| Objects:l.To investigate the mechanism of the carpal instability secondary to dorsally angulated malunited distal radius fractures so as to provide theory proofs of prevention and cure of carpal instability.2.A three-dimensional combination external fixator was applied to the unstable distal radius fracture,and its biomechanics property was studied and compared with cross K-wires,T-plate and Hizarov external fixator.The aim of the study is to bring forward an optimal treatment method for unstable distal radius fractures.Methods:1 .The gross anatomy, histologic description of palmar and dorsal radiocarpal ligament,and its biomechanics properties were studied by applying fresh-frozen and formalin-dip in cadaveric hand-wrist-forearm specimens.2.An experiment model of unstable distal radius fracture was made by a dorsally based wedge osteotomy used to stimulate a Frykman I distal radius fracture. A incision was made in the dorsal capsule to allow insertion of pressure-sensitive film (Fuji) into the radiocapal joint.The distribution of forces and changes in the pressure across the radiocarpal articular surface were analysed when the dorsal angulation of the distal radial fragment were increased from the normal palmar tilt to 50?of dorsal tilt.After this step finished,the palmar and dorsal radiocarpal ligaments was cut according to different test group,and then the same boimechanics test method of the experiment was operated again.X-ray films were then taken to evaluate carpal instability while the test of each group was being in theend.3.The three-dimensional movement of dorsal angulation was tested using the three-dimensional movement test system devised by the First Military Medical University.4.The cross K-wires,T-plate,nizarov fixator,and combination external fixator were installed to the unstable distal radius fracture,and its tiffness and the width change of wedge osteotomy gap were measured and compared.Results:l.The dorsal radiocarpal ligament was the most strongest of all wrist ligaments,and radiolunate ligament was the most strongest of palm radiocarpal ligaments.2.When the dorsal tilt exceeded 10?the radioscaphoid and radiolunate articular contact areas were markedly decreased(P<0.01)and shifted to the dorsal aspect of the radiocarpal joint,where the pressure load was significantly increased(P<0.01).A dorsal radiocarpal subluxation was liable to occur on the sagittal plane when the dorsal tilt exceeded 40?3.When the dorsal radiocarpal ligament was cut only and dorsal angulation exceeded 20?a dorsal radiocarpal subluxation would happen.Dorsal flexion instability(DISI) may appeared when radiolunate ligament only was cut and dorsal angulation was over 10?The dorsal radiocarpal subluxation and DISI would emerge when DRC ligament and radiolunate ligament were cut together and dorsal angulation was over 10?4.The three-dimensional kinematics analysis of palm tilt change of distal radius fracture showed that vorsal flextion,ulnar deviation,and pronation and supination were statistically decreased(P<0.01)when dorsal angulation excessed 10?5.The combination external fixator was not statistically different from the T-plateand and flizarov fixator in stiffness of compression,anteroposterior, and lateral bend,and cross K-wires was statistically different from the T-plate,the Ilizarov fixator, and the combination external fixator(P<0.01).Conclusions:1.The results showed that dorsal angulation over 10?caused statistically changes of the load distributions and contract areas of radiocarpal joint,and suggested that the change in dorsal angulation over 10?will result in the malaliganment of the articular surfaces and ligament disruption in the end after distal radius fracture and be the primary cause of carpal instability due to united distal radius fracture.2.Carpal instability can occur early in distal radius fracture when ligaments disruption of wrist joint exist.Therefore,the carpal instability diagnosis comfirmed by X-ray should be emphasized early after di...
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