2017 ISAKOS Biennial Congress ePoster #1173
Standardized Automated Clinical Knee Examination: The Lachman Test
Jon E. Browne, MD, Leawood, KS UNITED STATES
Thomas P. Branch, MD, Atlanta, GA UNITED STATES
Shaun Stinton, PhD, Atlanta, GA UNITED STATES
Nathan deJarnette, BS, Atlanta, GA UNITED STATES
Timothy Lording, MBBS, FRACS, Malvern East, VIC AUSTRALIA
Philippe Noel Neyret, MD, PhD, Prof., Lyon La Tour De Salvagny FRANCE
Orthopaedic & Sports Medicine Clinic of Kansas City, Leawood, KS, UNITED STATES
FDA Status Not Applicable
Kinematics of the tibia during an automated Lachman test were characterized in six degrees of freedom to provide a full understanding of primary and secondary motions in the knee to provide an objective measure of the extents of motion and the endpoint feel.
The Lachman test has been used to characterize ACL instability. It provides the clinician with the ‘feel’ of tibial motion in response to an anterior force. During the test, both primary motion in the direction of force application and secondary motions in other directions can be clinically important in diagnosis of injury. However, secondary motions are often ignored. Instrumented Lachman testing provides a single number to represent the condition of the ACL (mm of anterior translation). However, this single number does not describe complex knee motion or the endpoint feel. In 2004, Kocher reported that anterior tibial translation did not correlate with patient satisfaction after ACL reconstruction. Subsequently, the pivot shift gained popularity for characterization of ACL instability. A full biomechanical understanding of the motions of the tibia in response to an anterior force is needed to realize the full value of this test. The purpose of this study was to identify all motions of the proximal tibia in response to an automated Anterior/Posterior Lachman Test.
Six pelvis-to-toe cadavers (12 knees) were tested using an automated system that reproduced the Lachman Test using six motors and six torque sensors. The tibia was allowed unimpeded motion with respect to a stationary femur and foot to determine knee motion before and after ACL resection. Electromagnetic sensors were affixed to the tibia and femur. A lever arm was positioned under the calf with a strap extending around the leg. Torque was applied by the motor at the distal end of the lever arm resulting in an applied force of 200 N at a point 3/4 of the way up the lower leg. Initially, the system pushed both legs anteriorly until the force threshold was reached and then reversed direction until the same threshold was reached posteriorly. Torque data were collected and motions of the tibia relative to the femur were recorded in six degrees of freedom (3 rotations and 3 translations) using the electromagnetic system. For all motions, a load-deformation curve was constructed from kinematic and torque data. Endpoints of these curves were compared to each other and to the zero-force position using the Wilcox signed rank test.
Primary motion of the tibia occurred along the Anterior/Posterior Axis. Maximum posterior translation, position at zero force and maximum anterior translation were all statistically different from each other (p<0.001). Endpoints of secondary motions of the tibia were statistically different from each other (p<0.01) and from zero force position (p<0.01) except for Adduction/Abduction Rotation.
This study brings three-dimensional knee kinematics into the clinical realm by reproducing the Lachman Test. In response to an anterior force, the tibia moves anteriorly with accompanied internal rotation, lateral translation, flexion and compression. In response to a posterior force, the tibia moves posteriorly with accompanied external rotation, medial translation, extension and distraction. Load-deformation curves provide the clinician with information about both the extent of motion and endpoint feel. By recreating this commonly used test while recording precise three-dimensional kinematics, clinicians will be able to put these important kinematic motions into a useable context thereby improving treatment efficacy.