Asnis S E, Ernberg J J, Bostrom M P, Wright T M, Harrington R M, Tencer A, Peterson M
Department of Biomechanics, Hospital for Special Surgery, New York, New York, USA.
J Orthop Trauma. 1996;10(7):462-9. doi: 10.1097/00005131-199610000-00003.
This study was designed to isolate and evaluate the parameters of host density, outer diameter (OD), root diameter (RD), and pitch in cancellous bone screw design and their effect on holding power. Special emphasis was placed on screw pitch, which has been evaluated infrequently in the literature. Three groups of stainless steel V thread screws (group I, OD 4.5 mm, RD 3.0 mm; group II, OD 6.4 mm, RD 3.5 mm; group III, OD 6.4 mm, RD 4.2 mm) were machined with progressive increases in pitch from 12 to 32 threads per inch (TPI). Two densities of synthetic cancellous bone material (Pedilen, Ottobock, Minneapolis, MN, U.S.A.), 0.15 g/ml and 0.22 g/ml, were then prepared and molded into sheets 1.9 cm thick and the screw threads completely engaged. Push-out tests were performed using a servohydraulic testing machine (MTS, Minneapolis, MN, U.S.A.). Fifteen trials of each screw were tested in each material. The effect on holding power of the different parameters of the custom screws in order of importance was (a) host material density, (b) OD (c) pitch, and (d) RD. The groups with a 6.4-mm OD had a much greater holding power than did the group with a 4.5-mm OD (p < 0.001). A decrease in screw pitch (increased threads per inch) did itself have a significant improved effect on fixation for all groups in both pedilen densities (p < 0.001). In the two 6.4-mm screw groups studied, the difference in the two root diameters (4.2 mm vs. 3.5 mm) showed the smaller root diameter to give a greater holding power in the less dense 0.15 g/ml pedilen (p < 0.001). In the more dense 0.22 g/ml pedilen there was no difference (p = 0.26) between the root diameters. To optimize holding power, cancellous screws may be designed with a decreased pitch (increased TPI) over those commercially available today. Cannulated screws must have a larger cancellous thread root diameter to leave room for the central cannulation; this may decrease their holding power in less dense cancellous bone but not in denser bone.
本研究旨在分离并评估松质骨螺钉设计中宿主密度、外径（OD）、根径（RD）和螺距等参数及其对把持力的影响。特别强调了螺距，该参数在文献中较少被评估。加工了三组不锈钢V型螺纹螺钉（第一组，外径4.5 mm，根径3.0 mm；第二组，外径6.4 mm，根径3.5 mm；第三组，外径6.4 mm，根径4.2 mm），螺距从每英寸12牙逐渐增加到32牙（TPI）。然后制备了两种密度的合成松质骨材料（Pedilen，奥托博克公司，美国明尼阿波利斯），分别为0.15 g/ml和0.22 g/ml，并将其模制成1.9 cm厚的板材，使螺钉螺纹完全啮合。使用伺服液压试验机（MTS，美国明尼阿波利斯）进行推出试验。每种螺钉在每种材料中进行15次试验。定制螺钉不同参数对把持力的影响按重要性排序为：（a）宿主材料密度，（b）外径，（c）螺距，（d）根径。外径为6.4 mm的组比外径为4.5 mm的组具有更大的把持力（p < 0.001）。在两种Pedilen密度下，螺距减小（每英寸牙数增加）本身对所有组的固定都有显著的改善效果（p < 0.001）。在研究的两个外径为6.4 mm的螺钉组中，两种根径（4.2 mm对3.5 mm）的差异表明，在密度较小的0.15 g/ml Pedilen中，较小的根径具有更大的把持力（p < 0.001）。在密度较大的0.22 g/ml Pedilen中，根径之间没有差异（p = 0.26）。为了优化把持力，松质骨螺钉的设计螺距可能要比目前市面上的产品更小（每英寸牙数增加）。空心螺钉必须有更大的松质骨螺纹根径，以便为中心插管留出空间；这可能会降低其在密度较小的松质骨中的把持力，但在密度较大的骨中则不会。
