Smith Anna N, Strand Kathryn S, Levy Trent J, Ulsh Joseph B, Ching Stephen, Arroyo Edgardo J, Mauck Robert L, Hast Michael W
McKay Orthopaedic Research Lab, Department of Orthopaedic Surgery, University of Pennsylvania, Philadelphia, PA, USA.
McKay Orthopaedic Research Lab, Department of Orthopaedic Surgery, University of Pennsylvania, Philadelphia, PA, USA; Department of Mechanical Engineering, University of Delaware, Newark, DE, USA.
Clin Biomech (Bristol). 2025 Jun;126:106545. doi: 10.1016/j.clinbiomech.2025.106545. Epub 2025 May 9.
Although rigid interfragmentary fixation is required for fracture repair, overly stiff implants are known to cause stress shielding which ultimately inhibits healing. While gradual dynamization of the fracture site both accelerates and improves osteogenesis, this approach requires external fixators or secondary surgeries. This study leverages biodegradable implants as mechanisms of gradual, passive dynamization during fracture healing.
Using a rat femoral osteotomy model, additively manufactured poly-lactic-co-glycolic acid implants were compared to geometrically matched non-degradable biocompatible resin devices. Bone healing was assessed at 3 and 6 weeks via micro-computed tomography, histology, and mechanical testing. Implant degradation kinetics were assessed through testing of plates that were used in the rat model and with an unloaded in vitro degradation model.
Quantitative bone measures made with micro-computed tomography, histology, and mechanical testing of the healing femora revealed no differences between degradable and non-degradable implants at 3 or 6 weeks. Degradable implants caused significant increases in bone volume to total volume mean density (p < 0.0001) and callus to cortical volume (p < 0.05) ratios between 3 and 6 weeks. Poly-lactic-co-glycolic acid devices were significantly stiffer than resin at week 0, but the two groups were equivalent by week 6 due to in vivo degradation. In vivo ambulatory loading caused significant losses of degradable implant stiffness at both 3 (p < 0.05) and 6 (p < 0.01) weeks, but this was not observed in the unloaded in vitro model.
The results from this early timepoint study demonstrate the feasibility of passive, internal fracture dynamization driven by implant material mechanics.
尽管骨折修复需要坚强的骨折块间固定，但已知过于坚硬的植入物会导致应力遮挡，最终抑制愈合。虽然骨折部位的逐渐动力化可加速并改善骨生成，但这种方法需要外固定器或二次手术。本研究利用可生物降解植入物作为骨折愈合过程中逐渐被动动力化的机制。
使用大鼠股骨截骨模型，将增材制造的聚乳酸 - 乙醇酸共聚物植入物与几何形状匹配的不可降解生物相容性树脂装置进行比较。在3周和6周时通过微计算机断层扫描、组织学和力学测试评估骨愈合情况。通过对大鼠模型中使用的钢板进行测试以及体外无负载降解模型评估植入物的降解动力学。
对愈合股骨进行微计算机断层扫描、组织学和力学测试得出的定量骨测量结果显示，在3周或6周时，可降解和不可降解植入物之间没有差异。在3至6周期间，可降解植入物使骨体积与总体积平均密度（p < 0.0001）以及骨痂与皮质骨体积比（p < 0.05）显著增加。聚乳酸 - 乙醇酸共聚物装置在第0周时比树脂明显更硬，但由于体内降解，两组在第6周时相当。体内动态负荷导致可降解植入物在3周（p < 0.05）和6周（p < 0.01）时刚度显著降低，但在体外无负载模型中未观察到这种情况。
这项早期时间点研究的结果证明了由植入物材料力学驱动的被动、内部骨折动力化的可行性。
