Discoid Meniscus

DefinitionDiscoid Meniscus

 

Round or "D" shaped rather than crescenteric meniscus

- occupies > 70% of tibial surface

- 90% occur on lateral side

 

Epidemiology

 

Uncommon

- 1:100

- usually presents in children & adolescents

 

Case reports of

- medial

- bilateral

- medial and lateral in same knee

 

Aetiology

 

Controversial 

 

Theories

 

1.  Failure of resorption of embryological meniscus centre

- however the lateral meniscus is never discoid during normal development

 

2. Lack of normal fixation to posterior tibia

- discoid shape 2° hypertrophy of posterior horn

- due to excessive motion

 

Presentation

 

1.  Younger patients / adolescents < 15

- pain is commonest complaint

- clicking over lateral side

- recurrent effusions

- locking

 

2.  Adults

- may never be symptomatic

- some adults present with MRI showing discoid meniscus

- theory that meniscus is protective in these people

- have gone most of life without tearing meniscus

- only resect if unstable tear

 

Signs

 

Reproduce clicking at 110° flexion

 

Lateral joint line tenderness / mass

 

Effusion

 

Limitation of extension / FFD

 

Classification Watanabe

 

1.  Complete

- entire articular surface of tibial plateau covered by thickened abnormal meniscus

- minimal symptoms

- stable - i.e. capsular attachments intact

 

Complete Discoid MeniscusComplete discoid meniscus 2Complete Discoid Meniscus 3

 

2. Incomplete 

 

Normal peripheral attachments but not as extensive as complete type

 

Incomplete Discoid Meniscus

 

3. Wrisberg Type 

 

Unstable

- large posterior horn with no attachment to tibial plateau

- entire posterior portion hyper-mobile

- only attachment is Wrisberg Ligament

 

Most symptomatic

- displaced into intercondylar notch in extension

 

X-ray

 

Widened joint space

 

Discoid Meniscus Flattened Condyle Widened Joint Space

 

Flattening or cupping of plateau

 

Flat LFC

 

Hypoplastic Lateral Tibial Spine

 

MRI 

 

Obviously enlarged LM

See meniscus on 3 consecutive cuts

 

Discoid Meniscus MRI 1Discoid Meniscus MRI 2Discoid Meniscus MRI 3

 

Discoid Meniscus with intrasubstance degeneration

 

Management

 

Issue

 

There is a protective element to lateral meniscus

- resect only if painful tear / young patient

 

Aim

 

Convert unstable meniscus to a stable contoured one

 

Options

 

1.  Stable 

- partial central meniscectomy / saucerisation

 

2.  Unstable (Wrisberg type) 

- posterior capsular stabilisation / repair +/- saucerisation

 

Ahn et al Arthroscopy 2008

- 23 patients treated with posterior repair and partial central meniscectomy

- no reoperation at 51 months

- good symptomatic relief

 

3.  Prophylactic meniscectomy

- no role

 

Technique Saucerisation

 

Issues

- demanding and technically difficult

- takes 1 - 2 hours

- difficult to know how much to resect

- need to ensure don't damage chondral surfaces

- reported cases of rapid and severe chondrolysis post resection in young patients

 

Technique

- make incision with scissors in medial aspect

- resect posterior part

- saucerise laterally and anteriorly

- need to ensure don't detach anterior horn

 

Discoid Meniscus Saucerisation 1Discoid Meniscus Saucerisation 2Discoid Meniscus Saucerisation 3

 

Discoid Meniscus Saucerisation 4Discoid Meniscus Post Saucerisation