Since the 1970s, the 2%−10% rule has been used to describe the range of interfragmentary gap closure strains that are conducive for secondary bone healing. Interpreting the available evidence for the association between strain and bone healing remains challenging because interfragmentary strain is impossible to directly measure in vivo. The question of how much strain occurs within and around the fracture gap is also difficult to resolve using bench tests with osteotomy models because these do not reflect the complexity of injury patterns seen in the clinic. To account for these challenges, we used finite element modeling to assess the three-dimensional interfragmentary strain in a case series of naturally occurring distal femur fractures treated with lateral plating under load conditions representative of the early postoperative period. Preoperative computed tomography scans were used to construct patient-specific finite element models and plate fixation constructs to match the operative management of each patient. The simulations showed that gap strains were within 2%−10% only for the lowest load application level, 20% static body weight (BW). Moderate loading of 60% static BW and above caused gap strains that far exceeded 10%, but in all cases, strains in the periosteal region external to the fracture line remained low. Comparing these findings with postoperative radiographs suggests that in vivo secondary healing of distal femur fractures may be robust to early gap strains much greater than 10% because formation of new bone is initiated outside the gap where strains are lower, followed by later consolidation within the gap.

中文翻译：

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重新思考骨折愈合中的 10% 应变规则：股骨远端骨折系列病例

自 1970 年代以来，2%−10% 规则已用于描述有助于二次骨愈合的碎片间间隙闭合应变的范围。解释应变与骨愈合之间关联的现有证据仍然具有挑战性，因为碎片间应变不可能在体内直接测量。使用截骨术模型的台架试验也很难解决骨折间隙内和周围发生多少应变的问题，因为这些不能反映临床上看到的损伤模式的复杂性。为应对这些挑战，我们使用有限元模型评估了一系列自然发生的股骨远端骨折在代表术后早期的负荷条件下采用外侧钢板治疗的三维骨折块间应变。术前计算机断层扫描用于构建患者特定的有限元模型和钢板固定结构，以匹配每位患者的手术管理。模拟表明，间隙应变仅在最低负载应用水平（20% 静态体重 (BW)）下在 2%−10% 以内。60% 静态 BW 及以上的中等负荷导致间隙应变远远超过 10%，但在所有情况下，骨折线外部骨膜区域的应变仍然很低。将这些发现与术后 X 光片进行比较表明，股骨远端骨折的体内二次愈合可能对远大于 10% 的早期间隙应变很稳健，因为新骨的形成是在应变较低的间隙外开始的，随后在间隙内进行后期巩固.