The effects of hand dominance, fatigue, and sex on muscle activation during a repetitive overhead fatiguing task

Previous studies have shown that the dominant arm is generally stronger and more resistant to fatigue. However, whether there are side differences in shoulder muscle activation during a fatiguing upper limb task, and whether this varies according to sex, is unknown. Thirty right-handed adults (15 females) were recruited to complete two sessions of an overhead repetitive fatiguing task (shoulder flexion between 90 and 135° at 1 Hz), performed in two separate sessions with their dominant arm (DA) and non-dominant arm (NDA) until exhaustion. Electromyographic (EMG) data was collected from 11 shoulder muscles of the moving arm, and their activation amplitude (RMS) and activation variability (SD) were assessed. Results show that time to exhaustion was not affected by arm or by sex. There were some main arm effects on EMG activity amplitude, with higher activity on the DA's pectoralis major (p < 0.001), and on the NDA's middle (p = 0.009) and posterior deltoid (p = 0.001) and infraspinatus (p < 0.001). The pectoralis major was affected by arm and fatigue mostly in males. Their DA's pectoralis major activity amplitude was higher, and the amplitude variability was lower, compared to the NDA, with both parameters showing fatigue-dependent decreases at the NDA only (arm x sex x fatigue: RMS: p = 0.007; SD: p = 0.001). As for females, the DA variability of their lower trapezius was smaller, and that of their subscapularis was higher, compared to the NDA (sex x arm, p = 0.028, p = 0.05). There was also more EMG variability on the supraspinatus' dominant side, and on the posterior deltoid and infraspinatus ND side. Results show an overhead shoulder flexion task dependency on pectoralis major control in males, and on lower trapezius and shoulder girdle stabilizers in females, which could be related to both sex- and gender-based factors. This knowledge can help identify side-specific injury risk factors due to overhead work in males and females, and help determine the appropriateness of implementing sex-specific workplace protocols, including alternating arms as fatigue compensatory and recovery strategies.

Manual praxis and language-production networks, and their links to handedness

While Liepmann was one of the first researchers to consider a relationship between skilled manual actions (praxis) and language for tasks performed "freely from memory", his primary focus was on the relations between the organization of praxis and left-hemisphere dominance. Subsequent attempts to apply his apraxia model to all cases he studied - including his first patient, a "non-pure right-hander" treated as an exception - left the praxis-handedness issue unresolved. Modern neuropsychological and recent neuroimaging evidence either showed closer associations of praxis and language, than between handedness and any of these two functions, or focused on their dissociations. Yet, present-day developments in neuroimaging and statistics allow us to overcome the limitations of the earlier work on praxis-language-handedness links, and to better quantify their interrelationships. Using functional magnetic resonance imaging (fMRI), we studied tool use pantomimes and subvocal word generation in 125 participants, including righthanders (N_RH = 52), ambidextrous individuals (mixedhanders; N_MH = 31), and lefthanders (N_LH = 42). Laterality indices were calculated both in two critical cytoarchitectonic maps, and 180 multi-modal parcellations of the human cerebral cortex, using voxel count and signal intensity, and the most relevant regions of interest and their networks were further analyzed. We found that atypical organization of praxis was present in all handedness groups (RH = 25.0%, MH = 22.6%; LH = 45.2%), and was about two and a half times as common as atypical organization of language (RH = 3.8%; MH = 6.5%; LH = 26.2%), contingent on ROI selection/LI-calculation method. Despite strong associations of praxis and language, regardless of handedness and typicality, dissociations of atypically represented praxis from typical left-lateralized language were common (~20% of cases), whereas the inverse dissociations of atypically represented language from typical left-lateralized praxis were very rare (in ~2.5% of all cases). The consequences of the existence of such different phenotypes for theoretical accounts of manual praxis, and its links to language and handedness are modeled and discussed.

Some outcomes of patients treated operatively for distal humerus fractures are affected by hand dominance

PURPOSE

This study sought to compare postoperative outcomes and complications between patients with distal humerus fractures treated with open reduction and internal fixation (ORIF) of their non-dominant versus dominant arm.

METHODS

A retrospective review of all patients who sustained a distal humerus fracture treated operatively with ORIF at one academic institution between 2011 and 2015 was performed. Measured outcomes included complications, time to fracture union, painful hardware, removal of hardware, Mayo Elbow Performance Index (MEPI), and elbow range of motion. Differences in outcomes between patients who underwent surgery of their dominant upper extremity and those who underwent surgery of their non-dominant extremity were assessed.

RESULTS

Sixty-nine patients met inclusion criteria. Forty (58.0%) underwent ORIF of a distal humerus fracture on their non-dominant arm and 29 (42.0%) on their dominant arm. Groups did not differ with respect to demographics, injury information, or surgical management. Mean overall follow-up was 14.1 ± 10.5 months, with all patients achieving at least 6 months follow-up. The non-dominant cohort experienced a higher proportion of postoperative complications (P = 0.048), painful hardware (P = 0.018), and removal of hardware (P = 0.002). At latest follow-up, the non-dominant cohort had lower MEPI scores (P = 0.037) but no difference in elbow arc of motion (P = 0.314).

CONCLUSION

Patients who sustained a distal humerus fracture of their non-dominant arm treated with ORIF experienced more postoperative complications, reported a greater incidence of painful hardware, underwent removal of hardware more often, and had worse functional recovery in this study. Physicians should emphasize the importance of physical therapy and maintaining arm movement especially when the non-dominant arm is involved following distal humerus fracture repair.

LEVEL OF EVIDENCE

Level III.

Catheter-associated bloodstream infections in adults with cancer: a prospective randomized controlled trial

BACKGROUND

A common complication of central venous access devices (CVADs) is catheter-associated bloodstream infection (CABSI). We previously demonstrated that insertion of CVADs on the right side was associated with increased risk of CABSI, and hypothesized that this related to the predominance of right-handedness in the patient population, resulting in greater movement and bacterial contamination.

AIM

To perform a prospective randomized, controlled, non-blinded study to determine whether the side of CVAD insertion influenced the incidence of CABSI.

METHODS

Adult cancer patients were randomly allocated to either dominant or non-dominant side CVAD insertion. The primary endpoint of the study was the number of line-days until CABSI, determined in a blinded fashion by two assessors.

FINDINGS

In all, 640 CVADs were randomized to dominant (N = 322) or non-dominant (N = 318) side of insertion, 60% had haematological malignancies, and 40% solid tumours. CVADs were a peripherally inserted central catheter line (67%), tunnelled CVAD (23%), and non-tunnelled CVAD (10%). Twenty-two percent of CVADs were complicated by CABSI. The rate of CABSI per 1000 line-days was 3.49 vs 3.66 in the non-dominant vs dominant group (hazard ratio (HR): 0.91; 95% confidence interval (CI): 0.65-1.28). By multivariable analysis, the rate of CABSI was increased by: use of tunnelled CVADs compared to peripherally inserted central venous catheter lines (HR: 2.05; 95% CI: 1.45-2.91); having a haematological malignancy compared to non-gastrointestinal solid tumours (5.55; 2.47-12.5); but not dominant compared to non-dominant side of CVAD (0.97; 0.69-1.36).

CONCLUSION

CABSI in adult patients with cancer was not impacted by whether CVAD insertion was on the dominant or non-dominant side.

Human motor cortical organization is influenced by handedness

Although there is some evidence that handedness is associated with structural and functional differences in the motor cortex, findings remain inconclusive. Here, we evaluated whether handedness influences the location, size and overlap of the cortical representations of upper limb muscles across hemispheres in right- versus left-handed individuals. Using transcranial magnetic stimulation, the cortical representations of abductor pollicis brevis, flexor carpi radialis and biceps brachii muscles were mapped bilaterally with a 6 by 5 grid space. Results indicate that right-handers had more lateral and posterior representations in the non-dominant hemisphere as well as greater overall cortical territory compared to left-handers. Right- and left-handers did not differ in the extent of overlap between muscle representations. Our findings suggest that human motor cortical organization of upper limb muscles is indeed influenced by handedness, specifically with regard to the location of non-dominant cortical muscle representations and the size of cortical territory dedicated to upper limb muscle representations.

Handedness modulates proprioceptive drift in the rubber hand illusion

Preference for use of either the left or right hand (‘handedness’) has been linked with modulations of perception and sensory processing—both of space and the body. Here we ask whether multisensory integration of bodily information also varies as a function of handedness. We created a spatial disparity between visual and somatosensory hand position information using the rubber hand illusion, and use the magnitude of illusory shifts in hand position (proprioceptive ‘drift’) as a tool to probe the weighted integration of multisensory information. First, we found drift was significantly reduced when the illusion was performed on the dominant vs. non-dominant hand. We suggest increased manual dexterity of the dominant hand causes greater representational stability and thus an increased resistance to bias by the illusion induction. Second, drift was generally greatest when the hand was in its habitual action space (i.e., near the shoulder of origin), compared to when it laterally displaced towards, or across the midline. This linear effect, however, was only significant for the dominant hand—in both left- and right-handed groups. Thus, our results reveal patterns of habitual hand action modulate drift both within a hand (drift varies with proximity to action space), and between hands (differences in drift between the dominant and non-dominant hands). In contrast, we were unable to find conclusive evidence to support, or contradict, an overall difference between left- and right-handers in susceptibility to RHI drift (i.e., total drift, collapsed across hand positions). In sum, our results provide evidence that patterns of daily activity—and the subsequent patterns of sensory input—shape multisensory integration across space.

Assessment of upper limb use in children with typical development and neurodevelopmental disorders by inertial sensors: a systematic review

Understanding development of bimanual upper limb (UL) activities in both typical and atypical conditions in children is important for: i) tailoring rehabilitation programs, ii) monitoring progress, iii) determining outcomes and iv) evaluating effectiveness of treatment/rehabilitation. Recent technological advances, such as wearable sensors, offer possibilities to perform standard medical monitoring. Body-worn motion sensors, mainly accelerometers, have shown very promising results but, so far, these studies have mainly focused on adults. The main aim of this review was to report the evidence of UL activity of both typically developing (TD) children and children with neurodevelopmental disorders (NDDs) that are reliably reported and comparable, using a combination of multiple wearable inertial sensors, both in laboratory and natural settings. Articles were selected from three research databases (PubMed, Web of Science and EBSCO). Included studies reported data on children aged 0-20 years old simultaneously wearing at least two inertial sensors on upper extremities. The collected and reported data were relevant in order to describe the amount of physical activity performed by the two ULs separately. A total of 21 articles were selected: 11 including TD, and 10 regarding NDDs. For each article, a review of both clinical and technical data was performed. We considered inertial sensors used for following aims: (i) to establish activity intensity cut-points; (ii) to investigate validity and reliability of specified markers, placement and/or number of inertial sensors; (iii) to evaluate duration and intensity of natural UL movements, defined motor tasks and tremor; and (iv) to assess efficacy of certain rehabilitation protocols. Our conclusions were that inertial sensors are able to detect differences in use between both hands and that all reviewed studies support use of accelerometers as an objective outcome measure, appropriate in assessing UL activity in young children with NDDs and determining intervention effectiveness. Further research on responsiveness to interventions and consistency with use in real-world settings is needed. This information could be useful in planning UL rehabilitation strategies.

Force distribution of a cylindrical grip differs between dominant and nondominant hand in healthy subjects

INTRODUCTION

Grip strength and load distribution of the hand are important parameters for evaluating hand function. The purpose of this study was to analyze and compare grip force and load distribution of dominant and nondominant hands in right-handed healthy subjects.

METHODS

Gripping measurements were performed on 40 healthy right-handed subjects using a cylindrical gripping device. Two different cylinders with circumferences of 150 mm (small cylinder) and 200 mm (large cylinder), respectively, were used for the measurements. Subjects were assigned to either the small or the large cylinder with respect to their hand size. Maximum and mean force applied during three intervals of gripping as well as the percent contribution of each digit, thenar, and hypothenar in relation to the total load applied were acquired. Values of dominant and nondominant hands were compared.

RESULTS

Percent contribution of mean grip strength differed for the thumb (p = 0.007), ring finger (p < 0.001), little finger (p = 0.047), and palm (p < 0.001). Comparing the dominant and nondominant side, the dominant hand showed a lower contribution of the thumb, ring finger, and little finger, but a higher contribution of the palm. When analyzing maximum grip, percent contribution of the small fingers was equal between dominant and nondominant side (p = 0.1). Differences between dominant and nondominant thumb, ring finger, and palm persisted (p = 0.007, p = 0.001, p = 0.005, respectively). No differences could be shown for the index finger, middle finger, thenar, and hypothenar when analyzing both mean and maximum force.

DISCUSSION AND CONCLUSION

Percent contribution of the thumb and the fingers to total grip strength differed between dominant and nondominant hands with a change in distribution when assessing maximum grip force. In right-handed subjects, thumb and ring finger have important roles during gripping.

Load distribution of the hand during cylinder grip analyzed by Manugraphy

STUDY DESIGN

Clinical measurement and basic research.

INTRODUCTION

Manugraphy allows assessing dynamically all forces applied perpendicular to a cylinder surface by the whole contact area of the hand with a high spatial resolution.

PURPOSE OF THE STUDY

To identify the physiological load distribution of the whole contact area of the hand during cylinder grip.

METHODS

A sample of 152 healthy volunteers performed grip force tests with 3 cylinder sizes of the Manugraphy system (novel, Munich, Germany) on 3 different days. The whole contact area of the hand was sectioned into 7 anatomic areas, and the percent contribution of each area in relation to the total load applied was calculated. The load distribution of the dominant and nondominant hands and with different cylinder sizes was compared. Furthermore, the load distribution between the finger phalanges of each finger was analyzed.

RESULTS

The results for the dominant and nondominant hands were in all 7 areas of the hand similar with the percent contribution differing within a range of 1%-4% (P > .138). Load distribution changed significantly with different cylinder sizes: all 7 areas differed between 1% and 7% with P < .001, most pronounced for the thumb. The load distribution of the phalanges showed that the contribution of the distal phalanges increased with ascending cylinder size, whereas the contribution of the proximal phalanges decreased. The interindividual variability of the load distribution pattern was noticeable.

DISCUSSION

For the clinical practice, Manugraphy might be a useful supplement to traditional grip force measurement for identifying the individual characteristics of a patient's dysfunction and monitoring the progress of hand rehabilitation.

CONCLUSIONS

There is no universal or typical load distribution pattern of the hand but only an individual pattern. To evaluate a compromised hand, it is permissible to compare it with the healthy opposite hand as a reference. Several cylinder sizes should be used for load distribution testing. Using smaller handles in the daily life can help to compensate impairment of the thumb and fingertips.

LEVEL OF EVIDENCE

2.

There Are Indeed More Left-Handers Within the Autism Spectrum Disorder Compared with in the General Population, but the Many Mixed-Handers Is the More Interesting Finding

Letter to the editor in response to Howard Kushner's claims that our data on non-right-handedness within the autism spectrum disorder were organized, by sleight of hand, so they would give a significant result that would support our desired conclusion. Here, we have re-categorized our data, and present evidence that there are indeed more left-handers within the ASD. Furthermore, we refute claims that we have misinterpreted our results in order to conclude about a causal link between left-handedness and ASD, and highlight our original suggestion that mixed-handedness, more specifically unclear handedness, is the bigger problem, and that our findings of a total 60% non-right-handedness was the more interesting finding.

Prevalence of Absence of Palmaris Longus and Its Association with Gender, Hand Dominance and Absence of FDS Tendon to Little Finger Among Malay Population

BACKGROUND

Palmaris Longus is being widely used in reconstructive, plastic and cosmetic surgeries due to its long tendon. It is the most readily available source for tendon grafting. The objective of this study was to determine the prevalence of absence of Palmaris Longus and its association with gender, hand dominance and absence of FDS (flexor digitorum superficialis) tendon to little finger among Malay population.

METHODS

An analytical cross sectional study design was used and a self-administered proforma was distributed for data collection. 1239 Malay secondary school children in Putrajaya were tested for absence of Palmaris Longus using Schaffer's test. 4 additional tests namely Thompson's test, Mishra's test I, Mishra's test II and Pushpakumar's 'two-finger sign' method were used to confirm its absence in respondents with negative Schaffer's test. Function of Flexor Digitorum Superficialis tendon to little finger was determined by flexing PIP of little finger while hyperextend the other fingers.

RESULTS

The prevalence of absence of Palmaris Longus was 11.7%. Left side absence of Palmaris Longus was much common. There was a significant association between absence of Palmaris Longus with gender in which female had higher prevalence of absence of Palmaris Longus than male.

CONCLUSIONS

In conclusion, the prevalence of absence of Palmaris Longus in Malay population was lower than Indian but higher than Chinese population. Females had higher prevalence of absence of Palmaris Longus and no association can be found with hand dominance and absence of Flexor Digitorum Superficialis tendon to little finger.

The Effect of Hand Dominance on Patient-Reported Outcomes of Carpal Tunnel Release in Patients with Bilateral Carpal Tunnel Syndrome

BACKGROUND

There is a paucity of studies in published literature that examines the effect of hand dominance on the resolution of symptoms following a carpal tunnel release. The objective of this study is to examine the effect of hand dominance on the resolution of symptoms following surgical decompression in patients with severe and moderate carpal tunnel syndrome.

METHODS

Bilateral carpal tunnel release (total 90 open and 84 endoscopic) was performed on 87 patients (11 males, 76 females) presenting with bilateral severe or moderate carpal tunnel syndrome of equal severity. Patient-reported outcome of resolution of symptoms were recorded, with patients followed up until complete resolution of symptoms or last recorded consultation (mean follow-up duration 11.4 months, range 3.1 to 32.4 months).

RESULTS

In patients with bilateral severe carpal tunnel syndrome, a larger proportion of non-dominant hand (75.4%) achieved complete resolution compared to dominant hand (72.1%), and did so at a statistically shorter time (mean: 52.3 days) than the dominant hand (mean: 81.0 days). However, there was no statistically significant difference between proportion of patients and time taken before complete resolution of symptoms between dominant and non-dominant hand in patients with bilateral moderate carpal tunnel syndrome.

CONCLUSIONS

Symptoms in the non-dominant hand resolved faster after carpal tunnel release in patients with severe carpal tunnel syndrome. We postulate that greater daily activity by the dominant hand compared to the non-dominant hand may be a contributing factor to its slower rate of symptoms resolution post-surgically in patients with bilateral severe carpal tunnel syndrome. This effect of hand dominance is not evident in post-surgical patients with moderate carpal tunnel syndrome.

Comparison of Path Length and Ranges of Movement of the Center of Pressure and Reaction Time and Between Paired-Play and Solo-Play of a Virtual Reality Game

AIMS

To test whether paired-play will induce longer path length and ranges of movement of the center of pressure (COP), which reflects on balance performance and stability, compared to solo-play and to test the difference in the path length and ranges of movement of the COP while playing the virtual reality (VR) game with the dominant hand compared to playing it with the nondominant hand.

METHODS

In this cross-sectional study 20 children (age 6.1 ± 0.7 years old) played an arm movement controlled VR game alone and with a peer while each of them stood on a pressure measuring pad to track the path length and ranges of movement of the COP.

RESULTS

The total COP path was significantly higher during the paired-play (median 295.8 cm) compared to the COP path during the solo-play (median 189.2 cm). No significant differences were found in the reaction time and the mediolateral and anterior-posterior COP ranges between solo-play and paired-play. No significant differences were found between the parameters extracted during paired-play with the dominant or nondominant hand.

DISCUSSION

Our findings imply that the paired-play is advantageous compared to solo-play since it induces a greater movement for the child, during which, higher COP velocities are reached that may contribute to improving the balance control of the child. Apart from the positive social benefits of paired-play, this positive effect on the COP path length is a noteworthy added value in the clinical setting when treating children with balance disorder.

Both hands at work: the effect of aging on upper-limb kinematics in a multi-step activity of daily living

The kinematic performance of basic motor tasks shows a clear decrease with advancing age. This study examined if the rules known from such tasks can be generalized to activities of daily living. We examined the end-effector kinematics of 13 young and 13 elderly participants in the multi-step activity of daily living of tea-making. Furthermore, we analyzed bimanual behavior and hand dominance in the task using different conditions of execution. The elderly sample took substantially longer to complete the activity (almost 50%) with longer trajectories compared with the young sample. Models of multiple linear regression revealed that the longer trajectories prolonged the trial duration in both groups, and while movement speed influenced the trial duration of young participants, phases of inactivity negatively affected how long the activity took the elderly subjects. No differences were found regarding bimanual performance or hand dominance. We assume that in self-paced activities of daily living, the age-dependent differences in the kinematics are more likely to be based on the higher cognitive demands of the task rather than on pure motor capability. Furthermore, it seems that not all of the rules known from basic motor tasks can be generalized to activities of daily living.

The da vinci robot system eliminates multispecialty surgical trainees' hand dominance in open and robotic surgical settings

Background and Objectives:

Handedness, or the inherent dominance of one hand's dexterity over the other's, is a factor in open surgery but has an unknown importance in robot-assisted surgery. We sought to examine whether the robotic surgery platform could eliminate the effect of inherent hand preference.

Methods:

Residents from the Urology and Obstetrics/Gynecology departments were enrolled. Ambidextrous and left-handed subjects were excluded. After completing a questionnaire, subjects performed three tasks modified from the Fundamentals of Laparoscopic Surgery curriculum. Tasks were performed by hand and then with the da Vinci robotic surgical system (Intuitive Surgical, Sunnyvale, California). Participants were randomized to begin with using either the left or the right hand, and then switch. Left:right ratios were calculated from scores based on time to task completion. Linear regression analysis was used to determine the significance of the impact of surgical technique on hand dominance.

Results:

Ten subjects were enrolled. The mean difference in raw score performance between the right and left hands was 12.5 seconds for open tasks and 8 seconds for robotic tasks (P < .05). Overall left-right ratios were found to be 1.45 versus 1.12 for the open and robot tasks, respectively (P < .05). Handedness significantly differed between robotic and open approaches for raw time scores (P < .0001) and left-right ratio (P = .03) when controlling for the prior tasks completed, starting hand, prior robotic experience, and comfort level. These findings remain to be validated in larger cohorts.

Conclusion:

The robotic technique reduces hand dominance in surgical trainees across all task domains. This finding contributes to the known advantages of robotic surgery.

Symmetrical and asymmetrical influences on force production in 1:2 and 2:1 bimanual force coordination tasks

Results from a recent experiment (Kennedy et al. in Exp Brain Res 233:181-195, 2015) indicated consistent and identifiable distortion of the left limb forces that could be attributable to the production of right limb forces during a multi-frequency bimanual force task. However, distortions in the forces produced by the right limb that could be attributable to the production of force in the left limb were not observed. The present experiment was designed to replicate this finding and determine whether the influence of force produced by one limb on the contralateral limb is the result of the limb assigned the faster frequency on the limb performing the slower frequency or a bias associated with limb dominance. Participants (N = 10) were required to rhythmically coordinate a pattern of isometric forces in a 1:1, 1:2, or 2:1 coordination pattern. The 1:2 task required the right limb to perform the faster rhythm, while the 2:1 task required the left limb to perform the faster rhythm. The 1:1 task was used as a control. Participants performed 13 practice trials and 1 test trial per task. Lissajous displays were provided to guide performance. If the limb assigned the faster frequency was responsible for the distortions observed in the contralateral limb, it was hypothesized that distortions would only be observed in the force trace of the limb producing the slower pattern of force. If a bias associated with limb dominance was responsible for the distortions observed in the contralateral limb, it was hypothesized that in right-limb-dominant participants the right limb would influence the left limb, regardless of limb assignment. Replicating the results of the previous experiment, only distortions in the left limb were observed in the 1:2 coordination task that could be attributed to the production of force by the right limb. However, identifiable distortions were observed in the force produced by both the left and right limb in the 2:1 coordination task. Observed distortions in the left limb, when assigned the faster rhythm indicated that the source of interference is not limited to limb assignment but also a function of limb dominance.

The influence of dominant limb involvement on DASH and QuickDASH

PURPOSE

The purpose of this study is to determine whether involvement of the dominant limb affects Disabilities of the Arm Shoulder and Hand (DASH) scores.

METHODS

A convenience sample of 948 patients from 12 prospective studies that recorded hand dominance, affected side, diagnosis, and a DASH or QuickDASH score was used to assess the influence of involvement of the dominant limb on DASH scores. Diagnosis was categorized as traumatic and nontraumatic. Region was categorized as hand and wrist, elbow, and arm and shoulder.

RESULTS

In bivariate analysis, involvement of the dominant limb, diagnosis, region, and sex had significant influence on DASH/QuickDASH score. In multivariable analysis, dominant hand condition, traumatic diagnosis, arm and shoulder involvement, and female sex were associated with significantly higher DASH scores (more disability), but accounted for only 10 % of the variability in scores.

CONCLUSION

Upper extremity disability as measured by the DASH is slightly, but significantly greater when the dominant limb is involved.

LEVEL OF EVIDENCE

Prognostic level II.

Motor unit number index examination in dominant and non-dominant hand muscles

This study investigated the effect of handedness on motor unit number index (MUNIX). Maximal hand strength, compound muscle action potential (CMAP) and voluntary surface electromyography (EMG) signals were measured bilaterally for the first dorsal interosseous (FDI) and thenar muscles in 24 right-handed and 2 left-handed healthy subjects. Mean (±standard error) grip and pinch forces in the dominant hand were 43.99 ± 2.36 kg and 9.36 ± 0.52 kg respectively, significantly larger than those in the non-dominant hand (grip: 41.37 ± 2.29 kg, p < .001; pinch: 8.79 ± 0.46 kg, p < .01). Examination of myoelectric parameters did not show a significant difference among the CMAP area, the MUNIX or motor unit size index (MUSIX) between the two sides in the FDI and thenar muscles. In addition, there was a lack of correlation between the strength and myoelectric parameters in regression analysis. However, strong correlations were observed between dominant and non-dominant hand muscles in both strength and myoelectric measures. Our results indicate that the population of motor units or spinal motor neurons as estimated from MUNIX may not be associated with handedness. Such findings help understand and interpret the MUNIX during its application for clinical or laboratory investigations.

Differences in Brain Adaptive Functional Reorganization in Right and Left Total Brachial Plexus Injury Patients

OBJECTIVE

Total brachial plexus avulsion injury (BPAI) results in the total functional loss of the affected limb and induces extensive brain functional reorganization. However, because the dominant hand is responsible for more cognitive-related tasks, injuries on this side induce more adaptive changes in brain function. In this article, we explored the differences in brain functional reorganization after injuries in unilateral BPAI patients.

METHODS

We applied resting-state functional magnetic resonance imaging scanning to 10 left and 10 right BPAI patients and 20 healthy control subjects. The amplitude of low-frequency fluctuation (ALFF), which is a resting-state index, was calculated for all patients as an indication of the functional activity level of the brain. Two-sample t-tests were performed between left BPAI patients and controls, right BPAI patients and controls, and between left and right BPAI patients.

RESULTS

Two-sample t-tests of the ALFF values revealed that right BPAIs induced larger scale brain reorganization than did left BPAIs. Both left and right BPAIs elicited a decreased ALFF value in the right precuneus (P < 0.05, Alphasim corrected). In addition, right BPAI patients exhibited increased ALFF values in a greater number of brain regions than left BPAI patients, including the inferior temporal gyrus, lingual gyrus, calcarine sulcus, and fusiform gyrus.

CONCLUSION

Our results revealed that right BPAIs induced greater extents of brain functional reorganization than left BPAIs, which reflected the relatively more extensive adaptive process that followed injuries of the dominant hand.

The significance of hand dominance in hip osteoarthritis

OBJECTIVES

Hip arthroplasty registries, encompassing all-cause end-stage hip degeneration, have shown that slightly more right hip replacements are performed than left. Given that greater than 85% of individuals are right-handed, we sought to investigate the association between side of hand dominance and side of hip osteoarthritis.

METHODS

This Level III observational study evaluated exclusively end-stage osteoarthritis of the hip, using 3 independent centres totalling 386 consecutive arthroplasty patients. Logistic regression was used as a statistical model.

RESULTS

In total, 322 patients with hip osteoarthritis were included in the final analysis, including 146 (45.5%) women and 176 (54.5%) men, with a mean age of 68.1 years (SD = 9.5 years). There were 133 (41.2%) right, 73 (22.6%) left, and 116 (35.9%) bilateral hips where the contralateral side had been previously replaced. The proportion of individuals requiring unilateral hip arthroplasty on their dominant side was 67.4%.

CONCLUSIONS

In the development of hip osteoarthritis, one is significantly more likely to require hip arthroplasty on their dominant side than in the contralateral hip. Assessment of hand dominance identifies cerebral laterality as a contributing factor in predisposing one's dominant side to hip osteoarthritis.

Demographic profile of hand injuries in an industrial town of north India: a review of 436 patients

There are not many injuries that rival the injured hand in complexity. A better understanding of biologic, behavioral, and socioeconomic risk factors potentially associated with hand injuries can help identify those individuals most at risk and define potential preventative measures to help reduce the incidence. We present a prospective study of 436 consecutive patients of hand and forearm injury treated over a period of 2 years. A serial recording of the demographic profile of the patient along with the type & cause of injury sustained, hand dominance, duration of hospital stay, time lag between injury and admission, type surgery preformed with intra-operative findings and the cost analysis was done. An expected male dominance in economically viable individuals of 21 to 30 years formed 50 % of the patients of which 22.9 % were labourers and students each. The malady was altercation (27.5 %) followed by industrial & road accidents. Post prandial period was most notorious with multiple neuro (27.05 %) vasculo (39.34 %) tendinous (60.66 %) injury common with even simple lacerations. Dominant hand injury was commonest. It is challenging to assess and treat an injured hand. This study defines the demography and the etiology behind the various cases of hand and forearm injury with the detailed trauma profile. The limitation of the study was absence of functional outcome. The necessity of hand trauma registry is a pre-requisite to quantify the burden of hand injuries and formulate a prevention strategy.

Survey of Korean pedestrians' natural preference for walking directions

The primary objective of this study was to investigate the stereotypes of Koreans regarding preferred walking directions when encountering various public walking facilities, and to provide useful information to pedestrians and traffic policy legislators. To this end, this study was conducted in two phases. In the first phase, we conducted observational research on pedestrians' walking directions in ten different situations. In the second phase, six hundred Korean male and female subjects were selected to investigate the various statistics about their preferred walking directions and their employment characteristics in diverse walking facilities. The results showed that 59.3% abided by the Left-side Traffic rule while 40.7% abided by the Right-side rule. On the contrary, 73.7% of respondents showed preferences to the Right-side Traffic rule. Moreover, right-handed people showed strong tendencies to walk on the right side of the road and vice versa, hence suggesting that the direction people naturally prefer in walking should be a crucial determinant when regulating traffic policies.

The effect of hand dominance on neuromuscular monitoring at the adductor pollicis muscle

Background

Neuromuscular blockade of the adductor pollicis muscle may be influenced by hand dominance resulting in conflicting results of several studies. The current study examined whether hand dominance could influence the measurements of neuromuscular blockade with acceleromyography at the adductor pollicis.

Methods

The acceleromyographic responses from 0.6 mg/kg of rocuronium were monitored supramaximally in both hands in 31 patients after induction of anesthesia. Onset, maximum effect, and offset of rocuronium were measured and compared in both hands. The train-of-four (TOF) ratios to 0.9 were recorded in all patients.

Results

In total, 27 patients were right-handed and 4 patients were left-handed. The mean supramaximal threshold or initial TOF ratio was not different between dominant and nondominant hands. No statistically significant differences were found between 716 paired TOF ratios in both hands. A correlation was seen between the dominant and nondominant hand (Nondominant = 0.931·Dominant + 1.714, R = 0.929). The analysis by the Bland-Altman plot showed an excellent agreement with a bias of 1.6% and limits of agreement of -21.2 to 24.5%.

Conclusions

Dominant and nondominant hands can be used interchangeably for neuromuscular monitoring at the adductor pollicis.