Varying Femoral Tunnels Between the Anatomical Footprint and Isometric Positions

Department of Orthopaedic Surgery, University of Pittsburgh, Pittsburgh, Pennsylvania

^* To whom correspondence should be addressed. E-mail: arrisherlm{at}msx.upmc.edu.

	Abstract

Background: Knee kinematics and in situ forces resulting from anterior cruciate ligament reconstructions with 2 femoral tunnel positions were evaluated.

Hypothesis: A graft placed inside the anatomical footprint of the anterior cruciate ligament will restore knee function better than a graft placed at a position for best graft isometry.

Study Design: Controlled laboratory study.

Methods: Ten cadaveric knees were tested in response to a 134-N anterior load and a combined 10-N·m valgus and 5-N·m internal rotation load. A robotic universal force-moment sensor testing system was used to apply loads, and resulting kinematics were recorded. An active surgical robot system was used for positioning tunnels in 2 locations in the femoral notch: inside the anatomical footprint of the anterior cruciate ligament and a position for best graft isometry. The same quadrupled hamstring tendon graft was used for both tunnel positions. The 2 loading conditions were applied.

Results: At 30° of knee flexion, anterior tibial translation in response to the anterior load for the intact knee was 9.8 ± 3.1 mm. Both femoral tunnel positions resulted in significantly higher anterior tibial translation (position 1: 13.8 ± 4.6 mm; position 2: 16.6 ± 3.7 mm; P < .05). There was a significant difference between the 2 tunnel positions. At the same flexion angle, the anterior tibial translation in response to the combined load for the intact knee was 7.7 ± 4.0 mm. Both femoral tunnel positions resulted in significantly higher anterior tibial translation (position 1: 10.4 ± 5.5 mm; position 2: 12.0 ± 5.2 mm; P < .05), with a significant difference between the tunnel positions.

Conclusion: Neither femoral tunnel position restores normal kinematics of the intact knee. A femoral tunnel position inside the anatomical footprint of the anterior cruciate ligament results in knee kinematics closer to the intact knee than does a tunnel position located for best graft isometry.

Clinical Relevance: Anatomical femoral tunnel position is important in reproducing function of the anterior cruciate ligament.

Key Words: active robotic surgery, robotic/universal force-moment sensor (UFS) testing system, anterior cruciate ligament (ACL) reconstruction, femoral tunnel position

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