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Avulsion of the ring finger flexor digitorum profundus tendon: An experimental study
A vulsion o f the Ring Finger Flexor Digitorum Profundus Tendon: An Experimental Study Paul R. Manske and Peggy A. Lesker
AVULSION OF THE RING FINGER FLEXOR DIGITORUM P R O F U N D U S T E N D O N : AN E X P E R I M E N T A L STUDY PAUL R. M A N S K E AND PEGGY A. LESKER, St. Louis, Missouri SUMMARY The results of an experimental study of the breaking strength of the tendon-bone ]unction of the flexor digitorum profundus tendon in cadaver specimens indicates a significantly weaker insertion of the ring finger compared to the middle finger. This explains in part the more frequent occurrence of avulsion of the ring finger profundus tendon as observed clinically. INTRODUCTION The susceptibility to avulsion at the distal phalanx of the flexor digitorum profundus tendon to the ring finger has been recognised by several writers (Gunter, 1960, Blazina, 1966; Carroll, 1970: Chang, 1972; Wenger, 1973; Honner, 1975; Leddy, 1977). The injury usually occurs as the fingers are clutching an object which is forcibly pulling away. Although all the fingers are presumably involved in the grasping action, the ring finger profundus tendon is the most liable to avulsion. Gunter (1960) and Wenger (1973) attribute this increased susceptibility to the presence of a common muscle belly of the middle, ring and little fingers as anatomically defined by Kaplan (1965) and Hollinshead (1969). Leddy (1977) suggests that the little finger slips out of the way during forcible grasp. Although these concepts suggest how the profundus tendons of the index and little fingers are protected from avulsion injury, they do not account for the more frequent involvement of the ring finger as compared with the middle finger. Holden and Northmore-Ball (1975) determined that the average breaking strength of the flexor digitorum profundus tendon-bone junction was 39.5 kilograms, but did not indicate the breaking strength of the individual digits. In order to determine whether there is a difference in the breaking strength of the profundus tendon insertion which might explain the susceptibility of the ring finger to avulsion injury, the following experiment was performed. METHOD Fourteen fresh cadaver hands (average, sixty-five years old) were collected within twenty-four hours of death and preserved at -70 ~ C until ready for dissection. The profundus tendon of each finger was divided at the level of the metacarpal phalangeal joint. The distal phalanx was disarticulated through the distal interphalangeal joint and dissected free of all soft tissue, except for the attached insertion of the profundus tendon and volar ,plate into the bone. The phalanx was transfixed longitudinally in a polyethylene cup with a smooth Kirschner wire (Figure 1). Methyl methacrylate secured the wire and dorsal surface of the bone to the cup, but did not come in contact with the area of insertion of the tendon and volar plate (Figure 2). The Kirschner wires were secured in the upper clamp and the tendon fixed in the lower clamp of a Scott JXL-100 tensile testing machine (Figure 3) so that the flexor tendon was directed 90 ~ to the distal phalanx. The breaking strength (recorded in Paul R. Manske, M.D., Washington UniversitySchoolof Medicine,4960 Audubon Avenue, St. Louis, Missouri 63110~U.S.A. 52
The Hand--Vol. 10
No. 1
1978
Avulsion of the Ring Finger Flexor Digitorum Profundus Tendon: A n Experimental Study Paul R. Manske and Peggy A. Lesker
Fig. 1.
Distal phalanx transfixed in polyethylene cup.
Fig. 2.
Distal phalanx embedded in methyl methacrylate.
Fig. 3.
Specimen secured in tensile testing machine.
kilograms) of the tendon-osseous junction was determined constant speed of 10 cm/min. In all cases the tendon was small fragment of bone as described by Holden (I 975). In two additional hands, multiple longitudinal and eosin microscopical sections were made at the level of the each digit and examined for anatomical variations.
by distracting the clamps at a avulsed at its insertion with a transverse haematoxylin and insertion of tendon to bone in
RESULTS
The results are recorded in Table 1. The average breaking strength of the flexor digitorum profundus tendon of the ring finger is weaker than any other digit and the difference is statistically significant (p 0.02) in relationship to the middle finger. The breaking strength of the ring finger was less than that of the middle finger in eleven of the fourteen specimens and of equal strength in the remaining hands. The histological preparations showed similar attachment of the tendon fibres to the bone with no anatomical variation in any of the digits. DISCUSSION
In order to explain the vulnerability to avulsion injury of the flexor digitorum profundus tendon to the ring finger, we have measured the breaking strength of the tendon-bone junction of the profundus tendon of each finger in fourteen cadaveric The Hand--VoL 10
No. 1
1978
53
A vulsion o f the Ring Finger Flexor Digitorum Profundus Tendon: A n Experimental Study Paul R. Manske and Peggy A. Lesker TABLE 1 BREAKING STRENGTH OF THE PROFUNDUS T E N D O N INSERTION IN FOURTEEN H A N D S
Finger Index Middle Ring Little
Breaking Strength (kgs) 13,2 18.0 12.1 13.3
+ + + +
1.9 2.0 1.3 2.2
_ indicates standard error hands. By fixing the bone and pulling the tendon at 90 ~, we have attempted to reproduce the clinical situation of a strong forcible pull of the distal phalanx against resistance. Since the tendon always avulsed with a small chip of bone in our experimental model, we feel confident that we have reproduced the clinical situation. Our results indicate that the breaking strength of the flexor digitorum profundus insertion of the ring finger is in most cases significantly less than that of the middle finger. Although the breaking strength of the ring finger insertion was slightly less than that of the index and little fingers, the difference was not significant. However, the index finger profundus is protected since it has an independent muscle belly, and the little finger profundus is uninvolved as it slips away during forcible grasp. The anatomically weaker insertion of the ring finger profundus fails prior to that of the stronger middle finger. Our results indicate a lower average breaking strength (14.2 kg) of the flexor digitorum profundus insertion than that found by Holden (1975). The possible explanations for this discrepancy include: (1) distraction of the tendon at a 90 ~ angle to the phalanx rather than parallel to it; and (2) dynamic loading of the tendon in contrast to stepwise static loading. However, the purpose of this study was not to challenge the validity of their results, but was to define the relative breaking strength of the tendonbone junction of each digit. ACKNOWLEDGEMENT
This project was supported in part by the Scottish Rite Foundation of Missouri and Howmedica, Inc. Our sincere thanks to Roy Peterson, P h . D . , Department of Anatomy, Washington University School of Medicine for the cadaver specimens. REFERENCES
BLAZINA, M.E., and LANE, C. (1966). Rupture of the Insertion of the Flexor Digitorum Profundus Tendon in Student Athletes. The Journal of the American Collegeof Health Association, 14: 248-249. CARROLL, R. E., and MATCH, R. M. (1970) Avulsion of the Flexor Profundus Tendon Insertion. The Journal of Trauma, 10:1109-1118. CHANG, W. H. J., THOMS, O. J., and WHITE, W. L. (1972). Avulsion Injury of the Long Flexor Tendons. Plastic and Reconstructive Surgery, 50: 260-264. GUNTER, G. S. (1960). Traumatic Avulsion of the Insertion of Flexor Digitorum Profundus. The Australian and New Zealand Journal of Surgery, 30: 1-9. 54
The Hand--VoL 10
No. 1
1978
Avulsion o f the Ring Finger Flexor Digitorum Profundus Tendon: A n Experimental Study Paul R. Manske and Peggy A. Lesker HOLDEN, C. E. A., and NORTHMORE-BALL, M. D. (1975). The Strength of the Profundus Tendon Insertion. The Hand, 7: 238-240. HOLLINSHEAD, W. H. (1969). Anatomy for Surgeons, Volume Three, The Back and Limbs Second Edition, New York, Evanston/London, Harper and Row, p. 408. HONNER, R. (1975). The Late Management of the Isolated Lesion of the Flexor Digitorum Profundus Tendon. The Hand, 7: 171-174. KAPLAN, E. P. (1965). Functional and Surgical Anatomy of the Hand, Second Edition, Philadelphia and Montreal, J. B. Lippincott Company, p. 57. LEDDY, J. P., and PACKER, J. W. (1977). Avulsion of the profundus tendon insertion in athletes. The Journal of Hand Surgery, 2: 66-69. McMASTER, P. E. (1933). Tendon and Muscle Ruptures. Clinical and Experimental Studies on the Causes and Location of Subcutaneous Ruptures. The Journal of Bone and Joint Surgery, 15: 705722. WENGER, D. R. (1973). Avulsion of the Profundus Tendon Insertion in Football Players. Archives of Surgery, 106: 145-149.
The Hand--Vol. 10
No. 1
1978
55
AVULSION OF THE RING FINGER FLEXOR DIGITORUM P R O F U N D U S T E N D O N : AN E X P E R I M E N T A L STUDY PAUL R. M A N S K E AND PEGGY A. LESKER, St. Louis, Missouri SUMMARY The results of an experimental study of the breaking strength of the tendon-bone ]unction of the flexor digitorum profundus tendon in cadaver specimens indicates a significantly weaker insertion of the ring finger compared to the middle finger. This explains in part the more frequent occurrence of avulsion of the ring finger profundus tendon as observed clinically. INTRODUCTION The susceptibility to avulsion at the distal phalanx of the flexor digitorum profundus tendon to the ring finger has been recognised by several writers (Gunter, 1960, Blazina, 1966; Carroll, 1970: Chang, 1972; Wenger, 1973; Honner, 1975; Leddy, 1977). The injury usually occurs as the fingers are clutching an object which is forcibly pulling away. Although all the fingers are presumably involved in the grasping action, the ring finger profundus tendon is the most liable to avulsion. Gunter (1960) and Wenger (1973) attribute this increased susceptibility to the presence of a common muscle belly of the middle, ring and little fingers as anatomically defined by Kaplan (1965) and Hollinshead (1969). Leddy (1977) suggests that the little finger slips out of the way during forcible grasp. Although these concepts suggest how the profundus tendons of the index and little fingers are protected from avulsion injury, they do not account for the more frequent involvement of the ring finger as compared with the middle finger. Holden and Northmore-Ball (1975) determined that the average breaking strength of the flexor digitorum profundus tendon-bone junction was 39.5 kilograms, but did not indicate the breaking strength of the individual digits. In order to determine whether there is a difference in the breaking strength of the profundus tendon insertion which might explain the susceptibility of the ring finger to avulsion injury, the following experiment was performed. METHOD Fourteen fresh cadaver hands (average, sixty-five years old) were collected within twenty-four hours of death and preserved at -70 ~ C until ready for dissection. The profundus tendon of each finger was divided at the level of the metacarpal phalangeal joint. The distal phalanx was disarticulated through the distal interphalangeal joint and dissected free of all soft tissue, except for the attached insertion of the profundus tendon and volar ,plate into the bone. The phalanx was transfixed longitudinally in a polyethylene cup with a smooth Kirschner wire (Figure 1). Methyl methacrylate secured the wire and dorsal surface of the bone to the cup, but did not come in contact with the area of insertion of the tendon and volar plate (Figure 2). The Kirschner wires were secured in the upper clamp and the tendon fixed in the lower clamp of a Scott JXL-100 tensile testing machine (Figure 3) so that the flexor tendon was directed 90 ~ to the distal phalanx. The breaking strength (recorded in Paul R. Manske, M.D., Washington UniversitySchoolof Medicine,4960 Audubon Avenue, St. Louis, Missouri 63110~U.S.A. 52
The Hand--Vol. 10
No. 1
1978
Avulsion of the Ring Finger Flexor Digitorum Profundus Tendon: A n Experimental Study Paul R. Manske and Peggy A. Lesker
Fig. 1.
Distal phalanx transfixed in polyethylene cup.
Fig. 2.
Distal phalanx embedded in methyl methacrylate.
Fig. 3.
Specimen secured in tensile testing machine.
kilograms) of the tendon-osseous junction was determined constant speed of 10 cm/min. In all cases the tendon was small fragment of bone as described by Holden (I 975). In two additional hands, multiple longitudinal and eosin microscopical sections were made at the level of the each digit and examined for anatomical variations.
by distracting the clamps at a avulsed at its insertion with a transverse haematoxylin and insertion of tendon to bone in
RESULTS
The results are recorded in Table 1. The average breaking strength of the flexor digitorum profundus tendon of the ring finger is weaker than any other digit and the difference is statistically significant (p 0.02) in relationship to the middle finger. The breaking strength of the ring finger was less than that of the middle finger in eleven of the fourteen specimens and of equal strength in the remaining hands. The histological preparations showed similar attachment of the tendon fibres to the bone with no anatomical variation in any of the digits. DISCUSSION
In order to explain the vulnerability to avulsion injury of the flexor digitorum profundus tendon to the ring finger, we have measured the breaking strength of the tendon-bone junction of the profundus tendon of each finger in fourteen cadaveric The Hand--VoL 10
No. 1
1978
53
A vulsion o f the Ring Finger Flexor Digitorum Profundus Tendon: A n Experimental Study Paul R. Manske and Peggy A. Lesker TABLE 1 BREAKING STRENGTH OF THE PROFUNDUS T E N D O N INSERTION IN FOURTEEN H A N D S
Finger Index Middle Ring Little
Breaking Strength (kgs) 13,2 18.0 12.1 13.3
+ + + +
1.9 2.0 1.3 2.2
_ indicates standard error hands. By fixing the bone and pulling the tendon at 90 ~, we have attempted to reproduce the clinical situation of a strong forcible pull of the distal phalanx against resistance. Since the tendon always avulsed with a small chip of bone in our experimental model, we feel confident that we have reproduced the clinical situation. Our results indicate that the breaking strength of the flexor digitorum profundus insertion of the ring finger is in most cases significantly less than that of the middle finger. Although the breaking strength of the ring finger insertion was slightly less than that of the index and little fingers, the difference was not significant. However, the index finger profundus is protected since it has an independent muscle belly, and the little finger profundus is uninvolved as it slips away during forcible grasp. The anatomically weaker insertion of the ring finger profundus fails prior to that of the stronger middle finger. Our results indicate a lower average breaking strength (14.2 kg) of the flexor digitorum profundus insertion than that found by Holden (1975). The possible explanations for this discrepancy include: (1) distraction of the tendon at a 90 ~ angle to the phalanx rather than parallel to it; and (2) dynamic loading of the tendon in contrast to stepwise static loading. However, the purpose of this study was not to challenge the validity of their results, but was to define the relative breaking strength of the tendonbone junction of each digit. ACKNOWLEDGEMENT
This project was supported in part by the Scottish Rite Foundation of Missouri and Howmedica, Inc. Our sincere thanks to Roy Peterson, P h . D . , Department of Anatomy, Washington University School of Medicine for the cadaver specimens. REFERENCES
BLAZINA, M.E., and LANE, C. (1966). Rupture of the Insertion of the Flexor Digitorum Profundus Tendon in Student Athletes. The Journal of the American Collegeof Health Association, 14: 248-249. CARROLL, R. E., and MATCH, R. M. (1970) Avulsion of the Flexor Profundus Tendon Insertion. The Journal of Trauma, 10:1109-1118. CHANG, W. H. J., THOMS, O. J., and WHITE, W. L. (1972). Avulsion Injury of the Long Flexor Tendons. Plastic and Reconstructive Surgery, 50: 260-264. GUNTER, G. S. (1960). Traumatic Avulsion of the Insertion of Flexor Digitorum Profundus. The Australian and New Zealand Journal of Surgery, 30: 1-9. 54
The Hand--VoL 10
No. 1
1978
Avulsion o f the Ring Finger Flexor Digitorum Profundus Tendon: A n Experimental Study Paul R. Manske and Peggy A. Lesker HOLDEN, C. E. A., and NORTHMORE-BALL, M. D. (1975). The Strength of the Profundus Tendon Insertion. The Hand, 7: 238-240. HOLLINSHEAD, W. H. (1969). Anatomy for Surgeons, Volume Three, The Back and Limbs Second Edition, New York, Evanston/London, Harper and Row, p. 408. HONNER, R. (1975). The Late Management of the Isolated Lesion of the Flexor Digitorum Profundus Tendon. The Hand, 7: 171-174. KAPLAN, E. P. (1965). Functional and Surgical Anatomy of the Hand, Second Edition, Philadelphia and Montreal, J. B. Lippincott Company, p. 57. LEDDY, J. P., and PACKER, J. W. (1977). Avulsion of the profundus tendon insertion in athletes. The Journal of Hand Surgery, 2: 66-69. McMASTER, P. E. (1933). Tendon and Muscle Ruptures. Clinical and Experimental Studies on the Causes and Location of Subcutaneous Ruptures. The Journal of Bone and Joint Surgery, 15: 705722. WENGER, D. R. (1973). Avulsion of the Profundus Tendon Insertion in Football Players. Archives of Surgery, 106: 145-149.
The Hand--Vol. 10
No. 1
1978
55