2015 ISAKOS Biennial Congress ePoster #1245

Anterior Cruciate Ligament Stabilizing Function in Resisting Medial and Lateral Tibiofemoral Compartment Subluxations

Frank R. Noyes, MD, Cincinnati, OH UNITED STATES
Edward S. Grood, PhD
Samuel P. Harm, MD, Cincinnati, OH UNITED STATES
Andrew W. Jetter, BS, Cincinnati, OH UNITED STATES
Eric J. Gardner, MD, Cincinnati, OH UNITED STATES
Martin Levy, PhD, Cincinnati, OH UNITED STATES
Cincinnati Sportsmedicine and Orthopedic Center and the Noyes Knee Institute, Cincinnati, OH, USA

FDA Status Not Applicable

Summary: Anterior cruciate ligament biomechanical pivot shift studies that use an internal rotation-valgus loading profile constrains anterior tibial subluxation, whereas studies that use an anterior tibial loading and lower rotational torque allow maximum tibiofemoral subluxation.

Abstract:

Background

The stabilizing function of the anterior cruciate ligament (ACL) has typically been defined in biomechanical studies according to abnormal tibial rotations and translations, without knowledge of the actual position or subluxation of the tibiofemoral compartments. Rotational knee stability provided by the ACL in the pivot-shift phenomena involves analysis of more complex robotic testing profiles and resulting tibiofemoral compartment kinematics and subluxations.

Hypothesis

The in vitro simulation of the pivot-shift test with coupled anterior tibial loading and internal tibial-valgus loading produces major anterior subluxation of both tibiofemoral compartments not obtained with internal tibial rotation-valgus loading profiles. Increased internal rotation torque in pivot-shift testing constrains medial and central tibial compartment subluxations.
Study Design: Controlled laboratory study.

Methods

A 6 degree-of-freedom robotic knee testing system applied anterior translation and rotational loading profiles in 10 cadaveric knees before and after ACL sectioning. Changes in knee motion limits were measured and medial and lateral tibiofemoral compartment translations determined by digitization of tibial plateau anatomic landmarks. Loading profiles simulated Lachman, tibial rotation tests, and typical pivot-shift loading profiles from prior in-vitro and in-vivo studies.

Results

After ACL sectioning, anterior tibial translation increased 10.3 ± 3.7 mm at 25° flexion (P < .001). Internal tibial rotation increased 1.6 ± 1.1° (5 Nm, P > .05). In pivot-shift tests (AT 100 N, IR 1 Nm, Val 7 Nm), the tibial rotation center shifted outside the medial tibial margin, with abnormal anterior translation of both compartments (medial, 12.9 ±3.9 mm; lateral, 7.5 ± 3.7 mm; P < .001) and increased internal rotation of only 4.1 ± 3.5° (P < .05). A greater internal rotation torque (5 Nm compared with 1 Nm) in the pivot-shift test constrained and limited anterior tibial translation and prevented anterior subluxation of the medial compartment (P < .001).

Conclusions

ACL sectioning produces major increases in tibiofemoral compartment translations and only small increases in internal tibial rotation. The pivot-shift test with increased internal rotation torque constrains anterior tibial subluxation, while coupled anterior tibial loading with lower rotation torque allows greater tibiofemoral subluxations, required for testing ACL function and graft reconstructions.
Clinical Relevance: Future ACL in-vitro studies require analysis of the final position or subluxation of the tibiofemoral compartments in addition to motion limits, employing loading profiles suggested in this study.