Meniscal Injuries

Anatomy

Lateral meniscus

• More circular
• Covers a greater proportion of the (lateral) plateau area
• Carries 70% of the lateral compartment load with the knee in full extension
• More mobile

Medial meniscus

• More C-shaped
• Covers less its tibial plateau
• Carries 50% of medial compartment load
• Less mobile

Structure and function

• 90% type I collagen
• Peripherally vasacularised – 10-30%
  • More in children
• Move posteriorly in flexion, and anteriorly in extension
• Are secondary restraints of the knee

Meniscal lesions

Epidemiology

• Medial > lateral overall
  • Medial > lateral in isolated tears
  • Lateral > medial in ACL
• 10-15% are repairable

Patterns

1. Longitudinal

• • Vertically orientated tears running along A-P axis of the meniscus
  • More common in posterior meniscus
  • May be
    • Complete or incomplete
    • Reduced or displaced (bucket-handle)

2. Horizontal. Degenerate tears in older patients

3. Oblique

• • Vertically orientated tear running from inner edge obliquely towards outer rim
  • May be based posteriorly or anteriorly (and are described as such)

4. Radial

• • Vertically orientated tear running straight out (radially) from inner to outer rim
  • A parrot beak is an incomplete radial tear with anterior or posterior extension

5. Complex

• • Combinations of above

Natural history of meniscal tears

• Small peripheral tears may heal
• Most tears do not heal

Treatment

• Options are:

1. Meniscectomy
   1. Total
   2. Subtotal – Unstable component and a portion of the rim
   3. Partial – Unstable component, rim intact
2. Meniscal repair
   1. Inside-out
   2. Outside-in
   3. All inside

•  
  • Not done now – At 15 years OA is 40% Vs 6

Partial meniscectomy

Principles of arthroscopic meniscectomy

1. Removal of all mobile fragments

• • An unstable fragment is one which moves > 3mm on probing
  • Any fragment which can be pulled past the inner margin of the meniscus is unstable

2. Smooth the remaining meniscal rim to avoid sudden changes in contour causing further tears

• • A completely smooth margin is not necessary – rim remodelling is seen at repeat arthroscopy

3. Repeatedly probe to assess mobility and texture of rim
4. Leave the peripheral rim and menisco-capsular attachment intact wherever possible

• • This maintains meniscal stability and preserves the load transmission properties of the meniscus

5. Use both manual and motorised resection

1. Manual instruments allow more controlled resection, and motorised instruments remove loose debris and smooth frayed fragments

6. In uncertain situations leave more rather than less rim intact

• • Avoid segmental rim resection – this is functionally equivalent to a total meniscectomy

Results of partial meniscectomy

• Excellent short term results
  • 80-90% good to excellent in < 2 years
  • Better outcomes of partial Vs total meniscectomy (90 Vs 68% good to excellent)
• Decreasing long-term results
  • Over time the rate of OA in a knee having a partial meniscectomy increases compared with unaffected knee
  • This does not directly correlate with the subjective clinical outcomes (which remain good to excellent)
  • The major prognostic factor is the state of the articular cartilage at the time of meniscectomy
    • No articular cartilage injury à 95% good results at 12 years
    • Articular damage present à 60% good results at 12 years

·      Isolated medial meniscectomy has better outcomes than isolated lateral meniscectomy

Technique

• Cut through 90% of posterior limb, then detach anterior limb, and finally complete posterior limb

Meniscal repair

Indications

1. Young patient

• • Contrainidicated in patients > 45

2. Peripheral tear
   1. Red-red zone – outer 3mm

• • • Both sides vascularized

2. 2. Red-white zone – up to outer 1/3

• • • One side (outer side) vascularized

3. In association with ACL reconstruction

• • Better healing rates
  • Need a stable knee for the repair to survive

Contraindications

1. Central tears – White-white zone of inner 2/3
2. Complex tears
3. Stable tears < 1.5cm long

• • These will heal without intervention and do not require repair

General principles

1. Correct selection – as above
2. Meniscal bed preparation
   1. Debride loose edges
   2. Rasp the synovial fringe
   3. Trephination of the peripheral rim
3. Technique
   1. Inside-out

• Use double-arm sutures passed through the tear in a vertical fashion, and tied over the capsule through a limited open incision

• • • Advantages – Strongest repair
    • Disadvantages – NV injury, need for accessory incisions
    • Intervals :
      • Lateral – Between biceps femoris and ITB, posterior to LCL
      • Medial – Between sartorius and knee capsule

3. 2. Outside-in

• • • For anterior and middle 1/3 tears
    • Involves a small incision to capsule, passage of 2 18-G spinal needles across the tear from outside in, passage of a PDS suture which is retrieved out the anterior portals and tied to each other before the the resulting knot is pulled back against the meniscus to hold it in a reduced position while the free ends are tied down to capsule
      • Modified by use of a small wire snare to retrieve the intra-articular suture and avoid the need for a knot lying on the suture

3. 3. All inside

1. i.     Arthroscopic knot tying
2. ii.     Meniscal arrows
3. iii.     Fast-fix

• • • • Requires postero-medial or postero-lateral working portals

• • • • PLLA arrows
      • Place them 5-8mm apart
      • Use 10mm for anterior 1/3, 13mm middle 1/3, 16mm posterior 1/3

Rehabilitation

1. Brace for first 2 weeks (not necessary with the new available techniques)
2. WBAT but avoid flexion beyond 90° for 8 weeks
3. Run at 3 months
4. Pivoting sport > 6 months

Results

• Difficult to assess due to variety in groups and quantification of what is a “success”
• At follow-up arthroscopy
  • 50-80% healed
• Good clinical outcome in ~ 75%
• Revision surgery rate ~ 20%

Meniscal transplant

• Experimental
• Allografts do have potential to heal to peripheral capsule and remain viable
  • Re-populate with recipient cells – 95% host DNA at 1 year
  • But they do degenerate -  water and ¯ PG content at 6 months
• Require secure anterior and posterior horn fixation to mimic native biomechanics
  • Best achieved using bone plugs

Indications

1. Symptomatic joint line pain following previous meniscectomy where :
   1. Stable knee

• May perform concurrent stabilisation (ACL reconstruction)

1. 2. Normal anatomic alignment
   3. Minimal chondral damage

Technical factors

1. Graft selection

• • Options include Fresh, fresh-frozen, and cryopreserved grafts

2. Graft sizing – within 5% of native size

• • This is crucial
  • Pre-op MRI to size accurately

3. Surgical technique

• • Attach anterior and posterior horns via bone blocks, and suture rim to periphery
  • Any rim detachment (particularly anterior or posterior honrs) degrades the biomechanical benefit

Results

• Success in ~ 50%
• Better results in knees with minimal degenerative change