Three-dimensional biomechanical analysis of flexible intramedullary nailing constructs in length-unstable pediatric femur fractures

Flexible intramedullary nail fixation of pediatric femoral shaft fractures offers advantages such as shorter hospital stays, faster return to function, and less associated costs when compared with traction and casting. This study compared the biomechanical performance of three configurations: 2CS, 2CL, and 3CL. Thirty synthetic femur models with identical, length-unstable, spiral fractures were tested using a three-dimensional camera system to assess real-time micromotion. Three groups were analyzed: (a) 2CS – two 3.5 mm C- and S-shaped nails inserted anterograde, (b) 2CL – one ‘C’ and one ‘S’ shaped 3.5 mm titanium nail-inserted retrograde from a single lateral entry, (c) 3CL – two ‘C’ shaped 3.5 mm titanium nails inserted medially and laterally with a third ‘C’ shaped 2.5 mm nail placed retrograde from an anterolateral site. Torsional loading, cyclical loading, and load-to-failure tests were conducted. The 3CL configuration demonstrated superior biomechanical performance. It exhibited the highest torsional stiffness [0.67 ± 0.06 Nm/° for external rotation (ER), 0.404 = ± 0.06 Nm/° for internal rotation (IR); P = 0.002], least displacement (0.05 ± 0.02 vs. 0.30 ± 0.02 mm for 2CL and 0.57 ± 0.05 mm for 2CS; P = 0.012), and required the highest load-to-failure (162 ± 83 vs. 1064 ± 75 N for 2CL and 790 ± 34 N for 2CS; P = 0.016). The 3CL configuration provided superior strength and stability across all tests, supporting its role in the fixation of length-unstable pediatric femoral fractures.