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Excursion properties of tendon graft sources: Interaction between tendon and A2 pulley
Excursion Properties of Tendon Graft Sources: Interaction Between Tendon and A2 Pulley Jun Nishida, MD,* Peter C. Amadio, MD, Paul C. Bettinger, MD, Kai-Nan An, PhD, Rochester, MN We measured excursion resistance of 4 different tendons (flexor digitorum superficialis, the portion of the extensor indicis proprius tendon beneath the extensor retinaculum, the portion of the extensor indicis proprius tendon distal to the extensor retinaculum, and palmaris Iongus) beneath the A2 pulley. Intrasynovial tendons (i.e., flexor digitorum superficialis and the portion of the extensor indicis proprius beneath the extensor retinaculum) produced less excursion resistance than extrasynovial tendons (i.e., the portion of the extensor indicis proprius distal to the extensor retinaculum and palmaris Iongus). The excursion resistance of the intrasynovial portion of the extensor indicis proprius tendon was significantly lower than that of the extrasynovial portion of the same tendon. Intrasynovial tendons may be preferred to extrasynovial tendons when choosing a tendon graft source and graft gliding under a pulley is a consideration. (J Hand Surg 1998;23A:274-278. Copyright 9 1998 by the American Society for Surgery of the Hand.)
Many techniques have been reported for flexor tendon grafting. J-5 Restoration of gliding still presents serious problems for the hand surgeon, 1-3,6 and early passive mobilization is preferred to prevent adhesions and to obtain a successful result following flexor tendon grafting. 7-m Friction between the pulley and the tendon may limit tendon gliding, thereby promoting adhesion formation. An understanding of the extent of and the contributing factors for friction therefore may be important. However, little has been reported regarding the mechanical interaction of tendon graft and pulley, and whether the various poten-
tial tendon graft donors behave similar in this regard is unknown. A system that allows quantitative measurement of the friction between a tendon and its associated pulley has been developed. 1~'~2 In this study, gliding resistance between tendons, simulating tendon grafts, and an intact A2 pulley was evaluated in an in vitro human model. Gliding resistance was compared among the different potential flexor tendon graft donor sources.
Materials and Methods Models of Tendon Graft
From the Biomechanics Laboratory and Department of Orthopedics, May() Clinic and Mayo Foundation, Rochester, MN. Received for publication May 7, 1996; accepted in revised form January 16, 1998. No benefits in any *kJrm have been received or will be received from a commercial party related directly or indirectly to the subject of this article. * P r e s e n t a d d r e s s : Department of Orthopedic Surgery, School of Medicine, lwate Medical University, Morioka, Japan. Reprint requests: Peter C. Amadio, MD, Biomechanics Laboratory, Mayo Clinic, 200 First St SW, Rochester, MN 55905. Copyright 9 1998 by the American Society for Surgery of the Hand. 0363-5023/98/23A02-001453.00/0
274
The Journal of Hand Surgery
Seven middle fingers of 6 cadavers were used in each in vitro model. We used 3 female and 3 male cadavers, whose ages ranged from 61 to 85 years at the time of death (average age, 74 years). Excursion resistance between the A2 pulley and 5 different kinds of tendon was measured. The ipsilateral palmaris longus tendon, the portion of the ipsilateral extensor indicis proprius tendon distal to the extensor retinaculum, the portion of the ipsilateral extensor indicis proprius tendon beneath the extensor
The Journal of Hand Surgery / Vol. 23A No. 2 March 1998 275
retinaculum, and the flexor digitorum superficialis tendon of the adjacent ring finger were the sources for the tendon autograft. As a control, resistance was also measured for the flexor digitorum profundus tendon of each middle finger. Measurement of Interaction Between Tendon and Pulley The concept of friction measurement and its application to the tendon-pulley unit has been verified
and validated, as reported previously. T M j 2 A tendon sliding through a curved pulley is analogous to a cable wrapped around a fixed mechanical pulley. Assume that the tensions in the cable are recorded by transducers F1 and F2 on each end, respectively. If the impending motion of the cable is in the direction from transducer F1 to transducer F2, then the force at F2 is greater than the force at Fl due to the friction (f): f = F2 - F1. This model is the basis for our experimental setup, which is described below. A transverse incision through the synovial sheath was made just distal to the A2 pulley in each experimental digit to mark the lateral surface of the flexor digitorum profundus tendon with the finger in full extension. The tendon was then pulled proximally until full proximal interphalangeal and distal interphalangeal joint flexion was achieved. In this position, the tendon was again marked through the previous incision. The distance between these 2 marks represented the physiologic excursion range (17-23 mm; mean, 19 ram). The parietal synovial membrane proximal and distal to the A2 pulley, all pulleys except A2, and the flexor digitorum superficialis tendon were removed. The A2 pulley, the parietal membrane of the A2 pulley, and the visceral membrane of the flexor digitorum profundus tendon were preserved. To limit measurement to the interaction between the A2 pulley and the tendon, the bone distal to the distal edge of the A2 pulley, the bone proximal to the proximal edge of the A2 pulley, and the volar cortex of the proximal phalanx were all removed. A 1.5-ram Kirschner wire was inserted through the phalanx parallel to the longitudinal axis of the bone to help stabilize it on the testing device. Each specimen was then mounted on a custom testing device. The measurement system consisted of 1 mechanical actuator with a linear potentiometer, 2 tensile load transducers, and l pulley (Fig. 1). The volar side of the specimen faced upward, while the proximal side faced the device actuator. The longitudinal convex inner surface of the A2 pulley was
toad Figure 1. Experimental setup for the measurement of excursion resistance between the tendon and the A2 pulley. Tensions of F1 and F2 are measured by the tensile load transducers. Excursion is measured by a linear potentiometer. (Reprinted with permission, Mayo Foundation.)
similar to the arc of the mechanical pulley described above. The tendon corresponded to the cable around the mechanical pulley. A 250-g preload was used to simulate active mobilization of the finger.~3 Custom load transducers (accurate to < 1 g]~) were connected to the proximal and distal ends of the tendon using Dacron cord. The proximal load transducer (F2) was connected to a custom-built mechanical actuator. The distal transducer (F1) was connected to the weight. The actuator was positioned at the preselected angle c~, which was defined as the angle (in degrees) formed between the horizontal plane and the proximal cable extension. The mechanical pulley between the load and the distal load transducer was positioned at a preselected angle /3, which was defined as the angle formed between the horizontal plane and the distal cable extension. The sum of the angles c~ and/3 was considered the angle of the arc of contact. The tendon was pulled proximally at a continuous rate of 2.0 mm/s by the actuator, and opposed by the weight. The movement of the tendon toward the actuator was regarded as flexion. As the tendon moved, F1, F2, and the corresponding excursion were recorded by a digital computer at a sampling rate of l0 Hz. Excursion was limited to the distance between the 2 tendon markers. Angles c~ and/3 were varied to 5 different positions by raising or lowering the actuator and weight. Three trials were performed
276
Nishida et al. / Excursion Properties of Tendon Graft Sources 90-
for each tendon at each of 5 different positions (c~,/3): 15 ~ 5~ 20 ~, 10~ 30 ~ 10~ 30 ~ 20~ and 30 ~ 30 ~.
P group
-r
so O
R group
~IL~
E group
..A..
S group
7o:
Data Analysis
6o:
Plots of F1 and F2 measurements versus excursion were examined for each trial and evaluated by their shape. As the trials were generally identical and the first runs were considered to be preconditioning, the average of the last 2 runs was analyzed for each angle. The mean force difference of F2 and F1 for the whole excursion was obtained and regarded as the resistance at the interface between the tendon and the pulley for the given arc of contact. The tendons simulating tendon graft were classified as intrasynovial tendons (flexor digitorum superficialis tendon and the portion of the extensor indicis proprius tendon that would normally glide beneath the extensor retinaculum), extrasynovial tendons (palmaris longus tendon and the portion of the extensor indicis proprius tendon distal to the extensor retinaculum), and as a control, the flexor digitorum profundus tendon of each finger. The intrasynovia] and extrasynovial tendons were compared statistically with the control tendon. Intrasynovial and extrasynovial tendons were also statistically compared with each other. Significant differences in excursion resistance between tendons and at different angles was assessed by a 2-factor repeated measures analysis of variance. Fisher's a posteriori least significant difference test was then used for a post hoc comparison of individual means in the means effects. '4 The level of significance was set at c~ = .05. Results
The results are shown in Figure 2. The 2 types of intrasynovial tendon graft and the flexor digitorum profundus were not statistically different. The excursion resistance was significantly higher for both extrasynovial tendon grafts compared with the flexor digitorum profundus tendon at all angles with the exception of 20 ~ for the palmaris longus tendon (p < .05). The excursion resistance was higher in the portion of the extensor indicis proprius tendon distal to the extensor retinaculum than in the palmaris longus tendon; significant differences were found at all angles except 20 ~ (p < .05). Between the flexor digitorum superficialis tendon and palmaris longus tendon, the differences in excursion resistance were statistically significant (p < .05 at 20 ~ and p < .01 at 30 ~ 40 ~ 50 ~ and 60~ The excursion resistance of the palmaris longus tendons
,I --
T
El0-: 9
ii ,~ f~
:
.u 40o 30 -: 20-
....
10 20
30
40 Angle (degree)
50
60
Figure 2. Comparison between intrasynovial tendons and extrasynovial tendons: flexor digitorum superficialis (S group); palmaris longus tendon (P group); extrasynovial, extensor indicis proprius tendon (E group); and intrasynovial extensor indicis proprius (R group).
was more than twice that of the flexor digitorum superficialis tendons at all angles except at 20 ~ Between the flexor digitorum superficialis tendon and the extrasynovial portion of the extensor indicis proprius tendon, the differences in excursion resistance were statistically significant (p < .01) at all angles. The excursion resistance of the extrasynovial portion of the extensor indicis proprius tendon was approximately 3 times that of the flexor digitorum superficialis tendon at all angles. The difference in excursion resistance between the intrasynovial portion of the extensor indicis proprius tendon and the palmaris longus tendon was statistically significant (p < .05) at all angles. The excursion resistance of the extrasynovial portion of the extensor indicis proprius tendon was approximately twice that of the flexor digitorum superficialis tendon at all angles. The difference in excursion resistance between the 2 different portions of the extensor indicis proprius tendon was statistically significant (p < .01) at all angles. The excursion resistance of the extrasynovial portion of the extensor indicis proprius tendon was more than twice that of the intrasynovial portion of the extensor indicis proprius tendon at all angles. Discussion
Tendon grafts are frequently required in reconstructive surgery. The clinical results of tendon grafting may be affected by many factors, 1-3'~-~''5 and the
The Journal of Hand Surgery / Vol. 23A No. 2 March 1998
kinematics of tendon gliding are extremely complex.~,~2 An ideal solution would provide an environment that allows low-resistance gliding with optimal guidance to assure mechanical efficiency. Adhesions after tendon surgery have been discussed in many reports. ~3 Although the issue of what material to use for tendon grafts may be important, until recently it has been given little notice aside from the question of ease of u s e . 4'5"16 Several recent articles have reported the difference between intrasynovial and extrasynovial tendon grafts. These reports have focused on the problems of tendon healing and adhesion formation.~'5'~~ Intrasynovial tendon grafts show significant differences from extrasynovial tendon grafts in both surface morphology and vascularity.17 The synthesis of proteoglycan matrix proteins and DNA is also different between these 2 types of tendon. 18 Excursion resistance between a tendon and pulley is another important problem to consider. We developed a technique with which to measure 1 component affecting tendon gliding: frictional resistance between a tendon and pulley. ~j't2 The advantage of this technique is that the tendon-pulley interaction can be measured directly. in a previous study, we compared l type of intrasynovial tendon, flexor digitorum profundus, with 1 type of extrasynovial tendon, palmaris longus, and found significant differences in excursion resistance between the 2. j') In this study, we expanded on that work to determine whether the differences are generalizable to other intrasynovial and extrasynovial tendons. We again observed significant differences in gliding resistance between intrasynovial and extrasynovial tendons. The extrasynovial tendons produced far greater gliding resistance than did the intrasynovial tendons. More importantly, the excursion resistance of 2 potential sources of intrasynovial tendon graft were roughly the same as that of the normal flexor digitorum profundus tendon. Even though this result was obtained from an in vitro study, we believe that a clinical advantage could be expected in rehabilitation after tendon graft using an intrasynovial tendon as the graft source. The portion of the extensor indicis proprius tendon distal to the extensor retinaculum produced significantly greater gliding resistance than the proximal portion of the same tendon, which normally glides beneath the extensor retinaculum. Based on this observation, we believe that the segments of extensor tendon that lie beneath an extensor retinaculum may be considered preferentially for use as a tendon graft
277
when a lower-friction source is desired. Even when the segment to be grafted is longer than the subretinacular portion of such an extensor tendon, it may be possible to reverse or otherwise tailor the extensor tendon so that the subretinacular portion of the extensor tendon lies within the pulley/sheath area of the recipient bed. Of course, the flexor digitorum superficialis tendon also may be considered if it is available, but it usually is not. Although we expected the palmaris longus tendon and the extensor indicis proprius tendon distal to the extensor retinaculum area to give the same result, the extensor indicis proprius tendon distal to the extensor retinaculum area actually produced greater excursion resistance than the palmaris longus tendon. This may be due to a difference in microscopic surface structure, which has been postulated to affect gliding resistance in other situations/~'2~ We believe that the strength of this study lies in the direct measurement of the interaction of tendon and sheath. The study's limitations are that it was done in vitro, that the excursion resistance was only measured between the A2 pulley and tendon, and that the rate of tendon movement (2 m m / s ) i s not physiological. In the future, we plan to evaluate the morphologic characteristics of the surface of the extensor indicis proprius tendon. We also plan an in vivo extension of this work using an animal model.
References 1. Hunter J, Salisbury RE. Flexor-tendon reconstruction in severely damaged hands. A two-stage procedure using a silicon-Dacron reinforced gliding prosthesis prior to tendon grafting. J Bone Joint Surg 1971;53A:829-858. 2. McClinton MA, Curtis RM, Wilgis EFS. One hundred tendon grafts for isolated flexor digitorum profundus injuries. J Hand Surg 1982;7:224-229. 3. Strickland JW. Flexor tendon injuries. Part 4. Staged flexor tendon reconstruction and restoration of the flexor pulley. Orthop Rev 1987;16:78-90. 4. Wehb6 MA. Tendon graft donor sites. J Hand Surg 1992; 17A:1130-1132. 5. White WL. Tendon grafts: a consideration of their source, procurement and suitability. Surg Clin North Am 1960;40: 403-413 6. Amadio PC, Wood MB, Cooney WP III, Bogard SD. Staged flexor tendon reconstruction in the fingers and hand. J Hand Surg 1988;13A:559-562. 7. Bunker TD, Potter B, Barton NJ. Continuous passive motion following flexor tendon repair. J Hand Surg 1989;14B: 406-411. 8. Silfverski61d KL, May EJ, T6rnvall AH. Tendon excursions after flexor tendon repair in zone It: results with a new controlled-motion program. J Hand Surg 1993;18A: 403-410.
278
Nishida et al. / Excursion Properties of Tendon Graft Sources
9. Small JO, Brennen MD, Colville J. Early active mobilization following a flexor tendon repair in zone 2. J Hand Surg 1989:14B:383-391. 10. Woo SL-Y. Gelberman RH, Cobb NG, Amiel D, Lotrhinger K, Akeson WH. The importance of controlled passive mobilization on flexor tendon healing: a biomechanical study. Acta Orthop Scand 1981;52:615622. 11. An K-N, Berglund L, Uchiyama S, Coert JH. Measurement of friction between pulley and flexor tendon. Biomechanical Sciences Instrumentation, RMBS-ISA Paper #93-001. Research Triangle Park, NC: Instrument of Society of America, 1993;29: 1-7. 12. Uchiyama S, Coert JH, Berglund L, Amadio PC, An K-N. Method for the measurement of friction between tendon and pulley. J Orthop Res 1995;13:83-89. 13. Schuind F, Garcia-Elias M, Cooney WP III, An K-N. Flexor tendon forces: in vivo measurements. J Hand Surg 1992;17A:291-298.
14. Kirk RE. Experimental design: procedures for the behavioral sciences. Belmont: Brookes/Cole Publishing, 1968. 15. Strickland JW. Flexor tendon injuries: II. Operative technique. J Am Acad Orthop Surg 1995;3:55-62. 16. Harvey FJ, Chu G, Harvey PM. Surgical availability of the plantaris tendon. J Hand Surg 1983;8:243-247. 17. Seller JG, Gelberman RH, Williams CS, et al. Autogenous flexor tendon grafts: a biomechanical and morphological study in dogs. J Bone Joint Surg 1993;75A:1004-1014. 18. Abrahamsson S-O, Gelberman RH, Lohmander SL. Variations in cellular proliferation and matrix synthesis in intrasynovial and extrasynovial tendons: an in vitro study in dogs. J Hand Surg 1994;19A:259-265. 19. Uchiyama S, Amadio PC, Coert JH, Berglund L, An K-N. Gliding resistance of extrasynovial and intrasynovial tendon through A2 pulley. J Bone Joint Surg 1997;79A:219-227. 20. Uchiyama S, Amadio PC, lshikawa J, An K-N. Boundary lubrication between the tendon and the pulley in the finger. J Bone Joint Surg 1997;79A:213-218.
Many techniques have been reported for flexor tendon grafting. J-5 Restoration of gliding still presents serious problems for the hand surgeon, 1-3,6 and early passive mobilization is preferred to prevent adhesions and to obtain a successful result following flexor tendon grafting. 7-m Friction between the pulley and the tendon may limit tendon gliding, thereby promoting adhesion formation. An understanding of the extent of and the contributing factors for friction therefore may be important. However, little has been reported regarding the mechanical interaction of tendon graft and pulley, and whether the various poten-
tial tendon graft donors behave similar in this regard is unknown. A system that allows quantitative measurement of the friction between a tendon and its associated pulley has been developed. 1~'~2 In this study, gliding resistance between tendons, simulating tendon grafts, and an intact A2 pulley was evaluated in an in vitro human model. Gliding resistance was compared among the different potential flexor tendon graft donor sources.
Materials and Methods Models of Tendon Graft
From the Biomechanics Laboratory and Department of Orthopedics, May() Clinic and Mayo Foundation, Rochester, MN. Received for publication May 7, 1996; accepted in revised form January 16, 1998. No benefits in any *kJrm have been received or will be received from a commercial party related directly or indirectly to the subject of this article. * P r e s e n t a d d r e s s : Department of Orthopedic Surgery, School of Medicine, lwate Medical University, Morioka, Japan. Reprint requests: Peter C. Amadio, MD, Biomechanics Laboratory, Mayo Clinic, 200 First St SW, Rochester, MN 55905. Copyright 9 1998 by the American Society for Surgery of the Hand. 0363-5023/98/23A02-001453.00/0
274
The Journal of Hand Surgery
Seven middle fingers of 6 cadavers were used in each in vitro model. We used 3 female and 3 male cadavers, whose ages ranged from 61 to 85 years at the time of death (average age, 74 years). Excursion resistance between the A2 pulley and 5 different kinds of tendon was measured. The ipsilateral palmaris longus tendon, the portion of the ipsilateral extensor indicis proprius tendon distal to the extensor retinaculum, the portion of the ipsilateral extensor indicis proprius tendon beneath the extensor
The Journal of Hand Surgery / Vol. 23A No. 2 March 1998 275
retinaculum, and the flexor digitorum superficialis tendon of the adjacent ring finger were the sources for the tendon autograft. As a control, resistance was also measured for the flexor digitorum profundus tendon of each middle finger. Measurement of Interaction Between Tendon and Pulley The concept of friction measurement and its application to the tendon-pulley unit has been verified
and validated, as reported previously. T M j 2 A tendon sliding through a curved pulley is analogous to a cable wrapped around a fixed mechanical pulley. Assume that the tensions in the cable are recorded by transducers F1 and F2 on each end, respectively. If the impending motion of the cable is in the direction from transducer F1 to transducer F2, then the force at F2 is greater than the force at Fl due to the friction (f): f = F2 - F1. This model is the basis for our experimental setup, which is described below. A transverse incision through the synovial sheath was made just distal to the A2 pulley in each experimental digit to mark the lateral surface of the flexor digitorum profundus tendon with the finger in full extension. The tendon was then pulled proximally until full proximal interphalangeal and distal interphalangeal joint flexion was achieved. In this position, the tendon was again marked through the previous incision. The distance between these 2 marks represented the physiologic excursion range (17-23 mm; mean, 19 ram). The parietal synovial membrane proximal and distal to the A2 pulley, all pulleys except A2, and the flexor digitorum superficialis tendon were removed. The A2 pulley, the parietal membrane of the A2 pulley, and the visceral membrane of the flexor digitorum profundus tendon were preserved. To limit measurement to the interaction between the A2 pulley and the tendon, the bone distal to the distal edge of the A2 pulley, the bone proximal to the proximal edge of the A2 pulley, and the volar cortex of the proximal phalanx were all removed. A 1.5-ram Kirschner wire was inserted through the phalanx parallel to the longitudinal axis of the bone to help stabilize it on the testing device. Each specimen was then mounted on a custom testing device. The measurement system consisted of 1 mechanical actuator with a linear potentiometer, 2 tensile load transducers, and l pulley (Fig. 1). The volar side of the specimen faced upward, while the proximal side faced the device actuator. The longitudinal convex inner surface of the A2 pulley was
toad Figure 1. Experimental setup for the measurement of excursion resistance between the tendon and the A2 pulley. Tensions of F1 and F2 are measured by the tensile load transducers. Excursion is measured by a linear potentiometer. (Reprinted with permission, Mayo Foundation.)
similar to the arc of the mechanical pulley described above. The tendon corresponded to the cable around the mechanical pulley. A 250-g preload was used to simulate active mobilization of the finger.~3 Custom load transducers (accurate to < 1 g]~) were connected to the proximal and distal ends of the tendon using Dacron cord. The proximal load transducer (F2) was connected to a custom-built mechanical actuator. The distal transducer (F1) was connected to the weight. The actuator was positioned at the preselected angle c~, which was defined as the angle (in degrees) formed between the horizontal plane and the proximal cable extension. The mechanical pulley between the load and the distal load transducer was positioned at a preselected angle /3, which was defined as the angle formed between the horizontal plane and the distal cable extension. The sum of the angles c~ and/3 was considered the angle of the arc of contact. The tendon was pulled proximally at a continuous rate of 2.0 mm/s by the actuator, and opposed by the weight. The movement of the tendon toward the actuator was regarded as flexion. As the tendon moved, F1, F2, and the corresponding excursion were recorded by a digital computer at a sampling rate of l0 Hz. Excursion was limited to the distance between the 2 tendon markers. Angles c~ and/3 were varied to 5 different positions by raising or lowering the actuator and weight. Three trials were performed
276
Nishida et al. / Excursion Properties of Tendon Graft Sources 90-
for each tendon at each of 5 different positions (c~,/3): 15 ~ 5~ 20 ~, 10~ 30 ~ 10~ 30 ~ 20~ and 30 ~ 30 ~.
P group
-r
so O
R group
~IL~
E group
..A..
S group
7o:
Data Analysis
6o:
Plots of F1 and F2 measurements versus excursion were examined for each trial and evaluated by their shape. As the trials were generally identical and the first runs were considered to be preconditioning, the average of the last 2 runs was analyzed for each angle. The mean force difference of F2 and F1 for the whole excursion was obtained and regarded as the resistance at the interface between the tendon and the pulley for the given arc of contact. The tendons simulating tendon graft were classified as intrasynovial tendons (flexor digitorum superficialis tendon and the portion of the extensor indicis proprius tendon that would normally glide beneath the extensor retinaculum), extrasynovial tendons (palmaris longus tendon and the portion of the extensor indicis proprius tendon distal to the extensor retinaculum), and as a control, the flexor digitorum profundus tendon of each finger. The intrasynovia] and extrasynovial tendons were compared statistically with the control tendon. Intrasynovial and extrasynovial tendons were also statistically compared with each other. Significant differences in excursion resistance between tendons and at different angles was assessed by a 2-factor repeated measures analysis of variance. Fisher's a posteriori least significant difference test was then used for a post hoc comparison of individual means in the means effects. '4 The level of significance was set at c~ = .05. Results
The results are shown in Figure 2. The 2 types of intrasynovial tendon graft and the flexor digitorum profundus were not statistically different. The excursion resistance was significantly higher for both extrasynovial tendon grafts compared with the flexor digitorum profundus tendon at all angles with the exception of 20 ~ for the palmaris longus tendon (p < .05). The excursion resistance was higher in the portion of the extensor indicis proprius tendon distal to the extensor retinaculum than in the palmaris longus tendon; significant differences were found at all angles except 20 ~ (p < .05). Between the flexor digitorum superficialis tendon and palmaris longus tendon, the differences in excursion resistance were statistically significant (p < .05 at 20 ~ and p < .01 at 30 ~ 40 ~ 50 ~ and 60~ The excursion resistance of the palmaris longus tendons
,I --
T
El0-: 9
ii ,~ f~
:
.u 40o 30 -: 20-
....
10 20
30
40 Angle (degree)
50
60
Figure 2. Comparison between intrasynovial tendons and extrasynovial tendons: flexor digitorum superficialis (S group); palmaris longus tendon (P group); extrasynovial, extensor indicis proprius tendon (E group); and intrasynovial extensor indicis proprius (R group).
was more than twice that of the flexor digitorum superficialis tendons at all angles except at 20 ~ Between the flexor digitorum superficialis tendon and the extrasynovial portion of the extensor indicis proprius tendon, the differences in excursion resistance were statistically significant (p < .01) at all angles. The excursion resistance of the extrasynovial portion of the extensor indicis proprius tendon was approximately 3 times that of the flexor digitorum superficialis tendon at all angles. The difference in excursion resistance between the intrasynovial portion of the extensor indicis proprius tendon and the palmaris longus tendon was statistically significant (p < .05) at all angles. The excursion resistance of the extrasynovial portion of the extensor indicis proprius tendon was approximately twice that of the flexor digitorum superficialis tendon at all angles. The difference in excursion resistance between the 2 different portions of the extensor indicis proprius tendon was statistically significant (p < .01) at all angles. The excursion resistance of the extrasynovial portion of the extensor indicis proprius tendon was more than twice that of the intrasynovial portion of the extensor indicis proprius tendon at all angles. Discussion
Tendon grafts are frequently required in reconstructive surgery. The clinical results of tendon grafting may be affected by many factors, 1-3'~-~''5 and the
The Journal of Hand Surgery / Vol. 23A No. 2 March 1998
kinematics of tendon gliding are extremely complex.~,~2 An ideal solution would provide an environment that allows low-resistance gliding with optimal guidance to assure mechanical efficiency. Adhesions after tendon surgery have been discussed in many reports. ~3 Although the issue of what material to use for tendon grafts may be important, until recently it has been given little notice aside from the question of ease of u s e . 4'5"16 Several recent articles have reported the difference between intrasynovial and extrasynovial tendon grafts. These reports have focused on the problems of tendon healing and adhesion formation.~'5'~~ Intrasynovial tendon grafts show significant differences from extrasynovial tendon grafts in both surface morphology and vascularity.17 The synthesis of proteoglycan matrix proteins and DNA is also different between these 2 types of tendon. 18 Excursion resistance between a tendon and pulley is another important problem to consider. We developed a technique with which to measure 1 component affecting tendon gliding: frictional resistance between a tendon and pulley. ~j't2 The advantage of this technique is that the tendon-pulley interaction can be measured directly. in a previous study, we compared l type of intrasynovial tendon, flexor digitorum profundus, with 1 type of extrasynovial tendon, palmaris longus, and found significant differences in excursion resistance between the 2. j') In this study, we expanded on that work to determine whether the differences are generalizable to other intrasynovial and extrasynovial tendons. We again observed significant differences in gliding resistance between intrasynovial and extrasynovial tendons. The extrasynovial tendons produced far greater gliding resistance than did the intrasynovial tendons. More importantly, the excursion resistance of 2 potential sources of intrasynovial tendon graft were roughly the same as that of the normal flexor digitorum profundus tendon. Even though this result was obtained from an in vitro study, we believe that a clinical advantage could be expected in rehabilitation after tendon graft using an intrasynovial tendon as the graft source. The portion of the extensor indicis proprius tendon distal to the extensor retinaculum produced significantly greater gliding resistance than the proximal portion of the same tendon, which normally glides beneath the extensor retinaculum. Based on this observation, we believe that the segments of extensor tendon that lie beneath an extensor retinaculum may be considered preferentially for use as a tendon graft
277
when a lower-friction source is desired. Even when the segment to be grafted is longer than the subretinacular portion of such an extensor tendon, it may be possible to reverse or otherwise tailor the extensor tendon so that the subretinacular portion of the extensor tendon lies within the pulley/sheath area of the recipient bed. Of course, the flexor digitorum superficialis tendon also may be considered if it is available, but it usually is not. Although we expected the palmaris longus tendon and the extensor indicis proprius tendon distal to the extensor retinaculum area to give the same result, the extensor indicis proprius tendon distal to the extensor retinaculum area actually produced greater excursion resistance than the palmaris longus tendon. This may be due to a difference in microscopic surface structure, which has been postulated to affect gliding resistance in other situations/~'2~ We believe that the strength of this study lies in the direct measurement of the interaction of tendon and sheath. The study's limitations are that it was done in vitro, that the excursion resistance was only measured between the A2 pulley and tendon, and that the rate of tendon movement (2 m m / s ) i s not physiological. In the future, we plan to evaluate the morphologic characteristics of the surface of the extensor indicis proprius tendon. We also plan an in vivo extension of this work using an animal model.
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