The deep lateral femoral notch sign: a reliable diagnostic tool in identifying a concomitant anterior cruciate and anterolateral ligament injury

Knee Surg Sports Traumatol Arthrosc. 2021 Jun;29(6):1968-1976. doi: 10.1007/s00167-020-06278-w. Epub 2020 Sep 24.


Purpose: The aim of the present study was to investigate the validity and reliability of the deep lateral femoral notch sign (DLFNS) in identifying a concomitant anterior cruciate ligament (ACL)/anterolateral ligament (ALL) rupture and predicting the clinical outcomes following an anatomical single-bundle ACL reconstruction. It was hypothesized that patients with a concomitant ACL/ALL rupture would have an increased DLFNS compared to patients without a concomitant ACL/ALL rupture.

Methods: The lateral preoperative radiographs and MRI images of 100 patients with an ACL rupture and 100 control subjects were evaluated for the presence of a DLFNS and ACL/ALL rupture, respectively. The patients were evaluated clinically preoperatively and at a minimum 1 year following the ACL reconstruction. A receiver operator curve (ROC) analysis was performed to define the optimal cut-off value of the DLFNS for identifying a concomitant ACL/ALL injury. The relative risk (RR) was also calculated to determine whether the presence of the DLFNS was a risk factor for residual instability or ACL graft rupture following an ACL reconstruction.

Results: The prevalence of DLFNS was 52% in the ACL-ruptured patients and 15% in the control group. At a minimum 1-year follow-up, 35% (6/17) of the patients with DLFNS > 1.8 mm complained of persistent instability, and an MRI evaluation demonstrated a graft re-rupture rate of 12% (2/17). In patients with a DLFNS < 1.8 mm, 8% (7/83) reported a residual instability, and the graft rupture rate was 2.4% (2/83). A DLFNS > 1.8 mm demonstrated a sensitivity of 89%, a specificity of 95%, a negative predictive value of 98%, and a positive predictive value of 89% in identifying a concomitant ACL/ALL rupture. Patients with a DLFNS > 1.8 mm had 4.2 times increased risk for residual instability and graft rupture compared to patients with a DLFNS ≤ 1.8 mm.

Conclusions: A DLFNS > 1.8 mm could be a clinically relevant diagnostic tool for identifying a concomitant ACL/ALL rupture with high sensitivity and PPV. Patients with a DLFNS > 1.8 mm should be carefully evaluated for clinical and radiological signs of a concomitant ACL/ALL rupture and treated when needed with a combined intra-articular ACL reconstruction and extra-articular tenodesis to avoid a residual rotational instability and ACL graft rupture.

Level of evidence: III.

Keywords: Anterior cruciate ligament; Anterolateral ligament; Clinical outcomes; Deep lateral femoral notch sign; Radiograph.

MeSH terms

  • Adolescent
  • Adult
  • Anterior Cruciate Ligament Injuries / diagnostic imaging*
  • Anterior Cruciate Ligament Injuries / pathology*
  • Anterior Cruciate Ligament Injuries / surgery
  • Anterior Cruciate Ligament Reconstruction
  • Female
  • Femur / diagnostic imaging*
  • Femur / pathology*
  • Femur / surgery
  • Humans
  • Ligaments / diagnostic imaging
  • Magnetic Resonance Imaging
  • Male
  • Radiography
  • Reproducibility of Results
  • Retrospective Studies
  • Rupture / diagnostic imaging
  • Rupture / surgery
  • Tenodesis
  • Young Adult