Biomechanical study of extramedullary and intramedullary fixation in the treatment of unstable intertrochanteric reversed-tilt fractures of the femur

Guo-Liang Lu; Song-Jun Li; Wen-Xue Li

doi:10.21037/atm-22-93

Biomechanical study of extramedullary and intramedullary fixation in the treatment of unstable intertrochanteric reversed-tilt fractures of the femur

Ann Transl Med. 2022 Feb;10(4):191. doi: 10.21037/atm-22-93.

Authors

Guo-Liang Lu^#¹, Song-Jun Li^#², Wen-Xue Li³

Affiliations

¹ Department of Orthopedic Trauma, Foshan Hospital of TCM (The Eighth Affiliated Hospital of Guangzhou University of Traditional Chinese Medicine), Foshan, China.
² Department of Orthopedics, the Fifth Affiliated Hospital of Zunyi Medical University, Zhuhai, China.
³ Department of Orthopedics, Dongying Hospital of Traditional Chinese Medicine, Dongying, China.

^# Contributed equally.

Abstract

Background: To investigate the efficacy of the 135° hip screw, 95° intramedullary hip screw (IMHS) and 95° hip screw in the treatment of intertrochanteric reverse dip fracture of the femur.

Methods: We retrospectively analyzed 125 matched pairs of human femurs (median age 64 years) which were osteotomized at a 33° angle in the left femur and extended downward from the minor trochanter to simulate a reverse oblique intertrochanteric fracture. The right femur served as a control. The left femur (n=4) was implanted with a 135° hip screw, 95° hip screw, or IMHS. A strain detector was placed distal to the fracture site to monitor fragment strain. The lateral displacement of the proximal femur was measured by a linear variable differential transformer. An Instron tester measured stiffness, strain, and lateral displacement at 25° adduction, and 90° adduction with vertical loads on the femoral head. A 2 cm gap was then formed at the fracture site to simulate comminution and the mechanical test was repeated.

Results: Before the formation of the gap, there was no significant difference in stiffness among different bone structures (P>0.05), but after the formation of the gap, the stiffness of all the adduction structures decreased (P=0.03), and the difference in adduction was statistically significant (135° hip screw: 46.6%±3%; 95° hip screw: 22.9%±2%; IMHS: 53.7%±7.8%; P<0.05). Similar results were found for the abduction and buckling positions. There was no significant difference in the lateral displacement of the gap before (P=0.92) and after (P=0.26), but a significant difference in the failure load was found (135° hip screw: 1,222±560 N; 95° hip screw: 2,566±283 N; IMHS: 4,644±518 N; P=0.02).

Conclusions: There was no statistically significant difference in stiffness among different structures (P>0.05). However, in the presence of gaps, IMHS bone implant structures are much stiffer than 135° and 95° structures and have a greater destructive load.

Keywords: Hip screw; biomechanics; intertrochanteric reverse dip fracture; intramedullary nail; retrospective study.