The Use of an Electromagnetic Measurement System for Anterior Tibial Displacement During the Lachman Test

Purpose The purpose of this study was to assess quantitative anterior/posterior values during the Lachman test by an electromagnetic measurement system and to compare data with KT-1000 arthrometric measurements (MEDmetric, San Diego, CA), as well as the measurement of radiologic laxity by dynamic radiographs. Methods We used an electromagnetic device to quantitatively evaluate anterior knee displacements. We tested 82 knees in 41 patients (30 isolated anterior cruciate ligament [ACL]–deficient, 11 ACL-reconstructed, and 41 contralateral ACL-intact knees). Anterior displacements during the Lachman test were calculated by the electromagnetic measurement system and fluoroscopic measurement, and anterior displacements were also measured by the KT-1000 arthrometer. Anterior/posterior displacements measured by these methods were compared, and correlations were assessed. Results In ACL-deficient knees, mean anterior/posterior displacement (±SE) was 22.4 ± 0.8 mm in electromagnetic measurements, 22.0 ± 0.7 mm in fluoroscopic measurements, and 15.0 ± 0.6 mm in KT-1000 measurements. In contralateral ACL-intact knees, it was 15.7 ± 0.6 mm, 15.6 ± 0.5 mm, and 9.9 ± 0.4 mm, respectively. In ACL-reconstructed knees, it was 15.7 ± 0.7 mm, 16.2 ± 0.8 mm, and 11.2 ± 0.6 mm, respectively. In all knee conditions, significant differences between fluoroscopic measurements and KT-1000 measurements were detected ( P < .01). Significant differences were also detected between electromagnetic measurements and KT-1000 measurements ( P < .01). No significant differences were detected between fluoroscopic measurements and electromagnetic measurements. A strong correlation was obtained between KT-1000 measurements and fluoroscopic measurements ( r = 0.62, P < .01) and between electromagnetic measurements and KT-1000 measurements ( r = 0.64, P < .01). However, the strongest correlation was observed between electromagnetic measurements and fluoroscopic measurements ( r = 0.96, P < .01). Conclusions An electromagnetic measurement system to test anterior/posterior tibial translation determined that quantification of the Lachman test could be performed as accurately as fluoroscopic measurements. Level of Evidence Level II, development of diagnostic criteria on basis of consecutive patients with universally applied reference gold standard.