The Journal of Bone and Joint Surgery, Vol 72, Issue 9 1316-1322, Copyright © 1990 by Journal of Bone and Joint Surgery, Inc
Evaluation of an electrogoniometric instrument for measurement of laxity of the knee
WM Granberry, PC Noble and GW Woods
Eight lower extremities from cadavera were tested for anterior-posterior
laxity in two positions before and after transection of the anterior
cruciate ligament. At critical points in the tests, electrogoniometric and
radiographic measurements of tibiofemoral translation were compared. By
direct measurement, we determined the accuracy of the radiographic method
to +/- 0.4 millimeter (95 per cent) in measuring anterior-posterior
translations of the tibia with respect to the femur. The electrogoniometer
estimated displacement of the tibia with respect to the femur during the
anterior drawer test to be 3.5 +/- 8.2 millimeters at 90 degrees of flexion
of the knee and 11.1 +/- 16.1 millimeters at 30 degrees of flexion. Direct
comparison of these measurements with those obtained by means of the
radiographic technique showed that the electrogoniometer tended, on
average, to overestimate the tibial translation. The amount of
overestimation was 0.7 millimeter for intact knees and 1.9 millimeters
after sacrifice of the anterior cruciate ligament. Despite this small
average error in measurement of tibial translation, the difference between
individual electrogoniometric and radiographic measurements varied greatly,
with a 95 per cent confidence limit of +/- 5.5 millimeters. The error of
the electrogoniometric measurements varied with the angle of flexion of the
knee during testing, both the accuracy and the reliability of the
electrogoniometric measurements being greatly diminished at 30 degrees of
flexion. The electrogoniometric method also tended to overestimate tibial
internal rotation (by an average of 10.5 degrees) and external rotation (by
an average of 9.3 degrees); the reliability of these measurements was +/-
6.9 degrees.(ABSTRACT TRUNCATED AT 250 WORDS)