| Objective: Fractures of the distal radius are the most common fractures of the upper extremity accounting for 17% of all fractures. No matter the extra-articular fracture or intra-articular fracture may lead to malunion. The major components of distal radius malunion are angulation, shortening, and incongruity of the articular surfaces. They may lead to pain, limited motion, and decreased grip strength, produce influence for wrist joint function, and affect life quality. There have been many studies about the treatment of this fracture, but since wrist joint is little and complex, only a few studies concerning the biomechanics of the wrist after distal radius fracture. The purpose of this research lies in to use pressure-sensitive film (Fuji) measure the biomechanics influence of wrist joint, after a radial osteotomy used to simulate the distal radius fracture, with angulations, shortening, and incongruity of the articular surfaces. This would offer a reference for the treatment of this fracture and for the orthopedic of this deformity.Methods: 12 cadaver upper extremities were amputated at the midhumeral level. Every specimen was free of radiographic deformities and degenerative changes. The flexor and extensor muscle mass was then dissected, the wrist capsule, interosseousmembrane, the pronator quadratus, triangular fibrocartilage complex, and palmar and dorsal radiocarpal ligaments were left intact. Fingers were amputated at the metacarpophalangeal joins. Each specimen was fixed to a loading jig. The humerus was held horizontal and the elbow was flexed 90 degrees. The jig allowed the wrist to be postured in any position. The following processes stimulated malunited distal radius fractures: resecting 1.0 cm of the radius starting approximately 3 cm proximal to the distal radial articular surface; using an external fixation device to join the distal fragment to the proximal portion of the radius, the distal radial articular surface was angulated dorsally by means of the external fixator from 0 degrees to 30 degrees from the original position, was angulated radially from 0 degrees to 20 degrees from the original position. Intra-articula distal radius fracture malunions were simulated in the following way: A sagittal osteotomy extending between the scaphoid and lunate facets was then created. Uncoupling the external fixator created subsequent scaphoid fossa depressions of 1, 2 and 3 mm. In the same way, the lunate fossa depressions of 1, 2 and 3 mm were created. And placing customized metal blocks in the osteotomy to obtain and maintain the desired grade of angulations or shortening at the distal joint level. The specimen was mounted on a testing apparatus, the wrist in neutral flexion/extension. Film was inserted into the joint through a small incision in the dorsal capsule. A total load of 150 N was applied to the wrist, and the wrist was loaded for 2 minuets. The contact pressureswere measured with a densitometer and a pressure conversion instrument designed for use with the film. The contact area was measured with software named AutoCAD2004. Statistical analyses were done on the data by using of SPSS10.0.Resultl.The contact area and pressure of the normal wrists: Analysis of the pressure-sensitive film reveals that contact location of the scaphoid and the lunate were separate, and on the volar side for both. The entire contact area(>0.3 MPa) is about 126.2±8.9 mm2, the mean pressure is about 0.355±0.032 MPa, the peak pressure is about 0.415±0.024 MPa, the lunate contact area is about 63.9±8.4 mm2, the mean pressure is about 0.354±0.035 MPa, the peak pressure is about 0.416±0.038 MPa; The scaphoid contact area is about 62.0±9.1 mm , the mean pressure is about 0.352±0.037 MPa, and the peak pressure is about 0.413±0.032 MPa.2. Models of radial shortening: With radial shortening, the contact location for scaphoid moved to radial, the contact location for lunate moved to ulnar. The 2 mm of radial shortening did not display a statistically (p > 0.01)different from the normal state at the contact area and pressure of scaphoid and lunate. The 4 mm and 6 mm of radial shortening displayed a significantly more (pO.Ol) contact area and pressure of lunate, a significantly less (pO.Ol) contact area and pressure of scaphoid.3. Models of dorsal inclination: As the distal articularsurface was angulated dorsally, the contact location for scaphoid and lunate moved to dorsal, the contact area and pressure for scaphoid and lunate changed. The 0 degrees of palmer tilt did not display a statistically (p>0.01) different from the normal state at the contact area and pressure of scaphoid and lunate. Beyond 10 degrees (10, 20, 30 degrees) dorsal tilt displayed a significantly more (p<0.01) contact area and pressure of lunate, a significantly less (p<0.01) contact area and pressure of scaphoid.4.Models of radial inclination: Both radial inclination 10 degrees and 20 degrees showed less (p<0.01) contact area and pressure of scaphoid, more (p<0.01) contact area and pressure of lunate when compared with the normal state, but there is not a statistically (p > 0.01) different between the 10 degrees and 20 degrees radial inclination.5.Models of scaphoid fossa depression (SFD): With increased SFD, there was a trend to decreased the contact area and pressure of scaphoid and increased the contact area and pressure of lunate. The 1 mm stepoff of scaphoid fossa depression did not display a statistically(p > 0.01 )different from the normal state at the contact area and pressure of scaphoid and lunate. It became significant (p<0.01) at 2 mm and 3 mm stepoff.6. Models of lunate fossa depression (LFD): The 1 mmstepoff of lunate fossa depression did not display a statistically(p > 0.01) different from the normal state at the contact area... |
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