What causes the Ghost Meniscus Sign in the knee on MRI?
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Answer:
The ghost meniscus sign is a meniscus that cannot be identified on one or more
consecutive sagittal MRI slices, or whose normally dark tissue is replaced by high signal
at the posterior root attachment.[1] It means a complete radial tear or a posterior
root avulsion, which is biomechanically equivalent to a total meniscectomy.[2]
Why is it called so?
The meniscus is there on the slices either side and gone on the slice through the tear, so it
seems to vanish and come back like a ghost as you scroll. The name describes the scrolling
behaviour, not a disease. Most orthopaedic papers use the bare form ghost sign rather than
the full phrase.[1][3]
Pathophysiology
A radial tear runs perpendicular to the circumferential collagen bundles that carry hoop stress.
Once the tear is complete the fragments separate, the meniscal space at that level is empty, and a
sagittal slice through the gap contains no meniscal tissue. A posterior root avulsion does the same
thing at the tibial insertion. Either way the meniscus can no longer convert
axial load into circumferential hoop stress, and tibiofemoral contact pressures rise as they do
after a total meniscectomy.[2]
Alternative names: Ghost sign. Not the empty notch sign, which is an
absent anterior cruciate ligament in the intercondylar notch.
Other associated named signs: Truncation sign (truncated triangle sign), cleft
sign, marching cleft sign,[4] giraffe neck sign,[5] meniscus on a
string.[3]
How reliable is the ghost sign?
Good, and better than meniscal extrusion. Thirty patients with an arthroscopically proven medial
meniscal root tear were compared with 30 age-matched patients who had medial meniscal tears without
a root tear. The ghost meniscus sign on sagittal images reached a sensitivity, specificity, positive
predictive value and negative predictive value of 96.7% each, while extrusion managed 63.3%
sensitivity and 90% specificity.[6]
| Sign | Plane | What you see | Reported performance |
|---|---|---|---|
| Ghost meniscus | Sagittal | No identifiable meniscus on the slice, or high signal replacing the dark meniscus at the posterior root |
Sensitivity 96.7%, specificity 96.7%[6] |
| Radial defect | Axial | Linear fluid-signal cleft through the root | Sensitivity 93.3%, specificity 100%[6] |
| Truncation (truncated triangle) | Coronal | The meniscal triangle is blunted or cut off | Sensitivity 90%, specificity 100%[6] |
| Cleft and marching cleft | Coronal | Vertical linear high signal that tracks across consecutive slices | Described with the other radial-tear signs, no paired figures in that series[4] |
| Giraffe neck | Meniscal body shape | The body takes a long curved neck-like contour | Present in 81.7% of medial root tears against 3.3% of other medial tears[5] |
| Thickened meniscus | Coronal | Maximum medial meniscal thickness above 10 mm | Sensitivity 77.1%, specificity 92.8%, AUC 0.906[7] |
| Meniscal extrusion | Coronal | Body displaced 3 mm or more past the tibial margin[1] | Sensitivity 63.3%, specificity 90%, and common in non-root tears too[5][6] |
combination matters.
Why radial and root tears are the ones that get missed
Because nobody looks for them. In 196 consecutive knee arthroscopies by one surgeon, 29 patients
(15%) had a radial tear. Nineteen radial tears were found at surgery in the 18 patients imaged
in-house, and the original prospective MRI reports had called only seven of those 19
(37%) radial. On retrospective review using the four described signs, two
radiologists identified 17 of 19 (89%).[4] The signs are not exotic
trivia. They are the difference between a 37% read and an 89% read.
Do not call a root tear on one sign
- Extrusion separates root tears from normal menisci, not from other tears.
Extrusion was present in 94.4% of surgically proven medial posterior root tears against 10.5% of
intact menisci, with superficial medial collateral ligament signal change in 80.6% against 17.5%
and a significantly larger superficial MCL bowing angle.[8] Set against other medial
meniscal tears, though, extrusion is frequent in both groups and does not
discriminate.[5] - Two signs together do. Any two signs coexisting, extrusion excluded, were
present in 91.7% of medial meniscus posterior root tears against 5% of other medial meniscal
tears.[5] - Read the coronals as well as scrolling the sagittals. Coronal T2-weighted
imaging was the single most useful sequence for a medial root radial tear, with an overall accuracy
of 94% and interobserver kappa 0.93.[9] - Lateral roots behave differently. Extrusion is less common on the lateral
side,[2] so lean on the axial radial defect and the sagittal ghost. Lateral meniscus
posterior root injuries are seen in 12% to 15% of patients having anterior cruciate ligament
reconstruction.[3]
What else is called the “meniscus sign”?
The bare phrase is ambiguous. At least four unrelated findings carry it, and the ghost meniscus
of the knee is only one of them.
| Called the “meniscus sign” | Where | What it means |
|---|---|---|
| Ghost meniscus sign | Knee MRI | This page: a complete radial tear or a posterior root avulsion |
| Carman meniscus sign |
Barium meal | A large ulcerating gastric carcinoma, the classic barium sign of a malignant gastric ulcer |
| Flipped meniscus sign |
Knee MRI | The displaced fragment of a bucket-handle tear folded over and lying against the other meniscal horn |
| The plain “meniscus sign” on a radiograph or contrast study | Erect chest radiograph, contrast studies | Any crescent of fluid or contrast at a curved interface, for instance the upward-curving meniscus of a pleural effusion |
Frequently asked questions
What is the ghost meniscus sign on MRI?
It is the absence of an identifiable meniscus on a sagittal slice, or high signal replacing the
normally dark meniscal tissue at the posterior root attachment, with normal meniscus on the
neighbouring slices. The appearance marks a complete radial tear or a posterior root avulsion.
What is the ghost meniscus sign seen in?
A complete radial tear of the meniscus and a posterior meniscal root tear, most often the medial
posterior root. Root tears are either an avulsion of the tibial insertion or a complete radial tear
within 1 cm of it, and they account for 10% to 21% of all meniscal tears.
Is the ghost meniscus sign the same as the empty meniscus sign?
The phrase empty meniscus sign is occasionally written for the same appearance, but it is not an
established term in the indexed literature and it invites confusion with the empty notch sign,
which means an absent anterior cruciate ligament in the intercondylar notch. Ghost sign is the term
used in the orthopaedic and radiology literature.
Does a previous meniscectomy cause the ghost meniscus sign?
No published study lists it as a cause. The sign is described for complete radial tears and for
posterior root avulsions, and a resected meniscus is an absent meniscus with an operative history,
so the history is what tells the two apart. Treat an isolated signal gap on a single slice with
caution either way: 30% of 230 knees in asymptomatic sedentary adults had meniscal tears on 3.0 T
MRI, radial tears in 2% of knees.[10]
References
- Chahla J, LaPrade RF. Meniscal root tears. Arthroscopy. 2019;35(5):1304-1305. PMID: 31054709.
- Petersen W, Forkel P, Feucht MJ, Zantop T, Imhoff AB, Brucker PU. Posterior root tear of the medial and lateral meniscus. Arch Orthop Trauma Surg. 2014;134(2):237-55. PMID: 24323059.
- Gorbachova T, Ina JG, Krych AJ, Melenevsky Y. Lateral meniscal stabilizers, variants, and injuries of the knee. Skeletal Radiol. 2026;55(8):1747-1762. PMID: 41721857.
- Harper KW, Helms CA, Lambert HS 3rd, Higgins LD. Radial meniscal tears: significance, incidence, and MR appearance. AJR Am J Roentgenol. 2005;185(6):1429-34. PMID: 16303993.
- Furumatsu T, Fujii M, Kodama Y, Ozaki T. A giraffe neck sign of the medial meniscus: a characteristic finding of the medial meniscus posterior root tear on magnetic resonance imaging. J Orthop Sci. 2017;22(4):731-736. PMID: 28416188.
- Choi SH, Bae S, Ji SK, Chang MJ. The MRI findings of meniscal root tear of the medial meniscus: emphasis on coronal, sagittal and axial images. Knee Surg Sports Traumatol Arthrosc. 2012;20(10):2098-2103. PMID: 22113225.
- Suruga M, Iriuchishima T, Kozu T, Yahagi Y, Lee H, Nakanishi K. Magnetic resonance imaging measurements of maximum thickness of medial meniscus exceeding 10 mm are strongly associated with medial meniscus posterior root tear. Arthroscopy. 2025;41(9):3360-3368. PMID: 39914601.
- Yoon SJ, Ahn JM, Kang Y, Kim BR, Kang HS. Morphological changes in the superficial medial collateral ligament on knee MR imaging: association with medial meniscal extrusion and posterior root medial meniscus abnormality. Skeletal Radiol. 2022;51(7):1399-1405. PMID: 34913988.
- Lee SY, Jee WH, Kim JM. Radial tear of the medial meniscal root: reliability and accuracy of MRI for diagnosis. AJR Am J Roentgenol. 2008;191(1):81-5. PMID: 18562728.
- Horga LM, Hirschmann AC, Henckel J, Fotiadou A, Di Laura A, Torlasco C, et al. Prevalence of abnormal findings in 230 knees of asymptomatic adults using 3.0 T MRI. Skeletal Radiol. 2020;49(7):1099-1107. PMID: 32060622.
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