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1.  Association between Upper Extremity Musculoskeletal Disorders and Psychosocial Factors at Work: A Review on the Job DCS Model's Perspective 
Safety and Health at Work  2010;1(1):37-42.
Over years it has been increasingly concerned with how upper extremity musculoskeletal disorders (UEMSDs) are attributed to psychosocial job stressors. A review study was conducted to examine associations between UEMSDs and psychosocial work factors, and to recommend what to consider for the associations. For studies in which the job demand-control-support (DCS) model or its variables were specifically employed, published papers were selected and reviewed. A number of studies have reported relationships between UEMSDs symptoms and psychosocial exposure variables. For example, the findings are: higher numbness in the upper extremity was significantly attributed to by less decision latitude at work; work demands were significantly associated with neck and shoulder symptoms while control over time was associated with neck symptoms; and the combination of high psychosocial demands and low decision latitude was a significant predictor for shoulder and neck pain in a female working population. Sources of bias, such as interaction or study design, were discussed. UEMSDs were shown to be associated with psychosocial work factors in various studies where the job DCS model was addressed. Nonetheless, this review suggests that further studies should be conducted to much more clarify the association between UEMSDs and psychosocial factors.
PMCID: PMC3430936  PMID: 22953161
Upper extremity musculoskeletal disorders; Psychosocial work factors; Job DCS model
2.  MRI-identified abnormalities and wrist range of motion in asymptomatic versus symptomatic computer users 
Previous work has shown an association between restricted wrist range of motion (ROM) and upper extremity musculoskeletal disorders in computer users. We compared the prevalence of MRI-identified wrist abnormalities and wrist ROM between asymptomatic and symptomatic computer users.
MR images at 1.5 T of both wrists were obtained from 10 asymptomatic controls (8 F, 2 M) and 14 computer users (10 F, 4 M) with chronic wrist pain (10 bilateral; 4 right-side). Maximum wrist range of motion in flexion and radioulnar deviation was measured with an electrogoniometer.
Extraosseous ganglia were identified in 66.6% of asymptomatic wrists and in 75% of symptomatic wrists. Intraosseous ganglia were identified in 45.8% of asymptomatic wrists and in 75% of symptomatic wrists, and were significantly (p < .05) larger in the symptomatic wrists. Distal ECU tendon instability was identified in 58.4% of both asymptomatic and symptomatic wrists. Dominant wrist flexion was significantly greater in the asymptomatic group (68.8 ± 6.7 deg.) compared to the symptomatic group (60.7 ± 7.3 deg.), p < .01. There was no significant correlation between wrist flexion and intraosseous ganglion burden (p = .09)
This appears to be the first MRI study of wrist abnormalities in computer users.
This study demonstrates that a variety of wrist abnormalities are common in computer users and that only intraosseous ganglia prevalence and size differed between asymptomatic and symptomatic wrists. Flexion was restricted in the dominant wrist of the symptomatic group, but the correlation between wrist flexion and intraosseous ganglion burden did not reach significance. Flexion restriction may be an indicator of increased joint loading, and identifying the cause may help to guide preventive and therapeutic interventions.
PMCID: PMC2998464  PMID: 21108817
3.  Specific and non-specific upper extremity musculoskeletal disorder syndromes in automobile manufacturing workers 
A longitudinal cohort of automobile manufacturing workers (n = 1214) was examined for: 1) prevalence and persistence of specific upper extremity musculoskeletal disorders (UEMSDs) such as lateral epicondylitis and de Quervain's disease, and non-specific disorders (NSDs) defined in symptomatic individuals without any specific disorder, and 2) disorder prognoses based on symptom characteristics and other factors.
Eight specific disorders were identified through case definitions based on upper extremity physical examinations and symptom surveys administered on three occasions over six years.
At baseline, 41% of the cohort reported upper extremity symptoms; 18% (n = 214) of these had NSDs. In each survey, tendon-related conditions accounted for over half of the specific morbidity. Twenty-five percent had UEMSDs in multiple anatomical sites, and most with hand/wrist disorders had two or more hand/wrist UEMSDs. Persistence for all specific disorders decreased with length of follow-up. Specific UEMSDs were characterized by greater pain severity and functional impairment, and more lost work days than NSDs.
Upper extremity symptoms and diagnoses vary over time. NSDs may be the early stages of conditions that will eventually become more specific. NSDs and overlapping specific UEMSDs should be taken into account in UEMSD classification.
PMCID: PMC2997818  PMID: 19016265
4.  Muscle fatigue in relation to forearm pain and tenderness among professional computer users 
To examine the hypothesis that forearm pain with palpation tenderness in computer users is associated with increased extensor muscle fatigue.
Eighteen persons with pain and moderate to severe palpation tenderness in the extensor muscle group of the right forearm and twenty gender and age matched referents without such complaints were enrolled from the Danish NUDATA study of neck and upper extremity disorders among technical assistants and machine technicians. Fatigue of the right forearm extensor muscles was assessed by muscle twitch forces in response to low frequency (2 Hz) percutaneous electrical stimulation. Twitch forces were measured before, immediately after and 15 minutes into recovery of an extensor isometric wrist extension for ten minutes at 15 % Maximal Voluntary Contraction (MVC).
The average MVC wrist extension force and baseline stimulated twitch forces were equal in the case and the referent group. After the fatiguing contraction, a decrease in muscle average twitch force was seen in both groups, but the decrease was largest in the referent group: 27% (95% CI 17–37) versus 9% (95% CI -2 to 20). This difference in twitch force response was not explained by differences in the MVC or body mass index.
Computer users with forearm pain and moderate to severe palpation tenderness had diminished forearm extensor muscle fatigue response. Additional studies are necessary to determine whether this result reflects an adaptive response to exposure without any pathophysiological significance, or represents a part of a causal pathway leading to pain.
PMCID: PMC2245952  PMID: 18067676
5.  Secondary Reconstructive Procedures in Obstetrical Brachial Plexus Palsy: Forearm, Wrist, and Hand Deformities 
Seminars in Plastic Surgery  2005;19(1):96-102.
Obstetrical brachial plexus paralysis (OBPP) is a complex, multifaceted disorder with potentially disabling sequalae. Although the shoulder is the most frequently affected joint, the forearm, wrist, and hand may also display diabling deformities. In sequalae involving the forearm, the most frequent deformity is supination contractures followed by pronation contractures. Treatment of OBPP has recently focused on early microsurgical repair; nonetheless, palliative surgery still plays a critical role in the overall reconstructive planning in order to diminish the sequalae of OBPP and improve function of the upper extremity. The preferred palliative surgical proceures for the forearm and hand include flexor or extensor tendon transfers, free muscle transfers, opponensplasty, and bone fusion. The most commonly restored functions are elbow flexion and extension, finger flexion and extension, and, in some cases, shoulder abduction and intrinsic substitution.
PMCID: PMC2884735
Obstetrical paralysis; supination deformity; ulnar deviation; wrist drop
6.  Risk factors for upper-extremity musculoskeletal disorders in the working population 
Arthritis and Rheumatism  2009;61(10):1425-1434.
The study aimed to assess the relative importance of personal and occupational risk factors for upper-extremity musculoskeletal disorders (UEMSDs) in the working population.
A total of 3,710 workers (58% of men) participating in a surveillance program of MSDs in a French region in 2002–2005 were included. UEMSDs were diagnosed by 83 trained occupational physicians performing a standardized physical examination. Personal factors and work exposure were assessed by a self-administered questionnaire. Statistical associations between MSDs, personal and occupational factors were analyzed using logistic regression modeling.
A total of 472 workers suffered from at least one UEMSD. The risk of UEMSDs increased with age for both genders (P<0.001) (O.R. up to 4.9 in men and 5.0 and in women) and in cases of prior history of UEMSDs (OR 3.1 and 5.0, P<0.001). In men, UEMSDs were associated with obesity (OR 2.2, P=0.014), high level of physical demand (OR 2.0, P<0.001), high repetitiveness of the task (OR 1.5, P=0.027), postures with the arms at or above shoulder level (OR 1.7, P=0.009) or with full elbow flexion (OR 1.6, P=0.006), and high psychological demand (O.R. 1.5, P=0.005). In women, UEMSDs were associated with diabetes mellitus (O.R. 4.9, P=0.001), postures with extreme wrist bending (OR 2.0, P<0.001), use of vibrating hand tools (O.R. 2.2, P=0.025) and low level of decision authority (OR 1.4, P=0.042).
The study showed that personal and work-related physical and psychosocial factors were strongly associated with clinically-diagnosed UEMSDs.
PMCID: PMC3189514  PMID: 19790112
Musculoskeletal disorders; upper extremity; risk factors; personal factors; physical exposure; psychosocial factors; work; Adult; Employment; Female; Humans; Male; Middle Aged; Musculoskeletal Diseases; diagnosis; epidemiology; etiology; Occupational Diseases; diagnosis; epidemiology; etiology; Risk Factors; Safety Management; Upper Extremity; pathology; physiopathology
7.  Do workers with self-reported symptoms have an elevated risk of developing upper extremity musculoskeletal disorders three years later? 
Few prospective studies have evaluated outcomes of workers with self-reported symptoms of upper extremity musculoskeletal disorders (UEMSD). Our objective was to study the three-year outcomes of workers with self-reported symptoms, with or without a positive physical examination.
In 1993–1994, 598 subjects highly exposed to repetitive work filled out a Nordic-style questionnaire. They underwent a standardised physical examination at that time and again in 1996–1997 by the same occupational physician. The three-year outcomes (based on physical examination) of workers with a self-administered questionnaire positive at baseline for UEMSD, with or without a positive physical examination, were studied.
The three-year incidence rate was 44.1%, with one third of these incident cases who had self-reported symptoms in 1993–1994. Workers with a positive questionnaire had a significantly higher risk of UEMSD at physical examination three year later (80.1% UEMSD cases with positive questionnaires n=354, versus 44.2% cases without positive questionnaires n=69, p<0.0001). Moreover, workers with positive questionnaires but without UEMSD diagnosed in 1993–1994 (n=177) had also a significantly higher risk of UEMSD at physical examination three years later (60.5% cases with positive questionnaires n=26, versus 38.8% cases without positive questionnaires n=52, p=0.01). Results were similar when gender and age were taken into account.
Workers highly exposed to repetitive movements had a high risk of developing UEMSD and should be followed closely in surveillance programmes. Workers with self-reported symptoms without UEMSD diagnosed in physical examination represented only one third of new cases three years later. However, their risk to develop UEMSD was significantly increased, compared with those without symptoms.
PMCID: PMC2265784  PMID: 17766426
8.  Computer work and musculoskeletal disorders of the neck and upper extremity: A systematic review 
This review examines the evidence for an association between computer work and neck and upper extremity disorders (except carpal tunnel syndrome).
A systematic critical review of studies of computer work and musculoskeletal disorders verified by a physical examination was performed.
A total of 22 studies (26 articles) fulfilled the inclusion criteria. Results show limited evidence for a causal relationship between computer work per se, computer mouse and keyboard time related to a diagnosis of wrist tendonitis, and for an association between computer mouse time and forearm disorders. Limited evidence was also found for a causal relationship between computer work per se and computer mouse time related to tension neck syndrome, but the evidence for keyboard time was insufficient. Insufficient evidence was found for an association between other musculoskeletal diagnoses of the neck and upper extremities, including shoulder tendonitis and epicondylitis, and any aspect of computer work.
There is limited epidemiological evidence for an association between aspects of computer work and some of the clinical diagnoses studied. None of the evidence was considered as moderate or strong and there is a need for more and better documentation.
PMCID: PMC2874766  PMID: 20429925
9.  Carpal and Forearm Kinematics During a Simulated Hammering Task 
The Journal of hand surgery  2010;35(7):1097-1104.
Hammering is a functional task in which the wrist generally follows a path of motion from a position of combined radial deviation and extension to combined ulnar deviation and flexion, colloquially referred to as a dart thrower's motion (DTM). The purpose of this study was to measure wrist and forearm motion and scaphoid and lunate kinematics during a simulated hammering task. We hypothesized that the wrist follows an oblique path from radial extension to ulnar flexion and that there would be minimal radiocarpal motion during the hammering task.
13 healthy volunteers consented to have their wrist and distal forearm imaged with computed tomography at five positions in a simulated hammering task. The kinematics of the carpus and distal radial ulnar joint were calculated using established markerless bone registration methods. The path of wrist motion was described relative to the sagittal plane. Forearm rotation and radioscaphoid and radiolunate motion were computed as a function wrist position.
All volunteers performed the simulated hammering task using a path of wrist motion from radial extension to ulnar flexion that was oriented an average 41 ± 3° from the sagittal plane. These paths did not pass through the anatomic neutral wrist position; rather they passed through the neutral hammering position, which was offset by 36° ± 8° in extension. Rotations of the scaphoid and lunate were not minimal but averaged 40% and 41% respectively of total wrist motion. The range of forearm pronosupination during the task averaged 12 ± 8°.
The simulated hammering task was performed using a wrist motion that followed an oblique path, from radial extension to ulnar flexion. Scaphoid and lunate rotations were significantly reduced, but not minimized, when compared with rotations during pure wrist flexion/extension. This is likely due to the fact that an extended wrist position was maintained throughout the entire task studied.
PMCID: PMC2901240  PMID: 20610055
Carpal; Kinematics; Hammering; Scaphoid; Lunate
10.  Risk Factors for Neck and Upper Extremity Disorders among Computers Users and the Effect of Interventions: An Overview of Systematic Reviews 
PLoS ONE  2011;6(5):e19691.
To summarize systematic reviews that 1) assessed the evidence for causal relationships between computer work and the occurrence of carpal tunnel syndrome (CTS) or upper extremity musculoskeletal disorders (UEMSDs), or 2) reported on intervention studies among computer users/or office workers.
Methodology/Principal Findings
PubMed, Embase, CINAHL and Web of Science were searched for reviews published between 1999 and 2010. Additional publications were provided by content area experts. The primary author extracted all data using a purpose-built form, while two of the authors evaluated the quality of the reviews using recommended standard criteria from AMSTAR; disagreements were resolved by discussion. The quality of evidence syntheses in the included reviews was assessed qualitatively for each outcome and for the interventions.
Altogether, 1,349 review titles were identified, 47 reviews were retrieved for full text relevance assessment, and 17 reviews were finally included as being relevant and of sufficient quality. The degrees of focus and rigorousness of these 17 reviews were highly variable. Three reviews on risk factors for carpal tunnel syndrome were rated moderate to high quality, 8 reviews on risk factors for UEMSDs ranged from low to moderate/high quality, and 6 reviews on intervention studies were of moderate to high quality. The quality of the evidence for computer use as a risk factor for CTS was insufficient, while the evidence for computer use and UEMSDs was moderate regarding pain complaints and limited for specific musculoskeletal disorders. From the reviews on intervention studies no strong evidence based recommendations could be given.
Computer use is associated with pain complaints, but it is still not very clear if this association is causal. The evidence for specific disorders or diseases is limited. No effective interventions have yet been documented.
PMCID: PMC3093401  PMID: 21589875
11.  In Vivo Kinematics of the Scaphoid, Lunate, Capitate, and Third Metacarpal in Extreme Wrist Flexion and Extension 
The Journal of hand surgery  2012;38(2):278-288.
Insights into the complexity of active in vivo carpal motion have recently been gained using 3D imaging; however kinematics during extremes of motion have not been elucidated. The purpose of this study was to determine motion of the carpus during extremes of wrist flexion and extension.
Computed tomography scans of 12 healthy wrists were obtained in neutral-grip, extreme loaded flexion, and extreme loaded extension. Three-dimensional bone surfaces and 6-degree-of-freedom kinematics were obtained for the radius and carpal bones. The flexion and extension rotation from neutral-grip to extreme flexion and extreme extension of the scaphoid and lunate was expressed as a percentage of capitate flexion and extension and then compared to previous studies of active wrist flexion and extension. We also tested the hypothesis that the capitate and third metacarpal function as a single rigid body. Finally, joint space metrics at the radiocarpal and midcarpal joints were used to describe arthrokinematics.
In extreme flexion, the scaphoid and lunate flexed 70% and 46% of the amount the capitate flexed, respectively. In extreme extension, the scaphoid extended 74% and the lunate extended 42% of the amount the capitates extended, respectively. The third metacarpal extended 4° farther than the capitate in extreme extension. The joint contact area decreased at the radiocarpal joint during extreme flexion. The radioscaphoid joint contact center moved onto the radial styloid and volar ridge of the radius in extreme flexion from a more proximal and ulnar location in neutral.
The contributions of the scaphoid and lunate to capitate rotation were approximately 25% less in extreme extension compared to wrist motion through an active range of motion. More than half the motion of the carpus when the wrist was loaded in extension occured at the midcarpal joint.
Clinical Relevance
These findings highlight the difference in kinematics of the carpus during at the extremes of wrist motion, which occur during activities and injuries, and give insight into the possible etiologies of the scaphoid fractures, interosseous ligament injuries, and carpometacarpal bossing.
PMCID: PMC3557539  PMID: 23266007
Carpal; Kinematics; Lunate; Passive; Scaphoid
12.  Feasibility of Gestural Feedback Treatment for Upper Extremity Movement in Children With Cerebral Palsy 
External feedback of performance is an important component of therapy, especially for children with impairments due to cerebral palsy because they lack intrinsic experience of “good movements” to compare effort and determine performance outcomes. A robotic therapy system was developed to provide feedback for specific upper extremity movements (gestures) which are therapeutically desirable. The purpose of this study was to compare changes in forearm supination/pronation or wrist extension/flexion motion following conventional therapy and gestural robotic feedback therapy intervention. Six subjects with cerebral palsy (ages 5–18, GMFCS level IV—three subjects, level III—one subject, and level I—two subjects) participated in a blinded crossover design study of conventional and robotic feedback therapy targeting either forearm supination or wrist extension. Functional upper extremity motion at baseline and following conventional and robotic feedback therapy interventions were obtained using a motion capture system by personnel blinded to the intervention order. All activities were approved by IRB. Use of the robotic feedback system did result in slightly increased movement in the targeted gesture without change in un-targeted motions. Data also suggest a decrease in both agonist and antagonist motion following conventional therapy intervention. Results suggest improved motion when robotic feedback therapy intervention precedes conventional therapy intervention. Robotic feedback therapy is no different than conventional therapy to improve supination or wrist extension function in upper extremity impairments of children with cerebral palsy when changes were considered as aggregate data. In this very small group of diverse patients, individual subject results suggested that intervention order could be responsible for obscuring differences due to intervention type. Outcomes from several individual subjects suggest that results could be different given a more homogeneous group of subjects which future studies should be considered to ultimately determine efficacy of the robotic feedback therapy. Future studies should also address efficacy in other neuromuscular patient populations.
PMCID: PMC3910162  PMID: 23193461
Cerebral palsy (CP); movement feedback; robotic feedback; upper extremity
13.  New method of measuring wrist joint position sense avoiding cutaneous and visual inputs 
Aspects of afferent inputs, generally termed proprioception, are being increasingly studied. Extraneous factors such as cutaneous inputs can dramatically interfere while trying to design studies in order to determine the participation of the different structures involved in proprioception in the wrist position sense. We tried to determine validity and repeatability of a new wrist joint position measurement device using methodology designed to minimize extraneous factors and isolate muscle and joint inputs.
In order to test the reliability of the system, eighty young-adult subjects without musculoskeletal or neurologic impairments affecting the right upper extremity were tested using a custom made motion tracking system. Testing consisted of two conditions: active reproduction of active placement and passive reproduction of passive placement. Subjects performed two repetitions of each target position (10, 20, and 30° of flexion and extension) presented in a random order. Test- retest reliability was then tested.
The average constant error in the passive condition was -0.7° ± 4.7° as compared to the active condition at 3.7° ± 5.1°. Average absolute error in the passive condition was 4.9° ± 2.9° compared to the active condition in which absolute error was 5.9° ± 3.5°.
Test-retest repeatability in both conditions was less than the 5° magnitude typical of clinical goniometry. Errors in the active condition (less than 2°) were slightly smaller than the passive condition, and the passive condition was also associated with poorer consistency between apparatus sensors and skin sensors.
The current system for measurement of wrist joint proprioception allows the researcher to decrease extraneous influences that may affect joint position sense awareness, and will help in future study aiming to determine precisely the role of the different structure involved in proprioception.
PMCID: PMC2828456  PMID: 20146811
14.  Ergonomic stressors and upper extremity disorders in vehicle manufacturing: cross sectional exposure-response trends 
OBJECTIVE: To evaluate the association between upper extremity soft tissue disorders and exposure to preventable ergonomic stressors in vehicle manufacturing operations. METHODS: A cross sectional study was conducted in one vehicle stamping plant and one engine assembly plant. A standardised physical examination of the upper extremities was performed on all subjects. An interviewer administered questionnaire obtained data on demographics, work history, musculoskeletal symptoms, non-occupational covariates, and psycho-physical (relative intensity) ratings of ergonomic stressors. The primary exposure score was computed by summing the responses to the psychophysical exposure items. Multivariate regression analysis was used to model the prevalence of disorders of the shoulders or upper arms, wrists or hands, and all upper extremity regions (each defined both by symptoms and by physical examination plus symptoms) as a function of exposure quartile. RESULTS: A total of 1315 workers (85% of the target population) was examined. The prevalence of symptom disorders was 22% for the wrists or hands and 15% for the shoulders or upper arms; cases defined on the basis of a physical examination were about 80% as frequent. Disorders of the upper extremities, shoulders, and wrists or hands all increased markedly with exposure score, after adjustment for plant, acute injury, sex, body mass index, systemic disease, and seniority. CONCLUSIONS: Musculoskeletal disorders of the upper extremities were strongly associated with exposure to combined ergonomic stressors. The exposure- response trend was very similar for symptom cases and for physical examination cases. It is important to evaluate all dimensions of ergonomic exposure in epidemiological studies, as exposures often occur in combination in actual workplaces.
PMCID: PMC1757592  PMID: 9764102
15.  Musicians' Medicine: Musculoskeletal Problems in String Players 
Clinics in Orthopedic Surgery  2013;5(3):155-160.
There is increasing attention to medical problems of musicians. Many studies find a high prevalence of work-related musculoskeletal disorders in musicians, ranging from 73.4% to 87.7%, and string players have the highest prevalence of musculoskeletal problems. This paper examines the various positions and movements of the upper extremities in string players: 1) basic postures for holding instruments, 2) movements of left upper extremity: fingering, forearm posture, high position and vibrato, 3) movements of right upper extremity: bowing, bow angles, pizzicato and other bowing techniques. These isotonic and isometric movements can lead to musculoskeletal problems in musicians. We reviewed orthopedic disorders that are specific to string players: overuse syndrome, muscle-tendon syndrome, focal dystonia, hypermobility syndrome, and compressive neuropathy. Symptoms, interrelationships with musical performances, diagnosis and treatment of these problems were then discussed.
PMCID: PMC3758983  PMID: 24009899
Upper extremities; String players; Musculoskeletal problems
16.  Effects of Static Flexion-relaxation on Paraspinal Reflex Behavior 
Static trunk flexion working postures and disturbed trunk muscle reflexes are related to increased risk of low-back pain. Animal studies conclude that these factors may be related; passive tissue strain in spinal ligaments causes subsequent short-term changes in reflex. Although studies have documented changes in the myoelectric onset angle of flexion-relaxation following prolonged static flexion and cyclic flexion we could find no published evidence related to the human reflex response of the trunk extensor muscles following a period of static flexion-relaxation loading.
Eighteen subjects maintained static lumbar flexion for 15 min. Paraspinal muscle reflexes were elicited both before and after the flexion-relaxation protocol using pseudorandom stochastic force disturbances while recording EMG. Reflex gain was computed from the peak value of the impulse response function relating input force perturbation to EMG response using time-domain deconvolution analyses.
Reflexes showed a trend toward increased gain after the period of flexion-relaxation (P < 0.055) and were increased with trunk extension exertion (P < 0.021). Significant gender differences in reflex gain were observed (P < 0.01).
Occupational activities requiring extended periods of trunk flexion contribute to changes in reflex behavior of the paraspinal muscles. Results suggest potential mechanisms by which flexed posture work may contribute to low-back pain. Significant gender differences indicate risk analyses should consider personal factors when considering neuromuscular behavior.
PMCID: PMC1630677  PMID: 15567532
Low-back; Reflex; Flexion-relaxation
17.  Manual matching of perceived surface orientation is affected by arm posture–Evidence of calibration between proprioception and visual experience in near space 
Proprioception of hand orientation (orientation production using the hand) is compared with manual matching of visual orientation (visual surface matching using the hand) in two experiments. In Experiment 1, using self-selected arm postures, the proportions of wrist and elbow flexion spontaneously used to orient the pitch of the hand (20% and 80% respectively) are relatively similar across both manual matching tasks and manual orientation production tasks for most participants. Proprioceptive error closely matched perceptual biases previously reported for visual orientation perception, suggesting calibration of proprioception to visual biases. A minority of participants, who attempted to use primarily wrist flexion while holding the forearm horizontal, performed poorly at the manual matching task, consistent with proprioceptive error caused by biomechanical constraints of their self-selected posture. In Experiment 2, postural choices were constrained to primarily wrist or elbow flexion without imposing biomechanical constraints (using a raised forearm). Identical relative offsets were found between the two constraint groups in manual matching and manual orientation production. The results support two claims: (1) manual orientation matching to visual surfaces is based on manual proprioception and (2) calibration between visual and proprioceptive experiences guarantees relatively accurate manual matching for surfaces within reach despite systematic visual biases in perceived surface orientation.
PMCID: PMC3272330  PMID: 22086494
Slant perception; proprioception; action measure; perceptual bias; inter-sensory calibration
18.  Effects of the Different Screwdriver Handle Sizes on the Forearm Muscles Activities and Wrist Motion during Screw-driving Work 
[Purpose] This study investigated the difference screwdriver handle size has on forearm muscle activities and wrist motion during screw-driving work. [Subjects] Fourteen males aged 20–30 years, were recruited. [Methods] We measured the forearm muscle activities using a MP 150 System and wrist motion using a 3D motion system. The subjects performed screw-driving tasks with different screwdriver handle sizes. [Results] The wrist flexion and ulnar deviation angles and flexor carpi ulnaris muscle activity significantly increased and wrist extension angle significantly decreased during screwdriver work with a thin handle. [Conclusion] We consider that industrial workers should perform screw-driving work using a screwdriver with a thick handle.
PMCID: PMC3820410  PMID: 24259876
Handle size; Screw-driving work; Wrist pain
19.  Conformational Changes in the Carpus During Finger Traps Distraction 
The Journal of hand surgery  2010;35(2):237-244.
Wrist distraction is a common treatment maneuver used clinically for the reduction of distal radial fractures and mid-carpal dislocations. Wrist distraction is also required during wrist arthroscopy to access the radiocarpal joint and has been used as a test for scapholunate ligament injury. However, the effect of a distraction load on the normal wrist has not been well studied. The purpose of this study was to measure the 3-D conformational changes of the carpal bones in the normal wrist as a result of a static distractive load.
The dominant wrists of 14 healthy volunteers were scanned using computed tomography at rest and during application of 98N of distraction. Load was applied using finger traps and volunteers were encouraged to relax their forearm muscles and to allow distraction of the wrist. The motions of the bones in the wrist were tracked between the unloaded and loaded trial using markerless bone registration. The average displacement vector of each bone was calculated relative to the radius as well as the interbone distances for 20 bone-bone interactions. Joint separation was estimated at the radiocarpal, midcarpal and carpal-metacarpal joints in the direction of loading using the radius, lunate, capitate and 3rd metacarpal.
With loading, the distance between the radius and 3rd metacarpal increased an average of 3.3±3.1mm in the direction of loading. This separation was primarily located in the axial direction at the radiocarpal (1.0±1.0mm) and midcarpal (2.0±1.7mm) joints. There were minimal changes in the transverse direction within the distal row, although the proximal row narrowed by 0.98±0.7mm. Distraction between the radius and scaphoid (2.5±2.2mm) was 2.4 times greater than between the radius and lunate (1.0±1.0mm).
Carpal distraction has a significant effect on the conformation of the carpus, especially at the radiocarpal and midcarpal joints. In the normal wrist, external traction causes twice as much distraction at the lunocapitate joint than at the radiolunate joint.
PMCID: PMC2841473  PMID: 20141894
Carpal; Kinematics; Distraction; Scaphoid; Lunate
20.  Focal hand dystonia in a patient with thoracic outlet syndrome 
A patient affected by thoracic outlet syndrome, with an involvement of the left lower primary trunk due to a rudimentary cervical rib, developed a severe hand dystonia on the same side. The dystonic posture was characterised by a flexion of the wrist with the fingers curled into the palm. Polygraphic recordings performed on the left flexor digitorum superficialis (FDS4) and extensor digitorum superficialis (EDC4) muscles, during a repetitive tapping task of the fourth digit, showed a loss of well formed bursts without a clear silent period along with long duration bursts of cocontraction in antagonistic muscles. The study of reciprocal inhibition between forearm flexor and extensor muscles showed a reduced amount of inhibition in both the disynaptic and the later presynaptic phase of inhibition. The patient underwent an operation with resection of the cervical rib. Twelve hours after the operation the patient experienced a significant improvement of the hand dystonia; the distonia had disappeared completely by two months with a progressive normalisation of reciprocal inhibition.

PMCID: PMC2170179  PMID: 9703190
21.  The modulation of upper extremity musculoskeletal disorders for a knowledge worker with chiropractic care and applied ergonomics: a case study 
This report describes the case management of musculoskeletal disorders for an employee in a college work environment using both chiropractic care and applied ergonomics.
Clinical Findings
A 54-year-old male office worker presented with decreased motor function in both wrists; intermittent moderate-to-severe headaches; and pain or discomfort in the neck, both shoulders, left hand and wrist, and lumbosacral region resulting from injuries sustained during recreational soccer and from excessive forces and awkward postures when interacting with his home and office computer workstations.
Intervention and Results
Ergonomic training, surveillance, retrofitted equipment with new furniture, and an emphasis on adopting healthy work-style behaviors were applied in combination with regular chiropractic care. Baseline ergonomic job task analysis identified risk factors and delineated appropriate control measures to improve the subject's interface with his office workstation. Serial reevaluations at 3-month, 1-year, and 2-year periods recorded changes to the participant's pain, discomfort, and work-style behaviors. At end of study and relative to baseline, pain scale improved from 4/10 to 2/10; general disability improved from 4 to 0; and hand grip strength (pounds) increased from 20 to 105 (left) and 45 to 100 (right). Healthy work habits and postures adopted in the 3-month to 1-year period regressed to baseline exposures for 3 of 6 risk priorities identified in the ergonomic job task analysis.
The patient responded positively to the intervention of chiropractic care and applied ergonomics.
PMCID: PMC3610949  PMID: 23997724
Human engineering; Chiropractic; Musculoskeletal pain; Posture
22.  Developing a Framework for Predicting Upper Extremity Muscle Activities, Postures, Velocities, and Accelerations During Computer Use: The Effect of Keyboard Use, Mouse Use, and Individual Factors on Physical Exposures 
Prediction models were developed based on keyboard and mouse use in combination with individual factors that could be used to predict median upper extremity muscle activities, postures, velocities, and accelerations experienced during computer use. In the laboratory, 25 participants performed five simulated computer trials with different amounts of keyboard and mouse use ranging from a highly keyboard-intensive trial to a highly mouse-intensive trial. During each trial, muscle activity and postures of the shoulder and wrist and velocities and accelerations of the wrists along with percentage keyboard and mouse use were measured. Four individual factors (hand length, shoulder width, age, and gender) were also measured on the day of data collection. Percentage keyboard and mouse use explained a large amount of the variability in wrist velocities and accelerations. Although hand length, shoulder width, and age were each significant predictors of at least one median muscle activity, posture, velocity, or acceleration exposure, these individual factors explained very little additional variability in any of the physical exposures investigated. The amount of variability explained for models predicting median wrist velocities and accelerations ranged from 75 to 84% but were much lower for median muscle activities and postures (0–50%). RMS errors ranged between 8 to 13% of the range observed. While the predictions for wrist velocities and accelerations may be able to be used to improve exposure assessment for future epidemiologic studies, more research is needed to identify other factors that may improve the predictions for muscle activities and postures.
PMCID: PMC3486439  PMID: 23066993
anthropometry; biomechanics; task-based exposure assessment
23.  Meta-Analysis: Association Between Wrist Posture and Carpal Tunnel Syndrome Among Workers 
Safety and Health at Work  2014;5(1):27-31.
Carpal tunnel syndrome (CTS) is a common work-related peripheral neuropathy. In addition to grip force and repetitive hand exertions, wrist posture (hyperextension and hyperflexion) may be a risk factor for CTS among workers. However, findings of studies evaluating the relationship between wrist posture and CTS are inconsistent. The purpose of this paper was to conduct a meta-analysis of existing studies to evaluate the evidence of the relationship between wrist posture at work and risk of CTS.
PubMed and Google Scholar were searched to identify relevant studies published between 1980 and 2012. The following search terms were used: “work related”, “carpal tunnel syndrome”, “wrist posture”, and “epidemiology”. The studies defined wrist posture as the deviation of the wrist in extension or flexion from a neutral wrist posture. Relative risk (RR) of individual studies for postural risk was pooled to evaluate the overall risk of wrist posture on CTS.
Nine studies met the inclusion criteria. All were cross-sectional or case–control designs and relied on self-report or observer's estimates for wrist posture assessment. The pooled RR of work-related CTS increased with increasing hours of exposure to wrist deviation or extension/flexion [RR = 2.01; 95% confidence interval (CI): 1.646–2.43; p < 0.01: Shore-adjusted 95% CI: 1.32–2.97].
We found evidence that prolonged exposure to non-neutral wrist postures is associated with a twofold increased risk for CTS compared with low hours of exposure to non-neutral wrist postures. Workplace interventions to prevent CTS should incorporate training and engineering interventions that reduce sustained non-neutral wrist postures.
PMCID: PMC4048004  PMID: 24932417
carpal tunnel syndrome; meta-analysis; systematic review
24.  Dissection of a Single Rat Muscle-Tendon Complex Changes Joint Moments Exerted by Neighboring Muscles: Implications for Invasive Surgical Interventions 
PLoS ONE  2013;8(8):e73510.
The aim of this paper is to investigate mechanical functioning of a single skeletal muscle, active within a group of (previously) synergistic muscles. For this purpose, we assessed wrist angle-active moment characteristics exerted by a group of wrist flexion muscles in the rat for three conditions: (i) after resection of the upper arm skin; (ii) after subsequent distal tenotomy of flexor carpi ulnaris muscle (FCU); and (iii) after subsequent freeing of FCU distal tendon and muscle belly from surrounding tissues (MT dissection). Measurements were performed for a control group and for an experimental group after recovery (5 weeks) from tendon transfer of FCU to extensor carpi radialis (ECR) insertion. To assess if FCU tenotomy and MT dissection affects FCU contributions to wrist moments exclusively or also those of neighboring wrist flexion muscles, these data were compared to wrist angle-moment characteristics of selectively activated FCU. FCU tenotomy and MT dissection decreased wrist moments of the control group at all wrist angles tested, including also angles for which no or minimal wrist moments were measured when activating FCU exclusively. For the tendon transfer group, wrist flexion moment increased after FCU tenotomy, but to a greater extent than can be expected based on wrist extension moments exerted by selectively excited transferred FCU. We conclude that dissection of a single muscle in any surgical treatment does not only affect mechanical characteristics of the target muscle, but also those of other muscles within the same compartment. Our results demonstrate also that even after agonistic-to-antagonistic tendon transfer, mechanical interactions with previously synergistic muscles do remain present.
PMCID: PMC3742526  PMID: 23967344
25.  The Hysteresis Effect in Carpal Kinematics 
The Journal of hand surgery  2006;31(4):594-600.
Carpal bones show hysteresis that is dependent on the direction of wrist motion during a continuous active loading protocol. We describe an accurate methodology for analyzing the hysteresis effect and we apply this model to analyze the effect of sequential ligament sectioning on scapholunate instability.
In 8 fresh cadaver forearms scaphoid, lunate, and third metacarpal motions were recorded while each wrist was moved in continuous cycles of active motion in flexion–extension and radioulnar deviation. Motions were analyzed for the intact state and after sequential sectioning of the scapholunate interosseous, scaphotrapezium, and radioscapho-capitate ligaments. Carpal motion was curve-fitted with respect to the third metacarpal motion using optimization criteria. The area between the 2 curves that represents opposite directions of wrist motion was measured to give the total hysteresis area. Repeated-measures analysis of variance was used to determine significance.
In the flexion–extension trials the scaphoid and lunate total hysteresis area was significantly greater than the intact state only after all 3 ligaments were sectioned. In the radioulnar deviation trials the scaphoid total hysteresis area was significantly greater than the intact after just scapholunate interosseous ligament sectioning; however, the lunate total hysteresis area decreased with additional sequential sectionings in 4 of the 8 specimens as compared with the intact state. These 4 specimens started with a significantly greater intact total hysteresis area than the other 4 specimens.
The computation of the total hysteresis area from the hysteresis effect was found to be a sensitive technique to determine the subtle onset of abnormal carpal motion. By using this technique in a ligament sectioning study significant increases in the total hysteresis area were seen after just scapholunate interosseous ligament sectioning during wrist radioulnar deviation. This subtle change may signify the onset of dynamic scapholunate instability. The total hysteresis area of the lunate in a subset of lax specimens did not increase after ligament sectioning. This divergent behavior may explain why some patients with scapholunate instability do not develop dorsal intercalated segmental instability.
PMCID: PMC2041845  PMID: 16632053
Carpal motion; hysteresis; neutral zone; scapholunate instability

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