Effect of Trunk Position on Anterior Tibial Displacement Measured by the KT-1000 in Uninjured Subjects

Clinicians may obtain false-negative Lachman tests for tibial displacement when the trunk position of the athlete varies as the anterior cruciate ligament injury is assessed on the field, on the sideline, and in the clinic. We examined the influence of supine, semireclined, and sitting trunk positions on arthrometric laxity measurements of the knee.

Subjects in the 3 trunk-thigh test positions (15 degrees , 45 degrees , and 90 degrees of hip flexion) were passively supported and tested in a counterbalanced order. The right knee was maintained at 29.0 degrees +/- 3.1 degrees of flexion. A 133-N (30-1b) anterior force was applied to the right knee using a modified KT-1000 knee arthrometer equipped with a strain gauge that allowed for digital display of the displacement force.

Ten males and 5 females without present knee injury or history of knee ligament repair to the right lower extremity.

Three tibial displacement (mm) trials at each trunk position were averaged and used for analysis.

A 1-factor (trunk-thigh position) repeated-measures analysis of variance revealed no significant difference in anterior tibial displacement values among the 3 trunk-thigh positions (P > .05). Group means for displacement were 7.9 +/- 2.3 mm (supine), 8.1 +/- 2.5 mm (semireclined), and 8.3 +/- 2.6 mm (sitting).

These findings suggest that alterations in trunk position are not a problem in the instrumented assessment of anterior tibial displacement in an uninjured population. Further research should determine the relevance of these findings, as well as "end-feel" (ie, stiffness) in subjects with injury to the anterior cruciate ligament. Further research should also determine if these findings can be applied when comparing passive versus active (eg, propped on elbows or hands) trunk support in subjects with anterior cruciate ligament-injured knees.