Vibration energy absorption (VEA) in human fingers-hand-arm system.

A methodology for measuring the vibration energy absorbed into the fingers and the palm exposed to vibration is proposed to study the distribution of the vibration energy absorption (VEA) in the fingers-hand-arm system and to explore its potential association with vibration-induced white finger (VWF). The study involved 12 adult male subjects, constant-velocity sinusoidal excitations at 10 different discrete frequencies in the range of 16-1000 Hz, and four different hand-handle coupling conditions (finger pull-only, hand grip-only, palm push-only, and combined grip and push). The results of the study suggest that the VEA into the fingers is considerably less than that into the palm at low frequencies (< or = 25 Hz). They are, however, comparable under the excitations in the 250-1000 Hz frequency range. The finger VEA at high frequencies (> or = 100 Hz) is practically independent of the hand-handle coupling condition. The coupling conditions affect the VEA into the fingers and the palm very differently. The finger VEA results suggest that the ISO standardized frequency weighting (ISO 5349-1, 2001) may underestimate the effect of high frequency vibration on vibration-induced finger disorders. The proposed method may provide new opportunities to examine VEA and its association with VWF and other types of vibration-induced disorders in the hand-arm system.

A structural fingertip model for simulating of the biomechanics of tactile sensation.

Tactile performance of human fingertips is associated with activity of the nerve endings and sensitivity of the soft tissue within the fingertip to the static and dynamic skin indentation. The nerve endings in the fingertips sense the stress/strain states developed within the soft tissue, which are affected by the material properties of the tissues. The vibrotactile sensation and tactile performance are thus believed to be strongly influenced by the nonlinear and time-dependent properties of the soft tissues. The purpose of the present research is to simulate the biomechanics of tactile sensation. A two-dimensional model, which incorporates the essential anatomical structures of a finger (i.e. skin, subcutaneous tissue, bone, and nail), has been used for the analysis. The skin tissue is assumed to be hyperelastic and viscoelastic. The subcutaneous tissue is considered to be a nonlinear, biphasic material composed of a hyperelastic solid and an inviscid fluid phase. The nail and bone are considered to be linearly elastic. The advantages of the proposed fingertip model over the previous "waterbed" and "continuum" fingertip models include its ability to predict the deflection profile of the fingertip surface, the stress and strain distributions within the soft tissue, and most importantly, the dynamic response of the fingertip to mechanical stimuli. The proposed model is applied to simulate the mechanical responses of a fingertip under a line load, and in one-point (1PT) and two-point (2PT) tactile discrimination tests. The model's predictions of the deflection profiles of a fingertip surface under a line load agree well with the reported experimental data. Assuming that the mechanoreceptors in the dermis sense the stimuli associated with normal strains (the vertical and horizontal strains) and strain energy density, our numerical results suggest that the threshold of 2PT discrimination may lie between 2.0 and 3.0 mm, which is consistent with the published experimental data. The present study represents an effort to develop a structural model of the fingertip that incorporates its anatomical structure, and the nonlinear and time-dependent properties of the soft tissues.

Elimination of the friction effects in unconfined compression tests of biomaterials and soft tissues.

The mechanical properties of biomaterials and soft tissues are determined conventionally using unconfined compression tests. In such tests, frictionless specimen/platen contact in unconfined compression tests has to be assumed in determining the material properties of the materials. Previous theoretical analysis demonstrated, however, that the effects of the friction at the specimen/platen contact interface on the measured stress responses are non-negligible. In this study, a computational approach was proposed to eliminate the effects of friction. The friction coefficient between the specimen and the compression platens is measured first. Using a finite element model, the stress-strain relationship, without the influence of the friction effects, can be derived from the experimental data obtained in conventional unconfined compression tests. In order to validate the proposed approach, unconfined compressive tests of rubber have been performed.

Analysis of skin deformation profiles during sinusoidal vibration of fingerpad.

Vibrotactile perception threshold measurement has been widely used to diagnose the severity of peripheral neuropathy associated with hand-arm vibration syndrome and sensory losses in stroke and diabetic patients. The vibration perception threshold is believed to be influenced by many factors, such as contact force and vibration frequency. The present study is intended to analyze, theoretically, the time-dependent deformation profile of skin surface, strain distributions within soft tissue, and response force of a fingertip when it is stimulated by a probe vibrating with a sinusoidal movement. A two-dimensional finite element model, which incorporates the essential anatomical structures of a finger: skin, subcutaneous tissue, bone, and nail, has been proposed to analyze the effects of vibration amplitude, frequency, and preindentation on the dynamic interaction between the fingerpad and vibrating probe. The simulation results suggest that the fraction of time over which the skin separates from the probe during vibration increases with increasing vibration frequency and amplitude, and decreases with increased preindentation of the probe. The preindentation of the probe has been found to significantly reduce the trend of skin/probe decoupling. The simulation results show reasonably consistent trends with the reported experimental data.

Dynamic interaction between a fingerpad and a flat surface: experiments and analysis.

Many neural and vascular diseases in hands and fingers have been related to the degenerative responses of local neural and vascular systems in fingers to excessive dynamic loading. Since fingerpads serve as a coupling element between the hand and the objects, the investigation of the dynamic coupling between fingertip and subjects could provide important information for the understanding of the pathomechanics of these neural and vascular diseases. In the present study, the nonlinear and time-dependent force responses of fingertips during dynamic contact have been investigated experimentally and theoretically. Four subjects (2 male and 2 female) with an average age of 24 years participated in the study. The index fingers of right and left hands of each subject were compressed using a flat platen via a micro testing machine. A physical model was proposed to simulate the nonlinear and time-dependent force responses of fingertips during dynamic contact. Using a force relaxation test and a fast loading test at constant loading speed, the material/structural parameters underlying the proposed physical model could be identified. The predicted rate-dependent force/displacement curves and time-histories of force responses of fingertips were compared with those measured in the corresponding experiments. Our results suggest that the force responses of fingertips during the dynamic contacts are nonlinear and time-dependent. The physical model was verified to characterize the nonlinear, rate-dependent force-displacement behaviors, force relaxations, and time-histories of force responses of fingertips during dynamic contact.

Modeling of time-dependent force response of fingertip to dynamic loading.

An extended exposure to repeated loading on fingertip has been associated to many vascular, sensorineural, and musculoskeletal disorders in the fingers, such as carpal tunnel syndrome, hand-arm vibration syndrome, and flexor tenosynovitis. A better understanding of the pathomechanics of these sensorineural and vascular diseases in fingers requires a formulation of a biomechanical model of the fingertips and analyses to predict the mechanical responses of the soft tissues to dynamic loading. In the present study, a model based on finite element techniques has been developed to simulate the mechanical responses of the fingertips to dynamic loading. The proposed model is two-dimensional and incorporates the essential anatomical structures of a finger: skin, subcutaneous tissue, bone, and nail. The skin tissue is assumed to be hyperelastic and viscoelastic. The subcutaneous tissue was considered to be a nonlinear, biphasic material composed of a hyperelastic solid and an invicid fluid, while its hydraulic permeability was considered to be deformation dependent. Two series of numerical tests were performed using the proposed finger tip model to: (a) simulate the responses of the fingertip to repeated loading, where the contact plate was assumed to be fixed, and the bone within the fingertip was subjected to a prescribed sinusoidal displacement in vertical direction; (b) simulate the force response of the fingertip in a single keystroke, where the keyboard was composed of a hard plastic keycap, a rigid support block, and a nonlinear spring. The time-dependent behavior of the fingertip under dynamic loading was derived. The model predictions of the time-histories of force response of the fingertip and the phenomenon of fingertip separation from the contacting plate during cyclic loading agree well with the reported experimental observations.

A method for reducing adaptor misalignment when testing gloves using ISO 10819.

OBJECTIVES: International standard ISO 10819 was established in order to quantify the vibration attenuation characteristics of anti-vibration gloves. One problem that exists with the standard is possible misalignment of the palm adaptor that is placed underneath the test glove. If the adaptor becomes misaligned, the measured glove transmissibility will be lower than the actual value. A tri-axial accelerometer was installed in the adaptor and was used as the basis for providing visual feedback of the adaptor alignment to the test subjects. The objective of this study was to test the hypothesis that adaptor misalignment could be reduced by providing feedback to the test subjects. METHODS: Eight male volunteers (mean age 24.8 yr) were used in the study. Each subject performed two sets of tests: the standard ISO 10819 glove test and the modified version. Three different anti-vibration gloves were tested. Glove transmissibility and adaptor misalignment were calculated for each glove. A three-way analysis of variance was used to analyze the results. RESULTS: A comparison of the two testing methods showed that the modified glove testing method did reduce misalignment significantly, which, in turn, resulted in an increase in the measured glove transmissibility. CONCLUSIONS: The proposed method greatly improved the standard deviation of transmissibility and made the test results more consistent.

Mechanical behavior of the Lisfranc and dorsal cuneometatarsal ligaments: in vitro biomechanical study.

OBJECTIVES: To define the anatomy and mechanical properties of two ligaments stabilizing the medial tarsometatarsal joints: the Lisfranc ligament and the dorsal cuneometatarsal ligament. DESIGN: Cadaveric study in normal feet. SETTING: Biomechanics laboratory. PATIENTS OR PARTICIPANTS: Twelve fresh-frozen cadaveric feet were studied. INTERVENTION: The Lisfranc and dorsal cuneometatarsal ligaments were dissected, dimensions measured, and material properties determined with a servohydraulic MTS machine on bone-ligament-bone preparations. MAIN OUTCOME MEASUREMENTS: Stiffness, strain, stress, modulus, failure load, ligament length, width, thickness, and cross-sectional area were determined. RESULTS: Dorsal ligament stiffness was 66.3+/-18.3 newtons per millimeter and the Lisfranc ligament stiffness was 189.7+/-57.2 newtons per millimeter. The failure load of the dorsal ligament averaged 150.7+/-33.1 newtons and for the Lisfranc ligament, 368.8+/-126.8 newtons. CONCLUSIONS: The stiffness and load to failure of the dorsal cuneometatarsal ligament were much higher than anticipated, which indicates that it contributes significantly to stabilizing the second metatarsal to the first cuneiform.

Hand-transmitted vibration and biodynamic response of the human hand-arm: a critical review.

Hand-arm vibration syndrome (HAVS) has been associated with prolonged exposure to vibration transmitted to the human hand-arm system from hand-held power tools, vibrating machines, or hand-held vibrating workpieces. The biodynamic response of the human hand and arm to hand transmitted vibration (HTV) forms an essential basis for effective evaluations of exposures, vibration-attenuation mechanisms, and potential injury mechanisms. The biodynamic response to HTV and its relationship to HAVS are critically reviewed and discussed to highlight the advances and the need for further research. In view of its strong dependence on the nature of HTV and the lack of general agreement on the characteristics of HTV, the reported studies are first reviewed to enhance an understanding of HTV and related issues. The characteristics of HTV and relevant unresolved issues are discussed on the basis of measured data, proposed standards, and measurement methods, while the need for further developments in measurement systems is emphasized. The studies on biodynamic response and their findings are grouped into four categories based on the methodology used and the objective. These include studies on (1) through-the-hand-arm response, expressed in terms of vibration transmissibility; (2) to-the-hand response, expressed in terms of the force-motion relationship of the hand-arm system; (3) to-the-hand biodynamic response function, expressed in terms of vibration energy absorption; and (4) computer modeling of the biodynamic response characteristics.

Material properties of the trapezial and trapeziometacarpal ligaments.

Destabilization of the trapezium from its normal orientation with respect to the trapezoid, second metacarpal, and thumb metacarpal leads to incongruity at the trapeziometacarpal (TMC) joint. Abnormal shear forces may eventually result in TMC joint arthritis. By determining the relative stiffness and strength of the ligaments that stabilize this joint, one may infer their role in providing stability to the TMC joint. This study addresses the material properties of the ligaments stabilizing the trapezium and TMC joint to better understand the mechanics and kinematics of this joint. Fresh-frozen cadaveric hands (10 males and 10 females) were used to obtain bone-ligament-bone complexes from the dorsal and volar trapeziotrapezoid ligaments, dorsal and volar trapezio-second metacarpal ligaments, anterior oblique ligament, dorsoradial ligament, and trapezio-third metacarpal (T-III MC) ligament. The following material properties were derived from our data: ultimate load, ultimate stress (normalized failure load), ultimate strain (percent elongation), stiffness, toughness (energy to failure), and hysteresis. The dorsoradial ligament demonstrated the greatest ultimate load and toughness (energy to failure). The T-III MC ligament demonstrated the greatest ultimate stress (normalized failure load) and stiffness. The anterior oblique ligament demonstrated the least stiffness and the greatest hysteresis. The material properties of capsuloligamentous structures may be a good indicator of their importance to joint stability. Using these criteria we conclude that the T-III MC and dorsoradial ligaments are important stabilizers of the trapezium and TMC joint, respectively. These two ligaments were found to be the strongest, stiffest, and toughest ligaments, while the anterior oblique ligament was relatively weak and compliant. The dorsal trapezio-second metacarpal, volar trapezio-second metacarpal, and T-III MC ligaments were all relatively strong and are anatomically aligned to function as tension bands to restrain the trapezium against cantilever bending forces applied to it by the thumb during key or tip pinch.

Mechanical advantage of the thumb muscles.

The purpose of this study was to measure the moment arms of four extrinsic muscles (flexor pollicis longus, extensor pollicis longus, extensor pollicis brevis, and abductor pollicis longus) and four intrinsic muscles (flexor pollicis brevis, abductor pollicis brevis, adductor pollicis, and opponents pollicis) of the thumb at the interphalangeal, the metacarpophalangeal, and the carpometacarpal joints in the same cadaver specimens and to examine the specific role of each muscle. Measurements were made on seven fresh frozen cadaver hands. The moment arms were measured during flexion/extension of the interphalangeal joint, flexion/extension and adduction/abduction of the metacarpophalangeal joint, and flexion/extension and adduction/abduction of the carpometacarpal joint. Moment arms were computed using the slope of the tendon excursion joint angle relationship. The specific function of each muscle was determined by multiplying the measured moment arms by the maximum force that each muscle can generate. It was found that the flexor pollicis longus was a pure flexor while flexor pollicis brevis was an adductor as well as a flexor, the extensor pollicis longus was an extensor and an adductor, extensor pollicis brevis was an extensor and a mild abductor, the abductor pollicis longus was an extensor as well as an abductor, the abductor pollicis brevis was mainly an abductor, the adductor pollicis was a major flexor as well as an adductor, and the opponents pollicis was a flexor and an abductor.

Effects of static fingertip loading on carpal tunnel pressure.

The purpose of this study was to explore the relationship between carpal tunnel pressure and fingertip force during a simple pressing task. Carpal tunnel pressure was measured in 15 healthy volunteers by means of a saline-filled catheter inserted percutaneously into the carpal tunnel of the nondominant hand. The subjects pressed on a load cell with the tip of the index finger and with 0, 6, 9, and 12 N of force. The task was repeated in 10 wrist postures: neutral; 10 and 20 degrees of ulnar deviation; 10 degrees of radial deviation; and 15, 30, and 45 degrees of both flexion and extension. Fingertip loading significantly increased carpal tunnel pressure for all wrist angles (p = 0.0001). Post hoc analyses identified significant increase (p < 0.05) in carpal tunnel pressure between unloaded (0 N) and all loaded conditions, as well as between the 6 and 12 N load conditions. This study demonstrates that the process whereby fingertip loading elevates carpal tunnel pressure is independent of wrist posture and that relatively small fingertip loads have a large effect on carpal tunnel pressure. It also reveals the response characteristics of carpal tunnel pressure to fingertip loading, which is one step in understanding the relationship between sustained grip and pinch activities and the aggravation or development of median neuropathy at the wrist.

Roles of deltoid and rotator cuff muscles in shoulder elevation.

OBJECTIVE: The objective of this study was to measure abduction moment arms of the supraspinatus, subscapularis, infraspinatus, and deltoid (anterior, middle, and posterior portions) muscles during humeral elevation in the scapular plane (abduction). DESIGN: Moment arms were measured by conducting an in vitro experiment. BACKGROUND: The moment arm of a muscle represents its mechanical advantage, which is an important determinant of muscle function. METHODS: Measurements were made on 10 fresh frozen cadaveric specimens. Tendon excursions were measured as the humerus was elevated in the plane of the scapula. The principle of virtual work was used to estimate the muscle moment arm of each muscle by computing the slope of the tendon excursion versus joint angle relationship. RESULTS: Moment arms were affected by joint angle in a non-linear fashion. The anterior deltoid, middle deltoid, subscapularis, and infraspinatus muscles had abduction moment arms throughout most of the range of motion studied. The posterior deltoid had an adduction moment arm. Internal and external humeral rotation affected the elevation moment arms of all six muscles. CONCLUSIONS: Abduction moment arm magnitudes of the muscles studies vary throughout the arc of elevation. This study was limited by considering broad muscles to have a single line of action. RELEVANCE: The positive elevation moment arms of the infraspinatus and subscapularis muscles indicate that they can elevate the arm in addition to acting as stabilizers. Thus this study suggests a biomechanical explanation for the clinical success of conservative treatment for rotator cuff tears.

Accuracy of a video strain measurement system.

The purpose of this study was to determine the accuracy of a video system which our laboratory has been using to measure soft tissue strain. Both static and dynamic error analyses were performed to assess the accuracy of our video system. Static error was defined as the amount of movement reported by the video system for markers that were stationary. Dynamic error was defined as the difference between the motion of the markers as reported by the video system and their actual motion. Two sets of fluorescent markers were attached to a servo-hydraulic materials test machine. One marker set was attached to the hydraulic actuator (moving markers) and the other set was attached to the base of the machine (stationary markers). Five different marker sizes, five camera distances, and seven different loading rates were studied. Results indicated that the static error was independent of marker size, and that the dynamic error was independent of the loading rate and marker size for loading rates of 50% of the camera field of view (CFV) per second or slower. For loading rates greater than 50 percent of CFV per second, the marker size did have an affect on the dynamic error. The mean static error was found to be 0.026 percent of CFV and the mean dynamic error was found to be 0.062 percent of CFV.

Measurement of creep strain of flexor tendons during low-force high-frequency activities such as computer keyboard use.

The aim of this study was to measure tendon strain during low-force, high-frequency activities such as computer keyboard use. Prior to creep strain testing an estimate of flexor tendon force during keyboard use was made. Tendon force was measured indirectly by comparing electromyographic activity of the flexor and extensor digitorum muscles in five human volunteers for various hand activities. Results of the electromyographic study showed that flexor tendon forces during keyboard use may be as high as 60 N. Sixty eight flexor digitorum tendons from 17 fresh-frozen cadaver hands were used for the creep strain tests. Three loading conditions (static, 1 Hz cyclic, (1/4) Hz cyclic) and four load levels (10, 20, 50, 100 N) were used. Results of the creep study showed that for a flexor tendon force of 60 N the total strain of the tendon would be approximately 1.8%. This does not appear to be enough strain to cause permanent damage to the tendon according to current cumulative strain models. RELEVANCE: Recent studies have shown an increase in hand and wrist tendinitis among computer users. At the present time the aetiology is unknown, but risk factors commonly associated with tendinitis are hand forces, wrist postures, and frequency of finger movements. This research looks at tendon creep due to repeated force as a possible aetiology.

Evaluation of absorbable poly(ortho esters) for use in surgical implants.

Recent reports describe an unfavorable noninfective inflammatory response to acidic degradation products in clinical applications of bone fixation devices fabricated from bulk hydrolyzing polyglycolides and polylactides (PGA and PLA). The work described here suggests that poly(ortho esters) (POEs) offer an alternative. By comparison, hydrophobic POEs degrade predominately via surface hydrolysis, yielding first a combination of nonacidic degradation products, followed by alcoholic and acidic products gradually over time. POE specimens proved acutely nontoxic in United States Pharmacopeia tests of cellular, intracutaneous, systemic, and intramuscular implant toxicity. Hot-molded specimens degraded slowly in saline, retaining 92% initial stiffness (1.6 GPa flexion) and retaining 80% initial strength (66 MPa flexion) in 12 weeks. Degradation was almost unaffected by decreasing saline pH from 7.4 to 5.0. This demonstrated the relative hydrophobicity of POEs, since incorporation of small amounts of acid within the polymer markedly increases the degradation rate. Degradation rates were increased substantially by dynamic mechanical loading in saline. This may be true for other degradable polymers also, but no data could be found in the literature. Presumably, tensile loading opens microcracks, allowing water to enter. Solvent cast POE films were strong in tension (30 + MPa tensile yield) and reasonably tough (12-15% elongation to yield). Higher molecular weight films (41-67 kDa) showed no degradation in mechanical properties after 31 days in physiological buffer at body temperature. A 27-kDa film offered similar initial strength and stiffness but began showing mechanical degradation at 31 days. The films showed a decrease in weight with exposure time but no change in either molecular weight or water absorption at 31 days, further supporting the observation that POE degrades by surface hydrolysis rather than by bulk hydrolysis.

Investigation of low-force high-frequency activities on the development of carpal-tunnel syndrome.

The objective of this study was to determine the effects of repetitive motion on the flexor tendons and synovium in the carpal tunnel. One possible mechanism of tendon damage is fraying of the tendons as they slide past each other in the carpal tunnel. Increases in tendon friction were measured in human cadaver arms. The flexor tendons were loaded using pneumatic cylinders while load cells were used to measure tendon force both distal and proximal to the carpal tunnel. Results showed that tendon force distal to the carpal tunnel decreased by over 10% after 6 h, while tendon force proximal to the carpal tunnel remained constant. Two rhesus monkeys were used to further study the effects of repetitive motion. One arm of each animal was subjected to 729000 repetitive cycles over a 3-week period. Results of the animal study showed that highly repetitive motions encountered over a relatively short period of time had little effect on the tissue in and around the carpal tunnel.

Preliminary biocompatibility screening of several biodegradable phosphate fiber reinforced polymers.

This article describes preliminary biocompatibility screening of three degradable phosphate fibers containing K +, Ca +2/Na + and Na +/Ca +2/Al +3 ions in the polymer chain, and of several different degradable polymers reinforced with these fibers. Biodegradable phosphate fibers of calcium-sodium-metaphosphate (CSM) and sodium-calcium-aluminum-polyphosphate (NCAP) were acutely nontoxic in cellular, tissue, and whole animal evaluations, as determined by standard acute toxicity tests. Histological studies of bone implants sites fabricated from composites of copolymers of poly(E-caprolactone/L-lactide) and poly(ortho ester) reinforced with either CSM or NCAP fibers showed these composite materials to be nontoxic, with no abnormal inflammatory response. However, histological evaluation of muscle implants sites revealed the appearance of necrotic foci associated with implant sites in 12 of 22 NCAP containing composite specimens (p less than 0.05). Results of this preliminary biocompatibility screening suggest CSM fibers may be useful in reinforcing degradable polymers for production of completely biodegradable composites for implant use.

Biceps tendon and superior labral injuries.

Twenty-two patients sustained injury to the biceps tendon, rotator cuff interval, or superior labrum. Seven patients with "interval lesions" underwent biceps tenodesis, one biceps repair, and three subscapularis repairs. All were satisfied, although one tenodesis failed with distal biceps retraction. Key arthroscopic findings included biceps or subscapularis fraying. Thirteen patients with "S.L.A.P. (superior labrum anterior to posterior) lesions" underwent labral debridement. All but one obtained pain relief. Eight cadaveric shoulders exhibited extreme anatomic variability of the bicipital origin/superior labral attachment. Biomechanical study showed anterior-superior and posterior-superior labral strain with simulated biceps contraction to be greatest in shoulder abduction (p < 0.01). Biceps tendon strain was greatest in shoulder adduction (p < 0.05). A continuum of injuries to the biceps tendon exist, from the rotator cuff interval to the labral attachment. Key arthroscopic findings may assist in the difficult diagnosis of interval lesions. Individual anatomy and mechanism of injury may determine the site of the lesion.