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Avulsion of the flexor digitorum profundus: Anatomic and biomechanical considerations
The Journal of HAND SURGERY
Thomsen and Falstie-Jensen
8. Boyes JH, Wilson IN, Smith JW. Flexor tendon ruptures in the forearm and hand. J Bone Joint Surg I960;42A:637 . 9. Mannerfeldt L, Lund ON. Attrition ruptures of flexor tendons in rheumatoid arthritis caused by bony spurs in the carpal tunnel. A clinical and radiological study. J Bone Joint Surg 1969;5IB:270-7. 10. Southmayd WW, Millender LH, Nalebuff EA. Rupture of the flexor tendons of the index finger after Colles' fracture. Case report. J Bone Joint Surg 1975;57:562-3. II. Broder H. Rupture of the flexor tendons associated with a malunited Colles' fracture. J Bone Joint Surg 1954; 36A:404-5. 12. Younger CP, DeFiore JC. Rupture of flexor tendons to the fingers after a Colles' fracture. J Bone Joint Surg 1977;59A:828-9. 13. Boyes JH, Wilson IN. Flexor tendon ruptures in the forearm and hand. J Bone Joint Surg 1960;42A:637-45. 14. Masada K, Kawabata H, Ono K. Pathologic rupture of
flexor tendons due to longstanding Kienbock's disease. J HAND SURG 1987;12A:22-5. 15. Crosby EB, Linscheid RL. Rupture of the flexor profundus tendon of the ring finger secondary to ancient fracture of the hook of the hamate. J Bone Joint Surg 1974;56A:1076-8. 16. Stem PJ. Multiple flexor tendon ruptures following an old anterior dislocation of the lunate. A case report. . J Bone Joint Surg 1981;63A:489-9O. 17. Fanbrough RA, Green DP. Tendon rupture as a complication of screw fixation in the hand. A case report. J Bone Joint Surg 1979;61A:781-2. ' 18. James ]JP. A case of rupture of flexor tendons secondary to Kienbock's disease. J Bone Joint Surg 1949;31B: 521-3. 19. Hallet JP, Motta GR. Tendon rupture in the hand with particular reference to attrition ruptures in the carpal tunnel. Hand 1982;14:283-90.
Avulsion of the flexor digitorum profundus: Anatomic and biomechanical considerations Avulsion of the profundus insertion occurs most commonly in the ring finger. The exact reason for this predilection is unknown. Clinical observation of patients with this injury reveals that a common finding is that the ring fingertip is usually more prominent or "longer" than any other fingertip during grip. A laboratory investigation shows that during grip the ring fingertip becomes 5 mm more prominent than any other digit in 90% of subjects and that it absorbs more force than any other finger during pull-away testing. These factors contribute to the susceptibility of the ring finger to the profundus avulsion injury. (J HAND SURG 1988;13A:222·7.)
Donald K. Bynum, Jr., MD, and Jerome A. Gilbert, PhD, Chapel Hill, N.C. Avulsion of the flexor digitorum profundus from its insertion at the distal phalanx is a well recognized injury that occurs far more commonly in the ring finger than in any of the other digits. (·3 The exact From the Division of Orthopaedic Surgery, University of North Carolina School of Medicine, Chapel Hill, N.C. Presented at the 1985 meeting of the American Society for Surgery of the Hand, Las Vegas. Nevada, January 22, 1985. Received for publication Aug. 21, 1986; accepted in revised form July IS, 1987. 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: Donald K. Bynum, Jr., MD, Division of Orthopaedic Surgery, University of North Carolina School of Medicine, 250 Burnett-Womack Bldg. 229-H, Chapel Hill, NC 27514.
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THE JOURNALOF HAND SURGERY
reason for the prevalence of the ring finger in this type of injury is unknown, but several explanations have been proposed. Gunter' postulated that the common muscle belly of the ring, long, and small finger profundus tendons predisposes to the injury. Leddy I and Leddy and Packer implicated the extensor juncturae because they limit independent extension of the ring finger. Manske and Lesker' reported an experimental study in which they found the insertion of the profundus of the ring finger to be weaker than that of the long finger. We propose that one of the principle reasons the ring finger is most susceptible to this injury is that the ring fingertip becomes the "longest" or most prominent during grip. It thus becomes anatomically and biomechanically predisposed to the profundus avulsion injury
Vol. 13A, No.2 March 1988
Asulsion offlexor digitorum profundus
Fig. 1. The distance between the tips of the ring and long fingers were measured in full extension (A) and in profundus-minus grip (B). In profundus-minus grip the ring finger was "longer" in 90% of subjects and was equal to or greater than 5 mrn "longer" in 50%.
Fig. 2. The most prominent fingertip in both tight grip (A) and loose grip (B) is the ring fingertip.
223
224
The Journal of HAND SURGERY
Bynum and Gilbert
~
~
...
...
@ •••
Fig. 3. Sketch of the experimental set-up for force determination. Four different grip positions were tested. The turnbuckles were used to equalize tension against all digits before the pull-away maneuvers.
when any of several different mechanisms of injury occur.
Materials and methods Five patients between the ages of 12 and 68 had avulsion of the ring finger flexor digitorum profundus by several different mechanisms. A common finding in all of these patients was that the ring fingertip became more prominent or "longer" than any of the other fingertips when the fingers were flexed. This observation prompted the following anatomic and biomechanical studies. We examined the dominant hands of 110 subjects. First, with the digits in full extension, the difference in the apparent length of the ring and long fingertips was measured. The subject was then asked to close the hand into the profundus-minus position, and the difference in the apparent length of the ring and long fingertips was again measured (Fig. 1). The subject was then asked to close the hand in a tight grip and the palm was visualized by retracting the thumb (Fig. 2). The most prominent fingertip was judged to be the one most proximal and/or deepest in the palm. No digit was considered most prominent if the appearance was not clear-cut to the observer. The same observation was made with the grip held loosely closed, i.e., with the fingertips just touching the palm (Fig. 2). We found that the ring fingertip appeared most prominent during grip in 90% of the subjects. Furthermore, in 50% of the subjects the ring fingertip was "longer" than any other fingertip by 5 mm or more when the grip was
held loosely or when held in the profundus-minus position. In 10% the apparent length of the ring and long fingers was equal. We then tested the hypothesis that the apparent prominence of the ring finger in grip results in its tip being exposed to more force during sudden pull away (the most common mechanism of injury). A subset of 35 persons from the total population participated in the force determination experiment. The experimental set-up is shown in Fig. 3. A single Grass cantilever beam force transducer (Grass Instrument Co., Quincy, Mass.) with maximum force response of 100 N was used to measure the force exerted at the tip of each forefinger. The signals from the force transducers were amplified and recorded on a 6 channel (2 channels not used) Grass chart recorder. The force transducers were fixed side-by-side in a laboratory vise. The free ends were connected via monofilament lines (120 N test) to fingertip caps into which the fingers were inserted. The connecting lines were maintained perpendicular to the force transducers and parallel to each other with approximately 2 cm separation distance between adjacent lines. The length of the lines was approximately 0.5 m, with the capacity . for a plus or minus 2 em length/tension adjustment by an inline turnbuckle. Subjects were fitted with leather fingertip caps that they then placed within metal thimbles to which the monofilament lines were attached. The turnbuckles were adjusted so that no slack was present in any of the lines. The force against each fingertip was thus
Vol. 13A, No.2 March 1988
40
Avulsion offlexor digltorum profundus
225
+
t.. .~...........'-- _ LITTLE
20
z
40
w
20
u
Subject GG 20 0 Ulnar Dev. P. Minus RING
a::
o
U-
n::
w ~ u,
40 20
MIDDLE
40 20
INDEX
Fig. 4. A representative test sequence of 10 pulls in rapid succession. Two such series were averaged for each test position in each subject.
Fig. 5. The hand as viewed from the perspective of an object about to be grasped at the bottom of the picture. The ring finger is the most prominent, thus it is exposed to impact forces or entanglement.
finger and ring finger in forearm neutral, full grip was the only value that was not statistically significant by the student's t test. Greater differences resulted in the profundus minus position, both for the forearm pronated and the forearm in neutral.
Discussion equalized at the beginning of each test, and the force against each fingertip was thus measured simultaneously yet independently. The subjects were instructed to pull 10 times against the fixed end of the force transducer. Several series of pulls were repeated for full grip and profundus-minus grip positions with the forearm in neutral rotation and again with the forearm in full pronation.
Results The fingertip force measurements were evaluated by selecting two sets of repetitions of each of the four grip positions for each subject. One such set is depicted in Fig. 4. These two sets were averaged for the subject. The force against each fingertip on each repetition was measured, and the force for each of the four fingers was represented as a percentage of the sum of the four finger forces for a single pull. For example, if the force was the same at each fingertip, each would be assigned a value of25%. After the subjects' forces were normalized to ' the total force , they were averaged (n = 35). The means and standard deviations are presented in Table I along with the percentage difference of each force as compared with the force at the tip of the ring finger. The 5% difference between the small
Some previous explanations of why the ring finger is predisposed to the profundus injury focus on its lack of independent extension relative to the other digits.': 2. 6 The ring finger is generally less capable of independent metacarpal phalangeal joint extension than the other digits. The common tendon and muscle belly of the profundus and the presence of extensor juncturae interconnecting the long, ring, and small fingers have been set forth as reasons for this lack of independent ring finger extension. Not mentioned in these previous discussion s is the anatomic fact that the ring profundus serves as the origin for lumbrical muscles to the ring and small fingers and the fact that the ring finger .lumbrical muscle originates from both the long and ring finger profundus tendons. If the lack of independent ring finger metacarpal phalangeal extension were truly the cause of profundus avulsion, we would expect some of these other structures limiting extension to be injured rather than just the profundus at its insertion. Football players have given clear histories of sustain ing the "jersey finger" injury both when initially attempting to grasp an opponent and also when the grip has been broken and the ring finger is the last to become disentangled from the opponent's jersey. In both of these instances, the hand is nearly open but the digits are not in full extension. In our patients the injury also occurred
226
The Journal of HAND SURGERY
Bynum and Gilbert
Table I. Data as a percentage of total force and compared with the ring finger Forearm pronated
Forearm neutral
Profundus minus
Index Long Ring Small
24.1 24.5 26.8 24.6
=4.6 =4.4 =4.3 =4.3
8,
21.5 24.5 29.t 25.0
% Difference
= 3.8
=2.9 =4.4
=4.4
Full grip
22.8 24.3 27.2 25.8
Profundus minus
=4.5 = 3.8 =4.5
=4.8
5 NS
21.6 24.3 28.6 25.5
% Difference
=4.6 = 2.9 =4.6 =4.4
a = p < 0.05. b = p < 0.02. c = p < 0.01. d = P < O.OO!. NS . Not statistically significant.
when a dog's leash and a horse's rein were suddenly pulled away and when a youth slapped another on the head with his partially cupped hand . Frequently, however, the patient does not know the exact position of the hand when the injury occurred, except that usually the hand was not completely closed. When the hand is partially closed independent extension of the ring finger does not seem to be limited as much as when the hand is in full grip. What does occur however is that the tip of the ring finger becomes more prominent than that of the other digits and is thus more susceptible to injury. The shift in the relative length of the fingertips occurs very early during closure of the hand (Fig. 5), thus placing the ring fingertip in jeopardy of absorbing the initial forces before other digits come into. contact. Likewise if the hand is slightly closed, an opponent's jersey, a dog's leash, horse reins, etc. are more likely to be caught by the tip of the ring finger than any other. The explanation for the shift in the "length" of the long and ring fingers lies in the greater mobility of the fourth carpal-metacarpal joint and in the shorter fourth metacarpal. The ring fingertip becomes more palmar because of carpal-metacarpal joint flexion and more proximal because of the shorter (more proximal) location of its metacarpal-phalangeal joint. The phalanges of the long and ring fingers are nearly equal in length while the small finger phalanges are much shorter so that the shift in the position of the small fingertip is not as great a phenomenon and it does not come into prominence . The biomechanical force testing was done in such a way that the forces against each fingertip were equal at the start of each test. In the clinical situation it is more likely that the forces absorbed at the different fingertips do not begin simultaneously or equally. The most prominent digit will be subjected to the isolated, total force when initial contact is made or when it is the last to
lose contact. Thus the ring finger might experience an even larger proportion of the maximum total force than reported in this experiment. Stretching of the material being grasped and the direction of pull will also affect the forces at the individual fingertips. In those situations in which the small finger, because of its shortness, looses its purchase there would be a sudden shift of forces towards the ring finger. This phenomenon probably also plays an important role in the injury." The positions tested were chosen because they were reproducible from subject to subject. The most frequent mechanisms of injury probably occur when the hand is only partially closed although injury in almost any position is possible. The exact clinical situation cannot be duplicated in the laboratory becau se the injury occurs through a variety of mechanisms . It is interesting to note that the largest differences in forces measured at the ring finger compared with the other digits occurred in the profundus minus position; the position in which the ring finger is most prominent. This fact thus lends support to the theory that prominence of the ring finger at the time of injury contributes to the prevalence of profundus avulsion in the ring finger. We would like to emphasize that this biomechanical test did not measure the absolute or relative strengths of the digits but measured the relative force absorbed at each fingertip during sudden pull away. Previous investigators?" have noted the long finger to be the strongest when fingers were tested individually. We do not disagree with those observations, and it should be pointed out that they were testing an entirely different factor than that reported here .
REFERENCES I. Leddy JP. in: Green DP, cd. Operative hand surgery. New York: Churchill Livingstone, 1982:1364-5.
Vol. 13A. No.2 March 1988
2. Leddy 1P, Packer JT. Avulsion of the profundus tendon insertion in athletes. 1 HAND SURG 1977;2:66-9. 3. Reef 'I'C. Avulsion of the flexor digitorum profundus: an athletic injury . Am 1 Sports Med 1977;5:281-5. 4. Gunter GS . Traumatic avulsion of the insertion of flexor digitorum profundus. Aust NZ 1 Surg 1960;30:1-9. 5. Manske PRo Leske PA. Avulsion of the ring finger flexor digitorum profundus tendon : an experimental study. Hand 1978;10:52-5. 6. Wenger DR. Avulsion of the profundus tendon insertion in football players. Arch Surg 1973;106:145-9.
Avulsion offlexor digitorum profundus
7. Ejeskar A, Ortengren R. Isolated finger flexion force-a methodological study. Hand 1981;13:223·30. 8. HalI 51. Metacarpophalangeal flexion forces with respect to age, sex and exercise habits . Med Sci Sports Exerc 1981; 13:329-31. 9. Hazelton Fr. Smidt GL, Flatt AE, Stephens Rl. The influence of wrist position on the force produced by the finger flexors. 1 Biomech 1975;8:301-6.
Delayed repair of flexor profundus tendon in the palm (zone 3) with superficialis transfer Transfer of a flexor superficialis tendon was done in an attempt to restore flexor profundus function, as a secondary procedure, in the palm (zone 3) in 16 hands. These were cases in which direct repair was not possible. Eight patients achieved a total active motion (TAM) above 200 degrees and two more were above 180. Of those eight with TAM above 200 degrees four required a secondary tenolysis to improve to that level. Transfers in six patients were regarded as failures. failures were associated with a poor tendon bed and noncompliant patients. This is a procedure that has limited indication in a cooperative patient with a good tendon bed who reports late with both flexor tendons cut in zone 3. (J HAND SURG 1988j13A:227.30.)
Lawrence H.Schneider, MD, and Marwan A. Wehbe, MD, Philadelphia and Bryn Mawr, Penn,
T
he direct early repair of flexor tendon injuries in the palm, when wound conditions permit, has seldom been questioned and is the preferred treatment for these injuries. There are, however, a small group of patients who are seen initially with injuries in zone 3 (the palm) in whom the opportunity for direct, end-to-end repair has passed or in whom previous repair From the Division of Hand Surgery, Department of Orthopaedic Surgery, Jefferson Medical College of the Thomas Jefferson University. and the Hand Rehabilitation Center. Philadelphia. Penn. Received for publication Feb. 27, 1987; accepted in revised form Aug. 18, 1987. No benefits in any form have been received or will be received from a commercial party related directly or indirectly 10 the subject of this article. Reprint requests: Lawrence H. Schneider, MD. Hand Rehabilitation Center. 901 Walnut si., Philadelphia. PA 19107.
has failed. In this situation there are a few options left to the surgeon attempting to restore flexor function in these fingers. These include the use of a segmental interposition graft within zone 3 1 or the removal of the entire profundus tendon from the finger and insertion .of a palm- to-distal phalanx tendon graft. The interposition graft requires two junctures in the palm and therefore there are more opportunities for adhesions to form . The palm- to-distal phalanx tendon graft requires the removal of the flexor tendon in the clean, unscarred zone 2, which is unfortunate as this is the most difficult area in which to restore gliding function. A third possibility for delayed repair of the profundus in zone 3, when zone 2 is intact, is the use of a tendon transfer of an adjacent flexor digitorum superficialis (FDS) tendon in the palm to motor the distal profundus.' Mayer' first suggested this tendon transfer, which he
THE JOURNAL OF HAND SURGERY
227
Thomsen and Falstie-Jensen
8. Boyes JH, Wilson IN, Smith JW. Flexor tendon ruptures in the forearm and hand. J Bone Joint Surg I960;42A:637 . 9. Mannerfeldt L, Lund ON. Attrition ruptures of flexor tendons in rheumatoid arthritis caused by bony spurs in the carpal tunnel. A clinical and radiological study. J Bone Joint Surg 1969;5IB:270-7. 10. Southmayd WW, Millender LH, Nalebuff EA. Rupture of the flexor tendons of the index finger after Colles' fracture. Case report. J Bone Joint Surg 1975;57:562-3. II. Broder H. Rupture of the flexor tendons associated with a malunited Colles' fracture. J Bone Joint Surg 1954; 36A:404-5. 12. Younger CP, DeFiore JC. Rupture of flexor tendons to the fingers after a Colles' fracture. J Bone Joint Surg 1977;59A:828-9. 13. Boyes JH, Wilson IN. Flexor tendon ruptures in the forearm and hand. J Bone Joint Surg 1960;42A:637-45. 14. Masada K, Kawabata H, Ono K. Pathologic rupture of
flexor tendons due to longstanding Kienbock's disease. J HAND SURG 1987;12A:22-5. 15. Crosby EB, Linscheid RL. Rupture of the flexor profundus tendon of the ring finger secondary to ancient fracture of the hook of the hamate. J Bone Joint Surg 1974;56A:1076-8. 16. Stem PJ. Multiple flexor tendon ruptures following an old anterior dislocation of the lunate. A case report. . J Bone Joint Surg 1981;63A:489-9O. 17. Fanbrough RA, Green DP. Tendon rupture as a complication of screw fixation in the hand. A case report. J Bone Joint Surg 1979;61A:781-2. ' 18. James ]JP. A case of rupture of flexor tendons secondary to Kienbock's disease. J Bone Joint Surg 1949;31B: 521-3. 19. Hallet JP, Motta GR. Tendon rupture in the hand with particular reference to attrition ruptures in the carpal tunnel. Hand 1982;14:283-90.
Avulsion of the flexor digitorum profundus: Anatomic and biomechanical considerations Avulsion of the profundus insertion occurs most commonly in the ring finger. The exact reason for this predilection is unknown. Clinical observation of patients with this injury reveals that a common finding is that the ring fingertip is usually more prominent or "longer" than any other fingertip during grip. A laboratory investigation shows that during grip the ring fingertip becomes 5 mm more prominent than any other digit in 90% of subjects and that it absorbs more force than any other finger during pull-away testing. These factors contribute to the susceptibility of the ring finger to the profundus avulsion injury. (J HAND SURG 1988;13A:222·7.)
Donald K. Bynum, Jr., MD, and Jerome A. Gilbert, PhD, Chapel Hill, N.C. Avulsion of the flexor digitorum profundus from its insertion at the distal phalanx is a well recognized injury that occurs far more commonly in the ring finger than in any of the other digits. (·3 The exact From the Division of Orthopaedic Surgery, University of North Carolina School of Medicine, Chapel Hill, N.C. Presented at the 1985 meeting of the American Society for Surgery of the Hand, Las Vegas. Nevada, January 22, 1985. Received for publication Aug. 21, 1986; accepted in revised form July IS, 1987. 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: Donald K. Bynum, Jr., MD, Division of Orthopaedic Surgery, University of North Carolina School of Medicine, 250 Burnett-Womack Bldg. 229-H, Chapel Hill, NC 27514.
222
THE JOURNALOF HAND SURGERY
reason for the prevalence of the ring finger in this type of injury is unknown, but several explanations have been proposed. Gunter' postulated that the common muscle belly of the ring, long, and small finger profundus tendons predisposes to the injury. Leddy I and Leddy and Packer implicated the extensor juncturae because they limit independent extension of the ring finger. Manske and Lesker' reported an experimental study in which they found the insertion of the profundus of the ring finger to be weaker than that of the long finger. We propose that one of the principle reasons the ring finger is most susceptible to this injury is that the ring fingertip becomes the "longest" or most prominent during grip. It thus becomes anatomically and biomechanically predisposed to the profundus avulsion injury
Vol. 13A, No.2 March 1988
Asulsion offlexor digitorum profundus
Fig. 1. The distance between the tips of the ring and long fingers were measured in full extension (A) and in profundus-minus grip (B). In profundus-minus grip the ring finger was "longer" in 90% of subjects and was equal to or greater than 5 mrn "longer" in 50%.
Fig. 2. The most prominent fingertip in both tight grip (A) and loose grip (B) is the ring fingertip.
223
224
The Journal of HAND SURGERY
Bynum and Gilbert
~
~
...
...
@ •••
Fig. 3. Sketch of the experimental set-up for force determination. Four different grip positions were tested. The turnbuckles were used to equalize tension against all digits before the pull-away maneuvers.
when any of several different mechanisms of injury occur.
Materials and methods Five patients between the ages of 12 and 68 had avulsion of the ring finger flexor digitorum profundus by several different mechanisms. A common finding in all of these patients was that the ring fingertip became more prominent or "longer" than any of the other fingertips when the fingers were flexed. This observation prompted the following anatomic and biomechanical studies. We examined the dominant hands of 110 subjects. First, with the digits in full extension, the difference in the apparent length of the ring and long fingertips was measured. The subject was then asked to close the hand into the profundus-minus position, and the difference in the apparent length of the ring and long fingertips was again measured (Fig. 1). The subject was then asked to close the hand in a tight grip and the palm was visualized by retracting the thumb (Fig. 2). The most prominent fingertip was judged to be the one most proximal and/or deepest in the palm. No digit was considered most prominent if the appearance was not clear-cut to the observer. The same observation was made with the grip held loosely closed, i.e., with the fingertips just touching the palm (Fig. 2). We found that the ring fingertip appeared most prominent during grip in 90% of the subjects. Furthermore, in 50% of the subjects the ring fingertip was "longer" than any other fingertip by 5 mm or more when the grip was
held loosely or when held in the profundus-minus position. In 10% the apparent length of the ring and long fingers was equal. We then tested the hypothesis that the apparent prominence of the ring finger in grip results in its tip being exposed to more force during sudden pull away (the most common mechanism of injury). A subset of 35 persons from the total population participated in the force determination experiment. The experimental set-up is shown in Fig. 3. A single Grass cantilever beam force transducer (Grass Instrument Co., Quincy, Mass.) with maximum force response of 100 N was used to measure the force exerted at the tip of each forefinger. The signals from the force transducers were amplified and recorded on a 6 channel (2 channels not used) Grass chart recorder. The force transducers were fixed side-by-side in a laboratory vise. The free ends were connected via monofilament lines (120 N test) to fingertip caps into which the fingers were inserted. The connecting lines were maintained perpendicular to the force transducers and parallel to each other with approximately 2 cm separation distance between adjacent lines. The length of the lines was approximately 0.5 m, with the capacity . for a plus or minus 2 em length/tension adjustment by an inline turnbuckle. Subjects were fitted with leather fingertip caps that they then placed within metal thimbles to which the monofilament lines were attached. The turnbuckles were adjusted so that no slack was present in any of the lines. The force against each fingertip was thus
Vol. 13A, No.2 March 1988
40
Avulsion offlexor digltorum profundus
225
+
t.. .~...........'-- _ LITTLE
20
z
40
w
20
u
Subject GG 20 0 Ulnar Dev. P. Minus RING
a::
o
U-
n::
w ~ u,
40 20
MIDDLE
40 20
INDEX
Fig. 4. A representative test sequence of 10 pulls in rapid succession. Two such series were averaged for each test position in each subject.
Fig. 5. The hand as viewed from the perspective of an object about to be grasped at the bottom of the picture. The ring finger is the most prominent, thus it is exposed to impact forces or entanglement.
finger and ring finger in forearm neutral, full grip was the only value that was not statistically significant by the student's t test. Greater differences resulted in the profundus minus position, both for the forearm pronated and the forearm in neutral.
Discussion equalized at the beginning of each test, and the force against each fingertip was thus measured simultaneously yet independently. The subjects were instructed to pull 10 times against the fixed end of the force transducer. Several series of pulls were repeated for full grip and profundus-minus grip positions with the forearm in neutral rotation and again with the forearm in full pronation.
Results The fingertip force measurements were evaluated by selecting two sets of repetitions of each of the four grip positions for each subject. One such set is depicted in Fig. 4. These two sets were averaged for the subject. The force against each fingertip on each repetition was measured, and the force for each of the four fingers was represented as a percentage of the sum of the four finger forces for a single pull. For example, if the force was the same at each fingertip, each would be assigned a value of25%. After the subjects' forces were normalized to ' the total force , they were averaged (n = 35). The means and standard deviations are presented in Table I along with the percentage difference of each force as compared with the force at the tip of the ring finger. The 5% difference between the small
Some previous explanations of why the ring finger is predisposed to the profundus injury focus on its lack of independent extension relative to the other digits.': 2. 6 The ring finger is generally less capable of independent metacarpal phalangeal joint extension than the other digits. The common tendon and muscle belly of the profundus and the presence of extensor juncturae interconnecting the long, ring, and small fingers have been set forth as reasons for this lack of independent ring finger extension. Not mentioned in these previous discussion s is the anatomic fact that the ring profundus serves as the origin for lumbrical muscles to the ring and small fingers and the fact that the ring finger .lumbrical muscle originates from both the long and ring finger profundus tendons. If the lack of independent ring finger metacarpal phalangeal extension were truly the cause of profundus avulsion, we would expect some of these other structures limiting extension to be injured rather than just the profundus at its insertion. Football players have given clear histories of sustain ing the "jersey finger" injury both when initially attempting to grasp an opponent and also when the grip has been broken and the ring finger is the last to become disentangled from the opponent's jersey. In both of these instances, the hand is nearly open but the digits are not in full extension. In our patients the injury also occurred
226
The Journal of HAND SURGERY
Bynum and Gilbert
Table I. Data as a percentage of total force and compared with the ring finger Forearm pronated
Forearm neutral
Profundus minus
Index Long Ring Small
24.1 24.5 26.8 24.6
=4.6 =4.4 =4.3 =4.3
8,
21.5 24.5 29.t 25.0
% Difference
= 3.8
=2.9 =4.4
=4.4
Full grip
22.8 24.3 27.2 25.8
Profundus minus
=4.5 = 3.8 =4.5
=4.8
5 NS
21.6 24.3 28.6 25.5
% Difference
=4.6 = 2.9 =4.6 =4.4
a = p < 0.05. b = p < 0.02. c = p < 0.01. d = P < O.OO!. NS . Not statistically significant.
when a dog's leash and a horse's rein were suddenly pulled away and when a youth slapped another on the head with his partially cupped hand . Frequently, however, the patient does not know the exact position of the hand when the injury occurred, except that usually the hand was not completely closed. When the hand is partially closed independent extension of the ring finger does not seem to be limited as much as when the hand is in full grip. What does occur however is that the tip of the ring finger becomes more prominent than that of the other digits and is thus more susceptible to injury. The shift in the relative length of the fingertips occurs very early during closure of the hand (Fig. 5), thus placing the ring fingertip in jeopardy of absorbing the initial forces before other digits come into. contact. Likewise if the hand is slightly closed, an opponent's jersey, a dog's leash, horse reins, etc. are more likely to be caught by the tip of the ring finger than any other. The explanation for the shift in the "length" of the long and ring fingers lies in the greater mobility of the fourth carpal-metacarpal joint and in the shorter fourth metacarpal. The ring fingertip becomes more palmar because of carpal-metacarpal joint flexion and more proximal because of the shorter (more proximal) location of its metacarpal-phalangeal joint. The phalanges of the long and ring fingers are nearly equal in length while the small finger phalanges are much shorter so that the shift in the position of the small fingertip is not as great a phenomenon and it does not come into prominence . The biomechanical force testing was done in such a way that the forces against each fingertip were equal at the start of each test. In the clinical situation it is more likely that the forces absorbed at the different fingertips do not begin simultaneously or equally. The most prominent digit will be subjected to the isolated, total force when initial contact is made or when it is the last to
lose contact. Thus the ring finger might experience an even larger proportion of the maximum total force than reported in this experiment. Stretching of the material being grasped and the direction of pull will also affect the forces at the individual fingertips. In those situations in which the small finger, because of its shortness, looses its purchase there would be a sudden shift of forces towards the ring finger. This phenomenon probably also plays an important role in the injury." The positions tested were chosen because they were reproducible from subject to subject. The most frequent mechanisms of injury probably occur when the hand is only partially closed although injury in almost any position is possible. The exact clinical situation cannot be duplicated in the laboratory becau se the injury occurs through a variety of mechanisms . It is interesting to note that the largest differences in forces measured at the ring finger compared with the other digits occurred in the profundus minus position; the position in which the ring finger is most prominent. This fact thus lends support to the theory that prominence of the ring finger at the time of injury contributes to the prevalence of profundus avulsion in the ring finger. We would like to emphasize that this biomechanical test did not measure the absolute or relative strengths of the digits but measured the relative force absorbed at each fingertip during sudden pull away. Previous investigators?" have noted the long finger to be the strongest when fingers were tested individually. We do not disagree with those observations, and it should be pointed out that they were testing an entirely different factor than that reported here .
REFERENCES I. Leddy JP. in: Green DP, cd. Operative hand surgery. New York: Churchill Livingstone, 1982:1364-5.
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2. Leddy 1P, Packer JT. Avulsion of the profundus tendon insertion in athletes. 1 HAND SURG 1977;2:66-9. 3. Reef 'I'C. Avulsion of the flexor digitorum profundus: an athletic injury . Am 1 Sports Med 1977;5:281-5. 4. Gunter GS . Traumatic avulsion of the insertion of flexor digitorum profundus. Aust NZ 1 Surg 1960;30:1-9. 5. Manske PRo Leske PA. Avulsion of the ring finger flexor digitorum profundus tendon : an experimental study. Hand 1978;10:52-5. 6. Wenger DR. Avulsion of the profundus tendon insertion in football players. Arch Surg 1973;106:145-9.
Avulsion offlexor digitorum profundus
7. Ejeskar A, Ortengren R. Isolated finger flexion force-a methodological study. Hand 1981;13:223·30. 8. HalI 51. Metacarpophalangeal flexion forces with respect to age, sex and exercise habits . Med Sci Sports Exerc 1981; 13:329-31. 9. Hazelton Fr. Smidt GL, Flatt AE, Stephens Rl. The influence of wrist position on the force produced by the finger flexors. 1 Biomech 1975;8:301-6.
Delayed repair of flexor profundus tendon in the palm (zone 3) with superficialis transfer Transfer of a flexor superficialis tendon was done in an attempt to restore flexor profundus function, as a secondary procedure, in the palm (zone 3) in 16 hands. These were cases in which direct repair was not possible. Eight patients achieved a total active motion (TAM) above 200 degrees and two more were above 180. Of those eight with TAM above 200 degrees four required a secondary tenolysis to improve to that level. Transfers in six patients were regarded as failures. failures were associated with a poor tendon bed and noncompliant patients. This is a procedure that has limited indication in a cooperative patient with a good tendon bed who reports late with both flexor tendons cut in zone 3. (J HAND SURG 1988j13A:227.30.)
Lawrence H.Schneider, MD, and Marwan A. Wehbe, MD, Philadelphia and Bryn Mawr, Penn,
T
he direct early repair of flexor tendon injuries in the palm, when wound conditions permit, has seldom been questioned and is the preferred treatment for these injuries. There are, however, a small group of patients who are seen initially with injuries in zone 3 (the palm) in whom the opportunity for direct, end-to-end repair has passed or in whom previous repair From the Division of Hand Surgery, Department of Orthopaedic Surgery, Jefferson Medical College of the Thomas Jefferson University. and the Hand Rehabilitation Center. Philadelphia. Penn. Received for publication Feb. 27, 1987; accepted in revised form Aug. 18, 1987. No benefits in any form have been received or will be received from a commercial party related directly or indirectly 10 the subject of this article. Reprint requests: Lawrence H. Schneider, MD. Hand Rehabilitation Center. 901 Walnut si., Philadelphia. PA 19107.
has failed. In this situation there are a few options left to the surgeon attempting to restore flexor function in these fingers. These include the use of a segmental interposition graft within zone 3 1 or the removal of the entire profundus tendon from the finger and insertion .of a palm- to-distal phalanx tendon graft. The interposition graft requires two junctures in the palm and therefore there are more opportunities for adhesions to form . The palm- to-distal phalanx tendon graft requires the removal of the flexor tendon in the clean, unscarred zone 2, which is unfortunate as this is the most difficult area in which to restore gliding function. A third possibility for delayed repair of the profundus in zone 3, when zone 2 is intact, is the use of a tendon transfer of an adjacent flexor digitorum superficialis (FDS) tendon in the palm to motor the distal profundus.' Mayer' first suggested this tendon transfer, which he
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