Sedrish S A, Moore R M, Kelly K, Martin G S, Burba D J
Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, USA.
Vet Surg. 1998 Mar-Apr;27(2):143-9. doi: 10.1111/j.1532-950x.1998.tb00111.x.
To determine and compare the in vitro pullout strength of 5.5-mm cortical versus 6.5-mm cancellous bone screws inserted in the diaphysis and metaphysis of adult equine third metacarpal (MCIII) bones, in threaded 4.5-mm cortical bone screw insertion holes that were then overdrilled with a 4.5-mm drill bit to provide information relevant to the selection of a replacement screw if a 4.5-mm cortical screw is stripped.
In vitro pullout tests of 5.5-mm cortical and 6.5-mm cancellous screws in equine MCIII bones.
Two independent cadaver studies each consisting of 14 adult equine MCIII bones.
Two 4.5-mm cortical screws were placed either in the middiaphysis (study 1) or distal metaphysis (study 2) of MCIII bones. The holes were then overdrilled with a 4.5-mm drill bit and had either a 5.5-mm cortical or a 6.5-mm cancellous screw inserted; screw pullout tests were performed at a rate of 0.04 mm/second until screw or bone failure occurred.
In diaphyseal bone, the screws failed in all tests. Tensile breaking strength for 5.5-mm cortical screws (997.5 +/- 49.3 kg) and 6.5-mm cancellous screws (931.6 +/- 19.5 kg) was not significantly different. In metaphyseal bone, the bone failed in all tests. The holding power for 6.5-mm cancellous screws (39.1 +/- 4.9 kg/mm) was significantly greater than 5.5-mm cortical screws (23.5 +/- 3.5 kg/mm) in the metaphysis. There was no difference in the tensile breaking strength of screws in the diaphysis between proximal and distal screw holes; however, the holding power was significantly greater in the distal, compared with the proximal, metaphyseal holes.
Although tensile breaking strength was not different between 5.5-mm cortical and 6.5-mm cancellous screws in middiaphyseal cortical bone, holding power of 6.5-mm cancellous screws was greater than 5.5-mm cortical screws in metaphyseal bone of adult horses.
If a 4.5-mm cortical bone screw strips in MCIII diaphyseal bone of adult horses, either a 5.5-mm cortical or 6.5-mm cancellous screw, however, would have equivalent pullout strengths. A 6.5-mm cancellous screw, however, would provide greater holding power than a 5.5-mm cortical screw in metaphyseal bone.
确定并比较在成年马第三掌骨（MCIII）骨干和干骺端拧入的5.5毫米皮质骨螺钉与6.5毫米松质骨螺钉的体外拔出强度，这些螺钉拧入的是4.5毫米皮质骨螺钉的螺孔，之后用4.5毫米钻头扩孔，以提供有关在4.5毫米皮质骨螺钉滑丝时选择替代螺钉的相关信息。
对马MCIII骨中的5.5毫米皮质骨螺钉和6.5毫米松质骨螺钉进行体外拔出试验。
两项独立的尸体研究，每项研究包括14根成年马的MCIII骨。
在MCIII骨的骨干中部（研究1）或远端干骺端（研究2）拧入两枚4.5毫米皮质骨螺钉。然后用4.5毫米钻头扩孔，再拧入5.5毫米皮质骨螺钉或6.5毫米松质骨螺钉；以0.04毫米/秒的速度进行螺钉拔出试验，直至螺钉或骨发生断裂。
在骨干骨中，所有试验中的螺钉均发生断裂。5.5毫米皮质骨螺钉（997.5±49.3千克）和6.5毫米松质骨螺钉（931.6±19.5千克）的拉伸断裂强度无显著差异。在干骺端骨中，所有试验中的骨均发生断裂。在干骺端，6.5毫米松质骨螺钉的把持力（39.1±4.9千克/毫米）显著大于5.5毫米皮质骨螺钉（23.5±3.5千克/毫米）。骨干近端和远端螺孔中螺钉的拉伸断裂强度无差异；然而，与近端干骺端螺孔相比，远端干骺端螺孔的把持力显著更大。
虽然在骨干中部皮质骨中5.5毫米皮质骨螺钉和6.5毫米松质骨螺钉的拉伸断裂强度无差异，但在成年马干骺端骨中，6.5毫米松质骨螺钉的把持力大于5.5毫米皮质骨螺钉。
如果成年马MCIII骨干皮质骨中的4.5毫米皮质骨螺钉滑丝，那么5.5毫米皮质骨螺钉或6.5毫米松质骨螺钉的拔出强度相当。然而，在干骺端骨中，6.5毫米松质骨螺钉比5.5毫米皮质骨螺钉的把持力更大。
