BIOMECHANICS OF THE HUMAN HAND

The paper provides basic information on human hand's anatomical structure with the location of joints and consequent types of achievable movements. The biomechanics of the human hand is described using two different kinematic models of the hand. The differences between the models are described. The Schlesinger's classification of movements of the human hand is introduce

Clinical study of the factors affecting radioulnar deviation of the wrist joint

<p>Abstract</p> <p>Background</p> <p>The radioulnar carpal joint is critical for hand and wrist function. Radioulnar deviation indicates distal radioulnar joint flexibility and reflects the structure and function of the carpal bones, ulna, radius and ligaments. The present study examined whether radioulnar deviation is affected by gender, manual labor, playing a musical instrument, playing sport, handedness, previous fracture or prior inflammation. The study used clinical findings based on anatomical landmarks</p> <p>Methods</p> <p>The ulnar, radial and total deviations for both left and right hands were measured in 300 subjects (157 men and 143 women) of mean age 21.7 years. Measurements were made with the forearm in a fixed pronated position using a novel specially designed goniometer. The gender of each subject was recorded, and information on playing of sport, playing a musical instrument, manual labor, handedness, and history of fracture or inflammation was sought. Data were analyzed using a multifactor ANOVA test.</p> <p>Results</p> <p>No statistically significant difference (p-value > 0.05) was found between those comparing groups except the total deviation of athletes' left hand versus the total deviation of non athletes' left hand (p-value 0.041 < 0.05) and the radial deviation of manual workers' left hand and non manual workers' left hand (p-value 0.002 < 0.05).</p> <p>Conclusions</p> <p>This study was based on clinical findings using anatomical landmarks. We found that manual workers and athletes showed greater left hand flexibility. This suggests that activities that place chronic stress on the radiocarpal joint can independently affect radioulnar deviation.</p

The effect of forearm posture on wrist flexion in computer workers with chronic upper extremity musculoskeletal disorders

<p>Abstract</p> <p>Background</p> <p>Occupational computer use has been associated with upper extremity musculoskeletal disorders (UEMSDs), but the etiology and pathophysiology of some of these disorders are poorly understood. Various theories attribute the symptoms to biomechanical and/or psychosocial stressors. The results of several clinical studies suggest that elevated antagonist muscle tension may be a biomechanical stress factor. Affected computer users often exhibit limited wrist range of motion, particularly wrist flexion, which has been attributed to increased extensor muscle tension, rather than to pain symptoms. Recreational or domestic activities requiring extremes of wrist flexion may produce injurious stress on the wrist joint and muscles, the symptoms of which are then exacerbated by computer use. As these activities may involve a variety of forearm postures, we examined whether changes in forearm posture have an effect on pain reports during wrist flexion, or whether pain would have a limiting effect on flexion angle.</p> <p>Methods</p> <p>We measured maximum active wrist flexion using a goniometer with the forearm supported in the prone, neutral, and supine postures. Data was obtained from 5 subjects with UEMSDs attributed to computer use and from 13 control subjects.</p> <p>Results</p> <p>The UEMSD group exhibited significantly restricted wrist flexion compared to the control group in both wrists at all forearm postures with the exception of the non-dominant wrist with the forearm prone. In both groups, maximum active wrist flexion decreased at the supine forearm posture compared to the prone posture. No UEMSD subjects reported an increase in pain symptoms during testing.</p> <p>Conclusion</p> <p>The UEMSD group exhibited reduced wrist flexion compared to controls that did not appear to be pain related. A supine forearm posture reduced wrist flexion in both groups, but the reduction was approximately 100% greater in the UEMSD group. The effect of a supine forearm posture on wrist flexion is consistent with known biomechanical changes in the distal extensor carpi ulnaris tendon that occur with forearm supination. We infer from these results that wrist extensor muscle passive tension may be elevated in UEMSD subjects compared to controls, particularly in the extensor carpi ulnaris muscle. Measuring wrist flexion at the supine forearm posture may highlight flexion restrictions that are not otherwise apparent.</p

Ergonomics

ObjectiveAn equation was developed for estimating hand activity level (HAL) directly from tracked RMS hand speed (S) and duty cycle (D).BackgroundTable lookup, equation, or marker-less video tracking can estimate HAL from motion/exertion frequency (F) and D. Since automatically estimating F is sometimes complex, HAL may be more readily assessed using S.MethodsHands from 33 videos originally used for the HAL rating were tracked to estimate S, scaled relative to hand breadth (HB), and single-frame analysis was used to measure D. Since HBs were unknown, a Monte Carlo method was employed for iteratively estimating the regression coefficients from US Army anthropometry survey data.ResultsThe equation: =10[e\ue2\u2c6\u201915.87+0.02D+2.25lnS1+e\ue2\u2c6\u201915.87+0.02D+2.25lnS], R2 = 0.97, had a residual range \uc2\ub10.5 HAL.ConclusionsThe S equation superiorly fit the Latko (1997) data and predicted independently observed HAL values (Harris, 2011) better (MSE=0.16) than the F equation (MSE=1.28).Practitioner SummaryAn equation was developed for estimating the HAL rating for the ACGIH Threshold Limit Value\uc2\uae based on hand RMS speed and duty cycle. Speed is more readily evaluated from videos using semi-automatic markerless tracking, than frequency. The speed equation predicted observed HAL values much better than the F equation.R01 OH007914/OH/NIOSH CDC HHS/United StatesR01OH007914/OH/NIOSH CDC HHS/United StatesR21 EB014583/EB/NIBIB NIH HHS/United StatesR21 OH010221/OH/NIOSH CDC HHS/United StatesR21OH010221/OH/NIOSH CDC HHS/United States2015-12-01T00:00:00Z25343278PMC466488

Master of Science

thesisLateral epicondylalgia (LE), commonly known as tennis elbow, is an upper extremity musculoskeletal disorder that affects 1-3% of the general population. Despite the prevalence and persistence, specific diagnoses and a preferred treatment approach remain in question. Eccentric wrist extension therapy has recently shown promise in rehabilitation of LE. A device has been developed to assist in future research of eccentric therapy protocols. This device is capable of simulating conventional eccentric loading methods while offering additional functionality and features. A motion capture and surface electromyography study has been conducted to evaluate the ability of the device to supply comparable stimuli to three conventional loading methods. Study results indicate the developed device is capable of producing similar wrist kinematics and forearm extensor muscle potential to all three conventional methods. Wrist motion during wrist extensions shows some differences though not statistically significant. The similar wrist kinematics and forearm extensor muscle electromyography produced while using the device support the need for further studies and development of the device's relevance in rehabilitation of LE

Design characteristics to reduce inadvertent cross-axis coupling during side stick handling of aircraft pitch and roll axis control

« RÉSUMÉ : L’intégration d’un contrôle de vol tel que le mini-manche latéral (side stick) dans une cabine de pilotage occasionne des difficultés pour le pilote au niveau de la manœuvrabilité de l’avion. Il est plus difficile d’induire une commande dans un axe sans le faire par inadvertance dans l’axe opposé. Ce couplage des axes par inadvertance se fait plus facilement puisque les axes de roulis et de tangage (pitch) sont couplés. Le présent travail adresse trois caractéristiques de conception pour le montage du mini-manche latéral et de l’accoudoir pouvant aider à diminuer le couplage des axes par inadvertance. Les caractéristiques de conception prennent en considération la variabilité anthropométrique de la population pilote visée (1.57m femme à 1.9m homme). Sept pilotes ayant des mesures anthropométriques variées ont participé au test. Les tâches de vol demandées étaient des tâches sur un seul axe, soit en roulis ou en tangage qui ont été répétées pour chaque configuration. Pour comparer les configurations la variable durée ainsi que l’intégrale du couplage par inadvertance ont été analysées pour chaque manœuvre. Les résultats démontrent qu’un petit accoudoir, ne supportant qu’une partie de l’avant bras, diminue le couplage par inadvertance en roulis et la rotation de la boîte du mini-manche latéral vers l’extérieur diminue le couplage par inadvertance pour des manœuvres tangage.» «---------- ABSTRACT : Integrating a manual flight control inceptor with coupled axes such as the side stick within a flight deck creates challenges for the pilot to input a one-axis command without inadvertently inducing inputs in the opposite axis. The present paper studies three design features of the side stick and armrest setup believed to help reduce inadvertent cross-axis coupling occurrences. Design features address the aimed pilot population anthropometry (1.57m woman to 1.9m male)and their variability in upper segment measurements. Seven pilots of varying anthropometric sizes were asked to perform one-axis manoeuvres in pitch and roll for each setup configuration. To compare the setups both the duration and the definite integral of the unintended cross-axis input were processed and analyzed for each manoeuvre. Findings show that a short armrest reduces the occurrences of cross-axis input for the roll manoeuvre, whereas the side stick skew reduces inadvertent cross-axis coupling for the pitch manoeuvres.

The Effect of training, aim pattern and target type on the ergonomics and efficiency of handheld scanners

Handheld scanning is a prevalent industrial task that is prone to injury due to the repetitive motion of the task. Studies conducted with Rochester Institute of Technology and Honeywell have sought to discover the ergonomic and efficiency benefits of various scanning technologies and methods. One factor not fully investigated in these earlier works is the effect of training on the proper use of scanners. This thesis study compares trained and untrained user performance and ergonomics during a series of scanning tasks using a hand held omni-directional scanner. Comparison is based on such variables as target type (image that is scanned), aiming pattern (image projected from scanner) and time stress (self-paced versus time stress paced). Through this study is the potential to assess the value of training on efficiency and ergonomics during hand held scanner use. A trained and an untrained group (each consisting of eight subjects) performed scanning tasks daily for ten days. Wrist postures and task completion times were recorded throughout the study as well as perceived comfort and usability. Results show that the untrained group tended to have greater wrist deviations and thus poorer ergonomics overall. With the exception of the first day, the trained and untrained groups did not differ in terms of efficiency. As a result of this first day difference, level of training seemed to affect efficiency over time resulting in a quick learning curve for the untrained group. There was a significant aim pattern-target type relationship for both training groups in terms of ergonomics and efficiency. Results suggest aim pattern preference was a function of training level. Under time stress, the effect on ergonomics depended on wrist posture and training level, but the trained group tended to have a more detrimental effect to ergonomics than the untrained group. As expected, efficiency increased under time stress, but time stress had no significant effect on perceived usability and comfort

MRI Investigation of Computer Users With and Without Chronic Wrist Pain

Epidemiological studies have demonstrated a link between repetitive work and upper extremity musculoskeletal disorders (UEMSD), but the issue of causality remains controversial. Studies have shown an association between restricted wrist range of motion (ROM) and UEMSD in computer users. These restrictions were attributed to increased antagonist muscle tension. The first objective of this thesis was to compare wrist flexion ROM in computer users with UEMSD versus asymptomatic individuals with minimal computer exposure. The UEMSD group exhibited significantly reduced wrist flexion compared to controls. Measures of flexion with a supine forearm posture reduced wrist flexion in both groups, but the reduction was approximately 100% greater in the UEMSD group. The effect of a supine forearm posture on wrist flexion is consistent with known biomechanical changes in the distal extensor carpi ulnaris tendon. We infer from these results that wrist extensor muscle tension may be elevated in UEMSD subjects compared to controls. Increased antagonist muscle tension would alter the dynamics of the wrist joint and may alter carpal kinematics. The second objective of this thesis was to compare wrist flexion ROM and carpal flexion kinematics between UEMSD and asymptomatic computer users. The UEMSD group exhibited significantly reduced wrist flexion compared to controls. In both groups, maximum active wrist flexion decreased at the supine forearm posture compared to the prone posture. However, there was no significant difference in carpal flexion kinematics between groups. Abnormalities were tentatively identified in the kinematics MRI of 7 symptomatic wrists, and subsequent clinical imaging confirmed presumably post-traumatic injuries in 3 wrists and 12 intraosseous ganglia in 3 wrists. The etiology of intraosseous ganglia is controversial, but several theories implicates chronic ligament stress. The prevalence of abnormalities in the symptomatic wrists suggests that MRI may be useful in detecting wrist abnormalities related to UEMSD symptoms. The third objective of this thesis was to compare wrist flexion range of motion and the prevalence of MRI-identified abnormalities between UEMSD and asymptomatic computer users. The UEMSD group exhibited significantly reduced dominant wrist flexion compared to controls. There was no significant loss of flexion between the prone and supine forearm postures in either group, which may be related to the frequent finding of subluxation or dislocation of the distal extensor carpi ulnaris tendon. Extraosseous ganglia were common in both symptomatic and asymptomatic wrists, and there was no significant difference in their size. Intraosseous ganglia were more frequent and significantly larger in the symptomatic wrists. The symptoms associated with intraosseous ganglia may be related to their size, and symptoms were often well-localized to the sites of the larger intraosseous ganglia. The results of this study suggest that increased antagonist muscle tension in symptomatic computer users may increase ligament stress. To the best of our knowledge this is the first MRI study comparing the prevalence of wrist abnormalities between symptomatic and asymptomatic computer users