Pettine K A, Chao E Y, Kelly P J
Department of Orthopedics, Mayo Clinic/Mayo Foundation, Rochester, Minnesota 55905.
Clin Orthop Relat Res. 1993 Aug(293):18-27.
External fixator pins were inserted into tibiae of dogs under four in vivo loading conditions to examine the mechanism of pin loosening. Pins were quantitatively measured for pin torque resistance, and the pin tracts were studied radiographically and histologically. The pins holding an unstable fracture had more gross pin loosening. Pins also may become loose under static loads. Radiographic lucency of 1 mm or more in the cortical bone around a pin was evidence of gross pin loosening. Histologic examination showed that tight pin tracts were characterized by a lack of bone remodeling. Loose pin tracts were characterized by extensive bone resorption and inflammatory infiltrates. Pin loosening can be detected radiographically. Pin insertion technique is important to improve the initial pin torque resistance to minimize pin loosening. Sixty-nine percent of pins with an initial torque resistance of less than 68 Ncm became grossly loose compared with only 9% of pins with an initial torque resistance greater than 68 Ncm, regardless of the experimental group. Unstable external fracture fixation is another important factor in producing pin loosening. Pins loaded under unstable fracture fixation had the highest incidence of gross loosening. When applying an external fixator, the fracture rigidity should be critically evaluated and, if necessary, protected weight bearing must be introduced initially to minimize pin loosening.
在四种体内加载条件下，将外固定针插入犬的胫骨，以研究针松动的机制。对针的抗扭矩能力进行定量测量，并对针道进行放射学和组织学研究。固定不稳定骨折的针出现明显针松动的情况更多。在静载荷下针也可能会松动。针周围皮质骨出现1毫米或更宽的放射透亮区是明显针松动的证据。组织学检查显示，紧密针道的特征是缺乏骨重塑。松动针道的特征是广泛的骨吸收和炎症浸润。针松动可通过放射学检测到。针的插入技术对于提高初始针抗扭矩能力以尽量减少针松动很重要。初始抗扭矩能力小于68牛厘米的针中有69%出现明显松动，而初始抗扭矩能力大于68牛厘米的针中只有9%出现明显松动，无论实验组如何。不稳定的外固定是导致针松动的另一个重要因素。在不稳定骨折固定下加载的针出现明显松动的发生率最高。应用外固定器时，应严格评估骨折的刚度，如有必要，最初必须采用保护性负重以尽量减少针松动。
