Clinical features:
Common in young secondary to trauma
Present with locked knee or inability to extend fully
General features:
Usually displaced longitudinal vertical tear, but may be seen in longitudinal horizontal tear
MM 3 times more common than LL
Central fragment may be displaced into intercondylar notch
Associated injuries:
ACL injuries common
IMAGING FINDINGS:
Absent bow-tie sign:
May be only sign. Normally bow-tie should be seen in 2 sections on sagittal.
Foreshortened or truncated or displaced anterior horn/posterior horn/ both leads to absent normal bow-tie configuration
False positive occur in children, degenerate meniscus, radial tear, post-op
False negative occurs in discoid meniscus
Smaller posterior horn:
Normally the posterior horn of MM is wider with more height than anterior horn. If that is lost, suspect BH tear
Disproportionate posterior horn sign:
Large posterior horn on sagittal images closer to the root than periphery due to central displacement
Decreased width of the meniscus:
Due to displacement. May or may not show increased signal! In fact, the displaced fragment is of low signal band
Pseudohypertrophy of anterior horn:
If the posterior horn is displaced anteriorly, causes pseudohypertrophy of anterior horn, commonly seen in LM
Seen on Sagittal
Displacement of anterior horn anteriorly:
Displacement of anterior horn anteriorly may be seen
Best seen on sagittal and axials
Flipped meniscal sign:
Fragment is flipped anteriorly adjacent to the ipsilateral anterior horn
Anterior horn should not measure more than 6 mm normally, of so, suspect BH tear with anterior flip
Double anterior horn sign:
Similar to above, but mimicks 2 anterior horns
Double PCL sign (displacement of posterior horn posteriorly):
Displacement of posterior horn posteriorly (double PCL sign or pseudo-PCL sign: low signal displaced posterior horn parallel and anterior to the PCL)
Best seen on sagittals
Displaced fragment seen in intercondylar notch:
Low signal fragment best seen on coronal
Fragment in notch sign:
Fragment of meniscus is in intercondylar notch, not in same sagittal plane as PCL; often seen in LM tear
Truncated meniscus on coronal images:
Happens in 65% bucket handle tears
Quadruple cruciate sign:
Bilateral BH tear
References:
Stoller DW. MRI in orthopaedics & sports medicine; Second edition; 1997. Chapter 7: the knee. Lippincott Williams & Wilkins.
