A 14-year-old male patient was referred to our hospital because of trauma during football. He claimed medial knee pain following a moderate valgus injury 1 week before imaging. The physical examination showed tenderness in keeping with medial collateral ligament strain. The lateral compartment was asymptomatic. MRI examination was suggested.
MRI examination was performed with a 1.5 Tesla scanner (Vision Hybrid, Siemens Erlagen, Germany) using a phased-array knee coil. The examination protocol included axial and sagittal fat-saturated turbo spin echo PD-w (TR/TE, 3500/14 ms), sagittal T2*-w MEDIC (TR/TE 520/26) and coronal T1-w spin echo (TR/TE, 500/14 ms) MR sequences. Mild bone bruise was demonstrated in the medial tibial condyle (Fig. 1). In addition, a discoid-like lateral meniscus with flounce appearance and an elongated lower pole of the patella were found (Fig. 1-4).
A. The discoid meniscus is a thickened, disc-like meniscus and is referred as a normal anatomical variant in 3% of general population mostly seen on the lateral side [1]. Pathogenetically, the discoid meniscus may result from failure of the central resorption during the embryologic development [2]. Others believe that discoid appearance of the meniscus may result from failure of the meniscotibial ligamentous attachment of the posterior horn [3]. A flounce appearance on the other hand is a normal variant characterised by a single symmetric fold at the free edge of the meniscus. It is being seen most commonly at the medial side in 0.2-6% of patients [4, 5]. The meniscal flounce seen in a lateral discoid meniscus has not been previously reported to the best of our knowledge.
B. The discoid meniscus is either asymptomatic or presents with non-specific pain and functional limitation. It is also reported that discoid meniscus is a predisposing factor for meniscal tear and it might be associated with various musculoskeletal abnormalities [1]. In the case presented, an elongated lower pole of the patella was found. In contrast, meniscal flounce is considered to be of no clinical significance and indeed it may represent a positional-related finding. Meniscal flounce should not be misdiagnosed as a meniscal tear and thus arthroscopy of the knee is unnecessary.
C. Discoid meniscus is characterised by width of more than 15 mm in coronal slices or when the meniscal bow-tie is present in at least 3 consecutive 4 mm thick slices in the sagittal plane. Meniscal flounce is a wave or S-shaped deformity along the free edge of meniscal body on sagittal images without any high MR signal, to suggest a tear.
D. Our patient was treated conservatively regarding the bone bruise by ceasing the sports activities for 1 month and in the clinical follow-up there were no complaints.
E. Treatment is not required because both the discoid and flounce meniscus are normal variants.
Meniscal flounce seen in a discoid lateral meniscus
1. MRI in coronal, sagittal, and axial sequences shows the lateral meniscus appearing thickened and disk-like (Discoid Meniscus), with a wider range than a normal meniscus. On some slices, a “disc-like” appearance can be observed.
2. A wavy or “S”-shaped curvature (meniscal flounce) is found at the free edge of the lateral meniscus. No obvious high-signal lesion extending into the deep meniscal tissue is observed, and no clear linear tear signs are seen.
3. The medial knee compartment shows the medial collateral ligament (MCL) is intact in its course, but local soft tissue appears slightly swollen with signal changes, suggesting a mild ligament sprain.
4. Mild abnormal bone signal (bone contusion) is evident in the adjacent areas of the tibial or femoral articular surfaces on the affected side, with no obvious fracture line.
5. The cartilage surface is generally smooth, with no significant defect or extensive wear detected; the patella shows a mild morphological variation (an elongated inferior pole).
Taking into consideration the patient’s age, clinical symptoms, and MRI findings, the most likely final diagnosis is:
1. Conservative Treatment: As the discoid lateral meniscus and meniscal flounce represent normal/congenital variations without signs of tearing, and only mild ligament sprain is present, conservative treatment is advised.
• Reduce high-intensity or competitive sports activities to avoid further injury.
• During the soft tissue recovery period (usually 2–4 weeks), use elastic knee braces or supports to lessen local stress and protect the MCL.
2. Exercise Prescription and Rehabilitation: An individualized exercise plan should be developed according to the FITT-VP (Frequency, Intensity, Time, Type, Volume, and Progression) principles.
• Phase 1 (Acute Phase, 1–2 weeks):
– Rest, apply ice, and elevate the affected limb to reduce swelling.
– Perform gentle patellar mobilization exercises and straight leg raises, 2–3 times per day, 10–15 repetitions each, avoiding excessive weight-bearing on the knee.
– Gradually transition to non-weight-bearing range-of-motion exercises as pain permits.
• Phase 2 (Recovery Phase, 2–4 weeks):
– Gradually increase the range of motion within pain tolerance, such as stationary cycling (with the seat raised), for 15–20 minutes per day at low-to-moderate intensity.
– Strengthen the quadriceps and hamstrings with exercises like resistance band training and half-squats, avoiding heavy loads and deep squats.
• Phase 3 (Consolidation Phase, 4–6 weeks):
– With good ligament recovery, focus on balance and proprioceptive training (e.g., single-leg stance, balance board).
– Gradually progress to slow jogging and light jumping drills, controlling intensity and duration. Increase training volume by about 10–15% per week, ensuring minimal or no pain.
3. Surgical Intervention: If follow-up indicates significant joint locking, persistent pain, or any signs suggestive of a meniscal tear, arthroscopic evaluation and possible repair or reshaping may be considered. However, based on current imaging and clinical evaluation, there is no indication for surgery.
Disclaimer: This report is based solely on the current imaging and information available and is intended for reference only. It does not replace an in-person consultation or professional medical advice. If further questions arise or symptoms worsen, please seek medical attention and further evaluation promptly.
Meniscal flounce seen in a discoid lateral meniscus
