Key points
Treat the symptomatic discoid lateral meniscus (DLM), not the shape. When surgery is needed: saucerize, repair, stabilise, and preserve as much tissue as possible.
- DLM is the most common congenital meniscal anomaly: 3% to 5% in Western and 10% to 15% in Asian populations.
- It is structurally abnormal: disorganised collagen, poor central vascularity, mucoid change. It tears more easily and heals less well.
- Bilateral rates vary by method: 15% to 25% clinically, but 79% to 97% on contralateral MRI or arthroscopy in Asian series.
- Describe it by width (complete or incomplete), peripheral stability (anterior, posterior or both) and tear. Watanabe types do not guide treatment.
- Younger children: snapping knee from rim instability. Older children: pain and mechanical symptoms from tears.
- MRI confirms and plans, especially the Ahn shift pattern, but can miss incomplete DLM.
- Asymptomatic DLM: observe, including the contralateral knee. Do not operate prophylactically.
- Saucerize to leave a 6 to 8 mm stable rim. Repair retained tears and stabilise unstable segments.
- Avoid subtotal or total meniscectomy: more degeneration, and lateral femoral condyle OCD has been reported after it.
- Results decline over time. Older age, long symptom duration, more resection and valgus predict worse outcomes.
Epidemiology, origin and structure
Epidemiology
| Feature | Data | Source |
|---|---|---|
| Prevalence, lateral | 3% to 5% in the USA. 10.6% Korea, 13% Japan (10% to 15% in Asian populations). Range 0.4% to 17%. | Tapasvi 2021; Kim 2020 |
| Prevalence, medial | 0.06% to 0.3% | Saavedra 2020; Kim 2020 |
| Bilateral | 15% to 25% (clinical series). 79% to 97% on MRI or arthroscopy of the contralateral knee in symptomatic Asian patients. 89.5% in one arthroscopic series, 84.2% of identical shape. | Saavedra 2020; Tapasvi 2021 |
| In paediatric meniscal surgery | 25% of 880 children having arthroscopy had a discoid meniscus | Jackson 2019, via Asokan 2023 |
| Associated LFC OCD | About 15% | Geffroy 2021 |
True prevalence is unknown, because most DLMs are asymptomatic.
Origin
DLM is a congenital variant, not an arrested stage of development. Normal menisci are never discoid during fetal development. [Kaplan; Clark and Ogden, via Saavedra 2020] Kaplan proposed that deficient posterior meniscotibial attachment, with only the Wrisberg ligament remaining, leads to the discoid shape. This does not explain stable discoid menisci, but shape and instability are linked. Newer fetal studies suggest a discoid shape can appear early in gestation and remodel later, so the origin is still debated. [Tapasvi 2021]
Structure
- Vascularity: poorer than normal, especially centrally. Even the peripheral rim kept after saucerization has compromised blood supply.
- Collagen: lower density and disorganised. Seven layers with different orientations, compared with two in a normal meniscus. [Cui and Min, via Tapasvi 2021]
- Histology: mucoid degeneration similar to degenerative adult menisci.
- Stability: greater anterior and posterior horn instability than a normal lateral meniscus, even when intact. [Kim 2018, via Tapasvi 2021]
- Gait: reduced sagittal and axial knee excursion on the symptomatic side. [Harato 2016, via Tapasvi 2021]
Classification
Current consensus: describe width (complete or incomplete), peripheral stability, and tears. The Watanabe classification alone does not guide treatment. [Saavedra 2020; Tapasvi 2021]
Watanabe (arthroscopic, 1969)
| Type | Description |
|---|---|
| I, complete | Covers the whole lateral tibial plateau. Stable. |
| II, incomplete | Covers up to 80% of the plateau. Stable. |
| III, Wrisberg variant | Normal or slightly discoid shape. Unstable, with no posterior meniscotibial attachment. Only the Wrisberg ligament anchors it. |
Limits: types are not mutually exclusive, instability can be anterior or mid-body as well as posterior, and true type III is rare in modern series.
Good (2007) and Klingele (2004)
Peripheral rim instability occurred in about 28% of symptomatic DLMs, in both complete and incomplete types, anterior or posterior. Good proposed: complete or incomplete, then stable or unstable (anterior or posterior), then tear present or absent.
Ahn MRI classification (2009)
Based on the shift that results from peripheral detachment. It matches the arthroscopic tear pattern and helps plan surgery.
| MRI shift | Detachment | Arthroscopic equivalent |
|---|---|---|
| No shift | None | Meniscocapsular posterior (MC-P) tear |
| Anterocentral shift | Posterior horn | Posterolateral corner loss |
| Posterocentral shift | Anterior horn | Meniscocapsular anterior (MC-A) tear |
| Central shift | Posterolateral, whole meniscus displaced | Posterolateral corner loss |
In 76 MRIs, shift types were 43% but had more peripheral tears and were repaired more often. A thick, high-inserting Wrisberg ligament correlates with posterocentral shift. Posterolateral corner loss is hard to salvage and often ends in subtotal meniscectomy.
PRiSM classification (2022)
Developed by paediatric surgeons from 20 North American centres, and tested on 50 arthroscopic videos (median age 11). [Lee 2022]
| Feature | Grades |
|---|---|
| Width | W0 normal. W1 incomplete (under 90% of plateau). W2 near complete or complete (90% or more). |
| Height | H0 normal. H1 abnormal (thicker than the joint space suggests, or no central taper). |
| Stability | S0 normal. SA anterior half unstable. SP posterior half unstable. SAP both. |
| Tear (in the retained rim) | T0 none or only in the saucerized zone. TH horizontal (A, P or AP). TD degenerative, complex or radial (A, P or AP). |
Instability means absent attachments, lax attachments allowing translation past the apex of the lateral femoral condyle, or an unstable peripheral vertical tear. No isolated mid-body instability was seen in 119 videos.
| Feature | Interobserver kappa | Intraobserver kappa |
|---|---|---|
| Width | 0.75 | 0.79 |
| Height | 0.62 | 0.64 |
| Stability | 0.71 | 0.82 |
| Tear presence | 0.69 | 0.60 |
| Tear type | 0.62 | 0.56 |
| Tear location | 0.51 | 0.49 |
In the video set, posterior instability (29%) was more common than anterior (19%). Horizontal tears were the commonest retained tear (25%).
Presentation and examination
Most DLMs never cause symptoms. Symptoms usually mean instability or a tear, and onset is often insidious and atraumatic. [Saavedra 2020]
| Age group | Typical presentation | Usual cause |
|---|---|---|
| Under about 10 | Snapping or clunking knee, often painless, spontaneous and intermittent. Clunk at terminal flexion. Visible lateral bulge. | Peripheral rim instability, thick complete DLM |
| Older children and adolescents | Lateral joint line pain, effusion, locking, giving way | Tear, often horizontal cleavage, or degenerative or complex tear |
Examination
- Gait, alignment and quadriceps wasting
- Lateral joint line tenderness and swelling in flexion
- Range of motion: painful, clicking, protruding or blocked. Flexion contracture may only show as loss of normal hyperextension, so examine prone with the leg over the edge.
- McMurray (98% specific for meniscal injury in general), Apley and Thessaly tests. Children may find these hard.
- Always examine the other knee.
Clinical examination detected DLM with 88.9% sensitivity, compared with 39.8% for MRI, in one study. [Kocher 2001, via Kim 2020; Tapasvi 2021] Overall clinical sensitivity ranges from 29% to 93% across studies.
Predictors of cartilage injury
Higher BMI, female sex, symptoms for over 6 months and high activity level. Symptoms over 6 months plus extension block had the best sensitivity (71.4%) and specificity (75%). Pain from a tear lasting more than 6 months doubles the risk of associated cartilage lesions. [Tapasvi 2021; Saavedra 2020]
Imaging
Radiographs
The meniscus is not visible, so X-rays mainly exclude other diagnoses (fracture, tumour, OCD). Suggestive signs:
- lateral joint space widening to more than 11 mm
- squaring of the lateral femoral condyle
- cupping of the lateral tibial plateau
- hypoplasia of the lateral tibial spine
In children aged 10 to 16, these signs had a positive predictive value of 76.2% (sensitivity 65.3%, specificity 79.6%). [Ha 2017, via Saavedra 2020]
MRI criteria
| Plane | Criterion |
|---|---|
| Sagittal | Continuity of the meniscus between anterior and posterior horns on three or more consecutive 5 mm slices (bow-tie pattern) |
| Coronal | Meniscal width over 15 mm, or minimum meniscal width to maximum tibial width ratio over 20% |
| Axial | Lateral meniscus covering over 80% of the lateral plateau |
Signs of peripheral instability: absent meniscocapsular fascicles, high T2 signal between meniscus and capsule (mimicking a peripheral tear), and anterior subluxation of the posterior horn (Wrisberg variant).
MRI limits
- An incomplete DLM can look almost normal.
- MRI sensitivity and specificity were lower under 12 (61.7% and 90.2%) than at 12 to 16 (78.2% and 95.5%), for intra-articular knee disorders in general. [Kocher 2001, via Saavedra 2020]
- MRI can show intrasubstance degeneration and tears that are invisible at arthroscopy.
- Linear high signal in a DLM does not always mean a tear. [Geffroy 2021]
- MRI is most valuable for planning: identify the Ahn shift type before surgery.
Treatment algorithm
Discoid lateral meniscus treatment algorithm. Operate only for symptoms, then saucerize, repair and stabilise.
Symptoms, not shape, decide surgery. At arthroscopy, check width, stability and tears before and after saucerization. Repair and stabilisation can both be needed in the same knee.
Surgical technique
The goal is a stable meniscus of near-normal shape and width. [Saavedra 2020]
Stepwise approach
- Assess. Width, height, stability (probe anterior and posterior horns, viewing from both anterior portals) and tears.
- Reduce. In shifted DLMs, reduce the meniscus first, using a single stitch if needed, before trimming. [Kim 2020]
- Saucerize. Remove the central portion to restore a C shape.
- Repair tears in the retained rim.
- Stabilise any unstable segment to the capsule.
Saucerization tips
- Start centrally with a basket forceps. An arthroscopic knife helps for the anterior horn, and curved punches improve the trajectory. Smooth the edge with a shaver.
- If the tear is posterior on MRI, start far enough anteriorly to avoid meeting it too soon.
- Iris scissors help for anterior and middle portions. [Kim 2020]
- Alternate scope and instruments between portals to judge the result and avoid over-resection of the mid-body.
- Protect the anterior root.
- The natural tendency is to remove too much.
How much rim to leave
| Recommendation | Source | Rationale |
|---|---|---|
| 6 to 8 mm | Tapasvi 2021; Saavedra 2020; Asokan 2023 | Keeps hoop stresses. A larger rim re-tears more; a smaller rim degenerates. |
| 4 to 5 mm | Some earlier authors, via Kim 2020 | Lower impingement and re-tear risk |
| About 1 cm depth | Geffroy 2021 | Measured with a calibrated probe |
| 10 mm | Ohnishi 2018, via Tapasvi 2021 | Used with all-suture anchor stabilisation |
| Match the medial meniscus mid-body width | Kim 2020 | An anatomical reference for complete DLM |
A rim under 5 mm was linked with degenerative change. [Yamasaki 2017, via Kim 2020]
Repair and stabilisation
| Lesion | Technique |
|---|---|
| Anterior horn tear or detachment | Outside-in (most used) |
| Mid-body and posterior horn | Inside-out (gold standard, posterolateral incision between ITB and biceps) or all-inside |
| Horizontal cleavage (commonest DLM tear) | Reshape to symmetrical leaflets, then repair the leaflets together (all-inside or inside-out). Excise a small unstable leaflet. |
| Posterolateral corner loss | Difficult. Often subtotal meniscectomy. Augmentation with central discoid tissue has been described. |
| Unstable rim without tear | Capsular repair. Alternatives: anterior meniscopexy (open, suture anchors) or arthroscopic centralisation with all-suture anchors |
All-inside safety. The popliteal neurovascular bundle lies close to the posterior horn of the lateral meniscus in children. Avoid aiming all-inside devices from the anterolateral portal at the posterior horn. Use the anteromedial portal and limit depth. [Saavedra 2020; Geffroy 2021]
Repair without saucerization. Kinugasa reported peripheral reattachment alone in 4 adolescents, with no re-tear at 2 years. Some surgeons now consider this for isolated rim instability.
Rehabilitation
No universal protocol exists. It depends on the procedure and the child's age.
| Saucerization only | Saucerization with repair or stabilisation | |
|---|---|---|
| Weight-bearing | Immediate full | Partial with crutches for about 6 weeks (Kim 2020: protected 4 weeks, then partial 4 weeks) |
| Range of motion | Free | Hinged brace, 0 to 30 degrees for 6 weeks (Saavedra), or gradual increase to 120 degrees by about 8 weeks (Kim) |
| Physiotherapy | From 2 weeks (quadriceps) | From 2 weeks |
| Return to sport | Gradual from about 8 weeks | Usually after 3 to 4 months, based on motion and strength. There is no fixed timeline. |
- Under about 6 years: straight knee immobiliser for 4 weeks. [Saavedra 2020]
- Under 10: short immobilisation may help pain. [Geffroy 2021]
- Physiotherapy is especially useful after repair with multiple sutures, which can be painful.
Outcomes and prognostic factors
Short-term results are good whatever the procedure. Over time, results decline and more resection means more degeneration. [Tapasvi 2021; Kim 2020]
Key outcome studies
| Study | Patients | Procedure | Follow-up and results |
|---|---|---|---|
| Ahn 2015 | 48 knees, mean age 9.9 | A: saucerization and stabilisation (22). B: saucerization (18). C: subtotal meniscectomy (8). | 10.1 years. 94% good or excellent (Ikeuchi). Lysholm 74.9 to 97.6. Radiographic degeneration 23% (A), 39% (B), 88% (C). |
| Carter 2012 | 57 knees, mean age 11.7 | Saucerization and stabilisation (30) vs saucerization (27) | 15 months. Lysholm 94 vs 89. IKDC 86 vs 82. |
| Okazaki 2006 | 29 knees, mean age 17.9 | Saucerization | 16 years. IKDC 82 overall: 90 at age 25 or under, 72 at 30 or over. |
| Lee (10-year series, as tabulated in Saavedra 2020) | 73 knees, mean age 22.2 | Saucerization | 10 years. 64% good or excellent. Reoperation 32.9%. Degeneration on X-ray 54%. |
| Lee 2016 (MRI) | 21 knees | Saucerization | 6.8 years. Lysholm 85.8. Progressive degeneration of remnant and cartilage on MRI. |
Systematic reviews
- Lee 2017: Ikeuchi good or excellent 72.3% to 94%, IKDC normal or nearly normal 76.5% to 94.3%, regardless of procedure. Mild joint space narrowing common, advanced degeneration absent.
- Smuin 2017: saucerization better than complete resection. Suture repair did not improve outcomes over saucerization alone.
- Lee 2019 meta-analysis (partial vs total): similar clinical outcomes. Normal or mild cartilage in 87.4% vs 55.6% (OR 9.08).
- Short vs long term: excellent Ikeuchi results with partial meniscectomy were 75.3% under 4 years, but 53.6% at 4 years or more, compared with 38.2% after total meniscectomy at that point.
Hartman 2026 (newest paediatric review). 24 studies from 2013 to 2023, 1,225 children (1,401 knees), age 8.3 to 13.7, follow-up 1.2 to 10.1 years. Lysholm improved significantly with every technique.
| Technique | Complications | Reoperation |
|---|---|---|
| Saucerization only | 2.7% | 7.3% |
| Saucerization plus repair | 6.8% | 8.9% |
Osteoarthritis and OCD were the commonest complications. The authors judge the differences to reflect tear complexity and follow-up, not the procedure, since repaired knees were more complex. [Hartman 2026]
Prognostic factors
| Outcome | Factor | Effect size |
|---|---|---|
| Degenerative change | Subtotal vs partial meniscectomy | OR 13.56 [Ahn 2015] |
| Degenerative change | BMI 30 or over | OR 3.75 [Sabbag 2019] |
| Degenerative change | Older age | OR 1.02 to 1.04 per year |
| Re-tear | Open physes (vs closed) | OR 3.19 [Sabbag 2019] |
| Re-tear | Younger age | OR 0.96 per year older |
| Better Lysholm | Age under 10 | OR 2.37 [Yoo 2015] |
| Worse Lysholm | Longer symptom duration before surgery; valgus at follow-up | [Lee 2018] |
| Reduced remnant width | Preoperative meniscal shift | OR 12.0 [Kim 2019] |
| Less cartilage damage | Horizontal tear (vs other types) | OR 0.02 to 0.26 [Cho 2019] |
Remnant behaviour
On MRI, the residual meniscus keeps losing width and thickness over time and can extrude, even after saucerization with repair.
Lateral femoral condyle OCD
A recognised complication after partial or total meniscectomy for DLM, possibly from impact on immature cartilage and valgus change. Image the lateral condyle if new symptoms develop.
Critical appraisal and controversies
There are no level I or II studies comparing surgical treatments for DLM. The evidence is case series from many countries using different techniques. [Tapasvi 2021]
Open controversies
| Question | Positions |
|---|---|
| Does repair add benefit over saucerization alone? | Smuin 2017: no. Carter 2012 and Ahn 2015: slightly better function and less degeneration with stabilisation. |
| How wide should the rim be? | 4 to 5 mm, 6 to 8 mm, about 10 mm, or matched to the medial meniscus. No consensus. |
| Is reshaping needed at all for isolated rim instability? | Kinugasa: repair without saucerization in 4 patients. Unproven. |
| Should a painless snapping knee be operated on? | Debated. Most advise observation. |
| How common is bilateral DLM? | 15% to 25% in clinical series, but 79% to 97% when the other knee is imaged or scoped (mostly Asian cohorts) |
Points to notice in the sources
| Source | What to notice |
|---|---|
| Tapasvi 2021 | Commissioned ISAKOS review with a balanced view. Notes repair has not been proven to improve results. Its abstract states over 80% bilateral, which applies to imaged Asian cohorts only. |
| Saavedra 2020 | Narrative review. Outcome table mixes children and adults (ages 3 to 55). One citation in the table appears to be mislabelled. |
| Kim 2020 | Authors' own algorithm from a high-volume Korean centre. Rehabilitation and technique reflect one unit's practice. |
| Lee 2022 (PRiSM) | Reliability only, not validity or prognostic value. The 50 videos were selected for clarity, which may inflate agreement. Most authors report industry educational support. |
| Outcome studies | Many mix ages from early childhood to middle age. Age strongly affects results, so adult data may not apply to children. |
Research gaps
- Long-term healing rates after repair of DLM tissue
- Validated techniques for anterior and posterior rim stabilisation
- Whether the PRiSM classification predicts outcome
- The natural history of untreated asymptomatic DLM, which is unknown
References
- Written by: [author name, role]
- Reviewed by: [clinical reviewer, role]
- Next review due: Oct 4, 2027
Core sources
- Tapasvi S, Shekhar A, Eriksson K. Discoid lateral meniscus: current concepts. J ISAKOS 2021;6:14-21
- Saavedra M, Sepúlveda M, Tuca MJ, Birrer E. Discoid meniscus: current concepts. EFORT Open Rev 2020;5:371-379
- Kim JH, Ahn JH, Kim JH, Wang JH. Discoid lateral meniscus: importance, diagnosis, and treatment. J Exp Orthop 2020;7:81
- Lee RJ, Nepple JJ, Schmale GA et al. Reliability of a new arthroscopic discoid lateral meniscus classification system: a multicenter video analysis. Am J Sports Med 2022;50(5):1245-1253
- Geffroy L. Meniscal pathology in children and adolescents. Orthop Traumatol Surg Res 2021;107:102775
- Asokan A, Ayub A, Ramachandran M. Pediatric meniscal injuries: current concepts. J Child Orthop 2023;17(1):70-75
Cited within the core sources
- Watanabe M, Takeda S, Ikeuchi H. Atlas of arthroscopy. 2nd ed. Tokyo: Igaku-Shoin; 1969
- Klingele KE, Kocher MS, Hresko MT et al. Discoid lateral meniscus: prevalence of peripheral rim instability. J Pediatr Orthop 2004;24:79-82
- Good CR, Green DW, Griffith MH et al. Arthroscopic treatment of symptomatic discoid meniscus in children: classification, technique, and results. Arthroscopy 2007;23:157-163
- Ahn JH, Lee YS, Ha HC et al. A novel magnetic resonance imaging classification of discoid lateral meniscus based on peripheral attachment. Am J Sports Med 2009;37:1564-1569
- Ahn JH, Kim KI, Wang JH et al. Long-term results of arthroscopic reshaping for symptomatic discoid lateral meniscus in children. Arthroscopy 2015;31:867-873
- Carter CW, Hoellwarth J, Weiss JM. Clinical outcomes as a function of meniscal stability in the discoid meniscus. J Pediatr Orthop 2012;32:9-14
- Okazaki K et al. Arthroscopic resection of the discoid lateral meniscus: long-term follow-up for 16 years. Arthroscopy 2006;22:967-971
- Lee YS, Teo SH, Ahn JH et al. Systematic review of the long-term surgical outcomes of discoid lateral meniscus. Arthroscopy 2017;33:1884-1895
- Smuin DM, Swenson RD, Dhawan A. Saucerization versus complete resection of a symptomatic discoid lateral meniscus: a systematic review. Arthroscopy 2017;33:1733-1742
- Lee DH, D'Lima DD, Lee SH. Partial versus total meniscectomy in symptomatic discoid lateral meniscus: systematic review and meta-analysis. Orthop Traumatol Surg Res 2019;105:669-675
- Yamasaki S et al. Risk factors associated with knee joint degeneration after arthroscopic reshaping for juvenile discoid lateral meniscus. Am J Sports Med 2017;45:570-577
- Kinugasa K et al. Discoid lateral meniscal repair without saucerization for adolescents with peripheral longitudinal tear. Knee 2019;26:803-808
- Kocher MS et al. Diagnostic performance of clinical examination and selective MRI in children and adolescents. Am J Sports Med 2001;29:292-296
Recent reviews (2025 to 2026)
- Vivekanantha P, Thomas R, Kaplan GE et al. Surgical management of the discoid lateral meniscus: a systematic review of outcomes. Curr Rev Musculoskelet Med 2025. Abstract not available to us; read the full text before citing.
- Hartman H, Lessiohadi N, Saharan S et al. Outcomes of saucerization with or without repair for symptomatic discoid lateral meniscus in pediatric patients: a systematic review. Arthroscopy 2026 (now included above)