THE INFLUENCE OF WRIST POSITION ON THE FORCE PRODUCED BY THE FINGER FLEXORS*+
Suite 3300. lOjO-5th
FR-\x
T. HAZELTOS:
,Atcnue
S.E.. Cedar
Rapids,
IA 52102. USA
and GUY L. &DT.$ ADRIAYE. Ft_ATTliand RUPH I. STEPHEXS‘ The University of Iowa, Iowa City. IA 52242. L.S.A. paper describes the design, instrumentation. procedures and results of a study of the influence of wrist position on the forces produced by the finger flexors at the middle and distal phalanges. Measurement at each phalangeal level was made on all four fingers simultaneously in each of five different wrist positions. Results of the study suggest that the percentage distribution oi the total force produced by the finger flexors to each indtvidual finger bear a constant relationship regardless of wrist position. The magnitude of the total force produced does vary with wrist position. Abstract-This
The hand. its structure and function. represents a fertile field of study that is largely untapped. A few attempts have been made to measure grip strength and relate it to a variety of demographic and anthropometric factors, but we must look at the hand as an organ of grasp, prehension. sensation and expression. Basic functional concepts found in the hand can be seen in the design of hand tools such as pliers, wrenches. clamps, chucks, etc. The hand, under the control of the intellect, has enabled man to reduce his environment to basic components that can be controlled by switches, tools, buttons, zippers, wheels, etc. With the hand, we provide for our basic personal needs, carry out various forms of useful work. engage in creative art and give expression to our dreams and aspirations. Many years ago, Bunnell (1964) stated that, “Our hands become extensions of the intellect, because by hand movements the dumb converse, with specialized fingertips the blind read, and through the written word we learn from the past and transmit to the future”. If we are to profess the knowledge and ability to adequately cope with problems presented by the disabled we must look at the total scope of hand functions. ROLE OF THE WRIST 19 HASD FLNCTIOS
The influence of wrist position on hand function * Received 14 July 1974. t Portions of this studv are contained
in the thesis written by Mr. Hazelton in partial fulfillment of the requirement for the Master of Arts Degree in Physical Therapy at the liniversity of Iowa. This study was supported in part by grant AH GOCO7-W from the National Institutes of Health. + In private practice. j Associate Professor and Director. Programs in Physical Therapy. College of IMedicine. Professor-Dirccror. Division of Hand Surgerv. Department of Orthopaedic Surgery, Colleee of Medic&. ‘- Professor. Mechanical Engineering Department.
is difficult to study. Kaplan (1965) describes the wrist as the anatomic bridge uniting the forearm and hand. Flatt (1961, 1963) states that, “In the normal limb, the placing of the hand is largely controlled by the multi-axial wrist joint”. The upper extremity functions as an integrated whole to place the hand in position to carry out activities. This involves coordinated movement from proximal to distal that is graduated from coarse to fine. The shoulder and elbow place the hand in near proximity to the function it is to perform. The gross rotary motion of supination or pronation in the forearm, refines the hand position still further. The muscles that control wrist motion serve two important functions. They provide the fine adjustment of the hand into its functioning position, and once this position is achieved, they stabilize the wrist to provide a stable working platform for the hand. The wrist is considered by Flatt (1961) to be the key to all hand function. The muscles that provide the force for flexion of the interphalangeal joints of the fingers are located in the forearm. and their tendons pass through the carpal tunnel, anterior to the wrist joint before they fan out in their approach to the individual fingers. Bunnell (1964) reports that the excursion of the flexor digitorum profundus and sublimis tendons at the wrist joint vary as the wrist moves through its various planes of motion. This indicates that the musculotendinous units are changing lengths in response to changes in wrist position. One determinant for the capacity of a musculotendinous unit to generate force is the effective functional length. As wrist position changes. the effective functional length of the finger flexors change. and hypothetically the magnitude of force should also change. BASIC HASD
FUVCTIOSS
Several writers have suggested that hand function is divided into power and precision grip functions. Capener (1956) points out that the thumb. index and
F. T. HAZELTOSrr a[
302
long fingers form a tripod of prehension that is used in precision activity such as holding a pencil. In this function. the ring and little fingers are used for support and control. In the power grip, the ring and littlz fingers. assisted by the long and index fingers as necessary, form a mobile jaw to squeeze objects against the palm of the hand and the thenar eminence, with the thumb and index finger providing any necessary precision in the grip. Napier (1956) and others (Backhouse, 1968: Flatt, 1961. 1963) have described these functions in a similar manner. It is interesting to note that the innervation pattern of flexor functions in the hand roughly follows this division of function with the ulnar nerve distribution supplying the power grip functions, and the median nerve distribution supplying the precision grip functions. APPROACHES TO STUDY OF THE HASD iLlany approaches have been taken to the study of the hand, each dealing with some component of function. with the results being fitted back into the body of knowledge about the hand. Boivin et al. (1969), Landsmeer and Long (1965) and Long er nl. (1964, 1970). each used the electromyograph to study various muscle functions in the hand. Bechtol (1954), Landsmeer (1962), Mundale (1970), Nemethi (1952), Schmidt (1970) and Toews (1964) each used some form of the hand dynamometer to study various factors relating to grip strength. Anderson (1965) and Skovly (1967) using a hand dynamometer, demonstrated that the amount of force exhibited in the hand grip is influenced by wrist position. Our search of the literature failed to reveal any studies related to the influences of wrist position on the force of the finger flexors at each digit. PURPOSE
The purpose of this study was to compare the influence of five representative wrist positions on the magnitude of the force produced by the finger fiexors at: (1) the middle phalanx of each finger; (2) the distal phalanx of each finger; (3) the distal phalanges of all four fingers; and (4) the middle phalanges of all four fingers. >\IETHOD Subjects
The subjects used in this study consisted of thirty right-handed males who had no known or detectable abnormality in the right upper extremity. Their de* The Digital Dynamometer was developed through the joint effort of the Division of Hand Surgery, Department of Orthopedics, The Department of Mechanical Engineering and the Graduate Program in Physical Therapy, College of Medicine. University of Iowa. Iowa City. IA 32242, U.S.A. + Beckman Eight Channel Type R Dynograph Recorder, Offner Division of Beckman Instruments. Inc.. Schiller Park. Illinois, L’.S.A.
Table I. Descriptive data concerning
the thirty subjects
scriptive data appear in Table 1. Forty-two anthropometric measurements were made on the right upper extremity of each of the subjects. These were used as descriptive data, and were correlated with the force measurements.
The major items of equipment used in the study included: (1) Digital Dynamometer* and (2) Beckman eight channel dynograph recorder+ (Fig. 1). The Digital Dynamometer consisted of three major components: (1) the base assembly with arm and forearm restraints and a pulley assembly on the rear which was used in the calibration process; (1) the cage assembly which rotated around a horizontal axis; and (3) the transducer assemblies attached to a support bar that rotated around a vertical axis (Fig. 1). The rotation of the cage assembly around the horizontal axis permitted adjustments of the dynamometer for radial and ulnar deviation measurements, and the rotation of the transducer support bar around the the adjustment of axis vertical permitted dynamometer for volar flexion and dorsi flexion measurements (Figs. 2 and 3). The Digital Dynamometer as designed permitted a maximum of 45” of volar flexion, 60” of dorsi flexion. 71’ of ulnar deviation and 14’ of radial deviation. The base assembly was equipped with arm and forearm restraints that held the arm and forearm in stable position during testing (Fig. 4). The arm restraint prevented movement of the forearm toward the transducer assembly during testing. The forearm restraint prevented movement laterally or vertically during testing. The two restraints acted together to maintain the wrist in the desired position with respect to the functional axes of the dynamometer which were designed to coincide with the functional axes of the wrist. The transducer assemblies consisted of (1) a flexible woven wire mesh strap for attachment to the finger, (2) a proving ring with four incorporated strain gauges, (3) an adjustable arm with male and female components that were locked together by inserting a pin throuz@ holes drilled through the two components at one-quarter inch intervals and (4) a universal joint with attachment to the support bar. The universal joint assured uniaxial loading of the transducer assembly during testing procedures (Fig. 5). The cage assembly consisted of (1) the transducer mounting bar which was notched to permit mounting of the transducer assemblies in any desired position.
‘ig. 1. The Digital Dynamometer is in the foreground with cables leading to attachment to the Beskeight channel dynograph recorder. The weight hanging from the rear of the Digital Dynamoxter is attached by cable to one of the force transducers to permit accurate calibration of the instrumentation.
n xn
Fig. 2. Subject with the instrumentation attached for measuring forces with the wrist in volar dexion. Note that the asial length of the phalanx from which measurements are being made is perpendicular to the axial length of the transducer assembly. This is the position at which maximum force should be generated. Fig. 3. Subject with the instrumentation attached for measuring forces in ulnar deviation. The notched bar welded to the lower base plate permitted rotation around the horizontal axis for making force measurements in positions of radial and ulnar deviation. The transducer support bar is attached to and rotates around the periphery of the upper and lower base plates and permits adjustment for making measurements in volar and dorsi flexion.
5 Fig. 1. This photograph is taken from above, looking down on the arm and forearm restraints that securely locked the subject’s arm in position for testing. The cuffs over the biceps and on each side of of the forearm were made large to distribute the pressures being applied to achieve stabilization. The bar above the forearm also has a contoured cuff that prevents the forearm from rising vertically. Fig. 5 Transducer assembly: The small ring immediately to the left of the wire mesh finger attachment is the proving ring which has four strain gauges cemented to it. This unit was built by the Mechanical Engineering Department of the University of Iowa and has a design limitation for forces up to one hundred pounds. The maximum force recorded from any subject during the study was 44-1 kg or approx. 97 lb.
?I)2
The influence of wrist positlon (3) the transducer
support bar which was mounted on the edges of the upper and lower base plates and could be locked in any posirion along the periphery of the base plates, (3) fine adjustment screws that passed through the transducer support bar and arrached to the transducer mounting bar. permitting fins adjustment of the transducer arm length, (4) upper and lower base plates. each cut in identical arcs which had their center at the approximate axis of rotation of the wrist joint in the testing position, (5) a notched bar that locked onto a hook in the bass assembly and permitted rotation around (6) the horizontal axis bar (Figs. 2 and 3). The strain gauges in the transducer assemblies of the Digital Dynamometer were connected as one-half of each Wheatstone Bridge, the bridges being completed by components of the 9SO3 strain gauge couplers in the dynograph recorder. Forces applied to the proving rings, caused distortion of the rings, creating changes in the electrical resistance of the strain gauges. The Wheatstone Bridge senses these changes in resistance produced by the forces on the strain gauges, and by becoming unbalanced caused a corresponding pen deflection on the dynograph chart paper. The instrumentation was calibrated using knoun weights representative of the forces being measured. The calibration Leas checked prior to each testing session. All four channels used exhibited linearity benveen the known force and the millimeters of pen deflection on the dynograph recorder chart paper.
Procedirre
Demographic and anthropometric data was gathered on each subject prior to testing. The details of the force measurement procedure were explained and all questions answered. ‘4 completely randomized design with respect to phalangeal level being tested and the wrist position being tested was used. Selection of the phalangeal level was by coin toss, and the selection of the wrist position was made from a table of random numbers. Each subject was tested in each of ten positions, i.e. at both the middle and distal phalanx in each of five wrist positions. The wrist positions were (1) neutral, (2) voIar flexion. (3) dorsi flexion, (4) radial deviation and (51 ulnar deviation. The number of degrees used for volar Hexion and dorsi flexion was two-thirds of the active range of motion demonstrated by each subject. but not more than 45’ of volar flexion or 60 of dorsi flexion. Twenty-one degrees of ulnar deviation and I-1”of radial deviation were used for all subjects. Two force measurements were made from each phalanx in each wrist position. These force measurements represented two muscle contractions of three seconds each, separated by a 30 set rest period. The peak values of the two trials at each phalanx of each finger %-ere averaged and accepted as the measurement unit. During the course of the study. every fifth subject was retested as a means of checking the relia-
bility of the data being collected. The test-retest ~vas analyzed using product moment correlation.
RESULTS
Rebahility
The r’s for forces at individual phalanges ranged from O-69 through O-99 and averaged 0.88 among the 40 measurements taken for each subject. The r’s for the total force at the middle and distal phalanges ranged from @SS to @97 and averaged 0.93. The I.‘S for the wrist angles were 0.90 for volar Hexion and 0.99 for dorsi fiexion. Constant wrist angles Lvere used for radial and ulnar deviation for all subjects and there were no r’s for these (Table 2). The design limitations of the Digital Dynamometer prevented the use of exactly two-thirds of the demonstrated active range of motion, and those percentages actuali! used averaged 63% for volar flexion. 66”, for dorsi Resion. 73”, for uInar deviation and 63:~ for radial deviation. Forces ac ittdiridd
phalat~ges
The greatest mean force at the middle phalanx ~vas recorded in ulnar deviation, follo\ved in order by neutral, radial deviation, dorsi flexion and volar flexion. At the distal phalanx, the order was the same except that radial deviation and dorsi flexion were reversed in the order at the third and fourth positions. The maximum individual force recorded at the middle phalanx was 44.1 kg on the long finger in ulnar deviation. The maximum force on the distal phalanx was 37.7 kg recorded from the long finger in ulnar deviation. The force data from individual phalanges bvas analyzed using analysis of variance techniques. There were significant F ratios for the data from each of the ten positions tested. The Tukey Test was used to find the location of the significance among the means. Except for the patterns cited above. there \vas no consistent pattern among the significant values. Total force otz the four fingers
At the middle phalanx: the means of the total force (kg) at the middle phalanx were 72.6 in ulnar deviation. 70.1 in neutral, 66.3 in radial deviation. 634 in dorsi flexion and 62.1 in volar flexion. The percentages of total force allocated to each finger in any Table 2. Differences between active wrist motion. twothirds of active wrist motion and degrees of wrist motion tested in five wrist positions (.k’ = 30)
F. T. HAZELTOSt’c al.
30-l
Table 3. Distribution of force (“,Aof total force) at middle phalanx in five wrist positions(.V = 30)
Range
11.6-36.0
14.7-35.4
7.3-21.6
* 5th column should be headed p,,,
nFan kcmt*9e
25.4
StmCrd Deviation x,
20.9-46.9 31.9
3.6
5.0.
.-=
21.8-29.0
4.0
29.9-37.9
26.2 4.0 21.2-29.2
16.2 3.2 12.0-18.4
one of the wrist positions stant and finger with finger with ring finger
tested appears to be conthe mean values were 25.4 to the index a range of 13+36.P/& 33.9% to the long a range from 209 to 46.9x, 25.2% to the
with a range from 14.7 to 35.47; and 152% to the Iittle finger with a range from 7.3 to 21,6”/d (Table 3). At the distal phalanx: the means of the total force (kg) at the distal phalanx were 41.5 in volar Rexion, 45.2 in radial deviation. 46.5 in dorsi flexion, 47.8 in neutral and 49.4 in ulnar deviation. The percentage of the total force allocated to each finger in any wrist position tested appears to be a constant approximately equal to the values found at the middle phalanx and portrayed in Table 3. At the distal phalanx these values were 257pb for the index finger with a range from 18.4 to 38.9:;. 33.0”/, to the long finger with a range from 15.1 to 442”/ 23.6% for the ring finger with a range from 16.7 to 31.7x, and 17.2% to the little finger with a range from 9.8 to 26.7% (Table 4). Summary
oftotal
force
Table 3. Distribution of force (% of total force) at distal phalanx in five wrist positions (N = 30) Pollrfon
Index
Long
nlmle
Lltrlc
nwrra,
25.1
33.2
23.2
m.2
YDlW FICXlO”
25.1
33.1
23.9
18.0
D.wSl Flexlo”
26.0
11.0
23.9
18.1
Ulnar CaUIaLlO”
26.4
33.2
23.7
17.6
Rldtal ce*l,rfon
24.9
34.1
24.1
16.9
Range “Cd” Perccnt.9* Standard Dwiatlon
l&4-30.9
15.1-44.2
16.7-31.7
25.7
33.0
21.6
4.2
1.0
3.1
21.5-29.9
The per cent difference between the total forces at the middle phalanges and the total forces at the distal phalanges was approximately the same in all wrist positions tested except dorsi flexion. The percentage differences were 31~3% in neutral, 33.2% in volar flexion. 26.772 in dorsi flexion. 32.0% in ulnar deviation and 31.8% in radial deviation (Table 5). Relationships
among measurements
The mean force data was related to the anthropometric data, using product moment correlation. The r’s for the relationships between each of the 42 measurements and the force data were all positive and ranged from 004 to 0.65. Representative of the higher values were 0.32. 0.24, 0.36 and 0.28 for the anterior-posterior joint thickness of the index, long, ring and little finger respectively; 0.57 with the length of the extremity from the tip of the olecranon to the tip of the long finger; and @65 with the forearm girth at the distal end of the proximal one-third of the forearm. Values for force correlation with other anthropometric measurements such as wrist thickness, total extremity length, length of the hand and fingers, length of the individual phalanges, width of the hand at the metacarpal-phalangeal joints. etc., were all lower than these values.
at middle and distal phalanges
The magnitude of the total force at the middle phalanges ranges from 31.1 to 124.2 kg, and at the distal phalanges the total force ranged from 17.6 to 93.3 kg. The position of ulnar deviation exhibited the greatest force at both phalanges and volar flexion exhibited the least force at both phalanges.
Y c 5.0.
Table 5. Comparison of mean force (kg) at middle and distal phalanges in five wrist positions (.V = 30)
29.0-17.0
20.1-26.9
9.8-26.7 17.2 3.4 13.8-20.6
DISCUSSION This paper reports a first attempt to study forces at the individual fingers simultaneously. Analysis of the data shows four distinct patterns: (1) the patterns of force on individual fingers indicates that regardless of wrist position, the fingers exhibiting the greatest to least amount of force are the long finger with approximately 33.5% of the total force, the index and ring fingers with approximately 25.0% of the total force to each. and the little finger with approximately 16.59,;of the total force (Tables 3 and -I); (2) the differences between the total force seen at the middle and distal phalanges is approximately 32% in all wrist positions tested except dorsi flexion, where it is approximately 27% (Table 5); (3) the least force at either the middle or distal phalanx is exhibited in volar flexion: and (4) the greatest force at either phalanx is exhibited in ulnar deviation. The study of the forces acting on the fingers is masked by the three variables of (1) total force
The
mtluence
of
changes in response to changing wrist position. (2) different percentages of the total force allocated to each finger and (3) the differences in the magnitude of the force at the middle and distal phalanges. Each of these three variables is portrayed in Tables j-5. In an effort to portray their effect more dramatically. Table 6 is presented with variable number 1 (total force) held constant at 100 kg and variables 2 and 3 are assigned their apparent constant values for each finger and phalangeal level. In Table 6. the patterns of force distribution become apparent. It should also be apparent that if the total force were allowed to vary as it normally does with changing wrist position, Table 6 would become a senseless mass of data, although the underlying patterns of force distribution vvould still be present. but applied to individual digits only. There are many different factors that may contribute to the force patterns exhibited in the fingers: (1) The angles at which the tendons of the extrinsic flexors of the fingers approach each finger changes vvith wrist position and therefore should divide the forces acting through that tendon into two components. (2) The capacity of musculotendinous unit to generate force is dependent in part upon its effective functional length. Bunnell and Anderson (1965) has demonstrated that the excursion of the tendons of the Hexor subiimis and profundus vary greatly at the wrist joint. This would seem to indicate that the musculotendinous units are changing length, and with such changes their capacity to generate force should also change. (3) During a pilot study that was used to determine the efficacy of this study, it was observed that when subjects were allowed to watch the tracing being made on the pen recorder. they would independently vary the forces on the individual fingers in an effort Table 6. Hypothetical distribution of force (kg) at the middle and distal phalanges in five wrist positions assuming I00 kg of I‘orce at the middle phalanx in each wrist position
*The percentage of the total force allocated to each finger is approximately: index finger, 250”,; long finger, 33.5”;; ring finger, 250”,: and little finger. 163”, +The percentage difference between the total force at the middle and distal phalanx in each wrist position is: neutral. 32.0” 0; volar Hesion. 3?0”,; dorsi Rexion. 27.04,; ulnar deviation. 32.0” o, and radial deviation. 33.0”,
wrist
position
3nj
to balance them. This suggests a highly responsive neuromuscular mechanism that has segmental innervation for the portions of the two muscles that drive the individual fingers. This. in effect. says that even though patterns of force distribution may be present. the human nervous system, in response to other sensory input. can override the patterns of distribution. (1) The total forces acting at the ring and little fingers appear to be a constant 70 per cent of those acting on the long and index fingers. For this to remain constant in spite of changes in wrist position suggests that the sstrinsic finger flexors must be hi~zgly responsive to proprioceptive input from joint position receptors at the wrist along with other sensory input. (5) Radonjic and Long (1971) and others. using electromyographic techniques have demonstrated that one function of the wrist and finger extensors is to control movement initiated by the wrist 2nd tinger Heuors. All of the same principles that apply to the ability of the tlexors to generate force must aiso apply to the extensors. The a.rist. hand. and fingers represent a column of bones that are maintained in proper apposition to one another by a very delicate balance of the Hesors and extensors. Controlled movement within this delicate balance would seem to indicate the presence of rapidly responding reciprocal innervation mechanisms. (6) The intrinsic muscles of the hands pla) a very vital role in maintaining the balance between the flexors and extensors of the fingers and perhaps play some role in determining the force distribution of the finger flexors. (7) Steindler (19%) has accepted 3.65 kg per cm’ of cross section as the force generating potential of a muscle. Johnston (1965) pointed out that the true cross sectional area of a muscle having parallel fibers is easily determined. but that it is difficult to measure cross sectional area of a muscle like the profundus which has a compound structure with many of its fibers diagonal to the axial length of the muscle.
The first look at the muscle forces acting on the individual phalanx reinforces the appreciation of the complexity of hand function and the long road ahead that will lead to more complete understanding of normal function that can be used as the basis for evaluating and planning the treatment of the abnormal hand. This study allows us to make the following generalizations about the normal functioning hand: (I) regardless of wrist position. the per cent of total force allocated to each finger is constant: (2) the wrist position in which the least force is generated ar the middle and distal phalanx is volar Hesion: (31 the wrist position in which the greatest force is esertsd at the middle and distal phalanx is ulnar deviation: (4) the differences between the total force exhibited at the
306
F. T. HAZELTOSet al.
middle and distal phalanx is ulnar deviation; (4) the distal phalanges is approximately 31Y0 in all wrist positions except dorsi flexion where it is approximatelv 27”,; (5) power grip must be considered a total hand function in which the little. ring and long fingers supply the grip force, and the thumb assisted by the index finger supply the necessary precision in the power grip; and (6) precision handling, or precision grip should be considered a special function of the thumb and index finger, assisted as necessary by the long finger. These last two functions probably represent special conditions of the force distribution, that is controlled by segmental innervation from higher centers. The results of this study indicate that the total force exerted on the little and ring fingers at either the middle or distal phalanx is probably a constant 709; of the total force exerted on the long and index fingers in each of the wrist positions tested. APPLICXTIOX
The rtsults of this study provide information that can be used by physical therapists and physicians in evaluating and treating the manifestations of injury and disease in the hand. The fact that the percentage of total force that is exhibited on each finger bears a constant relationship to each other in any wrist position on either the middle or distal phalanx, makes it possible to determine the amount of functional loss on an objective basis. The remaining function can be measured and compared with the values from the contralateral side. The results of this study could lend greater objectivity to the evaluation of functional loss for compensation purposes. These constant values can be used in determining the design and strength of casts and braces used to restrain function during healing. or the design of orthotic or prosthetic devices to assist the partially functioning hand. The constant values might also be used in designing surgical procedures and in evaluating the results of such procedures. The results of this study also have important implications for industrial design. Any job involves some elements of hand dexterity, and the use of force components within the hand. The constant relationship of forces among the fingers should contribute to the functional design of hand tools and instruments that will contribute to greater comfort and efficiency in job performance.
REFERENCES Anderson. C. T. (1965) Wrist joint position influences normal hand function. Unpublished Master’s Thesis, University of Iowa. Backhouse, K. M. (1965) Functional anatomy of the hand. Physiothrrqy 54. 111117. Bechtol. C. 0. (195-QGrip test. the use of the dynamometer
with adjustable hand spacings. J. Bone Jnr Surg. 46-A, 820-X
32.
Boivin. G. L.. Wadsworth. G. E., Landsmeer. J. M. F. and Long. C. I., II. (1969) Electromyographic kinesiology of the hand: muscles driving the index finger. Arch. Phps. .Lled. Rehahil. SO. 17-26.
Boyes. J. H. (1965) Burmrll’s Surgery of rhe Hand, 5th Edn. iippincott. Philadelphia, PA. Caoener. N. (1956) Hand in surgery. _ . J. Bone Jm Sura.Y j8-B. 1%l>l. ’ Flatt, A. E. (1963) Tl~r Care ofrhe Rhvumutoid Hand, pp. 6-22. Mosby. St. Louis. Flatt. A. E. (196 I) Kinesiology of the hand. American Academy of’ Orthopedic Surgeons Instruction Course Lectures, 18, 266251.
Johnston. R. J. (1965) Kinesiology of the wrist and hand. Unpublished Study, University of Iowa. Kaplan. E. B. (1965) Functional and Surgical Anatomy of the Hand. 2nd Edn. Lippincott. Philadelphia. P.A. Landsmeer. J. M. (1962) Power grip and precision handling. Arm. Rheum. Diss. 22, 164-70. Landsmeer, J. M. and Long. C. (1965) Mechanisms of finger control based on electromyograms and location analysis. rlctn Anot. 60, 330-47. Long. C. and Brown, M. E. (1964) Electromyographic kinesiology of the hand: muscles moving the long finger. J. Bow Jnt Suro. 46-A. 1683-1706. Long, C., Conrad: P. W:, Hall, E. A. and Furler, S. L. (1970) Intrinsic-extrinsic muscle control of the hand in power grip and precision handling-an electromyographic study. J. Bone Jut Surg. 52-.L 85367. Mundale. M. 0. (1970) Relationship of intermittent isometric exercises to fatigue of hand grip. Arch. Phys. Med. Rehabil.
51, 32-39.
Napier, J. R. (1956) Prehensile movements of the human hand. J. Bone Jnt Surg. 38-B. 902-913. Nemthi, C. E. (1952) Ai evaluation of the hand grip in industrv. fndus. Med. Sure. 21. 65-69. Radonjic:D. and Long, C. (?971) Kinesiology of the wrist. Am. J. Phys. Med. -50, 57-71. Schmidt. R. T. (1970) Grip strength as measured by the jaymar dynamometer. Arch. Phys. Med. Rehabil. 51, 321-27.
Skovly, R. C. (1967) A study of the power grip strength and how it is influenced by wrist joint position. Unpublished Master’s Thesis, University of Iowa. Steindler, A. (1955) Kinesiolog_v of rhe Hrmun Body, pp. 51640. Charles Thomas, Springfield. Toews, J. V. (1964) A grip strength study among steel workers. Arch. Phys. Med. Rehabil. 45. 113-17.
Suite 3300. lOjO-5th
FR-\x
T. HAZELTOS:
,Atcnue
S.E.. Cedar
Rapids,
IA 52102. USA
and GUY L. &DT.$ ADRIAYE. Ft_ATTliand RUPH I. STEPHEXS‘ The University of Iowa, Iowa City. IA 52242. L.S.A. paper describes the design, instrumentation. procedures and results of a study of the influence of wrist position on the forces produced by the finger flexors at the middle and distal phalanges. Measurement at each phalangeal level was made on all four fingers simultaneously in each of five different wrist positions. Results of the study suggest that the percentage distribution oi the total force produced by the finger flexors to each indtvidual finger bear a constant relationship regardless of wrist position. The magnitude of the total force produced does vary with wrist position. Abstract-This
The hand. its structure and function. represents a fertile field of study that is largely untapped. A few attempts have been made to measure grip strength and relate it to a variety of demographic and anthropometric factors, but we must look at the hand as an organ of grasp, prehension. sensation and expression. Basic functional concepts found in the hand can be seen in the design of hand tools such as pliers, wrenches. clamps, chucks, etc. The hand, under the control of the intellect, has enabled man to reduce his environment to basic components that can be controlled by switches, tools, buttons, zippers, wheels, etc. With the hand, we provide for our basic personal needs, carry out various forms of useful work. engage in creative art and give expression to our dreams and aspirations. Many years ago, Bunnell (1964) stated that, “Our hands become extensions of the intellect, because by hand movements the dumb converse, with specialized fingertips the blind read, and through the written word we learn from the past and transmit to the future”. If we are to profess the knowledge and ability to adequately cope with problems presented by the disabled we must look at the total scope of hand functions. ROLE OF THE WRIST 19 HASD FLNCTIOS
The influence of wrist position on hand function * Received 14 July 1974. t Portions of this studv are contained
in the thesis written by Mr. Hazelton in partial fulfillment of the requirement for the Master of Arts Degree in Physical Therapy at the liniversity of Iowa. This study was supported in part by grant AH GOCO7-W from the National Institutes of Health. + In private practice. j Associate Professor and Director. Programs in Physical Therapy. College of IMedicine. Professor-Dirccror. Division of Hand Surgerv. Department of Orthopaedic Surgery, Colleee of Medic&. ‘- Professor. Mechanical Engineering Department.
is difficult to study. Kaplan (1965) describes the wrist as the anatomic bridge uniting the forearm and hand. Flatt (1961, 1963) states that, “In the normal limb, the placing of the hand is largely controlled by the multi-axial wrist joint”. The upper extremity functions as an integrated whole to place the hand in position to carry out activities. This involves coordinated movement from proximal to distal that is graduated from coarse to fine. The shoulder and elbow place the hand in near proximity to the function it is to perform. The gross rotary motion of supination or pronation in the forearm, refines the hand position still further. The muscles that control wrist motion serve two important functions. They provide the fine adjustment of the hand into its functioning position, and once this position is achieved, they stabilize the wrist to provide a stable working platform for the hand. The wrist is considered by Flatt (1961) to be the key to all hand function. The muscles that provide the force for flexion of the interphalangeal joints of the fingers are located in the forearm. and their tendons pass through the carpal tunnel, anterior to the wrist joint before they fan out in their approach to the individual fingers. Bunnell (1964) reports that the excursion of the flexor digitorum profundus and sublimis tendons at the wrist joint vary as the wrist moves through its various planes of motion. This indicates that the musculotendinous units are changing lengths in response to changes in wrist position. One determinant for the capacity of a musculotendinous unit to generate force is the effective functional length. As wrist position changes. the effective functional length of the finger flexors change. and hypothetically the magnitude of force should also change. BASIC HASD
FUVCTIOSS
Several writers have suggested that hand function is divided into power and precision grip functions. Capener (1956) points out that the thumb. index and
F. T. HAZELTOSrr a[
302
long fingers form a tripod of prehension that is used in precision activity such as holding a pencil. In this function. the ring and little fingers are used for support and control. In the power grip, the ring and littlz fingers. assisted by the long and index fingers as necessary, form a mobile jaw to squeeze objects against the palm of the hand and the thenar eminence, with the thumb and index finger providing any necessary precision in the grip. Napier (1956) and others (Backhouse, 1968: Flatt, 1961. 1963) have described these functions in a similar manner. It is interesting to note that the innervation pattern of flexor functions in the hand roughly follows this division of function with the ulnar nerve distribution supplying the power grip functions, and the median nerve distribution supplying the precision grip functions. APPROACHES TO STUDY OF THE HASD iLlany approaches have been taken to the study of the hand, each dealing with some component of function. with the results being fitted back into the body of knowledge about the hand. Boivin et al. (1969), Landsmeer and Long (1965) and Long er nl. (1964, 1970). each used the electromyograph to study various muscle functions in the hand. Bechtol (1954), Landsmeer (1962), Mundale (1970), Nemethi (1952), Schmidt (1970) and Toews (1964) each used some form of the hand dynamometer to study various factors relating to grip strength. Anderson (1965) and Skovly (1967) using a hand dynamometer, demonstrated that the amount of force exhibited in the hand grip is influenced by wrist position. Our search of the literature failed to reveal any studies related to the influences of wrist position on the force of the finger flexors at each digit. PURPOSE
The purpose of this study was to compare the influence of five representative wrist positions on the magnitude of the force produced by the finger fiexors at: (1) the middle phalanx of each finger; (2) the distal phalanx of each finger; (3) the distal phalanges of all four fingers; and (4) the middle phalanges of all four fingers. >\IETHOD Subjects
The subjects used in this study consisted of thirty right-handed males who had no known or detectable abnormality in the right upper extremity. Their de* The Digital Dynamometer was developed through the joint effort of the Division of Hand Surgery, Department of Orthopedics, The Department of Mechanical Engineering and the Graduate Program in Physical Therapy, College of Medicine. University of Iowa. Iowa City. IA 32242, U.S.A. + Beckman Eight Channel Type R Dynograph Recorder, Offner Division of Beckman Instruments. Inc.. Schiller Park. Illinois, L’.S.A.
Table I. Descriptive data concerning
the thirty subjects
scriptive data appear in Table 1. Forty-two anthropometric measurements were made on the right upper extremity of each of the subjects. These were used as descriptive data, and were correlated with the force measurements.
The major items of equipment used in the study included: (1) Digital Dynamometer* and (2) Beckman eight channel dynograph recorder+ (Fig. 1). The Digital Dynamometer consisted of three major components: (1) the base assembly with arm and forearm restraints and a pulley assembly on the rear which was used in the calibration process; (1) the cage assembly which rotated around a horizontal axis; and (3) the transducer assemblies attached to a support bar that rotated around a vertical axis (Fig. 1). The rotation of the cage assembly around the horizontal axis permitted adjustments of the dynamometer for radial and ulnar deviation measurements, and the rotation of the transducer support bar around the the adjustment of axis vertical permitted dynamometer for volar flexion and dorsi flexion measurements (Figs. 2 and 3). The Digital Dynamometer as designed permitted a maximum of 45” of volar flexion, 60” of dorsi flexion. 71’ of ulnar deviation and 14’ of radial deviation. The base assembly was equipped with arm and forearm restraints that held the arm and forearm in stable position during testing (Fig. 4). The arm restraint prevented movement of the forearm toward the transducer assembly during testing. The forearm restraint prevented movement laterally or vertically during testing. The two restraints acted together to maintain the wrist in the desired position with respect to the functional axes of the dynamometer which were designed to coincide with the functional axes of the wrist. The transducer assemblies consisted of (1) a flexible woven wire mesh strap for attachment to the finger, (2) a proving ring with four incorporated strain gauges, (3) an adjustable arm with male and female components that were locked together by inserting a pin throuz@ holes drilled through the two components at one-quarter inch intervals and (4) a universal joint with attachment to the support bar. The universal joint assured uniaxial loading of the transducer assembly during testing procedures (Fig. 5). The cage assembly consisted of (1) the transducer mounting bar which was notched to permit mounting of the transducer assemblies in any desired position.
‘ig. 1. The Digital Dynamometer is in the foreground with cables leading to attachment to the Beskeight channel dynograph recorder. The weight hanging from the rear of the Digital Dynamoxter is attached by cable to one of the force transducers to permit accurate calibration of the instrumentation.
n xn
Fig. 2. Subject with the instrumentation attached for measuring forces with the wrist in volar dexion. Note that the asial length of the phalanx from which measurements are being made is perpendicular to the axial length of the transducer assembly. This is the position at which maximum force should be generated. Fig. 3. Subject with the instrumentation attached for measuring forces in ulnar deviation. The notched bar welded to the lower base plate permitted rotation around the horizontal axis for making force measurements in positions of radial and ulnar deviation. The transducer support bar is attached to and rotates around the periphery of the upper and lower base plates and permits adjustment for making measurements in volar and dorsi flexion.
5 Fig. 1. This photograph is taken from above, looking down on the arm and forearm restraints that securely locked the subject’s arm in position for testing. The cuffs over the biceps and on each side of of the forearm were made large to distribute the pressures being applied to achieve stabilization. The bar above the forearm also has a contoured cuff that prevents the forearm from rising vertically. Fig. 5 Transducer assembly: The small ring immediately to the left of the wire mesh finger attachment is the proving ring which has four strain gauges cemented to it. This unit was built by the Mechanical Engineering Department of the University of Iowa and has a design limitation for forces up to one hundred pounds. The maximum force recorded from any subject during the study was 44-1 kg or approx. 97 lb.
?I)2
The influence of wrist positlon (3) the transducer
support bar which was mounted on the edges of the upper and lower base plates and could be locked in any posirion along the periphery of the base plates, (3) fine adjustment screws that passed through the transducer support bar and arrached to the transducer mounting bar. permitting fins adjustment of the transducer arm length, (4) upper and lower base plates. each cut in identical arcs which had their center at the approximate axis of rotation of the wrist joint in the testing position, (5) a notched bar that locked onto a hook in the bass assembly and permitted rotation around (6) the horizontal axis bar (Figs. 2 and 3). The strain gauges in the transducer assemblies of the Digital Dynamometer were connected as one-half of each Wheatstone Bridge, the bridges being completed by components of the 9SO3 strain gauge couplers in the dynograph recorder. Forces applied to the proving rings, caused distortion of the rings, creating changes in the electrical resistance of the strain gauges. The Wheatstone Bridge senses these changes in resistance produced by the forces on the strain gauges, and by becoming unbalanced caused a corresponding pen deflection on the dynograph chart paper. The instrumentation was calibrated using knoun weights representative of the forces being measured. The calibration Leas checked prior to each testing session. All four channels used exhibited linearity benveen the known force and the millimeters of pen deflection on the dynograph recorder chart paper.
Procedirre
Demographic and anthropometric data was gathered on each subject prior to testing. The details of the force measurement procedure were explained and all questions answered. ‘4 completely randomized design with respect to phalangeal level being tested and the wrist position being tested was used. Selection of the phalangeal level was by coin toss, and the selection of the wrist position was made from a table of random numbers. Each subject was tested in each of ten positions, i.e. at both the middle and distal phalanx in each of five wrist positions. The wrist positions were (1) neutral, (2) voIar flexion. (3) dorsi flexion, (4) radial deviation and (51 ulnar deviation. The number of degrees used for volar Hexion and dorsi flexion was two-thirds of the active range of motion demonstrated by each subject. but not more than 45’ of volar flexion or 60 of dorsi flexion. Twenty-one degrees of ulnar deviation and I-1”of radial deviation were used for all subjects. Two force measurements were made from each phalanx in each wrist position. These force measurements represented two muscle contractions of three seconds each, separated by a 30 set rest period. The peak values of the two trials at each phalanx of each finger %-ere averaged and accepted as the measurement unit. During the course of the study. every fifth subject was retested as a means of checking the relia-
bility of the data being collected. The test-retest ~vas analyzed using product moment correlation.
RESULTS
Rebahility
The r’s for forces at individual phalanges ranged from O-69 through O-99 and averaged 0.88 among the 40 measurements taken for each subject. The r’s for the total force at the middle and distal phalanges ranged from @SS to @97 and averaged 0.93. The I.‘S for the wrist angles were 0.90 for volar Hexion and 0.99 for dorsi fiexion. Constant wrist angles Lvere used for radial and ulnar deviation for all subjects and there were no r’s for these (Table 2). The design limitations of the Digital Dynamometer prevented the use of exactly two-thirds of the demonstrated active range of motion, and those percentages actuali! used averaged 63% for volar flexion. 66”, for dorsi Resion. 73”, for uInar deviation and 63:~ for radial deviation. Forces ac ittdiridd
phalat~ges
The greatest mean force at the middle phalanx ~vas recorded in ulnar deviation, follo\ved in order by neutral, radial deviation, dorsi flexion and volar flexion. At the distal phalanx, the order was the same except that radial deviation and dorsi flexion were reversed in the order at the third and fourth positions. The maximum individual force recorded at the middle phalanx was 44.1 kg on the long finger in ulnar deviation. The maximum force on the distal phalanx was 37.7 kg recorded from the long finger in ulnar deviation. The force data from individual phalanges bvas analyzed using analysis of variance techniques. There were significant F ratios for the data from each of the ten positions tested. The Tukey Test was used to find the location of the significance among the means. Except for the patterns cited above. there \vas no consistent pattern among the significant values. Total force otz the four fingers
At the middle phalanx: the means of the total force (kg) at the middle phalanx were 72.6 in ulnar deviation. 70.1 in neutral, 66.3 in radial deviation. 634 in dorsi flexion and 62.1 in volar flexion. The percentages of total force allocated to each finger in any Table 2. Differences between active wrist motion. twothirds of active wrist motion and degrees of wrist motion tested in five wrist positions (.k’ = 30)
F. T. HAZELTOSt’c al.
30-l
Table 3. Distribution of force (“,Aof total force) at middle phalanx in five wrist positions(.V = 30)
Range
11.6-36.0
14.7-35.4
7.3-21.6
* 5th column should be headed p,,,
nFan kcmt*9e
25.4
StmCrd Deviation x,
20.9-46.9 31.9
3.6
5.0.
.-=
21.8-29.0
4.0
29.9-37.9
26.2 4.0 21.2-29.2
16.2 3.2 12.0-18.4
one of the wrist positions stant and finger with finger with ring finger
tested appears to be conthe mean values were 25.4 to the index a range of 13+36.P/& 33.9% to the long a range from 209 to 46.9x, 25.2% to the
with a range from 14.7 to 35.47; and 152% to the Iittle finger with a range from 7.3 to 21,6”/d (Table 3). At the distal phalanx: the means of the total force (kg) at the distal phalanx were 41.5 in volar Rexion, 45.2 in radial deviation. 46.5 in dorsi flexion, 47.8 in neutral and 49.4 in ulnar deviation. The percentage of the total force allocated to each finger in any wrist position tested appears to be a constant approximately equal to the values found at the middle phalanx and portrayed in Table 3. At the distal phalanx these values were 257pb for the index finger with a range from 18.4 to 38.9:;. 33.0”/, to the long finger with a range from 15.1 to 442”/ 23.6% for the ring finger with a range from 16.7 to 31.7x, and 17.2% to the little finger with a range from 9.8 to 26.7% (Table 4). Summary
oftotal
force
Table 3. Distribution of force (% of total force) at distal phalanx in five wrist positions (N = 30) Pollrfon
Index
Long
nlmle
Lltrlc
nwrra,
25.1
33.2
23.2
m.2
YDlW FICXlO”
25.1
33.1
23.9
18.0
D.wSl Flexlo”
26.0
11.0
23.9
18.1
Ulnar CaUIaLlO”
26.4
33.2
23.7
17.6
Rldtal ce*l,rfon
24.9
34.1
24.1
16.9
Range “Cd” Perccnt.9* Standard Dwiatlon
l&4-30.9
15.1-44.2
16.7-31.7
25.7
33.0
21.6
4.2
1.0
3.1
21.5-29.9
The per cent difference between the total forces at the middle phalanges and the total forces at the distal phalanges was approximately the same in all wrist positions tested except dorsi flexion. The percentage differences were 31~3% in neutral, 33.2% in volar flexion. 26.772 in dorsi flexion. 32.0% in ulnar deviation and 31.8% in radial deviation (Table 5). Relationships
among measurements
The mean force data was related to the anthropometric data, using product moment correlation. The r’s for the relationships between each of the 42 measurements and the force data were all positive and ranged from 004 to 0.65. Representative of the higher values were 0.32. 0.24, 0.36 and 0.28 for the anterior-posterior joint thickness of the index, long, ring and little finger respectively; 0.57 with the length of the extremity from the tip of the olecranon to the tip of the long finger; and @65 with the forearm girth at the distal end of the proximal one-third of the forearm. Values for force correlation with other anthropometric measurements such as wrist thickness, total extremity length, length of the hand and fingers, length of the individual phalanges, width of the hand at the metacarpal-phalangeal joints. etc., were all lower than these values.
at middle and distal phalanges
The magnitude of the total force at the middle phalanges ranges from 31.1 to 124.2 kg, and at the distal phalanges the total force ranged from 17.6 to 93.3 kg. The position of ulnar deviation exhibited the greatest force at both phalanges and volar flexion exhibited the least force at both phalanges.
Y c 5.0.
Table 5. Comparison of mean force (kg) at middle and distal phalanges in five wrist positions (.V = 30)
29.0-17.0
20.1-26.9
9.8-26.7 17.2 3.4 13.8-20.6
DISCUSSION This paper reports a first attempt to study forces at the individual fingers simultaneously. Analysis of the data shows four distinct patterns: (1) the patterns of force on individual fingers indicates that regardless of wrist position, the fingers exhibiting the greatest to least amount of force are the long finger with approximately 33.5% of the total force, the index and ring fingers with approximately 25.0% of the total force to each. and the little finger with approximately 16.59,;of the total force (Tables 3 and -I); (2) the differences between the total force seen at the middle and distal phalanges is approximately 32% in all wrist positions tested except dorsi flexion, where it is approximately 27% (Table 5); (3) the least force at either the middle or distal phalanx is exhibited in volar flexion: and (4) the greatest force at either phalanx is exhibited in ulnar deviation. The study of the forces acting on the fingers is masked by the three variables of (1) total force
The
mtluence
of
changes in response to changing wrist position. (2) different percentages of the total force allocated to each finger and (3) the differences in the magnitude of the force at the middle and distal phalanges. Each of these three variables is portrayed in Tables j-5. In an effort to portray their effect more dramatically. Table 6 is presented with variable number 1 (total force) held constant at 100 kg and variables 2 and 3 are assigned their apparent constant values for each finger and phalangeal level. In Table 6. the patterns of force distribution become apparent. It should also be apparent that if the total force were allowed to vary as it normally does with changing wrist position, Table 6 would become a senseless mass of data, although the underlying patterns of force distribution vvould still be present. but applied to individual digits only. There are many different factors that may contribute to the force patterns exhibited in the fingers: (1) The angles at which the tendons of the extrinsic flexors of the fingers approach each finger changes vvith wrist position and therefore should divide the forces acting through that tendon into two components. (2) The capacity of musculotendinous unit to generate force is dependent in part upon its effective functional length. Bunnell and Anderson (1965) has demonstrated that the excursion of the tendons of the Hexor subiimis and profundus vary greatly at the wrist joint. This would seem to indicate that the musculotendinous units are changing length, and with such changes their capacity to generate force should also change. (3) During a pilot study that was used to determine the efficacy of this study, it was observed that when subjects were allowed to watch the tracing being made on the pen recorder. they would independently vary the forces on the individual fingers in an effort Table 6. Hypothetical distribution of force (kg) at the middle and distal phalanges in five wrist positions assuming I00 kg of I‘orce at the middle phalanx in each wrist position
*The percentage of the total force allocated to each finger is approximately: index finger, 250”,; long finger, 33.5”;; ring finger, 250”,: and little finger. 163”, +The percentage difference between the total force at the middle and distal phalanx in each wrist position is: neutral. 32.0” 0; volar Hesion. 3?0”,; dorsi Rexion. 27.04,; ulnar deviation. 32.0” o, and radial deviation. 33.0”,
wrist
position
3nj
to balance them. This suggests a highly responsive neuromuscular mechanism that has segmental innervation for the portions of the two muscles that drive the individual fingers. This. in effect. says that even though patterns of force distribution may be present. the human nervous system, in response to other sensory input. can override the patterns of distribution. (1) The total forces acting at the ring and little fingers appear to be a constant 70 per cent of those acting on the long and index fingers. For this to remain constant in spite of changes in wrist position suggests that the sstrinsic finger flexors must be hi~zgly responsive to proprioceptive input from joint position receptors at the wrist along with other sensory input. (5) Radonjic and Long (1971) and others. using electromyographic techniques have demonstrated that one function of the wrist and finger extensors is to control movement initiated by the wrist 2nd tinger Heuors. All of the same principles that apply to the ability of the tlexors to generate force must aiso apply to the extensors. The a.rist. hand. and fingers represent a column of bones that are maintained in proper apposition to one another by a very delicate balance of the Hesors and extensors. Controlled movement within this delicate balance would seem to indicate the presence of rapidly responding reciprocal innervation mechanisms. (6) The intrinsic muscles of the hands pla) a very vital role in maintaining the balance between the flexors and extensors of the fingers and perhaps play some role in determining the force distribution of the finger flexors. (7) Steindler (19%) has accepted 3.65 kg per cm’ of cross section as the force generating potential of a muscle. Johnston (1965) pointed out that the true cross sectional area of a muscle having parallel fibers is easily determined. but that it is difficult to measure cross sectional area of a muscle like the profundus which has a compound structure with many of its fibers diagonal to the axial length of the muscle.
The first look at the muscle forces acting on the individual phalanx reinforces the appreciation of the complexity of hand function and the long road ahead that will lead to more complete understanding of normal function that can be used as the basis for evaluating and planning the treatment of the abnormal hand. This study allows us to make the following generalizations about the normal functioning hand: (I) regardless of wrist position. the per cent of total force allocated to each finger is constant: (2) the wrist position in which the least force is generated ar the middle and distal phalanx is volar Hesion: (31 the wrist position in which the greatest force is esertsd at the middle and distal phalanx is ulnar deviation: (4) the differences between the total force exhibited at the
306
F. T. HAZELTOSet al.
middle and distal phalanx is ulnar deviation; (4) the distal phalanges is approximately 31Y0 in all wrist positions except dorsi flexion where it is approximatelv 27”,; (5) power grip must be considered a total hand function in which the little. ring and long fingers supply the grip force, and the thumb assisted by the index finger supply the necessary precision in the power grip; and (6) precision handling, or precision grip should be considered a special function of the thumb and index finger, assisted as necessary by the long finger. These last two functions probably represent special conditions of the force distribution, that is controlled by segmental innervation from higher centers. The results of this study indicate that the total force exerted on the little and ring fingers at either the middle or distal phalanx is probably a constant 709; of the total force exerted on the long and index fingers in each of the wrist positions tested. APPLICXTIOX
The rtsults of this study provide information that can be used by physical therapists and physicians in evaluating and treating the manifestations of injury and disease in the hand. The fact that the percentage of total force that is exhibited on each finger bears a constant relationship to each other in any wrist position on either the middle or distal phalanx, makes it possible to determine the amount of functional loss on an objective basis. The remaining function can be measured and compared with the values from the contralateral side. The results of this study could lend greater objectivity to the evaluation of functional loss for compensation purposes. These constant values can be used in determining the design and strength of casts and braces used to restrain function during healing. or the design of orthotic or prosthetic devices to assist the partially functioning hand. The constant values might also be used in designing surgical procedures and in evaluating the results of such procedures. The results of this study also have important implications for industrial design. Any job involves some elements of hand dexterity, and the use of force components within the hand. The constant relationship of forces among the fingers should contribute to the functional design of hand tools and instruments that will contribute to greater comfort and efficiency in job performance.
REFERENCES Anderson. C. T. (1965) Wrist joint position influences normal hand function. Unpublished Master’s Thesis, University of Iowa. Backhouse, K. M. (1965) Functional anatomy of the hand. Physiothrrqy 54. 111117. Bechtol. C. 0. (195-QGrip test. the use of the dynamometer
with adjustable hand spacings. J. Bone Jnr Surg. 46-A, 820-X
32.
Boivin. G. L.. Wadsworth. G. E., Landsmeer. J. M. F. and Long. C. I., II. (1969) Electromyographic kinesiology of the hand: muscles driving the index finger. Arch. Phps. .Lled. Rehahil. SO. 17-26.
Boyes. J. H. (1965) Burmrll’s Surgery of rhe Hand, 5th Edn. iippincott. Philadelphia, PA. Caoener. N. (1956) Hand in surgery. _ . J. Bone Jm Sura.Y j8-B. 1%l>l. ’ Flatt, A. E. (1963) Tl~r Care ofrhe Rhvumutoid Hand, pp. 6-22. Mosby. St. Louis. Flatt. A. E. (196 I) Kinesiology of the hand. American Academy of’ Orthopedic Surgeons Instruction Course Lectures, 18, 266251.
Johnston. R. J. (1965) Kinesiology of the wrist and hand. Unpublished Study, University of Iowa. Kaplan. E. B. (1965) Functional and Surgical Anatomy of the Hand. 2nd Edn. Lippincott. Philadelphia. P.A. Landsmeer. J. M. (1962) Power grip and precision handling. Arm. Rheum. Diss. 22, 164-70. Landsmeer, J. M. and Long. C. (1965) Mechanisms of finger control based on electromyograms and location analysis. rlctn Anot. 60, 330-47. Long. C. and Brown, M. E. (1964) Electromyographic kinesiology of the hand: muscles moving the long finger. J. Bow Jnt Suro. 46-A. 1683-1706. Long, C., Conrad: P. W:, Hall, E. A. and Furler, S. L. (1970) Intrinsic-extrinsic muscle control of the hand in power grip and precision handling-an electromyographic study. J. Bone Jut Surg. 52-.L 85367. Mundale. M. 0. (1970) Relationship of intermittent isometric exercises to fatigue of hand grip. Arch. Phys. Med. Rehabil.
51, 32-39.
Napier, J. R. (1956) Prehensile movements of the human hand. J. Bone Jnt Surg. 38-B. 902-913. Nemthi, C. E. (1952) Ai evaluation of the hand grip in industrv. fndus. Med. Sure. 21. 65-69. Radonjic:D. and Long, C. (?971) Kinesiology of the wrist. Am. J. Phys. Med. -50, 57-71. Schmidt. R. T. (1970) Grip strength as measured by the jaymar dynamometer. Arch. Phys. Med. Rehabil. 51, 321-27.
Skovly, R. C. (1967) A study of the power grip strength and how it is influenced by wrist joint position. Unpublished Master’s Thesis, University of Iowa. Steindler, A. (1955) Kinesiolog_v of rhe Hrmun Body, pp. 51640. Charles Thomas, Springfield. Toews, J. V. (1964) A grip strength study among steel workers. Arch. Phys. Med. Rehabil. 45. 113-17.
