Halsey D, Fleming B, Pope M H, Krag M, Kristiansen T
University of Vermont College of Medicine, McClure Musculoskeletal Research Center, Department of Orthopaedics and Rehabilitation, Burlington 05401.
Clin Orthop Relat Res. 1992 May(278):305-12.
The integrity of the bone-pin interface is the critical link in the stability of external fixation systems. External fixation pins placed in cancellous metaphyseal bone frequently loosen over time, resulting in fixation failure and an increased risk of infection. To design an external fixation pin with optimal bone-metal interface strength in cancellous bone, a systematic study of various thread design features was performed. Combinations of pitch, tooth profile, and minor diameter in 5 mm self-tapping half pins were evaluated in coaxial pullout testing using a fresh bovine cancellous bone. A significant increase in pullout strength was found with a decrease in minor diameter. No statistical differences were found in pullout strength attributable to thread profile and pitch. There were no significant interactions between minor diameter and tooth profile or minor diameter and pitch. The data obtained suggest significantly greater holding power in cancellous bone can be achieved by using an external fixation pin with a smaller minor diameter or a larger interference. Additional pullout testing of five commercially available external fixator pins was performed. Of these, the two pins with the largest interference demonstrated greater pullout strength. Therefore, within a range of acceptable major diameters and adequate minor diameters for the torsional strength requirements, an optimal interference for cancellous pin application may exist and it may well be larger than that present in currently available external fixation pins.
骨-针界面的完整性是外固定系统稳定性的关键环节。置于干骺端松质骨的外固定针常随时间推移而松动，导致固定失败及感染风险增加。为设计一种在松质骨中具有最佳骨-金属界面强度的外固定针，对各种螺纹设计特征进行了系统研究。在新鲜牛松质骨上进行同轴拔出试验，评估了5mm自攻半针的螺距、牙型和小径的组合。发现随着小径减小，拔出强度显著增加。在拔出强度方面，未发现因螺纹牙型和螺距而产生的统计学差异。小径与牙型或小径与螺距之间不存在显著相互作用。所获数据表明，使用小径较小或过盈量较大的外固定针可在松质骨中实现显著更大的把持力。对五种市售外固定针进行了额外的拔出试验。其中，过盈量最大的两种针表现出更大的拔出强度。因此，在满足扭转强度要求的可接受大径范围和足够小径范围内，可能存在松质骨针应用的最佳过盈量，且其很可能大于现有外固定针的过盈量。
