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Partially retained small finger flexor digitorum profundus function despite complete tendon loss in the forearm 1
Partially Retained Small Finger Flexor Digitorum Profundus Function Despite Complete Tendon Loss in the Forearm Mark W. Scanlan, MD, New York, NY, Randall V. Ehrlich, MD, Bronx, NY, Robert J. Strauch, MD, New York, NY
A case of traumatic laceration of the small finger flexor digitorum profundus (FDP) tendon in the distal forearm with retained partial active flexion at the small finger distal interphalangeal joint (DIP) joint is described. Tendinous interconnections between the ring and small FDP tendons and lumbrical muscles may permit partial FDP function at the DIP joint despite a complete deficit of the proximal tendon. (J Hand Surg 2004;29A:591–594. Copyright © 2004 by the American Society for Surgery of the Hand.) Key words: Flexor digitorum profundus tendon, tendon rupture, lumbricals.
Laceration of the flexor digitorum profundus (FDP) tendon proximally in the forearm would intuitively preclude active motion at the distal interphalangeal joint (DIP) joint of the small finger. Anatomic studies reveal that interconnections between the FDP tendons and bipennate origins of the lumbrical muscles from the adjacent ring and small finger FDP tendons are not uncommon.1 These interconnections could therefore permit limited active flexion of the DIP joint by the distal segment of a small finger FDP tendon severed proximal to the lumbrical. As a consequence, laceration of the FDP tendon to the small From the Department of Orthopaedic Surgery, New York-Presbyterian Hospital, Columbia University, New York, NY; Department of Orthopaedic Surgery, Montefiore Medical Center, Bronx, NY. Received for publication November 5, 2003; accepted in revised form January 22, 2004. 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: Robert J. Strauch, MD, 622 W. 168th St, PH 111115, New York, NY 10032. Copyright © 2004 by the American Society for Surgery of the Hand 0363-5023/04/29A04-0007$30.00/0 doi:10.1016/j.jhsa.2004.01.019
finger proximal to the lumbrical muscle may be difficult to detect clinically owing to partially preserved active DIP flexion. We present a case of a completely severed small finger FDP tendon in the forearm with retained partial active flexion distally at the DIP joint.
Case Report An otherwise healthy 47-year-old right-handed bicyclist was struck by an automobile, sustaining a Gustillo grade II open fracture of the right ulna at the midforearm level. He denied any previous injury to his right upper extremity. Intraoperative exploration revealed that the flexor carpi ulnaris and extensor carpi ulnaris tendons were severed completely and that the FDP tendon to the small finger also was severed completely, all with segmental loss, precluding direct repair. The extensive wound enabled a view of the FDP of the small finger to the distal forearm level, and it appeared separate from the other FDP tendons. All other tendons, including the flexor digitorum superficialis to the small finger, were noted to be intact. There was no neurovascular injury. The ulnar fracture was repaired with a compression platThe Journal of Hand Surgery
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ing technique and the wound was left open. Four days later the patient was returned to the operating room for repeat irrigation and debridement and delayed primary closure of the wound. He was referred to the senior author (R.J.S.) 1 week after surgery to manage his postoperative course, for the patient’s geographic convenience. Physical examination at that time revealed that despite his severing the FDP tendon to the small finger he was able to actively flex the DIP joint of the small finger to 45° with the metacarpophalangeal (MCP) joint held in full extension (Fig. 1). As the MCP joint flexed to 45° the patient lost the ability to actively flex the DIP joint (Fig. 2). His wounds healed with local wound care and the fracture solidly united by 8 weeks after surgery. He declined surgical reconstruction of his extensor carpi ulnaris, flexor carpi ulnaris, and FDP to the small finger because he believed his hand already to be at an extremely functional level by 8 weeks after surgery. One year after surgery he retained the ability to flex the small finger DIP joint to 45° actively with the MCP joint held in full extension, while losing that active flexion as the MCP joint flexed to 45°. He retained full active proximal interphalangeal (PIP) and MCP flexion of the small finger.
Figure 2. Composite fist attempted. Note that active DIP flexion is lost at the small finger DIP joint.
Anatomic Study A dissection was performed of 2 fresh-frozen cadaveric forearm specimens. In each specimen the ring and small finger FDP tendons were exposed in the forearm, wrist, and hand. The third and fourth lumbrical muscles also were exposed carefully in the hand. The tendons were found to be completely separate to the lumbrical level. Interconnections between a bipennate fourth lumbrical muscle and the FDP tendons of the ring and small fingers were evident in both specimens (Fig. 3). In one specimen, tendinous connections between the FDP tendons of the ring and small tendons also were noted at the level of the lumbrical. In both specimens, when traction was applied to the FDP tendon of the ring finger proximal to the origin of the lumbricals, some flexion of the distal phalanx of the small finger was noted. Presumably a portion of the proximally directed force applied to the FDP tendon of the ring finger was transmitted to the distal end of the FDP tendon of the small finger by the lumbrical/tendinous connections between the 2 tendons.
Discussion Figure 1. With the MCP joint in extension, 45° of active DIP flexion is possible.
Although the FDP tendons and their insertions tend to be anatomically constant within the finger, there is
Scanlan, Ehrlich, and Strauch / FDP Function
593
Figure 3. Cadaver dissection showing FDP of small finger (dotted line), FDP of ring finger (dashed line), and the lumbrical muscle connecting both tendons. A small slip of the small finger FDP also blends into the lumbrical muscle (arrow). Orientation of distal component of the digit at left of figure.
great variability in their interconnections proximal to the lumbrical origins. The FDP to the index finger consistently separates from the other tendons in the forearm; however, the remaining 3 tendons often have varying connections up to the level of the palm.2 Leijnse et al3,4 showed that proximal to the lumbrical origins there can be a frequent and notable exchange and reorganization of tendon fiber material between the FDP tendons with tendon fibers crossing over between different tendons, inserting into the lumbrical muscles, and/or dissolving into the synovial membranes. de Roos and Zeeman5 described a complete tendinous fusion up to the level of the lumbrical origin between the FDP tendons of the ring and small finger in the case of an intratendinous rupture of the FDP tendon to the small finger. The investigators postulated that the connection between the 2 tendons and subsequent lack of independent motion of the small finger predisposed the tendon to rupture. Davis and Armstrong6 reported a similar injury and described a single ring and small finger FDP tendon that bifurcated at the midpalmar level. The FDP tendons also may be connected to one another by the bitendinous origins of the lumbrical muscles. Eladoumikdachi et al7 dissected 14 fresh cadaveric specimens and reviewed the literature in an effort to better define the anatomy of the lumbrical muscles of the hand. They concluded that the lumbricals originate variably from the FDP tendons and
may be bipennate in many instances. Fifty-seven percent of specimens had fourth lumbrical muscles that originated from the ulnar side of the ring finger FDP as well as from the radial side of the small finger FDP tendon. Twenty-one percent of specimens had some muscle fibers of the fourth lumbrical that originated from the adjacent third lumbrical muscle. It is likely that the same anatomic variations that in some reports have been found to limit the independence of the FDP tendon to the small finger also may serve to preserve some function in the tendon distally after a complete proximal laceration. Contraction of the intact ring finger FDP muscle tendon may exercise a pull on the distal segment of the severed small finger FDP tendon via the aforementioned lumbrical and tendinous connections. This would permit some active motion at the DIP joint of the small finger and might lead the clinician to overlook the proximal tendon laceration. In the present case, during the original surgical procedure the FDP tendons of the ring and small finger appeared separate up to the distal forearm area, leading to our hypothesis that interconnections at the lumbrical level likely were responsible for the partial small finger FDP function. Paradoxical PIP joint extension (extension of the PIP joint with attempted DIP flexion) occurs in situations in which the lumbrical becomes taut before the FDP to that finger becomes taut, causing PIP extension as opposed to flexion. The usual culprit is
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loss of terminal attachment of the FDP tendon or an excessively long FDP graft. In the situation presented in this article the proximal end of the FDP was not attached to the distal end, but the anatomy in the zone of the lumbrical and beyond was normal; therefore no tendon length imbalance existed in the region normally posited to cause paradoxic PIP extension, which may explain its clinical absence in this case. In addition, no strong proximal force sufficient to cause paradoxical extension existed in this finger because the tendon had been cut proximally. If the clinician were unaware of the complete proximal disruption of the FDP to the small finger in this case, or if this were a simple forearm stab wound that otherwise did not require surgical exploration, it might be presumed that the FDP tendon of the small finger was intact based on the physical finding of partially preserved active DIP flexion. We hypothesize that muscle-tendinous connections between the FDP tendons of the ring and small fingers at the
lumbrical level accounted for the partially retained small finger active DIP flexion in this patient.
References 1. Furnas DW. Muscle-tendon variations in the flexor compartment of the wrist. Plast Reconstr Surg 1965;36:320 –324. 2. McMinn RMH. Last’s Anatomy. Regional and Applied. 9th ed. New York: Churchill Livingstone, 1994:91. 3. Leijnse JNAL, Walbeehm ET, Sonneveld GJ, Hovius SER, Kauer JMG. Connections between the tendons of the musculus flexor digitorum profundus involving the synovial sheaths in the carpal tunnel. Acta Anat (Basel) 1997;160:112–122. 4. Leijnse JNAL. A generic morpholological model of the anatomic variability in the M. flexor digitorum profundus, M. flexor pollicis longus and Mm. lumbricales complex. Acta Anat (Basel) 1997;160:62–74. 5. de Roos WK, Zeeman RJ. A flexor tendon rupture in the palm of the hand. J Hand Surg 1991;16A:663– 665. 6. Davis C, Armstrong J. Spontaneous flexor tendon rupture in the palm: the role of a variation of tendon anatomy. J Hand Surg 2003;28A:149 –152. 7. Eladoumikdachi F, Valkov PL, Thomas J, Netscher DT. Anatomy of the intrinsic hand muscles revisited: part II. Lumbricals. Plast Reconstr Surg 2002;110:1225–1231.
A case of traumatic laceration of the small finger flexor digitorum profundus (FDP) tendon in the distal forearm with retained partial active flexion at the small finger distal interphalangeal joint (DIP) joint is described. Tendinous interconnections between the ring and small FDP tendons and lumbrical muscles may permit partial FDP function at the DIP joint despite a complete deficit of the proximal tendon. (J Hand Surg 2004;29A:591–594. Copyright © 2004 by the American Society for Surgery of the Hand.) Key words: Flexor digitorum profundus tendon, tendon rupture, lumbricals.
Laceration of the flexor digitorum profundus (FDP) tendon proximally in the forearm would intuitively preclude active motion at the distal interphalangeal joint (DIP) joint of the small finger. Anatomic studies reveal that interconnections between the FDP tendons and bipennate origins of the lumbrical muscles from the adjacent ring and small finger FDP tendons are not uncommon.1 These interconnections could therefore permit limited active flexion of the DIP joint by the distal segment of a small finger FDP tendon severed proximal to the lumbrical. As a consequence, laceration of the FDP tendon to the small From the Department of Orthopaedic Surgery, New York-Presbyterian Hospital, Columbia University, New York, NY; Department of Orthopaedic Surgery, Montefiore Medical Center, Bronx, NY. Received for publication November 5, 2003; accepted in revised form January 22, 2004. 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: Robert J. Strauch, MD, 622 W. 168th St, PH 111115, New York, NY 10032. Copyright © 2004 by the American Society for Surgery of the Hand 0363-5023/04/29A04-0007$30.00/0 doi:10.1016/j.jhsa.2004.01.019
finger proximal to the lumbrical muscle may be difficult to detect clinically owing to partially preserved active DIP flexion. We present a case of a completely severed small finger FDP tendon in the forearm with retained partial active flexion distally at the DIP joint.
Case Report An otherwise healthy 47-year-old right-handed bicyclist was struck by an automobile, sustaining a Gustillo grade II open fracture of the right ulna at the midforearm level. He denied any previous injury to his right upper extremity. Intraoperative exploration revealed that the flexor carpi ulnaris and extensor carpi ulnaris tendons were severed completely and that the FDP tendon to the small finger also was severed completely, all with segmental loss, precluding direct repair. The extensive wound enabled a view of the FDP of the small finger to the distal forearm level, and it appeared separate from the other FDP tendons. All other tendons, including the flexor digitorum superficialis to the small finger, were noted to be intact. There was no neurovascular injury. The ulnar fracture was repaired with a compression platThe Journal of Hand Surgery
591
592
The Journal of Hand Surgery / Vol. 29A No. 4 July 2004
ing technique and the wound was left open. Four days later the patient was returned to the operating room for repeat irrigation and debridement and delayed primary closure of the wound. He was referred to the senior author (R.J.S.) 1 week after surgery to manage his postoperative course, for the patient’s geographic convenience. Physical examination at that time revealed that despite his severing the FDP tendon to the small finger he was able to actively flex the DIP joint of the small finger to 45° with the metacarpophalangeal (MCP) joint held in full extension (Fig. 1). As the MCP joint flexed to 45° the patient lost the ability to actively flex the DIP joint (Fig. 2). His wounds healed with local wound care and the fracture solidly united by 8 weeks after surgery. He declined surgical reconstruction of his extensor carpi ulnaris, flexor carpi ulnaris, and FDP to the small finger because he believed his hand already to be at an extremely functional level by 8 weeks after surgery. One year after surgery he retained the ability to flex the small finger DIP joint to 45° actively with the MCP joint held in full extension, while losing that active flexion as the MCP joint flexed to 45°. He retained full active proximal interphalangeal (PIP) and MCP flexion of the small finger.
Figure 2. Composite fist attempted. Note that active DIP flexion is lost at the small finger DIP joint.
Anatomic Study A dissection was performed of 2 fresh-frozen cadaveric forearm specimens. In each specimen the ring and small finger FDP tendons were exposed in the forearm, wrist, and hand. The third and fourth lumbrical muscles also were exposed carefully in the hand. The tendons were found to be completely separate to the lumbrical level. Interconnections between a bipennate fourth lumbrical muscle and the FDP tendons of the ring and small fingers were evident in both specimens (Fig. 3). In one specimen, tendinous connections between the FDP tendons of the ring and small tendons also were noted at the level of the lumbrical. In both specimens, when traction was applied to the FDP tendon of the ring finger proximal to the origin of the lumbricals, some flexion of the distal phalanx of the small finger was noted. Presumably a portion of the proximally directed force applied to the FDP tendon of the ring finger was transmitted to the distal end of the FDP tendon of the small finger by the lumbrical/tendinous connections between the 2 tendons.
Discussion Figure 1. With the MCP joint in extension, 45° of active DIP flexion is possible.
Although the FDP tendons and their insertions tend to be anatomically constant within the finger, there is
Scanlan, Ehrlich, and Strauch / FDP Function
593
Figure 3. Cadaver dissection showing FDP of small finger (dotted line), FDP of ring finger (dashed line), and the lumbrical muscle connecting both tendons. A small slip of the small finger FDP also blends into the lumbrical muscle (arrow). Orientation of distal component of the digit at left of figure.
great variability in their interconnections proximal to the lumbrical origins. The FDP to the index finger consistently separates from the other tendons in the forearm; however, the remaining 3 tendons often have varying connections up to the level of the palm.2 Leijnse et al3,4 showed that proximal to the lumbrical origins there can be a frequent and notable exchange and reorganization of tendon fiber material between the FDP tendons with tendon fibers crossing over between different tendons, inserting into the lumbrical muscles, and/or dissolving into the synovial membranes. de Roos and Zeeman5 described a complete tendinous fusion up to the level of the lumbrical origin between the FDP tendons of the ring and small finger in the case of an intratendinous rupture of the FDP tendon to the small finger. The investigators postulated that the connection between the 2 tendons and subsequent lack of independent motion of the small finger predisposed the tendon to rupture. Davis and Armstrong6 reported a similar injury and described a single ring and small finger FDP tendon that bifurcated at the midpalmar level. The FDP tendons also may be connected to one another by the bitendinous origins of the lumbrical muscles. Eladoumikdachi et al7 dissected 14 fresh cadaveric specimens and reviewed the literature in an effort to better define the anatomy of the lumbrical muscles of the hand. They concluded that the lumbricals originate variably from the FDP tendons and
may be bipennate in many instances. Fifty-seven percent of specimens had fourth lumbrical muscles that originated from the ulnar side of the ring finger FDP as well as from the radial side of the small finger FDP tendon. Twenty-one percent of specimens had some muscle fibers of the fourth lumbrical that originated from the adjacent third lumbrical muscle. It is likely that the same anatomic variations that in some reports have been found to limit the independence of the FDP tendon to the small finger also may serve to preserve some function in the tendon distally after a complete proximal laceration. Contraction of the intact ring finger FDP muscle tendon may exercise a pull on the distal segment of the severed small finger FDP tendon via the aforementioned lumbrical and tendinous connections. This would permit some active motion at the DIP joint of the small finger and might lead the clinician to overlook the proximal tendon laceration. In the present case, during the original surgical procedure the FDP tendons of the ring and small finger appeared separate up to the distal forearm area, leading to our hypothesis that interconnections at the lumbrical level likely were responsible for the partial small finger FDP function. Paradoxical PIP joint extension (extension of the PIP joint with attempted DIP flexion) occurs in situations in which the lumbrical becomes taut before the FDP to that finger becomes taut, causing PIP extension as opposed to flexion. The usual culprit is
594
The Journal of Hand Surgery / Vol. 29A No. 4 July 2004
loss of terminal attachment of the FDP tendon or an excessively long FDP graft. In the situation presented in this article the proximal end of the FDP was not attached to the distal end, but the anatomy in the zone of the lumbrical and beyond was normal; therefore no tendon length imbalance existed in the region normally posited to cause paradoxic PIP extension, which may explain its clinical absence in this case. In addition, no strong proximal force sufficient to cause paradoxical extension existed in this finger because the tendon had been cut proximally. If the clinician were unaware of the complete proximal disruption of the FDP to the small finger in this case, or if this were a simple forearm stab wound that otherwise did not require surgical exploration, it might be presumed that the FDP tendon of the small finger was intact based on the physical finding of partially preserved active DIP flexion. We hypothesize that muscle-tendinous connections between the FDP tendons of the ring and small fingers at the
lumbrical level accounted for the partially retained small finger active DIP flexion in this patient.
References 1. Furnas DW. Muscle-tendon variations in the flexor compartment of the wrist. Plast Reconstr Surg 1965;36:320 –324. 2. McMinn RMH. Last’s Anatomy. Regional and Applied. 9th ed. New York: Churchill Livingstone, 1994:91. 3. Leijnse JNAL, Walbeehm ET, Sonneveld GJ, Hovius SER, Kauer JMG. Connections between the tendons of the musculus flexor digitorum profundus involving the synovial sheaths in the carpal tunnel. Acta Anat (Basel) 1997;160:112–122. 4. Leijnse JNAL. A generic morpholological model of the anatomic variability in the M. flexor digitorum profundus, M. flexor pollicis longus and Mm. lumbricales complex. Acta Anat (Basel) 1997;160:62–74. 5. de Roos WK, Zeeman RJ. A flexor tendon rupture in the palm of the hand. J Hand Surg 1991;16A:663– 665. 6. Davis C, Armstrong J. Spontaneous flexor tendon rupture in the palm: the role of a variation of tendon anatomy. J Hand Surg 2003;28A:149 –152. 7. Eladoumikdachi F, Valkov PL, Thomas J, Netscher DT. Anatomy of the intrinsic hand muscles revisited: part II. Lumbricals. Plast Reconstr Surg 2002;110:1225–1231.