspinatus. It was hypothesized that the rotator cuff muscles would display reduced activity during pain, and that reductions in activity would remain after the pain had dissipated. Both of the rotator cuff muscles measured did indeed display reduced activity in a majority of the dynamic, isometric, and maximal contractions. Many of those reductions remained after the pain had subsided. [ABSTRACT FROM AUTHOR]

The present study investigated the effect of visual offset (visuo-proprioceptive mismatch) in joint repositioning task in a three-dimensional virtual reality (VR) environment when participants were instructed to ignore vision. Twenty-five physically healthy young individuals performed shoulder joint position sense test. Repositioning accuracy was tested under two visual conditions, accurate and offset visions, and two instructions, no guidance or ignore vision. In accurate vision trials, the virtual hand of the tested limb seen in VR was congruent with where the participant placed their hand. In the offset vision condition, the virtual hand was seen 8° above or below their actual hand in the vertical plane. Repositioning error (i.e. constant error) in offset vision trials was lower when the participants were instructed to ignore vision compared to when no instruction about the visual offset was given (p < 0.001). However, constant error in offset vision trials was larger than accurate vision trials when the participants tried to ignore vision in both visual conditions (p < 0.001). Our results suggest that humans may be able to down-weight vision to some extent by conscious effort, while the influence of vision is difficult to eliminate when vision is present. [ABSTRACT FROM AUTHOR]

Context: Shoulder muscle activation in patients with subacromial impingement is highly cited and variable in the literature. Differences between studies could be due to artifacts introduced by normalization practices in the presence of pain. Ultimately, this lack of knowledge pertaining to pathogenesis limits the clinical treatment and restoration of muscular function. Design: A total of 21 patients with stage 2 subacromial impingement and 21 matched controls were recruited for EMG testing of their affected shoulder during an arm elevation task. The patients were tested before and after receiving an injection to their subacromial bursa. Methods: The EMG from 7 shoulder muscles were measured before and after treatment during humeral motion in the scapular plane. Results: Our findings indicate an increase in anterior deltoid, middle deltoid, and upper trapezius activity following the injection; further, this trend extended to the controls. The control subjects had a greater activation of the latissimus dorsi at peak arm elevation when compared with the patient group postinjection. Conclusions: Our results indicate that a reduction in subacromial pain is associated with changes in shoulder muscle recruitment, primarily of the deltoid. This change in deltoid activity may lend evidence to rotator cuff function in patients without rotator cuff tears. [ABSTRACT FROM AUTHOR]

The objective of this study was to explore whether hypersensitivity in patients with subacromial pain syndrome (SPS) manifests purely as localized peripheral sensitization or central sensitization, is influenced by the presence of subacromial pain, and presents similarly in male and female patients. Pressure pain threshold was assessed in both a patient cohort with unilateral SPS and an uninjured matched control group. Control subjects were assessed twice, with a 15 minute rest period between testing, while patients were assessed at baseline and after an almost instantaneous reduction in pain arising from an anesthetic injection in patients. Patients received a subacromial injection consisting of both anesthetics (3 cc of 2% lidocaine and 6 cc 0.5% Marcaine with Epinephrine) and a corticosteroid agent (1 cc DepoMedrol). Patients demonstrated hypersensitivity across the involved shoulder only, providing evidence for peripheral sensitization. There were trends for hypersensitivity across remote joints, however when separated by sex, only female patients demonstrated both peripheral and central sensitization. Immediate pain reduction had no influence on hypersensitivity in the short‐term. Clinical Significance: Neuropathic components are likely present in some patients with subacromial pain syndrome, and female patients may be particularly at risk for presenting with neuropathic pain. These findings are applicable towards understanding the heterogeneous etiology underlying subacromial pain syndrome and informing clinical management. [ABSTRACT FROM AUTHOR]

Proprioception is assessed more often through joint position sense and kinesthesia than force sense. The purpose of this study is to investigate force sense at the shoulder. A total of 12 subjects were recruited. An ipsilateral force reproduction protocol at the shoulder at 50°, 70°, and 90° and 120%, 140%, and 160% baseline torque. Dependent variables were constant error (CE) and root mean square error. An effect was found for load on absolute (p = .001) and normalized CE (p < .001). CE decreased with increased load. An effect for angle was found for absolute root mean square error (p = .002), more accurate at 50° (p = .01), but no effect when normalized (p = .19). With increased loads, subjects undershot the target and CE approached zero. Because of the differing behavior in CE and root mean square error, and absolute and normalized data, force sense studies should examine error from these perspectives. [ABSTRACT FROM AUTHOR]

Context: The relationship between overhead throwing and its effect on proprioception is not well understood. It is important to gain a better understanding of how these are related, to protect overhead athletes from an increased risk of injury. Objective: To investigate proprioceptive alterations in the overhead thrower’s shoulder. Design: Cross-sectional study. Independent variables are limb (dominant and nondominant), group (thrower or control), and target angle. Dependent variables are joint position sense and range of motion. Setting: An orthopedic biomechanics lab and university athletic training facility. Participants: Twelve Division I baseball pitchers and 13 nonthrowing control subjects. Intervention: Shoulder proprioception was assessed using an active joint repositioning task administered with an iPod Touch. Main Outcome Measure: Root mean square error and constant error of repositioning angles were used to assess accuracy and directional patterns, respectively. Results: Both groups demonstrated significantly higher joint acuity at the 80° external rotation target angle compared with 60° (1.5° [0.5°], P =.01). There were no differences in accuracy between groups. Constant error revealed differing repositioning patterns between limbs for the pitchers and also between groups for the dominant side. Although the throwing shoulder overshot the target angles by 0.4°, all nonthrowing shoulders undershot by an average of 2.7°. Conclusions: There is no difference in shoulder joint position sense accuracy between throwers and nonthrowers, although both groups display increased accuracy closer to their end range of external rotation. The throwing shoulder demonstrates a different repositioning pattern, overshooting the desired target angle, while all other shoulders undershoot. [ABSTRACT FROM AUTHOR]

ABSTRACT. Joint position sense (JPS) is important in the maintenance of optimal movement coordination of limb segments in functional activities. Researchers have shown that the sensitivity of musculotendinous mechanoreceptors increases [...]

The EMG and load relationship is commonly measured with multiple submaximal isometric contractions. This method is both time consuming and may introduce fatigue. The purpose of this study was to determine if the electromyography (EMG) amplitude from the middle deltoid was reliable during isometric ramp contractions (IRCs) at different angles of elevation and rates of force application. Surface EMG was measured at 3 shoulder elevation angles during IRCs at 4 submaximal levels of maximum voluntary contraction (MVC). Data were reliable in all conditions except during the rate relative to the subjects' MVC at 90° for 30% and 40% MVC. The main effect for angle on EMG amplitude was found to be significant, p < .01. EMG at 90° was greater than at 60° (p < .017) and at 30° (p < .017). The main effect of force level on EMG amplitude was significant, p < .01 and follow-up contrast demonstrated a significant (p < .001) linear increase of EMG amplitude with force level. We conclude that EMG amplitude from IRCs are reliable across all shoulder elevation angles and up to 40% MVC. IRCs are a feasible method for recording EMG at the deltoid. [ABSTRACT FROM AUTHOR]

While synchronous movement of the glenohumeral and scapulothoracic joints has been emphasized in previous kinematics studies, most investigations of shoulder joint position sense have treated the shoulder complex as a single joint. The purposes of this study were to investigate the joint position sense errors of the humerothoracic, glenohumeral, and scapulothoracic joints at different elevation angles and to examine whether the errors of the glenohumeral and scapulothoracic joints contribute to the errors of the humerothoracic joint. Fifty-one subjects with healthy shoulders were recruited. Active joint position sense of the humerothoracic, glenohumeral, and scapulothoracic joints was measured at 50°, 70°, and 90° of humerothoracic elevation in the scapular plane. The results showed that while scapulothoracic joint position sense errors were not affected by target angles, there was an angle effect on humerothoracic and glenohumeral errors, with errors decreasing as the target angles approached 90° of elevation. The results of a multiple regression analysis revealed that glenohumeral errors explained most of the variance of the humerothoracic errors and that scapulothoracic errors had a weaker predictive relationship with humerothoracic errors. Therefore, it may be necessary to test scapular joint position sense separately in addition to the assessment of the overall shoulder joint position sense. [ABSTRACT FROM AUTHOR]

Nucleus replacement by a synthetic material is a recent trend for treatment of lower back pain. Hydrogel nucleus implants were prepared with variations in implant modulus, height, and diameter Human lumbar intervertebral discs (IVDs) were tested in compression for intact, denucleated, and implanted condition. Implantation of nucleus implants with different material and geometric parameters into a denucleated IVD significantly altered the IVD compressive stiffness. Variations in the nucleus implant parameters significantly change the compressive stiffness of the human lumbar IVD. Implant geometrical variations were more effective than those of implant modulus variations in the range examined. Keywords: Lumbar Spine, Intervertebral Disc, Nucleus Pulposus, Hydrogel Nucleus Implant, Compressive Stiffness, Lower Back Pain

Weighted integration of visual and proprioceptive information is important in movement planning and execution. The present study used a virtual reality system to determine how upper limb movement consistency and accuracy are altered when (a) vision of the limb is removed and (b) proprioception and vision of the limb are misaligned. A one degree of freedom upper limb movement task was performed under three visual conditions of the limb; accurate vision, no vision, and offset vision. Movement consistency was unaltered by the change in visual condition. Compared to the accurate vision condition, movement accuracy was unchanged in the no vision condition but decreased with a visual offset. When available, vision was relied upon more heavily than proprioception for task completion. [ABSTRACT FROM AUTHOR]

In this study, we aimed to determine if electromyography (EMG) normalization to maximal voluntary isometric contractions (MVIC) was influenced by subacromial pain in patients with subacromial impingement syndrome. Patients performed MVICs in unique testing positions for each shoulder muscle tested before and after subacromial injection of local anesthetic. In addition to collection of MVIC data, EMG data during an arm elevation task were recorded before and after injection. From a visual analog pain scale, patients had a 64% decrease in pain following the injection. Significant increases in MVICs were noted in 4 of the 7 shoulder muscles tested: anterior, middle and posterior deltoid, and lower trapezius. No significant differences were noticed for the upper trapezius, latissimus dorsi, or serratus anterior. MVIC condition (pre and post injection) had a significant influence on EMG normalization for the anterior deltoid and lower trapezius muscle. Results indicate that subacromial pain can influence shoulder muscle activity, especially for the deltoid muscles and lower trapezius. In addition, normalization to MVIC in the presence of pain can have unpredictable results. Caution should be taken when normalizing EMG data to MVIC in the presence of pain. [ABSTRACT FROM AUTHOR]