What causes the lateral femoral notch sign in the knee on radiographs or MRI?
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Answer:
The deep lateral femoral notch sign is an impaction fracture of the lateral femoral condyle: the condylopatellar sulcus driven deeper than 1.5 mm on the lateral knee radiograph. [1] It marks an anterior cruciate ligament (ACL) tear. It appears in a minority of tears, so it excludes nothing, but when present it points to lateral meniscus and medial collateral ligament injury.
Why is it called so?
Every lateral femoral condyle carries a shallow transverse groove, the lateral condylopatellar sulcus, also called the terminal sulcus. That groove is normal: in 62 knees with an intact ACL its mean depth was 0.45 mm and not one exceeded 1.2 mm. [1] The sign is the same groove driven abnormally deep, which is why the literature calls it the deep lateral femoral notch. The notch is anatomy. The depth is the injury.
Pathophysiology
It is an impaction injury. During the pivot shift that ruptures the ACL, the posterior part of the lateral tibial plateau is driven against the anterocentral lateral femoral condyle and compresses the terminal sulcus. [2] The company the sign keeps fits those forces: across 590 patients imaged within three weeks of an ACL injury, a superficial medial collateral ligament (MCL) tear, younger age and a medial posterior tibial bone bruise were the independent predictors of a notch 2 mm or deeper. [3]
Alternative names: Deep lateral femoral notch sign, lateral notch sign, deep lateral sulcus sign, lateral femoral sulcus sign, deep sulcus sign of the lateral femoral condyle (not to be confused with the unrelated “deep sulcus sign” of pneumothorax on a supine chest radiograph)
Other associated named signs: Segond fracture (lateral capsular sign) and reverse Segond fracture, and the empty notch sign, all separate indirect markers of ACL and ligamentous knee injury
How deep is a pathological notch?
Four cut-offs are in use and they do not agree, so the millimetres matter more than the label.
| Cut-off | What it rests on |
|---|---|
| 1.5 mm | Three standard deviations above a normal mean of 0.45 mm on lateral radiographs. The original and most quoted threshold [1] |
| 1.0 mm | Positive predictive value 96% against arthroscopy, in 65 ACL-injured versus 53 control knees. Observer agreement for the measurement was 0.93 between readers and 0.96 within readers [4] |
| 1.8 mm | ROC-derived cut-off for a concomitant anterolateral ligament tear: sensitivity 89%, specificity 95%, negative predictive value 98% [5] |
| 2.0 mm | Used by the largest cohorts, and the depth above which rotatory laxity increased [6] [3] [11] |
How often is the notch actually present?
Rarely, and that is the most useful thing to know about it. A depression of 2 mm or more appeared on radiographs in only 9 of 120 knees (7.5%) with an acute ACL disruption, with depths of 2 to 6 mm over a length of 20 to 25 mm. [6] In 34 consecutive arthroscopically proven acute tears, the notch was deep in no patient at all, and the authors concluded it was not a useful acute sign. [7] Across the wider literature the figure reaches 52%, depending entirely on the threshold and the modality. [2] A double notch, meaning more than one notch on the condyle, was 100% specific but only 17.2% sensitive for a complete tear. [8]
Specificity moves with the cut-off too. No ACL-intact knee in the original radiographic series had a sulcus deeper than 1.2 mm, [1] yet 15% of control knees in a later series carried the sign against 52% of ruptured knees. [5] A deep notch is strong evidence rather than proof.
What a positive notch sign should send you looking for
This is where the sign earns its keep. It is a poor screening test for a ligament that MRI will
diagnose anyway, but a good pointer to the injuries that change the operation.
| Look for | With the sign | Without it |
|---|---|---|
| Posterior root tear of the lateral meniscus | 39.4% | 5.2% in isolated ACL tears. A root tear made the sign 5.3 times more likely [9] |
| Lateral meniscus tear of any kind | 10 of 11 knees (91%) | 58 of 147 knees (39%) [6] |
| Grade II or III superficial MCL tear | 34.6% | 12.6% for grade 0 or I, giving a 3.7-fold risk at 87.4% specificity [3] |
| Residual instability after reconstruction, notch above 1.8 mm | 6 of 17 patients (35%), graft re-rupture 2 of 17 (12%) | 7 of 83 (8%) and 2 of 83 (2.4%) below that depth [5] |
- Give the depth in millimetres rather than only “present”. Beyond 1.5 mm is abnormal and the
measurement is reproducible. [4] - Interrogate the posterior root of the lateral meniscus deliberately. [9]
- Check the superficial MCL and the medial posterior tibial plateau for a bone bruise. [3]
- On a technically limited study with an intact-looking ACL, a deep notch is reason to look
again.
Whether the depth measures instability is genuinely unsettled, and the two best studies disagree. In 84 ACL-injured patients, notch depth correlated with neither lateral compartment translation nor tibial acceleration on a quantitative pivot shift, although the same study found deeper notches in knees that had a lateral meniscus tear (1.0 versus 0.6 mm on radiographs). [10] Navigation-based quantification reached the opposite conclusion, with greater rotatory laxity above a 2 mm notch. [11] An international consensus panel could not agree in 2025 on whether the sign should drive the decision to add a lateral extra-articular procedure to reconstruction. [12] Report the sign and its depth, and leave that argument to the surgeon.
Frequently asked questions
What is the deep lateral femoral notch sign?
It is an impaction fracture of the lateral femoral condyle that deepens the normal lateral condylopatellar sulcus beyond 1.5 mm on a lateral knee radiograph. It is an indirect sign of an anterior cruciate ligament tear, produced when the posterior part of the lateral tibial plateau is driven against the condyle during the pivot shift.
How deep does the lateral femoral notch have to be to be abnormal?
Deeper than 1.5 mm on the lateral radiograph, which is three standard deviations above the normal mean of 0.45 mm. No knee with an intact ligament in the original series exceeded 1.2 mm. Later work uses 1.0 mm, 1.8 mm and 2.0 mm cut-offs, so report the depth you measured rather than only that the sign is present.
Is the lateral femoral notch sign the same as the deep sulcus sign?
Around the knee, yes. Deep lateral sulcus sign and lateral femoral sulcus sign are the same finding. The unrelated deep sulcus sign of pneumothorax is a deep lateral costophrenic angle on a supine chest radiograph. The two share a name and nothing else.
What does a deep lateral femoral notch mean for the menisci?
Hunt for a posterior root tear of the lateral meniscus. Its prevalence was 39.4% in knees with the sign against 5.2% in isolated ACL tears, and a root tear made the sign 5.3 times more likely. A lateral meniscus tear of any type was present in 10 of 11 knees with the sign against 58 of 147 without it.
References
- Cobby MJ, Schweitzer ME, Resnick D. The deep lateral femoral notch: an indirect sign of a torn anterior cruciate ligament. Radiology. 1992;184(3):855-8. PMID: 1509079.
- Mostowy M, Ruzik K, Ebisz M, et al. Impaction fractures of the lateral femoral condyle related to anterior cruciate ligament injury: a scoping review concerning diagnosis, prevalence, clinical importance, and management. Clin Orthop Surg. 2023;15(5):781-92. PMID: 37811510.
- Inoue J, Nukuto K, Park YL, et al. Deep lateral femoral notch sign is associated with superficial medial collateral ligament tear in patients with anterior cruciate ligament injury. J ISAKOS. 2025;15:100999. PMID: 40930221.
- Lodewijks PCAM, Delawi D, Bollen TL, et al. The lateral femoral notch sign: a reliable diagnostic measurement in acute anterior cruciate ligament injury. Knee Surg Sports Traumatol Arthrosc. 2019;27(2):659-64. PMID: 30317524.
- Dimitriou D, Reimond M, Foesel A, et al. 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;29(6):1968-76. PMID: 32974801.
- Garth WP, Greco J, House MA. The lateral notch sign associated with acute anterior cruciate ligament disruption. Am J Sports Med. 2000;28(1):68-73. PMID: 10653546.
- Jones AR, Finlay DB, Learmonth DJ. A deep lateral femoral notch as a sign of acutely torn anterior cruciate ligament. Injury. 1993;24(9):601-2. PMID: 8288379.
- Grimberg A, Shirazian H, Torshizy H, et al. Deep lateral notch sign and double notch sign in complete tears of the anterior cruciate ligament: MR imaging evaluation. Skeletal Radiol. 2015;44(3):385-91. PMID: 25408377.
- Berthold DP, Muench LN, Herbst E, et al. High prevalence of a deep lateral femoral notch sign in patients with anterior cruciate ligament (ACL) and concomitant posterior root tears of the lateral meniscus. Knee Surg Sports Traumatol Arthrosc. 2021;29(4):1018-24. PMID: 32440714.
- Kanakamedala AC, Burnham JM, Pfeiffer TR, et al. Lateral femoral notch depth is not associated with increased rotatory instability in ACL-injured knees: a quantitative pivot shift analysis. Knee Surg Sports Traumatol Arthrosc. 2018;26(5):1399-405. PMID: 29119285.
- Lucidi GA, Grassi A, Di Paolo S, et al. The lateral femoral notch sign is correlated with increased rotatory laxity after anterior cruciate ligament injury: pivot shift quantification with a surgical navigation system. Am J Sports Med. 2021;49(3):649-55. PMID: 33449808.
- Sonnery-Cottet B, Carrozzo A, Saithna A, et al. Indications for lateral extra-articular procedures in the anterior cruciate ligament-reconstructed knee: part I of an international consensus statement. Arthroscopy. 2025;41(9):3303-12. PMID: 40544926.
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