Lateral meniscus tear is the traumatic or degenerative disruption of the fibrocartilaginous meniscus in the lateral compartment of the knee. The lateral meniscus has a more mobile and rounder (nearly circular) structure compared to the medial meniscus — capsular attachments are looser and it is completely separated from the capsule at the popliteal hiatus. This mobility makes the lateral meniscus more resistant to trauma, making isolated lateral meniscus tears less common than medial tears. However, lateral meniscus tears frequently co-occur with ACL tears (50-70% of ACL tear cases) — particularly the posterior horn and popliteal hiatus region are affected. Radial tear is the most common tear type in the lateral meniscus, typically occurring at the junction of the anterior 1/3 and middle 1/3 of the free edge. The presence of discoid meniscus significantly increases lateral meniscus tear risk. MRI is the gold standard for diagnosis with Grade 1-3 intrameniscal signal assessment on sagittal PD fat-suppressed sequences.
Age Range
15-50
Peak Age
30
Gender
Male predominant
Prevalence
Common
The lateral meniscus is a crescent-shaped fibrocartilaginous structure in the lateral compartment of the tibial plateau, covering a wider area compared to the medial meniscus. Important anatomic features of the lateral meniscus determine tear pathophysiology: (1) Popliteal hiatus — due to the opening for the popliteus tendon, there is no capsular support at the posterior horn, making this region more susceptible to rotational stresses. (2) Meniscofemoral ligaments (Humphry and Wrisberg) — stabilize the posterior horn by connecting it to the femoral condyle, but can become a tear line under excessive rotation. (3) More circular geometry — creates less geometric mismatch than the medial meniscus with more homogeneous load distribution. The association with ACL tear is explained by pivot-shift mechanism: after ACL rupture, anterior tibial translation increases and the lateral femoral condyle impacts the posterolateral tibial plateau — this impaction compresses and tears the lateral meniscus posterior horn. The concentration of radial tears at the free edge relates to this region being in the avascular white zone and the point where circumferential fibers are weakest against radial forces. In discoid meniscus, disc-shaped thick meniscal tissue is present instead of normal triangular cross-section — this abnormal morphology predisposes to mucoid degeneration and tearing because increased tissue volume is supplied by inadequate vascularity and mechanical stresses distribute irregularly.
On sagittal PD fat-suppressed MRI, the lateral meniscus appears notably smaller and as if truncated/cut. This finding is the characteristic sagittal plane manifestation of a radial tear — since the radial tear line extends parallel to the sagittal section plane, it does not appear directly as a line but manifests as decreased meniscal tissue volume. Radial tear is the most common tear type in the lateral meniscus and severely disrupts meniscal function by cutting circumferential fibers.
On sagittal PD fat-suppressed images, linear hyperintense signal reaching the articular surface is seen in the lateral meniscus (especially posterior horn and body region) (Grade 3). In radial tears, meniscal size is notably decreased on sagittal images — the meniscal tissue appears 'truncated' (truncated meniscus sign). On coronal images, radial tear appears as a vertical line/cleft. Tears at the popliteal hiatus region are best evaluated on coronal oblique planes.
Report Sentence
Hyperintense signal reaching the articular surface is seen in the posterior horn of the lateral meniscus, consistent with a Grade 3 tear.
On sagittal PD fat-suppressed images, notable decrease in normal lateral meniscus size — meniscal tissue appears truncated as if cut. This finding represents the sagittal plane appearance of a radial tear. The radial tear at the free edge cuts circumferential fibers full-thickness and completely eliminates load-bearing capacity at this location. Radial tears in the lateral meniscus most commonly occur at the anterior horn-body junction.
Report Sentence
Notable decrease in meniscal tissue size at the lateral meniscus anterior horn-body junction (truncated meniscus) is seen, consistent with a radial tear.
On T2 fat-suppressed or STIR sequences, bone marrow edema is seen in the posterolateral tibial plateau and anterolateral-to-mid lateral femoral condyle — this 'pivot-shift contusion pattern' is a typical associated finding of lateral meniscus tear with ACL tear. The bone edema results from anterior tibial subluxation during ACL rupture and impaction of the lateral femoral condyle against the posterolateral tibial plateau. This contusion pattern has strong predictive value for lateral meniscus posterior horn tear.
Report Sentence
Bone marrow edema consistent with pivot-shift contusion pattern is seen in the posterolateral tibial plateau and lateral femoral condyle, associated with ACL tear and lateral meniscus tear.
On coronal PD or T2 images, a vertical hyperintense line/cleft is seen at the free edge of the lateral meniscus — this is the direct visualization of radial tear in the coronal plane. The tear line extends from the free edge toward the center (capsule). Full-thickness radial tear completely disrupts circumferential fibers creating a functionally equivalent meniscectomy effect. Partial radial tear is limited to the free edge region only.
Report Sentence
A radial tear line extending full-thickness through the meniscal tissue is seen at the free edge of the lateral meniscus on coronal images.
On sagittal PD images, the lateral meniscus appears significantly larger and thicker than normal — bow-tie cross-section is obtained in more than 3 consecutive sagittal slices (2 slices in normal meniscus). Superimposed tear on discoid meniscus appears as intrameniscal hyperintense signal increase, usually in horizontal or complex pattern. The thick, irregular structure and inadequate internal vascularity of discoid meniscus facilitates degeneration and tearing.
Report Sentence
The lateral meniscus is in discoid configuration with intrameniscal degenerative signal increase and findings consistent with superimposed tear.
In a significant proportion (50-70%) of cases with lateral meniscus tear, ACL tear coexists. On T2 fat-sat sagittal images, ACL fibers appear discontinuous, thickened, and hyperintense (complete tear) or partial hyperintense signal increase is seen in fibers (partial tear). With ACL tear, pivot-shift bone contusion (posterolateral tibial plateau + anterolateral femoral condyle), anterior tibial translation, and lateral meniscus posterior horn tear form the typical triad.
Report Sentence
ACL fibers are discontinuous and hyperintense consistent with complete tear; associated with lateral meniscus posterior horn tear and pivot-shift contusion pattern.
Criteria
Tear extending from free edge toward capsule — cuts circumferential fibers perpendicularly
Distinct Features
Most common type in lateral meniscus, truncated meniscus sign, functionally equivalent to meniscectomy, associated with meniscal extrusion
Criteria
Traumatic tear in posterior horn with ACL tear — pivot-shift mechanism
Distinct Features
Pivot-shift contusion pattern, young athlete, acute trauma, usually longitudinal or oblique tear pattern
Criteria
Degenerative or traumatic tear superimposed on discoid meniscus (>3 bow-tie slices)
Distinct Features
Symptomatic in childhood/adolescence, snapping knee syndrome, horizontal or complex tear pattern, frequently requires surgery
Distinguishing Feature
Medial meniscus tear is more common, associated with MCL injury, bucket-handle tear more prevalent; lateral meniscus tear associated with ACL, radial tear more common, discoid meniscus risk
Distinguishing Feature
Discoid meniscus can be symptomatic without tear (snapping knee); bow-tie sign seen in >3 slices, when tear is added intrameniscal signal increase appears
Distinguishing Feature
ACL tear is a primary ligament pathology in different anatomic structure from lateral meniscus tear; however they frequently coexist and should be evaluated together
Urgency
urgentManagement
surgicalBiopsy
Not NeededFollow-up
specialist-referralLateral meniscus tear treatment is planned based on tear type, location, ACL status, and discoid meniscus presence. Lateral meniscus tear with ACL tear is addressed as concomitant meniscal pathology during ACL reconstruction. Meniscal repair (suture) is preferred for peripheral tears. Radial tears and central zone tears generally require partial meniscectomy. In discoid meniscus, saucerization (reshaping to normal geometry) + tear repair/partial resection is performed. Meniscal root tears completely disrupt meniscal function and root repair must be achieved surgically — rapid osteoarthritis development is expected without repair. Conservative treatment is only applicable for small, stable, asymptomatic degenerative tears.
Lateral meniscus tears, especially when associated with ACL injury, influence surgical planning. Radial tears disrupt circumferential hoop stress distribution, potentially leading to early degenerative changes. Tears in discoid meniscus more frequently require surgery in young patients.