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Immunohistochemical Analysis of Wrist Ligament Innervation in Relation to Their Structural Composition
Immunohistochemical Analysis of Wrist Ligament Innervation in Relation to Their Structural Composition Elisabet Hagert, MD, Marc Garcia-Elias, MD, PhD, Sture Forsgren, MD, PhD, Björn-Ove Ljung, MD, PhD From the Department of Hand Surgery, Karolinska Institutet, Inst of Clinical Research, Stockholm Söder Hospital, Stockholm, Sweden; Department of Hand and Upper Extremity Surgery, Institut Kaplan, Barcelona, Spain; and the Department of Integrative Medical Biology, Section for Anatomy, Umeå University, Umeå, Sweden.
Purpose: To analyze ligament innervation and the structural composition of wrist ligaments to investigate the potential differences in sensory and biomechanical functions. Methods: The ligaments analyzed were the dorsal radiocarpal, dorsal intercarpal, scaphotriquetral, dorsal scapholunate interosseous, scaphotrapeziotrapezoid, radioscaphoid, scaphocapitate, radioscaphocapitate, long radiolunate, short radiolunate, ulnolunate, palmar lunotriquetral interosseous, triquetrocapitate, and triquetrohamate ligaments. The ligaments were harvested from 5 cadaveric, fresh-frozen specimens. By using the immunohistochemical markers p75, Protein Gene Product 9.5, and S-100 protein, the mechanoreceptors and nerve fibers could be identified. Results: The innervation pattern in the ligaments was found to vary distinctly, with a pronounced innervation in the dorsal wrist ligaments (dorsal radiocarpal, dorsal intercarpal, scaphotriquetral, dorsal scapholunate interosseous), an intermediate innervation in the volar triquetral ligaments (palmar lunotriquetral interosseous, triquetrocapitate, triquetrohamate), and only limited/occasional innervation in the remaining volar wrist ligaments. The innervation pattern also was reflected in the structural differences between the ligaments. When present, mechanoreceptors and nerve fibers were consistently found in the loose connective tissue in the outer region (epifascicular region) of the ligament. Hence, ligaments with abundant innervation had a large epifascicular region, as compared with the ligaments with limited innervation, which consisted mostly of densely packed collagen fibers. Conclusions: The results of our study suggest that wrist ligaments vary with regard to sensory and biomechanical functions. Rather, based on the differences found in structural composition and innervation, wrist ligaments are regarded as either mechanically important ligaments or sensory important ligaments. The mechanically important ligaments are ligaments with densely packed collagen bundles and limited innervation. They are located primarily in the radial, force-bearing column of the wrist. The sensory important ligaments, by contrast, are richly innervated although less dense in connective tissue composition and are related to the triquetrum. The triquetrum and its ligamentous attachments are regarded as key elements in the generation of the proprioceptive information necessary for adequate neuromuscular wrist stabilization. (J Hand Surg 2007;32A: 30 –36. Copyright © 2007 by the American Society for Surgery of the Hand.) Key words: Immunohistochemistry, ligaments, mechanoreceptors, proprioception, wrist.
oint stability is dependent on proper skeletal alignment, passive restraint from ligaments, and the muscular compressive forces acting on the joint. These components work together to ensure an anatomically, kinetically, and kinematically stable
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joint.1 Limited ligament disrupture does not automatically entail instability as long as there are motor tendons crossing the joint that can compensate for the ligament function failure. The concept of joint muscular stability is perceived to be influenced by the
Hagert et al / Innervation and Structure of Wrist Ligaments
proprioceptive information transmitted from the mechanoreceptors in ligaments and capsule, reacting to changes in joint angle, joint velocity, mechanical distortion, and changes in intra-articular pressure.2,3 Although the various concepts of carpal kinetics and kinematics have been studied extensively, little is yet known about the proprioceptive characteristics of the wrist. In a recently published article, we analyzed 7 wrist ligaments with regard to the presence of mechanoreceptors and nerves.4 Although certain ligaments were found to be richly innervated, others were found to have little innervation. Hence, it was suggested that wrist ligaments might have innate differences with regard to their respective roles in wrist proprioception and stability. The purpose of the present study was to analyze the innervation and structural composition of the 14 more important wrist ligaments to increase our knowledge on the proprioceptive and biomechanical functions.
Materials and Methods Materials The 14 ligaments analyzed in this study were excised from 5 fresh-frozen cadaver wrists, sampled from a unique collection at the Department of Anatomy at the University of Barcelona, where approval exists regarding scientific studies on anatomic specimens. In 3 of the specimens a precise determination of origin was possible (male cadavers aged 81, 66, and 66 years, respectively). The 2 remaining specimens were from approximately similarly aged female cadavers, albeit no exact age could be determined. The design of this study was approved by the Regional Ethical Review Board at the Karolinska Institutet in Stockholm, Sweden. Ligaments The ligaments obtained from all 5 subjects were as follows: dorsal radiocarpal (DRC), dorsal intercarpal (DIC), scaphotriquetral (STq), dorsal scapholunate interosseous (dSLI), scaphotrapeziotrapezoid (STT), radioscaphoid (RS), scaphocapitate (SC), radioscaphocapitate (RSC), long radiolunate (LRL), short radiolunate (SRL), ulnolunate (UL), palmar lunotriquetral interosseous (pLTqI), triquetrocapitate (TqC), and triquetrohamate (TqH) (Fig. 1). All ligaments were excised in their entirety, as close to the insertions into bone as possible. The longer ligaments (DRC, DIC, STq, RS, SC, RSC, LRL, UL) were suture-marked for orientation, from proximalto-distal or radial-to-ulnar. The radiocarpal and mid-
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Figure 1. Ligaments analyzed in this study as seen in the dorsal (A) and volar (B) wrist.
carpal joints were assessed during dissection, and no signs of ligament injury or osteoarthritis could be detected. Immunohistochemistry The ligaments were fixed overnight in a solution of 4% formaldehyde in 0.1 mol/L phosphate buffer, pH 7.0. They then were washed thoroughly in 4°C Tyrode’s solution (Milab, Malmö, Sweden) containing 10% sucrose. The ligaments were mounted in OCT embedding medium (Miles Laboratories, Naperville, IL), frozen in liquid propane chilled with liquid nitrogen, and stored at ⫺80°C. Series of 8-m–thick sections were cut with a cryostat, mounted on gelatin-coated glass slides, dried, and stained to show low-affinity neurotrophic receptor p75 (p75; Sigma, St. Louis, MO), Protein Gene Product (PGP) 9.5 (Biogenesis, Poole, UK), or S-100 protein (S-100; Sigma) immunoreactivity, or colored for hematoxylin (HTX)-eosin for tissue morphology. Each series contained 15 sections. In addition, the suture-marked ligaments were sectioned at each end, with the DIC and STq additionally sectioned in the middle. The sections from the different positions were thereafter mounted on the same slide for concurrent analysis of the various regions of the ligaments. Each section was analyzed with regard to the presence of innervation (mechanoreceptors/nerve fibers) and the structural composition (epifascicular/fascicular regions). Immunohistochemical Procedures Immunohistochemical staining used EnVision (DakoCytomation, Glostrap, Denmark) detection. With this technique, microwave antigen retrieval was used to show epitopes hidden by the formaldehyde fixation. The slides were placed in jars filled with 0.01
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mol/L citrate buffer (pH 6.0), thereafter boiled in a microwave oven at 650 W for 3 ⫻ 5 minutes. The slides were transferred to fresh citrate buffer solution at room temperature after each cycle. After cooling for 20 minutes, the sections were rinsed in phosphate-buffered saline (PBS) for 3 ⫻ 5 minutes, and thereafter incubated in a 1% Triton X-100 solution (Kebo Lab, Stockholm, Sweden) for 20 minutes, before another rinse in PBS for 3 ⫻ 5 minutes was performed. Incubation for 30 minutes in 1% H2O2 blocked endogenous peroxidase activity, and the slides were rinsed for 3 ⫻ 5 minutes in PBS once again. Incubation with normal 5% goat serum in PBS, supplemented with 0.1% bovine serum albumin, was performed for 15 minutes, followed by incubation with primary antibodies for 60 minutes at room temperature. After rinsing with PBS for 3 ⫻ 5 minutes and a new incubation with normal goat serum for 15 minutes, the secondary antibody complex was applied (Dako EnVision⫹, goat antirabbit immunoglobulin G conjugated to a peroxidase-tagged polymer, K4002; undiluted; DakoCytomation, Glostrup, Denmark), for a 30-minute incubation in room temperature. The sections were rinsed in PBS for 3 ⫻ 5 minutes once again and developed in diaminobenzidine solution for 5 minutes. Thereafter the sections were stained with Mayers HTX (Histolab, Gothenburg, Sweden) for general tissue morphology. The slides then were dehydrated and mounted in Pertex microscopy mounting medium (Histolab). When staining for PGP 9.5 was performed, the slides initially were pretreated with acid potassium permanganate (KMnO4) for 2 minutes,5 and then rinsed in PBS for 3 ⫻ 5 minutes before treatment with Triton X-100, as described previously. Antibodies Rabbit antiserum against p75, PGP 9.5, and S-100 were used. For a description of these antibodies and the control stainings performed, please refer to our previous study.4 Analysis and Imaging The immunohistochemical sections were examined using a microscope (Zeiss Axioskop II plus; Carl Zeiss MicroImaging, Göttingen, Germany), equipped with a digital camera (Olympus DP70; Olympus Optical, London, UK). The resulting digital images were labeled and mounted in an imaging program (Adobe Photoshop 8.0; Adobe Systems Inc, San Jose, CA) to allow adequate comparison of images. The autofluorescent component of eosin in HTX-
eosin staining enabled the HTX images to be captured using a fluorescence laser confocal microscope system (UltraVIEW ERS; Perkin Elmer, Wellesley, MA), courtesy of the Karolinska Institutet Visualization Core Facility.
Results Ligament Composition The tissue in the sections examined showed a structural composition typically encountered in ligaments, consisting of densely packed collagen fibers (fascicles) in the core of the ligament and surrounded by an area of loose connective tissue in the outer regions. The core henceforth is referred to as the fascicular region and the area with loose connective tissue is referred to as the epifascicular region. Although the ligaments showed a general resemblance with regard to ligament histology, the ratio of epifascicular to fascicular regions was found to vary greatly between the ligaments. When examining the histologic sections at the lowest magnification (⫻2.5), it became apparent that certain ligaments consisted predominately of fascicular regions, the densely packed collagen fibers covering a majority of the section analyzed. In these instances, the epifascicular region was observed as a minor entity in the margins of the section. Other ligaments, however, had a more equal magnitude of epifascicular/fascicular areas. The exception to this observation was the SRL, which was found to consist mostly of loose disorganized connective tissue. In Figure 2, the differences in ligament composition are shown. The UL (Fig. 2A) appears as a ligament composed mainly of densely packed, parallel collagen fibers. The SRL (Fig. 2B) is composed mostly of loose connective tissue, whereas the dSLI (Fig. 2C) has a prominent epifascicular and a deeper fascicular region. Mechanoreceptors In accordance with the methodology used in our previous publication,4 immunohistochemical markers targeted for mechanoreceptors, with their different compositions, were used to identify pacinian corpuscles (Fig. 3), Ruffini receptors, or unclassifiable mechanoreceptors. The mechanoreceptors were consistently found within the epifascicular layer, and located in the vicinity of nerve fibers and blood vessels. Innervation Pattern in the Ligaments A consistent observation regarding the magnitude of innervation in the ligaments, as visualized in staining
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Figure 2. Comparison of the variable structural compositions found in different wrist ligaments, as seen in HTX stains using an autofluorescent technique (magnification, ⫻10). (A) Section of a UL ligament showing predominately densely packed parallel collagen fibers. (B) Section of a SRL ligament consisting of disorganized loose connective tissue and no apparent collagenous structure. (C) Section of an STq ligament with a vascularized (A) and innervated (N) epifascicular region (E) located close to the surface of the ligament and collagenous structures found in the deeper fascicular layers (F).
for PGP 9.5, was that the ligaments with a large epifascicular region also showed a pronounced innervation, whereas ligaments with a predominant fascicular region of densely packed collagen had a limited innervation. The longer ligaments that were analyzed had been suture-marked for orientation (see the Materials and Methods section for more detail). Hence, we were able to study these ligaments with regard to possible regional variations in the innervation pattern. We found that the density of nerve structures and vessels appeared greater in the regions close to the ligament insertions.
Magnitude of Innervation in Ligaments The level of occurrence of nerves and/or mechanoreceptors was analyzed semiquantitatively in all of the ligaments. A distinct difference in the degree of innervation was observed between the ligaments (Table 1). A pronounced innervation was observed in the DRC, DIC, STq, and dSLI, where both nerves and mechanoreceptors were found in all of the sections studied from all of the specimens. An intermediate innervation was seen in the TqC, TqH, and pLTqI ligaments, with both nerves and mechanoreceptors in 3 of 5 studied specimens. A limited innervation pattern, with both nerves and mechanoreceptors in 1 of 5 studied specimens, was seen in the RSC, RS, STT, and UL ligaments. Occasional innervation was shown in the LRL and SC ligaments, with only scant occurrence of nerves in 3 of 5 and 2 of 5 specimens, respectively, and no mechanoreceptors. Finally, the SRL was found to be almost without innervation, with 1 single nerve ending in 1 of 5 studied specimens, and no mechanoreceptors.
Discussion
Figure 3. Pacinian corpuscle found in an STq ligament, p75 stain (magnification, ⫻63). Characteristic onion-like layers of the perineurial capsule (arrows) can be seen.
The results of our study suggest that wrist ligaments are not equal in composition and innervation, possibly indicating a difference with regard to sensory and biomechanical functions. Although the radial wrist ligaments were found to consist of densely packed collagen bundles and little innervation, the dorsal wrist ligament complex and the ligaments related to the triquetrum were found to have a rich occurrence
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Table 1. Semiquantitative Estimation of the Degree of Innervation Found in Each Wrist Ligament Excised From 5 Cadaveric Specimens DRC DIC STq dSLI TqC pLTqI TqH RS RSC STT UL LRL SC SRL
⫹⫹⫹ ⫹⫹⫹ ⫹⫹⫹ ⫹⫹⫹ ⫹⫹ ⫹⫹ ⫺ ⫺ ⫹⫹ ⫺ ⫹ ⫹ ⫺ ⫺
⫹⫹⫹ ⫹⫹⫹ ⫹⫹⫹ ⫹⫹ ⫹ ⫹⫹ ⫹⫹ ⫹⫹ ⫹ ⫺ ⫹⫹ ⫺ ⫺ ⫹
⫹⫹⫹ ⫹⫹⫹ ⫹⫹ ⫹⫹⫹ ⫹⫹ ⫹ ⫹ ⫹ ⫺ ⫹ ⫺ ⫺ ⫺ ⫺
⫹⫹⫹ ⫹⫹⫹ ⫹⫹⫹ ⫹⫹⫹ ⫹ ⫹⫹ ⫹⫹ ⫹ ⫹ ⫹ ⫺ ⫹ ⫹ ⫺
⫹⫹⫹ ⫹⫹⫹ ⫹⫹⫹ ⫹⫹ ⫹⫹ ⫹ ⫹⫹ ⫹ ⫹ ⫹⫹ ⫹ ⫹ ⫹ ⫺
Mean
Type
3 3 2.8 2.6 1.6 1.6 1.4 1 1 0.8 0.8 0.6 0.4 0.2
P P P P I I I L L L L O O R
⫹⫹⫹, richly innervated with several nerve fascicles (N) and mechanoreceptors (R); ⫹⫹, single N/R; ⫹, N but no R; ⫺, no signs of innervation. Type of innervation: P, pronounced; I, intermediate; L, limited; O, occasional; R, rare.
of nerves and mechanoreceptors. When present, the nerve fibers were consistently found in the epifascicular regions of the ligaments, with signs of a higher density of innervation close to the ligament insertions. The latter topographic observation correlates to previous observations on general ligament histology and function,6 as well as the findings in a recent publication on the distribution of mechanoreceptors in the human DRC.7 The epifascicular region of ligaments previously has been referred to as the epiligamentous sheath,8 denoting a structure surrounding, and not part of, a ligament. This area, however, has been proposed to be of importance for ligament nutrition and protection, as well as for providing support to the neurovascular bundles in the ligament.9 Therefore, we prefer to refer to this region as the epifascicular region, indicating that it is an area surrounding the fascicular collagen bundles, rather than a sheath surrounding the ligament. When analyzing the structural composition of the ligaments, distinct qualitative differences in ligament configuration became apparent. Ligaments with a pronounced innervation were found to have a relatively equal ratio of epifascicular to fascicular regions. Contrarily, ligaments with a limited innervation were found to consist of a larger area of collagen fibers and a smaller epifascicular region, as compared with the abundantly innervated ligaments. These morphologic diversities were correlated to the observation that the overall innervation was consis-
tently found within the epifascicular regions and not within the fascicular regions. Previous publications on the structural composition of wrist ligaments have shown variations in collagen configuration when comparing intrinsic (SLI-LTqI) and extrinsic (RSC-RL) ligaments.10 The extrinsic ligaments were reported to consist of a higher ratio of type I collagen compared with type III (81%:19%), as compared with the intrinsic ligaments, which showed a more equal composition of collagen types I and III (59%:41%). Although type I collagen is known to consist of tightly packed collagen fibrils, type III collagen is looser and shows greater flexible and elastic properties.11 In correlation to this, the extrinsic RSC and LRL ligaments in our study were found to consist mostly of densely packed collagen fibers and limited innervation, whereas the intrinsic dSLI and pLTqI ligaments had a more equal distribution of fascicular to epifascicular regions and, thus, greater occurrence of innervation. Furthermore, biomechanical studies on these ligaments have shown marked functional differences between the intrinsic and extrinsic ligaments with regard to viscoelastic behavior12 and tension levels,13 indicating that the differing structural composition of the ligaments correlates to differences in kinetic and kinematic capabilities. Based on these publications, and in conjunction with our findings on ligament innervation and composition, we propose that wrist ligaments have innately different prerequisites with regard to biome-
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chanical and sensory functions. Ligaments with a limited or occasional innervation, which display compact areas of collagen and minor epifascicular areas, are suggested to be mechanically important ligaments. Ligaments with rich innervation, on the other hand, are proposed to be sensory important ligaments, in addition to their kinetic and kinematic functions. Hence, the DRC, DIC, STq, and dSLI are suggested to be regarded as sensory important ligaments, whereas the SC, LRL, UL, STT, RS, and RSC should be regarded as mechanically important ligaments. The SRL, on the other hand, differs markedly from these groups of ligaments and is proposed to be regarded as a capsular reinforcement, rather than a ligament proper. When examining the overall distribution of innervation in the wrist, it became apparent that the dorsal wrist ligaments were consistently richly innervated, with nerves and mechanoreceptors found in all of the specimens studied. The volar wrist ligaments, on the other hand, were found to have a more variable innervation pattern. These findings are in agreement with our previously published findings on the innervation of selected wrist ligaments.4,14 Innervation of the dorsal wrist capsule and ligaments has been described to be supplied by the posterior interosseous nerve (PIN),15 with some minor contributions from the dorsal branch of the ulnar nerve and from the sensory branch of the radial nerve.16 A preserved joint innervation has been shown to enhance the regeneration capability of mechanoreceptors in reconstructed anterior cruciate ligaments17 and to restore the ligamentomuscular reflexes around the knee joint.18 Denervation of ligaments, on the other hand, have been shown to dramatically impair healing capabilities.19 Similarly, the PIN can be assumed to be important both for the regenerating and reinnervating capabilities of the richly innervated dorsal wrist ligaments. Hence, to routinely excise the PIN during procedures in the dorsal wrist might be a more invasive procedure, affecting the entire dorsal wrist ligament complex, than previously believed. Surgical techniques to approach the dorsal wrist capsule while causing the least possible damage to the nerve thus probably should be considered. However, further investigations still are needed to elucidate the true role of the PIN in a possible ligamentomuscular reflex of the wrist joint. It is of importance to relate the innervation patterns with the biomechanical functions of the studied ligaments. The kinetic and kinematic functions of the wrist have been proposed by Weber20 to be divided
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Figure 4. Ligaments associated with the triquetrum. The dorsal triquetral ligaments have a pronounced innervation (⫹⫹⫹), with nerves/mechanoreceptors found in all sections studied. The volar triquetral ligaments have an intermediate innervation (⫹⫹), with nerves/mechanoreceptors in 3 of 5 studied specimens.
into a force-bearing column, consisting of the radial side of the carpus (capitate, lunate, scaphoid), and a control column, consisting of the ulnar side of the wrist and, more particularly, centered around the triquetrum. Although the force-bearing column is responsible for transmitting major loads onto the distal radius, it is proposed that the triquetrum and the control column play an important role in maintaining kinematic stability throughout global wrist motion. The triquetrum is connected volarly to the lunate and the capitate via the strong pLTqI, TqC, and TqH ligaments (Fig. 4). These short ligaments are believed to be important in maintaining the stability of the proximal carpal row and across the midcarpal joint.21 Dorsally, a fan-shaped construction of large capsular ligaments, the DRC, DIC, and STq, create a unique arrangement described by Viegas et al22 as a “lateral V” construct. These ligaments are considered to have an important role in reinforcing the SLI and LTqI ligaments, preventing dorsal instability of the midcarpal joint by stabilizing the head of the capitate, and attributing a restriction to the dorsal lunate thought to prevent the development of VISI (volar intercalated segmental instability) deformity,23 all throughout a large range of wrist motion. From the previous discussion, it becomes apparent that all the ligaments related to the triquetrum—the LTqI, TqC, TqH, DRC, DIC, and STq—work together to stabilize the wrist throughout the entire range of wrist motion. These ligaments are all among the most innervated ligaments in the wrist. Thus, it appears that the triquetrum is not only a keystone in
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the kinematically important control column, but, in conjunction with its ligamentous attachments, is also a key element in the generation of proprioceptive information mediating neuromuscular control of the carpus throughout global wrist motion. The force-bearing column, on the other hand, is important in transmitting loads from the hand onto the forearm (ie, transmission of forces through the radial metacarpals to the distal carpal row [trapezoid, capitate] via the scaphoid-lunate articulation and finally onto the distal radius). These articulations are restricted by ligamentous attachments, of which we have analyzed the RSC, RS, SC, STT, dSLI, and LRL ligaments in the present study. Noting the composition and innervation pattern of these radial ligaments, it becomes apparent that they consist of large fascicular regions with only limited occurrence of innervation, the dSLI being an exception to this with its pronounced innervation pattern. Hence, it appears that the majority of the ligaments in the force-bearing column are compact collagenous structures designed for a kinetic function, rather than the proprioceptive potential found in the triquetral ligaments in the control column of the wrist. The authors wish to thank Ulla Hedlund for her skillful help with the tissue preparations. The authors also wish to express their sincere gratitude to Dr. Manuel Llusá, Department of Anatomy, University of Barcelona, for his generous assistance in the laboratory work. Received for publication July 19, 2006; accepted in revised form October 6, 2006. Supported by funding from the Swedish National Center for Research in Sports, Karolinska Institutet, and the Faculty of Medicine, Umeå University. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Corresponding author: Elisabet Hagert, MD, Karolinska Institutet, Department of Hand Surgery, Stockholm Söder Hospital, 118 83 Stockholm, Sweden; e-mail: [email protected]. Copyright © 2007 by the American Society for Surgery of the Hand 0363-5023/07/32A01-0004$32.00/0 doi:10.1016/j.jhsa.2006.10.005
References 1. Garcia-Elias M, Geissler WB. Carpal instabilities. In: Green DP, Hotchkiss RN, Pederson WC, Wolfe SW, eds. Green’s operative hand surgery. Philadelphia: Elsevier Churchill Livingstone, 2005:535– 604. 2. Johansson H, Sjolander P, Sojka P. A sensory role for the cruciate ligaments. Clin Orthop 1991;268:161–178. 3. Sjolander P, Johansson H, Djupsjobacka M. Spinal and supraspinal effects of activity in ligament afferents. J Electromyogr Kinesiol 2002;12:167–176. 4. Hagert E, Forsgren S, Ljung BO. Differences in the presence of mechanoreceptors and nerve structures between wrist ligaments may imply differential roles in wrist stabilization. J Orthop Res 2005;23:757–763.
5. Hansson M, Forsgren S. Immunoreactive atrial and brain natriuretic peptides are co-localized in Purkinje fibres but not in the innervation of the bovine heart conduction system. Histochem J 1997;29:329 –336. 6. Frank CB. Ligament structure, physiology and function. J Musculoskeletal Neuronal Interact 2004;4:199 –201. 7. Lin YT, Berger RA, Berger EJ, Tomita K, Jew JY, Yang C, An KN. Nerve endings of the wrist joint: a preliminary report of the dorsal radiocarpal ligament. J Orthop Res 2006;24:1225–1230. 8. Berger RA. The ligaments of the wrist. A current overview of anatomy with considerations of their potential functions. Hand Clin 1997;13:63– 82. 9. Chowdhury P, Matyas JR, Frank CB. The “epiligament” of the rabbit medial collateral ligament: a quantitative morphological study. Connect Tissue Res 1991;27:33–50. 10. Johnston RB, Seiler JG, Miller EJ, Drvaric DM. The intrinsic and extrinsic ligaments of the wrist. A correlation of collagen typing and histologic appearance. J Hand Surg 1995;20B:750 –754. 11. Riechert K, Labs K, Lindenhayn K, Sinha P. Semiquantitative analysis of types I and III collagen from tendons and ligaments in a rabbit model. J Orthop Sci 2001;6:68 –74. 12. Logan SE, Nowak MD. Intrinsic and extrinsic wrist ligaments: biomechanical and functional differences. ISA Trans 1988;27:37– 41. 13. Kristal P, Tencer AF, Trumble TE, North E, Parvin D. A method for measuring tension in small ligaments: an application to the ligaments of the wrist carpus. J Biomech Eng 1993;115:218 –224. 14. Hagert E, Ljung BO, Forsgren S. General innervation pattern and sensory corpuscles in the scapholunate interosseous ligament. Cells Tissues Organs 2004;177:47–54. 15. Ferreres A, Suso S, Ordi J, Llusa M, Ruano D. Wrist denervation. Anatomical considerations. J Hand Surg 1995; 20B:761–768. 16. Van de Pol GJ, Koudstaal MJ, Schuurman AH, Bleys RL. Innervation of the wrist joint and surgical perspectives of denervation. J Hand Surg 2006;31A:28 –34. 17. Shimizu T, Takahashi T, Wada Y, Tanaka M, Morisawa Y, Yamamoto H. Regeneration process of mechanoreceptors in the reconstructed anterior cruciate ligament. Arch Orthop Trauma Surg 1999;119:405– 409. 18. Tsuda E, Okamura Y, Otsuka H, Komatsu T, Tokuya S. Direct evidence of the anterior cruciate ligament-hamstring reflex arc in humans. Am J Sports Med 2001;29:83– 87. 19. Ivie TJ, Bray RC, Salo PT. Denervation impairs healing of the rabbit medial collateral ligament. J Orthop Res 2002;20: 990 –995. 20. Weber ER. Concepts governing the rotational shift of the intercalated segment of the carpus. Orthop Clin North Am 1984;15:193–207. 21. Garcia-Elias M. Kinetic analysis of carpal stability during grip. Hand Clin 1997;13:151–158. 22. Viegas SF, Yamaguchi S, Boyd NL, Patterson RM. The dorsal ligaments of the wrist: anatomy, mechanical properties, and function. J Hand Surg 1999;24A:456 – 468. 23. Mitsuyasu H, Patterson RM, Shah MA, Buford WL, Iwamoto Y, Viegas SF. The role of the dorsal intercarpal ligament in dynamic and static scapholunate instability. J Hand Surg 2004;29A:279 –288.
Purpose: To analyze ligament innervation and the structural composition of wrist ligaments to investigate the potential differences in sensory and biomechanical functions. Methods: The ligaments analyzed were the dorsal radiocarpal, dorsal intercarpal, scaphotriquetral, dorsal scapholunate interosseous, scaphotrapeziotrapezoid, radioscaphoid, scaphocapitate, radioscaphocapitate, long radiolunate, short radiolunate, ulnolunate, palmar lunotriquetral interosseous, triquetrocapitate, and triquetrohamate ligaments. The ligaments were harvested from 5 cadaveric, fresh-frozen specimens. By using the immunohistochemical markers p75, Protein Gene Product 9.5, and S-100 protein, the mechanoreceptors and nerve fibers could be identified. Results: The innervation pattern in the ligaments was found to vary distinctly, with a pronounced innervation in the dorsal wrist ligaments (dorsal radiocarpal, dorsal intercarpal, scaphotriquetral, dorsal scapholunate interosseous), an intermediate innervation in the volar triquetral ligaments (palmar lunotriquetral interosseous, triquetrocapitate, triquetrohamate), and only limited/occasional innervation in the remaining volar wrist ligaments. The innervation pattern also was reflected in the structural differences between the ligaments. When present, mechanoreceptors and nerve fibers were consistently found in the loose connective tissue in the outer region (epifascicular region) of the ligament. Hence, ligaments with abundant innervation had a large epifascicular region, as compared with the ligaments with limited innervation, which consisted mostly of densely packed collagen fibers. Conclusions: The results of our study suggest that wrist ligaments vary with regard to sensory and biomechanical functions. Rather, based on the differences found in structural composition and innervation, wrist ligaments are regarded as either mechanically important ligaments or sensory important ligaments. The mechanically important ligaments are ligaments with densely packed collagen bundles and limited innervation. They are located primarily in the radial, force-bearing column of the wrist. The sensory important ligaments, by contrast, are richly innervated although less dense in connective tissue composition and are related to the triquetrum. The triquetrum and its ligamentous attachments are regarded as key elements in the generation of the proprioceptive information necessary for adequate neuromuscular wrist stabilization. (J Hand Surg 2007;32A: 30 –36. Copyright © 2007 by the American Society for Surgery of the Hand.) Key words: Immunohistochemistry, ligaments, mechanoreceptors, proprioception, wrist.
oint stability is dependent on proper skeletal alignment, passive restraint from ligaments, and the muscular compressive forces acting on the joint. These components work together to ensure an anatomically, kinetically, and kinematically stable
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joint.1 Limited ligament disrupture does not automatically entail instability as long as there are motor tendons crossing the joint that can compensate for the ligament function failure. The concept of joint muscular stability is perceived to be influenced by the
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proprioceptive information transmitted from the mechanoreceptors in ligaments and capsule, reacting to changes in joint angle, joint velocity, mechanical distortion, and changes in intra-articular pressure.2,3 Although the various concepts of carpal kinetics and kinematics have been studied extensively, little is yet known about the proprioceptive characteristics of the wrist. In a recently published article, we analyzed 7 wrist ligaments with regard to the presence of mechanoreceptors and nerves.4 Although certain ligaments were found to be richly innervated, others were found to have little innervation. Hence, it was suggested that wrist ligaments might have innate differences with regard to their respective roles in wrist proprioception and stability. The purpose of the present study was to analyze the innervation and structural composition of the 14 more important wrist ligaments to increase our knowledge on the proprioceptive and biomechanical functions.
Materials and Methods Materials The 14 ligaments analyzed in this study were excised from 5 fresh-frozen cadaver wrists, sampled from a unique collection at the Department of Anatomy at the University of Barcelona, where approval exists regarding scientific studies on anatomic specimens. In 3 of the specimens a precise determination of origin was possible (male cadavers aged 81, 66, and 66 years, respectively). The 2 remaining specimens were from approximately similarly aged female cadavers, albeit no exact age could be determined. The design of this study was approved by the Regional Ethical Review Board at the Karolinska Institutet in Stockholm, Sweden. Ligaments The ligaments obtained from all 5 subjects were as follows: dorsal radiocarpal (DRC), dorsal intercarpal (DIC), scaphotriquetral (STq), dorsal scapholunate interosseous (dSLI), scaphotrapeziotrapezoid (STT), radioscaphoid (RS), scaphocapitate (SC), radioscaphocapitate (RSC), long radiolunate (LRL), short radiolunate (SRL), ulnolunate (UL), palmar lunotriquetral interosseous (pLTqI), triquetrocapitate (TqC), and triquetrohamate (TqH) (Fig. 1). All ligaments were excised in their entirety, as close to the insertions into bone as possible. The longer ligaments (DRC, DIC, STq, RS, SC, RSC, LRL, UL) were suture-marked for orientation, from proximalto-distal or radial-to-ulnar. The radiocarpal and mid-
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Figure 1. Ligaments analyzed in this study as seen in the dorsal (A) and volar (B) wrist.
carpal joints were assessed during dissection, and no signs of ligament injury or osteoarthritis could be detected. Immunohistochemistry The ligaments were fixed overnight in a solution of 4% formaldehyde in 0.1 mol/L phosphate buffer, pH 7.0. They then were washed thoroughly in 4°C Tyrode’s solution (Milab, Malmö, Sweden) containing 10% sucrose. The ligaments were mounted in OCT embedding medium (Miles Laboratories, Naperville, IL), frozen in liquid propane chilled with liquid nitrogen, and stored at ⫺80°C. Series of 8-m–thick sections were cut with a cryostat, mounted on gelatin-coated glass slides, dried, and stained to show low-affinity neurotrophic receptor p75 (p75; Sigma, St. Louis, MO), Protein Gene Product (PGP) 9.5 (Biogenesis, Poole, UK), or S-100 protein (S-100; Sigma) immunoreactivity, or colored for hematoxylin (HTX)-eosin for tissue morphology. Each series contained 15 sections. In addition, the suture-marked ligaments were sectioned at each end, with the DIC and STq additionally sectioned in the middle. The sections from the different positions were thereafter mounted on the same slide for concurrent analysis of the various regions of the ligaments. Each section was analyzed with regard to the presence of innervation (mechanoreceptors/nerve fibers) and the structural composition (epifascicular/fascicular regions). Immunohistochemical Procedures Immunohistochemical staining used EnVision (DakoCytomation, Glostrap, Denmark) detection. With this technique, microwave antigen retrieval was used to show epitopes hidden by the formaldehyde fixation. The slides were placed in jars filled with 0.01
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mol/L citrate buffer (pH 6.0), thereafter boiled in a microwave oven at 650 W for 3 ⫻ 5 minutes. The slides were transferred to fresh citrate buffer solution at room temperature after each cycle. After cooling for 20 minutes, the sections were rinsed in phosphate-buffered saline (PBS) for 3 ⫻ 5 minutes, and thereafter incubated in a 1% Triton X-100 solution (Kebo Lab, Stockholm, Sweden) for 20 minutes, before another rinse in PBS for 3 ⫻ 5 minutes was performed. Incubation for 30 minutes in 1% H2O2 blocked endogenous peroxidase activity, and the slides were rinsed for 3 ⫻ 5 minutes in PBS once again. Incubation with normal 5% goat serum in PBS, supplemented with 0.1% bovine serum albumin, was performed for 15 minutes, followed by incubation with primary antibodies for 60 minutes at room temperature. After rinsing with PBS for 3 ⫻ 5 minutes and a new incubation with normal goat serum for 15 minutes, the secondary antibody complex was applied (Dako EnVision⫹, goat antirabbit immunoglobulin G conjugated to a peroxidase-tagged polymer, K4002; undiluted; DakoCytomation, Glostrup, Denmark), for a 30-minute incubation in room temperature. The sections were rinsed in PBS for 3 ⫻ 5 minutes once again and developed in diaminobenzidine solution for 5 minutes. Thereafter the sections were stained with Mayers HTX (Histolab, Gothenburg, Sweden) for general tissue morphology. The slides then were dehydrated and mounted in Pertex microscopy mounting medium (Histolab). When staining for PGP 9.5 was performed, the slides initially were pretreated with acid potassium permanganate (KMnO4) for 2 minutes,5 and then rinsed in PBS for 3 ⫻ 5 minutes before treatment with Triton X-100, as described previously. Antibodies Rabbit antiserum against p75, PGP 9.5, and S-100 were used. For a description of these antibodies and the control stainings performed, please refer to our previous study.4 Analysis and Imaging The immunohistochemical sections were examined using a microscope (Zeiss Axioskop II plus; Carl Zeiss MicroImaging, Göttingen, Germany), equipped with a digital camera (Olympus DP70; Olympus Optical, London, UK). The resulting digital images were labeled and mounted in an imaging program (Adobe Photoshop 8.0; Adobe Systems Inc, San Jose, CA) to allow adequate comparison of images. The autofluorescent component of eosin in HTX-
eosin staining enabled the HTX images to be captured using a fluorescence laser confocal microscope system (UltraVIEW ERS; Perkin Elmer, Wellesley, MA), courtesy of the Karolinska Institutet Visualization Core Facility.
Results Ligament Composition The tissue in the sections examined showed a structural composition typically encountered in ligaments, consisting of densely packed collagen fibers (fascicles) in the core of the ligament and surrounded by an area of loose connective tissue in the outer regions. The core henceforth is referred to as the fascicular region and the area with loose connective tissue is referred to as the epifascicular region. Although the ligaments showed a general resemblance with regard to ligament histology, the ratio of epifascicular to fascicular regions was found to vary greatly between the ligaments. When examining the histologic sections at the lowest magnification (⫻2.5), it became apparent that certain ligaments consisted predominately of fascicular regions, the densely packed collagen fibers covering a majority of the section analyzed. In these instances, the epifascicular region was observed as a minor entity in the margins of the section. Other ligaments, however, had a more equal magnitude of epifascicular/fascicular areas. The exception to this observation was the SRL, which was found to consist mostly of loose disorganized connective tissue. In Figure 2, the differences in ligament composition are shown. The UL (Fig. 2A) appears as a ligament composed mainly of densely packed, parallel collagen fibers. The SRL (Fig. 2B) is composed mostly of loose connective tissue, whereas the dSLI (Fig. 2C) has a prominent epifascicular and a deeper fascicular region. Mechanoreceptors In accordance with the methodology used in our previous publication,4 immunohistochemical markers targeted for mechanoreceptors, with their different compositions, were used to identify pacinian corpuscles (Fig. 3), Ruffini receptors, or unclassifiable mechanoreceptors. The mechanoreceptors were consistently found within the epifascicular layer, and located in the vicinity of nerve fibers and blood vessels. Innervation Pattern in the Ligaments A consistent observation regarding the magnitude of innervation in the ligaments, as visualized in staining
Hagert et al / Innervation and Structure of Wrist Ligaments
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Figure 2. Comparison of the variable structural compositions found in different wrist ligaments, as seen in HTX stains using an autofluorescent technique (magnification, ⫻10). (A) Section of a UL ligament showing predominately densely packed parallel collagen fibers. (B) Section of a SRL ligament consisting of disorganized loose connective tissue and no apparent collagenous structure. (C) Section of an STq ligament with a vascularized (A) and innervated (N) epifascicular region (E) located close to the surface of the ligament and collagenous structures found in the deeper fascicular layers (F).
for PGP 9.5, was that the ligaments with a large epifascicular region also showed a pronounced innervation, whereas ligaments with a predominant fascicular region of densely packed collagen had a limited innervation. The longer ligaments that were analyzed had been suture-marked for orientation (see the Materials and Methods section for more detail). Hence, we were able to study these ligaments with regard to possible regional variations in the innervation pattern. We found that the density of nerve structures and vessels appeared greater in the regions close to the ligament insertions.
Magnitude of Innervation in Ligaments The level of occurrence of nerves and/or mechanoreceptors was analyzed semiquantitatively in all of the ligaments. A distinct difference in the degree of innervation was observed between the ligaments (Table 1). A pronounced innervation was observed in the DRC, DIC, STq, and dSLI, where both nerves and mechanoreceptors were found in all of the sections studied from all of the specimens. An intermediate innervation was seen in the TqC, TqH, and pLTqI ligaments, with both nerves and mechanoreceptors in 3 of 5 studied specimens. A limited innervation pattern, with both nerves and mechanoreceptors in 1 of 5 studied specimens, was seen in the RSC, RS, STT, and UL ligaments. Occasional innervation was shown in the LRL and SC ligaments, with only scant occurrence of nerves in 3 of 5 and 2 of 5 specimens, respectively, and no mechanoreceptors. Finally, the SRL was found to be almost without innervation, with 1 single nerve ending in 1 of 5 studied specimens, and no mechanoreceptors.
Discussion
Figure 3. Pacinian corpuscle found in an STq ligament, p75 stain (magnification, ⫻63). Characteristic onion-like layers of the perineurial capsule (arrows) can be seen.
The results of our study suggest that wrist ligaments are not equal in composition and innervation, possibly indicating a difference with regard to sensory and biomechanical functions. Although the radial wrist ligaments were found to consist of densely packed collagen bundles and little innervation, the dorsal wrist ligament complex and the ligaments related to the triquetrum were found to have a rich occurrence
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Table 1. Semiquantitative Estimation of the Degree of Innervation Found in Each Wrist Ligament Excised From 5 Cadaveric Specimens DRC DIC STq dSLI TqC pLTqI TqH RS RSC STT UL LRL SC SRL
⫹⫹⫹ ⫹⫹⫹ ⫹⫹⫹ ⫹⫹⫹ ⫹⫹ ⫹⫹ ⫺ ⫺ ⫹⫹ ⫺ ⫹ ⫹ ⫺ ⫺
⫹⫹⫹ ⫹⫹⫹ ⫹⫹⫹ ⫹⫹ ⫹ ⫹⫹ ⫹⫹ ⫹⫹ ⫹ ⫺ ⫹⫹ ⫺ ⫺ ⫹
⫹⫹⫹ ⫹⫹⫹ ⫹⫹ ⫹⫹⫹ ⫹⫹ ⫹ ⫹ ⫹ ⫺ ⫹ ⫺ ⫺ ⫺ ⫺
⫹⫹⫹ ⫹⫹⫹ ⫹⫹⫹ ⫹⫹⫹ ⫹ ⫹⫹ ⫹⫹ ⫹ ⫹ ⫹ ⫺ ⫹ ⫹ ⫺
⫹⫹⫹ ⫹⫹⫹ ⫹⫹⫹ ⫹⫹ ⫹⫹ ⫹ ⫹⫹ ⫹ ⫹ ⫹⫹ ⫹ ⫹ ⫹ ⫺
Mean
Type
3 3 2.8 2.6 1.6 1.6 1.4 1 1 0.8 0.8 0.6 0.4 0.2
P P P P I I I L L L L O O R
⫹⫹⫹, richly innervated with several nerve fascicles (N) and mechanoreceptors (R); ⫹⫹, single N/R; ⫹, N but no R; ⫺, no signs of innervation. Type of innervation: P, pronounced; I, intermediate; L, limited; O, occasional; R, rare.
of nerves and mechanoreceptors. When present, the nerve fibers were consistently found in the epifascicular regions of the ligaments, with signs of a higher density of innervation close to the ligament insertions. The latter topographic observation correlates to previous observations on general ligament histology and function,6 as well as the findings in a recent publication on the distribution of mechanoreceptors in the human DRC.7 The epifascicular region of ligaments previously has been referred to as the epiligamentous sheath,8 denoting a structure surrounding, and not part of, a ligament. This area, however, has been proposed to be of importance for ligament nutrition and protection, as well as for providing support to the neurovascular bundles in the ligament.9 Therefore, we prefer to refer to this region as the epifascicular region, indicating that it is an area surrounding the fascicular collagen bundles, rather than a sheath surrounding the ligament. When analyzing the structural composition of the ligaments, distinct qualitative differences in ligament configuration became apparent. Ligaments with a pronounced innervation were found to have a relatively equal ratio of epifascicular to fascicular regions. Contrarily, ligaments with a limited innervation were found to consist of a larger area of collagen fibers and a smaller epifascicular region, as compared with the abundantly innervated ligaments. These morphologic diversities were correlated to the observation that the overall innervation was consis-
tently found within the epifascicular regions and not within the fascicular regions. Previous publications on the structural composition of wrist ligaments have shown variations in collagen configuration when comparing intrinsic (SLI-LTqI) and extrinsic (RSC-RL) ligaments.10 The extrinsic ligaments were reported to consist of a higher ratio of type I collagen compared with type III (81%:19%), as compared with the intrinsic ligaments, which showed a more equal composition of collagen types I and III (59%:41%). Although type I collagen is known to consist of tightly packed collagen fibrils, type III collagen is looser and shows greater flexible and elastic properties.11 In correlation to this, the extrinsic RSC and LRL ligaments in our study were found to consist mostly of densely packed collagen fibers and limited innervation, whereas the intrinsic dSLI and pLTqI ligaments had a more equal distribution of fascicular to epifascicular regions and, thus, greater occurrence of innervation. Furthermore, biomechanical studies on these ligaments have shown marked functional differences between the intrinsic and extrinsic ligaments with regard to viscoelastic behavior12 and tension levels,13 indicating that the differing structural composition of the ligaments correlates to differences in kinetic and kinematic capabilities. Based on these publications, and in conjunction with our findings on ligament innervation and composition, we propose that wrist ligaments have innately different prerequisites with regard to biome-
Hagert et al / Innervation and Structure of Wrist Ligaments
chanical and sensory functions. Ligaments with a limited or occasional innervation, which display compact areas of collagen and minor epifascicular areas, are suggested to be mechanically important ligaments. Ligaments with rich innervation, on the other hand, are proposed to be sensory important ligaments, in addition to their kinetic and kinematic functions. Hence, the DRC, DIC, STq, and dSLI are suggested to be regarded as sensory important ligaments, whereas the SC, LRL, UL, STT, RS, and RSC should be regarded as mechanically important ligaments. The SRL, on the other hand, differs markedly from these groups of ligaments and is proposed to be regarded as a capsular reinforcement, rather than a ligament proper. When examining the overall distribution of innervation in the wrist, it became apparent that the dorsal wrist ligaments were consistently richly innervated, with nerves and mechanoreceptors found in all of the specimens studied. The volar wrist ligaments, on the other hand, were found to have a more variable innervation pattern. These findings are in agreement with our previously published findings on the innervation of selected wrist ligaments.4,14 Innervation of the dorsal wrist capsule and ligaments has been described to be supplied by the posterior interosseous nerve (PIN),15 with some minor contributions from the dorsal branch of the ulnar nerve and from the sensory branch of the radial nerve.16 A preserved joint innervation has been shown to enhance the regeneration capability of mechanoreceptors in reconstructed anterior cruciate ligaments17 and to restore the ligamentomuscular reflexes around the knee joint.18 Denervation of ligaments, on the other hand, have been shown to dramatically impair healing capabilities.19 Similarly, the PIN can be assumed to be important both for the regenerating and reinnervating capabilities of the richly innervated dorsal wrist ligaments. Hence, to routinely excise the PIN during procedures in the dorsal wrist might be a more invasive procedure, affecting the entire dorsal wrist ligament complex, than previously believed. Surgical techniques to approach the dorsal wrist capsule while causing the least possible damage to the nerve thus probably should be considered. However, further investigations still are needed to elucidate the true role of the PIN in a possible ligamentomuscular reflex of the wrist joint. It is of importance to relate the innervation patterns with the biomechanical functions of the studied ligaments. The kinetic and kinematic functions of the wrist have been proposed by Weber20 to be divided
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Figure 4. Ligaments associated with the triquetrum. The dorsal triquetral ligaments have a pronounced innervation (⫹⫹⫹), with nerves/mechanoreceptors found in all sections studied. The volar triquetral ligaments have an intermediate innervation (⫹⫹), with nerves/mechanoreceptors in 3 of 5 studied specimens.
into a force-bearing column, consisting of the radial side of the carpus (capitate, lunate, scaphoid), and a control column, consisting of the ulnar side of the wrist and, more particularly, centered around the triquetrum. Although the force-bearing column is responsible for transmitting major loads onto the distal radius, it is proposed that the triquetrum and the control column play an important role in maintaining kinematic stability throughout global wrist motion. The triquetrum is connected volarly to the lunate and the capitate via the strong pLTqI, TqC, and TqH ligaments (Fig. 4). These short ligaments are believed to be important in maintaining the stability of the proximal carpal row and across the midcarpal joint.21 Dorsally, a fan-shaped construction of large capsular ligaments, the DRC, DIC, and STq, create a unique arrangement described by Viegas et al22 as a “lateral V” construct. These ligaments are considered to have an important role in reinforcing the SLI and LTqI ligaments, preventing dorsal instability of the midcarpal joint by stabilizing the head of the capitate, and attributing a restriction to the dorsal lunate thought to prevent the development of VISI (volar intercalated segmental instability) deformity,23 all throughout a large range of wrist motion. From the previous discussion, it becomes apparent that all the ligaments related to the triquetrum—the LTqI, TqC, TqH, DRC, DIC, and STq—work together to stabilize the wrist throughout the entire range of wrist motion. These ligaments are all among the most innervated ligaments in the wrist. Thus, it appears that the triquetrum is not only a keystone in
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the kinematically important control column, but, in conjunction with its ligamentous attachments, is also a key element in the generation of proprioceptive information mediating neuromuscular control of the carpus throughout global wrist motion. The force-bearing column, on the other hand, is important in transmitting loads from the hand onto the forearm (ie, transmission of forces through the radial metacarpals to the distal carpal row [trapezoid, capitate] via the scaphoid-lunate articulation and finally onto the distal radius). These articulations are restricted by ligamentous attachments, of which we have analyzed the RSC, RS, SC, STT, dSLI, and LRL ligaments in the present study. Noting the composition and innervation pattern of these radial ligaments, it becomes apparent that they consist of large fascicular regions with only limited occurrence of innervation, the dSLI being an exception to this with its pronounced innervation pattern. Hence, it appears that the majority of the ligaments in the force-bearing column are compact collagenous structures designed for a kinetic function, rather than the proprioceptive potential found in the triquetral ligaments in the control column of the wrist. The authors wish to thank Ulla Hedlund for her skillful help with the tissue preparations. The authors also wish to express their sincere gratitude to Dr. Manuel Llusá, Department of Anatomy, University of Barcelona, for his generous assistance in the laboratory work. Received for publication July 19, 2006; accepted in revised form October 6, 2006. Supported by funding from the Swedish National Center for Research in Sports, Karolinska Institutet, and the Faculty of Medicine, Umeå University. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Corresponding author: Elisabet Hagert, MD, Karolinska Institutet, Department of Hand Surgery, Stockholm Söder Hospital, 118 83 Stockholm, Sweden; e-mail: [email protected]. Copyright © 2007 by the American Society for Surgery of the Hand 0363-5023/07/32A01-0004$32.00/0 doi:10.1016/j.jhsa.2006.10.005
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5. Hansson M, Forsgren S. Immunoreactive atrial and brain natriuretic peptides are co-localized in Purkinje fibres but not in the innervation of the bovine heart conduction system. Histochem J 1997;29:329 –336. 6. Frank CB. Ligament structure, physiology and function. J Musculoskeletal Neuronal Interact 2004;4:199 –201. 7. Lin YT, Berger RA, Berger EJ, Tomita K, Jew JY, Yang C, An KN. Nerve endings of the wrist joint: a preliminary report of the dorsal radiocarpal ligament. J Orthop Res 2006;24:1225–1230. 8. Berger RA. The ligaments of the wrist. A current overview of anatomy with considerations of their potential functions. Hand Clin 1997;13:63– 82. 9. Chowdhury P, Matyas JR, Frank CB. The “epiligament” of the rabbit medial collateral ligament: a quantitative morphological study. Connect Tissue Res 1991;27:33–50. 10. Johnston RB, Seiler JG, Miller EJ, Drvaric DM. The intrinsic and extrinsic ligaments of the wrist. A correlation of collagen typing and histologic appearance. J Hand Surg 1995;20B:750 –754. 11. Riechert K, Labs K, Lindenhayn K, Sinha P. Semiquantitative analysis of types I and III collagen from tendons and ligaments in a rabbit model. J Orthop Sci 2001;6:68 –74. 12. Logan SE, Nowak MD. Intrinsic and extrinsic wrist ligaments: biomechanical and functional differences. ISA Trans 1988;27:37– 41. 13. Kristal P, Tencer AF, Trumble TE, North E, Parvin D. A method for measuring tension in small ligaments: an application to the ligaments of the wrist carpus. J Biomech Eng 1993;115:218 –224. 14. Hagert E, Ljung BO, Forsgren S. General innervation pattern and sensory corpuscles in the scapholunate interosseous ligament. Cells Tissues Organs 2004;177:47–54. 15. Ferreres A, Suso S, Ordi J, Llusa M, Ruano D. Wrist denervation. Anatomical considerations. J Hand Surg 1995; 20B:761–768. 16. Van de Pol GJ, Koudstaal MJ, Schuurman AH, Bleys RL. Innervation of the wrist joint and surgical perspectives of denervation. J Hand Surg 2006;31A:28 –34. 17. Shimizu T, Takahashi T, Wada Y, Tanaka M, Morisawa Y, Yamamoto H. Regeneration process of mechanoreceptors in the reconstructed anterior cruciate ligament. Arch Orthop Trauma Surg 1999;119:405– 409. 18. Tsuda E, Okamura Y, Otsuka H, Komatsu T, Tokuya S. Direct evidence of the anterior cruciate ligament-hamstring reflex arc in humans. Am J Sports Med 2001;29:83– 87. 19. Ivie TJ, Bray RC, Salo PT. Denervation impairs healing of the rabbit medial collateral ligament. J Orthop Res 2002;20: 990 –995. 20. Weber ER. Concepts governing the rotational shift of the intercalated segment of the carpus. Orthop Clin North Am 1984;15:193–207. 21. Garcia-Elias M. Kinetic analysis of carpal stability during grip. Hand Clin 1997;13:151–158. 22. Viegas SF, Yamaguchi S, Boyd NL, Patterson RM. The dorsal ligaments of the wrist: anatomy, mechanical properties, and function. J Hand Surg 1999;24A:456 – 468. 23. Mitsuyasu H, Patterson RM, Shah MA, Buford WL, Iwamoto Y, Viegas SF. The role of the dorsal intercarpal ligament in dynamic and static scapholunate instability. J Hand Surg 2004;29A:279 –288.