Meniscocapsular Separation

Meniscocapsular separation is a subtype of meniscal tear in which the posterior meniscus horn pulls away from the capsule resulting in a separation of the posterior meniscal signal and the posterior tibial plateau greater than 8-10 mm. ⁶

meniscocapsular separation

Meniscocapsular Separation: Injuries

Meniscocapsular separation is a type of tear which may affect the posteromedial corner (PMC). Displacement of the posterior horn of the medial meniscus 5 mm anterior to the uncovered tibial articular cartilage suggests the presence of detachment [detachments less than 1cm in length are treated conservatively].⁶Definitive detachment is indicated by a meniscus that extrudes, “folds”, and / or migrates. Often, the other components of the PMC are affected including the posterior oblique ligament (POL), oblique popliteal ligament (OPL), or the semimembranosus tendon and its expansions.

Tears typically take place in association with other ligamentous injuries, but can also take place in isolation less commonly.⁴

Meniscocapsular Separation: Complications

Meniscal mobility could potentially increase resulting in meniscal tearing.⁵This phenomenon of meniscus hypermobility is known as loss of “the brake stop” mechanism.

Meniscocapsular Separation: Differentials

Normal menisco-synovial recess / perimeniscal recess and meniscal cysts should be considered on MRI.¹

Meniscocapsular Separation: MRI

Diagnosis typically takes place arthroscopically
Positive predictive value (PPV) is low (9% medially, 13% laterally)⁷
Low PPV findings on MRI include:

Interposition of fluid between the meniscus and the medial collateral ligament²
Meniscal corner tears: according to one study had a PPV of 0% medially and 50% laterally⁷
Perimeniscal fluid²
Meniscofemoral and meniscotibial extension tears³
Irregular meniscal outline³
Increased distance between the meniscus and the medial collateral ligament³
Visualisation of fluid from the superior to the inferior end of the meniscus is a more suggestive feature⁵

Meniscocapsular Separation: Pearls

Most common in the posteromedial meniscocapsular interface
Ganglia, increased meniscocapsular fat and capsulosynovial redundancy can simulate meniscocapsular separation
In true separation, the meniscus moves anteriorly, folds, flips, extrudes, or migrates
Separation without associated meniscal tear, bone or cartilage or PMC injury is rare⁶
Injury to the posterolateral fascicles in the popliteus hiatus can allow the meniscus to spin, twirl, or displace, causing clinical locking. This can occur with tear of just one fascicle.

Meniscocapsular Separation: Treatment

Meniscocapsular separations may be treated conservatively, or may be treated via arthroscopy by repairing or suturing the meniscus into the capsule.

Meniscocapsular Separation: References

Callaghan JJ, Rosenberg AG, Rubash HE et-al. The adult knee. LWW. ISBN:0781732476.
De Maeseneer M, Lenchik L, Starok M et-al. Normal and abnormal medial meniscocapsular structures: MR imaging and sonography in cadavers. AJR Am J Roentgenol. 1998;171 (4): 969-76.
De Maeseneer M, Shahabpour M, Vanderdood K et-al. Medial meniscocapsular separation: MR imaging criteria and diagnostic pitfalls. Eur J Radiol. 2002;41 (3): 242-52.
Luijkx T, Weerakkody Y, et-al. Meniscocapsular Separation: Radiopaedia (sourced 10Jan2018): https://radiopaedia.org/articles/meniscocapsular-separation
Musculoskeletal Imaging. Saunders. (2014) ISBN:1455708135.
Pomeranz SJ. Gamuts & Pearls in MRI & Orthopedics. Ohio, The Merten Company, 1997.
Rubin DA, Britton CA, Towers JD et-al. Are MR imaging signs of meniscocapsular separation valid?. Radiology. 1996;201 (3): 829-36.

Meniscocapsular Separation: Example

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This patient is a 32-year-old male, status post ACL reconstruction, with new twisting injury two weeks prior. MR findings include intact ACL graft, low-grade MCL sprain, stable post-operative appearance of the medial meniscus status post sub-total meniscectomy, and dominant finding is lateral meniscocapsular separation with flipped meniscal fragment into the anterior notch.

Meniscocapsular separation is a relatively uncommon traumatic injury, where the meniscus is separated from the joint capsular attachments. It is more common medially than laterally, and occurs in conjunction with other traumatic injuries of the knee.

A key finding of a meniscocapsular separation is increased fluid typically between the meniscus and the capsule posteriorly. This occurs from the tear, with swelling or blood hemorrhage into the capsular space.

stir long te axial t2w tse

Image 1 - STIR_longTE Image 2 - Axial T2W_TSE

In image 1, arrow one indicates the posterior aspect of the lateral meniscus posterior horn. There is a moderate amount of fluid, and the short arrow indicates the posterior capsule. In the following axial view image, one can see the fluid tracking between the meniscus posterior horn and body extending to nearly the anterior horn.

Other findings which may suggest a meniscocapsular separation or injury are: injury to the meniscofemoral and meniscotibial fascicles in the popliteus hiatus, irregularity of the meniscocapsular surface, or increased fluid between the meniscal body and collateral ligaments.

Meniscocapsular separations may not be clearly identified, especially in acute cases with large amounts of swelling or effusion, as the fluid may mask structures, especially in the posteromedial corner. Additionally, vertical tears of the posterior horn, such as those occurring with pivot-shift type injuries (Wrisberg ligament tear or vertical medial meniscus tear) may mimic a meniscocapsular separation, leading the reader to mistake the vertical tear for the posterior meniscal border. The key to delineating a vertical tear from meniscocapsular injury is the presence of fluid in the posterior meniscal space along with meniscal (a) rotatum, (b) anterior displacement, (c) extrusion peripherally, or (d) folding or flipping.