Meniscal Injuries

Anatomy

  • Load bearing through the Meniscus
    • Extension
      • at least 50% of the compressive load of the knee joint
    • Flexion
      • approx 85% of the load is transmitted in 90° flexion.
    • Post Total Meniscectomy
      • meniscectomised knee the contact area is reduced approx 50%
    • Partial meniscectomy also ↑ the contact pressures
  • Shock absorption
    • menisci may attenuate the intermittent shock waves generated by impulse loading during gait
    • shock absorbing capacity of normal knees is ~ 20% higher than in meniscectomised knees.
    • The ability of a system to absorb shock has been implicated in development of Osteoarthritis
  • Knee joint stability
    • meniscectomy alone may not seriously affect stability.
    • However, in associated with ACL tears, meniscectomy ↑ anterior laxity of the knee
  • Lubrication
  • Proprioception
    • type 1 & type 2 nerve endings in the anterior & posterior horns of the menisci

Epidemiology

  • 1000 meniscal injuries
    • Medial
      • 70% were medial
      • Average age
        • 39 years medial
        • 30 years lateral meniscus injuries
  • Mechanism of Injury
    • Young
      • Occur only when weight is being taken,
      • knee is flexed & there is a twisting strain,
    • Older patients
      • may result from minor force

History

  • Acute history of injury
  • localised pain
  • ± locking
    • locked knee will flex but not extend fully
    • history of unlocking is characteristic of a mechanical block
  • Local signs will depend on
    • time the joint is examined
    • whether or not it is still locked (usually locked in 10° – 20° flexion)
  • Medial or lateral joint line tenderness
  • clicking with knee rotation in full flexion

Investigations

  • MRI
    • sensitivity 69-88%
    • Specificity 57-84%
    • Accuracy 72-89%

Classification

Type Description
1Complete
2Incomplete
3Wrisberg type witha mobile posterior horn due to a lack of any posterior menisco-tibial attachment
Classification of Discoid Meniscus

Discoid meniscus

  • In the foetus the meniscus is disc like & if this shape persists symptoms are likely
  • Characteristic clunk at 110° of flexion & at 10° as the knee is being extended

Differential Diagnosis

  • Loose bodies
  • Recurrent dislocation of the patella
  • Ligament injuries
  • Chondromalacia patellae

Treatment

Nonoperative

  • restrict activity

Operative

  • Options
    • arthroscopic partial menisectomy
  • Discoid meniscus
    • excise the central portion of the disc for Types I & II
    • resect the meniscus if Type III (Wrisberg Type)
  • Meniscal cysts
    • need to address pathology in the joint & not just the cyst as excision of the cyst alone is likely to recurrence
  • Meniscal transplantation- experimental

Meniscal repair

  • Blood supply
    • age dependent
    • in the adult the periph 3mm as well as the anterior & posterior horns are well vascularised
    • Blood supply originates from the lateral + medial geniculate arteries ( sup & inf)- branches
    • give rise to a perimeniscal capillary plexus in the synovial & capsular tissue
    • supplies the meniscus on its peripheral attachment to the joint capsule
    • degree of vascular penetration is 10-30% of medial & 10-25% of lateral meniscus.
  • repair
    • should be reserved for traumatic tears in the vascular region of the meniscus
    • within 3mm of periphery = vascular ( = red- red tears)
    • 3-5 mm from periphery = grey zone ( = red- white tears)
    • > 5mm from periphery = avascular ( = white- white tears)
  • Healing
    • similar to other connective tissue
      • exudation,
      • organisation,
      • vascularisation cellular proliferation
      • remodelling
    • following injury there is formation of a fibrin clot rich is inflammatory cells.
    • Vessels from the perimeniscal capillary plexus proliferate into this fibrin scaffold , followed by mesenchymal cell proliferation forming a cellular fibrovascular scar.
    • Modulation of this scar tissue into normal appearing fibrocartilage requires several months
    • Approx 80% of repairable menisci are found in knees with an acute or chronic tear of the ACL
      • thus repair of the meniscus is linked to the management of the ACL tear
    • NB risk of injury to peroneal n in lateral meniscus repair, saphenous n in medial repair
  • Aftercare
    • 6 weeks
    • maximal protection to allow initial healing
    • Minimal touch down WB 6 weeks in hinged splint, initially locked
    • Isometric Q+H setting exercises begun immediately post op
    • limited ROM 30-70° at 2 weeks
    • remove splint 4 weeks , ↑ stretching exercises between 4-6 weeks
    • from 6 weeks WB ↑ to FWB by 8 weeks
    • Low impact activity from 3 months
    • subsequent 6 mth
      • protection from vigorous stresses to allow for maturation of the healing collagen tissue
    • Full activity at 6 mths
  • Results of meniscal suture
    • 62% heal, 17% heal incompletely & 21% do not heal
    • 92% are clinically stable
    • 80% return to active sport
    • NB: 30-40% failure rate in 5 years in meniscal repair in knees that are ACL deficient- therefore need to reconstruct ACL to protect meniscal repair
    • the success rate in stable knees is ~ 90% at 9 years