Impact of finger posture on mapping from muscle activation to joint torque

BACKGROUND: The mapping from muscle activation to joint torque production can be difficult to determine for the multi-articular muscles of the fingers. This relationship was examined in vivo as a function of posture in the index finger. METHODS: Five healthy adults participated in an experiment in which the seven muscles of the index finger were sequentially electrically stimulated using intramuscular electrodes. Each muscle was stimulated at 12 different finger postures consisting of specified flexion of the metacarpophalangeal, proximal interphalangeal, and distal interphalangeal joints, while fingertip forces and moments were recorded. FINDINGS: Repeated measures analysis of variance revealed that joint torques resulting from the stimulation were significantly dependent upon finger posture (p < 0.05). The magnitude of the change in joint torque across postures was generally greater than 60%. This value is much larger than the difference attributable to the increase in active muscle force that occurs at longer muscle length, in accordance with the force-length curve (10-20% for the estimated length changes). In addition, the relative distribution of the joint torques generated by a given muscle activation was dependent upon finger posture for the intrinsic muscles and the long finger flexors (p < 0.05); the ratio of one joint torque to another varied with posture for these muscles, in some cases by more than 50%. INTERPRETATION: Joint torque is a product of both muscle force and the corresponding moment arm. As the change in active muscle force was limited, these data suggest that substantial changes in muscle moment arms occur with posture. Therefore, this postural dependence should be considered when constructing biomechanical models of the hand or planning tendon transfers for the fingers.     

Measurement of external three-dimensional interphalangeal loads applied during activities of daily living.

OBJECTIVE: To measure the external three-dimensional loads applied to the interphalangeal joints during activities of daily living. DESIGN: A six-degree-of-freedom force transducer was used in conjunction with motion analysis studies. BACKGROUND: There is a lack of accurate three-dimensional load data available for input into biomechanical models of the hand. METHODS: A new force transducer has been incorporated into several housings representing objects in domestic use: a jar, a tap, a key in a lock and a jug kettle. Three-dimensional kinematic data were acquired using a six-camera VICON motion analysis system. Twelve healthy volunteers took part in the study, which compared power and precision grips in 'opening' and 'closing' activities. RESULTS: Large external forces and moments are applied to the middle and distal phalanges in sagittal, coronal and axial directions. Average inter-segmental forces of up to 25 N and average moments of up to 1.8 Nm are experienced at the proximal interphalangeal joint. CONCLUSIONS: The results show that complex loading patterns are associated with routine activities of daily living. RELEVANCE: Biomechanical models of the interphalangeal joints are limited in their ability to accurately predict tendon and joint forces by the quality of the input data obtained by conventional measurement techniques. Models have tended to rely on hypothetical values of external forces acting on the hand and are over-simplified or limited to two-dimensions. The results from the current study challenge the validity of these simplified models and offer a more complete picture of the complex loading system applied to the finger during daily life.     

Effect of simulated rock climbing finger postures on force sharing among the fingers

OBJECTIVE: To study the forces applied by each finger in different joint postures simulating rock climbing gripping postures. DESIGN: Subjects in sitting posture applied fingertip forces perpendicular to horizontal force sensors in three different finger postures. BACKGROUND: Data provided by the literature indicate that middle and ring finger are commonly injured. However, no quantitative assessment of the forces applied by each finger related to the joint postures has been made. METHODS: Six elite rock climbers performed finger flexion in a single-finger task and a four-finger task. The tests were conducted in an extended posture, a curved posture (the joints belonging to the finger were flexed) and an intermediate posture (the joints were flexed, except the distal one which was fully extended). Each fingertip force was expressed in absolute value and in percentage of the maximal force capacity of the finger. RESULTS: The greater force was applied by the middle finger (20.8 N), whatever the posture. The relative involvement amounted to 105% for the ring finger in the curved posture. CONCLUSIONS: The great force applied by the middle finger and the great relative involvement of the ring finger in the curved posture seem to be the main factors of injuries of these fingers. RELEVANCE: The analysis of force sharing among the fingers during different joint postures mimicking rock climbing is essential to a better understanding of finger injuries.     

Perforator-based reverse radial forearm flap to reconstruct multiple third-degree burn defects of the fingers.

Adequate soft-tissue coverage is a cornerstone for successful hand reconstruction in burn patients allowing for hand mobilization and rehabilitation. Multiple finger injuries that involve separate soft-tissue defects with complex wounds challenge the reconstruction dilemma. In this case report, a modified application of reverse radial forearm flap for the simultaneous reconstruction of multiple separate finger defects for burn cases is presented. A 23-year-old heavy industry worker is presented with a history of third-degree electrical burn of left index and middle fingers. The proximal interphalangeal (PIP) joint of the both fingers were exposed. A distally based radial forearm flap with a dimension 7.5 x 6 cm was planned. The flap was transposed to the distal defect and splitted. The bilobed flap was inset. A tendon graft is used to span the gap of extensor apparatus before insetting the flaps in both fingers. The donor defect was closed primarily. A satisfactory coverage is observed in the recipient areas. Finger functions including full range of motion of the metacarpophalangeal and PIP joints of the index and PIP and distal interphalangeal joints of long fingers were observed. The technique presented here is advantageous as it is easy to perform, covers multiple finger defects simultaneously, avoids long-term immobilization, saves the operative time, avoids microsurgery. Donor site is closed primarily and finally this approach ensures a simultaneous repair of complex wounds with multiple vital anatomical structures i.e. bone, tendon, joint, and soft tissue.     

Clinical x-ray dynamics of patients with Kashin-Bek disease and in subjects at risk

During expeditions clinical and roentgenological symptoms were studied in 129 persons aged under 25 and 53 persons aged over 25 with threatened Kashin-Bek disease and afflicted with it, who were followed-up. Observation over time showed that preclinical signs in the form of x-ray morphological changes in the hand joints were the following: a niche in the fifth finger middle phalanx metaphysis or (less frequently) in the thumb ungual phalanx and foci of epiphyseal outer resorption. The initial characteristic clinical signs of the disease were deformity of the proximal interphalangeal joints of the II-V fingers and brachydactyly of the fifth finger. Early clinical and roentgenological signs of Kashin-Bek disease were specified in the time course of the study improving thus the diagnosis and follow-up of such patients.     

The design and development of a gloveless endoskeletal prosthetic hand

Current prosthetic hands, although functional, have the potential of being improved significantly. We report here the design and development of a novel prosthetic hand that is lighter in weight, less expensive, and more functional than current hands. The new prosthesis features an endoskeleton embedded in self-skinning foam that provides a realistic look and feel and obviates the need for a separate cosmetic glove. The voluntary-closing mechanism offers variable grip strength. Placement of joints at three locations (metacarpophalangeal and proximal and distal interphalangeal) within each of four fingers affords realistic finger movement. High-strength synthetic cable attached to the distal phalanx of each finger is used to effect flexion. A multiposition passive thumb provides both precision and power grips. The new prosthesis can securely grasp objects with various shapes and sizes. Compared to current hands, weight has been reduced by approximately 50%, and cable excursion required for full finger flexion by more than 50%. The new endoskeletal prosthesis requires approximately 12-24% less force input to grasp a variety of everyday objects, largely due to its adaptive grip. Production cost estimates reveal the new prosthesis to be significantly less expensive than current prosthetic hands.     

Passive properties of the forearm musculature with reference to hand and finger postures

OBJECTIVE: To quantify individual forearm muscle passive forces and evaluate their impact on hand function. DESIGN: The passive force-length properties of the 24 extrinsic hand and wrist muscles were determined in five fresh frozen cadaver arms. BACKGROUND: Muscle force production is a summation of the active and passive force components. The passive properties of the extrinsic finger musculature and wrist musculature appear to strongly affect both hand posture and hand movement. METHODS: The passive force-length properties of extrinsic hand and wrist muscles were determined by applying a slow, continuous extension to each muscle and recording the resulting tension. Each force-length curve was fit using exponential regression and were related to specific joint rotations and seven hand postures by calculating the muscle excursions for those postures. RESULTS: The exponential passive force-length relationship explained over 97% of the experimental variance. The largest passive forces were elicited in the digital extensors in grips involving large flexion angles such as tip pinch, key pinch, and a briefcase grip. CONCLUSIONS: The passive properties of the extrinsic finger musculature and wrist musculature affect both hand posture and movement especially in postures with flexed wrist and fingers.     

Forked finger fillet flap for segmental extensor tendon coverage of an adjacent digit.

Finger fillet flaps have been used to treat a variety of complex hand deformities providing stable soft tissue coverage and preventing pathologic contractures. Fillet flaps have not been reported in the coverage of segmental extensor tendon deficit in an adjacent digit. A 20-year-old man involved in a motor vehicle crash sustaining a 30% total body surface area burn, primarily to left arm and bilateral lower extremities. In particular, his left index finger extensor mechanism was disrupted with exposure of the proximal interphalangeal (PIP) joint. In addition, the middle finger had a segmental exposure of the extensor tendon. The nonfunctional index finger was sacrificed to provide coverage, via a forked fillet finger flap, of the exposed extensor tendon at the PIP and metacarpophalangeal (MCP) joints. Total active motion of left fingers at 12 months consisted of the third digit 0 to 86 degrees at the MCP joint, 0 to 88 degrees at the PIP joint and 0 to 33 degrees at the distal interphalangeal joint. Gross grip strength improved to 26 lb at 1 year follow-up. Adequate soft tissue coverage of extensor tendons can be challenging in the traumatic hand. With this novel approach of a forked finger fillet flap we were able to provide adequate soft tissue coverage of exposed tendons and joints improving the patient's strength and active range of motion especially in the middle finger. Prevention of postburn boutonnière deformity was an additional benefit.     

Effect of prior experience and task stability on the intrinsic muscle activity of the thumb

Manual techniques involving the use of the thumb are commonly employed by physical therapists for treating patients with vertebral disorders. The demands on the intrinsic muscles of the thumb in these manual tasks are very different from those of the pinch tasks. The aim of this study was to investigate the influence of clinical experience and different mobilization techniques on the electromyographic activity (EMG) of thumb intrinsic muscles. Fifteen participants without exposure to manual techniques (the Novice Group) and fifteen physical therapists with at least 3 years of orthopaedic experience (the Experienced Group) participated. Each participant exerted thumb tip forces with 3 different posterioanterior (PA) glide techniques including unsupported, with digital support and with thumb interphalangeal joint supported by the index finger. The exerted force was increased from 25% to 100% maximum force at 25% increments on a 6 component load cell. The thumb tip force and EMG activity of four intrinsic muscles (flexor pollicis brevis, adductor pollicis, abductor pollicis brevis, first dorsal interosseus) were recorded with surface electrodes. Both experience and technique influenced intrinsic muscle activity of the thumb. While participants of both groups generated the same magnitude of force, experienced participants generated less intrinsic muscle activity while performing PA glide through practice. However, novice participants increased activity of the intrinsic muscles in accordance with the stability status of the technique. PA glide with thumb interphalangeal joint supported by the index finger was a more stable technique as evidenced by smallest relative errors of thumb tip force.     

Isometric torque of the finger extensors at the metacarpophalangeal joints

A pilot study was undertaken to evaluate the isometric torque produced at the metacarpophalangeal joint during finger extension. Fifteen women with normal right hands, aged 21 to 29 years, participated. Each subject was tested for maximal force of isometric extension at the metacarpophalangeal joint angles of 0, 30, and 60 degrees on each of the four fingers. Torque was computed by multiplying the recorded tension and measured length of the proximal phalanx (lever arm). The mean torque for the long finger was significantly greater than the average torque for each of the other three fingers. The mean torque at the joint angle of 60 degrees was significantly greater than at 0 degrees but not at 30 degrees. Reasons for the findings are discussed.     

Middle and ring fingers are more exposed to pulley rupture than index and little during sport-climbing: a biomechanical explanation

BACKGROUND: Finger pulley injury is a common incident observed during sport-climbing. The total rupture of one or several pulleys is highly debilitating and requires surgical reconstruction and/or rehabilitation programs. Literature reports show that fingers are not equally exposed to this injury. The ring and middle fingers are usually injured while the index and little fingers are less exposed. The objective of this study was to determine the biomechanical factors leading to the enhanced exposure of ring and middle finger pulleys. METHOD: Eight subjects were required to exert maximal four-finger force in a specific sport-climbing finger posture. External fingertip forces and finger joint postures were used as input data of a specifically developed biomechanical model of the four fingers (i.e., index, middle, ring and little). This model was based on classical Newton static laws and used an optimization process to quantify the flexor tendon tensions and the pulley forces in each finger. Passive participation of ligaments was also considered into mechanical equations. FINDINGS: Results showed that two main factors could explain the enhanced exposure of ring and middle fingers. Firstly, the fingertip force intensities applied by these two fingers were higher than those observed for the index and little fingers. Secondly, results show that the pulley forces of the ring and middle fingers were close to their rupture thresholds, while it was not the case for the two other fingers. This could be explained by a specific localisation of the finger pulleys of the ring and middle fingers leading to enhanced pulley forces. INTERPRETATION: These results are relevant and could help clinicians to understand finger pulley pathologies and adapt the surgical interventions to reconstruct the fingers pulleys.     

La luxation palmaire de l’articulation interphalangienne proximale du doigt : indication du traitement orthopédique. À propos d’un cas

Volar dislocation of the proximal interphalangeal joint phalanx of the fingers is a very rare entity. Indeed, there is still no consensus that specifies the treatment of this injury. The closed reduction external maneuver should always be tried first intention, but it can lead to failure and will be followed by surgical treatment. We report the case of palmar dislocation of the proximal interphalangeal joint phalangeal pure treated by closed reduction.     

Quantitative evidence of kinematics and functional differences in different graded trigger fingers

Background

Clinical diagnosis and classification of trigger fingers is traditionally based on physical examinations and certain obvious symptoms. However, it might lack quantitative evidence to describe the different graded trigger digits. This study provides quantitative evidence of kinematics and functional differences among different graded trigger fingers based on Froimson's classification.

Methods

Forty-seven patients with fifty-five trigger fingers and graded twenty-three, eleven, and twenty-one fingers as grades II, III, and IV, respectively. The QuickDASH questionnaire evaluated the subject's self-perception of hand symptoms and functions. The study measured maximal workspace of the fingertip motion and range of motion of the finger joints during an assigned tendon-gliding task using an electromagnetic tracking device. In addition, R_α, defined as the ratio range of angular acceleration during finger extension to the range during finger flexion of each joint, quantified the triggering effect.

Findings

The QuickDASH score results show that functional performances have significant differences among three grades (P < 0.05). Workspace, range of motion of proximal interphalangeal joint and R_α of proximal interphalangeal and distal interphalangeal joint of trigger fingers also significantly differ among three grades (P < 0.05). These findings quantitatively show that trigger fingers in different impairment levels have different kinematics and functional performances.

Interpretation

The results serve as evidence-based knowledge for clinics. The more practical and immediate application of this study would be to facilitate the assessment, design and execution of rehabilitation for patients with trigger fingers.     

In vitro investigation of biomechanical changes of the hip after Salter pelvic osteotomy

BACKGROUND: Salter innominate osteotomy of the pelvis is widely used to improve the coverage of the femoral head in developmental dysplasia of the hip, but the biomechanical and geometric changes after this osteotomy are not well understood. METHODS: A CT dataset of an 8-year-old child with severe dysplasia of both hips was used to create a polyamide model of the left hemipelvis and proximal femur. The hemipelvis was mounted to a holding device and the proximal femur attached to a sensor guided industrial robot. The robot was programmed to apply joint forces and torques based on single-leg stance. Two major muscles were represented by wires connected to hydraulic cylinders; muscle forces were adjusted to balance the joint moments. Resulting joint forces were measured using a pressure measuring sensor before and after Salter osteotomy of the hip. Geometric changes were recorded using a three-dimensional ultrasound measurement system. FINDINGS: The preoperative hip joint resultant force was 583N (270% body weight), while after the operation a mean force of 266N (120% body weight) was measured. Postoperative muscle forces were roughly half the preoperative values. The hip joint was translated medially and caudally. Postoperatively, the length of gluteus medius and maximus muscles increased. INTERPRETATION: The preoperative value of the resultant hip joint force is comparable to values reported in the literature. The results suggest that Salter innominate osteotomy leads to a reduction of hip joint and muscle forces in addition to increasing joint contact area.     

A biomechanical analysis of the rheumatoid index finger after joint arthroplasty

OBJECTIVE: To determine the mechanisms responsible for the recurrence of ulnar drift after metacarpophalangeal joint arthroplasty in the rheumatoid hand. DESIGN: A three-dimensional biomechanical model of the index finger joints was used to predict the implant loads during several activities of daily living. BACKGROUND: Post-operative clinical evaluation of Sutter metacarpophalangeal prostheses shows a high incidence of fracture and recurrent deformity. METHODS: A six-component force transducer in conjunction with a six-camera motion analysis system were used to obtain kinematic and external loading data from eight patients with rheumatoid arthritis during several simulated activities. These data were used as input into a three-dimensional biomechanical model of the implant and interphalangeal joints of the index finger. Tendon lines of action and moment arms were obtained using a series of MRI scans and CAD modelling techniques. RESULTS: Implant forces were oriented in a radial and dorsal direction to resist the ulnarpalmarly pull of tendons associated with the metacarpophalangeal joint. CONCLUSIONS: The recurrence of ulnar drift is attributable to fatigue failure of the prostheses. After fracture the implant is unable to support the repetitive loading patterns experienced during activities of daily living. RELEVANCE: Understanding the mechanisms responsible for the recurrence of ulnar drift and implant failure is a step towards improving the prosthesis design, surgical procedures and ultimately the patient's prognosis.     

The effects of finger extension on shoulder muscle activity

[Purpose] This study aims to examine the effects of the extension of the fingers (distal upper limb) on the activity of the shoulder muscles (proximal upper limb). [Subjects and Methods] This study involved 14 healthy male adults with no musculoskeletal disorder or pain related to the shoulders and hands. The subjects in a sitting posture abducted the angle of the shoulder joints at 60° and had their palms in the front direction. Electromyography (EMG) was comparatively analyzed to look at the activities of the infraspinatus (IS) and rhomboid major (RM) when the fingers were extended and relaxed. [Results] The activity of the IS was statistically significantly higher when the fingers were extended than when they were relaxed. [Conclusion] According to the result of this study, finger extension is considered to affect the muscles for connected shoulder joint stability.Key words: Infraspinatus, Rhomboid major, Finger extension     

Blood pressure measurement of all five fingers by strain gauge plethysmography.

The aim of the present paper was to study the methodological problems involved in measuring systolic blood pressure in all five fingers by the strain gauge technique. In 24 normal subjects, blood pressure at the proximal phalanx of finger I and both at the proximal and the intermediate phalanx of the other fingers was measured using a 24-mm-wide cuff. Blood pressure at the proximal phalanx was higher than that at the intermediate phalanx in all fingers except finger V. The difference of blood pressure values corresponded well with circumference of the finger. In 15 normal subjects, blood pressure at the proximal phalanx was compared in fingers I, III, IV, and V, using 16, 20, 24 and 24 mm wide cuffs. Finger blood pressure was closest to arm systolic blood pressure when a 24-mm or 27-mm-wide cuff was used in fingers I, III, and IV, and with a 20-mm-wide cuff in finger V. As the standard deviation of the mean values was larter with the 27-mm-wide cuff than with the 24-mm-wide cuff, the 24-mm-wide cuff was considered to be most suitable for clinical use in fingers I, II, III, and IV. By using the 20-mm-wide cuff in finger V and the 24-mm-wide cuff in the other fingers, normal value of finger blood pressure was determined for both proximal and intermediate phalanxes.     

Traction splint for maximum interphalangeal joint flexion

Several splints are being used, both dynamic and static, for the purpose of increasing finger flexion. The joints affected by the splint as well as the maximum degree of motion feasible vary with the splint design. This paper suggests a splint design for which the specific goal is maximum flexion of the distal and proximal interphalangeal joints (DIP and PIP) while maintaining metacarpophalangeal joint (MCP) flexion.     

Double dislocation of the proximal and distal interphalangeal joints of the little finger

A 32-year-old amateur goalkeeper sustained simultaneous dislocation of the proximal and distal interphalangeal joints following a hyperextension injury. This was reduced under a digital nerve block. Neighbour finger strapping and early mobilisation achieved a full range of movements at both joints when reviewed three weeks after the initial injury.     

Fingertip injuries

The family physician often provides the first and only medical intervention for fingertip injuries. Proper diagnosis and management of fingertip injuries are vital to maintaining proper function of the hand and preventing permanent disability. A subungual hematoma is a painful condition that involves bleeding beneath the nail, usually after trauma. Treatment requires subungual decompression, which is achieved by creating small holes in the nail. A nail bed laceration is treated by removing the nail and suturing the injured nail bed. Closed fractures of the distal phalanx may require reduction but usually are minimally displaced and stable, and can be splinted. Open or intra-articular fractures of the distal phalanx may warrant referral. Patients with mallet finger cannot extend the distal interphalangeal joint because of a disruption of the extensor mechanism. Radiographs help to differentiate between tendinous and bony mallet types. Most mallet finger injuries heal with six to eight weeks of splinting, but some require referral. Flexor digitorum profundus avulsion always requires referral. Dislocations of the distal interphalangeal joint are rare and usually occur dorsally.