Manual Lachman Test Underestimates Tibial Translation Compared to Standardized Generated Force: A Biomechanical Study of Cadaveric Anterior Cruciate Ligament Repair Using Internal Brace (205)
Authors: Amirouche Farid , Carlson Andrew , Lee Cody , Koh Jason , Beltagi Amir , Pradhan Sonia , Qin Charles , Athiviraham Aravind 
Published: October 2021

Objectives: With an increasing incidence over time, anterior cruciate ligament (ACL) rupture can produce functionally limiting knee instability that requires operative treatment to address the instability as well as prevent the development of osteoarthritis. Anteroposterior instability forms the basis of the most sensitive physical exam maneuver to examine the ACL for rupture, the Lachman test. This investigation has two goals: to assess the precision and accuracy of the manual Lachman test by comparing anterior tibial translation generated to that of a standardized applied force Lachman test, and to compare the anteroposterior stability of cadaver specimens with simulated ACL ruptures which were repaired with and without internal suture tape augmentation. Methods: The tibial plateau in ten cadaveric knees was divided into medial, middle and lateral reference points, which were monitored digitally during testing using Optotrak. Intact knees were subjected to both manual Lachman tests at 30 degrees of flexion and standardized 150N force Lachman tests utilizing a hook and pulley system with force transducer. The ACL’s of all specimens were then transected, and the ACL deficient knees were subjected to both the manual and standardized Lachman tests. The specimens were then randomly divided into two groups to be repaired with or without internal suture tape augmentation, and subsequently underwent 100, 250, and 500 cycles from 90 degrees of flexion through full extension with a frequency of .1Hz, after which the same standardized Lachman test was performed on all repaired specimens. Comparison of variances were made using a two-sample F-Test for variances. Comparison of means were made using a two sample t-test assuming unequal variances and one-way ANOVA. Significance was set at p </= 0.05. Results: Comparing ACL intact to ACL deficient states, the standardized Lachman test detected a significant difference in tibial translation at the medial (14.1mm versus 20.3mm, p=.031), middle (17.5mm versus 24.6mm, p=.011), and lateral (14.8mm versus 21.5mm, p=.050) reference points while the manual Lachman test only detected a significant difference at the middle (12.6mm versus 19.8mm, p=.026) reference point. In ACL deficient knees, there was a statistically significant underestimation in tibial translation when using the manual method as compared to the standardized method (17.4mm versus 22.3mm, p=0.046). When comparing the precision of the testing methods, F-Tests for variance did not yield significant differences between variances in measured tibial translation for the manual and standardized Lachman tests in either intact or ACL deficient knees. There were no statistically significant differences in measured tibial translation between specimens with intact ACL, ACL repair, and ACL repair with internal brace at the medial (14.1mm versus 13.7mm versus 16.45mm, p=0.462), middle (17.5mm versus 16.6mm versus 18.3mm, p=0.767), lateral (14.8mm versus 15.9mm versus 15.9mm, p=0.934), or call (15.5mm versus 15.2mm versus 16.9mm, p=0.748) reference points. Conclusions: Tibial translation generated by Lachman tests performed manually may be underestimated when compared to Lachman tests performed with a standard force, lending to difficulty detecting the ACL deficient state. ACL repair both with and without internal brace augmentation allowed for a return to pre-rupture levels of anteroposterior stability.