Cell Biochem Biophys DOI 10.1007/s12013-014-0040-3
ORIGINAL PAPER
Extensor Tendon Injury Due to Repetitive Wrist Dorsiflexion: Morphological Study of Extensor Retinaculum and Extensor Tendon Chang-long Zhou • Xin-tao Wang • Zhi-yong Chi Jing-long Yan
•
Ó Springer Science+Business Media New York 2014
Abstract Most etiological studies of extensor tendon injury were based on the normal anatomy of extensor tendon and extensor retinaculum of the wrist. Further understanding of the morphological changes of the extensor tendon and extensor retinaculum during wrist dorsiflexion might contribute to improved and more accurate understanding of the etiology. The morphology of the extensor tendon of the mid-finger and the fourth compartment of the wrist extensor retinaculum was studied by sonography, and the anatomy was studied in 15 extremities from 11 young male cadavers. Compared with anatomical images, ultrasonography provides similar morphological observations of the extensor retinaculum of the wrist and extensor tendon. Ultrasonography findings revealed that as the dorsiflexion angle changed, the extensor retinaculum of the wrist formed different shaped trochleas. The trochlea guides the rotation of the extensor tendon at the wrist, but it does not form a sharp corner with the extensor tendon; thus, the extensor tendon is not compressed. As the dorsiflexion angle increased from 0° to 60°, the length of the trochlea gradually decreases. The shortening of the trochlea length will lead to a smaller frictional contact area between the extensor tendon and the extensor retinaculum. Consequently, the friction is centralized. During wrist dorsiflexion, the extensor retinaculum provides a trochlea for the extensor tendon. Extensor tendon injury of repetitive wrist dorsiflexion might be caused by centralized friction at the small contact area.
C. Zhou X. Wang Z. Chi J. Yan (&) Department of Orthopaedics, The First Affiliated Hospital of Harbin Medical University, Harbin 150001, Heilongjiang, China e-mail: [email protected]
Keywords Repetitive wrist dorsiflexion Extensor retinaculum Extensor tendon Extensor tendon injury Ultrasonography Trochlea
Introduction Spontaneous tendon rupture is a relatively rare disease. Potential causes are usually as a consequence of fracture malunion, arthromeningitis, and rheumatoid arthritis [1–3]. However, in the absence of such causes, spontaneous tendon rupture also occurs in certain individuals that frequently repeat flexion and extension of the wrist or fingers, including athletes, pastry cooks, production line workers, painters, rice farmers, among others [4–8]. It has been previously inferred that extensor tendon rupture was due to the formation of a sharp turn angle at the leading edge of the wrist extensor retinaculum, which led to physical deterioration of the tendon [4]. Through a mechanical model, others have inferred that the rotation of the extensor tendon occurred at the leading edge of the wrist extensor retinaculum [9]. VanHeest et al. dissected 10 wrists and showed the clear leading edge of the wrist extensor retinaculum [5]. Both VanHeest et al. [5] and Khazzam et al. [6] believed that a collision occurred between the extensor tendon and the wrist extensor retinaculum. It was proposed that this collision caused extensor tendon rupture at the wrist extensor retinaculum. Consequently, the leading edge of the wrist extensor retinaculum was resected in surgical procedures [5, 6]. However, the studies described above were based on the normal anatomy of the extensor tendon and the wrist extensor retinaculum. Morphological studies of the extensor tendon and wrist extensor retinaculum can be used to assess flexion and extension maneuvers of the wrist and fingers,
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and can lead to more accurate appreciation of disease etiology. The structure and morphology of the extensor tendon of the mid-finger and the fourth compartment of the wrist extensor retinaculum during wrist dorsiflexion were assessed by sonography and anatomy in the current study. Additionally, the etiology of the extensor tendon rupture of repetitive wrist dorsiflexion was analyzed and comprehensively discussed.
Materials and Methods
Fig. 1 The measurement of the trochlea of the extensor tendon
Processing and Grouping of Upper Limb Specimens Fifteen upper extremity specimens from 11 young males were provided by the Department of Anatomy at Harbin Medical University, including 10 fresh frozen specimens and five formalin-fixed specimens. X-ray examination was performed and all 15 wrist joints were confirmed to have no degenerative or pathological changes. The 15 specimens were divided into three groups. Group A was comprised seven extremities that were anatomically observed in the neutral position of the wrist (dorsiflexion angle 0°). Group B was comprised seven extremities, which were fresh frozen specimens from subjects that underwent an initial ultrasonographic examination. This was followed by anatomical observation in the dorsiflexion 60° position. Group C was comprised the excised extensor retinaculum of the wrist, and the inner surface of this specimen was observed. This research focused on the extensor tendon of the mid-finger and the fourth compartment of the wrist extensor retinaculum. The fresh frozen specimens were thawed 12 h before the experiment. After pretreatment of the specimens, a chuck clamped the extensor digitorum. The specimens were then fixed on a loaded bracket. The chuck and tension meter were then connected by a thin steel wire. The tension meter was connected with weights, and a pulley at the turning point. A traction of 5 N was then loaded on each finger.
Ultrasonography Examination of the Specimens Specimens in Group B were examined by ultrasonography (Mylab90, 18 MHz high-frequency probe, Esaote Company, Italy). The relationship between extensor tendon and wrist extensor retinaculum and the morphological changes of the wrist extensor retinaculum were observed when the wrist dorsiflexion angle was adjusted from an angle of 0° to 60°, with each finger loaded with 5 N. An ultrasonic measuring tool determined the length and thickness of the wrist extensor retinaculum and the length of the trochlea.
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On tomographic ultrasound sagittal imaging, an extension line was made along the surface formed by the distal and proximal ends of the tendon. The trochlea length was the part of tendon that deviated from the extension line and produced a radian, which was measured on the image (Fig. 1). Anatomy of Specimens Wrists from Group A were fixed in the neutral position by using a kirschner wire, with each finger loaded with 5 N. After ultrasonographic examination, wrist specimens in Group B were fixed at an angle of 60° dorsiflexion, with each finger loaded with 5 N. All the specimens were placed in the freezer at -60 °C for 24 h, and then confirmed that specimens were frozen at the initial position. Specimens were frozen in gelatin for an additional 24 h, following which they were trimmed to a square shape and fixed using a milling machine (X53 K, Beijing First Machine Tool Plant, China). The specimens were chipped layer-by-layer in the sagittal plane, with 1 mm for each layer to expose the extensor tendon and wrist extensor retinaculum. Images that displayed the relationship between the extensor tendon and the wrist extensor retinaculum were photographed, following which immediate measurement of the length and thickness of the wrist extensor retinaculum was made. For Group C, the wrist extensor retinaculum was resected along two deep inserting flanks of the fourth compartment. The inner surface of the wrist extensor retinaculum was examined to observe aggregation of the interior fibers to the leading edge of the wrist extensor retinaculum. Statistical Analyses Data were described as the mean ± standard deviation. Differences between groups were analyzed by the Student’s t test. An a value of P \ 0.05 was considered
Cell Biochem Biophys
Fig. 2 Comparison of ultrasonographic images and anatomical images. a Ultrasonographic image in neutral position of the wrist; b anatomical image in neutral position of the wrist, with each finger loaded with 5 N; c ultrasonographic image at a wrist dorsiflexion
angle at 60°; d anatomical image at a wrist dorsiflexion angle at 60°, with each finger loaded with 5 N. The wrist extensor retinaculum is located between the two arrows. The extensor tendon (E), radius (R), lunate (L), and capitate bone (C) are also shown
statistically significant. Comparisons among groups with different wrist angles were performed using one-way analysis of variance (ANOVA), and pair-wise comparisons were conducted using the SNK-q test. Statistical analyses were performed using the SPSS statistical software package (SPSS Inc., Chicago, IL, USA).
ultrasonographic images found for Group B. In addition, there was an insignificant difference seen in the length and thickness of the wrist extensor retinaculum measured on the anatomical image as compared to those of measured from the ultrasonographic images (2.018 ± 0.246 cm and 1.20 ± 0.082 mm vs. 2.136 ± 0.263 cm and 1.243 ± 0.079 mm, P [ 0.05). For wrist dorsiflexion at an angle of 60°, the ultrasonographic images from Group B showed that the wrist extensor retinaculum was an inverted triangle structure with a blunt turn angle. Furthermore, extensor tendons were lined below the wrist extensor retinaculum with a smooth transition, and the contact interface of the extensor tendons and the wrist extensor retinaculum was smooth (Fig. 2c). The rotation of the extensor tendons occurred in the middle wrist extensor retinaculum and there was no evidence of a sharp turn angle or collision. Additionally, the entire wrist extensor retinaculum moved toward the proximal end. By contrast, the distal part of the wrist extensor retinaculum moved toward the dorsal side (Fig. 2c). The morphological anatomy results were essentially consistent with those determined by ultrasonography. However, anatomical images showed more clearly the movement of the major part of the wrist extensor retinaculum to the dorsal side of the distal radius (Fig. 2d). No
Results Ultrasonographic as Compared with Anatomical Images Ultrasonography was performed for Group B in the neutral position of the wrist. In the sagittal plane, the wrist extensor retinaculum was displayed as a mixed hypoechoic structure. The major part of the wrist extensor retinaculum was located at the dorsal side of the semilunar bone as a flake structure, and it was continuous with a deep fascia from the posterior forearm to the dorsum of the hand. The extensor tendon showed heterogeneous and medium level echoes in a cord-like shape (Fig. 2a). There was a hyperechoic shadow on the surface of the radius, semilunar bone, and the capitate bone. Anatomical images of Group A (Fig. 2b) were essentially consistent with the
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Fig. 3 The images show morphological changes of the wrist extensor retinaculum at angles of 0° to 60° of the wrist dorsiflexion. a The wrist extensor retinaculum was flake shaped at 0°; b the wrist extensor retinaculum was spindle shaped at 15°; c the wrist extensor retinaculum was spindle shaped at 30°; d the wrist extensor
retinaculum was spindle shaped at 45°; e the wrist extensor retinaculum in the shape of an inverted triangle with a blunt turn angle. The wrist extensor retinaculum is located between two arrows. The extensor tendon (E), radius (R), lunate (L), and capitate bone are also shown (C)
significant difference was seen between the wrist extensor retinaculum parameters measured on the anatomical images (1.404 ± 0.151 cm in length; 2.429 ± 0.399 mm in thickness) and those measured from the ultrasonographic images (1.526 ± 0.186 cm in length; 2.514 ± 0.414 mm in thickness), P [ 0.05. The consistency of the morphological anatomy observations and ultrasonographic examinations suggested that ultrasonographic assessment could accurately identify wrist extensor retinaculum and extensor tendons.
wrist extensor retinaculum changed from flake to spindle, and finally to triangle with a blunt turn angle (Fig. 3). However, the contact interface between the extensor tendons and the wrist extensor retinaculum was always smooth. For the wrist dorsiflexion at an angle of 0°, the wrist extensor retinaculum was the mixed hypoechoic structure that was located at the dorsal side of the extensor tendons in the shape of flake (Fig. 3a). Extensor tendons showed heterogeneous and medium level echoes in a cord-like shape. For the wrist dorsiflexion at an angle of 15°, the wrist extensor retinaculum was arc shaped at the dorsal side of the extensor tendons (Fig. 3b1, b2). The length of the wrist extensor retinaculum was shorter, and its thickness was increased. The changes occurred in the anterior and middle portions of the extensor retinaculum. The rotation of the
Morphological Changes of the Wrist Extensor Retinaculum During Wrist Dorsiflexion Ultrasonographic findings showed that along with wrist dorsiflexion at angles from 0° to 60°, the shape of the
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extensor tendons occurred in the middle part of the wrist extensor retinaculum, and the extensor retinaculum changed to a spindle shape. There was also evidence of a smooth contact interface between the extensor tendons and the wrist extensor retinaculum. For wrist dorsiflexion at an angle of 30°, the extensor tendons formed a smooth arc that was located below the trochlea that was formed by the wrist extensor retinaculum (Fig. 3c1, c2). The length of the trochlea was further shortened as compared to that of the wrist dorsiflexion at an angle of 15°. The thickness was also increased, and the radian decreased. The observed changes occurred predominantly in the anterior and middle part of the wrist extensor retinaculum. The anterior and middle part of the wrist extensor retinaculum moved toward the dorsal side and the entire wrist extensor retinaculum moved toward the proximal end. For wrist dorsiflexion at an angle of 45°, the extensor tendons were still smooth arc shaped below the trochlea that was formed by the wrist extensor retinaculum (Fig. 3d1, d2). The length of trochlea was further shortened, the thickness increased, and the radian decreased. The entire wrist extensor retinaculum had obvious morphological changes. It was seen that the arch-shaped trochlea was formed predominantly by the middle part of the wrist extensor retinaculum. The anterior and middle part of the wrist extensor retinaculum moved further toward the dorsal side, and the entire wrist extensor retinaculum moved further toward the proximal end. Ultrasonographic echoes of the wrist extensor retinaculum were also enhanced. For wrist dorsiflexion at an angle of 60°, the middle part of the wrist extensor retinaculum contributed to the formation of the arch-shaped trochlea (Fig. 3e1, e2). The wrist extensor retinaculum was inverted triangle shaped with a blunt turn angle. In addition, the anterior and middle part of the wrist extensor retinaculum moved further toward the dorsal side, and the entire wrist extensor retinaculum moved further toward the proximal end. There was significant deformation of the entire wrist extensor retinaculum. Ultrasonographic echoes of the wrist extensor retinaculum were enhanced, the length of the trochlea was shortened, its thickness was increased, and its radian was decreased. However, the extensor tendons retained a smooth arc shape, and there was no evidence of collision or compression. Additionally, the major part of the wrist extensor retinaculum moved to the distal radial articular surface. Using ultrasonographic image analysis and measurement, the trochlea length decreased gradually during wrist dorsiflexion from an angle of 15° to an angle of 30°–45° and finally to an angle of 60°. Pairwise comparisons between groups showed statistically significant differences (P \ 0.05) (Fig. 4).
Morphological Changes of the Inner Face of the Wrist Extensor Retinaculum During Wrist Dorsiflexion The anatomical studies of the wrist of Group C revealed that there were three layers, i.e., the synovial membrane,
Fig. 4 The trochlea lengths at different wrist dorsiflexion angles
Fig. 5 a The images show the synovial membrane, synovial fluid, and synovial membrane in the contact surface between the extensor tendons and the wrist extensor retinaculum. b Showing the anatomic image of the inner face of the wrist extensor retinaculum in the neutral position of wrist. c Showing morphological changes of the inner surface of the wrist extensor retinaculum on simulating the wrist dorsiflexion. E Showing the thickened anterior part of the wrist extensor retinaculum
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the synovia, and the synovial membrane at the contact surface between the extensor tendons and the wrist extensor retinaculum (Fig. 5a). Additionally, there was an obvious leading edge of the inner face and during wrist dorsiflexion, the anterior fibers aggregated toward the leading edge of the wrist extensor retinaculum, which flattened the leading edge, at least to an extent (Fig. 5c), and smoothed the inner surface of the wrist extensor retinaculum. The synovial membrane also formed wrinkles in the dispersed anterior fibers in an attempt to retain the entire wrist extensor retinaculum smooth during movement.
Discussion Ultrasonography is a non-invasive and real-time approach to the study of the superficial motor system. Previous studies [10–12] have helped to establish the theoretical foundation for high-frequency ultrasonographic diagnosis of tendon injury. In this study, ultrasonographic images were highly consistent with anatomical images, and there were no significant differences in either the length or the thickness of the wrist extensor retinaculum in the context of measurements taken from ultrasonographic images as compared to those of anatomic images. This suggested that ultrasound could be applied in both the description and research of the wrist extensor retinaculum. Previous studies on the cause of extensor tendon injury insist that the rotation of the tendons occurs in front of the wrist extensor retinaculum, and a sharp turn angle is formed [4–6, 9]. In this study, it was observed that the wrist extensor retinaculum formed different shaped smooth trochleas at different dorsiflexion angles, which aided the rotation of the extensor tendons. The contact surface of the wrist extensor retinaculum and extensor tendons was smooth, and no sharp turn angle existed. Extensor tendons entered the wrist extensor retinaculum from the proximal end, rotated toward the dorsal side, completed the rotation when it passed through the trochlea, and slipped out at the distal end toward the dorsal side of the palm. The morphological changes of the wrist extensor retinaculum during wrist dorsiflexion restrained the movement of the extensor tendons, which serves to prevent the bowstring effect, and thus helps avoid the sharp turn angle. Kutsumi et al. [13] measured the friction that occurred on the interface of the wrist extensor retinaculum and tendons of the extensor pollicis longus and extensor indicis. This group inferred that the spontaneous rupture of the tendons was related to the intensity of friction. The friction acted on the extensor pollicis longus tendon, and was greater than the friction that was observed to act on the extensor indicis tendon. This might explain why
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spontaneous tendon rupture occurred more often in the extensor pollicis longus than the extensor indicis. Friction was the product of the friction coefficient and pressure. The friction coefficient is determined by the property of two interfaces. There were two layers of the synovial membrane between the wrist extensor retinaculum and extensor tendons, so the friction coefficient (l) is substantially stable. Thus, the intensity of friction depends on the partial pressure distribution. According to the mechanical model established previously [9], with the tendon tension unchanged, if the dorsiflexion angle (A) increased, the pulley pressure (FN) increased, and thus the intensity of friction increased (F = l 9 FN). However, this study showed that when the dorsiflexion angle (A) increased, the trochlea length (L) was shortened, and the width (w) of the contact surface between the wrist extensor retinaculum and the extensor tendons almost remained the same, which led to shrinking of the contact surface between the wrist extensor retinaculum and the extensor tendon (A = L 9 w). Consequently, the gradually enhanced friction was focused on the gradually shrinking contact surface, which was a key risk factor of structure abrasion. Rice farmers usually put a wide handkerchief or wrist guard on their wrists and gymnasts use a baffle or a strong belt to fix their wrists. According to the results of our study, the above methods could prevent significant wrist dorsiflexion angle and stress concentration and thus prevent tendon abrasion. Based on observations from our study, the trochlea structure could be damaged via the resection of the leading edge of the wrist extensor retinaculum. Therefore, in surgical procedures, it is recommended to reserve the integrity of the wrist extensor retinaculum. In this study, we found that the wrist extensor retinaculum provided a trochlea for the extensor tendons during wrist dorsiflexion. When the dorsiflexion angel increased, the trochlea length decreased, leading to a focus of friction on the contact surface of the extensor tendons and the wrist extensor retinaculum. These effects contributed to extensor tendon injuries.
Conflict of interest The authors have declared that there was no real or perceived conflict of interest in regard the conduct of this study or in the writing of the typescript.
References 1. Shinoda, M., Motokawa, H., Suzuki, Y., & Ishihara, A. (1963). Pathological rupture of the Finger extensors caused by chronic tenosynovitis. Orthopedic Surgery, 14, 737–738. 2. Cooper, H. J., Shevchuk, M. M., Li, X., & Yang, S. S. (2009). Proliferative extensor tenosynovitis of the wrist in the absence of rheumatoid arthritis. American Journal of Hand Surgery, 34, 1827–1831.
Cell Biochem Biophys 3. Engkvist, O., & Lundborg, G. (1979). Rupture of the extensor pollicis longus tendon after fracture of the lower end of the radius—a clinical and microangiographic study. Hand, 11, 76–86. 4. Takami, H., Takahashi, S., & Inanami, H. (1991). Post-traumatic rupture of the extensor digitorum communis tendon. The Journal of Hand Surgery, 16, 327–328. 5. VanHeest, A. E., Luger, N. M., House, J. H., & Vener, M. (2007). Extensor retinaculum impingement in the athlete: A new diagnosis. American Journal of Sports Medicine, 35, 2126–2130. 6. Khazzam, M., Patillo, D., & Gainor, B. J. (2008). Extensor tendon triggering by impingement on the extensor retinaculum: A report of 5 cases. American Journal of Hand Surgery, 33, 1397–1400. 7. Tanaka, H., Mitsui, T., & Nishida, M. (1967). Spontaneous rupture of the common extensor tendons caused by agricultural work. Orthopedic Surgery, 18, 348–349. 8. Wilson, S. M., Dubert, T., & Rozenblat, M. (2006). Extensor tendon impingement in a gymnast. Journal of Hand Surgery, 31, 66–67.
9. Moore, J. S. (2002). Biomechanical models for the pathogenesis of specific distal upper extremity disorders. American Journal of Industrial Medicine, 41, 353–369. 10. Lee, J. C., & Healy, J. C. (2005). Normal sonographic anatomy of the wrist and hand. Radiographics, 25, 1577–1590. 11. Jacob, D., Cohen, M., & Bianchi, S. (2007). Ultrasound imaging of non-traumatic lesions of wrist and hand tendons. European Radiology, 17, 2237–2247. 12. Robertson, B. L., Jamadar, D. A., Jacobson, J. A., KalumeBrigido, M., Caoili, E. M., Margaliot, Z., et al. (2007). Extensor retinaculum of the wrist: Sonographic characterization and pseudotenosynovitis appearance. AJR American Journal of Roentgenology, 188, 198–202. 13. Kutsumi, K., Amadio, P. C., Zhao, C., Zobitz, M. E., & An, K. N. (2004). Measurement of gliding resistance of the extensor pollicis longus and extensor digitorum communis ii tendons within the extensor retinaculum. American Journal of Hand Surgery, 29, 220–224.
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ORIGINAL PAPER
Extensor Tendon Injury Due to Repetitive Wrist Dorsiflexion: Morphological Study of Extensor Retinaculum and Extensor Tendon Chang-long Zhou • Xin-tao Wang • Zhi-yong Chi Jing-long Yan
•
Ó Springer Science+Business Media New York 2014
Abstract Most etiological studies of extensor tendon injury were based on the normal anatomy of extensor tendon and extensor retinaculum of the wrist. Further understanding of the morphological changes of the extensor tendon and extensor retinaculum during wrist dorsiflexion might contribute to improved and more accurate understanding of the etiology. The morphology of the extensor tendon of the mid-finger and the fourth compartment of the wrist extensor retinaculum was studied by sonography, and the anatomy was studied in 15 extremities from 11 young male cadavers. Compared with anatomical images, ultrasonography provides similar morphological observations of the extensor retinaculum of the wrist and extensor tendon. Ultrasonography findings revealed that as the dorsiflexion angle changed, the extensor retinaculum of the wrist formed different shaped trochleas. The trochlea guides the rotation of the extensor tendon at the wrist, but it does not form a sharp corner with the extensor tendon; thus, the extensor tendon is not compressed. As the dorsiflexion angle increased from 0° to 60°, the length of the trochlea gradually decreases. The shortening of the trochlea length will lead to a smaller frictional contact area between the extensor tendon and the extensor retinaculum. Consequently, the friction is centralized. During wrist dorsiflexion, the extensor retinaculum provides a trochlea for the extensor tendon. Extensor tendon injury of repetitive wrist dorsiflexion might be caused by centralized friction at the small contact area.
C. Zhou X. Wang Z. Chi J. Yan (&) Department of Orthopaedics, The First Affiliated Hospital of Harbin Medical University, Harbin 150001, Heilongjiang, China e-mail: [email protected]
Keywords Repetitive wrist dorsiflexion Extensor retinaculum Extensor tendon Extensor tendon injury Ultrasonography Trochlea
Introduction Spontaneous tendon rupture is a relatively rare disease. Potential causes are usually as a consequence of fracture malunion, arthromeningitis, and rheumatoid arthritis [1–3]. However, in the absence of such causes, spontaneous tendon rupture also occurs in certain individuals that frequently repeat flexion and extension of the wrist or fingers, including athletes, pastry cooks, production line workers, painters, rice farmers, among others [4–8]. It has been previously inferred that extensor tendon rupture was due to the formation of a sharp turn angle at the leading edge of the wrist extensor retinaculum, which led to physical deterioration of the tendon [4]. Through a mechanical model, others have inferred that the rotation of the extensor tendon occurred at the leading edge of the wrist extensor retinaculum [9]. VanHeest et al. dissected 10 wrists and showed the clear leading edge of the wrist extensor retinaculum [5]. Both VanHeest et al. [5] and Khazzam et al. [6] believed that a collision occurred between the extensor tendon and the wrist extensor retinaculum. It was proposed that this collision caused extensor tendon rupture at the wrist extensor retinaculum. Consequently, the leading edge of the wrist extensor retinaculum was resected in surgical procedures [5, 6]. However, the studies described above were based on the normal anatomy of the extensor tendon and the wrist extensor retinaculum. Morphological studies of the extensor tendon and wrist extensor retinaculum can be used to assess flexion and extension maneuvers of the wrist and fingers,
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and can lead to more accurate appreciation of disease etiology. The structure and morphology of the extensor tendon of the mid-finger and the fourth compartment of the wrist extensor retinaculum during wrist dorsiflexion were assessed by sonography and anatomy in the current study. Additionally, the etiology of the extensor tendon rupture of repetitive wrist dorsiflexion was analyzed and comprehensively discussed.
Materials and Methods
Fig. 1 The measurement of the trochlea of the extensor tendon
Processing and Grouping of Upper Limb Specimens Fifteen upper extremity specimens from 11 young males were provided by the Department of Anatomy at Harbin Medical University, including 10 fresh frozen specimens and five formalin-fixed specimens. X-ray examination was performed and all 15 wrist joints were confirmed to have no degenerative or pathological changes. The 15 specimens were divided into three groups. Group A was comprised seven extremities that were anatomically observed in the neutral position of the wrist (dorsiflexion angle 0°). Group B was comprised seven extremities, which were fresh frozen specimens from subjects that underwent an initial ultrasonographic examination. This was followed by anatomical observation in the dorsiflexion 60° position. Group C was comprised the excised extensor retinaculum of the wrist, and the inner surface of this specimen was observed. This research focused on the extensor tendon of the mid-finger and the fourth compartment of the wrist extensor retinaculum. The fresh frozen specimens were thawed 12 h before the experiment. After pretreatment of the specimens, a chuck clamped the extensor digitorum. The specimens were then fixed on a loaded bracket. The chuck and tension meter were then connected by a thin steel wire. The tension meter was connected with weights, and a pulley at the turning point. A traction of 5 N was then loaded on each finger.
Ultrasonography Examination of the Specimens Specimens in Group B were examined by ultrasonography (Mylab90, 18 MHz high-frequency probe, Esaote Company, Italy). The relationship between extensor tendon and wrist extensor retinaculum and the morphological changes of the wrist extensor retinaculum were observed when the wrist dorsiflexion angle was adjusted from an angle of 0° to 60°, with each finger loaded with 5 N. An ultrasonic measuring tool determined the length and thickness of the wrist extensor retinaculum and the length of the trochlea.
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On tomographic ultrasound sagittal imaging, an extension line was made along the surface formed by the distal and proximal ends of the tendon. The trochlea length was the part of tendon that deviated from the extension line and produced a radian, which was measured on the image (Fig. 1). Anatomy of Specimens Wrists from Group A were fixed in the neutral position by using a kirschner wire, with each finger loaded with 5 N. After ultrasonographic examination, wrist specimens in Group B were fixed at an angle of 60° dorsiflexion, with each finger loaded with 5 N. All the specimens were placed in the freezer at -60 °C for 24 h, and then confirmed that specimens were frozen at the initial position. Specimens were frozen in gelatin for an additional 24 h, following which they were trimmed to a square shape and fixed using a milling machine (X53 K, Beijing First Machine Tool Plant, China). The specimens were chipped layer-by-layer in the sagittal plane, with 1 mm for each layer to expose the extensor tendon and wrist extensor retinaculum. Images that displayed the relationship between the extensor tendon and the wrist extensor retinaculum were photographed, following which immediate measurement of the length and thickness of the wrist extensor retinaculum was made. For Group C, the wrist extensor retinaculum was resected along two deep inserting flanks of the fourth compartment. The inner surface of the wrist extensor retinaculum was examined to observe aggregation of the interior fibers to the leading edge of the wrist extensor retinaculum. Statistical Analyses Data were described as the mean ± standard deviation. Differences between groups were analyzed by the Student’s t test. An a value of P \ 0.05 was considered
Cell Biochem Biophys
Fig. 2 Comparison of ultrasonographic images and anatomical images. a Ultrasonographic image in neutral position of the wrist; b anatomical image in neutral position of the wrist, with each finger loaded with 5 N; c ultrasonographic image at a wrist dorsiflexion
angle at 60°; d anatomical image at a wrist dorsiflexion angle at 60°, with each finger loaded with 5 N. The wrist extensor retinaculum is located between the two arrows. The extensor tendon (E), radius (R), lunate (L), and capitate bone (C) are also shown
statistically significant. Comparisons among groups with different wrist angles were performed using one-way analysis of variance (ANOVA), and pair-wise comparisons were conducted using the SNK-q test. Statistical analyses were performed using the SPSS statistical software package (SPSS Inc., Chicago, IL, USA).
ultrasonographic images found for Group B. In addition, there was an insignificant difference seen in the length and thickness of the wrist extensor retinaculum measured on the anatomical image as compared to those of measured from the ultrasonographic images (2.018 ± 0.246 cm and 1.20 ± 0.082 mm vs. 2.136 ± 0.263 cm and 1.243 ± 0.079 mm, P [ 0.05). For wrist dorsiflexion at an angle of 60°, the ultrasonographic images from Group B showed that the wrist extensor retinaculum was an inverted triangle structure with a blunt turn angle. Furthermore, extensor tendons were lined below the wrist extensor retinaculum with a smooth transition, and the contact interface of the extensor tendons and the wrist extensor retinaculum was smooth (Fig. 2c). The rotation of the extensor tendons occurred in the middle wrist extensor retinaculum and there was no evidence of a sharp turn angle or collision. Additionally, the entire wrist extensor retinaculum moved toward the proximal end. By contrast, the distal part of the wrist extensor retinaculum moved toward the dorsal side (Fig. 2c). The morphological anatomy results were essentially consistent with those determined by ultrasonography. However, anatomical images showed more clearly the movement of the major part of the wrist extensor retinaculum to the dorsal side of the distal radius (Fig. 2d). No
Results Ultrasonographic as Compared with Anatomical Images Ultrasonography was performed for Group B in the neutral position of the wrist. In the sagittal plane, the wrist extensor retinaculum was displayed as a mixed hypoechoic structure. The major part of the wrist extensor retinaculum was located at the dorsal side of the semilunar bone as a flake structure, and it was continuous with a deep fascia from the posterior forearm to the dorsum of the hand. The extensor tendon showed heterogeneous and medium level echoes in a cord-like shape (Fig. 2a). There was a hyperechoic shadow on the surface of the radius, semilunar bone, and the capitate bone. Anatomical images of Group A (Fig. 2b) were essentially consistent with the
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Fig. 3 The images show morphological changes of the wrist extensor retinaculum at angles of 0° to 60° of the wrist dorsiflexion. a The wrist extensor retinaculum was flake shaped at 0°; b the wrist extensor retinaculum was spindle shaped at 15°; c the wrist extensor retinaculum was spindle shaped at 30°; d the wrist extensor
retinaculum was spindle shaped at 45°; e the wrist extensor retinaculum in the shape of an inverted triangle with a blunt turn angle. The wrist extensor retinaculum is located between two arrows. The extensor tendon (E), radius (R), lunate (L), and capitate bone are also shown (C)
significant difference was seen between the wrist extensor retinaculum parameters measured on the anatomical images (1.404 ± 0.151 cm in length; 2.429 ± 0.399 mm in thickness) and those measured from the ultrasonographic images (1.526 ± 0.186 cm in length; 2.514 ± 0.414 mm in thickness), P [ 0.05. The consistency of the morphological anatomy observations and ultrasonographic examinations suggested that ultrasonographic assessment could accurately identify wrist extensor retinaculum and extensor tendons.
wrist extensor retinaculum changed from flake to spindle, and finally to triangle with a blunt turn angle (Fig. 3). However, the contact interface between the extensor tendons and the wrist extensor retinaculum was always smooth. For the wrist dorsiflexion at an angle of 0°, the wrist extensor retinaculum was the mixed hypoechoic structure that was located at the dorsal side of the extensor tendons in the shape of flake (Fig. 3a). Extensor tendons showed heterogeneous and medium level echoes in a cord-like shape. For the wrist dorsiflexion at an angle of 15°, the wrist extensor retinaculum was arc shaped at the dorsal side of the extensor tendons (Fig. 3b1, b2). The length of the wrist extensor retinaculum was shorter, and its thickness was increased. The changes occurred in the anterior and middle portions of the extensor retinaculum. The rotation of the
Morphological Changes of the Wrist Extensor Retinaculum During Wrist Dorsiflexion Ultrasonographic findings showed that along with wrist dorsiflexion at angles from 0° to 60°, the shape of the
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extensor tendons occurred in the middle part of the wrist extensor retinaculum, and the extensor retinaculum changed to a spindle shape. There was also evidence of a smooth contact interface between the extensor tendons and the wrist extensor retinaculum. For wrist dorsiflexion at an angle of 30°, the extensor tendons formed a smooth arc that was located below the trochlea that was formed by the wrist extensor retinaculum (Fig. 3c1, c2). The length of the trochlea was further shortened as compared to that of the wrist dorsiflexion at an angle of 15°. The thickness was also increased, and the radian decreased. The observed changes occurred predominantly in the anterior and middle part of the wrist extensor retinaculum. The anterior and middle part of the wrist extensor retinaculum moved toward the dorsal side and the entire wrist extensor retinaculum moved toward the proximal end. For wrist dorsiflexion at an angle of 45°, the extensor tendons were still smooth arc shaped below the trochlea that was formed by the wrist extensor retinaculum (Fig. 3d1, d2). The length of trochlea was further shortened, the thickness increased, and the radian decreased. The entire wrist extensor retinaculum had obvious morphological changes. It was seen that the arch-shaped trochlea was formed predominantly by the middle part of the wrist extensor retinaculum. The anterior and middle part of the wrist extensor retinaculum moved further toward the dorsal side, and the entire wrist extensor retinaculum moved further toward the proximal end. Ultrasonographic echoes of the wrist extensor retinaculum were also enhanced. For wrist dorsiflexion at an angle of 60°, the middle part of the wrist extensor retinaculum contributed to the formation of the arch-shaped trochlea (Fig. 3e1, e2). The wrist extensor retinaculum was inverted triangle shaped with a blunt turn angle. In addition, the anterior and middle part of the wrist extensor retinaculum moved further toward the dorsal side, and the entire wrist extensor retinaculum moved further toward the proximal end. There was significant deformation of the entire wrist extensor retinaculum. Ultrasonographic echoes of the wrist extensor retinaculum were enhanced, the length of the trochlea was shortened, its thickness was increased, and its radian was decreased. However, the extensor tendons retained a smooth arc shape, and there was no evidence of collision or compression. Additionally, the major part of the wrist extensor retinaculum moved to the distal radial articular surface. Using ultrasonographic image analysis and measurement, the trochlea length decreased gradually during wrist dorsiflexion from an angle of 15° to an angle of 30°–45° and finally to an angle of 60°. Pairwise comparisons between groups showed statistically significant differences (P \ 0.05) (Fig. 4).
Morphological Changes of the Inner Face of the Wrist Extensor Retinaculum During Wrist Dorsiflexion The anatomical studies of the wrist of Group C revealed that there were three layers, i.e., the synovial membrane,
Fig. 4 The trochlea lengths at different wrist dorsiflexion angles
Fig. 5 a The images show the synovial membrane, synovial fluid, and synovial membrane in the contact surface between the extensor tendons and the wrist extensor retinaculum. b Showing the anatomic image of the inner face of the wrist extensor retinaculum in the neutral position of wrist. c Showing morphological changes of the inner surface of the wrist extensor retinaculum on simulating the wrist dorsiflexion. E Showing the thickened anterior part of the wrist extensor retinaculum
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the synovia, and the synovial membrane at the contact surface between the extensor tendons and the wrist extensor retinaculum (Fig. 5a). Additionally, there was an obvious leading edge of the inner face and during wrist dorsiflexion, the anterior fibers aggregated toward the leading edge of the wrist extensor retinaculum, which flattened the leading edge, at least to an extent (Fig. 5c), and smoothed the inner surface of the wrist extensor retinaculum. The synovial membrane also formed wrinkles in the dispersed anterior fibers in an attempt to retain the entire wrist extensor retinaculum smooth during movement.
Discussion Ultrasonography is a non-invasive and real-time approach to the study of the superficial motor system. Previous studies [10–12] have helped to establish the theoretical foundation for high-frequency ultrasonographic diagnosis of tendon injury. In this study, ultrasonographic images were highly consistent with anatomical images, and there were no significant differences in either the length or the thickness of the wrist extensor retinaculum in the context of measurements taken from ultrasonographic images as compared to those of anatomic images. This suggested that ultrasound could be applied in both the description and research of the wrist extensor retinaculum. Previous studies on the cause of extensor tendon injury insist that the rotation of the tendons occurs in front of the wrist extensor retinaculum, and a sharp turn angle is formed [4–6, 9]. In this study, it was observed that the wrist extensor retinaculum formed different shaped smooth trochleas at different dorsiflexion angles, which aided the rotation of the extensor tendons. The contact surface of the wrist extensor retinaculum and extensor tendons was smooth, and no sharp turn angle existed. Extensor tendons entered the wrist extensor retinaculum from the proximal end, rotated toward the dorsal side, completed the rotation when it passed through the trochlea, and slipped out at the distal end toward the dorsal side of the palm. The morphological changes of the wrist extensor retinaculum during wrist dorsiflexion restrained the movement of the extensor tendons, which serves to prevent the bowstring effect, and thus helps avoid the sharp turn angle. Kutsumi et al. [13] measured the friction that occurred on the interface of the wrist extensor retinaculum and tendons of the extensor pollicis longus and extensor indicis. This group inferred that the spontaneous rupture of the tendons was related to the intensity of friction. The friction acted on the extensor pollicis longus tendon, and was greater than the friction that was observed to act on the extensor indicis tendon. This might explain why
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spontaneous tendon rupture occurred more often in the extensor pollicis longus than the extensor indicis. Friction was the product of the friction coefficient and pressure. The friction coefficient is determined by the property of two interfaces. There were two layers of the synovial membrane between the wrist extensor retinaculum and extensor tendons, so the friction coefficient (l) is substantially stable. Thus, the intensity of friction depends on the partial pressure distribution. According to the mechanical model established previously [9], with the tendon tension unchanged, if the dorsiflexion angle (A) increased, the pulley pressure (FN) increased, and thus the intensity of friction increased (F = l 9 FN). However, this study showed that when the dorsiflexion angle (A) increased, the trochlea length (L) was shortened, and the width (w) of the contact surface between the wrist extensor retinaculum and the extensor tendons almost remained the same, which led to shrinking of the contact surface between the wrist extensor retinaculum and the extensor tendon (A = L 9 w). Consequently, the gradually enhanced friction was focused on the gradually shrinking contact surface, which was a key risk factor of structure abrasion. Rice farmers usually put a wide handkerchief or wrist guard on their wrists and gymnasts use a baffle or a strong belt to fix their wrists. According to the results of our study, the above methods could prevent significant wrist dorsiflexion angle and stress concentration and thus prevent tendon abrasion. Based on observations from our study, the trochlea structure could be damaged via the resection of the leading edge of the wrist extensor retinaculum. Therefore, in surgical procedures, it is recommended to reserve the integrity of the wrist extensor retinaculum. In this study, we found that the wrist extensor retinaculum provided a trochlea for the extensor tendons during wrist dorsiflexion. When the dorsiflexion angel increased, the trochlea length decreased, leading to a focus of friction on the contact surface of the extensor tendons and the wrist extensor retinaculum. These effects contributed to extensor tendon injuries.
Conflict of interest The authors have declared that there was no real or perceived conflict of interest in regard the conduct of this study or in the writing of the typescript.
References 1. Shinoda, M., Motokawa, H., Suzuki, Y., & Ishihara, A. (1963). Pathological rupture of the Finger extensors caused by chronic tenosynovitis. Orthopedic Surgery, 14, 737–738. 2. Cooper, H. J., Shevchuk, M. M., Li, X., & Yang, S. S. (2009). Proliferative extensor tenosynovitis of the wrist in the absence of rheumatoid arthritis. American Journal of Hand Surgery, 34, 1827–1831.
Cell Biochem Biophys 3. Engkvist, O., & Lundborg, G. (1979). Rupture of the extensor pollicis longus tendon after fracture of the lower end of the radius—a clinical and microangiographic study. Hand, 11, 76–86. 4. Takami, H., Takahashi, S., & Inanami, H. (1991). Post-traumatic rupture of the extensor digitorum communis tendon. The Journal of Hand Surgery, 16, 327–328. 5. VanHeest, A. E., Luger, N. M., House, J. H., & Vener, M. (2007). Extensor retinaculum impingement in the athlete: A new diagnosis. American Journal of Sports Medicine, 35, 2126–2130. 6. Khazzam, M., Patillo, D., & Gainor, B. J. (2008). Extensor tendon triggering by impingement on the extensor retinaculum: A report of 5 cases. American Journal of Hand Surgery, 33, 1397–1400. 7. Tanaka, H., Mitsui, T., & Nishida, M. (1967). Spontaneous rupture of the common extensor tendons caused by agricultural work. Orthopedic Surgery, 18, 348–349. 8. Wilson, S. M., Dubert, T., & Rozenblat, M. (2006). Extensor tendon impingement in a gymnast. Journal of Hand Surgery, 31, 66–67.
9. Moore, J. S. (2002). Biomechanical models for the pathogenesis of specific distal upper extremity disorders. American Journal of Industrial Medicine, 41, 353–369. 10. Lee, J. C., & Healy, J. C. (2005). Normal sonographic anatomy of the wrist and hand. Radiographics, 25, 1577–1590. 11. Jacob, D., Cohen, M., & Bianchi, S. (2007). Ultrasound imaging of non-traumatic lesions of wrist and hand tendons. European Radiology, 17, 2237–2247. 12. Robertson, B. L., Jamadar, D. A., Jacobson, J. A., KalumeBrigido, M., Caoili, E. M., Margaliot, Z., et al. (2007). Extensor retinaculum of the wrist: Sonographic characterization and pseudotenosynovitis appearance. AJR American Journal of Roentgenology, 188, 198–202. 13. Kutsumi, K., Amadio, P. C., Zhao, C., Zobitz, M. E., & An, K. N. (2004). Measurement of gliding resistance of the extensor pollicis longus and extensor digitorum communis ii tendons within the extensor retinaculum. American Journal of Hand Surgery, 29, 220–224.
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