| Background: Scapholunate dissociation is the most frequent disease in carpal instability. There are lots of data confirms the importance of the SLIL in stabilizing the scaphoid and lunate. The common symptom of scapholunate dissociation is wrist pain, even the occurrence of wrist arthritis. However, the correlative anatomy, diagnosis and therapy about scapholunate dissociation are still insufficiency. The purpose of this study was to comprehend the correlative knowledge on scapholunate dissociation deeply.Part one: Macromicrodissection study of intracarpal joints and ligamentsObjects: To observe and measure the anatomic properties of intracarpal articulation and partial carpal ligaments, such as the figuration of intracarpal joint, the relationship between scapholunate interval and wrist's coronary plane, the location and shape of intracarpal ligaments, the perforations or disruptions ratio of scapholunate interosseous ligament (SLIL) and lunotriquetral interosseous ligament (LTIL), and so on. Meanwhile, using observations made from adult human cadaver specimens, the histological anatomy of the SLIL were designed to determine if regional anatomic differences exist.Materials and methods: Sixty adult cadaver upper extremities were used in this investigation, including 18 fresh-frozen (10 right wrists, 8 left wrists) and 42 formalin-fixed (21 right wrists, 21 left wrists) specimens. All anatomic specimenswere obtained from our department of anatomy. Each specimen was screened to exclude the pre-existing osseous deformities. All specimens were dissected from a dorsal approach. All dissections were carried out under room temperature. The instruments were used in this study are as follows: operating knife, surgical forceps, surgical scissors, blood vessel forceps, and so on. Eight SLIL specimens were harvested and submitted to fix using 4% formic acid, then dehydrated and mounted in paraffin molds. After mounting the sections on glass, every section was stained with hematoxylin and eosin and viewed using standard light microscopy.Results: The anatomy measurement of SLIL and LTIL showed that among the three subregions, the proximal subregions is weakest; the dorsal and palmar subregions are stronger. According anatomic measure data, the dorsal trapezoid-to-second metacarpal (average width, 9.12 mm; average length, 3.13 mm; average thickness, 3.28 mm) and dorsal capitate-to-third metacarpal ligaments (average width, 11.87 mm; average length, 3.45 mm; average thickness, 3.03 mm) could match the size of dorsal SLIL by adequate modifying; however, the dorsal capitate-to-third metacarpal joint had the more similar outline to the scapholunate joint. There was one intraarticular ligament (average width, 0.25 mm; average length, 1.01 mm; average thickness, 0.23 mm), which was located between the 3rd/4th metacarpal and the capitate/hamate and provided stability for the 3rd metacarpal and capitate bone. This ligament existed in all of specimens. The histological observations shows the different structure between proximal SLIL subregion and dorsal(palmar) subregion, photomicrograph of a cross-section of the dorsal and palmar region of the SLIL displayed the classic architecture of a true ligament: multiple collagen fascicles separated by loose perifascicular tissue containing numerous neurovascular structure, while the proximal regions of SLIL demonstrating its fibrocartilagenous composition. The disruptions ratio of SLIL and LTIL in formalin-fixed specimens is higher than in fresh-frozen specimens obviously.Conclusions: The construction and shape of bone, ligament and articular in wrist are complicated. The stability of the third metacarpal bone was strengthened by the intracarpal ligament between the third metacarpal and capitate bone. Anatomically, the SLIL are composed of three discrete regions: dorsal, proximal (or membranous), and palmar. The SL ligaments are composed of true ligaments dorsally and palmary, asdefined by histological studies. Because of the high perforation ratio of SLIL and LTIL, arthrography rarely gives any additional information concerning the ligament tear. Arthroscopy is more informative than arthrography because it provides information concerning the exact location and extent of the tear.Part two: Biomechanical measurement on partial wrist ligaments:Objects: To find an ideal replacement for the reconstruction of injured SLIL, this study were designed to compare the anatomical and biomechanical properties of the subregions of the scapholunate interosseous ligament (SLIL) and two intracarpal ligaments.Materials and methods: Bone-ligament-bone specimens of the scaphoid-lunate, trapezoid-to-second metacarpal, capitate-to-third metacarpal were harvested for biomechanical analysis from fresh-frozen adult human cadaver arms. The specimens were stored at -20°C in tightly sealed containers. According to different subregion, the scaphoid-lunate interosseous ligaments were split to three parts by using a thin osteotome. Using an electric vernier caliper, their anatomical parameters were measured by the same investigator. Bone blocks were then embedded in commercially available dental base acrylic resin powder; the embedded specimens were mounted on a servo hydraulic materials testing system (MTS 858, USA) using a 10-kN load cell for all tensile tests. During the testing, the specimens were kept moist with saline to avoid dehydration. The ligaments were tested at a displacement rate of lOmm/min until failure, the force-versus-displacement curves were recorded for each specimen. Their respective load to failure and stiffness were calculated on the basis of force and displacement measurements and compared.Results: Among the 3 subregions of SLIL, the dorsal and palmar ligaments had an almost equivalent load to failure [ie, (170.2±35.1) N and (193.1±42.3) N, respectively. P>0.05] and stiffness[ie, (80.7±13.8)N/mm and (72.3±22.8)N/mm, respectively. P>0.05], and the proximal ligament had the greatest minimum load to failure [(51.1±16.1) N] and stiffness [(21.6±11.0) N/mm]. The load to failure of trapezoid-to-second metacarpal and capitate-to-third metacarpal ligaments was (228.9±52.8) N and (277.6±66.2) N, respectively; their stiffness was (100.2±48.2)N/mm and (143.6±44.1)N/mm, which means that they had strongermechanical property than the dorsal SLIL. According anatomic measure data, the trapezoid-to-second metacarpal and capitate-to-third metacarpal ligaments could match the size of dorsal SLIL by adequate modifying; however, the capitate-to-third metacarpal joint had the more similar outline to the scapholunate joint.Conclusions: In all the three subregions of SLIL, the dorsal and palmar subregion had an almost equivalent load to failure and stiffness; the proximal subregion had the weakest biomechanical characteristics. Because of the similar anatomical and biomechanical characteristic, the trapezoid-to-second metacarpal and capitate-to-third metacarpal ligaments could be considered as an appropriate surrogate for the dorsal SLIL subregion.Part three: Model reconstructions of radiocarpal joints with 3D laser scan techniqueObjects: In order to construct a convenient method for the three dimensional (3D) reconstruction of radiocarpal joint model, a new and rapid technique using 3D laser scanner was adapted. Another purpose of this study was to explore a nice method for the 3D measurement on the position alleosis of scaphoid and lunate during wrist joint movement.Materials and methods: Six fresh-frozen human cadaver upper extremities were used in this experiment. No joint abnormality was detected by radiographic examination. The specimens were stored at -20 °C in tightly sealed refrigerator and were allowed to thaw bathe using current water at room temperature in preparation for testing. All specimens were amputated at midforearm level 5cm from elbow joint. The radius and ulna were transfixed with a Steinmann pin with the forearm in neutral rotation. Both the radius and ulna were then sectioned, proximally scraped clean of soft tissue, and rigidly mounted in special holding devices using polymethylmethacrylate. 3D laser scan technique was used to reconstruct the three-dimensional model of radiocarpal joint. The scaphoid, lunate and radial bone was marked from wrist dorsal approach respectively. The wrist joint with marker was mounted on an apparatus which allows wrist joint motion in both flexion-extension and radial-ulnar deviation unconventionally and then scanned by 3D laser scanner at different wrist position. The surface of scaphoid, lunate and radial bone wasrescanned from different direction after the soft tissues around them were cleaned completely. The scan images were stored in computer and were analyzed with professional software for reverse engineering (Geomagic Studio 5). In this study, a high performance computer was employed to reconstruct the structure of the radiocarpal joints in three dimensions.Results: All structure reconstructed in this way could be displayed literally alone or in all. The dynamic state of scaphoid and lunate bone during radiocarpal joint movement could be displayed exactly, at the same time, the 3D positional parameter of scaphoid and lunate bone could be calculated exactly with professional software.Conclusions: Compared with previous method, the model of radiocarpal joint osseous structure reconstructed by 3D laser scan technique could satisfactorily display the anatomic relationship and dynamic state of radiocarpal joint simultaneously. Meanwhile, the 3D position change of scaphoid and lunate during wrist joint motion could be calculated exactly. This is a novel method for the 3D reconstruction and 3D position measurement of wrist bone.Part four: Effects of SLIL and its subregions on the movement of scaphoid and lunateObjects: According to the 3D laser scan and reconstruction technique established in our previous study, the 3D motion of scaphoid and lunate on the normal and sequential sectioning of SLEL subregions wrist joints during wrist flexion-extension and wrist radial-ulnar deviation were determined. The purpose of this study was to evaluate the stabilizing function of the SLIL and its subregions (ie. proximal, palmar and dorsal subregion) ligaments on the scaphoid and lunate in a biomechanical cadaver experiment.Materials and methods: The specimens used in this study were treated as the third part of our topic does, and were divided to five groups: the intact wrist, the wrist with proximal subregion of SLIL were sectioned, the wrist with proximal and dorsal subregion of SLIL were sectioned, the wrist with proximal and palmar subregion of SLIL were sectioned, the wrist with whole SLIL were sectioned. There are 6 specimens in each group. Static 3D scan data were collected for the marker of scaphoid, lunate, and distal radius in neutral wrist position (standard position). Thenall specimens were scanned during wrists radial-ulnar deviation (from radial deviation 25° to ulnar deviation 35°), at 5° increments, and during flexion-extension motion (from flexion 90° to extension 70°), at 10° increments. The scan data were stored in computer's hard disk and were analyzed by using professional software for reverse engineering. Because the carpal bones and its marker can be considered rigid bodies, the rotation motion of marker is equal to that of corresponding carpal bones marked. So the position change of scaphoid and lunate can be calculated by means of the calculation of its marker. Changes in carpal bone motion owing to ligament sectioning were analyzed by using analysis of variance (ANOVA) at each degree of wrist flexion-extension or radial-ulnar deviation. A P value of less than 0.05 was considered significant for these comparisons.Results: 1) In the intact specimen during wrist flexion-extension the scaphoid followed the wrist's flexion-extension movement, although to a lesser magnitude. Thus, when the wrist flexed 90° the scaphoid flexed (48.83±8.46) °, the lunate flexed (28.6±4.89) °. When the wrist extended 70°, the scaphoid extended (53.26±8.55) °, the lunate extended (34.3±11.64) °. At the same time, there was little out-of-plane movement in the plane of radial-ulnar deviation of the scaphoid and lunate during wrist flexion-extension. There was minimal scaphoid and lunate pronation-supination during wrist flexion-extension. In the intact specimen during wrist radial-ulnar deviation, the scaphoid flexed (7.40±2.55) ° and radial deviated (5.39±2.03) ° during radial deviation of 25°, and scaphoid extended (23.58±10.23) ° and ulnar deviated (19.92±5.88) ° during ulnar deviation of 35°. As to lunate, the lunate flexed (10.34±2.84) ° and radial deviated (4.00±2.13) ° during radial deviation of 25°, and lunate extended (12.07±5.36) °and ulnar deviated (15.29±4.67) °during ulnar deviation of 35°. There was minimal scaphoid and lunate pronation-supination during wrist radial-ulnar deviation. 2) The motion of scaphoid and lunate after SLIL or its subregions were sectioned. With sectioning of proximal subregions of the SLIL, no significant kinematics changes were observed in the scaphoid and lunate bones. After sectioning the proximal and palmar (or dorsal) subregions of the SLIL, there are some different movement were found compared with intact wrist specimen. Such as the increase radial-ulnar deviation motion of scaphoid during wrist flexion and extension, the increased palmar flex motion of scaphoid during wrist flexion, the increasedpalmar flex motion of scaphoid and decreased motion of lunate during wrist radial deviation. After sectioning the whole SLIL, there are obvious change on the motion of scaphoid and lunate during wrist motion, especially on flexion of scaphoid and lunate during wrist movement.Conclusions: During wrist radial-ulnar deviation and flexion-extension motion, the scaphoid and lunate bone have out of plane movement except for the same direction movement with wrist. SLIL and its dorsal, palmar subregion play an important role on the normal scaphoid and lunate movement. However, the proximal subregion of SLIL has no prominent effect on the motion of scaphoid and lunate. We conclude that the findings of this study point to the fact that no current theory can sufficiently explain wrist kinematics and stress once more the need for more 3-D in vivo studies in carpal kinematics, especially during continuous wrist motion.Part five: Effect of SLIL Sequential Sectioning on the Scapholunate IntervalObjects: This study evaluated the effects of sectioning the different scapholunate interosseous ligament subregions sequentially on the scapholunate interval, through which we can evaluate the role of different subregion of SLIL in maintain the normal scapholunate space, and provide a reference for the diagnosis of scapholunate dissociation.Materials and methods: Twelve fresh cadaver upper extremities were used in this study. The wrist x-rays were taken in the intact state, after the proximal subregion of SLIL were cut, after the proximal and dorsal subregion of SLBL were cut, after the proximal and palmar subregion of SLEL were cut, after all of the SLIL were cut. Each x-rays were taken at neutral and ulnar deviation position, at rest and under stress. Scapholunate interval measurements were made at the mid-scapholunate joint. Comparison of the data was performed using one-way ANOVA. The level of significance was attributed to P<0.05.Results: Sectioning of the proximal subregion of the SLIL did not change the scapholunate interval from the intact stage. Furthermore, additional sectioning of the dorsal or palmar subregion did not change scapholunate interval too. When the SLIL was sectioned completely, a small but statistically significant scapholunate interval change was noted. However, when the x-rays were taken at loaded wrist, thescapholunate intervals have significant changes compared with non-loaded wrist. The scapholunate interval has no significant difference between the neutral and ulnar position in all groups.Conclusions: This study demonstrated that the proximal subregion of SLIL has no significant effect in maintaining the normal scapholunate relationship. When the SLIL was damaged severely, the abnormal scapholunate interval could be found more easily on wrist stress x-ray than non-stress x-ray. Thus, the x-ray taken at stress position was useful in the diagnosis of scaphoid lunate dissociation, especially when the SLIL was not damaged completely.Summary: The apparent disparity of SLIL subregions were confirmed though the gross and histological observation. Therefore, the SLIL should be deepening study from subregion level. By using biomechanical contrasting study, it is indicated that there are suitable ligaments surrogate for dorsal SLIL, such as the the trapezoid-to-second metacarpal and capitate-to-third metacarpal ligament. In this study, a new and rapid technique using 3D laser scanner was adapted to reconstruct the 3D model of radiocarpal joint, and the 3D positional parameter of scaphoid and lunate bone could be calculated exactly with professional software. Subsequent studies by using this technique have shown that the dorsal subregion of SLIL play an important role on the movement of scaphoid and lunate. When the SLIL was damaged severely, the abnormal scapholunate interval could be found more easily on wrist stress x-ray than non-stress x-ray.
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