- Email: [email protected]
Strength of human pulleys
Strength of H u m a n Pulleys--Paul R. Manske and Peggy A. Lesker
STRENGTH OF HUMAN PULLEYS PAUL R. MANSKE and PEGGY A. LESKER, St. Louis, Missouri. SUMMARY The length, breaking strength, and tensile strength of each of the annular fibroosseous pulleys of digital flexor sheath in ten fresh human cadaver specimens were measured. The first annular pulley and the fourth annular pulley were found to be the strongest, while the second annular pulley was the weakest. The design of artificial pulleys should reproduce the strength of the first annular and fourth annular pulleys. Suggested minimum requirements for the breaking strength of artificial implant pulleys may be made based on these studies. INTRODUCTION
The importance of the fibro-osseous pulleys to flexor tendon function is well recognised by hand surgeons. With the development of implants as joint spacers, carpal bones and tendons, it is conceivable that artificial replacement pulleys will also be developed. Bader (1968) has designed polyester reinforced silastic pulleys and reported favourable short term results. Wray (1974) implanted dacron arterial graft material as pulleys, used in conjunction with silicone rods in the reconstruction of digital tendon sheaths. An artificial pulley which can be implanted and used immediately has obvious advantages in clinical situations such as tenolysis, tendon grafting, and flexor tendon synovectomy. However, the development of such a pulley would require information regarding the strength of the pulleys of the human hand. Such information has not yet been reported. Smith (1966) calculated the volar force units at the metacarpophalangeal joint to be three times the pinch force at the fingertip. Doyle (1975) defined four annular and three cruciate pulleys in the flexor tendon sheath of human digits and determined the optimum placement of the pulleys for effective flexor function. The critical pulleys were the second annular (a 2) and the fourth annular 0 4) at the mid-portion of the middle phalanx. It is the purpose of this study to measure the breaking strength and tensile strength of the annular fibro-osseous pulleys of the digital flexor sheath in the human hand. We feel such information is necessary for the development of artificial pulleys. METHODS AND MATERIALS
Ten fresh cadaver hands (age twenty-eight to seventy-two years old) obtained within twenty-four hours of death were frozen and preserved at - 7 0 ~ until ready for dissection. We avoided the use of embalmed specimens because of the potential deleterious effect on the collagen molecule (Evans, 1973). The flexor sheath of each finger was carefully dissected from the surrounding soft tissue but left attached to the bone. The annular and cruciate pulleys as described by Doyle (1975) were defined. The third annular (a~) pulley was not present in all specimens, being absent P. R. Manske, M.D., Washington University School of Medicine, St. Louis, Missouri 63110, U.S.A. The H a n d - - V o L 9
No. 2
1977
147
Strength oJ H u m a n Pulleys--Paul R. Manske and Peggy A. Lesker
Fig. 1.
The A S pulley in the testing machine. A smooth Kirschner wire has been passed across the metacarpo-phalangeal and interphalangeal joints of the little finger. The proximal phalanx has been secured with a heavy towel clip and secured to the upper clamp of the tensiometer. A loop of tendon has been passed through the pulley and is secured to the lower clamp.
in four little, two middle, and one index fingers. The remaining annular pulleys were all present. The cruciate pulleys were too small for accurate measurement. The length and thickness of each annular pulley were measured. The digits were then stabilised by longitudinal Kirschner wires through the metacarpal and phalanges of each finger. The breaking strength of each annular pulley was measured on a Scott JXL-10I tensile testing machine. The bone was secured to the upper clamp of the tensiometer. A length of tendon was looped through each pulley and secured to the lower clamp. The clamps were distracted at a constant speed of 10 cm per minute, thereby pulling the pulley apart. The breaking strength of each annular pulley was measured and recorded in kilograms (Kg.). The tensile strength of each pulley was determined by dividing the breaking strength by the product of the length and thickness of each pulley and recorded as K g / m m ~. Various synthetic materials were fashioned into 10ram circumferential loops in the form of pulleys. These were pulled apart on the tensile testing machine in the 148
The Hand--Vol. 9
No. 2
1977
Strength of H u m a n Pulleys--Paul R. Manske and Peggy A. Lesker
Fig. 2. Close up view of the phalanx, pulley and tendon. manner described previously. The materials included Dow Coming dacron reinforced silastic sheeting .007in, Dow Coming dacron reinforced silastic sheeting .020in, woven 6ram dacron arterial graft, and DuPont kevlar-49 aramid fibres (10 strands of 1140 denier fibre).
RESULTS
The average length of each pulley (as well as the range) is recorded in Table I. The second annular pulley (a ~) is the longest, followed in order by a 1, a 4 and a'L The pulleys of the little finger were not as long as those of the index, middle and ring fingers. The thickness of each pulley was 0.5ram. The average breaking strength for each pulley (as well as the range) is recorded in Table II. The a ~- pulley is the strongest, followed in order by aL a S and aL The pulleys of the middle finger are the strongest, followed closely in strength by the ring finger and the index finger. The average tensile strength for each pulley (as well as the range), recorded in Table Ill, parallels the results of the breaking strength. These figures indicate that the a ~ and a ~ pulleys are relatively equal in tensile strength. The longest pulley (a ~) has, in fact, the lowest tensile strength. The breaking strength of the synthetic pulleys was as follows: Dacron reinforced silastic sheeting .007in, 10Kg.; dacron reinforced silastic sheeting .020in, 10Kg,; 6mm woven dacron arterial graft, 57Kg; and kevlar-49 (10 strands of 1140 denier fibres), 97Kg. The t~and--Vol, 9
No. 2
1977
149
Strength of H u m a n Pulleys--Paul R. Manske and Peggy A. Lesker TABLE 1 AVERAGE
LENGTH*
Little Finger Ring Finger Middle Finger Index Finger Average All Fingers
OF THE PULLEYS
a1 10 (5-13) 11 (8-16) 10 (6-13) 12 (11-14)
a2 12 (10-14) 18 (15-20) 22 (20-24) 17 (13-20)
4 (2-5) 5 (2-11) 5 (2-11) 4 (2-6)
a4 7 (5-9) 8 (5-10) 8 (6-11) 8 (6-10)
11 (5-16)
17 (i0-24)
5 (2-11)
8 (5-16)
( ) Indicates Range of Specimens
a3
* mm
TABLE 2 AVERAGE
BREAKING
STRENGTH*
OF THE PULLEYS
a1
a2
az
a4
Little Finger
21.5----- 3.0 (40.4-10.3)
11.8• 1.8 (24.0- 6.4)
4.7• 1.0 (8.7-- 3.0)
18.4 + 3.4 (40.5- 6.8)
Ring Finger
33.6• 3.5 (55.0-20.3)
12.6• 1.4 (22.0-- 8.3)
8.6-+ 1.4 (18.3- 3.9)
20.1-+ 2.2 (35.0-12.8)
Middle Finger
39,1~ 5,3 (80.8-28.0)
18.3• 2.3 (29.9- 7.0)
9.4• 1.9 (16.3- 3.0)
20.8• 2.3 (34.6-11.6)
Index Finger
32.3• 3.9 (60.3-21.4)
13.4-+ 1.5 (23.0-- 8.5)
5.4• 0.4 (7.5- 4.0)
19.7• 1.3 (26.1-13.3)
Average All Fingers
31.6• 1.8 (80.8-10.3)
14.0-+ 0.5 (27.0-- 5.1)
7.1• 0.2 (18.3-- 3.0)
19.7-+ 0.8 (40.5-- 6.8)
* Kg
• Indicates Standard Error
( ) Indicates Range of Specimens TABLE 3
AVERAGE
STRENGTH*
OF THE PULLEYS
a1
a2
a3
a4
Little Finger
4.24• 0.46 (6.22- 1.58)
1.88• 0.22 (3.45- 1.26)
2.51• 0.21 (3.10- 1.84)
5.33• 0.79 (10.13- 2.27)
Ring Finger
5.67• 0.41 (8.46- 4.34)
1.38• 0.15 (2.32- 0.83)
4.07~ + 0.79 (9.33- 1.40)
5.50-+ 0,68 10.00- 3.20)
Middle Finger
7.50• 0.84 (13.47- 5.09)
1.69• 0.21 (2.72- 0.64)
3.72• 0.86 (7.53- 1.50)
4.97~ 0.53 (8.65-- 3.31)
Index Finger
5.42-+ 0.67 (10.05- 3.31)
1.61-+ 0.17 (2.56- 0.88)
2.90• 0.33 (4.60- 1.60)
5.34• 0.60 (8.70-- 2s
Average All Fingers
5.73~ + 0.30 (13.47- 1.58)
1.64~ + 0.07 (3.45-- 0.64)
3.37~ + 0.25 (9.33- 1.40)
5.28• 0.19 10.13- 2.66)
* Kg/mm 2
150
TENSILE
( ) Indicates Range of Specimens
Indicates Standard Error The Hand---Vol. 9
No. 2
1977
Strength of H u m a n Pulleys--Paul R. M a n s k e and Peggy A. Lesker DISCUSSION
Our studies, in general, confirm Doyle's findings (8-10mm for a 1, 18-20mm for a s, 3-4mm for a 3 and 10-12ram for a 4) regarding the average length of the human pulleys. However, our studies do indicate the variation in length for each individual finger. Littler (1947), Boyes (1971), Rank (1973), and Doyle (1975) agree that pulleys at the base of the proximal phalanx and at the mid-portion of the middle phalanx are important for proper flexor function of the finger. Although the a s pulley is the longest pulley and has been described as the most critical with respect to flexion of the finger (Doyle, 1975) it is somewhat disconcerting that it is relatively weak compared with a 1 and a 4 pulleys as determined by our breaking strength and tensile strength studies. The a ~ pulley, which has been thought to be expendable (Doyle, 1975), may provide strength needed to hold the tendon adjacent to the bone in power pinch and power grip. Therefore, a replacement pulley at the base of the proximal phalanx should correspond to the strength of the a ~ pulley, and the replacement pulley at the mid-portion of the middle phalanx should correspond to the breaking strength of the a 4 pulley. The breaking strength of the a ~-pulley averaged 31.6Kg for all fingers. However, the breaking strength range up to 80.8Kg for the middle finger, 60Kg for the index finger, and 55Kg for the ring finger. The higher values were found in specimens from young cadavers. The maximum breaking strength of the a ~ pulley was 36 to 38Kg in cadavers more than sixty years old. This difference reflects the loss of tissue strength associated with the ageing process. The breaking strength of the a 4 pulley averaged 19.7Kg, but ranged up to 40.5Kg. In cadaver specimens more than sixty years old, the maximum breaking strength was 29.6Kg. On the basis of these studies, one can conclude that a replacement pulley at the base of the proximal phalanx should have a minimum breaking strength of 80Kg. The minimum breaking strength for replacement of the a ~ pulley should be approximately 40Kg. If the replacement pulleys are considered for older patients, the minimum breaking strength would need to be 40Kg and 30Kg for the a 1 and a ~ pulleys. There are other obvious factors such as fatigue wear, elastic deformation, etc., which must be taken into consideration in designing an artificial pulley. We did not attempt to investigate these factors in this study. Our studies suggest that materials which have previously been used as replacement pulleys, such as dacron reinforced silastic and woven dacron arterial grafts, are not strong enough to reproduce the strength of the human pulley. Stronger materials are needed. It is our opinion that the design of any replacement pulley should consider the basic breaking strength of the fibro-osseous pulley. The strength of the implant should be tested under investigative conditions similar to those described. ACKNOWLEDGEMENT
We are most grateful to the Scottish Rite Foundation of Missouri for their donation for purchase of the Scott Tester. Our sincere thanks to Roy Peterson, Ph.D., Department of Anatomy, Washington University School of Medicine, for the cadaver specimens. The Hand--Vol. 9
No. 2
1977
151
Strength of Human Pulleys--Paul R. Manske and Peggy A. Lesker REFERENCES
BADER, K. F., SETHI, G., and CURTIN, J. W. (1968) Silicone Pulleys and Underlays in Tendon Surgery. Plastic and Reconstructive Surgery, 41: 157-164. BOYES, J. H., and STARK, H. H. (1971) Flexor Tendon Grafts in the Fingers and Thumb. A Study of Factors Influencing Results in 1000 cases. The Journal of Bone and Joint Surgery, 53A: 1332-1342. DOYLE, J. R., and BLYTHE, W. (1975). The Finger Flexor Tendon Sheath and Pulleys: Anatomy and Reconstruction. American Academy of Orthopaedic Surgeons Symposium on Tendon Surgery in the Hand. St. Louis, The C.V. Mosby Co., pp. 81-87. EVANS, F. G. (1973) Mechanical Properties of Bone. Preservation Effects, Chapter V. Springfield, Illinois, Charles C. Thomas, pp. 56-60. LITTLER, J. W. (1947) Free Tendon Grafts in Secondary Flexor Tendon Repair. American Journal of Surgery, 74: 315-321. RANK, B. K., WAKEFIELD, A. R., and HUESTON, J. T. (1973) Surgery of Repair as Applied to Hand Injuries, 4th Edition, Baltimore, William and Wilkins Co. pp. 34-35, 248-249. SMITH, E. M., JUVINALL, R. C., BENDER, L. F., and PEARSON, J. R. (1966) Flexor Forces and Rheumatoid Metacarpo-phalangeal Deformity. The Journal of The American Medical Association, 198: 130-134. WRAY, R. C. Jr., and WEEKS, P. M. (1974) Reconstruction of Digital Pulleys. Plastic and Reconstructive Surgery, 53: 534-536.
152
The H a n d - - V o l . 9
No. 2
1977
STRENGTH OF HUMAN PULLEYS PAUL R. MANSKE and PEGGY A. LESKER, St. Louis, Missouri. SUMMARY The length, breaking strength, and tensile strength of each of the annular fibroosseous pulleys of digital flexor sheath in ten fresh human cadaver specimens were measured. The first annular pulley and the fourth annular pulley were found to be the strongest, while the second annular pulley was the weakest. The design of artificial pulleys should reproduce the strength of the first annular and fourth annular pulleys. Suggested minimum requirements for the breaking strength of artificial implant pulleys may be made based on these studies. INTRODUCTION
The importance of the fibro-osseous pulleys to flexor tendon function is well recognised by hand surgeons. With the development of implants as joint spacers, carpal bones and tendons, it is conceivable that artificial replacement pulleys will also be developed. Bader (1968) has designed polyester reinforced silastic pulleys and reported favourable short term results. Wray (1974) implanted dacron arterial graft material as pulleys, used in conjunction with silicone rods in the reconstruction of digital tendon sheaths. An artificial pulley which can be implanted and used immediately has obvious advantages in clinical situations such as tenolysis, tendon grafting, and flexor tendon synovectomy. However, the development of such a pulley would require information regarding the strength of the pulleys of the human hand. Such information has not yet been reported. Smith (1966) calculated the volar force units at the metacarpophalangeal joint to be three times the pinch force at the fingertip. Doyle (1975) defined four annular and three cruciate pulleys in the flexor tendon sheath of human digits and determined the optimum placement of the pulleys for effective flexor function. The critical pulleys were the second annular (a 2) and the fourth annular 0 4) at the mid-portion of the middle phalanx. It is the purpose of this study to measure the breaking strength and tensile strength of the annular fibro-osseous pulleys of the digital flexor sheath in the human hand. We feel such information is necessary for the development of artificial pulleys. METHODS AND MATERIALS
Ten fresh cadaver hands (age twenty-eight to seventy-two years old) obtained within twenty-four hours of death were frozen and preserved at - 7 0 ~ until ready for dissection. We avoided the use of embalmed specimens because of the potential deleterious effect on the collagen molecule (Evans, 1973). The flexor sheath of each finger was carefully dissected from the surrounding soft tissue but left attached to the bone. The annular and cruciate pulleys as described by Doyle (1975) were defined. The third annular (a~) pulley was not present in all specimens, being absent P. R. Manske, M.D., Washington University School of Medicine, St. Louis, Missouri 63110, U.S.A. The H a n d - - V o L 9
No. 2
1977
147
Strength oJ H u m a n Pulleys--Paul R. Manske and Peggy A. Lesker
Fig. 1.
The A S pulley in the testing machine. A smooth Kirschner wire has been passed across the metacarpo-phalangeal and interphalangeal joints of the little finger. The proximal phalanx has been secured with a heavy towel clip and secured to the upper clamp of the tensiometer. A loop of tendon has been passed through the pulley and is secured to the lower clamp.
in four little, two middle, and one index fingers. The remaining annular pulleys were all present. The cruciate pulleys were too small for accurate measurement. The length and thickness of each annular pulley were measured. The digits were then stabilised by longitudinal Kirschner wires through the metacarpal and phalanges of each finger. The breaking strength of each annular pulley was measured on a Scott JXL-10I tensile testing machine. The bone was secured to the upper clamp of the tensiometer. A length of tendon was looped through each pulley and secured to the lower clamp. The clamps were distracted at a constant speed of 10 cm per minute, thereby pulling the pulley apart. The breaking strength of each annular pulley was measured and recorded in kilograms (Kg.). The tensile strength of each pulley was determined by dividing the breaking strength by the product of the length and thickness of each pulley and recorded as K g / m m ~. Various synthetic materials were fashioned into 10ram circumferential loops in the form of pulleys. These were pulled apart on the tensile testing machine in the 148
The Hand--Vol. 9
No. 2
1977
Strength of H u m a n Pulleys--Paul R. Manske and Peggy A. Lesker
Fig. 2. Close up view of the phalanx, pulley and tendon. manner described previously. The materials included Dow Coming dacron reinforced silastic sheeting .007in, Dow Coming dacron reinforced silastic sheeting .020in, woven 6ram dacron arterial graft, and DuPont kevlar-49 aramid fibres (10 strands of 1140 denier fibre).
RESULTS
The average length of each pulley (as well as the range) is recorded in Table I. The second annular pulley (a ~) is the longest, followed in order by a 1, a 4 and a'L The pulleys of the little finger were not as long as those of the index, middle and ring fingers. The thickness of each pulley was 0.5ram. The average breaking strength for each pulley (as well as the range) is recorded in Table II. The a ~- pulley is the strongest, followed in order by aL a S and aL The pulleys of the middle finger are the strongest, followed closely in strength by the ring finger and the index finger. The average tensile strength for each pulley (as well as the range), recorded in Table Ill, parallels the results of the breaking strength. These figures indicate that the a ~ and a ~ pulleys are relatively equal in tensile strength. The longest pulley (a ~) has, in fact, the lowest tensile strength. The breaking strength of the synthetic pulleys was as follows: Dacron reinforced silastic sheeting .007in, 10Kg.; dacron reinforced silastic sheeting .020in, 10Kg,; 6mm woven dacron arterial graft, 57Kg; and kevlar-49 (10 strands of 1140 denier fibres), 97Kg. The t~and--Vol, 9
No. 2
1977
149
Strength of H u m a n Pulleys--Paul R. Manske and Peggy A. Lesker TABLE 1 AVERAGE
LENGTH*
Little Finger Ring Finger Middle Finger Index Finger Average All Fingers
OF THE PULLEYS
a1 10 (5-13) 11 (8-16) 10 (6-13) 12 (11-14)
a2 12 (10-14) 18 (15-20) 22 (20-24) 17 (13-20)
4 (2-5) 5 (2-11) 5 (2-11) 4 (2-6)
a4 7 (5-9) 8 (5-10) 8 (6-11) 8 (6-10)
11 (5-16)
17 (i0-24)
5 (2-11)
8 (5-16)
( ) Indicates Range of Specimens
a3
* mm
TABLE 2 AVERAGE
BREAKING
STRENGTH*
OF THE PULLEYS
a1
a2
az
a4
Little Finger
21.5----- 3.0 (40.4-10.3)
11.8• 1.8 (24.0- 6.4)
4.7• 1.0 (8.7-- 3.0)
18.4 + 3.4 (40.5- 6.8)
Ring Finger
33.6• 3.5 (55.0-20.3)
12.6• 1.4 (22.0-- 8.3)
8.6-+ 1.4 (18.3- 3.9)
20.1-+ 2.2 (35.0-12.8)
Middle Finger
39,1~ 5,3 (80.8-28.0)
18.3• 2.3 (29.9- 7.0)
9.4• 1.9 (16.3- 3.0)
20.8• 2.3 (34.6-11.6)
Index Finger
32.3• 3.9 (60.3-21.4)
13.4-+ 1.5 (23.0-- 8.5)
5.4• 0.4 (7.5- 4.0)
19.7• 1.3 (26.1-13.3)
Average All Fingers
31.6• 1.8 (80.8-10.3)
14.0-+ 0.5 (27.0-- 5.1)
7.1• 0.2 (18.3-- 3.0)
19.7-+ 0.8 (40.5-- 6.8)
* Kg
• Indicates Standard Error
( ) Indicates Range of Specimens TABLE 3
AVERAGE
STRENGTH*
OF THE PULLEYS
a1
a2
a3
a4
Little Finger
4.24• 0.46 (6.22- 1.58)
1.88• 0.22 (3.45- 1.26)
2.51• 0.21 (3.10- 1.84)
5.33• 0.79 (10.13- 2.27)
Ring Finger
5.67• 0.41 (8.46- 4.34)
1.38• 0.15 (2.32- 0.83)
4.07~ + 0.79 (9.33- 1.40)
5.50-+ 0,68 10.00- 3.20)
Middle Finger
7.50• 0.84 (13.47- 5.09)
1.69• 0.21 (2.72- 0.64)
3.72• 0.86 (7.53- 1.50)
4.97~ 0.53 (8.65-- 3.31)
Index Finger
5.42-+ 0.67 (10.05- 3.31)
1.61-+ 0.17 (2.56- 0.88)
2.90• 0.33 (4.60- 1.60)
5.34• 0.60 (8.70-- 2s
Average All Fingers
5.73~ + 0.30 (13.47- 1.58)
1.64~ + 0.07 (3.45-- 0.64)
3.37~ + 0.25 (9.33- 1.40)
5.28• 0.19 10.13- 2.66)
* Kg/mm 2
150
TENSILE
( ) Indicates Range of Specimens
Indicates Standard Error The Hand---Vol. 9
No. 2
1977
Strength of H u m a n Pulleys--Paul R. M a n s k e and Peggy A. Lesker DISCUSSION
Our studies, in general, confirm Doyle's findings (8-10mm for a 1, 18-20mm for a s, 3-4mm for a 3 and 10-12ram for a 4) regarding the average length of the human pulleys. However, our studies do indicate the variation in length for each individual finger. Littler (1947), Boyes (1971), Rank (1973), and Doyle (1975) agree that pulleys at the base of the proximal phalanx and at the mid-portion of the middle phalanx are important for proper flexor function of the finger. Although the a s pulley is the longest pulley and has been described as the most critical with respect to flexion of the finger (Doyle, 1975) it is somewhat disconcerting that it is relatively weak compared with a 1 and a 4 pulleys as determined by our breaking strength and tensile strength studies. The a ~ pulley, which has been thought to be expendable (Doyle, 1975), may provide strength needed to hold the tendon adjacent to the bone in power pinch and power grip. Therefore, a replacement pulley at the base of the proximal phalanx should correspond to the strength of the a ~ pulley, and the replacement pulley at the mid-portion of the middle phalanx should correspond to the breaking strength of the a 4 pulley. The breaking strength of the a ~-pulley averaged 31.6Kg for all fingers. However, the breaking strength range up to 80.8Kg for the middle finger, 60Kg for the index finger, and 55Kg for the ring finger. The higher values were found in specimens from young cadavers. The maximum breaking strength of the a ~ pulley was 36 to 38Kg in cadavers more than sixty years old. This difference reflects the loss of tissue strength associated with the ageing process. The breaking strength of the a 4 pulley averaged 19.7Kg, but ranged up to 40.5Kg. In cadaver specimens more than sixty years old, the maximum breaking strength was 29.6Kg. On the basis of these studies, one can conclude that a replacement pulley at the base of the proximal phalanx should have a minimum breaking strength of 80Kg. The minimum breaking strength for replacement of the a ~ pulley should be approximately 40Kg. If the replacement pulleys are considered for older patients, the minimum breaking strength would need to be 40Kg and 30Kg for the a 1 and a ~ pulleys. There are other obvious factors such as fatigue wear, elastic deformation, etc., which must be taken into consideration in designing an artificial pulley. We did not attempt to investigate these factors in this study. Our studies suggest that materials which have previously been used as replacement pulleys, such as dacron reinforced silastic and woven dacron arterial grafts, are not strong enough to reproduce the strength of the human pulley. Stronger materials are needed. It is our opinion that the design of any replacement pulley should consider the basic breaking strength of the fibro-osseous pulley. The strength of the implant should be tested under investigative conditions similar to those described. ACKNOWLEDGEMENT
We are most grateful to the Scottish Rite Foundation of Missouri for their donation for purchase of the Scott Tester. Our sincere thanks to Roy Peterson, Ph.D., Department of Anatomy, Washington University School of Medicine, for the cadaver specimens. The Hand--Vol. 9
No. 2
1977
151
Strength of Human Pulleys--Paul R. Manske and Peggy A. Lesker REFERENCES
BADER, K. F., SETHI, G., and CURTIN, J. W. (1968) Silicone Pulleys and Underlays in Tendon Surgery. Plastic and Reconstructive Surgery, 41: 157-164. BOYES, J. H., and STARK, H. H. (1971) Flexor Tendon Grafts in the Fingers and Thumb. A Study of Factors Influencing Results in 1000 cases. The Journal of Bone and Joint Surgery, 53A: 1332-1342. DOYLE, J. R., and BLYTHE, W. (1975). The Finger Flexor Tendon Sheath and Pulleys: Anatomy and Reconstruction. American Academy of Orthopaedic Surgeons Symposium on Tendon Surgery in the Hand. St. Louis, The C.V. Mosby Co., pp. 81-87. EVANS, F. G. (1973) Mechanical Properties of Bone. Preservation Effects, Chapter V. Springfield, Illinois, Charles C. Thomas, pp. 56-60. LITTLER, J. W. (1947) Free Tendon Grafts in Secondary Flexor Tendon Repair. American Journal of Surgery, 74: 315-321. RANK, B. K., WAKEFIELD, A. R., and HUESTON, J. T. (1973) Surgery of Repair as Applied to Hand Injuries, 4th Edition, Baltimore, William and Wilkins Co. pp. 34-35, 248-249. SMITH, E. M., JUVINALL, R. C., BENDER, L. F., and PEARSON, J. R. (1966) Flexor Forces and Rheumatoid Metacarpo-phalangeal Deformity. The Journal of The American Medical Association, 198: 130-134. WRAY, R. C. Jr., and WEEKS, P. M. (1974) Reconstruction of Digital Pulleys. Plastic and Reconstructive Surgery, 53: 534-536.
152
The H a n d - - V o l . 9
No. 2
1977