Anatomic landmarks utilized for physeal-sparing, anatomic anterior cruciate ligament reconstruction: an MRI-based study.

BACKGROUND: Anterior cruciate ligament (ACL) injury and reconstruction in the skeletally immature patient are becoming more common. The purpose of this study was to develop a reproducible anatomic ACL reconstruction technique, based on intra-articular and extra-articular landmarks, that reliably produces a femoral tunnel of adequate length and diameter while avoiding the distal femoral physis.
METHODS: Magnetic resonance images (MRIs) of one hundred and eighty-eight children (age range, six to seventeen years) were evaluated. Two extra-articular landmarks, the femoral insertion of the popliteus tendon and the lateral femoral epicondyle, and one intra-articular landmark, the central portion of the femoral footprint of the ACL, were identified. Computer software was used to plot these landmarks in all three planes and to draw lines representing two potential femoral tunnels. The first line connected the center of the ACL femoral footprint with the insertion of the popliteus tendon, and the second connected the center of the ACL femoral footprint with the lateral femoral epicondyle. The length of each tunnel, the shortest distance from the center of each tunnel to the distal femoral physis, and the height of the lateral femoral condyle from the physis to the chondral surface and to the base of the cartilage cap were calculated. A three-dimensional MRI reconstruction was used to confirm that placement of a femoral tunnel with use of the chosen landmarks would avoid the distal femoral physis.
RESULTS: The mean distance from the center of the preferred ACL tunnel, which connected the center of the ACL femoral footprint with the insertion of the popliteus tendon, to the distal femoral physis was 12 mm, independent of sex (p = 0.94) or age, and the shortest distance was 8 mm. The length of this proposed tunnel averaged 30.1 mm in the boys and 27.4 mm in the girls (p < 0.001), and it averaged 25.4 mm at an age of six years and 29.7 mm at an age of seventeen years. The mean distance from the center of the alternative tunnel, which connected the center of the ACL femoral footprint with the lateral epicondyle, to the distal femoral physis was 8.8 mm in the boys and 8.9 mm in the girls (p = 0.55). The mean length of this alternative tunnel was 34.3 mm in the boys and 31.6 mm in the girls (p < 0.001).
CONCLUSIONS: Drilling from the center of the ACL femoral footprint to the insertion of the popliteus tendon would have resulted in a mean tunnel length of 27 to 30 mm, and it would have allowed the safe placement of a femoral tunnel at least 7 mm in diameter in a patient six to seventeen years old. The center of the ACL femoral footprint and the popliteus insertion are easily identifiable landmarks and will allow safe, reproducible, anatomic ACL reconstruction in the skeletally immature patient.