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The Effect of Tibial Positioning on the Diagnosis of Posterolateral Rotatory Instability in the Posterior Cruciate Ligament Deficient Knee
  1. Eric J Strauss (ericstraussmd{at}gmail.com)
  1. NYU-Hospital For Joint Diseases, United States
    1. Charbel Ishak (charbelishak{at}gmail.com)
    1. NYU-Hospital For Joint Diseases, United States
      1. Christopher Inzerillo (christopher.inzerillo{at}med.nyu.edu)
      1. NYU-Hospital For Joint Diseases, United States
        1. Michael Walsh (michael.walsh{at}med.nyu.edu)
        1. NYU-Hospital For Joint Diseases, United States
          1. Peter Walker (peter.walker{at}med.nyu.edu)
          1. NYU-Hospital For Joint Diseases, United States
            1. Laith Jazrawi (laith.jazrawi{at}med.nyu.edu)
            1. NYU-Hospital For Joint Diseases, United States
              1. Jeffrey Rosen (jeffrey.rosen{at}med.nyu.edu)
              1. NYU-Hospital For Joint Diseases, United States

                Abstract

                Objective: To determine if positioning of the tibia affects the degree of tibial external rotation seen during a dial test in the setting of a posterior cruciate ligament deficient knee.

                Design: Laboratory investigation

                Setting: Biomechanics Laboratory

                Hypothesis: An anterior force applied to the tibia in the combined posterior cruciate-posterolateral corner deficient knee will yield increased tibial external rotation during a dial test.

                Methods: The degree of tibial external rotation was measured with 5 Newton-meters of external rotation torque applied to the tibia at both 30 degrees and 90 degrees of knee flexion. Before the torque was applied, either an anterior force, a posterior force, or neutral (normal, reduced control) force was applied to the tibia. External rotation measurements were repeated after sequential sectioning of the posterior cruciate ligament, the posterolateral structures and the fibular collateral ligament.

                Results: Baseline testing of the intact specimens demonstrated a mean external rotation of 18.6° with the knee flexed to 30° (range 16.1-21.0°) and a mean external rotation of 17.3° with the knee flexed to 90° (range 13.8- 20.0°). Sequential sectioning of the PCL, popliteus and popliteofibular ligament, and the FCL led to a significant increase in tibial external rotation compared to the intact knee for all testing scenarios. After sectioning of the popliteus and popliteofibular ligament, the application of an anterior force during testing led to a mean tibial external rotation which was 5° greater than testing in the neutral position and 7.5° greater than testing with a posterior force. In the PCL, popliteus/popliteofibular ligament and FCL deficient knee, external rotation was 9° and 12° greater with the application of an anterior force during testing compared to neutral positioning and the application of a posterior force respectively.

                Conclusion: An anterior force applied to the tibia during the dial test in a combined PCL-PLC injured knee increased the overall amount of observed tibial external rotation during the dial test. The anterior force reduced the posterior tibial subluxation associated with posterior cruciate ligament injury, which is analogous to what is observed when the dial test is performed with the patient in the prone position. Reducing the tibia with either an anterior force when the patient is supine or performing the dial test with the patient prone, increases the ability of an examiner to detect a concomitant posterolateral corner injury in the setting of a posterior cruciate ligament deficient knee.

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