Usage and acceptability of data normalization in baseball pitching.

In baseball pitching biomechanics, kinetic values are commonly ratio 'normalised' by dividing by mass or mass*height to allow for comparison between athletes of different sizes. However, creating a normalised ratio variable should meet certain statistical assumptions. Our purpose was to determine if elbow valgus torque predicted by pitching velocity is influenced by normalisation using regression model comparison with and without normalised torque values. Motion capture data for youth to professional pitchers (n = 1988) were retrospectively analysed. Normalisation assumptions were tested by comparing linear regression models to analogous models with an intercept fixed at zero and by examining remaining correlations between the confounding variable and new, normalised variable. Both mass (p < 0.001) and mass*height (p < 0.001) normalisation did not remove their respective relationship with torque. After accounting for mass or mass and height, velocity predicted 10% of variance in elbow valgus torque, whereas velocity predicted 59% of mass normalised torque and 45% of mass*height normalised torque. Ratio normalisation does not fully account for anthropometric variables that differ across pitchers and leads to different conclusions in the magnitude of velocity's predictive effect on elbow valgus torque. Therefore, we recommend using regression model comparison to account for anthropometric variables in baseball pitching kinetic data.

Experimentally Induced Pain Results in Reduced Activity of the Rotator Cuff Muscles in Healthy Subjects.

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.

Joint Position Accuracy Is Influenced by Visuoproprioceptive Congruency in Virtual Reality.

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.

Clinical Outcomes and Shoulder Kinematics for the "Gray Zone" Extra-articular Scapula Fracture in 5 Patients.

AIMS: There is a subset of scapula fractures, which can be considered in the "gray zone," where treatment guidelines are not clear-cut, based on published literature. Our paper presents the outcomes of five such scapula fractures treated non-operatively. METHODS: Adult patients who had been treated non-operatively at our institution for an isolated scapula fracture from 2003-2012 were found using Current Procedural Terminology (CPT) codes. Based on injury imaging, these five patients had scapula fractures in the "gray zone."Subjects completed questionnaires [Simple Shoulder Test (SST), PROMIS Global Health Scale vs 1.1, PROMIS SF vs 1.0 Physical Function 12a, and the American Shoulder and Elbow Surgeons Score (ASES)] and physical exams were performed to assess range of motion and strength. Glenohumeral kinematics were obtained via motion analysis using the Trackstar 6 Degree of Freedom (DOF) motion tracking system by Northern Digital Incorporated. RESULTS: All subjects were right hand dominant. 3/5 fractures involved left, non-dominant, scapulae. Motion analysis demonstrated similar recruitment of the scapula during the glenohumeral rhythm for the fractured shoulders compared with the same arm of age matched control subjects. No significant differences occurred in either range of motion (ROM) or scapula-humeral coordination when comparing uninjured scapulae to the same arm of age matched control subjects. CONCLUSIONS: All subjects' demonstrated acceptable clinical outcomes when treated non-operatively. Minor differences were seen in subjective surveys. However, the kinematic analysis showed no differences in measured scapula-humeral rhythm or range of motion. It is proposed that immediate controlled range of motion and rehabilitation be considered in these patients and could be the focus of a larger prospective study. LEVEL OF EVIDENCE: Level IV (Case Series).

Shoulder and elbow joint position sense assessment using a mobile app in subjects with and without shoulder pain - between-days reliability.

OBJECTIVES: To determine between-days reliability and the minimal detectable change for shoulder and elbow joint position sense assessment using a validated mobile app, in subjects with and without shoulder pain. DESIGN: Reliability study. SETTING: Clinical measurement. PARTICIPANTS: Subjects with (n = 25) and without shoulder pain (n = 29). MAIN OUTCOME MEASURES: Subjects were assessed by the same examiner in two sessions, with one-week interval. Active joint repositioning tests of shoulder flexion and scaption and elbow flexion were assessed at the target-angles of 50°, 70°, 90° and 110°. Intra-class correlation coefficient, standard error of measurement and minimal detectable change were calculated for constant, absolute, total and variable errors. RESULTS: Good to excellent reliability was found for constant, absolute and total errors at the target-angle of 50° of scaption for healthy subjects; at 110° of shoulder flexion and all target-angles for elbow for both groups. CONCLUSIONS: The mobile app is a reliable tool and may be useful for assessing shoulder joint position sense mainly at 110° of flexion and for elbow between 50° and 110° of flexion in subjects with and without shoulder pain. Minimal detectable changes were demonstrated and may help clinicians to follow-up rehabilitation and researchers to interpret findings of studies.

Feasibility of using a fully immersive virtual reality system for kinematic data collection.

Commercially-available Virtual Reality (VR) systems have the potential to be effective tools for simultaneous visual manipulation and kinematic data collection. Previously, these systems have been integrated with research-grade motion capture systems to provide both functionalities; however, they are yet to be used as stand-alone systems for kinematic data collection. The present study aimed to validate the HTC VIVE VR system for kinematic data collection by evaluating the accuracy of its position and orientation signals. The VIVE controller and tracker were each compared to a Polhemus Liberty magnetic tracking system sensor for angular and translational measurement error and signal drift. A sensor from each system was mounted to opposite ends of a rigid segment which was driven through fifty rotations and fifty translations. Mean angular errors for both the VIVE tracker and controller were below 0.4°. Mean translational error for both sensors was below 3 mm. Drift in the Liberty signal components was consistently lower than drift in VIVE components. However, all mean rotational drift measures were below 0.1° and all mean translational measures were below 0.35 mm. These data indicate that the HTC VIVE system has the potential to be a valid and reliable means of kinematic data collection. However, further investigation is necessary to determine the VIVE's suitability for capturing extremely minute or high-volume movements.

Kinesio taping of the deltoid does not reduce fatigue induced deficits in shoulder joint position sense.

BACKGROUND: Muscle fatigue is known to decrease shoulder proprioceptive acuity, potentially contributing to injuries. It has been suggested that Kinesio taping can improve proprioception. Therefore, the aim of this study was to investigate the effects of Kinesio taping on shoulder joint position sense after muscle fatigue. METHODS: Twenty-four healthy subjects were evaluated in a randomized, crossover, single-blind study design. Shoulder joint position sense was assessed during active repositioning tests at the target angles of 50°, 70° and 90° of arm elevation in scapular plane, in three sessions: control (no taping), Kinesio taping (Kinesio taping applied over the deltoid muscle with tension) and sham (Kinesio taping applied over deltoid without tension). Joint position sense was assessed three times: before taping; following taping application or rest, in the control session; and following a fatigue protocol. The constant error (repositioned angle-target angle) was considered for statistical analysis, using a 3-way repeated-measure ANOVA (within subject factors: taping, time and target angle). FINDINGS: There was no interaction or main effect involving taping. An interaction between time and angle was found and the simple effect showed that the constant error increased following fatigue at 70° and 90°, but not at 50°. INTERPRETATION: The results of this study does not support the use of Kinesio taping applied over the deltoid muscle for compensating or preventing shoulder joint position sense deficits caused by muscle fatigue of shoulder abductors.

Humeral head translation after a suprascapular nerve block.

Subacromial impingement syndrome is the most common shoulder disorder. Abnormal superior translation of the humeral head is believed to be a major cause of this pathology. The first purpose of the study was to examine the effects of suprascapular nerve block on superior translation of the humeral head and scapular upward rotation during dynamic shoulder elevation. The secondary purpose was to assess muscle activation patterns during these motions. Twenty healthy subjects participated in the study. Using fluoroscopy and electromyography, humeral head translation and muscle activation were measured before and after a suprascapular nerve block. The humeral head was superiorly located at 60 degrees of humeral elevation, and the scapula was more upwardly rotated from 30 to 90 degrees of humeral elevation after the block. The differences were observed during midrange of motion. In addition, the deltoid muscle group demonstrated increased muscle activation after the nerve block. The study's results showed a compensatory increase in humeral head translation, scapular upward rotation, and deltoid muscle activation due to the nerve block. These outcomes suggest that increasing muscular strength and endurance of the supraspinatus and infraspinatus muscles could prevent any increased superior humeral head translation. This may be beneficial in reducing shoulder impingement or rotator cuff tears over time.

Sensors on the humerus are not necessary for an accurate assessment of humeral kinematics in constrained movements.

The measurement of humeral kinematics with a sensor on the humerus is susceptible to large errors due to skin motion artifacts. An alternative approach is to use data from a forearm sensor, combined with data from either a scapular or thoracic sensor. We used three tasks to assess the errors of these approaches: humeral elevation, elbow flexion and humeral internal rotation. Compared with the humeral method, the forearm methods (using either a scapular or thoracic sensor) demonstrated significantly smaller root mean square errors in humeral elevation and humeral internal rotation tasks. Although the errors of the forearm methods were significantly larger than those of the humeral method during elbow flexion, the errors of the forearm methods still were below 3°. Therefore, these forearm methods may be able to accurately measure humeral motion. In addition, since no difference was found between the forearm methods using the scapular or thoracic sensor, it may be possible to accurately assess both shoulder and elbow kinematics with only two sensors: one on the forearm and one on the scapula.

Similarities in the neural control of the shoulder and elbow joints belie their structural differences.

Movement of the hand in three dimensional space is primarily controlled by the orientation of the shoulder and elbow complexes. Due to discrepancies in proprioceptive acuity, overlap in motor cortex representation and grossly different anatomies between these joints, we hypothesized that there would be differences in the accuracy of aimed movements between the two joints. Fifteen healthy young adults were tested under four conditions - shoulder motion with the elbow constrained and unconstrained, and elbow motion with the shoulder constrained and unconstrained. End point target locations for each joint were set to coincide with joint excursions of 10, 20 or 30 degrees of either the shoulder or elbow joint. Targets were presented in a virtual reality environment. For the constrained condition, there were no significant differences in angular errors between the two joints, suggesting that the central nervous system represents linked segment models of the limb in planning and controlling movements. For the unconstrained condition, although angle errors were higher, hand position errors remained the same as those of the constrained trials. These results support the idea that the CNS utilizes abundant degrees of freedom to compensate for the potentially different contributions to end-point errors introduced by each joint.

Understanding the biomechanical nature of musculoskeletal tissue.

This article provides a general overview of the biomechanical principles associated with hand therapy. Specifically, it reviews the basic topics of material properties (including both theoretical principles and practical concepts), static analysis (including forces, moments, muscle forces, and Newton's laws), and ends with a clinical example involving analysis of the risk of damage to the A3 pulley.

Wrist activity monitor counts are correlated with dynamic but not static assessments of arm elevation exposure made with a triaxial accelerometer.

There is evidence in the literature of a link between workplace arm elevation exposure and atraumatic shoulder injuries. However, there are several methods that can be used to assess this exposure. The goal of the present study was to compare the outcomes of an activity monitor attached to the wrist and a triaxial accelerometer mounted on the humerus. Twenty-one workers wore both sensors over the course of a full workday. While the activity monitor data was not significantly correlated with any static humeral parameters, it was strongly correlated with all dynamic parameters. The use of a simple, commercially available activity monitor might offer an inexpensive alternative for the assessment of a large number of subjects over multiple workdays to determine the relationship between dynamic motion and occupation shoulder injuries in the future. PRACTITIONER SUMMARY: Arm overuse has been linked to occupation-related shoulder injuries. An activity monitor attached to the wrist and a triaxial accelerometer mounted on the humerus were compared in a field trial. The results demonstrate that, under certain conditions, a commercially available activity monitor might be a useful tool for exposure assessment.

Scapular kinematics and subacromial-impingement syndrome: a meta-analysis.

CONTEXT: The literature does not present a consistent pattern of altered scapular kinematics in patients with shoulder-impingement syndrome (SIS). OBJECTIVES: To perform meta-analyses of published comparative studies to determine the consistent differences in scapular kinematics between subjects with SIS and controls. In addition, the purpose was to analyze factors of the data-collection methods to explain the inconsistencies in reported kinematics. The results of this study will help guide future research and enable our understanding of the relationship between scapular kinematics and SIS. EVIDENCE ACQUISITION: A search identified 65 studies; 9 papers met inclusion criteria. Sample sizes, means, and SDs of 5 scapular-kinematic variables were extracted or obtained from each paper's lead author. Standard difference in the mean between SIS and controls was calculated. Moderator variables were plane of arm elevation, level of arm elevation (ARM) and population (POP). EVIDENCE SYNTHESIS: Overall, the SIS group had less scapular upward rotation (UR) and external rotation (ER) and greater clavicular elevation (ELE) and retraction (RET) but no differences in scapular posterior tilt (PT). In the frontal plane, SIS subjects showed greater PT and ER, and in the scapular plane, less UR and ER and greater ELE and RET. There was also greater ELE and RET in the sagittal plane. There was less UR at the low ARM and greater ELE and RET at the high ARM with SIS. Athletes and overhead workers showed less UR, while athletes showed greater PT and workers showed less PT and ER. The general population with SIS had greater ELE and RET only. CONCLUSIONS: Subjects with SIS demonstrated altered scapular kinematics, and these differences are influenced by the plane, ARM, and POP. Athletes and overhead workers have a different pattern of scapular kinematics than the general population. The scapular plane is most likely to demonstrate altered kinematics. These factors should be considered when designing futures studies to assess the impact of altered kinematics in patients with SIS.

Three-dimensional repositioning tasks show differences in joint position sense between active and passive shoulder motion.

Proprioception is important in maintaining shoulder joint stability. Previous studies investigated the effects of unconstrained multiplanar motion, with subjects able to move freely in space, on repositioning tasks for active shoulder motion but not passive motion. We sought to further explore joint position sense with 3D passive, robot-guided motions. We hypothesized that target repositioning error would be greater in the case of passively placed targets than for actively placed targets. To investigate, 15 healthy individuals participated (8 female, 7 male), who were at most 6 ft (183 cm) tall to accommodate the equipment, and who had no history of shoulder injury, surgery, or significant participation in throwing sports. Target orientations were centered at 44° of elevation and 32° of horizontal rotation from the frontal plane. Two sets of 10 trials were performed. The first set involved active placement followed by active replacement, and the second set involved passive, robot-guided, placement followed by active replacement. Repositioning error was greater following passive placement than active placement (p < 0.001). These results further our understanding of the differences between active and passive joint position sense at the shoulder.

Altered scapular orientation during arm elevation in patients with insidious onset neck pain and whiplash-associated disorder.

STUDY DESIGN: Controlled laboratory study using a cross-sectional design. OBJECTIVES: To investigate whether there is a pattern of altered scapular orientation during arm elevation in patients with insidious onset neck pain (IONP) and whiplash-associated disorder (WAD) compared to asymptomatic people. BACKGROUND: Altered activity in the axioscapular muscles and impairments in scapular orientation are considered to be important features in patients with cervical disorders. Scapular orientation has until now not been investigated in these patients. METHODS: A 3-dimensional tracking device measured scapular orientation during arm elevation in patients with IONP (n = 21) and WAD (n = 23). An asymptomatic group was selected for comparison (n = 20). RESULTS: The groups demonstrated a significantly reduced clavicle retraction on the dominant side compared to the nondominant side. The WAD group demonstrated an increased elevation of the clavicle compared to the asymptomatic group and the IONP group, and reduced scapular posterior tilt on the nondominant side compared to the IONP group. CONCLUSION: Altered dynamic stability of the scapula may be present in patients with cervical disorders, which may be an important mechanism for maintenance of recurrence or exacerbation of symptoms in these patients. Patients with cervical disorders may demonstrate a difference in impairments, based on their diagnosis of IONP or WAD.

The reliability of side to side measurements of upper extremity activity levels in healthy subjects.

BACKGROUND: In both clinical and occupational settings, ambulatory sensors are becoming common for assessing all day measurements of arm motion. In order for the motion of a healthy, contralateral side to be used as a control for the involved side, the inherent side to side differences in arm usage must be minimal. The goal of the present study was to determine the reliability of side to side measurements of upper extremity activity levels in healthy subjects. METHODS: Thirty two subjects with no upper extremity pathologies were studied. Each subject wore a triaxial accelerometer on both arms for three and a half hours. Motion was assessed using parameters previously reported in the literature. Side to side differences were compared with the intraclass correlation coefficient, standard error of the mean, minimal detectable change scores and a projected sample size analysis. RESULTS: The variables were ranked based on their percentage of minimal detectable change scores and sample sizes needed for paired t-tests. The order of these rankings was found to be identical and the top ranked parameters were activity counts per hour (MDC% = 9.5, n = 5), jerk time (MDC% = 15.8, n = 8) and percent time above 30 degrees (MDC% = 34.7, n = 9). CONCLUSIONS: In general, the mean activity levels during daily activities were very similar between dominant and non-dominant arms. Specifically, activity counts per hour, jerk time, and percent time above 30 degrees were found to be the variables most likely to reveal significant difference or changes in both individuals and groups of subjects. The use of ambulatory measurements of upper extremity activity has very broad uses for occupational assessments, musculoskeletal injuries of the shoulder, elbow, wrist and hand as well as neurological pathologies.

In vivo measurement of humeral elevation angles and exposure using a triaxial accelerometer.

OBJECTIVE: The aim of this study was to measure the capability of a triaxial accelerometer (Virtual Corset) to collect humeral elevation angles and exposure parameters in a simulated occupational environment. BACKGROUND: There is a need for an economical ambulatory device to estimate elevation angles and exposure parameters in occupational groups. METHOD: A magnetic tracking device was used to assess the ability of the Virtual Corset to evaluate humeral elevation angles and identify exposure parameters with in vivo dynamic conditions for 16 female dental hygienists. RESULTS: Significant differences were found for the reaching task with the Virtual Corset, underestimating the means of the average humeral elevation angle by 10 degrees and the means for the range of the humeral elevation by 4 degrees. Furthermore, significant differences were found for the exposure parameters with the Virtual Corset, overestimating the jerk by 4% and underestimating the percentage time above 40 degrees and 60 degrees by 9% and 4%, respectively. However, the Virtual Corset was able to identify similar kinematics patterns and exposure data when compared with a magnetic tracking device. CONCLUSION: The outcomes of the study suggest that the Virtual Corset may be useful for data collection during a dental hygienist workday. Professions that have similar patterns of angular velocity and acceleration and humeral range of elevation as the dental hygienist flossing technique may benefit from the use of the Virtual Corset. APPLICATION: This study provides evidence that the Virtual Corset can be used to reconstruct humeral elevation angles and identify exposure parameters in some tasks of dental hygienists.

Measuring humeral head translation using fluoroscopy: a validation study.

Numerous techniques have been employed to monitor humeral head translation due to its involvement with several shoulder pathologies. However, most of the techniques were not validated. The objective of this study is to compare the accuracy of manual digitization and contour registration in measuring superior translation of the humeral head. Eight pairs of cadaver scapulae and humerii bones were harvested for this study. Each scapula and humerus was secured in a customized jig that allowed for control of humeral head translations and a vise that permitted rotations of the scapula about three axes. Fluoroscopy was used to take images of the shoulder bones. Scapular orientation was manipulated in different positions while the humerus was at 90 degrees of humeral elevation in the scapular plane. Humeral head translation was measured using the two methods and was compared to the known translation. Additionally, accuracy of the contour registration method to measure 2-D scapular rotations was assessed. The range for the root mean square (RMS) error for manual digitization method was 0.27 mm-0.43 mm and the contour registration method had a RMS error ranging from 0.18 mm-0.40 mm. In addition, the RMS error for the scapular angle rotation using the contour registration method was 2.4 degrees . Both methods showed acceptable errors. However, on average, the contour registration method showed lesser measurement error compared to the manual digitization method. In addition, the contour registration method was able to show good accuracy in measuring rotation that is useful in 2-D image analysis.

Scapular kinematics in constrained and functional upper extremity movements.

STUDY DESIGN: Controlled laboratory study using a single-group, repeated-measures design. OBJECTIVES: To investigate scapular kinematics during both constrained and functional shoulder movements. BACKGROUND: Abnormal scapulothoracic joint motion has been associated with pathologies such as shoulder impingement. Constrained protocols are commonly used in the measurement of shoulder kinematics; however, few studies have measured motion during functional tasks. METHODS: Twenty-five healthy subjects participated in this study. Three-dimensional kinematic data from the scapula and humerus with respect to the thorax were collected with a magnetic tracking system. Functional testing consisted of 6 different tasks representing common activities of daily living. Constrained testing consisted of at least 42 arm elevations in various planes. Two-way analyses of variance with repeated measures were used to compare scapular rotations between constrained and functional movements at the same humeral elevation and plane of elevation angles. Intersubject variability was compared between the overhead tasks and the constrained humeral elevation in the scapular plane by using the coefficient of multiple correlations. RESULTS: Significant differences between constrained trials and functional tasks were found for all scapular rotations. A similar pattern was observed for scapular rotations variability between overhead tasks and constrained arm elevation in the scapular plane. CONCLUSION: Care needs to be taken when comparing and generalizing scapular kinematic data from constrained humeral movements and applying it to functional humeral movements.

Differences in feedforward trunk muscle activity in subgroups of patients with mechanical low back pain.

OBJECTIVE: To investigate alterations in trunk muscle timing patterns in subgroups of patients with mechanical low back pain (MLBP). Our hypothesis was that subjects with MLBP would demonstrate delayed muscle onset and have fewer muscles functioning in a feedforward manner than the control group. We further hypothesized that we would find differences between subgroups of our patients with MLBP, grouped according to diagnosis (segmental instability and noninstability). DESIGN: Case-control. SETTING: Laboratory. PARTICIPANTS: Forty-three patients with chronic MLBP (25 instability, 18 noninstability) and 39 asymptomatic controls. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Surface electromyography was used to measure onset time of 10 trunk muscles during a self-perturbation task. Trunk muscle onset latency relative to the anterior deltoid was calculated and the number of muscles functioning in feedforward determined. RESULTS: Activation timing patterns (P<.01; eta=.50; 1-beta=.99) and number of muscles functioning in feedforward (P=.02; eta=.30; 1-beta=.83) were statistically different between patients with MLBP and controls. The control group activated the external oblique, lumbar multifidus, and erector spinae muscles in a feedforward manner. The heterogeneous MLBP group did not activate the trunk musculature in feedforward, but responded with significantly delayed activations. MLBP subgroups demonstrated significantly different timing patterns. The noninstability MLBP subgroup activated trunk extensors in a feedforward manner, similar to the control group, but significantly earlier than the instability subgroup. CONCLUSIONS: Lack of feedforward activation of selected trunk musculature in patients with MLBP may result in a period of inefficient muscular stabilization. Activation timing was more impaired in the instability than the noninstability MLBP subgroup. Training specifically for recruitment timing may be an important component of the rehabilitation program.