| Objective:To develop a combined external fixation used for scapular fractures, and evaluate its biomechanical characteristics, looking forward to provide a new method for the surgical treatment of scapular fractures.Methods:(1) 40 adult intact scapular dry specimens (eighteen on the left and twenty-two on the right) were elected and numbered. Firstly, observe the general shape and regional anatomy of specimens, and then divide each of them into three zones:neck area of the scapular, the inside mesoscapula and inferior angle of scapula, measured to determine the fixing spot and depth. And then measure the length between glenoid cavity trailing edge midpoint and inside edge of scapula, length between glenoid cavity inferior border and inferior angle of scapular, length between medial mesoscapula and inferior angle of scapular, to confirm the length of stainless steel tube. The above lengths are measured by method of imageology and anatomy. Use protractor to measure the glenoid tilt angle:choose another additional six adult cadavers (four male and two female), fixed with 4% formalin, and then measure the angle between scapula and coronal plane to confirm the nail angle.(2) Based on the measurements, design the external fixation used for scapular body fractures.(3) Random selecting twelve samples of scapular dry specimens (eight right and four left), divide them to three random groups, marked as A, B and C. Saw the specimens horizontal to make fracture models. Based on the measurements, Group A is the experimental group, both Group B and C are control groups. Each specimens of Group A twist three screw vertically on axillary margin of scapular 1.0cm from glenoid cavity,1.0cm from inferior angle of scapular, and 1.0cm from medial mesoscapula, and fix them by using the external fixation. Each specimens of Group B are fixed by two piece of general six holes reconstruction plate on the inner and outside edge. Each specimens of Group C are fixed by one piece of general six holes reconstruction plate on the inner edge. Each group was tested by non-destructive and destructive axial compression and torsion experiment with data recorded.Result:(1) Measured value of scapular's related areas are as follows:the included Angle of the scapula and the coronal plane (P) was 34.7°±4.2°, range between 32°～39°. The glenoid tilt angle(O)was 8.2°±4.7°, range between 2°～16°, and all of them were retroversion; the length(L) of glenoid cavity trailing edge midpoint to margo medialis scapular was 101.2±7.1mm, The length(M) of glenoid cavity inferior border to inferior angle of scapular was 122.4±8.1mm; The length(N) of medial mesoscapula to inferior angle of scapular was 113.3±6.9mm; The thickness(A) of scapular to inferior angle 1.0cm was 6.8±2.4mm; the thickness(D) of scapular to lateral border and inferior border of glenoid cavity 1.0cm was 13.2±2.8mm; the thickness(J) of scapular to medial mesoscapula 1.0cm was 9.1±2.6mm.the data above supported screw fixing, and there was no significant difference between CT measure and anatomic measure.(2) We drew the picture according to the measurement, and then we adopted 304 stainless steel for production of combined external fixation, which included three screws, three pairs of connecting plates, three pairs of F-arm, three pairs of U-slot and three stainless steel tubes. The above materials could be assembled as a solid triangle with three sides lying on the same horizontal plane.(3) According to the thickness measurements of scapula's relevant area, combined external fixation and fixed fracture were stable when the screws broke contralateral cortical bone vertically by 1.5 thread at the spot to inferior angle of scapular 1.0cm, medial mesoscapula 1.0cm, lateral border and inferior border of glenoid cavity 1.0cm. Biomechanical testing results of the three kind of fixation are as follows:the maximum compressure and twisting intensity of the combined external fixation group (Group A) were 232.07±4.21N,4.31±1.24N-m; which in the couple of reconstruction plate group (Group B) were 354.25±3.56N, 9.26±0.87 N-m; which in the single reconstruction plate group (Group C) were 281.96±3.86N,4.00±1.37N-m. Referring to the anti-twisting capacity of combined external fixation, Group A was superior to the Group B, while inferior to the Group C; The capacity for anti-axial compression of Group A and Group C presented no significant difference, however, both of the two groups showing an inferior capacity compared to Group C.Conclusion:Combined external fixation could meet the biomechanical requirements of fixing scapular body fractures as similar as the single reconstruction plate. It provided some experimental evidence for clinical transition. |
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