Surgically oriented measurements for three-dimensional characterization of tunnel placement in anterior cruciate ligament reconstruction

Abstract

Objective: To develop and evaluate the feasibility and reliability of an alternative three-dimensional (3D) measurement system capable of characterizing tunnel position and orientation in ACL reconstructed knees. Methods: We developed a surgically oriented 3D measurement system for characterizing femoral and tibial drill tunnels from ACL reconstructions. This is accomplished by simulating the positioning of the drill bit originally used to create the tunnels within the bone, which allows for angular and spatial descriptions along defined axes that are established with respect to previously described anatomic landmarks and radiographic views. Computer-generated digital phantoms composed of simplified geometries were used to verify proper calculation of angular and spatial measurements. We also evaluated the inter-observer reliability of the measurements using 10 surfaces generated from cadaveric knees in which ACL tunnels were drilled. The reliability of the measurements was evaluated by intraclass correlation coefficients. Results: The digital phantom evaluation verified the measurement methods by computing angular and spatial values that matched the known values in all cases. The intraclass correlation coefficient was calculated for four users and was found to range from 0.95 to 0.99 for the femoral and tibial measurements, demonstrating near-perfect agreement. Conclusions: The characterization of ACL tunnels has historically concentrated on two-dimensional (2D) measurements; however, it can be difficult to define ACL tunnel placement using 2D methods. We have presented novel techniques for defining graft tunnel placement from 3D surface representations of the ACL reconstructed knee. These measurements provide exact tunnel location spatially and along axes that offer the potential to comparatively analyze ACL reconstructions post-operatively using advanced imaging. These methods are reliable, and have been demonstrated to be applicable to multiple single-bundle techniques for ACL reconstruction.

Three-Dimensional Characterization of the Anterior Cruciate Ligament's Femoral Footprint

“…12,16 However, in 3D renderings, there is substantial anatomic undulation and variability of Blumensaat line, which can induce variability into measurements because determining the slope of the start point can be challenging. 17 The measurements employed in this study are based on easily defined radiographic landmarks and a previously defined radiographic coordinate system. 12,19 Therefore, this study is novel because it presents 3D surface measures of the ACL footprint on the basis of direct open dissections and a tested measurement system with outstanding reliability.…”

“…Previous studies have used coordinate systems to measure and analyze femoral ACL tunnels. 12,17,19 These previous works have measured the location of ACL tunnels drilled in the location of the ACL bundles after arthroscopic dissection 12 of the native ACL, or after ACL tunnel placement by multiple surgeons in a cadaveric study. 19 Beyond providing a mathematical reference for the native femoral ACL footprint in traditional orientation, we reoriented our data to provide a description of the footprint that is surgically oriented relative to the intercondylar roof.…”

“…Using VTK and Paraview (Kitware Inc., Clifton Park, New York), four spheres were placed on the surface of each specimen representing the distal-most, proximal-most, anterior-most, and posterior-most margins of the ACL footprint. Spatial localization of the footprint borders were conducted using the measurement methods described by Ramme et al, 17 in which the position of the sphere center point was measured as a proportion of the distance from the distal-most aspect of the lateral condyle (c) with respect to the total diameter of the lateral condyle (C) (►Fig. 3), and also as the proportion of the distance from the posterior-most aspect of the lateral condyle (n) with respect to the apex of the intercondylar notch (N) (►Fig.…”

“…Intraclass correlation coefficients for the described n/N and c/C measurements were found to be 0.98 and 0.98 for femoral specimens in a previous study on this radiography based coordinate measurement technique. 17,19 Footprint Overlap Mapping Footprint overlap mapping allows for simultaneous visualization of multiple ACL footprints on a representative femur surface model. Using the aforementioned method of orient-ing the femur surface models, each specimen's ACL footprint is also aligned to a representative femoral surface in the described standardized orientation.…”

Anterior Cruciate Ligament Tunnel Placement

“…A 3D Cartesian coordinate system was used to analyze tunnel location as previously described. 18 This coordinate system allows reproducible specimen orientation and radiographic measures based on anatomic landmarks around the knee. It is applicable to cadaveric and clinical studies.…”