Locking plate constructs in subtrochanteric fixation: a biomechanical comparison of LCP screws and AO-nuts

T.P.A Baltes,A.J Van Der Veen,L Blankevoort,J.C.E Donders,P Kloen

doi:10.1016/j.jcot.2020.12.026

T.P.A Baltes, A.J Van Der Veen + Show 3 more

Open Access

https://doi.org/10.1016/j.jcot.2020.12.026

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Abstract

ObjectivesVarious studies have reported the use of the 95-degree condylar blade plate in the treatment of a subtrochanteric fracture or non-union. However, the holding power of standard screws in the metaphyseal and diaphyseal area is often diminished due to osteopenia. The alternative in this area is the use of locking plates, Schühlis or AO-nuts. With the latter two, non-locking screws in the blade plate can be converted to a fixed angle fixation. The objective of this study was to compare the stiffness and strength of the AO-nut augmented 95-degree condylar blade plate construct with that of a locking plate construct. In addition, a clinical series of eight patients treated with the AO-nut augmented 95-degree condylar blade plate construct is presented. MethodsSingle screw-plate constructs of a 5.0 mm locking screw/locking compression plate (LCP) and a 4.5 mm non-locking screw/4.5 mm dynamic compression plate (DCP), converted to a fixed-angle screw construct using AO-nuts, were tested by cantilever bending. During loading, force and displacement were recorded, from which the bending stiffness (N/mm) and the yield strength (N) were determined. Secondarily, all patients that underwent surgical treatment for subtrochanteric fracture, malunion or non-union by the senior author using this technique, underwent chart review. ResultsThe stiffness of the locking screws was about four times higher compared to the AO-nut augmented construct. The yield strength was 2.3 times higher for the locking screw construct. In none of the eight patients treated with the fixed-angle blade plate, failure of the AO-nut augmented construct occurred. ConclusionsAlthough the stiffness and strength of the AO-nut augmented construct is less than of the locking screw, excellent clinical outcomes can be achieved utilizing this construct.

Highlights

Subtrochanteric femur fractures constitute 7e34% of all proximal femur fractures.[1]
Revision fixation in the subtrochanteric region can represent a significant challenge, as they often present with large bone voids, scarring, osteopenia, failed hardware and deformity
With corresponding 4.5 mm non-locking screws, the 4.5 mm dynamic compression plate (DCP) was converted to a fixed-angle construct using AO-nuts

Summary

Introduction

Subtrochanteric femur fractures constitute 7e34% of all proximal femur fractures.[1] When treated with contemporary methods of fixation, most fractures heal well. A subset of patients develops a non-union or malunion. Revision fixation in the subtrochanteric region can represent a significant challenge, as they often present with large bone voids, scarring, osteopenia, failed hardware and deformity. Various options have been described in the treatment of subtrochanteric non-unions, including revision to larger intramedullary implants, plate fixation or hip arthroplasty in older patients.[2] Others have recognized the 95-degree condylar blade plate as the workhorse in a subtrochanteric non-union, as it is an inexpensive plate and a reliable surgical technique.[3,4] In addition, the blade plate allows for correction in multiple planes

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