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Leg Length Calliper

The system also consists of a leg length calliper which is used for checking leg length before and after the operation. By inserting a pin into the femur and one into the pelvis the calliper can be slid over the pins and the distance between can be measured. The calliper is removed but the pins are left in place as the operation is performed. At the end once the implant is positioned the calliper can be slid back onto the pins and the distance checked again, if the measurement remains the same it means no leg length discrepancy is present. The calliper can also be used throughout the operation for taking other measurements such as implant depth, this can be usefully during an emergency surgery for example where there was no time to create and print a jig.

Position Accuracy

The jigs were prototyped using a model femur, the femur was 3D scanned a long with an implant allowing the scan meshes to be used for templating in Solidworks. This provided a planned position for the implant and the jigs could be created using this as reference. A simulated surgery was then performed using the 3D printed jigs and the implanted femur was then re-scanned allowing the achieved implant position to be compared with the planned position. The overall leg length discrepancy achieved using the jigs was 0.36mm (a discrepancy this low would not be perceived by the patient), this was a very promising result considering leg length discrepancies produced using the current methods range from 3mm to 70mm.

Prototype Test / Usage Scenario

Exploded Drawings

Thomas James Brew

Major project

Accurate Positioning Of The Femoral Prosthesis During Hip Replacement Surgery