Characteristics of the femoral tunnel of anatomical and isometric single bundle anterior cruciate ligament reconstruction: a modeling analysis based on quadrant method and anatomical landmarks

Abstract

Purpose: To investigate the anatomical features of the femoral tunnel in anatomical and isometric single-bundle ACL reconstruction.

Method: Thirty-two 3-dimensional knee models were reconstructed based on CT scan (average age: 26.5 ± 6.7 years, 18 males and 14 females, 17 left and 15 right). Multiple anatomical landmarks were identified. Virtual femoral tunnels were created at the deep and high portion of ACL footprint, close to the lateral intercondylar ridge to achieve best anatomy and isometry, simulating an anteromedial portal reconstruction. Anatomical features of the femoral tunnels were analyzed. The position of the femoral tunnel was quantified by the distance to anatomical landmarks and using quadrant methods. The spatial angles, length and outer opening of the femoral tunnels were also evaluated.

Results: Acceptable tunnels were created in all models. The center of femoral tunnel was slightly higher than the apex of deep cartilage, near the deep one-third point across the shallow-deep dimension of the lateral femoral condyle. Using the quadrant method, the tunnel was located at 28.4% ± 2.2% and 22.2% ± 3.6%, parallel and perpendicular to the Blumensaat line, respectively. The spatial angles of the tunnel were 40°, 33.5° ± 4.1° and 38.2° ± 4.4° on the sagittal, transverse, and coronal planes, respectively. The average tunnel length was 34.8 mm ± 3.8 mm. The outer opening of the tunnels was located at the posterior one-third of the femoral metaphysis.

Conclusion: The anatomical and isometric positioning of the femoral tunnel can be achieved through anteromedial portal with satisfied tunnel characteristics. The apex of deep cartilage may be used as an anatomical reference for tunnel positioning. When drilled at appropriate orientation, favorable tunnel length, integrity and position of the outer opening can be obtained.

Keywords: Anatomical isometric ACL reconstruction; Anatomical landmarks; Femoral tunnel; Model simulation; Quadrant method.

Fig. 1

The medial wall of lateral femoral condyle oriented in accordance with arthroscopy. The red and green dots represent the apex of deep cartilage (ADC) and the intercondylar roof, respectively. The black, red and green dotted lines represent the lateral intercondylar ridge (LIR), cartilage margin and the deep condylar edge (DCE), respectively. The red and blue areas represent the ACL femoral footprint of anteromedial (AM) bundle and posterolateral (PL) bundle, respectively

Fig. 2

Quantification of the position of the femoral tunnel. (a) Distance to anatomical landmarks. (b) Quadrant method. The red, green and gray dots represent the apex of deep cartilage (ADC), the intercondylar roof and the center of femoral tunnel, respectively. The black, red and green dotted lines represent the lateral intercondylar ridge (LIR), the cartilage margin and the deep condylar edge (DCE), respectively. The red area and the gray area represent the femoral footprint of ACL and the inner opening of the femoral tunnel, respectively. L1 and L2 represent the distances to the DCE and the front cartilage margin, respectively. h1, h2 and h3 represent the distances to the ADC, intercondylar ridge and low cartilage margin, respectively

Fig. 3

Spatial parameters of the femoral tunnel. (a) The angle with the femoral shaft on the sagittal plane (θ1). (b) The angle with the condylar tangent on the transverse plane (θ2). (c) The angle with the condylar tangent on the coronal plane (θ3). (d) The position of the outer opening of the femoral tunnel. L1, L2 and L3 represent the distance to lateral femoral epicondyle along proximodistal direction, distance to posterior and anterior femoral cortex along the anteroposterior direction, respectively