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Effect of Pisiform Excision or Pisotriquetral Arthrodesis as a Treatment for Pisotriquetral Arthritis: A Biomechanical Study
SCIENTIFIC ARTICLE
Effect of Pisiform Excision or Pisotriquetral Arthrodesis as a Treatment for Pisotriquetral Arthritis: A Biomechanical Study Kevin D. O’Keefe, MD, Frederick W. Werner, MME, Melissa Boyette, MD, Andrew K. Palmer, MD, Marc Garcia-Elias, MD, Brian J. Harley, MD Purpose To determine whether flexor carpi ulnaris (FCU) forces and tendon displacements change after pisotriquetral arthrodesis or after pisiform excision. Methods Nine cadaver wrists were moved through 4 variations of a dart throw motion, each having an oblique plane of motion, but with different ranges of motion and different antagonistic forces. The FCU tendon force and movement were measured in the intact wrist, following pisotriquetral arthrodesis, and following pisiform excision. Changes in force and tendon movement were compared using a repeated measures analysis of variance. Results After excision of the pisiform, a significantly greater FCU force was required during the 2 variations of the dart throw motion having a larger range of motion and during the smaller motion having a larger antagonistic force. Pisotriquetral arthrodesis did not cause a significant increase in the peak FCU force. Excision of the pisiform caused the FCU tendon to significantly retract during all wrist motions as compared to the intact wrist or after pisotriquetral arthrodesis. Conclusions Greater FCU forces are required to move the wrist when the pisiform with its moment arm function has been removed. This occurs during large oblique plane wrist motions and also in a smaller motion when greater antagonistic forces are applied. Excision of the pisiform also allows the FCU to move proximally, again because its moment arm function has been eliminated. Clinical relevance Excision of the pisiform requires greater FCU forces during large wrist motions and during motions that include large gripping forces such that excision may be a concern in high-demand patients with pisotriquetral arthritis. Although pisotriquetral arthrodesis does not alter the mechanical advantage of the FCU, its use in high-demand patients with pisotriquetral osteoarthritis cannot yet be recommended until the effects of that arthrodesis on midcarpal kinematics are further clarified. (J Hand Surg 2013;38A:1913e1918. Copyright Ó 2013 by the American Society for Surgery of the Hand. All rights reserved.) Key words Pisiform, pisotriquetral arthritis, wrist forces.
HE PISIFORM LIES WITHIN the fibers of the flexor carpi ulnaris (FCU) and articulates with the triquetrum.1,2 Beckers and Koebke3 found that the pisiform functions as a fulcrum to control the
T
From the Department of Orthopedic Surgery, SUNY Upstate Medical University, Syracuse, NY; Institut Kaplan, Barcelona, Spain. Received for publication April 26, 2013; accepted in revised form July 22, 2013. No benefits in any form have been received or will be received related directly or indirectly to the subject of this article.
triquetrum and also suggested that it protects the neurovascular structures in the Guyon canal. They noted that approximately half of the FCU tendon attaches to the pisiform and the rest is a bundle of Corresponding author: Frederick W. Werner, MME, Department of Orthopedic Surgery, SUNY Upstate Medical University, 3214 Institute for Human Performance, 750 E. Adams Street, Syracuse, NY 13210; e-mail: [email protected]. 0363-5023/13/38A10-0004$36.00/0 http://dx.doi.org/10.1016/j.jhsa.2013.07.021
Ó 2013 ASSH
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Published by Elsevier, Inc. All rights reserved.
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fibers functioning as a roof over the pisiform as these fibers continues distally. Pisiform excision is generally considered the standard treatment for patients with pisotriquetral arthritis and chronic pain. Although it has generally resulted in good clinical results,4,5 1 study6 found a slight reduction in wrist strength when compared to the contralateral side. Beckers and Koebke3 suggested that the excision of the pisiform should be reconsidered. In high-demand athletes who require maximal grip, any reduction in grip may decrease their athletic potential. Because of this concern, other authors7,8 reported on the results of pisotriquetral arthrodesis in patients with pisotriquetral instability. These authors were concerned about increased movement of the triquetrum3 and postoperative decrease in wrist flexion strength following pisiformectomy.6 The goal of this study was to determine the biomechanical consequences of pisiform excision and of pisotriquetral arthrodesis, specifically during an oblique wrist motion that has a similar orientation as the true dart throw wrist motion, because this is the motion during which many activities of daily living occur.9e11 These include high-demand functional activities such as hammering12 and sporting activities such as golfing and tennis. Because in a cadaver experiment we cannot directly measure postoperative changes in grip strength, we assumed changes in measured in vitro FCU forces were an indicator of changes of in vivo clinical grip strength. The purpose of this study was to determine whether there was a difference in FCU force and tendon displacement during these motions between the intact wrist and after a pisotriquetral arthrodesis or pisiform excision. METHODS Nine fresh-frozen right cadaver wrists (average, 68 years; 5 female, 4 male) were tested in a wrist joint motion simulator13 by pulling on 5 wrist flexor and extensor tendons to cause wrist motion under computer control (Fig. 1). Each wrist was thawed the previous day and prepared for testing by dissecting 3 wrist extensors (extensor carpi ulnaris, extensor carpi radialis brevis, and extensor carpi radialis longis) and 2 wrist flexors (FCU and flexor carpi radialis). The flexor and extensor retinaculums were preserved. A pin cemented into the humerus was attached to the loading frame, and the elbow was pinned at 90 flexion and supported by a platform. The forearm was kept in neutral forearm rotation by a plastic fork surrounding the radius and ulna. Each tendon was connected in series to a load cell, which measured the JHS
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FIGURE 1: Volar view of intact cadaver wrist in wrist simulator. Clamps are attached to each individual tendon. Load cells are in series beneath each clamp. An electromagnetic sensor is attached to the third metacarpal to measure wrist motion. The clamps and load cells for the 3 extensor tendons are not shown.
force in the tendon as a hydraulic actuator pulled on the respective tendon. While each wrist was moving in the desired wrist motion, the agonist tendons were under velocity feedback control, and the antagonist tendons were under force feedback control. The antagonist tendons provided a constant resistive force to the desired motion. The agonist tendon forces were controlled by an algorithm that minimized the error between the desired and actual wrist motion.13 These roles for each tendon switched at the extreme of wrist motion. Wrist motion was measured by an electromagnetic sensor attached to the dorsum of the third metacarpal. It detected its position (and therefore, the wrist position) relative to an electromagnetic source. Four different motions in the oblique plane with a similar orientation as the true dart throw plane of motion were studied. Each might be considered a variation of the true dart throw motion. However, they had different ranges of motion and different antagonistic forces. These motions were assumed to be most representative of those used during highdemand activities and selected based on previous studies of dart throw motion.11 Two variations of a
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FIGURE 2: The FCU tendon force during a large wrist motion with the pisiform intact, after pisotriquetral arthrodesis, and after pisiform excision in an illustrative specimen. The greatest FCU force occurred as the wrist was coming out of extension and radial deviation while the FCU was acting as an agonist to cause the motion. From wrist flexion and ulnar deviation to wrist extension and radial deviation, the FCU functioned primarily as an antagonistic with an 18 N resistive force. Increases from the 18 N force occurred because the FCU also acted as an ulnar deviator to correct slight out-of-plane motions.
dart throw motion had smaller ranges of wrist motion (30 extension and 10 radial deviation to 30 flexion and 10 ulnar deviation), and 2 had larger ranges of wrist motion (40 extension and 10 radial deviation to 40 flexion to 10 ulnar deviation). In 1 small and 1 large wrist motion, small antagonistic forces14 (8.9 N per tendon) were used, and in the other small and large motions, 18 N per tendon antagonistic forces were used. The increased antagonistic force, chosen arbitrarily, was used to simulate a higher-demand activity. The antagonistic force was applied to each tendon while that tendon was functioning as an antagonist such that it resisted the desired wrist motion. When a tendon was functioning as an agonist, so that it was causing the desired wrist motion, the force was continuously recomputed every 12.2 ms to cause a smooth, sinusoidal cyclic motion. Thus, as the wrist was moving from extension and radial deviation, the FCU was acting as an agonist, and the force was varied under computer control to cause the motion. As the wrist was moving from flexion and ulnar deviation to extension and radial deviation, the FCU was acting as an antagonist. However, every 12.2 ms, the role of the FCU was recomputed. If, for example, the wrist was moving out of the plane of the dart motion and was in slight radial deviation, the FCU would also function as an ulnar deviator, causing a force greater than the antagonistic level, to move the wrist back into the plane of motion. As shown in JHS
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Figure 2, as the wrist was moving from flexion to extension, these corrective forces were moderate. Six cycles of each motion were performed. During each motion, the FCU tendon force and movement were measured. An increase in the FCU force after either pisotriquetral arthrodesis or excision during wrist motions identical to the intact condition was thought to be an indicator of a negative benefit for that procedure. Tendon movement was measured using a linear potentiometer connected to the tendon’s actuator. A negative value corresponded to a proximal motion of the tendon. All data were collected at a rate of 82 Hz. Pisotriquetral arthrodesis was performed by positioning the wrist in neutral flexion-extension and making a medial incision directly over the pisiform. The tendon attachment was well visualized and left intact. Two 1.6-mm (0.062 in.) K-wires were then placed in converging fashion into the pisotriquetral joint. No cartilage was removed from either the pisiform or triquetrum. Each wrist was then moved through the 4 wrist motions, and FCU force and movement data were collected. After testing the simulated pisotriquetral arthrodesis, the stability of the fixation was checked to verify there was no relative translation or rotation of the bones. Next, the pisiform was excised by carefully carving it out of its attachment to the FCU. The surrounding tissues were sutured back together using a direct side-to-side repair
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FIGURE 3: The FCU tendon movement during a large wrist motion with the pisiform intact, after pisotriquetral arthrodesis, and after pisiform excision in an illustrative specimen. With wrist flexion (and ulnar deviation) the tendon moved proximally, and with extension (and radial deviation) it moved distally.
TABLE 1.
Average Peak FCU Force (N) During 4 Variations of a Dart Throw Motion Small Dart Motion
Large Dart Motion
Low Antagonistic Force
Small Dart Motion
Large Dart Motion
High Antagonistic Force
Intact wrist (SD)
48.3 (8.9)
56.0 (14.0)
64.0 (11.2)
69.2 (14.1)
After pisotriquetral arthrodesis (SD)
49.6 (10.2)
55.9 (15.4)
66.1 (13.3)
71.1 (15.1)
After pisiform excision (SD)
51.6 (15.2)
72.0 (16.0)
76.3 (13.3)
89.5 (13.8)
of the incised tendon by using a running 3-0 suture. Care was taken to not alter the FCU length. Each wrist was then again moved through the 4 wrist motions. At the conclusion of the experiment, each wrist was dissected to evaluate the quality of the soft tissue repair following pisiform excision and for degenerative changes to the pisiform (already excised) and the triquetrum. The repair in the first limb tested was found to be inadequate; therefore, the results are based on 8 specimens. In the first limb, the sutures used to repair the tendon after pisiform excision had torn through the tissues due to poor tissue quality. All other repairs were intact. At each increment of wrist motion during the fourth cycle of wrist motion (819 increments per cycle of motion), the peak force (Fig. 2) and the most distal value of the tendon position was determined. The most distal value of the tendon position corresponded to the wrist being in extension and radial deviation (Fig. 3). Changes in FCU force and tendon movement were statistically analyzed using a JHS
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repeated measures, 1-way analysis of variance on the last 8 arms. RESULTS After excision of the pisiform, a significantly greater FCU force (Table 1, Fig. 2) was required to move the wrist during both of the larger wrist motions (P < .002) and during the smaller wrist motion with a larger antagonistic force (P < .001) compared to the intact wrist. In the smaller wrist motion with the smaller antagonistic force, there was not a significant difference in the FCU force between pisiform excision and the intact wrist (P > .99). There was no significant difference in the peak FCU force between the intact wrist and after pisotriquetral arthrodesis (P > .99) in any of the wrist motions. However, during both of the larger wrist motions, there was a significantly greater peak FCU force with pisiform excision compared to pisotriquetral arthrodesis (P > .013). During both of the
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TABLE 2. Average Change in FCU Excursion (mm) as Compared to Intact, During 4 Variations of a Dart Throw Wrist Motion Small Dart Motion
Large Dart Motion
Low Antagonistic Force
Small Dart Motion
Large Dart Motion
High Antagonistic Force
After pisotriquetral arthrodesis (SD)
0.5 (0.8)
0.4 (1.0)
0.3 (0.7)
0.6 (0.7)
After pisiform excision (SD)
6.0 (3.0)
6.1 (3.0)
6.2 (3.0)
6.7 (3.1)
A negative value indicates a retraction of the FCU (more proximal).
smaller wrist motions, there was not a significant difference in the peak FCU force between pisotriquetral arthrodesis and pisiform excision (P > .07). Excision of the pisiform caused the FCU tendon to significantly (P < .003) move proximally during all wrist motions as compared to the intact wrist or compared with a pisotriquetral arthrodesis (Fig. 3, Table 2). No difference in the FCU movement was observed between the intact wrist and pisotriquetral arthrodesis (P > .18). Dissection of the specimens after testing revealed no arthritic changes to the triquetrum in 4 of the 8 limbs, triquetral distal pole degeneration in 3, and arthritic changes on the entire periphery (but not centrally) in the remaining 1. On the pisiforms, there was mild peripheral degeneration in 1, degenerative changes ulnarly and proximally in 1, degenerative changes distally and radially in 1, degenerative changes only radially in 2, degenerative changes only distally in 2, and no changes in 1. DISCUSSION During high-demand wrist activities, such as in competitive sports or in heavy manual tasks, greater wrist tendon forces are required. The purpose of this study was to determine whether greater FCU forces might be required in simulated low-demand and highdemand activities with pisiform excision. We differentiated between low-demand and high-demand activities by changing the amount of the force resisting (antagonistic to) a wrist motion. In the simulated low-demand patient (lower antagonistic force), we found there was no difference in the required FCU force for the smaller range of wrist motion following pisiform excision. This may suggest that excision of the pisiform may not limit low-force activities. This matches the clinical observation by Lam et al15 that function could be restored with a painless wrist following removal of the pisiform. However, in the simulated high-demand patient (higher antagonistic force levels and greater range of JHS
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wrist motion), we found greater FCU forces (up to 29% greater than in the intact wrist) were required to have the same wrist motion after pisiform excision. This suggests that laborers or high-performance athletes may be limited in their ability to perform the same motion following pisiform excision. Even a slight decrease in strength may alter an athlete’s performance. Lam et al,15 as noted earlier, felt that pisiform resection restored function, yet they then reported that, based on examination of the confidence intervals in their data, there was at most a 10% loss in grip strength, a 10% to 17% loss in static strength, and a 5% loss in dynamic power. Another factor may be the type of activity. Helal16 removed the pisiform in 3 squash players and 1 badminton player. All returned to their sporting activities without any complications. For all motions and antagonistic forces, we found that excision of the pisiform caused the FCU to retract proximally 6 to 7 mm. Palmieri5 saw a change of about 5 mm in his series of 21 patients and suggested that it was not enough to reduce the strength of the FCU. We suggest that additional studies may be needed to determine whether this change in the forceeelongation relationship of the FCU muscle is clinically important. We found pisotriquetral arthrodesis did not cause a significant difference in the FCU force or tendon movement compared to the intact wrist. The force and movement patterns and magnitudes after arthrodesis were similar to those in the intact wrist. This would suggest that pisotriquetral arthrodesis does not alter the mechanical advantage of the FCU. Therefore, pisotriquetral arthrodesis may be an alternative to consider in high-demand individuals. However, the effect of a pisotriquetral arthrodesis on midcarpal kinematics is unknown. If the pisiform is fixed distally on the triquetrum (allowing the FCU to be relatively lax distal to the pisiform) the midcarpal joint may become more lax. If the pisiform is fixed proximally on the triquetrum (causing the FCU to be relatively tighter distal to the pisiform) the midcarpal joint may become stiffer. Depending upon where the pisiform is fixed on the
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triquetrum, a different pathology may develop. Until the effect of where the pisiform is fused to the triquetrum on midcarpal kinematics is determined, we caution against concluding that our findings support pisotriquetral arthrodesis. Limitations to this study include that it was a cadaver study in which the effect of healing was not included, and we could not directly measure postoperative changes in grip strength. We, therefore, had to assume that the changes we measured in the in vitro FCU forces would be an indicator of changes of in vivo clinical grip strength. Only 4 variations of a dart throw wrist motion were studied. Other motions, such as a pure flexion-extension or pure radioulnar deviation motion, were not studied. However, we felt that the selected variations of a dart throw motion were representative of what might occur in different levels of patient demand and that each arm served as its own control. Another limitation to this study is that we did not decorticate the pisiform or triquetrum at the time of simulated arthrodesis. Doing so would have potentially decreased the FCU moment arm and altered the mechanical advantage of the FCU. Another limitation is that little is known about the in vivo force in the wrist tendons, especially how much more might be needed during a strenuous activity. Mendelson et al17 intraoperatively measured the forces in the extensor carpi radialis brevis and extensor carpi radialis longus to be an average of 63 N and 82 N, respectively. However, these were not during a high-demand activity. Finally, the speed of the wrist motion in this experiment was much less than that which occurs during sporting activities or heavy labor tasks and, therefore, did not include any major dynamic effects. However, we were still able to detect changes in tendon loading with pisiform excision, which should also occur during high-speed activities.
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REFERENCES 1. Hoepfner PE. Pisotriquetral arthritis. Tech Orthop. 2009;24(1): 42e44. 2. Yamaguchi S, Viegas SF, Patterson RM. Anatomic study of the pisotriquetral joint: ligament anatomy and cartilagenous change. J Hand Surg Am. 1998;23(4):600e606. 3. Beckers A, Koebke J. Mechanical strain at the pisotriquetral joint. Clin Anat. 1998;11(5):320e326. 4. Carroll RE, Coyle MP Jr. Dysfunction of the pisotriquetral joint: treatment by excision of the pisiform. J Hand Surg Am. 1985;10(5): 703e707. 5. Palmieri TJ. Pisiform area pain treatment by pisiform excision. J Hand Surg Am. 1982;7(5):477e480. 6. Arner M, Hagberg L. Wrist flexion strength after excision of the pisiform bone. Scand. J Plast Reconstr Surg. 1984;18(2):241e245. 7. Abrams R, Tontz W. Pisotriquetral arthrodesis as an alternative to excision for pisotriquetral instability in high-demand patients: a case report in a gymnast. J Hand Surg Am. 2006;31(4):611e614. 8. Singer G, Eberl R, Hoellwarth ME. Pisotriquetral arthrodesis for pisotriquetral instability: case report. J Hand Surg Am. 2010;36(2): 299e303. 9. Brigstocke GH, Hearnden A, Holt C, Whatling G. In-vivo confirmation of the use of the dart thrower’s motion during activities of daily living. J Hand Surg Eur Vol. 2012 Oct 11. [Epub ahead of print.] 10. Crisco JJ, Coburn JC, Moore DC, et al. In vivo radiocarpal kinematics and the dart thrower’s motion. J Bone Joint Surg Am. 2005;87(12): 2729e2740. 11. Werner FW, Green JK, Short WH, et al. Scaphoid and lunate motion during a wrist dart throw motion. J Hand Surg Am. 2004;29(3): 418e422. 12. Leventhal EL, Moore DC, Adelman E, et al. Carpal and forearm kinematics during a simulated hammering task. J Hand Surg Am. 2010;35(7):1097e1104. 13. Werner FW, Palmer AK, Somerset JH, et al. Wrist joint motion simulator. J Orthop Res. 1996;14(4):639e646. 14. Short WH, Werner FW, Green JK, et al. The effect of sectioning the dorsal radiocarpal ligament and insertion of a pressure sensor into the radiocarpal joint on scaphoid and lunate kinematics. J Hand Surg Am. 2002;27(1):68e76. 15. Lam KS, Woodbridge S, Burke FD. Wrist function after excision of the pisiform. J Hand Surg Br. 2003;28(1):69e72. 16. Helal B. Chronic overuse injuries of the piso-triquetral joint in racquet game players. Br J Sports Med. 1978;12(4):195e198. 17. Mendelson LS, Peckham PH, Freehafer AA, et al. Intraoperative assessment of wrist extensor muscle force. J Hand Surgery Am. 1988;13(6):832e836.
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Effect of Pisiform Excision or Pisotriquetral Arthrodesis as a Treatment for Pisotriquetral Arthritis: A Biomechanical Study Kevin D. O’Keefe, MD, Frederick W. Werner, MME, Melissa Boyette, MD, Andrew K. Palmer, MD, Marc Garcia-Elias, MD, Brian J. Harley, MD Purpose To determine whether flexor carpi ulnaris (FCU) forces and tendon displacements change after pisotriquetral arthrodesis or after pisiform excision. Methods Nine cadaver wrists were moved through 4 variations of a dart throw motion, each having an oblique plane of motion, but with different ranges of motion and different antagonistic forces. The FCU tendon force and movement were measured in the intact wrist, following pisotriquetral arthrodesis, and following pisiform excision. Changes in force and tendon movement were compared using a repeated measures analysis of variance. Results After excision of the pisiform, a significantly greater FCU force was required during the 2 variations of the dart throw motion having a larger range of motion and during the smaller motion having a larger antagonistic force. Pisotriquetral arthrodesis did not cause a significant increase in the peak FCU force. Excision of the pisiform caused the FCU tendon to significantly retract during all wrist motions as compared to the intact wrist or after pisotriquetral arthrodesis. Conclusions Greater FCU forces are required to move the wrist when the pisiform with its moment arm function has been removed. This occurs during large oblique plane wrist motions and also in a smaller motion when greater antagonistic forces are applied. Excision of the pisiform also allows the FCU to move proximally, again because its moment arm function has been eliminated. Clinical relevance Excision of the pisiform requires greater FCU forces during large wrist motions and during motions that include large gripping forces such that excision may be a concern in high-demand patients with pisotriquetral arthritis. Although pisotriquetral arthrodesis does not alter the mechanical advantage of the FCU, its use in high-demand patients with pisotriquetral osteoarthritis cannot yet be recommended until the effects of that arthrodesis on midcarpal kinematics are further clarified. (J Hand Surg 2013;38A:1913e1918. Copyright Ó 2013 by the American Society for Surgery of the Hand. All rights reserved.) Key words Pisiform, pisotriquetral arthritis, wrist forces.
HE PISIFORM LIES WITHIN the fibers of the flexor carpi ulnaris (FCU) and articulates with the triquetrum.1,2 Beckers and Koebke3 found that the pisiform functions as a fulcrum to control the
T
From the Department of Orthopedic Surgery, SUNY Upstate Medical University, Syracuse, NY; Institut Kaplan, Barcelona, Spain. Received for publication April 26, 2013; accepted in revised form July 22, 2013. No benefits in any form have been received or will be received related directly or indirectly to the subject of this article.
triquetrum and also suggested that it protects the neurovascular structures in the Guyon canal. They noted that approximately half of the FCU tendon attaches to the pisiform and the rest is a bundle of Corresponding author: Frederick W. Werner, MME, Department of Orthopedic Surgery, SUNY Upstate Medical University, 3214 Institute for Human Performance, 750 E. Adams Street, Syracuse, NY 13210; e-mail: [email protected]. 0363-5023/13/38A10-0004$36.00/0 http://dx.doi.org/10.1016/j.jhsa.2013.07.021
Ó 2013 ASSH
r
Published by Elsevier, Inc. All rights reserved.
r
1913
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fibers functioning as a roof over the pisiform as these fibers continues distally. Pisiform excision is generally considered the standard treatment for patients with pisotriquetral arthritis and chronic pain. Although it has generally resulted in good clinical results,4,5 1 study6 found a slight reduction in wrist strength when compared to the contralateral side. Beckers and Koebke3 suggested that the excision of the pisiform should be reconsidered. In high-demand athletes who require maximal grip, any reduction in grip may decrease their athletic potential. Because of this concern, other authors7,8 reported on the results of pisotriquetral arthrodesis in patients with pisotriquetral instability. These authors were concerned about increased movement of the triquetrum3 and postoperative decrease in wrist flexion strength following pisiformectomy.6 The goal of this study was to determine the biomechanical consequences of pisiform excision and of pisotriquetral arthrodesis, specifically during an oblique wrist motion that has a similar orientation as the true dart throw wrist motion, because this is the motion during which many activities of daily living occur.9e11 These include high-demand functional activities such as hammering12 and sporting activities such as golfing and tennis. Because in a cadaver experiment we cannot directly measure postoperative changes in grip strength, we assumed changes in measured in vitro FCU forces were an indicator of changes of in vivo clinical grip strength. The purpose of this study was to determine whether there was a difference in FCU force and tendon displacement during these motions between the intact wrist and after a pisotriquetral arthrodesis or pisiform excision. METHODS Nine fresh-frozen right cadaver wrists (average, 68 years; 5 female, 4 male) were tested in a wrist joint motion simulator13 by pulling on 5 wrist flexor and extensor tendons to cause wrist motion under computer control (Fig. 1). Each wrist was thawed the previous day and prepared for testing by dissecting 3 wrist extensors (extensor carpi ulnaris, extensor carpi radialis brevis, and extensor carpi radialis longis) and 2 wrist flexors (FCU and flexor carpi radialis). The flexor and extensor retinaculums were preserved. A pin cemented into the humerus was attached to the loading frame, and the elbow was pinned at 90 flexion and supported by a platform. The forearm was kept in neutral forearm rotation by a plastic fork surrounding the radius and ulna. Each tendon was connected in series to a load cell, which measured the JHS
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FIGURE 1: Volar view of intact cadaver wrist in wrist simulator. Clamps are attached to each individual tendon. Load cells are in series beneath each clamp. An electromagnetic sensor is attached to the third metacarpal to measure wrist motion. The clamps and load cells for the 3 extensor tendons are not shown.
force in the tendon as a hydraulic actuator pulled on the respective tendon. While each wrist was moving in the desired wrist motion, the agonist tendons were under velocity feedback control, and the antagonist tendons were under force feedback control. The antagonist tendons provided a constant resistive force to the desired motion. The agonist tendon forces were controlled by an algorithm that minimized the error between the desired and actual wrist motion.13 These roles for each tendon switched at the extreme of wrist motion. Wrist motion was measured by an electromagnetic sensor attached to the dorsum of the third metacarpal. It detected its position (and therefore, the wrist position) relative to an electromagnetic source. Four different motions in the oblique plane with a similar orientation as the true dart throw plane of motion were studied. Each might be considered a variation of the true dart throw motion. However, they had different ranges of motion and different antagonistic forces. These motions were assumed to be most representative of those used during highdemand activities and selected based on previous studies of dart throw motion.11 Two variations of a
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FIGURE 2: The FCU tendon force during a large wrist motion with the pisiform intact, after pisotriquetral arthrodesis, and after pisiform excision in an illustrative specimen. The greatest FCU force occurred as the wrist was coming out of extension and radial deviation while the FCU was acting as an agonist to cause the motion. From wrist flexion and ulnar deviation to wrist extension and radial deviation, the FCU functioned primarily as an antagonistic with an 18 N resistive force. Increases from the 18 N force occurred because the FCU also acted as an ulnar deviator to correct slight out-of-plane motions.
dart throw motion had smaller ranges of wrist motion (30 extension and 10 radial deviation to 30 flexion and 10 ulnar deviation), and 2 had larger ranges of wrist motion (40 extension and 10 radial deviation to 40 flexion to 10 ulnar deviation). In 1 small and 1 large wrist motion, small antagonistic forces14 (8.9 N per tendon) were used, and in the other small and large motions, 18 N per tendon antagonistic forces were used. The increased antagonistic force, chosen arbitrarily, was used to simulate a higher-demand activity. The antagonistic force was applied to each tendon while that tendon was functioning as an antagonist such that it resisted the desired wrist motion. When a tendon was functioning as an agonist, so that it was causing the desired wrist motion, the force was continuously recomputed every 12.2 ms to cause a smooth, sinusoidal cyclic motion. Thus, as the wrist was moving from extension and radial deviation, the FCU was acting as an agonist, and the force was varied under computer control to cause the motion. As the wrist was moving from flexion and ulnar deviation to extension and radial deviation, the FCU was acting as an antagonist. However, every 12.2 ms, the role of the FCU was recomputed. If, for example, the wrist was moving out of the plane of the dart motion and was in slight radial deviation, the FCU would also function as an ulnar deviator, causing a force greater than the antagonistic level, to move the wrist back into the plane of motion. As shown in JHS
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Figure 2, as the wrist was moving from flexion to extension, these corrective forces were moderate. Six cycles of each motion were performed. During each motion, the FCU tendon force and movement were measured. An increase in the FCU force after either pisotriquetral arthrodesis or excision during wrist motions identical to the intact condition was thought to be an indicator of a negative benefit for that procedure. Tendon movement was measured using a linear potentiometer connected to the tendon’s actuator. A negative value corresponded to a proximal motion of the tendon. All data were collected at a rate of 82 Hz. Pisotriquetral arthrodesis was performed by positioning the wrist in neutral flexion-extension and making a medial incision directly over the pisiform. The tendon attachment was well visualized and left intact. Two 1.6-mm (0.062 in.) K-wires were then placed in converging fashion into the pisotriquetral joint. No cartilage was removed from either the pisiform or triquetrum. Each wrist was then moved through the 4 wrist motions, and FCU force and movement data were collected. After testing the simulated pisotriquetral arthrodesis, the stability of the fixation was checked to verify there was no relative translation or rotation of the bones. Next, the pisiform was excised by carefully carving it out of its attachment to the FCU. The surrounding tissues were sutured back together using a direct side-to-side repair
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FIGURE 3: The FCU tendon movement during a large wrist motion with the pisiform intact, after pisotriquetral arthrodesis, and after pisiform excision in an illustrative specimen. With wrist flexion (and ulnar deviation) the tendon moved proximally, and with extension (and radial deviation) it moved distally.
TABLE 1.
Average Peak FCU Force (N) During 4 Variations of a Dart Throw Motion Small Dart Motion
Large Dart Motion
Low Antagonistic Force
Small Dart Motion
Large Dart Motion
High Antagonistic Force
Intact wrist (SD)
48.3 (8.9)
56.0 (14.0)
64.0 (11.2)
69.2 (14.1)
After pisotriquetral arthrodesis (SD)
49.6 (10.2)
55.9 (15.4)
66.1 (13.3)
71.1 (15.1)
After pisiform excision (SD)
51.6 (15.2)
72.0 (16.0)
76.3 (13.3)
89.5 (13.8)
of the incised tendon by using a running 3-0 suture. Care was taken to not alter the FCU length. Each wrist was then again moved through the 4 wrist motions. At the conclusion of the experiment, each wrist was dissected to evaluate the quality of the soft tissue repair following pisiform excision and for degenerative changes to the pisiform (already excised) and the triquetrum. The repair in the first limb tested was found to be inadequate; therefore, the results are based on 8 specimens. In the first limb, the sutures used to repair the tendon after pisiform excision had torn through the tissues due to poor tissue quality. All other repairs were intact. At each increment of wrist motion during the fourth cycle of wrist motion (819 increments per cycle of motion), the peak force (Fig. 2) and the most distal value of the tendon position was determined. The most distal value of the tendon position corresponded to the wrist being in extension and radial deviation (Fig. 3). Changes in FCU force and tendon movement were statistically analyzed using a JHS
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repeated measures, 1-way analysis of variance on the last 8 arms. RESULTS After excision of the pisiform, a significantly greater FCU force (Table 1, Fig. 2) was required to move the wrist during both of the larger wrist motions (P < .002) and during the smaller wrist motion with a larger antagonistic force (P < .001) compared to the intact wrist. In the smaller wrist motion with the smaller antagonistic force, there was not a significant difference in the FCU force between pisiform excision and the intact wrist (P > .99). There was no significant difference in the peak FCU force between the intact wrist and after pisotriquetral arthrodesis (P > .99) in any of the wrist motions. However, during both of the larger wrist motions, there was a significantly greater peak FCU force with pisiform excision compared to pisotriquetral arthrodesis (P > .013). During both of the
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TABLE 2. Average Change in FCU Excursion (mm) as Compared to Intact, During 4 Variations of a Dart Throw Wrist Motion Small Dart Motion
Large Dart Motion
Low Antagonistic Force
Small Dart Motion
Large Dart Motion
High Antagonistic Force
After pisotriquetral arthrodesis (SD)
0.5 (0.8)
0.4 (1.0)
0.3 (0.7)
0.6 (0.7)
After pisiform excision (SD)
6.0 (3.0)
6.1 (3.0)
6.2 (3.0)
6.7 (3.1)
A negative value indicates a retraction of the FCU (more proximal).
smaller wrist motions, there was not a significant difference in the peak FCU force between pisotriquetral arthrodesis and pisiform excision (P > .07). Excision of the pisiform caused the FCU tendon to significantly (P < .003) move proximally during all wrist motions as compared to the intact wrist or compared with a pisotriquetral arthrodesis (Fig. 3, Table 2). No difference in the FCU movement was observed between the intact wrist and pisotriquetral arthrodesis (P > .18). Dissection of the specimens after testing revealed no arthritic changes to the triquetrum in 4 of the 8 limbs, triquetral distal pole degeneration in 3, and arthritic changes on the entire periphery (but not centrally) in the remaining 1. On the pisiforms, there was mild peripheral degeneration in 1, degenerative changes ulnarly and proximally in 1, degenerative changes distally and radially in 1, degenerative changes only radially in 2, degenerative changes only distally in 2, and no changes in 1. DISCUSSION During high-demand wrist activities, such as in competitive sports or in heavy manual tasks, greater wrist tendon forces are required. The purpose of this study was to determine whether greater FCU forces might be required in simulated low-demand and highdemand activities with pisiform excision. We differentiated between low-demand and high-demand activities by changing the amount of the force resisting (antagonistic to) a wrist motion. In the simulated low-demand patient (lower antagonistic force), we found there was no difference in the required FCU force for the smaller range of wrist motion following pisiform excision. This may suggest that excision of the pisiform may not limit low-force activities. This matches the clinical observation by Lam et al15 that function could be restored with a painless wrist following removal of the pisiform. However, in the simulated high-demand patient (higher antagonistic force levels and greater range of JHS
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wrist motion), we found greater FCU forces (up to 29% greater than in the intact wrist) were required to have the same wrist motion after pisiform excision. This suggests that laborers or high-performance athletes may be limited in their ability to perform the same motion following pisiform excision. Even a slight decrease in strength may alter an athlete’s performance. Lam et al,15 as noted earlier, felt that pisiform resection restored function, yet they then reported that, based on examination of the confidence intervals in their data, there was at most a 10% loss in grip strength, a 10% to 17% loss in static strength, and a 5% loss in dynamic power. Another factor may be the type of activity. Helal16 removed the pisiform in 3 squash players and 1 badminton player. All returned to their sporting activities without any complications. For all motions and antagonistic forces, we found that excision of the pisiform caused the FCU to retract proximally 6 to 7 mm. Palmieri5 saw a change of about 5 mm in his series of 21 patients and suggested that it was not enough to reduce the strength of the FCU. We suggest that additional studies may be needed to determine whether this change in the forceeelongation relationship of the FCU muscle is clinically important. We found pisotriquetral arthrodesis did not cause a significant difference in the FCU force or tendon movement compared to the intact wrist. The force and movement patterns and magnitudes after arthrodesis were similar to those in the intact wrist. This would suggest that pisotriquetral arthrodesis does not alter the mechanical advantage of the FCU. Therefore, pisotriquetral arthrodesis may be an alternative to consider in high-demand individuals. However, the effect of a pisotriquetral arthrodesis on midcarpal kinematics is unknown. If the pisiform is fixed distally on the triquetrum (allowing the FCU to be relatively lax distal to the pisiform) the midcarpal joint may become more lax. If the pisiform is fixed proximally on the triquetrum (causing the FCU to be relatively tighter distal to the pisiform) the midcarpal joint may become stiffer. Depending upon where the pisiform is fixed on the
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triquetrum, a different pathology may develop. Until the effect of where the pisiform is fused to the triquetrum on midcarpal kinematics is determined, we caution against concluding that our findings support pisotriquetral arthrodesis. Limitations to this study include that it was a cadaver study in which the effect of healing was not included, and we could not directly measure postoperative changes in grip strength. We, therefore, had to assume that the changes we measured in the in vitro FCU forces would be an indicator of changes of in vivo clinical grip strength. Only 4 variations of a dart throw wrist motion were studied. Other motions, such as a pure flexion-extension or pure radioulnar deviation motion, were not studied. However, we felt that the selected variations of a dart throw motion were representative of what might occur in different levels of patient demand and that each arm served as its own control. Another limitation to this study is that we did not decorticate the pisiform or triquetrum at the time of simulated arthrodesis. Doing so would have potentially decreased the FCU moment arm and altered the mechanical advantage of the FCU. Another limitation is that little is known about the in vivo force in the wrist tendons, especially how much more might be needed during a strenuous activity. Mendelson et al17 intraoperatively measured the forces in the extensor carpi radialis brevis and extensor carpi radialis longus to be an average of 63 N and 82 N, respectively. However, these were not during a high-demand activity. Finally, the speed of the wrist motion in this experiment was much less than that which occurs during sporting activities or heavy labor tasks and, therefore, did not include any major dynamic effects. However, we were still able to detect changes in tendon loading with pisiform excision, which should also occur during high-speed activities.
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REFERENCES 1. Hoepfner PE. Pisotriquetral arthritis. Tech Orthop. 2009;24(1): 42e44. 2. Yamaguchi S, Viegas SF, Patterson RM. Anatomic study of the pisotriquetral joint: ligament anatomy and cartilagenous change. J Hand Surg Am. 1998;23(4):600e606. 3. Beckers A, Koebke J. Mechanical strain at the pisotriquetral joint. Clin Anat. 1998;11(5):320e326. 4. Carroll RE, Coyle MP Jr. Dysfunction of the pisotriquetral joint: treatment by excision of the pisiform. J Hand Surg Am. 1985;10(5): 703e707. 5. Palmieri TJ. Pisiform area pain treatment by pisiform excision. J Hand Surg Am. 1982;7(5):477e480. 6. Arner M, Hagberg L. Wrist flexion strength after excision of the pisiform bone. Scand. J Plast Reconstr Surg. 1984;18(2):241e245. 7. Abrams R, Tontz W. Pisotriquetral arthrodesis as an alternative to excision for pisotriquetral instability in high-demand patients: a case report in a gymnast. J Hand Surg Am. 2006;31(4):611e614. 8. Singer G, Eberl R, Hoellwarth ME. Pisotriquetral arthrodesis for pisotriquetral instability: case report. J Hand Surg Am. 2010;36(2): 299e303. 9. Brigstocke GH, Hearnden A, Holt C, Whatling G. In-vivo confirmation of the use of the dart thrower’s motion during activities of daily living. J Hand Surg Eur Vol. 2012 Oct 11. [Epub ahead of print.] 10. Crisco JJ, Coburn JC, Moore DC, et al. In vivo radiocarpal kinematics and the dart thrower’s motion. J Bone Joint Surg Am. 2005;87(12): 2729e2740. 11. Werner FW, Green JK, Short WH, et al. Scaphoid and lunate motion during a wrist dart throw motion. J Hand Surg Am. 2004;29(3): 418e422. 12. Leventhal EL, Moore DC, Adelman E, et al. Carpal and forearm kinematics during a simulated hammering task. J Hand Surg Am. 2010;35(7):1097e1104. 13. Werner FW, Palmer AK, Somerset JH, et al. Wrist joint motion simulator. J Orthop Res. 1996;14(4):639e646. 14. Short WH, Werner FW, Green JK, et al. The effect of sectioning the dorsal radiocarpal ligament and insertion of a pressure sensor into the radiocarpal joint on scaphoid and lunate kinematics. J Hand Surg Am. 2002;27(1):68e76. 15. Lam KS, Woodbridge S, Burke FD. Wrist function after excision of the pisiform. J Hand Surg Br. 2003;28(1):69e72. 16. Helal B. Chronic overuse injuries of the piso-triquetral joint in racquet game players. Br J Sports Med. 1978;12(4):195e198. 17. Mendelson LS, Peckham PH, Freehafer AA, et al. Intraoperative assessment of wrist extensor muscle force. J Hand Surgery Am. 1988;13(6):832e836.
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