Introduction
Methods
Experimental materials and equipment
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Matching sleeves: The two sleeves (Fig. 4) used were a set of standard sleeves, with centers identical to the center of the hole on the locking plate. The near eccentric sleeve had an eccentricity of 1 mm (Fig. 4 shows the 1 mm difference between H1 and H2). Figure 5 shows the side view of the sleeve. The drilling effects of the drill and matching sleeves are shown in Fig. 1.
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Forty-two left artificial femurs (SAWBONE, Shanghai Yino Culture Communication Co., LTD Company, FEL201912): Forty-two, six-hole left lateral femoral anatomical locking plates (titanium alloy, combined hole), 66 titanium alloy screws with a diameter of 5.0 mm and length of 40 mm, and 354 titanium alloy locking screws with a diameter of 5.0 mm and length of 55 mm were used.
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Mechanical test equipment: Instron 5569 mechanical tester (Norwood, MA, USA).
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Data collection: Bluehill 2 (Instron, USA).
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Image acquisition and analysis: VIC-3D (XR-9 M, Correlated Solutions Company, Westford, MA, USA).
Fracture fixation model and grouping
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Fracture model: In the 42 left artificial femurs, a horizontal osteotomy at a distance of 4.5 cm from the distal articular surface and a fracture model with a gap of 2 cm were established to simulate a comminuted fracture (AO/OTA 33-A3) (Fig. 7).
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Grouping: The 42 fracture models were divided into a control group and an experimental group. For the six cases in the control group (i.e., standard screw hole group, group X, X126), we used standard sleeves and drill. A six-hole distal femoral anatomical locking plate was used to fix the fracture. The femoral condyle was drilled with a standard sleeve, and six locking screws with a diameter of 5.0 mm and length of 55 mm were screwed into it. Drilling holes were made at positions 1, 2, and 6 at the proximal end of the fracture (“1” was closest to the fracture line and “6” was the farthest from it). For position 1, a titanium alloy screw with a diameter of 5.0 mm and length of 40 mm was used. For positions 5 and 6, titanium alloy screws with a diameter of 5.0 mm and length of 55 mm were used. The experimental group (i.e., the elliptical screw hole group, group N) was also fixed with the same steel plate. The screws and drilling methods at the part distal to the fracture were the same as those in the control group. For the proximal segment, the newly designed drill and sleeves were used to form an eccentric screw hole (i.e., eccentric to the proximal end). The locking screws were sequentially screwed in, in accordance with the grouping criterion. According to the number and distribution of screws in the part proximal to the fracture, the experimental group was divided into six subgroups (i.e., N126, N136, N1256, N1356, N12356, and N123456) with six cases in each group. The arrangement and grouping of the screws are shown in Table 1 and Figs. 6, 7.
Position | X126 | N126 | N136 | N1256 | N1356 | N12356 | N123456 |
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1 | X | N | N | N | N | N | N |
2 | X | N | N | N | N | ||
3 | N | N | N | N | |||
4 | N | ||||||
5 | N | N | N | N | |||
6 | X | N | N | N | N | N | N |