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Effect of fracture levels on the strength of bone-implant constructs in subtrochanteric fracture models fixed using short cephalomedullary nails: A finite element analysis

•The stresses around short cephalomedullary nails (CMNs) fixed in subtrochanteric (ST) transverse fractures at various levels and cortical bone around CMNs were different according to the nails’ length and number of distal locking screws.•Short CMNs 170 or 200 mm in length with 1 distal locking scre...

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Bibliographic Details
Published in:Injury 2019-11, Vol.50 (11), p.1883-1888
Main Authors: Jang, Chul-Young, Bang, Sun-Hee, Kim, Won-Hyeon, Lee, Sung-Jae, Lee, Hyung-Min, Kwak, Dae-Kyung, Yoo, Je-Hyun
Format: Article
Language:English
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Summary:•The stresses around short cephalomedullary nails (CMNs) fixed in subtrochanteric (ST) transverse fractures at various levels and cortical bone around CMNs were different according to the nails’ length and number of distal locking screws.•Short CMNs 170 or 200 mm in length with 1 distal locking screw should be used limitedly in relatively high ST fractures ≤ 30 mm below the lesser trochanter under the assumptions of anatomical reduction and fracture gap ≤ 1 mm.•Short CMNs 200 mm in length with 2 distal locking screws may be an available treatment option in most of ST transverse fractures regardless of the fracture level under the same assumptions. This study was conducted to investigate the stress around nails and cortical bones in subtrochanteric (ST) fractures fixed using short cephalomedullary nails (CMNs) in finite element models (FEMs) and to determine the appropriate short CMN type for different fracture levels. The following three types of short CMNs were used: type A, which is 170 mm in length and has 1 distal locking screw; type B, 200 mm in length and 1 distal screw; and type C, 200 mm in length and 2 distal screws. A total of 24 FEMs were tested on a transverse ST fracture at 8 levels [0, 10, 20, 25, 30, 35, 40 and 50 mm below the lower margin of lesser trochanter (LT)], and were fixed using 3 different CMN types. Finite element analysis was then performed to evaluate the stress around the cortical bones and the CMNs under the assumption of anatomical reduction and fracture gap of 1 mm. Peak von Mises stress (PVMS) was greatest on the cortical bone around the distal screw hole and was greater than the yield strength at fracture levels ≥ 35 mm below the LT in FEMs fixed with type A and B. In contrast, FEMs fixed with type C showed PVMS less than the yield strength at all fracture levels. The PVMS within the implant was greater than the yield strength at the junction of the nail with the distal screw and distal screw itself at fracture levels ≥ 35 mm below the LT in FEMs fixed using type A. Conversely, in FEMs fixed using type B and C, all PVMSs within the implant were less than the yield strength, regardless of the fracture level. Short CMNs 170 or 200 mm in length with 1 distal screw may be used in a limited manner in high ST transverse fractures under the assumptions of anatomical reduction and fracture gap ≤ 1 mm. Meanwhile, short CMN 200 mm in length with 2 distal screws may be an available treatment option in most of ST transverse fractures
ISSN:0020-1383
1879-0267
DOI:10.1016/j.injury.2019.08.014