Load bearing versus load sharing

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 Introduction
 Load-bearing osteosynthesis
 Load-sharing osteosynthesis
 Different levels of force distribution
Introduction

There are two basic types of fracture fixation, load-bearing osteosynthesis (A) and load-sharing osteosynthesis (B).


Load-bearing osteosynthesis

(stabilization by splinting)
The plate bears the forces of function at the fracture site. This is accomplished with a locking reconstruction plate. Clinical uses are the management of atrophic edentulous fractures, comminuted fractures, defect fractures, and other complex mandibular fractures.


Load-sharing osteosynthesis

General consideration
Stability at the fracture site is created by the frictional resistance between the bone ends and the hardware used for fixation. This requires adequate bony buttressing at the fracture site. Examples of load-sharing osteosynthesis include lag screw fixation technique and compression plating . Load-sharing osteosynthesis cannot be used with defect fractures or comminuted fractures, due to the lack of bony buttressing at the fracture site.


Another form of load-sharing osteosynthesis is the miniplate fixation technique popularized by Champy. This is also known as functionally adequate fixation or semi-rigid fixation.

Ideal lines of osteosynthesis
Champy popularized the treatment of mandible fractures with miniplate fixation along the ideal lines of osteosynthesis. This is a form of load-sharing osteosynthesis to be applied in simple fracture patterns having an acceptable amount of bone stock.

Click here for a description of the biomechanics of the mandible.


Different levels of force distribution

Overview
In the load-bearing situation the plate assumes all the forces, in the load-sharing situation there are different levels of force distribution between the plate(s) and the bone.


Load bearing
In load-bearing fixation the plate assumes 100% of the functional loads.


This is an example of load-bearing osteosynthesis for the treatment of a defect fracture in the angular region. The osteosynthesis assumes all the masticatory loads while the bone graft matures and consolidates in a protected environment.


Intermediate load-sharing situation
Intermediate load-sharing situation where the osteosynthesis and the bone share the functional loads almost equally.


This is an example of load-sharing osteosynthesis for the treatment of a simple angular fracture. The two miniplates share the loads with the bone in an anatomical region where the bone stock and force distribution are not ideal.


Ideal load-sharing situation
Ideal load-sharing situation where the bone assumes most of the functional loads.


In this example a simple mandibular body fracture was considered suitable for a single miniplate osteosynthesis in the neutral zone because of the good bone stock and optimal force distribution.