ANTERIOR CRUCIATE LIGAMENT

ANTERIOR CRUCIATE LIGAMENT 

Anatomy

• longitudinal bundles of collagen in fasciular subunits with larger functional bands
• surrounded by synovium – extra synovial
• inserts to tibial plateau – anterolateral to ant tibial spine – depressed area – just medial to the insertion of ant horn of lat meniscus – oval insertion – tibial insertion more stronger than femoral
• pass posteriorly – laterally - cephalad
• inserts to femur – posterior on lat wall of intercondylar notch – circular insertion
• both insertions nearly planar
• insertional area – three times the cross sectional area of ACL

• 31-35mm long – 31.3mm² cross sec area
• fibers of ACL are not of same length – least variation along anteromedial aspect of ligt
• large areas of insertions – results in various lengths of fibers
• extension – all fibers in tension
• flexion – relax – posterior and lateral fibers relax more
• 90⁰ flexion – ligament rotates 180⁰ – ie. Anterior fibers at their attachment at femur reaches posterior
• injury to one portion of the ligament results in total functional abnormality
• Drawer test – anterior portion of ACL- increased laxity
• Lachman test – posterior portion of ACL – increased anterior translation
• blood supply
  • resides completely inside the femur notch
  • no capsular attachments
  • 1⁰ supply – middle geniculate artery – pierces the post capsule – enters intercondylar notch near femoral attachment
  • additional supply – retropatellar fat pad – inferior , medial, lateral geniculate arteries – more important when ligt injures
• posterior articular nerve – br of tibial nerve – innervates
• have proprioceptive function
• knee – 6 degrees of freedom of motion – 3 rotations and 3 translations
  • translations – anteroposterior (5-10mm), compression and distraction (2-5mm), mediolateral (1-2mm)
  • rotations – flexion and extension, varus and valgus, IR and ER

ACL Injury

• occurs when bone of l/l twist in opposite directions

• non contact deceleration mechanism – sudden stopping, cutting, jumping – pop is heard – may be able to continue activity – knee swelling – hemarthrosis
• h/o + hemarthrosis – 70% hemarthrosis
• contact injuries – multi ligament injuries – O'Donoghue's triad – valgus load on knee – ACL, MCL and med meniscus
• acute traumatic hemarthrosis – r/o patellar subluxation/ dislocation, osteochondral injury, peripheral meniscus tear, intra articular fracture

Epidemiology

• femoral intercondylar notch width index =
• tunnel view of X ray knee
• normal is .231
• higher in men
• non contact ACL injuries more in athletes with less width index
• meniscal tears associated with 50-70% ACL injury – lat meniscus more common
• ACL deficient knee – abnormal load sharing – puts lat meniscus at more risk in early injury
  • late injury – medial meniscal tear common - firmer attachment to capsule

Diagnosis

• Clinical test
  • Anterior Drawer test
    • supine – hip flex 45⁰ – knee 90⁰ – sit on dorsum foot – pull tibia forward - >6-8mm – ACL rupture
    • differentiate between PCL tear – ie. Tibia from post subluxation to neutral than neutral to anterior displacement
      • both knees placed in Drawer test position – thumb placed on anteromedial jt line of each knee
      • tibial margin palpated prominently as an anterior step off (nearly 10mm) in relation to anterior aspect of medial femoral condyle
      • posterior drop back – PCL tear
      • in flush with the condyle – grade II laxity
  • Lachman test
    • knee 20-30⁰ flexion – one hand support thigh just above knee – other grasp tibia upper end – extend of glide noted
    • Grade I
      • end feel appreciation – 0-5mm displacement
    • Grade II
      • visible displacement tibia – 5-10mm
    • Grade III
      • gross anterior tibial translation - >10mm
  • Jerk test of Hughston
    • supine – 90⁰ knee flex – valgus force on knee – IR tibia – slow extension
    • lateral tibial condyle subluxates at 30⁰ – relocates as extends further
  • Pivot shift test
    • supine – knee extension – valgus stress on knee – tibia IR – knee flexed
    • subluxation at 30-40⁰
    • false negative in bucket handle meniscal tears – complete MCL tear – lateral extra articular tenodesis
  • Slocum anterior rotatory drawer test
    • anterior drawer – anterior translation of tibia noted
    • test done in 15⁰ IR, 30⁰ER and neutral rotation
    • posterior drawer – increased in 30⁰ IR – reduced in 15⁰ IR – anteromedial instability
• Knee ligament arthrometers
  • compare the maximal anterior displacement on both knees
  • difference >3mm high chance of ACL injury
• Imaging studies
  • X ray – may be normal – tibial eminence # - avulsion of tibial attachment of ACL
    • Segond # or avulsion # of lateral capsule also seen in ACL injury
    • stress X ray in c/c PCL injuries
  • MRI
    • tears 70-100%
    • non orthogonal plane – entire ACL in one frame – external rotating knee 15⁰
• Arthroscopy

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