Vol. 17A, No. 2 March 1992
Flexor tendon lacerations in zone V
39. Wynn-Parry CB, Salter M. Sensory re-education after median nerve lesions. Hand 1976;8:250-7. 40. Bedford RF, Wollman H. Complications of percutaneous radial artery cannulation. Anesthesiology 1973;38: 228-36. 41. Leriche R, Fontaine R, Dupertuis SM. Arterectomy. Surg Gynecol Obstet 1937;64:149-55. 42. Mozersky LJ, Buckley CJ, Hargood CO. Ultrasonic evaluation of the palmar circulation-a useful adjunct to radial artery cannulation. Am J Surg 1973;126:810-2. 43. Lawrence HW. The collateral circulation in the hand. Indust Med 1937;6:410-1. 44. Gelberman RH, Blasingame JP, Fronek A, Dimick MP. Forearm arterial injuries. J HAND SURG 1979;4:401-8.
45. Potenza AD. Flexor tendon injuries. Orthop Clin North Am 1970;1:355-73. 46. Butsch JL, Janes JM. Injuries of the superficial palmar arch. J Trauma 1963;3:505-16. 47. Kleinert HE, Volianitis GJ. Thrombosis of the palmar arterial arch and its tributaries: etiology and newer concepts in treatment. J Trauma 1965;5:447-57. 48. Littler JW. The severed flexor tendon. Surg Clin North Am 1959;39:435-47. 49. Strickland JW. Management of acute flexor tendon injuries. Orthop Clin North Am 1983;14:827-49.
Flexor tendon forces: In vivo measurements S-shaped force transducers were developed for measurement of the forces along intact tendons. After calibration, the transducers were applied to the flexor pollicis longus and flexor digitorum superticialis and profundus tendons of the index finger in five patients operated on for treatment of carpal tunnel syndrome. The tendon forces generated during passive and active motion of the wrist and fingers were recorded. For pinch function, the amount of the applied load was measured with a speciai pinch meter. Tendon forces in the range of 0.1 to 0.6 kgf were measured during passive mobilization of the wrist. Tendon forces up to 0.9 kgf were present during passive mobilization of the fingers. Tendon forces up to 3.5 kgf were present during active unresisted finger motion. Tendon forces up to 12.0 kgf were recorded during tip pinch, with a mean applied pinch force of 3.5 kgf. These results have potential application in determining the amount of force that a tendon repair would have to resist during passive as well as active postsurgical mobilizations. (J HAND SURC1992;17A:291-8.)
FrCdCric Schuind, MD, Marc Garcia-Elias, MD, William P. Cooney III, MD, and Kai-Nan An. PhD, Rochester, Minn.
From the Orthopedics Biomechanics Laboratory, Department of Orthopedics, Mayo Clinic/Mayo Foundation, Rochester. Minn. This study was supported AR17172. Received for publication Aug. 23, 1991.
by National
Institutes
April 5. 1990: accepted
of Health Grant in revised form
No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Reprint requests: William P. Cooney III. MD, Orthopedics Biomechanics Laboratory, Department of Orthopedics, Mayo Clinic/Mayo Foundation, Rochester, MN 55905. 311134137
T
he magnitude of the joint and tendon forces generated during isometric hand functions has been previously calculated by a static force analysis. Forces as high as 1.5 to 6 times the applied external force are assumed to be present along the flexor tendons. ‘~’ The amount of the actual forces along the tendons is clinically important if one is to estimate (1) the tendon suture-holding power to resist forces present during passive or active motion6-‘; (2) the amount of stress at the junctions of an active tendon prosthesis. or the amount of stress applied to a finger or a wrist joint implant; (3)
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Urbaniak,6 who used a large force transducer in which the tension was a factor of the actual tendon force and the angle of deflection applied to the tendon by the transducer. Bright et al. reported a resting tension of 0.1 kgf and forces between 1 kgf and 2.5 kgf during active and passive finger motion. Maximum forces, up to 20 kgf, were anticipated during power grip. Bright et al. did not measure the actual applied pinch or grasp force simultaneously with tendon force measurement. As a result, they were unable to evaluate the maximum patient effort or to calculate the ratio of tendon force to the applied force. The purpose of this study was to evaluate a newly designed low-profile force transducer to measure the in vivo flexor tendon forces together with applied forces during different types of pinch and grasp and during passive and unresisted active motion of the wrist and fingers.
Materials and methods
Fig. 1. “Buckle” transducer developed for measurement of forces along tendons (N.K. Biotechnical Engineering, Minneapolis, Minn.). This photograph was taken during the calibration procedure.
the potential force of a tendon transfer* and the optimal amount of “pretension” under which the transfer should be set’; and (4) the subluxing forces related to the flexor and extensor tendons in the normal and the arthritic hand (necessary for an understanding of the physiologic restraints and the pathologic deformities). ‘o-‘2 The only previous attempt to measure the active flexor tendon forces in vivo was reported by Bright and
Tranducers. A special S-shaped force transducer (N. K. Biotechnical Engineering, Minneapolis, Minn.) was developed in our biomechanical laboratory for the specific purpose of measuring the forces along intact tendons.13 The transducer is an S-shaped stainless steel frame with four strain gauges attached on its central beam (Fig. 1). When the transducer is applied to a tendon, the application of muscle force through the tendon creates a torque on the central beam, which is sensed by the strain gauges. The design uses the principle that a deformed tendon tends to straighten under a tensile load.“’ Before the in vivo study, the individual transducers were calibrated. Human finger flexor tendons of various sizes were obtained from fresh frozen and thawed upper limb specimens. The thickness of the tendons was first measured at a constant load. The size measurements were highly reproducible (coefficient of variation: 0.1%). The tendons were then mounted in a servo hydraulic universal material testing machine (MTS, Minneapolis, Minn.) with a 500-pound load cell (Fig. 1). The tendons were loaded to a maximal of 66.7 newtons (15 pounds). The load and output (in volts) of the transducers were monitored with a strip chart recorder. The force transducers were found to have a linear response to increased tendon tensile load. The tendon diameter was noted to influence the relationship of tendon load to transducer output. Therefore a conversion factor was calculated for each transducer as a function of the tendon size.13 The calibration characteristics were
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Fig. 2. Operative view, before insertion of first transducer.
1
15 N
ACTIVE FINGER MOTION
FDP
-
FPL
0‘EC THUMB IP FLEXION
THUMB IP EXTENSION
INDEX DIP FLEXION
INDEX PIP FLEXION
Fig. 3. Typical force curves in one patient during active motion of thumb and index ringer.
unique to each transducer because of slight differences in fabrication. The reproducibility of the tension measurements from the same tendon was found to be within 4.4%. The creep effect was found to cause a small decrease in output of 0.5% per minute.
In vivo measurements. Direct measurement of the flexor tendon forces were performed during carpal tunnel surgery on nine patients under local anesthesia. All patients gave informed consent to participation in the study. Five patients (three men, two women) had complete recordings, which provided the data presented in
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Table I. Forces recorded along the flexor tendons during passive motion of the wrist and fingers Passive motion
Wrist Aexion-extension Mean Standard deviation Range Wrist extension Mean Standard deviation Range Thumb IP flexion-extension Mean Standard deviation Range Thumb IP hyperextension Mean Standard deviation Range Index DIP flexion-extension Mean Standard deviation Range Index PIP flexion-extension Mean Standard deviation Range
FPL
FDP
FLX
fkf)
kf)
(kfl
0.0 0.0 0.0
0.01
0.06
0.02
0.06 0.0-0.2
0.3 0.2
0.3 0.3
0.0-0.4
0.0-0.6
0.2 0.2 0.0-0.3
0.3 0.2 0.1-0.6
0.1 0.1 0.0-0.2
0.0 0.0 0.0
0.6 0.2 0.3-0.9
0.3 0.4 0.0-0.9
0.0 0.0 0.0
0.0 0.0 0.0
0.01 0.01 0.01-0.2
0.0 0.0 0.0
0.1 0.1 0.0-0.2
0.1 0.2 0.02-0.3
0.2 0.1 0.15-0.24
this article. Data for the remaining four patients were incomplete, but the findings of both active and passive tendon forces were consistent with the results reported in this article. After decompression of the median nerve, the tourniquet was released and hemostasis was obtained. After a 12- to 15minute period to allow for tissue reperfusion, the flexor pollicis longus (FPL), flexor digitorum superficialis (FIX), and flexor digitorum profundus (FDP) tendons of the index finger were isolated within the carpal tunnel. The tendon size was measured, and the location of the measurement was marked with methyl blue. The transducers were then applied to all three tendons at the site of the tendon marks (Fig. 2). With the patient comfortable, a series of tendon force measurements were made with the active participation of the subject. The forces were measured during the following functions: (1) passive and active flexion-extension of the wrist (with the fingers in a resting position); (2) passive flexion-extension and hyperextension of the interphalangeal joint of the thumb, with the wrist in neutral position; (3) passive flexion-extension of the distal and proximal interphalangeal joints of the index finger; (4) active flexion of the interphalangeal joint of the thumb as well as the distal and proximal interphalangeal joints of the index finger to study the
0.0-0.04
independent FPL, FDP, and FDS tendon forces; (5) thumb-to-index tip pinch; (6) thumb-to-index lateral or keypinch; and (7) grasp (thumb and composite fingers). Each test was repeated three times. For pinch functions, the amount of the applied load was simultaneously measured with a sterilized straingauge instrumented pinch meter.3. I5 The simultaneous output of the three tendon transducers and the pinch dynamometer was prepared for careful data analysis and interpretation with a four-channel strip chart recorder. The peak recordings of the transducers and the dynamometer were chosen for calculation of the tendon forces and the applied pinch force with the appropriate conversion factors. The mean from the three measurements was calculated. As a consequence of the intraoperative tendon force measurements, 10 to 12 minutes was added to the length of the operative procedure. There were no adverse sequelae to the patients as a result of the intraoperative tendon force measurements.
Results A typical example of the tendon forces recorded in one patient during active finger motion is presented (Fig. 3). Wrist motion. During passive and active flexion-
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Flexor tendon forces
March 1992
extension of the wrist, forces were recorded within the flexor tendon (Tables I and II); the magnitude of these forces (0 to 0.3 kg) was similar, whether the motion was passive or active. The forces along the flexor tendons were usually higher during full wrist extension than from wrist flexion to neutral position of flexionextension, but the difference was not significant. In one of the patients, the maximal force along the FDP reached 0.6 kgf during passive wrist extension. The average maximum flexor tendon forces were observed when the wrist was passively moved from full flexion to full extension. Thumb motion. During passive flexion-extension and hyperextension of the interphalangeal joint of the thumb, forces were generated along the FPL and, to a lesser degree, within the FDP (Table I). The forces within the FPL were higher during passive hyperextension than during passive extension from the flexed position (p < 0.05, based on the analysis of variance). Active hyperextension of the thumb generated a pattern of forces similar to that recorded for passive hyperextension (Tables I and II). Forces up to 0.9 kgf were present in one patient during passive hyperextension of the joint. During active unresisted flexion of the interphalangeal joint of the thumb, higher forces were present along the FPL (mean, 1.8 kgf; Table II) than with passive motion. Index finger motion. During passive flexion-extension of the distal interphalangeal joint of the index finger, forces were recorded along the FDP tendon. During passive flexion-extension of the proximal interphalangeal joint, forces were recorded within both flexor tendons. The force magnitude varied from less than 0.1 kgf to a maximum of 0.3 kgf. Active unresisted flexion of the distal interphalangeal joint of the index finger was due to the contraction of the FDP with a range of 0.1 to 2.9 kgf and a mean of 1.9 kgf (Table II). Active unresisted flexion of the proximal joint was the result of a contraction of the FDS with some participation of the FDP tendon; the FDS tendon forces ranged from 0.3 kgf to 1.3 kgf, with a mean of 0.9 kgf (Table II). During passive flexion-extension tests of the thumb and index fingers, like that of the wrist, the peak forces were recorded during extension from a maximum flexed position. Pinch and grasp. During prehensile pinch and grasp, higher forces were present along the flexor tendons. During tip pinch (applied pinch up to 3.5 kgf), forces up to 6.0 kgf were present within the FPL; the FDP carried even more force, up to 12.0 kgf. Lateral pinch (applied force up to 4.7 kgf) had reactive tendon forces up to 7.2 kgf within the FPL and up to 6.6 kgf within the FDP. Lower forces were present within the FDS. During grasp, forces up to 6.4 kgf were measured along
295
Table II. Forces recorded along the flexor
tendons during active motion of the wrist and fingers Active motion
Wrist tlexion Mean Standard deviation Range Wrist extension Mean Standard deviation Range Thumb IP flexion Mean Standard deviation Range Thumb IP extension Mean Standard deviation Range Index DIP flexion Mean Standard deviation Range Index PIP flexion Mean Standard deviation Range Tip pinch Mean Standard deviation Range Lateral pinch Mean Standard deviation Range Grasp Mean Standard deviation Range
FPL
FDP
FLIS
&f)
&f)
f&f)
0.0 0.0 0.0
0.2 0.2 0.0-0.3
0.2 0.2 0.0-0.3
0.2 0.2 0.0-0.4
0.2 0.1 0.0-0.3
0.3 0.1 0.2-0.4
1.8 I.1 0.4-3.5
0.1 0.3 0.0-0.6
0.0 0.0 0.0
0.4 0.5 0.1-1.1
0.2 0.1 0.0-0.3
0.2 0.2 0.0-0.3
0.0 0.0 0.0
1.9 1.6 0.1-2.9
0.02 0.04 0.0-O 1
0.1 0.1 0.0-0.2
0.1 0.1 0.0-0.2
0.9 0.5 0.3-I 3
2.1 2.1 0.8-6.0
8.3 4.0 2.0-12.0
1.9 1.1 0.3-3.5
3.8 2.1 1.4-7.2
3.5 2.8 0.3-6.6
1.4 1.3 0.0-3. I
1.9 1.4 0.7-4.2
4.0 3.4 1.9-6.4
0.6 0.3 0.0-0.9
the FDP and up to 4.2 kgf along the FPL. In general, the tendon forces were proportional to the external forces. To normalize the tendon forces, the ratio between the tendon and the applied forces was used (Table III). These values were compared with the predicted forces from the static force analysis (Table III). Although the measured ratio was higher than expected for the FDP during tip pinch, the differences were not significant . Discussion
Through the application of low-profile force transducers placed within the carpal tunnel during surgery under local anesthesia, it has been possible to directly
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Table III. Comparison external pinch force)
of measured
and predicted tendon forces during pinch (expressed
in ratio of
Measurements
Tendon
Mean
Standard deviation
3.60 1.92 1.73
4.62 6.33 1.51
2.28-3.52
3.05 2.90 0.71
3.04 2.61 0.69
2.47-3.84 I .37-5.95
Predicted values*
Tip pinch FPL FDP FDS Lateral pinch FPL FDP FDS
1.93-2.08 1.75-2.16
*From: An et al.‘. 1975; Chao et al.‘, 1989; Cooney et al.J. 1977
record the forces within flexor tendons during passive and active motion as well as during pinch and grasp. Buckle transducers have been used by others to record forces along extensor tendonsI or along ligaments.” We observed that moderate forces were present during passive finger flexion-extension and during wrist motion, These forces were higher during passive hyperextension of the wrist and of the thumb than during passive flexion-extension. It was interesting to note a simultaneous force within the FDP when the FPL was under tension. We believe this is related to a combination of the crossover tendon slips between both tendons in the distal forearm” and the identical innervation by the anterior interosseous nerve. Higher tendon forces were recorded during active finger flexion than during passive motion. During thumb interphalangeal Aexion solely due to the contraction of the FPL, tendon force ranging from 0.4 to 3.5 kg (mean, 1.8 kg) were recorded, whereas with active extension of the thumb, much lower tendon forces (mean, 0.4 kg) were observed. Index finger distal interphalangeal flexion, the result of the contraction of the FDP, produced a tendon force of 1.9 kg (mean), which was significantly higher than the FDP force recorded during passive finger extension or flexion. (Contraction of the FDP was present along with contraction of the FDS during active unresisted flexion of the proximal interphalangeal joint of the index finger, bringing the total FDP tendon force to a mean of 2.0 kg for active finger flexion.) Pinch and grasp movements are complex functions. The participation of the intrinsic muscles was not recorded in the present study. High forces were recorded along the FDP and FPL during tip and lateral pinch. The maximal values recorded are probably on the lower
side of the potential forces, since the tests were performed during surgery on patients who could not see their hands and who had some anesthesia in the sensory territory of the median nerve. The standard deviation recorded between patients is also a reflection of anesthesia in the area of median innervation as well as posttourniquet muscle ischemia. Forces present during postsurgical mobilization. In primary or secondary tendon surgery, it is important to estimate the forces that the tendon repair will have to resist during passive or active motion. Passive mobilization has been recommended after flexor tendon repair.“-“3 Our study demonstrates that forces in the range of 0.1 to 0.6 kgf can be expected at the level of the suture during passive mobilization of the wrist, and in the range of 0.1 to 0.9 kgf during passive mobilization of the fingers, provided the mobilization is strictly passive and the tendon gliding is not impaired. Therefore, given the currently reported breaking forces of tendon repair, passive motion of either the wrist or the fingers should not have a deleterious effect on tendon healing or tendon gap formation (Fig. 4). Forces up to 0.4 kgf might be expected during unresisted active mobilization of the wrist and up to 3.5 kgf during unresisted active mobilization of the fingers. The amount of flexor tendon forces during active motion of the fingers is therefore greater than the current strength of the common flexor tendon repairs.“. ” Improved strength of tendon repairs above 3.5 kgf could provide the option for active tendon forces. Validation of the theoretical model. From a broader perspective, the validation of forces predicted from previous theoretical force analysis has potential value in modeling of finger joint reconstructive procedures and
Vol. 17A, No. 2 March 1992
Flexor
tendon jut-ces
297
PASSIVE MOTION 3
q q n
FPL FDP FDS W Breaking force of tendon repair
2
$ 1
0
Wfid hyperextension
Thumb hyperextension
Index pip f&x-extension
ACTIVE MOTION 14 :
A$ed
n n
FDP FDS
force
12 10 8 B
6 4 2 0
T’p‘Inch
3 CGl27215X-1
Wrist hyperextension
Thumb hyperextension
index pip flex-extension
I Lateral pinch
B Fig. 4. Forces measured during passive motion (A) and during active motion (B) as compared with breaking strength of modified Kessler nylon suture and of nylon looped suture.:’
in the design of finger and thumb joint prosthetic replacements. In attempting to determine the force across a joint, resisted by a ligament or carried by a tendon, the dilemma of force analysis in the hand has been indeterminate, since the total number of unknown variables
exceeds the number of available equations for solution. Assumptions regarding forces in the finger, such as the extensor tendons carrying no force, were required to solve these problems.‘” Force analyses of both finger and thumb’-’ were reported from mechanical modeling of the hand and from static force analysis, but there
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has been an obvious need to validate these calculations by measurements in living human subjects. In this study, forces were recorded in a manner similar to the theoretical calculations previously determined (Table III). Higher forces than anticipated were present in the FDP during tip pinch, but these variations are probably due to the fact that the position adopted by the patients during the performance of the test is not necessarily the position used for the theoretical calculations. We believe the results of the present study are in agreement with and validate the previous theoretical calculations. Other theoretical results, including the joint contact forces, can therefore be interpreted as being correct. For example, forces of up to 13.4 times the applied force should be present at the trapezia1 metacarpal joint of the thumb during tip or lateral pinch.“ The magnitude of tendon forces recorded in this study was quite similar to values reported by Bright et al. ,6 although direct comparison is not possible since in Bright’s study the applied force was not measured. In addition, the maximal forces recorded in our patients
were of the same magnitude as those obtained by Brand et al,* when the physiologic cross-sectional area was multiplied by a factor called the “tension-producing capability” (a factor of 3.6 kg/cm’ is currently admitted in the literature*. 19).These forces were in agreement with those predicted from measurement of the maximal external moment generated during finger flexion2’ The technical assistance of Lawrence Berglund in recording intraoperative tendon and force data was essential to this study, as was the S-shaped buckle transducer developed by E.Y.S. Chao, Ph.D., Director, Orthopedic Biomechanics Laboratory, Mayo Clinic, and manufactured and standardized by Nebojsa Kovacevic, N.K. Biotechnical Engineering, Minneapolis,
7
8
9
10
11
properties of human flexor tendons in relation to artificial tendons. J HAND SURG 1985;10B:331-6. Brand PW,Beach RB, Thompson DE. Relative tension and potential excursion of muscles in the forearm and hand. J HAND SURG 1981;6:209-18. Freehafer AA, Peckham PH, Keith MW. Determination of muscle-tendon unit properties during tendon transfer. J HAND SURG 1979;4:331-9. Flatt AE. Fracture-dislocation of an index metacarpophalanageal joint and an ulnar deviating force in the flexor tendons. J Bone Joint Surg 1966;48A:lOO-4. Flatt AE. Fischer GW. Restraints of the metacarpopha-
langeal joints: a force analysis. Surg Forum 1968;19:45960. 12. Smith EM, Juvinall RC, Bender LF, Pearson JR. Role
13.
14.
15.
16.
17.
18.
19.
Minn. 20.
REFERENCES 1. An KN, Chao EYS, Cooney WP, Linscheid RL. Forces in the normal and abnormal hand. J Orthop Res 1985;3:202-11. 2. Chao EYS, Opgrande JD, Axmear FE. Three-dimensional force anlaysis of finger joints in selected isometric hand functions. J Biomech 1976;9:387-96. 3. Chao EYS, An KN, Cooney WP, Linscheid RL. Biomechanics of the hand: a basic research study. Singapore: World Scientific, 1989. 4. Cooney WP, Chao EYS. Biomechanical analysis of static forces in the thumb during hand function. J Bone Joint Surg 1977;59A:27-36. 5. Toft R, Berme N. A biomechanical analysis of the joints of the thumb. J Biomech 1980;13:353-60. 6. Bright DS, Urbaniak JS. Direct measurements of flexor tendon tension during active and passive digit motion and its application to flexor tendon surgery. Tram Orthop Res Sot 1976;240.
Pring DJ, Amis AA, Coombs RRH. The mechanical
21.
22
23
24.
of the finger flexors in rheumatoid deformities of the metacarpophalangeal joints. Arthritis Rheum 1964; 7:467-80. An KN, Berglund L, Cooney WP, Chao EYS. Kovacevic N. Direct in vivo tendon force measurement system. J Biomech 1990:23:1269-71. Barnes GRG, Pinder DN. In vivo tendon tension and bone strain measurement and correlation. J Biomech 1974;7:35-42. An KN, Chao EYS, Askew LJ. Hand strength measurement instruments. Arch Phys Med Rehabil 1980;61: 366-8. Mendelson LS, Peckham PH, Freehafer AA, Keith MW. Intraoperative assessment of wrist extensor muscle force. J HAND SURG 1988;13A:832-6. Lewis JL, Lew WD, Schmidt J. A note on the application and evaluation of the buckle transducer for knee ligament force measurement. J Biomed Eng 1982; 104: 125-8. Linburg RM, Constock BE. Anomalous tendon slips from the flexor pollicis longus to the flexor digitorum profundus. J HAND SURG 1979;4:79-83. Steindler A. Volume III: Diagnosis and indications. In: Postgraduate lectures in orthopedics. Springfield. Illinois: Charles C Thomas, 1950. Ketchum LD, Thompson D, Pocock G, Wallingford D. A clinical study of forces generated by the intrinsic muscles of the index finger and the extrinsic flexor and extensor muscles of the hand. J HAND SURG 1978;3: 571-8. Cooney WP, Lin GT, An KN. Improved tendon excursion following flexor tendon repair. J Hand Ther 1989; 102-6. Gelberman RH, Nunley JA, Osterman AL, Woo SLY. Influence of the protected passive mobilization interval on flexor tendon healing (a prospective randomized clinical study). Trans Orthop Res Sot 1990;8. Kleinert HE, Kutz JE, Ashbell TS, Martinez E. Primary repair of lacerated flexor tendons in no man’s land; proceedings of the American Society for Surgery of the Hand. J Bone Joint Surg 1967;49A:577. Haddad RJ, Kester MA, McCluskey GM, Brunet ME. Comparative mechanical analysis of a looped-suture tendon repair. J HAND SURG 1988;13A4:709-13.
Flexor tendon lacerations in zone V
39. Wynn-Parry CB, Salter M. Sensory re-education after median nerve lesions. Hand 1976;8:250-7. 40. Bedford RF, Wollman H. Complications of percutaneous radial artery cannulation. Anesthesiology 1973;38: 228-36. 41. Leriche R, Fontaine R, Dupertuis SM. Arterectomy. Surg Gynecol Obstet 1937;64:149-55. 42. Mozersky LJ, Buckley CJ, Hargood CO. Ultrasonic evaluation of the palmar circulation-a useful adjunct to radial artery cannulation. Am J Surg 1973;126:810-2. 43. Lawrence HW. The collateral circulation in the hand. Indust Med 1937;6:410-1. 44. Gelberman RH, Blasingame JP, Fronek A, Dimick MP. Forearm arterial injuries. J HAND SURG 1979;4:401-8.
45. Potenza AD. Flexor tendon injuries. Orthop Clin North Am 1970;1:355-73. 46. Butsch JL, Janes JM. Injuries of the superficial palmar arch. J Trauma 1963;3:505-16. 47. Kleinert HE, Volianitis GJ. Thrombosis of the palmar arterial arch and its tributaries: etiology and newer concepts in treatment. J Trauma 1965;5:447-57. 48. Littler JW. The severed flexor tendon. Surg Clin North Am 1959;39:435-47. 49. Strickland JW. Management of acute flexor tendon injuries. Orthop Clin North Am 1983;14:827-49.
Flexor tendon forces: In vivo measurements S-shaped force transducers were developed for measurement of the forces along intact tendons. After calibration, the transducers were applied to the flexor pollicis longus and flexor digitorum superticialis and profundus tendons of the index finger in five patients operated on for treatment of carpal tunnel syndrome. The tendon forces generated during passive and active motion of the wrist and fingers were recorded. For pinch function, the amount of the applied load was measured with a speciai pinch meter. Tendon forces in the range of 0.1 to 0.6 kgf were measured during passive mobilization of the wrist. Tendon forces up to 0.9 kgf were present during passive mobilization of the fingers. Tendon forces up to 3.5 kgf were present during active unresisted finger motion. Tendon forces up to 12.0 kgf were recorded during tip pinch, with a mean applied pinch force of 3.5 kgf. These results have potential application in determining the amount of force that a tendon repair would have to resist during passive as well as active postsurgical mobilizations. (J HAND SURC1992;17A:291-8.)
FrCdCric Schuind, MD, Marc Garcia-Elias, MD, William P. Cooney III, MD, and Kai-Nan An. PhD, Rochester, Minn.
From the Orthopedics Biomechanics Laboratory, Department of Orthopedics, Mayo Clinic/Mayo Foundation, Rochester. Minn. This study was supported AR17172. Received for publication Aug. 23, 1991.
by National
Institutes
April 5. 1990: accepted
of Health Grant in revised form
No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Reprint requests: William P. Cooney III. MD, Orthopedics Biomechanics Laboratory, Department of Orthopedics, Mayo Clinic/Mayo Foundation, Rochester, MN 55905. 311134137
T
he magnitude of the joint and tendon forces generated during isometric hand functions has been previously calculated by a static force analysis. Forces as high as 1.5 to 6 times the applied external force are assumed to be present along the flexor tendons. ‘~’ The amount of the actual forces along the tendons is clinically important if one is to estimate (1) the tendon suture-holding power to resist forces present during passive or active motion6-‘; (2) the amount of stress at the junctions of an active tendon prosthesis. or the amount of stress applied to a finger or a wrist joint implant; (3)
THE JOURNAL OF HAND SURGERY
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292
The Journal of HAND SURGERY
Schuind et al.
Urbaniak,6 who used a large force transducer in which the tension was a factor of the actual tendon force and the angle of deflection applied to the tendon by the transducer. Bright et al. reported a resting tension of 0.1 kgf and forces between 1 kgf and 2.5 kgf during active and passive finger motion. Maximum forces, up to 20 kgf, were anticipated during power grip. Bright et al. did not measure the actual applied pinch or grasp force simultaneously with tendon force measurement. As a result, they were unable to evaluate the maximum patient effort or to calculate the ratio of tendon force to the applied force. The purpose of this study was to evaluate a newly designed low-profile force transducer to measure the in vivo flexor tendon forces together with applied forces during different types of pinch and grasp and during passive and unresisted active motion of the wrist and fingers.
Materials and methods
Fig. 1. “Buckle” transducer developed for measurement of forces along tendons (N.K. Biotechnical Engineering, Minneapolis, Minn.). This photograph was taken during the calibration procedure.
the potential force of a tendon transfer* and the optimal amount of “pretension” under which the transfer should be set’; and (4) the subluxing forces related to the flexor and extensor tendons in the normal and the arthritic hand (necessary for an understanding of the physiologic restraints and the pathologic deformities). ‘o-‘2 The only previous attempt to measure the active flexor tendon forces in vivo was reported by Bright and
Tranducers. A special S-shaped force transducer (N. K. Biotechnical Engineering, Minneapolis, Minn.) was developed in our biomechanical laboratory for the specific purpose of measuring the forces along intact tendons.13 The transducer is an S-shaped stainless steel frame with four strain gauges attached on its central beam (Fig. 1). When the transducer is applied to a tendon, the application of muscle force through the tendon creates a torque on the central beam, which is sensed by the strain gauges. The design uses the principle that a deformed tendon tends to straighten under a tensile load.“’ Before the in vivo study, the individual transducers were calibrated. Human finger flexor tendons of various sizes were obtained from fresh frozen and thawed upper limb specimens. The thickness of the tendons was first measured at a constant load. The size measurements were highly reproducible (coefficient of variation: 0.1%). The tendons were then mounted in a servo hydraulic universal material testing machine (MTS, Minneapolis, Minn.) with a 500-pound load cell (Fig. 1). The tendons were loaded to a maximal of 66.7 newtons (15 pounds). The load and output (in volts) of the transducers were monitored with a strip chart recorder. The force transducers were found to have a linear response to increased tendon tensile load. The tendon diameter was noted to influence the relationship of tendon load to transducer output. Therefore a conversion factor was calculated for each transducer as a function of the tendon size.13 The calibration characteristics were
Vol. 17A. No. 3 March 1993
Flexor tendon forr,es
293
Fig. 2. Operative view, before insertion of first transducer.
1
15 N
ACTIVE FINGER MOTION
FDP
-
FPL
0‘EC THUMB IP FLEXION
THUMB IP EXTENSION
INDEX DIP FLEXION
INDEX PIP FLEXION
Fig. 3. Typical force curves in one patient during active motion of thumb and index ringer.
unique to each transducer because of slight differences in fabrication. The reproducibility of the tension measurements from the same tendon was found to be within 4.4%. The creep effect was found to cause a small decrease in output of 0.5% per minute.
In vivo measurements. Direct measurement of the flexor tendon forces were performed during carpal tunnel surgery on nine patients under local anesthesia. All patients gave informed consent to participation in the study. Five patients (three men, two women) had complete recordings, which provided the data presented in
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Table I. Forces recorded along the flexor tendons during passive motion of the wrist and fingers Passive motion
Wrist Aexion-extension Mean Standard deviation Range Wrist extension Mean Standard deviation Range Thumb IP flexion-extension Mean Standard deviation Range Thumb IP hyperextension Mean Standard deviation Range Index DIP flexion-extension Mean Standard deviation Range Index PIP flexion-extension Mean Standard deviation Range
FPL
FDP
FLX
fkf)
kf)
(kfl
0.0 0.0 0.0
0.01
0.06
0.02
0.06 0.0-0.2
0.3 0.2
0.3 0.3
0.0-0.4
0.0-0.6
0.2 0.2 0.0-0.3
0.3 0.2 0.1-0.6
0.1 0.1 0.0-0.2
0.0 0.0 0.0
0.6 0.2 0.3-0.9
0.3 0.4 0.0-0.9
0.0 0.0 0.0
0.0 0.0 0.0
0.01 0.01 0.01-0.2
0.0 0.0 0.0
0.1 0.1 0.0-0.2
0.1 0.2 0.02-0.3
0.2 0.1 0.15-0.24
this article. Data for the remaining four patients were incomplete, but the findings of both active and passive tendon forces were consistent with the results reported in this article. After decompression of the median nerve, the tourniquet was released and hemostasis was obtained. After a 12- to 15minute period to allow for tissue reperfusion, the flexor pollicis longus (FPL), flexor digitorum superficialis (FIX), and flexor digitorum profundus (FDP) tendons of the index finger were isolated within the carpal tunnel. The tendon size was measured, and the location of the measurement was marked with methyl blue. The transducers were then applied to all three tendons at the site of the tendon marks (Fig. 2). With the patient comfortable, a series of tendon force measurements were made with the active participation of the subject. The forces were measured during the following functions: (1) passive and active flexion-extension of the wrist (with the fingers in a resting position); (2) passive flexion-extension and hyperextension of the interphalangeal joint of the thumb, with the wrist in neutral position; (3) passive flexion-extension of the distal and proximal interphalangeal joints of the index finger; (4) active flexion of the interphalangeal joint of the thumb as well as the distal and proximal interphalangeal joints of the index finger to study the
0.0-0.04
independent FPL, FDP, and FDS tendon forces; (5) thumb-to-index tip pinch; (6) thumb-to-index lateral or keypinch; and (7) grasp (thumb and composite fingers). Each test was repeated three times. For pinch functions, the amount of the applied load was simultaneously measured with a sterilized straingauge instrumented pinch meter.3. I5 The simultaneous output of the three tendon transducers and the pinch dynamometer was prepared for careful data analysis and interpretation with a four-channel strip chart recorder. The peak recordings of the transducers and the dynamometer were chosen for calculation of the tendon forces and the applied pinch force with the appropriate conversion factors. The mean from the three measurements was calculated. As a consequence of the intraoperative tendon force measurements, 10 to 12 minutes was added to the length of the operative procedure. There were no adverse sequelae to the patients as a result of the intraoperative tendon force measurements.
Results A typical example of the tendon forces recorded in one patient during active finger motion is presented (Fig. 3). Wrist motion. During passive and active flexion-
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No. 2
Flexor tendon forces
March 1992
extension of the wrist, forces were recorded within the flexor tendon (Tables I and II); the magnitude of these forces (0 to 0.3 kg) was similar, whether the motion was passive or active. The forces along the flexor tendons were usually higher during full wrist extension than from wrist flexion to neutral position of flexionextension, but the difference was not significant. In one of the patients, the maximal force along the FDP reached 0.6 kgf during passive wrist extension. The average maximum flexor tendon forces were observed when the wrist was passively moved from full flexion to full extension. Thumb motion. During passive flexion-extension and hyperextension of the interphalangeal joint of the thumb, forces were generated along the FPL and, to a lesser degree, within the FDP (Table I). The forces within the FPL were higher during passive hyperextension than during passive extension from the flexed position (p < 0.05, based on the analysis of variance). Active hyperextension of the thumb generated a pattern of forces similar to that recorded for passive hyperextension (Tables I and II). Forces up to 0.9 kgf were present in one patient during passive hyperextension of the joint. During active unresisted flexion of the interphalangeal joint of the thumb, higher forces were present along the FPL (mean, 1.8 kgf; Table II) than with passive motion. Index finger motion. During passive flexion-extension of the distal interphalangeal joint of the index finger, forces were recorded along the FDP tendon. During passive flexion-extension of the proximal interphalangeal joint, forces were recorded within both flexor tendons. The force magnitude varied from less than 0.1 kgf to a maximum of 0.3 kgf. Active unresisted flexion of the distal interphalangeal joint of the index finger was due to the contraction of the FDP with a range of 0.1 to 2.9 kgf and a mean of 1.9 kgf (Table II). Active unresisted flexion of the proximal joint was the result of a contraction of the FDS with some participation of the FDP tendon; the FDS tendon forces ranged from 0.3 kgf to 1.3 kgf, with a mean of 0.9 kgf (Table II). During passive flexion-extension tests of the thumb and index fingers, like that of the wrist, the peak forces were recorded during extension from a maximum flexed position. Pinch and grasp. During prehensile pinch and grasp, higher forces were present along the flexor tendons. During tip pinch (applied pinch up to 3.5 kgf), forces up to 6.0 kgf were present within the FPL; the FDP carried even more force, up to 12.0 kgf. Lateral pinch (applied force up to 4.7 kgf) had reactive tendon forces up to 7.2 kgf within the FPL and up to 6.6 kgf within the FDP. Lower forces were present within the FDS. During grasp, forces up to 6.4 kgf were measured along
295
Table II. Forces recorded along the flexor
tendons during active motion of the wrist and fingers Active motion
Wrist tlexion Mean Standard deviation Range Wrist extension Mean Standard deviation Range Thumb IP flexion Mean Standard deviation Range Thumb IP extension Mean Standard deviation Range Index DIP flexion Mean Standard deviation Range Index PIP flexion Mean Standard deviation Range Tip pinch Mean Standard deviation Range Lateral pinch Mean Standard deviation Range Grasp Mean Standard deviation Range
FPL
FDP
FLIS
&f)
&f)
f&f)
0.0 0.0 0.0
0.2 0.2 0.0-0.3
0.2 0.2 0.0-0.3
0.2 0.2 0.0-0.4
0.2 0.1 0.0-0.3
0.3 0.1 0.2-0.4
1.8 I.1 0.4-3.5
0.1 0.3 0.0-0.6
0.0 0.0 0.0
0.4 0.5 0.1-1.1
0.2 0.1 0.0-0.3
0.2 0.2 0.0-0.3
0.0 0.0 0.0
1.9 1.6 0.1-2.9
0.02 0.04 0.0-O 1
0.1 0.1 0.0-0.2
0.1 0.1 0.0-0.2
0.9 0.5 0.3-I 3
2.1 2.1 0.8-6.0
8.3 4.0 2.0-12.0
1.9 1.1 0.3-3.5
3.8 2.1 1.4-7.2
3.5 2.8 0.3-6.6
1.4 1.3 0.0-3. I
1.9 1.4 0.7-4.2
4.0 3.4 1.9-6.4
0.6 0.3 0.0-0.9
the FDP and up to 4.2 kgf along the FPL. In general, the tendon forces were proportional to the external forces. To normalize the tendon forces, the ratio between the tendon and the applied forces was used (Table III). These values were compared with the predicted forces from the static force analysis (Table III). Although the measured ratio was higher than expected for the FDP during tip pinch, the differences were not significant . Discussion
Through the application of low-profile force transducers placed within the carpal tunnel during surgery under local anesthesia, it has been possible to directly
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Schuind et al.
Table III. Comparison external pinch force)
of measured
and predicted tendon forces during pinch (expressed
in ratio of
Measurements
Tendon
Mean
Standard deviation
3.60 1.92 1.73
4.62 6.33 1.51
2.28-3.52
3.05 2.90 0.71
3.04 2.61 0.69
2.47-3.84 I .37-5.95
Predicted values*
Tip pinch FPL FDP FDS Lateral pinch FPL FDP FDS
1.93-2.08 1.75-2.16
*From: An et al.‘. 1975; Chao et al.‘, 1989; Cooney et al.J. 1977
record the forces within flexor tendons during passive and active motion as well as during pinch and grasp. Buckle transducers have been used by others to record forces along extensor tendonsI or along ligaments.” We observed that moderate forces were present during passive finger flexion-extension and during wrist motion, These forces were higher during passive hyperextension of the wrist and of the thumb than during passive flexion-extension. It was interesting to note a simultaneous force within the FDP when the FPL was under tension. We believe this is related to a combination of the crossover tendon slips between both tendons in the distal forearm” and the identical innervation by the anterior interosseous nerve. Higher tendon forces were recorded during active finger flexion than during passive motion. During thumb interphalangeal Aexion solely due to the contraction of the FPL, tendon force ranging from 0.4 to 3.5 kg (mean, 1.8 kg) were recorded, whereas with active extension of the thumb, much lower tendon forces (mean, 0.4 kg) were observed. Index finger distal interphalangeal flexion, the result of the contraction of the FDP, produced a tendon force of 1.9 kg (mean), which was significantly higher than the FDP force recorded during passive finger extension or flexion. (Contraction of the FDP was present along with contraction of the FDS during active unresisted flexion of the proximal interphalangeal joint of the index finger, bringing the total FDP tendon force to a mean of 2.0 kg for active finger flexion.) Pinch and grasp movements are complex functions. The participation of the intrinsic muscles was not recorded in the present study. High forces were recorded along the FDP and FPL during tip and lateral pinch. The maximal values recorded are probably on the lower
side of the potential forces, since the tests were performed during surgery on patients who could not see their hands and who had some anesthesia in the sensory territory of the median nerve. The standard deviation recorded between patients is also a reflection of anesthesia in the area of median innervation as well as posttourniquet muscle ischemia. Forces present during postsurgical mobilization. In primary or secondary tendon surgery, it is important to estimate the forces that the tendon repair will have to resist during passive or active motion. Passive mobilization has been recommended after flexor tendon repair.“-“3 Our study demonstrates that forces in the range of 0.1 to 0.6 kgf can be expected at the level of the suture during passive mobilization of the wrist, and in the range of 0.1 to 0.9 kgf during passive mobilization of the fingers, provided the mobilization is strictly passive and the tendon gliding is not impaired. Therefore, given the currently reported breaking forces of tendon repair, passive motion of either the wrist or the fingers should not have a deleterious effect on tendon healing or tendon gap formation (Fig. 4). Forces up to 0.4 kgf might be expected during unresisted active mobilization of the wrist and up to 3.5 kgf during unresisted active mobilization of the fingers. The amount of flexor tendon forces during active motion of the fingers is therefore greater than the current strength of the common flexor tendon repairs.“. ” Improved strength of tendon repairs above 3.5 kgf could provide the option for active tendon forces. Validation of the theoretical model. From a broader perspective, the validation of forces predicted from previous theoretical force analysis has potential value in modeling of finger joint reconstructive procedures and
Vol. 17A, No. 2 March 1992
Flexor
tendon jut-ces
297
PASSIVE MOTION 3
q q n
FPL FDP FDS W Breaking force of tendon repair
2
$ 1
0
Wfid hyperextension
Thumb hyperextension
Index pip f&x-extension
ACTIVE MOTION 14 :
A$ed
n n
FDP FDS
force
12 10 8 B
6 4 2 0
T’p‘Inch
3 CGl27215X-1
Wrist hyperextension
Thumb hyperextension
index pip flex-extension
I Lateral pinch
B Fig. 4. Forces measured during passive motion (A) and during active motion (B) as compared with breaking strength of modified Kessler nylon suture and of nylon looped suture.:’
in the design of finger and thumb joint prosthetic replacements. In attempting to determine the force across a joint, resisted by a ligament or carried by a tendon, the dilemma of force analysis in the hand has been indeterminate, since the total number of unknown variables
exceeds the number of available equations for solution. Assumptions regarding forces in the finger, such as the extensor tendons carrying no force, were required to solve these problems.‘” Force analyses of both finger and thumb’-’ were reported from mechanical modeling of the hand and from static force analysis, but there
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has been an obvious need to validate these calculations by measurements in living human subjects. In this study, forces were recorded in a manner similar to the theoretical calculations previously determined (Table III). Higher forces than anticipated were present in the FDP during tip pinch, but these variations are probably due to the fact that the position adopted by the patients during the performance of the test is not necessarily the position used for the theoretical calculations. We believe the results of the present study are in agreement with and validate the previous theoretical calculations. Other theoretical results, including the joint contact forces, can therefore be interpreted as being correct. For example, forces of up to 13.4 times the applied force should be present at the trapezia1 metacarpal joint of the thumb during tip or lateral pinch.“ The magnitude of tendon forces recorded in this study was quite similar to values reported by Bright et al. ,6 although direct comparison is not possible since in Bright’s study the applied force was not measured. In addition, the maximal forces recorded in our patients
were of the same magnitude as those obtained by Brand et al,* when the physiologic cross-sectional area was multiplied by a factor called the “tension-producing capability” (a factor of 3.6 kg/cm’ is currently admitted in the literature*. 19).These forces were in agreement with those predicted from measurement of the maximal external moment generated during finger flexion2’ The technical assistance of Lawrence Berglund in recording intraoperative tendon and force data was essential to this study, as was the S-shaped buckle transducer developed by E.Y.S. Chao, Ph.D., Director, Orthopedic Biomechanics Laboratory, Mayo Clinic, and manufactured and standardized by Nebojsa Kovacevic, N.K. Biotechnical Engineering, Minneapolis,
7
8
9
10
11
properties of human flexor tendons in relation to artificial tendons. J HAND SURG 1985;10B:331-6. Brand PW,Beach RB, Thompson DE. Relative tension and potential excursion of muscles in the forearm and hand. J HAND SURG 1981;6:209-18. Freehafer AA, Peckham PH, Keith MW. Determination of muscle-tendon unit properties during tendon transfer. J HAND SURG 1979;4:331-9. Flatt AE. Fracture-dislocation of an index metacarpophalanageal joint and an ulnar deviating force in the flexor tendons. J Bone Joint Surg 1966;48A:lOO-4. Flatt AE. Fischer GW. Restraints of the metacarpopha-
langeal joints: a force analysis. Surg Forum 1968;19:45960. 12. Smith EM, Juvinall RC, Bender LF, Pearson JR. Role
13.
14.
15.
16.
17.
18.
19.
Minn. 20.
REFERENCES 1. An KN, Chao EYS, Cooney WP, Linscheid RL. Forces in the normal and abnormal hand. J Orthop Res 1985;3:202-11. 2. Chao EYS, Opgrande JD, Axmear FE. Three-dimensional force anlaysis of finger joints in selected isometric hand functions. J Biomech 1976;9:387-96. 3. Chao EYS, An KN, Cooney WP, Linscheid RL. Biomechanics of the hand: a basic research study. Singapore: World Scientific, 1989. 4. Cooney WP, Chao EYS. Biomechanical analysis of static forces in the thumb during hand function. J Bone Joint Surg 1977;59A:27-36. 5. Toft R, Berme N. A biomechanical analysis of the joints of the thumb. J Biomech 1980;13:353-60. 6. Bright DS, Urbaniak JS. Direct measurements of flexor tendon tension during active and passive digit motion and its application to flexor tendon surgery. Tram Orthop Res Sot 1976;240.
Pring DJ, Amis AA, Coombs RRH. The mechanical
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22
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of the finger flexors in rheumatoid deformities of the metacarpophalangeal joints. Arthritis Rheum 1964; 7:467-80. An KN, Berglund L, Cooney WP, Chao EYS. Kovacevic N. Direct in vivo tendon force measurement system. J Biomech 1990:23:1269-71. Barnes GRG, Pinder DN. In vivo tendon tension and bone strain measurement and correlation. J Biomech 1974;7:35-42. An KN, Chao EYS, Askew LJ. Hand strength measurement instruments. Arch Phys Med Rehabil 1980;61: 366-8. Mendelson LS, Peckham PH, Freehafer AA, Keith MW. Intraoperative assessment of wrist extensor muscle force. J HAND SURG 1988;13A:832-6. Lewis JL, Lew WD, Schmidt J. A note on the application and evaluation of the buckle transducer for knee ligament force measurement. J Biomed Eng 1982; 104: 125-8. Linburg RM, Constock BE. Anomalous tendon slips from the flexor pollicis longus to the flexor digitorum profundus. J HAND SURG 1979;4:79-83. Steindler A. Volume III: Diagnosis and indications. In: Postgraduate lectures in orthopedics. Springfield. Illinois: Charles C Thomas, 1950. Ketchum LD, Thompson D, Pocock G, Wallingford D. A clinical study of forces generated by the intrinsic muscles of the index finger and the extrinsic flexor and extensor muscles of the hand. J HAND SURG 1978;3: 571-8. Cooney WP, Lin GT, An KN. Improved tendon excursion following flexor tendon repair. J Hand Ther 1989; 102-6. Gelberman RH, Nunley JA, Osterman AL, Woo SLY. Influence of the protected passive mobilization interval on flexor tendon healing (a prospective randomized clinical study). Trans Orthop Res Sot 1990;8. Kleinert HE, Kutz JE, Ashbell TS, Martinez E. Primary repair of lacerated flexor tendons in no man’s land; proceedings of the American Society for Surgery of the Hand. J Bone Joint Surg 1967;49A:577. Haddad RJ, Kester MA, McCluskey GM, Brunet ME. Comparative mechanical analysis of a looped-suture tendon repair. J HAND SURG 1988;13A4:709-13.
