LIVRE JDG 2016

A. SONI, V. MUSAHL

(fig. 2). The skin markers are attached to three

bony landmarks on lateral side of the knee i.e,

lateral epicondyle, Gerdy’s tubercle, and the

fibular head. The software is able to calculate

the relative motion of tibia in relation to femur

by recording and analyzing the video of the

knee motion during pivot shift test. The lateral

compartment translation measured by this

technique has shown to be strongly correlated

with bony motion measured invasively by

electromagnetic tracking system. In distances

less than or equal to 175cm between iPad and

marker position this calculation has less than

6% error, which provides sufficient accuracy

for the clinical set-up. Considering the analysis

time of 10-15 seconds, image analysis

constitutes an easily applicable tool for the

daily clinical work [9].

INERTIAL SENSOR

TECHNOLOGY

The acceleration during the tibial reduction of

the pivot shift is significantly higher in ACL

deficient knees and correlates with the clinical

grading of the pivot shift [7]. Different types of

inertial sensors (accelerometers, gyroscopes,

micro-electromechanical system sensors) have

been used to quantify this acceleration, rotation

and velocity of the bony motion. Similar to the

principle of image analysis, the sensors are

attached to the lateral aspect of the proximal

tibia, close to Gerdy`s tubercle. Transmitting

the gathered acceleration

via

Bluetooth to a

tablet software, named Kira (Orthokey LLC,

Lewes, DE, USA), the data is subsequently

analyzed, plotted and saved in a patient data

base (fig. 3). The applicability and reliability of

this technology was demonstrated in laboratory

setting as well as in the clinical use [10].

Together these devices provide comprehensive

insight to joint rotatory laxity.

During a test, the tablet’s camera records the

movement of the markers while the knee is

being examined (fig. 3). The software scans the

images in real time and utilizes custom

algorithms that shade the entire image except

the markers by adjusting the brightness and

contrast. The software then automatically

tracks the movement of the markers and

calculates the translation of the pivot point

defined by the intersection of the line between

markers on the fibular head and Gerdy’s

Fig. 2:

Testing set-up for the quantitative pivot shift measurement by image analysis technology

and inertial sensors. For image analysis technology markers are attached to the bony landmarks

fibular head, Gerdy’s tubercle and femoral epicondyle to quantify lateral compartment

translation. Inertial sensors are utilized to measure the acceleration of the tibia in the reduction

phase of the pivot shift. Both systems use tablet-software to acquire and analysis the data.