Introduction The most widely used instrument to measure anterior tibial is the Rolimeter®. Little is known about how knee flexion in the interval 10-40 degrees affects laxity measures. For smaller children the standard Rolimeter® is too long to fit onto tibia, so we have modified the Rolimeter®, reducing the length by 1/3. The aim of the study was to investigate whether anterior tibial translation measured by the Rolimeter® varies with degree of knee flexion in the interval 10-40 degrees, and with use of a standard or a shortened (“pediatric”) Rolimeter®.

Materials & Methods Fourty-eight children and adults with an isolated ACL-rupture had anterior tibial translation measured with the standard Rolimeter® and the “pediatric” Rolimeter® in 10°, 20°, 30° and 40° degrees of flexion by two independent observers.

Results The weighted kappa showed moderate agreement between measurements made with the standard Rolimeter® and the ”pediatric” version. T-tests demonstrated that anterior tibial laxity was significantly affected by the degree of knee flexion showing higher values with increasing flexion in the range 10°-40°. However, laxity of the injured and the non-injured knee changed with knee flexion to the same extent.

Conclusions It is important that repeated measurements of anterior tibial translation are made with the same degree of knee flexion. The variance in laxity dependent on flexion can be compensated for by comparison with the non-injured side. The shortened, “pediatric” Rolimeter® can be used in the daily clinic to supply valid instrumented measurements of ACL stability in smaller children.