Aims There are concerns regarding nail/medullary canal mismatch and initial stability after cephalomedullary nailing in unstable pertrochanteric fractures. This study aimed to investigate the effect of an additional anteroposterior blocking screw on fixation stability in unstable pertrochanteric fracture models with a nail/medullary canal mismatch after short cephalomedullary nail (CMN) fixation. Methods Eight finite element models (FEMs), comprising four different femoral diameters, with and without blocking screws, were constructed, and unstable intertrochanteric fractures fixed with short CMNs were reproduced in all FEMs. Micromotions of distal shaft fragment related to proximal fragment, and stress concentrations at the nail construct were measured. Results Micromotions in FEMs without a blocking screw significantly increased as nail/medullary canal mismatch increased, but were similar between FEMs with a blocking screw regardless of mismatch. Stress concentration at the nail construct was observed at the junction of the nail body and lag screw in all FEMs, and increased as nail/medullary canal mismatch increased, regardless of blocking screws. Mean stresses over regions of interest in FEMs with a blocking screw were much lower than regions of interest in those without. Mean stresses in FEMs with a blocking screw were lower than the yield strength, yet mean stresses in FEMs without blocking screws having 8 mm and 10 mm mismatch exceeded the yield strength. All mean stresses at distal locking screws were less than the yield strength. Conclusion Using an additional anteroposterior blocking screw may be a simple and effective method to enhance fixation stability in unstable pertrochanteric fractures with a large nail/medullary canal mismatch due to osteoporosis. Cite this article: Bone Joint Res 2022;11(3):152–161.
Although cerclage wiring is a very useful implant, it has many problems. We manufactured an alphabet C-shaped clip with nitinol (C-clip) that has superelastic property to replace the cerclage wiring.This study aimed to compare the biomechanical stability of cerclage cable and the C-clip. Eighteen synthetic femora were tested. An unstable VB1 fractures model was constructed that oblique fracture line was 8cm below the lesser trochanter with fracture gab. The distal fixation was repaired with a locking plate and four bi-cortical screws. The proximal fixation was repaired two different methods: (1) four-threaded cerclage cables and (2) four new C-clip. In axial compression test, the C-clip was stiffer than the cerclage cable (median stiffness of C-clip = 39.28 N/mm [IQR; 38.84-41.19], cerclage cable = 34.90 N/mm [34.84-35.08], p<0.05). In the torsion test, the C-clip was 0.44 Nm/° [IQR; 0.44-0.45] and cerclage cable = 0.30 Nm/° [0.30-0.33], p<0.05). In the four-point bending test, the C-clip = 39.35 N/mm [IQR; 38.91-40.97] and cerclage cable = 28.38 N/mm, [28.33-30.79], p<0.05) The C-clip may be biomechanically superior to cerclage wiring in terms of stiffness, axial compression, torsion, and four-point bending tests and is a valuable alternative in Vancouver type B1 periprosthetic femoral fracture.
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