The deep lateral femoral notch sign (DLFNS) is associated with concomitant knee injuries in skeletally immature patients with anterior cruciate ligament injuries

Purpose
The aim of this study was to investigate the prevalence of the deep lateral femoral notch sign (DLFNS) in skeletally immature patients with anterior cruciate ligament (ACL) injuries and its potential association with trauma-related and clinical factors.

Methods
A total of 87 skeletally immature patients with ACL injuries and a minimum follow-up of 1 year were included and matched based on sex and skeletal age with 44 controls. The presence of the DLFNS, defined as a notch depth of >1.5 mm, was assessed on MRI. Intra- and inter-observer reliability were calculated, and prevalence was determined. Associations between the DLFNS and trauma mechanism, trauma-related bone lesions, concomitant injuries, clinical instability, and treatment at both baseline and follow-up were assessed using Fisher's exact tests.

Results
The prevalence of DLFNS was 11.5% (10/87) among skeletally immature patients with ACL injuries compared to 0% (0/44) in controls (p = 0.02). DLFNS depth demonstrated excellent intra- and inter-observer reliability (ICC > 0.90). Furthermore, a significant positive association was identified between the DLFNS and overall concomitant knee injuries (p = 0.02), including ligamentous, meniscus, and cartilage injuries. Further subgroup analysis did not reveal any statistically significant associations with individual injury types. All patients presenting with a DLFNS ultimately received operative treatment, either during initial management or follow-up. This revealed a significant positive association between the DLFNS and primary operative treatment (p = 0.02).

Conclusion
The prevalence of the DLFNS in skeletally immature patients with ACL injuries was 11.5%. When present, the DLFNS was associated with overall concomitant knee injuries and primary ACL reconstruction. The DLFNS may therefore be an important sign to take into consideration on the primary MRI in skeletally immature patients with ACL injuries.