Abstract
Background:
The Lateral Femoral Notch Sign (LFNS) is a depression on the lateral femoral condyle that can occur during an injury to the anterior cruciate ligament (ACL). This impaction injury can be visualized on radiographs and MRI of the affected knee and may impact outcomes following ACL injury and reconstruction. Previous work has identified the incidence of the LFNS to be between 20 and 30% in a general adult ACL population ranging from 20-40, however, little has been documented about the incidence of this injury in the teenage population. The purpose of this study was to determine the incidence of the LFNS in teenagers with ACL injuries.
Hypothesis:
The incidence of the LFNS will be different in a teenage population than in previously studied adult populations.
Methods:
Retrospective chart review that examined 131 patients aged 12-19 years old who had experienced an acute ACL tear and underwent an ACL reconstruction at an academic medical center. Nearly all patients injured their knee during participation in sports. Pre-operative radiographs and MRI scans were evaluated. Lateral femoral condyle impaction injuries were measured on lateral radiographs and sagittal MRIs with the sagittal slice containing the deepest impression of the notch being used. To measure the defect, a line tangential to the LFNS defect was made, and the length of a perpendicular line to the deepest portion of the defect was recorded. Those with an impaction < 2.0 mm in depth were classified as a normal physiological sulcus sign, 2.0 – 3.9 mm were classified as Grade I notches, and > 4.0 mm were classified as Grade II notches.
Results:
The study sample included 131 patients with a mean age of injury of 17.9 ± 1.2 years. On lateral plain radiographs, 12 out of 131 patients (9.2%) were found to have a Grade 1 notch, and on sagittal MRI, 22 out of 131 patients (16.8%) were found to have a Grade I notch. The remaining patients were found to only have physiological sulci. No Grade II notches were identified. The mean depths of the LFNS of all patients on radiograph and MRI were 0.96 mm ± 0.64 and 1.35 mm ± 0.60, respectively.
Conclusion:
In the teenage ACL tear population, the incidence of the LFNS may be lower than previously documented in the general ACL-injured population.