Journal of Plastic, Reconstructive & Aesthetic Surgery (2014) 67, 822e827
The role of proximal pulleys in preventing tendon bowstringing: Pulley rupture and tendon bowstringing* S. Leeflang*, J.H. Coert Erasmus MC University Medical Centre, Rotterdam, The Netherlands Received 8 February 2013; accepted 28 January 2014
KEYWORDS A2 pulley; Bowstringing; Climbers; Ultrasonography
Summary Purpose: The aim of this study was to investigate factors that contribute to tendon bowstringing at the proximal phalanx. We hypothesised that: (1) a partial rupture of the A2 pulley leads to significant bowstringing, (2) the location of the A2 rupture, starting proximally or distally, influences bowstringing, (3) an additional A3 pulley rupture causes a significant increase in bowstringing following a complete A2 pulley rupture and (4) the skin and tendon sheath may prevent bowstringing in A2 and A3 pulley ruptures. Methods: Index, middle and ring fingers of eight freshly frozen cadaver arms were used. A loading device pulled with 100 N force was attached to the flexor digitorum profundus (FDP). The flexor digitorum superficialis (FDS) was preloaded with 5 N. Bowstringing was measured and quantified by the size of the area between the FDP tendon and the proximal phalanx over a distance of 5 mm with ultrasonography (US). Results: US images showed that already a 30% excision of the A2 pulley resulted in significant bowstringing. In addition, a partial distal incision of the A2 pulley showed significantly more bowstringing compared to a partial proximal incision. Additional A3 pulley incision and excision of the proximal tendon sheath did not increase bowstringing. Subsequently, removing the skin did increase the bowstringing significantly. Conclusion: A partial A2 pulley rupture causes a significant bowstringing. A partial rupture of the A2 pulley at the distal rim of the A2 pulley resulted in more bowstringing than a partial rupture at the proximal rim. ª 2014 British Association of Plastic, Reconstructive and Aesthetic Surgeons. Published by Elsevier Ltd. All rights reserved.
*
Presented at: 1) 03 April 2009 e Dutch Society of Plastic Surgery (NVPC), 2) 20 June 2009 e Dutch Society of Hand Surgery (NVvH), 3) 24 June 2010 e 15th FESSH congress, Bucharest, Romania. * Corresponding author. Department of Plastic and Reconstructive Surgery, Erasmus MC University Medical Centre, Rotterdam, The Netherlands. Tel.: þ31 620718438. E-mail address: [email protected] (S. Leeflang). 1748-6815/$ - see front matter ª 2014 British Association of Plastic, Reconstructive and Aesthetic Surgeons. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.bjps.2014.01.041
Pulley rupture and tendon bowstringing Sport climbers may have pulley strains or partial pulley ruptures without detectable bowstringing. This was the initial idea to conduct this study. Sport climbing has grown in popularity: new pathologies involving the hand, elbow and shoulder have been presented.1e5 About 75% of sport climbers experience overuse syndromes or injuries of the upper extremity. The fingers and the wrist are the most commonly involved structures, with pulley ruptures being the most frequently seen injuries. Annular pulleys are important to keep the flexor tendons close to the phalanges to assure optimal mechanical efficiency.6e8 Forces on pulleys can become close to 400 N during climbing.4,9,10 Several papers focussed on effects of pulley ruptures on the finger excursion; some authors removed the skin or the flexor tendon sheath to do so.3,7,8,11e13 Other studies tested the pulleys, while the finger was disarticulated from the hand.7,14,15 However, the skin and the flexor tendon sheath themselves could function as a mechanical pulley for flexor tendons. Several studies have shown that ultrasonography (US) allows good imaging of finger pulley injuries in sport climbers. Hauger et al. (2000) noted that the finger pulley system could be evaluated directly with US using cadaver fingers. Part of the study was done with fingers in the flexed position; the US images were made in the transverse plane. Their results showed that they could identify uninjured A2 pulleys in 100% and uninjured A4 pulleys in 67% of the cases.16 Following partial and complete lesions of the pulleys, correct diagnosis was possible with US in 79e100% of the cases. Their study shows that US can be useful in diagnosing pulley injury: they could identify all pulleys and they could adequately detect if they were ruptured. The aim of this report was to simulate the situation of climbing and study factors that could play a role in bowstringing at the proximal phalanx: 1) partial rupture of the A2 pulley 2) location (proximal/distal) of the rupture of the A2 pulley 3) subsequent A3 pulley rupture. In addition, the effect of the skin and the proximal tendon sheath in preventing bowstringing was studied in case of a rupture of the A2 and the A3 pulley.
Materials and methods
823
Figure 1
Custom-made jig for the arm to secure its position.
two tie wraps preventing the wrist from moving when the tendon was pulled. The hand was resting on a plate that reached to the proximal side of the metacarpophalangeal (MCP) joint. The fingers were positioned on two plates forming an angle of 15 . Proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints were held in an angle of 15 by using Velcro over the DIP joints. The incision in the skin was made on the palmar side of the fingers. However, the incision of the pulley is made at the lateral side of the fingers.
The loading device Tendons were pulled using a Testometric M250e2.5 kN (The Testometric Company Ltd. UK). Flexor digitorum profundus (FDP) and flexor digitorum superficialis (FDS) tendons at the level of the distal forearm were connected to the machine (Figure 2). The Testometric machine was pulling from the proximal side in a straight line with the forearm by using a pulley. The FDP was loaded to 100 N. The FDS tendon was preloaded with 5 N each time to simulate a natural tension. The tendon was pulled with a speed of 50 mm min1 tendon movement until a force of 100 N was reached. Then, this position was held for 5 min followed by reversing the movement to the starting position with the same speed. The tension was taken off the FDP tendon and the fingers were relaxed again for retesting. During the relaxation and
The specimens Eight freshly frozen forearms were obtained from individuals who had a mean age of 76 years (range 73e82 years) at the time of death. The forearms were thawed 24 h before testing. For testing, only the second through fourth fingers were used, as those are the most common sites of injury and they are most comparable to each other.4,5,16
Arm preparation The arms were immobilised in a custom-made jig (Figure 1). The proximal and distal sides of the forearm were fixed on the lateral sides. A Kirschner wire (K-wire) was placed through the distal radius. The K-wire was held in place with
Figure 2
Attachment of the Testometric to the tendons.
824
S. Leeflang, J.H. Coert
the 5 min of 100 N force, the size of the area between the flexor tendons and the phalanx was visualised using US (Figure 3).
24 fingers
US technique To visualise the distance between the flexor tendon and the phalanges, the Visual Sonics (Vevo 770, Version: 2.3.0) was used. The 704 014 head was used with the following specifics: depth on screen: 1e10 mm, field of view: 17.9 mm, focal length: 6 mm, frequency band: 20e60 MHz and centre frequency: 40 MHz. The head of the Visual Sonics was placed at the palmar side of the proximal phalanx. The MCP joint was identified. Measurements were consistently taken 10 mm distal to the joint level to determine the same placement of the US head.
12 fingers: A2 pulley incision from distal to proximal
6 fingers: skin removed
Measurements The amount of bowstringing was determined by measuring the size of the area between the flexor tendon and the proximal phalanx over a distance of 5 mm on the screen of the US device (Figure 3). First, the amount of bowstringing was measured in all intact fingers. These measurements are the control values. For the subsequent tests, each finger served as its own control. All measurements were repeated three times and were then averaged. Figure 4 shows the flow chart of all 24 fingers. Measurement 1 A Brunner incision was made at the palmar side of the finger. The A2 pulley was identified and subsequently the length was measured with a calliper. In four hands, the pulley was incised for one-third from proximal to distal. In the other four hands, the pulley was incised from distal to proximal. After this, the skin of all fingers was temporally sutured with interrupted sutures.
12 fingers: A2 pulley incision from proximal to distal
6 fingers: A3 pulley incision
3 fingers: flexor tendon sheath incision from A1 to A3
Figure 4
Flow chart for dividing the fingers.
Measurement 2 The original incision was extended to include 2/3 of the A2 pulley’s length. The skin was then sutured. Measurement 3 The incision was extended so that the A2 pulley was completely incised in all 24 fingers. The skin was sutured. Measurement 4 In two of the hands, the skin was removed and the amount of bowstringing was measured again. Measurement 5 In one hand, part of the flexor tendon sheath was removed between the A1 pulley and the A3 pulley. The A1 and A3 pulleys were left intact. For this, the Brunner incision was extended to reach the A1 and A3 pulleys. Measurement 6 Finally, in two hands the A3 pulley was cut completely.
Data analysis
Figure 3 Picture from Vevo 770; measurement of the area between proximal phalanx and flexor tendon.
An experienced US technician performed all tests. Each test was repeated three times and the data of these three tests were averaged. The images from the Visual Sonics were analysed on a personal computer. For each measurement, one image was selected for each finger. The amount of bowstringing was measured by looking at the size of the surface between the flexor tendon and the proximal phalanx over a distance of 5 mm. We assumed that the area over a distance of 5 mm provides a more accurate measurement of the amount of bowstringing than using several separate measurements at random points between flexor tendon and proximal phalanx. In addition, every measurement was taken from the same place under the tendon.
Pulley rupture and tendon bowstringing
825
The mean values were calculated. These results were analysed using SPSS 16.0. Paired t-tests were used to compare the groups and to determine if and at which point a partial rupture of the A2 pulley gave significant bowstringing. Furthermore, the direction of incising the pulley was studied. Paired t-tests were also done after removing the A3 pulley, the skin and proximal tendon sheath. The groups were compared to study potential increase in bowstringing after sectioning of the A2 pulley.
Results Excision A2 pulley All 24 fingers were tested together and the results are shown in Figure 5. When the A2 pulley was incised for 1/3, a significant bowstringing was seen, when compared with an intact A2 pulley (p < 0.001). A comparison of incisions of 1/3 with 2/3 and 2/3 with a completely incised A2 pulley showed a significant increase in bowstringing for the index, middle as well as for the ring finger separately (p < 0.003, p < 0.001, p < 0.004).
Excision proximal tendon sheath After excision of the A2 pulley, the tendon sheath between the A1 and the A3 pulley was also excised. Group analysis showed a significant difference between excision the proximal sheath and just excision of the A2 pulley only (p < 0.05). Results for the index and middle finger, separately, showed a significant difference, when compared to the excision of solely the complete A2 pulley (respectively, p Z 0.023 and p Z 0.007). However, measurements of the ring finger showed no significant difference when compared to a complete excision of the A2 pulley (Figure 6).
Excision A3 pulley The results of excising the A3 pulley are shown in Figure 6.
Figure 6 Mean area between proximal phalanx and flexor tendon when excising the A3 pulley, the proximal sheath and the skin.
In one hand, the sheath was excised and subsequently the A3 pulley was excised. In the index and middle fingers, the subsequently excised A3 pulley did not show a significant difference when compared to only the A2 pulley completely excised. For the ring finger, the difference between an excised proximal sheath and an excision of the A3 pulley was significant (p Z 0.028). In one hand, the A2 pulley was completely excised and the A3 pulley was subsequently excised. For the index finger, this made a significant difference (p Z 0.017), but for the middle finger, there was no significant difference.
Removal of the skin The results from removing the skin from the proximal phalanx are shown in Figure 6. Removal of the skin in comparison with an excised A2 pulley made a significant difference in all digits (respectively, p Z 0.001, p Z 0.010 and p < 0.001). A group analysis demonstrated that skin removal significantly influenced bowstringing (p Z 0.017).
Direction of incising the pulley The results from excising the A2 pulley at the proximal side and at the distal side are shown in Figure 7. Incising the A2 pulley at the distal side for 1/3 showed significantly more bowstringing than an incision at the proximal side (p Z 0.005). The same goes for an incision of 2/3 at the distal side in comparison with the proximal side (p Z 0.002).
Discussion
Figure 5 Mean area between proximal phalanx and flexor tendon when excising the A2 pulley.
Sport climbers in action often experience pain of unknown cause over the proximal phalanx. Our hypothesis was that this may be caused by insufficiency of the A2 pulley without clinical evidence of bowstringing. In the current study, we closely simulated the situation of climbing to test this hypothesis.
826
Figure 7 Mean area between proximal phalanx and flexor tendon when excising the A2 pulley from distal to proximal and from proximal to distal.
It was found that even a partial incision of the A2 pulley gives significant measurable bowstringing, indicating that a partial tear can cause symptoms. In addition, as a partial incision at the distal rim of the A2 pulley shows significantly more bowstringing than an identical incision at the proximal rim, we suggest that also the location of the rupture of the A2 pulley plays a crucial role. In sport climbers, the A2 and A3 pulleys are the most frequently injured pulleys.3,9,10,17,18 We focussed mainly on the A2 pulley, as an intact A3 pulley may not be able to prevent bowstringing in distal tears of the A2 pulley. The A3 pulley is considered to be the most flexible of all pulleys,1,7 and in many studies,7,19,20 it was found to be the weakest, which may explain why we did not find any significant difference in most fingers upon subsequent excision of the A3 pulley. We found that bowstringing is less when the tear was made at the proximal side of the A2 pulley. Of note, several researchers found that the A2 pulley is the strongest, followed by the A1 and the A4 pulleys.7,19,20 In our study, the A1 pulley was kept intact, which may explain why there is significantly less bowstringing when the A2 pulley was ruptured from proximal to distal. The A1 pulley could have held the flexor tendon to the bone and could have prevented most of the bowstringing on the proximal side of the A2 pulley. Furthermore, it has been reported that the A2 pulley, when it ruptures, failed from the distal to the proximal end and the A4 pulley failed from the proximal to the distal end. The A3 pulley would rupture lastly.3 We anticipate that this has been caused by the flexible A3 pulley. In our study, incision of the A3 pulley did not give exclusive indication whether the bowstringing would increase, which may be explained by the fact that the A3 pulley is the most flexible of all pulleys1,7 and only ruptures when the bowstringing reaches its maximum. During our study, the removal of the tendon sheath between the A1 increased the bowstringing significantly, suggesting that the tendon sheath plays an important role in preventing bowstringing. Furthermore, upon additional excision of the A3 pulley, no further increase in bowstringing was observed.
S. Leeflang, J.H. Coert Our findings suggest that the tendon sheath may play a role in preventing bowstringing apart from prevention of adhesions or nutritional aspects. Currently, in the clinical situation, the tendon sheath is often not closed after tendon repair.13 Results from this article do suggest closing the tendon sheath after tendon repair to prevent tendon bowstringing. During this study, incision of the skin was made on the palmar side of the finger. It could be argued that the incision of the skin should have been made on the radial side of the finger, because this would minimise damage of the palmar skin. However, we experienced that the pulleys could not be exposed sufficiently through a radial or ulnar incision. Therefore, we chose to make a Brunner incision on the palmar side of the finger. The incision of the pulleys was made on the radial side of the finger, to keep the chance of ‘strangulation’ of the FDP tendon in the pulley or in Camper’s chiasm as low as possible. Previously, it has been reported that when fingers were in flexion, the chiasm approximated to the distal end of the A2 pulley, resulting in more friction between the tendons and the pulley.21 In our study, it was found that results of the ring finger differ from the results of the other fingers. At this point, the reasons for the results of the ring finger being different from the other fingers are not entirely clear. One explanation would be that the localisation of the pulleys plays a role in the amount of bowstringing by pulley rupture. It has been reported previously that in the middle, as well as in the ring finger, the localisation of the pulleys caused lower angles and therefore higher forces on the pulleys when the fingers where flexed.22 However, the limitation of this study is the small number of fingers tested. Further studies in which a larger number of fingers are tested would be necessary to confirm whether the localisation of the pulleys plays a statistically significant role in tendon bowstringing by pulley rupture. The current article focusses on pulley rupture and bowstringing experienced by sport climbers. However, theoretically, pulley rupture can be caused by any activity with large forces on the fingers. Closed A2 pulley ruptures have only been reported in sport climbers. Based on our findings, we cannot conclude whether an A2 pulley rupture, with or without bowstringing, will result in a significant deficit. Prior studies, however, support that a rupture of the A2 pulley does not result in a significant deficit, based on a better outcome upon tendon surgery, when venting of the A2 pulley is done.23 The low morbidity associated with a rupture of the A2 pulley makes it likely that this injury frequently remains unrecognised.24 The limited morbidity associated with a rupture of the A2 pulley makes it possible that it is an injury that frequently goes unrecognised.24 In summary, partial injuries of the A2 pulley may cause significant tendon bowstringing, which could explain the pain without signs of obvious clinical bowstringing often experienced by sport climbers. The direction of the rupture is crucial for the severity of bowstringing, because a rupture of the A2 pulley from the distal to the proximal side will result in more bowstringing than vice versa. The role of the A3 pulley and flexor tendon sheath remains inconclusive; more research is required to determine their role in tendon bowstringing.
Pulley rupture and tendon bowstringing In conclusion, when bowstringing is not obvious upon clinical examination of symptomatic patients, it is useful to look for partial pulley ruptures, as these may be the cause of the unexplained pain over the proximal phalanx.
Conflict of interest/funding None.
References 1. Roloff I, Scho ¨ffle VR, Vigouroux L, Quaine F. Biomechanical model for the determination of the forces acting on the finger pulley system. J Biomech 2006;39:915e23. 2. Peters P. Orthopedic problems in sport climbing. Wilderness Environ Med 2001;12:100e10. 3. Marco RA, Sharkey NA, Smith TS, Zissimos AG. Pathomechanics of closed rupture of the flexor tendon pulleys in rock climbers. J Bone Joint Surg 1998;80(A):1012e9. 4. Bollen S. Injury to the A2 pulley in rock climbers. J Hand Surg Br 1990;15:268e70. 5. Gabl M, Rangger C, Lutz M, Fink C, Rudisch A, Pechlaner S. Disruption of the finger flexor pulley system in elite rock climbers. Am J Sports Med 1998;26(5):651e5. 6. Peterson WW, Manske PR, Bollinger BA, Lesker PA, McCarthy JA. Effect of pulley excision on flexor tendon biomechanics. J Orthop Res 1986;4:96e101. 7. Lin GT, Cooney WP, Amadio PC, An KN. Mechanical properties of human pulleys. J Hand Surg Br 1990;15:429e34. 8. Manske PR, Lesker PA. Strength of human pulleys. Hand 1977; 9(2):147e52. 9. Scho ¨ffl VR, Scho ¨ffl I. Injuries to the finger flexor pulley system in rock climbers: current concepts. J Hand Surg Am 2006;31: 647e54. 10. Scho ¨ffl V, Hochholzer T, Winkelmann HP, Strecker W. Pulley injuries in rock climbers. Wilderness Environ Med 2003;14(2): 94e100. 11. Rispler D, Greenwald D, Shumway S, Allan C, Mass D. Efficiency of the flexor tendon pulley system in human cadaver hands. J Hand Surg Am 1996;21:444e50.
827 12. Amirouche F, Gonzalez M, Koldoff J, Tioco J, Ham K. A biomechanical study of the finger pulley system during repair. Technol Health Care 2002;10(1):23e31. 13. Savage R. The mechanical effect of partial resection of the digital fibrous flexor sheath. J Hand Surg Br 1990;15:435e42. 14. Mitsionis G, Bastidas JA, Grewal R, Pfaeffle HJ, Fischer KJ, Tomaino MM. Feasibility of partial A2 and A4 pulley excision: effect on finger flexor tendon biomechanics. J Hand Surg Am 1999;24:310e4. 15. Tomaino M, Mitsionis G, Bastidas J, Grewal R, Pfaeffle J. The effect of partial excision of the A2 and A4 pulleys on the biomechanics of finger flexion. J Hand Surg Br 1998;23(1): 50e2. 16. Hauger O, Chung CB, Lektrakul N, et al. Pulley system in the fingers: normal anatomy and simulated lesions in cadavers at MR imaging, CT, and US with and without contrast material distention of the tendon sheath. Radiology 2000;217(1): 201e12. 17. Moutet F, Forli A, Voulliaume D. Pulley rupture and reconstruction in rock climbers. Tech Hand Up Extrem Surg 2004; 8(3):149e55. 18. Klauser A, Frauscher F, Bodner G, et al. Finger pulley injuries in extreme rock climbers: depiction with dynamic US. Radiology 2002;222(3):755e61. 19. Kubiak EN, Klugman JA, Bosco JA. Hand injuries in rock climbers. Bull NYU Hosp Jt Dis 2006;64(3e4):172e7. 20. Warme WJ, Brooks D. The effect of circumferential taping on flexor tendon pulley failure in rock climbers. Am J Sports Med 2000;28(5):674e8. 21. Walbeehm E, McGrouther D. An anatomical study of the mechanical interactions of flexor digitorum superficialis and profundus and the flexor tendon sheath in zone 2. J Hand Surg Br 1995 Jun;20(3):269e80. 22. Vigouroux L, Quaine F, Paclet F, Colloud F, Moutet F. Middle and ring fingers are more exposed to pulley rupture than index and little during sport-climbing: a biomechanical explanation. Clin Biomech 2008 Jun;23(5):562e70. 23. Dowd M, Fuentes E. Closed traumatic A2 pulley rupture: rare mechanism of injury. J Hand Surg Eur Vol 2009 Aug;34(4): 548e9. 7. 24. Tang JB, Cao Y, Wu YF, Wang GH. Effect of A2 pulley release on repaired tendon gliding resistance and rupture in a chicken model. J Hand Surg Am 2009 JuleAug;34(6):1080e7.
The role of proximal pulleys in preventing tendon bowstringing: Pulley rupture and tendon bowstringing* S. Leeflang*, J.H. Coert Erasmus MC University Medical Centre, Rotterdam, The Netherlands Received 8 February 2013; accepted 28 January 2014
KEYWORDS A2 pulley; Bowstringing; Climbers; Ultrasonography
Summary Purpose: The aim of this study was to investigate factors that contribute to tendon bowstringing at the proximal phalanx. We hypothesised that: (1) a partial rupture of the A2 pulley leads to significant bowstringing, (2) the location of the A2 rupture, starting proximally or distally, influences bowstringing, (3) an additional A3 pulley rupture causes a significant increase in bowstringing following a complete A2 pulley rupture and (4) the skin and tendon sheath may prevent bowstringing in A2 and A3 pulley ruptures. Methods: Index, middle and ring fingers of eight freshly frozen cadaver arms were used. A loading device pulled with 100 N force was attached to the flexor digitorum profundus (FDP). The flexor digitorum superficialis (FDS) was preloaded with 5 N. Bowstringing was measured and quantified by the size of the area between the FDP tendon and the proximal phalanx over a distance of 5 mm with ultrasonography (US). Results: US images showed that already a 30% excision of the A2 pulley resulted in significant bowstringing. In addition, a partial distal incision of the A2 pulley showed significantly more bowstringing compared to a partial proximal incision. Additional A3 pulley incision and excision of the proximal tendon sheath did not increase bowstringing. Subsequently, removing the skin did increase the bowstringing significantly. Conclusion: A partial A2 pulley rupture causes a significant bowstringing. A partial rupture of the A2 pulley at the distal rim of the A2 pulley resulted in more bowstringing than a partial rupture at the proximal rim. ª 2014 British Association of Plastic, Reconstructive and Aesthetic Surgeons. Published by Elsevier Ltd. All rights reserved.
*
Presented at: 1) 03 April 2009 e Dutch Society of Plastic Surgery (NVPC), 2) 20 June 2009 e Dutch Society of Hand Surgery (NVvH), 3) 24 June 2010 e 15th FESSH congress, Bucharest, Romania. * Corresponding author. Department of Plastic and Reconstructive Surgery, Erasmus MC University Medical Centre, Rotterdam, The Netherlands. Tel.: þ31 620718438. E-mail address: [email protected] (S. Leeflang). 1748-6815/$ - see front matter ª 2014 British Association of Plastic, Reconstructive and Aesthetic Surgeons. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.bjps.2014.01.041
Pulley rupture and tendon bowstringing Sport climbers may have pulley strains or partial pulley ruptures without detectable bowstringing. This was the initial idea to conduct this study. Sport climbing has grown in popularity: new pathologies involving the hand, elbow and shoulder have been presented.1e5 About 75% of sport climbers experience overuse syndromes or injuries of the upper extremity. The fingers and the wrist are the most commonly involved structures, with pulley ruptures being the most frequently seen injuries. Annular pulleys are important to keep the flexor tendons close to the phalanges to assure optimal mechanical efficiency.6e8 Forces on pulleys can become close to 400 N during climbing.4,9,10 Several papers focussed on effects of pulley ruptures on the finger excursion; some authors removed the skin or the flexor tendon sheath to do so.3,7,8,11e13 Other studies tested the pulleys, while the finger was disarticulated from the hand.7,14,15 However, the skin and the flexor tendon sheath themselves could function as a mechanical pulley for flexor tendons. Several studies have shown that ultrasonography (US) allows good imaging of finger pulley injuries in sport climbers. Hauger et al. (2000) noted that the finger pulley system could be evaluated directly with US using cadaver fingers. Part of the study was done with fingers in the flexed position; the US images were made in the transverse plane. Their results showed that they could identify uninjured A2 pulleys in 100% and uninjured A4 pulleys in 67% of the cases.16 Following partial and complete lesions of the pulleys, correct diagnosis was possible with US in 79e100% of the cases. Their study shows that US can be useful in diagnosing pulley injury: they could identify all pulleys and they could adequately detect if they were ruptured. The aim of this report was to simulate the situation of climbing and study factors that could play a role in bowstringing at the proximal phalanx: 1) partial rupture of the A2 pulley 2) location (proximal/distal) of the rupture of the A2 pulley 3) subsequent A3 pulley rupture. In addition, the effect of the skin and the proximal tendon sheath in preventing bowstringing was studied in case of a rupture of the A2 and the A3 pulley.
Materials and methods
823
Figure 1
Custom-made jig for the arm to secure its position.
two tie wraps preventing the wrist from moving when the tendon was pulled. The hand was resting on a plate that reached to the proximal side of the metacarpophalangeal (MCP) joint. The fingers were positioned on two plates forming an angle of 15 . Proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints were held in an angle of 15 by using Velcro over the DIP joints. The incision in the skin was made on the palmar side of the fingers. However, the incision of the pulley is made at the lateral side of the fingers.
The loading device Tendons were pulled using a Testometric M250e2.5 kN (The Testometric Company Ltd. UK). Flexor digitorum profundus (FDP) and flexor digitorum superficialis (FDS) tendons at the level of the distal forearm were connected to the machine (Figure 2). The Testometric machine was pulling from the proximal side in a straight line with the forearm by using a pulley. The FDP was loaded to 100 N. The FDS tendon was preloaded with 5 N each time to simulate a natural tension. The tendon was pulled with a speed of 50 mm min1 tendon movement until a force of 100 N was reached. Then, this position was held for 5 min followed by reversing the movement to the starting position with the same speed. The tension was taken off the FDP tendon and the fingers were relaxed again for retesting. During the relaxation and
The specimens Eight freshly frozen forearms were obtained from individuals who had a mean age of 76 years (range 73e82 years) at the time of death. The forearms were thawed 24 h before testing. For testing, only the second through fourth fingers were used, as those are the most common sites of injury and they are most comparable to each other.4,5,16
Arm preparation The arms were immobilised in a custom-made jig (Figure 1). The proximal and distal sides of the forearm were fixed on the lateral sides. A Kirschner wire (K-wire) was placed through the distal radius. The K-wire was held in place with
Figure 2
Attachment of the Testometric to the tendons.
824
S. Leeflang, J.H. Coert
the 5 min of 100 N force, the size of the area between the flexor tendons and the phalanx was visualised using US (Figure 3).
24 fingers
US technique To visualise the distance between the flexor tendon and the phalanges, the Visual Sonics (Vevo 770, Version: 2.3.0) was used. The 704 014 head was used with the following specifics: depth on screen: 1e10 mm, field of view: 17.9 mm, focal length: 6 mm, frequency band: 20e60 MHz and centre frequency: 40 MHz. The head of the Visual Sonics was placed at the palmar side of the proximal phalanx. The MCP joint was identified. Measurements were consistently taken 10 mm distal to the joint level to determine the same placement of the US head.
12 fingers: A2 pulley incision from distal to proximal
6 fingers: skin removed
Measurements The amount of bowstringing was determined by measuring the size of the area between the flexor tendon and the proximal phalanx over a distance of 5 mm on the screen of the US device (Figure 3). First, the amount of bowstringing was measured in all intact fingers. These measurements are the control values. For the subsequent tests, each finger served as its own control. All measurements were repeated three times and were then averaged. Figure 4 shows the flow chart of all 24 fingers. Measurement 1 A Brunner incision was made at the palmar side of the finger. The A2 pulley was identified and subsequently the length was measured with a calliper. In four hands, the pulley was incised for one-third from proximal to distal. In the other four hands, the pulley was incised from distal to proximal. After this, the skin of all fingers was temporally sutured with interrupted sutures.
12 fingers: A2 pulley incision from proximal to distal
6 fingers: A3 pulley incision
3 fingers: flexor tendon sheath incision from A1 to A3
Figure 4
Flow chart for dividing the fingers.
Measurement 2 The original incision was extended to include 2/3 of the A2 pulley’s length. The skin was then sutured. Measurement 3 The incision was extended so that the A2 pulley was completely incised in all 24 fingers. The skin was sutured. Measurement 4 In two of the hands, the skin was removed and the amount of bowstringing was measured again. Measurement 5 In one hand, part of the flexor tendon sheath was removed between the A1 pulley and the A3 pulley. The A1 and A3 pulleys were left intact. For this, the Brunner incision was extended to reach the A1 and A3 pulleys. Measurement 6 Finally, in two hands the A3 pulley was cut completely.
Data analysis
Figure 3 Picture from Vevo 770; measurement of the area between proximal phalanx and flexor tendon.
An experienced US technician performed all tests. Each test was repeated three times and the data of these three tests were averaged. The images from the Visual Sonics were analysed on a personal computer. For each measurement, one image was selected for each finger. The amount of bowstringing was measured by looking at the size of the surface between the flexor tendon and the proximal phalanx over a distance of 5 mm. We assumed that the area over a distance of 5 mm provides a more accurate measurement of the amount of bowstringing than using several separate measurements at random points between flexor tendon and proximal phalanx. In addition, every measurement was taken from the same place under the tendon.
Pulley rupture and tendon bowstringing
825
The mean values were calculated. These results were analysed using SPSS 16.0. Paired t-tests were used to compare the groups and to determine if and at which point a partial rupture of the A2 pulley gave significant bowstringing. Furthermore, the direction of incising the pulley was studied. Paired t-tests were also done after removing the A3 pulley, the skin and proximal tendon sheath. The groups were compared to study potential increase in bowstringing after sectioning of the A2 pulley.
Results Excision A2 pulley All 24 fingers were tested together and the results are shown in Figure 5. When the A2 pulley was incised for 1/3, a significant bowstringing was seen, when compared with an intact A2 pulley (p < 0.001). A comparison of incisions of 1/3 with 2/3 and 2/3 with a completely incised A2 pulley showed a significant increase in bowstringing for the index, middle as well as for the ring finger separately (p < 0.003, p < 0.001, p < 0.004).
Excision proximal tendon sheath After excision of the A2 pulley, the tendon sheath between the A1 and the A3 pulley was also excised. Group analysis showed a significant difference between excision the proximal sheath and just excision of the A2 pulley only (p < 0.05). Results for the index and middle finger, separately, showed a significant difference, when compared to the excision of solely the complete A2 pulley (respectively, p Z 0.023 and p Z 0.007). However, measurements of the ring finger showed no significant difference when compared to a complete excision of the A2 pulley (Figure 6).
Excision A3 pulley The results of excising the A3 pulley are shown in Figure 6.
Figure 6 Mean area between proximal phalanx and flexor tendon when excising the A3 pulley, the proximal sheath and the skin.
In one hand, the sheath was excised and subsequently the A3 pulley was excised. In the index and middle fingers, the subsequently excised A3 pulley did not show a significant difference when compared to only the A2 pulley completely excised. For the ring finger, the difference between an excised proximal sheath and an excision of the A3 pulley was significant (p Z 0.028). In one hand, the A2 pulley was completely excised and the A3 pulley was subsequently excised. For the index finger, this made a significant difference (p Z 0.017), but for the middle finger, there was no significant difference.
Removal of the skin The results from removing the skin from the proximal phalanx are shown in Figure 6. Removal of the skin in comparison with an excised A2 pulley made a significant difference in all digits (respectively, p Z 0.001, p Z 0.010 and p < 0.001). A group analysis demonstrated that skin removal significantly influenced bowstringing (p Z 0.017).
Direction of incising the pulley The results from excising the A2 pulley at the proximal side and at the distal side are shown in Figure 7. Incising the A2 pulley at the distal side for 1/3 showed significantly more bowstringing than an incision at the proximal side (p Z 0.005). The same goes for an incision of 2/3 at the distal side in comparison with the proximal side (p Z 0.002).
Discussion
Figure 5 Mean area between proximal phalanx and flexor tendon when excising the A2 pulley.
Sport climbers in action often experience pain of unknown cause over the proximal phalanx. Our hypothesis was that this may be caused by insufficiency of the A2 pulley without clinical evidence of bowstringing. In the current study, we closely simulated the situation of climbing to test this hypothesis.
826
Figure 7 Mean area between proximal phalanx and flexor tendon when excising the A2 pulley from distal to proximal and from proximal to distal.
It was found that even a partial incision of the A2 pulley gives significant measurable bowstringing, indicating that a partial tear can cause symptoms. In addition, as a partial incision at the distal rim of the A2 pulley shows significantly more bowstringing than an identical incision at the proximal rim, we suggest that also the location of the rupture of the A2 pulley plays a crucial role. In sport climbers, the A2 and A3 pulleys are the most frequently injured pulleys.3,9,10,17,18 We focussed mainly on the A2 pulley, as an intact A3 pulley may not be able to prevent bowstringing in distal tears of the A2 pulley. The A3 pulley is considered to be the most flexible of all pulleys,1,7 and in many studies,7,19,20 it was found to be the weakest, which may explain why we did not find any significant difference in most fingers upon subsequent excision of the A3 pulley. We found that bowstringing is less when the tear was made at the proximal side of the A2 pulley. Of note, several researchers found that the A2 pulley is the strongest, followed by the A1 and the A4 pulleys.7,19,20 In our study, the A1 pulley was kept intact, which may explain why there is significantly less bowstringing when the A2 pulley was ruptured from proximal to distal. The A1 pulley could have held the flexor tendon to the bone and could have prevented most of the bowstringing on the proximal side of the A2 pulley. Furthermore, it has been reported that the A2 pulley, when it ruptures, failed from the distal to the proximal end and the A4 pulley failed from the proximal to the distal end. The A3 pulley would rupture lastly.3 We anticipate that this has been caused by the flexible A3 pulley. In our study, incision of the A3 pulley did not give exclusive indication whether the bowstringing would increase, which may be explained by the fact that the A3 pulley is the most flexible of all pulleys1,7 and only ruptures when the bowstringing reaches its maximum. During our study, the removal of the tendon sheath between the A1 increased the bowstringing significantly, suggesting that the tendon sheath plays an important role in preventing bowstringing. Furthermore, upon additional excision of the A3 pulley, no further increase in bowstringing was observed.
S. Leeflang, J.H. Coert Our findings suggest that the tendon sheath may play a role in preventing bowstringing apart from prevention of adhesions or nutritional aspects. Currently, in the clinical situation, the tendon sheath is often not closed after tendon repair.13 Results from this article do suggest closing the tendon sheath after tendon repair to prevent tendon bowstringing. During this study, incision of the skin was made on the palmar side of the finger. It could be argued that the incision of the skin should have been made on the radial side of the finger, because this would minimise damage of the palmar skin. However, we experienced that the pulleys could not be exposed sufficiently through a radial or ulnar incision. Therefore, we chose to make a Brunner incision on the palmar side of the finger. The incision of the pulleys was made on the radial side of the finger, to keep the chance of ‘strangulation’ of the FDP tendon in the pulley or in Camper’s chiasm as low as possible. Previously, it has been reported that when fingers were in flexion, the chiasm approximated to the distal end of the A2 pulley, resulting in more friction between the tendons and the pulley.21 In our study, it was found that results of the ring finger differ from the results of the other fingers. At this point, the reasons for the results of the ring finger being different from the other fingers are not entirely clear. One explanation would be that the localisation of the pulleys plays a role in the amount of bowstringing by pulley rupture. It has been reported previously that in the middle, as well as in the ring finger, the localisation of the pulleys caused lower angles and therefore higher forces on the pulleys when the fingers where flexed.22 However, the limitation of this study is the small number of fingers tested. Further studies in which a larger number of fingers are tested would be necessary to confirm whether the localisation of the pulleys plays a statistically significant role in tendon bowstringing by pulley rupture. The current article focusses on pulley rupture and bowstringing experienced by sport climbers. However, theoretically, pulley rupture can be caused by any activity with large forces on the fingers. Closed A2 pulley ruptures have only been reported in sport climbers. Based on our findings, we cannot conclude whether an A2 pulley rupture, with or without bowstringing, will result in a significant deficit. Prior studies, however, support that a rupture of the A2 pulley does not result in a significant deficit, based on a better outcome upon tendon surgery, when venting of the A2 pulley is done.23 The low morbidity associated with a rupture of the A2 pulley makes it likely that this injury frequently remains unrecognised.24 The limited morbidity associated with a rupture of the A2 pulley makes it possible that it is an injury that frequently goes unrecognised.24 In summary, partial injuries of the A2 pulley may cause significant tendon bowstringing, which could explain the pain without signs of obvious clinical bowstringing often experienced by sport climbers. The direction of the rupture is crucial for the severity of bowstringing, because a rupture of the A2 pulley from the distal to the proximal side will result in more bowstringing than vice versa. The role of the A3 pulley and flexor tendon sheath remains inconclusive; more research is required to determine their role in tendon bowstringing.
Pulley rupture and tendon bowstringing In conclusion, when bowstringing is not obvious upon clinical examination of symptomatic patients, it is useful to look for partial pulley ruptures, as these may be the cause of the unexplained pain over the proximal phalanx.
Conflict of interest/funding None.
References 1. Roloff I, Scho ¨ffle VR, Vigouroux L, Quaine F. Biomechanical model for the determination of the forces acting on the finger pulley system. J Biomech 2006;39:915e23. 2. Peters P. Orthopedic problems in sport climbing. Wilderness Environ Med 2001;12:100e10. 3. Marco RA, Sharkey NA, Smith TS, Zissimos AG. Pathomechanics of closed rupture of the flexor tendon pulleys in rock climbers. J Bone Joint Surg 1998;80(A):1012e9. 4. Bollen S. Injury to the A2 pulley in rock climbers. J Hand Surg Br 1990;15:268e70. 5. Gabl M, Rangger C, Lutz M, Fink C, Rudisch A, Pechlaner S. Disruption of the finger flexor pulley system in elite rock climbers. Am J Sports Med 1998;26(5):651e5. 6. Peterson WW, Manske PR, Bollinger BA, Lesker PA, McCarthy JA. Effect of pulley excision on flexor tendon biomechanics. J Orthop Res 1986;4:96e101. 7. Lin GT, Cooney WP, Amadio PC, An KN. Mechanical properties of human pulleys. J Hand Surg Br 1990;15:429e34. 8. Manske PR, Lesker PA. Strength of human pulleys. Hand 1977; 9(2):147e52. 9. Scho ¨ffl VR, Scho ¨ffl I. Injuries to the finger flexor pulley system in rock climbers: current concepts. J Hand Surg Am 2006;31: 647e54. 10. Scho ¨ffl V, Hochholzer T, Winkelmann HP, Strecker W. Pulley injuries in rock climbers. Wilderness Environ Med 2003;14(2): 94e100. 11. Rispler D, Greenwald D, Shumway S, Allan C, Mass D. Efficiency of the flexor tendon pulley system in human cadaver hands. J Hand Surg Am 1996;21:444e50.
827 12. Amirouche F, Gonzalez M, Koldoff J, Tioco J, Ham K. A biomechanical study of the finger pulley system during repair. Technol Health Care 2002;10(1):23e31. 13. Savage R. The mechanical effect of partial resection of the digital fibrous flexor sheath. J Hand Surg Br 1990;15:435e42. 14. Mitsionis G, Bastidas JA, Grewal R, Pfaeffle HJ, Fischer KJ, Tomaino MM. Feasibility of partial A2 and A4 pulley excision: effect on finger flexor tendon biomechanics. J Hand Surg Am 1999;24:310e4. 15. Tomaino M, Mitsionis G, Bastidas J, Grewal R, Pfaeffle J. The effect of partial excision of the A2 and A4 pulleys on the biomechanics of finger flexion. J Hand Surg Br 1998;23(1): 50e2. 16. Hauger O, Chung CB, Lektrakul N, et al. Pulley system in the fingers: normal anatomy and simulated lesions in cadavers at MR imaging, CT, and US with and without contrast material distention of the tendon sheath. Radiology 2000;217(1): 201e12. 17. Moutet F, Forli A, Voulliaume D. Pulley rupture and reconstruction in rock climbers. Tech Hand Up Extrem Surg 2004; 8(3):149e55. 18. Klauser A, Frauscher F, Bodner G, et al. Finger pulley injuries in extreme rock climbers: depiction with dynamic US. Radiology 2002;222(3):755e61. 19. Kubiak EN, Klugman JA, Bosco JA. Hand injuries in rock climbers. Bull NYU Hosp Jt Dis 2006;64(3e4):172e7. 20. Warme WJ, Brooks D. The effect of circumferential taping on flexor tendon pulley failure in rock climbers. Am J Sports Med 2000;28(5):674e8. 21. Walbeehm E, McGrouther D. An anatomical study of the mechanical interactions of flexor digitorum superficialis and profundus and the flexor tendon sheath in zone 2. J Hand Surg Br 1995 Jun;20(3):269e80. 22. Vigouroux L, Quaine F, Paclet F, Colloud F, Moutet F. Middle and ring fingers are more exposed to pulley rupture than index and little during sport-climbing: a biomechanical explanation. Clin Biomech 2008 Jun;23(5):562e70. 23. Dowd M, Fuentes E. Closed traumatic A2 pulley rupture: rare mechanism of injury. J Hand Surg Eur Vol 2009 Aug;34(4): 548e9. 7. 24. Tang JB, Cao Y, Wu YF, Wang GH. Effect of A2 pulley release on repaired tendon gliding resistance and rupture in a chicken model. J Hand Surg Am 2009 JuleAug;34(6):1080e7.
