Donahue S W, Sharkey N A, Modanlou K A, Sequeira L N, Martin R B
Musculoskeletal Research Laboratory, The Pennsylvania State University, Hershey, PA 17033-0850, USA.
Bone. 2000 Dec;27(6):827-33. doi: 10.1016/s8756-3282(00)00402-6.
Microcracks in bone have been implicated in the development of stress fractures. The goal of this study was to evaluate bone strain and microcracks at locations where stress fractures are common (second metatarsal diaphysis) and rare (fifth metatarsal diaphysis) in an attempt to increase our understanding of the pathogenesis of stress fractures. A dynamic gait simulator was used to simulate normal walking with cadaver feet. The feet were loaded over the entire stance phase of gait and diaphyseal strains were recorded in second and fifth metatarsals. Microcrack density (Cr.Dn) and surface density (Cr.S.Dn) were determined in metatarsal cross sections from the contralateral feet. Bone strain was significantly higher in second metatarsals (-1897 +/- 613 microstrain) than in fifth metatarsals (-908 +/- 503 microstrain). However, second metatarsal Cr.Dn (0.23 +/- 0.15 #/mm(2)) was not significantly different from fifth metatarsal Cr.Dn (0.35 +/- 0.19 #/mm(2)). There was also no significant difference between Cr.S.Dn in second (17.64 +/- 10.99 microm/mm(2)) and fifth (26.70 +/- 15.53 microm/mm(2)) metatarsals. There were no significant relationships between the microcrack parameters and peak strain in either metatarsal. Cracks that occurred in trabecular struts (92 +/- 33 microm) were significantly longer than those found ending at cement lines (71 +/- 15 microm) and within osteons (57 +/- 16 microm). There were no significant relationships between the microcrack parameters and age in either metatarsal. Peak strain was more than twofold greater in second metatarsals than in fifth metatarsals for simulations of normal walking; however, microcrack parameters were unable to explain the greater incidence of second metatarsal stress fractures.
骨微裂纹与应力性骨折的发生有关。本研究的目的是评估应力性骨折常见部位（第二跖骨干）和罕见部位（第五跖骨干）的骨应变和微裂纹，以增进我们对应力性骨折发病机制的理解。使用动态步态模拟器对尸体足部进行正常行走模拟。在步态的整个支撑期对足部加载，并记录第二和第五跖骨的骨干应变。从对侧足部的跖骨横截面确定微裂纹密度（Cr.Dn）和表面密度（Cr.S.Dn）。第二跖骨的骨应变（-1897±613微应变）显著高于第五跖骨（-908±503微应变）。然而，第二跖骨的Cr.Dn（0.23±0.15#/mm(2)）与第五跖骨的Cr.Dn（0.35±0.19#/mm(2)）无显著差异。第二跖骨（17.64±10.99微米/毫米(2)）和第五跖骨（26.70±15.53微米/毫米(2)）的Cr.S.Dn也无显著差异。任一跖骨的微裂纹参数与峰值应变之间均无显著关系。发生在小梁支柱中的裂纹（92±33微米）明显长于在骨水泥线处终止的裂纹（71±15微米）和在骨单位内的裂纹（57±16微米）。任一跖骨的微裂纹参数与年龄之间均无显著关系。在正常行走模拟中，第二跖骨的峰值应变比第五跖骨大两倍多；然而，微裂纹参数无法解释第二跖骨应力性骨折发生率更高的原因。
