1. Effect of Tunnel Position in Graft Failure with Single-Bundle Anterior Cruciate Ligament Reconstruction
1Soheil Sabzevari, MD; 1Amir Ata Rahnemai-azar, MD; 1Libin Zheng, MD; 2Brandon Marshall, MS; 2Junjun Zhu, MS; 1Monica A. Linde, BS; 1,2Patrick Smolinski, PhD; 1,2Freddie H. Fu, MD
1Department of Orthopaedic Surgery, University of Pittsburgh, Pittsburgh, U.S.A.
2Department of Mechanical Engineering, University of Pittsburgh, Pittsburgh, PA, U.S.A
Introduction
Results
Anatomic anterior cruciate ligament (ACL) reconstruction is gaining favor in the clinical community and can lead to different tunnel position and graft location than traditional trans-tibial reconstruction. With a different graft position, there can be difference in the graft in situ force under knee loading [1] which could affect graft failure.
There is a significant difference (p < 0.05) between the two reconstructions for failure load, however there is not a significant difference for displacement at the failure load. The mean failure load of the anatomic group ( ± ) is significantly higher than that of the non-anatomic group ( ± 33.42) (Fig. 2). The mean displacement at failure of the anatomic group (48.52 ± 22.12) was not significantly different than the non-anatomic group (66.42 ± 33.24) (Fig. 3).
Objective
The objective of this study was to evaluate the anterior tibial (AT) load causing failure of single-bundle (SB) anatomic and high ACL (non-anatomic) reconstructions, where a high graft position is defined as having a high inclination angle [2]. The hypothesis of this study was that anatomic ACL reconstruction would result have higher AT failure load (tensile strength) than high ACL reconstruction.
Methods
Fig. 2 Mean AT failure load (N) (*p<0.05)
Fig. 3 Mean displacement (mm) at failure
Twelve fresh, frozen porcine knees were used for testing and were divided randomly into two groups: non-anatomic ACL reconstruction and anatomic ACL reconstruction. The knees were sectioned approximately 15 cm from the joint line at the femur and the tibia, and then ends of bones secured in cylinders. By arthrotomy the native ACL was removed, 9 mm tunnels were drilled, and the ACL was reconstructed using grafts from bovine extensor tendons. The grafts were folded over and whip stitched with no. 5 suture (Ethicon, Somerville, NJ) having an 8 mm diameter. The grafts were fixed at 30°of flexion (full porcine extension) with 40 N of tension [1], and fixed with a spiked screw and washer on both the tibia and femur.
The dissected knees were placed in a custom made testing fixture that was attached to an axial testing machine at 30°of flexion (Fig. 1) and an anterior tibia load was applied. The knees were then loaded at a rate of 60 mm/min until graft failure.
Data was analyzed using the Mann-Whitney U test, and statistical significance was set at p < 0.05.
The graft location, as determined by the graft inclination angle (Fig. 4), for each of the methods of reconstruction determines the anterior tibial failure load (shown as ‘F’). The angle that the graft makes with the horizontal axis of the anatomic group (shown as ‘θa’) is smaller than the non-anatomic group (shown as ‘θb’). Thus, assuming that the graft tensile strength (shown as ‘T’) is the same in both groups, the difference in the graft angle in the two groups will result in a higher AT failure load in the anatomic group based on a horizontal force balance (Fig. 4). This matches the data above (Fig. 2).
Fig. 4 Horizontal force balance in the knee showing F (anterior tibial load) and T (graft tensile strength)
Conclusion
This study indicates that the graft position during ACL reconstruction affects the failure load. The failure load of the anatomic ACL reconstruction is higher than the non-anatomic ACL reconstruction, however, dissection of the knees can affect the ACL graft loading and the result may differ in the undissected knee.
Fig. 1 Testing setup showing fixture and AT load
Corresponding Author
References
Freddie H. Fu, M.D.
David Silver Professor and Chairman
Department of Orthopaedic Surgery
University of Pittsburgh
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