Tibial rotation influences anterior knee stability - a robot-aided in-vitro study

•Tibial rotation has a large influence on anterior tibial translation.•Maximum anterior translation was found in a slightly externally rotated position of the tibia.•During the Lachman test greatest ACL influence was found at 5-10° of external rotation.•ACL replacement effectively reduced anterior translation at all flexion & rotational angles.•Attention on tibial rotation should be paid during clinical examination of the knee.

BackgroundAnterior cruciate ligament rupture can lead to symptomatic instability, especially during pivoting activities, which are often associated with increased anterior and rotational tibial loading. Therefore, the purpose of our robot-aided in-vitro study was to analyze the influence of tibial rotation on anterior knee stability under three anterior cruciate ligament conditions.MethodsTen human knee specimens were examined using a robotic system. Anterior tibial translations were measured during anterior force application at internally and externally rotated positions of the tibia (5° steps until 4 Nm was reached) at 20°, 60°, and 90° of flexion. The native knee was compared with the knee with deficient and replaced anterior cruciate ligament.FindingsTibial rotation significantly influenced anterior tibial translation (P < 0.001), with differences of up to 12 mm between the largest and smallest anterior translation in the deficient knee. The largest influence of the anterior cruciate ligament on anterior translation was found in slightly externally rotated positions of the tibia (5°-10° at 20° of flexion; 0°-5° at 90° of flexion). Significantly increased anterior tibial translation (up to 7 mm) was measured after anterior cruciate ligament resection, which could be almost completely restored by the replacement (remaining difference < 1 mm) over a wide range of tibial rotations.InterpretationTibial rotation clearly influences anterior tibial translation. Because the greatest effect of the anterior cruciate ligament was found in slightly externally rotated positions of the tibia, increased attention to tibial rotation should be paid when performing the Lachman and anterior drawer tests.