Direct Measurement of Graft Tension in Anatomic Versus Non-anatomic ACL Reconstructions during a Dynamic Pivoting Maneuver

Transcription

1 Direct Measurement of Graft Tension in Anatomic Versus Non-anatomic ACL Reconstructions during a Dynamic Pivoting Maneuver Scott A. Buhler 1, Newton Chan 2, Rikin Patel 2, Sabir K. Ismaily 2, Brian Vial 1, Walter R. Lowe 3, Philip C. Noble 2,1. 1 Baylor College of Medicine, Houston, TX, USA, 2 Institute of Orthopedic Research and Education, Houston, TX, USA, 3 University of Texas Health Sciences Center, Houston, TX, USA. Disclosures: S.A. Buhler: None. N. Chan: None. R. Patel: None. S.K. Ismaily: None. B. Vial: None. W.R. Lowe: 2; Arthrex, Inc.. 3B; Stryker. 3C; DJ Orthopaedics. P.C. Noble: 1; Zimmer, Stryker, Omni Sciences Inc., Springer. 2; Zimmer. 3B; Zimmer, Omni Sciences Inc., DePuy, Johnson & Johnson. 5; Synthes, Zimmer. 7; Springer. Introduction: Despite the success of ACL (anterior cruciate ligament) reconstructions in restoring knee function after ligament injury, recurrent procedures do not completely restore the initial stability of the knee, especially in twisting and pivoting activities, leading to an unacceptable incidence of early failures. Attempts to improve the performance of ACL reconstructions have led to numerous innovations, including accurate replication of the sites of origin and insertion of the injured ligament, intra-operative use of surgical navigation to guide graft placement, and the use of the double-bundle technique in an attempt to mimic the morphology of the native ACL. Despite these measures, non-anatomic reconstruction places the graft in a location different from the native ACL, whereas anatomic reconstruction attempts to replicate the anatomical placement of the native ACL. This difference in placement may cause discrepancies in load distribution and kinematics of the knee. In this study we test the hypothesis that anatomic vs. and non-anatomic grafts are exposed to different loads during dynamic pivoting maneuvers. Methods: Eight cadaveric knees were tested in a custom-built testing machine. The knees were tested using a simulated dynamic pivoting maneuver applying varying forces on the iliotibial band, internal rotation moments, and valgus moments. The conditions of maximum instability of each knee were determined by subjecting each specimen to a battery of 36 combinations of IT band load (50N, 75N, 100N, 125N, 150N), internal rotation torque (1Nm, 2Nm, 3Nm), and valgus torque (5Nm, 7Nm). Conditions leading to the largest translation of the lateral femoral condyle were considered the most provocative of instability. Each knee was tested intact, after division of the ACL, and after single bundle ACL reconstruction, with anatomic and nonanatomic graft placement. Bone-tendon-bone allografts were used in all reconstructions. Loads supported by the ACL graft were measured directly by passing each graft through an articulating sleeve lining the walls of the tibial tunnel and applying tension externally. A load cell was attached inline to the graft to provide continuous measurement of the tension placed on the ACL grafts throughout the motion of the knee. The accuracy and reproducibility of this measurement method was confirmed in preliminary testing in which the true tension within the graft was measured using an additional force transducer with an open exposure of the knee joint. Two methods of ACL reconstruction were undertaken in each specimen: (i) Anatomic ACL reconstruction: the center of the tibial tunnel was located on the native ACL footprint, with the posterior edge of the tunnel located on the posterior edge of the anterior horn of the lateral meniscus. The femoral tunnel was located at the center of the native ACL footprint between the antero-medial and postero-lateral bundles. (ii) Non-anatomic ACL reconstruction was performed after the anatomic tunnels were filled with bone plugs. A 7mm PCL referencing guide was used to locate the tibial tunnel and a 10mm tunnel was drilled. A 3D computer model was generated from CT scans and native ACL footprints on the femur were located using a digitizing stylus. Standardization of the non-anatomic femoral tunnel was accomplished following the methods of Kopf et al. who identified the most common location of tunnel placement following trans-tibial ACL reconstructions. The load supported by the ACL graft was measured during the dynamic pivoting maneuver provoking the greatest instability in initial testing Results: After application of the loads, the initial tension of the anatomic ACL grafts were 38% higher than the tension in the non-anatomic grafts (anatomic: 42.2N, non-anatomic: 30.5N; p=0.005) at 15 of flexion (Figure 1). As the knee flexed to 90, the differences between the two graft placements became less significant (at 30 : p=0.13; at 45 : p = 0.31) and less pronounced in absolute terms (at 30 : 12.6N (anatomic) and 7.6N (non-anatomic); at 45 : 6.3N (anatomic) and 4.1N (non-anatomic). The maximum difference in graft tension was 11.8N at 15 flexion. Differences decreased to 5.0N at 30 flexion and 2.2N at 45 flexion. Discussion: During the simulated pivoting maneuver, the anatomic ACL reconstruction was loaded at a higher tension than the non-anatomic reconstruction throughout the movement, despite equal tensioning of the graft in an unloaded knee. Our results suggest that the anatomic reconstruction may play a bigger role in stabilizing the knee during the pivoting maneuver than a nonanatomic reconstruction. The results suggest that greater differences as the knee goes into extension. Due to the lower tension in the non-anatomic graft, the forces in the knee during a pivoting maneuver may be transferred to the surrounding soft tissues allowing for greater potential for re-injury in the repaired knee. Significance: By measuring graft tension in the knee during a simulated dynamic pivoting maneuver following anatomic and non-

2 anatomic ACL reconstruction, we evaluate the effects on tunnel placement on the load distribution of the ACL graft. Acknowledgments: References:

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4 ORS 2014 Annual Meeting Poster No: 1367

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