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# Can Markers Injected Into a Single-Loop Anterior Cruciate Ligament Graft Define the Axes of the Tibial and Femoral Tunnels? A Cadaveric Study Using Roentgen Stereophotogrammetric Analysis

[+] Author and Article Information

Biomedical Engineering Program, One Shields Avenue, University of California, Davis, CA 95616

M. L. Hull1

Biomedical Engineering Program, One Shields Avenue, University of California, Davis, CA 95616; Department of Mechanical Engineering, One Shields Avenue, University of California, Davis, CA 95616mlhull@ucdavis.edu

S. M. Howell

Department of Mechanical Engineering, One Shields Avenue, University of California, Davis, CA 95616

1

Corresponding author.

J Biomech Eng 130(4), 044503 (May 23, 2008) (4 pages) doi:10.1115/1.2907766 History: Received February 07, 2007; Revised September 19, 2007; Published May 23, 2008

## Abstract

Lengthening of a soft-tissue anterior cruciate ligament (ACL) graft construct over time, which leads to an increase in anterior laxity following ACL reconstruction, can result from relative motions between the graft and fixation devices and between the fixation devices and bone. To determine these relative motions using Roentgen stereophotogrammetry (RSA), it is first necessary to identify the axes of the tibial and femoral tunnels. The purpose of this in vitro study was to determine the error in using markers injected into the portions of a soft-tissue tendon graft enclosed within the tibial and femoral tunnels to define the axes of these tunnels. Markers were injected into the tibia, femur, and graft in six cadaveric legs the knees of which were reconstructed with single-loop tibialis grafts. The axes of the tunnels were defined by marker pairs that were injected into the bones on lines parallel to the walls of the tibial and femoral tunnels (i.e., standard). By using marker pairs injected into the portions of the graft enclosed within the tibial and femoral tunnels and the marker pairs aligned with the tunnel axes, the directions of vectors were determined by using RSA, while a $150N$ anterior force was transmitted at the knee. The average and standard deviations of the angle between the two vectors were $5.5±3.3deg$. This angle translates into an average error and standard deviation of the error in lengthening quantities (i.e., relative motions along the tunnel axes) at the sites of fixation of $(0.6±0.8)%$. Identifying the axes of the tunnels by using marker pairs in the graft rather than marker pairs in the walls of the tunnels will shorten the surgical procedure by eliminating the specialized tools and time required to insert marker pairs in the tunnel walls and will simplify the data analysis in in vivo studies.

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## Figures

Figure 1

A-P view of the knee showing marker placement. T1–T6 are markers implanted in the tibia, F1–F6 are markers implanted in the femur, G1–G8 are markers implanted in the graft, EL is a marker attached to the femoral fixation, WL1 and WL2 are markers attached to the tibial fixation, PT2∕T1 and PF2∕F1 are vectors aligned with the axes of the femoral and tibial tunnels, respectively, while PG2∕G1 is a vector computed using a pair of graft markers.

Figure 2

Photograph of a cadaveric leg specimen in the loading apparatus. A pneumatic actuator applied either a posterior or an anterior force to the tibia, while the thigh and ankle were fixed with the specimen in a supine position and the knee flexed to 25deg. Two load cells measured the applied force and the reaction force at the ankle joint. The shear force transmitted at the knee was computed from the measured loads in conjunction with the weight of the specimen.

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