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Introduction
  • Incidence
    • ~400,000 ACL reconstructions / year
  • Mechanism is a non-contact pivoting injury
    • video showing ACL tear in elite athlete
  • Often associated with a meniscal tear
    • lateral meniscal tears in 54% of acute ACL tears  
  • Chronic ACL deficient knees associated with
    • chondral injuries
    • complex unrepairable meniscal tears
    • relation with arthritis is controversial
  • Sex-related differences
    • ACL injury more common in female athlete (4.5:1 ratio) due to 
    • landing biomechanics and neuromuscular activation patterns (quadriceps dominant) play the biggest role  
    • females get ACL injuries at a younger age than males
    • females get more ACL injuries on the supporting leg (males get more ACL injuries on the kicking leg)
    • table of differences  
Anatomy
  • ACL Function   
    • provides 85% of the stability to prevent anterior translation of the tibia relative to the femur
    • acts as a secondary restraint to tibial rotation and varus/valgus rotation
  • ACL Anatomy
    • 32mm length x 7-12mm width in size
    • two bundles
      • anteromedial bundle
        • more isometric
        • tight throughout knee ROM, but tightest in flexion
        • primairly responsible for restraining anterior tibial translation (anterior drawer test)
      • posterolateral bundle 
        • greater length changes
        • tightest in extension, slack in mid-flexion
        • primarily responsible for rotational stability (pivot shift test)
    • femoral attachment  
      • lateral intercondylar ridge demarcates the anterior edge of the ACL
      • bifurcate ridge separates the anteromedial and posterolateral bundle attachment
    • tibial attachment
      • anterior tibia, between intercondylar eminences
  • ACL Blood supply
    • middle geniculate artery  
  • ACL Innervation
    • posterior articular nerve ( a branch of tibial nerve)
  • ACL Composition
    • 90% Type I collagen 
    • 10% Type III collagen
  • ACL Strength: 2200 N (anterior)
Presentation
  • Presentation
    • felt a "pop"
    • pain deep in the knee
    • immediate swelling (70%) / hemarthrosis
  • Physical exam
    • effusion
    • quadricep avoidance gait (does not actively extend knee)
    • Lachman's test  
      • most sensitive exam test
      • grading
        • A= firm endpoint, B= no endpoint
        • Grade 1: 3-5 mm translation
        • Grade 2 A/B: 5-10mm translation
        • Grade 3 A/B: > 10mm translation
      • PCL tear may give "false" Lachman due to posterior subluxation
    • Pivot shift   
      • extension to flexion: reduces at 20-30° of flexion
      • patient must be completely relaxed (easier to elicit under anesthesia)
      • mimics the actual giving way event
    • KT-1000 
      • useful to quantify anterior laxity
      • measured with the knee in slight flexion and externally rotated 10-30° 
Imaging
  • Radiographs
    • usually normal
    • Segond fracture (avulsion fracture of the proximal lateral tibia) is pathognomonic for an ACL tear
      • represents bony avulsion by the anterolateral ligament (ALL)
      • associated with ACL tear 75-100% of the time
    • deep sulcus (terminalis) sign  
      • depression on the lateral femoral condyle at the terminal sulcus, a junction between the weight bearing tibial articular surface and the patellar articular surface of the femoral condyle.
  • MRI
    • findings of torn ACL
      • sagittal view
        • ACL fibers
          • discontinuity of fibers on T2
          • abnormal orientation 
            • too "flat" compared with intercondylar roof / Blumensaat's line  
            • this acute angle is common in chronic cases where ACL scars to the PCL
          • non-visualization of ACL
        • bone bruising in > half of acute ACL tears  
          • middle 1/3 of LFC (sulcus terminalis)
          • posterior 1/3 of the lateral tibial plateau
          • subchondral changes on MRI can persist years after injury
      • coronal view
        • discontinuity of fibers (do not reach the femur)  
        • fluid against the lateral wall ("empty notch sign")  
    • findings of normal ACL
      • fibers steeper than the intercondylar roof
      • continuity of fibers all the way from the tibia to femur
Treatment
  • Nonoperative
    • physical therapy & lifestyle modifications
      • low demand patients with decreased laxity
      • increased meniscal/cartilage damage linked to
        • loss of meniscal integrity
        • the frequency of buckling episodes
        • level I and II activity (e.g. jumping, cutting, side-to-side sports, heavy manual labor)
  • Operative
    • ACL reconstruction
      • indications
        • younger, more active patients (reduces the incidence of meniscal or chondral injury)
        • children (strongly consider operative as activity limitation is not realistic)
        • older active patients (age >40 is not a contraindication if high demand athlete)
        • prior ACL reconstruction failure
      • associated injuries
        • MCL injury
          • allow MCL to heal (varus/valgus stability) and then perform ACL reconstruction
          • varus/valgus instability can jeopardize graft
        • meniscal tear
          • perform the meniscal repair at the same time as ACL reconstruction
            • increased meniscal healing rate when repaired at the same time as ACL
        • posterolateral corner injury
          • reconstruct at the same time as ACL or as 1st stage of 2 stage reconstruction
      • outcomes
        • return to play
          • largely influenced by psychological, demographic and functional outcomes  
    • ligament repair
      • traditionally has a high failure rate
      • arthroscopic bridge-enhanced ACL repair (BEAR) trial with a bridging scaffold is ongoing  
    • revision ACL reconstruction
      • indications
        • failure of prior ACL reconstruction
Surgical Techniques
  • Femoral tunnel placement  
    • proper placement    
      • sagittal plane
        • 1-2 mm rim of bone between the tunnel and posterior cortex of the femur
      • coronal plane
        • the tunnel should be placed on the lateral wall (9-10 o'clock position) to create a more horizontal graft
  • Tibial tunnel placement
    • proper placement
      • sagittal plane
        • the center of tunnel entrance into joint should be 10-11mm in front of the anterior border of PCL insertion  
      • coronal plane
        • tunnel trajectory of < 75° from horizontal
          • obtain by moving tibial starting point halfway between tibial tubercle and a posterior medial edge of the tibia.
  • Graft placement
    • graft preconditioning
      • can reduce stress relaxation up to 50%
    • graft tensioning 
      • graft tensioning at 20N or 40N had no clinical outcome effects in a level 1 study
      • fix the graft in 20-30° of flexion
  • High tibial osteotomy
    • limb malalignment in both the coronal and sagittal plane must be addressed before or at the same time as ligament reconstruction
  • Revision ACL reconstruction
    • technique post
      • use high strength grafts (quad tendon, hamstring, allograft)
      • use dual fixation (suspension + interference screws)
      • bone grafting (tunnel dilation, decreased bone stock, staged)
      • re-harvesting BTB is contraindicated
    • postoperative
      • conservative rehab
Graft Selection
  • Bone-patellar-bone autograft post post
    • advantages of autograft
      • using patient's own tissue 
      • most common source of graft
      • faster incorporation
      • less immune reaction
      • no chance of acquiring someone else's infection
    • pros and cons of bone-patella-bone
      • the longest history of use and considered the "gold standard"
      • bone to bone healing
      • ability to rigidly fix the joint line (screws)
      • the highest incidence of anterior knee pain (up to 10-30%)  
      • maximum load to failure is 2600 Newtons (intact ACL is 1725 Newtons)
    • complications
      • patella fracture (usually postop during rehab), patellar tendon rupture 
      • re-rupture
        • associated with age < 20 years and graft size < 8mm 
  • Quadruple hamstring autograft
    • technique
      • may be taken from contralateral side in revision situation when allograft is not desirable or available
    • pros and cons
      • smaller incision, less perioperative pain, less anterior knee pain 
      • fixation strength may be less than Bone-PT-Bone
      • maximum load to failure is approximately 4000 Newtons  
      • decreased peak flexion strength at 3 years compared to Bone-PT-Bone
      • concern about hamstring weakness in female athletes leading to increased risk of re-rupture
    • complications
      • "windshield wiper" effect (suspensory fixation away from joint line causes tunnel abrasion and expansion with flexion/extension of knee)
      • residual hamstring weakness
  • Allograft
    • pros & cons
      • useful in revisions
      • longer incorporation time
      • risk of disease transmission (HIV is < 1:1 million, hepatitis is even greater)
      • increased risk of re-rupture in young athletes  
        • odds of graft re-rupture are 4.3 x higher in allograft for athletes aged 10-19
    • graft processing
      • supercritical CO2: decreases the structural and mechanical properties 
      • radiation3 Mrads is required to kill HIV (this, however, decreases the structural and mechanical properties)
        • 2-2.8 Mrad decreases stiffness by 30%
        • 1-1.2 Mrad decreases stiffness by 20%
      • deep freezing: destroys cells but does not affect the strength of the graft
      • 4% chlorhexidine gluconate: destroys cells but does not affect the strength of the graft
  • Quadriceps tendon autograft
    • taken with patella bone plug
    • much less common
Pediatric Considerations
  • Physis
    • < 14 yrs with open physis
    • the onset of menarche is the best determinant of skeletal maturity in females 
  • Treatment  
    • Nonoperative
      • indications
        • compliant, low demand patient with no additional intra-articular pathologies 
        • partial ACL tear (60% of adolescents have partial tears) with near normal Lachman and pivot shift
    • Surgery
      • indications
        • complete ACL tear
  • Techniques
    • intra-articular
      • physis-sparing (all intra-epiphyseal)  
      • transphyseal (males ≤13-16, females ≤ 12-14)
      • partial transphyseal 
        • leave either distal femoral or proximal tibial physis undisturbed 
      • no significant difference in growth disturbances between techniques
    • combined intra- and extra-articular (males ≤12, females ≤ 11)  
      • autogenous ITB harvested free proximally, left attached distally to Gerdy's tubercle
      • looped through the knee in over the top position
      • passed through the notch and under intermeniscal ligament anteriorly
      • sutured to lateral femoral condyle and proximal tibia
    • adult type reconstruction (males >=16, females >=14)
  • Graft Selection
    • transphyseal soft tissue grafts rarely lead to growth disturbances
  • Instrumentation
    • Factors found to increase physeal injury include: 
      • large tunnel diameter (>12mm) is most important 
        • 8mm tunnel corresponds to <3% physeal cross-sectional area
        • 12mm tunnel corresponds to >7-9% of physeal cross-sectional area is violated
      • oblique tunnel position 
      • interference screw fixation
      • high-speed tunnel reaming 
      • lateral extra-articular tenodesis
      • dissection close to the perichondral ring of LaCroix
      • suturing near tibial tubercle
  • Complications
    • physeal disruption without growth disturbance (10%)
Rehabilitation
  • Early postoperative
    • immediate
      • aggressive cryotherapy (ice)
      • immediate weight bearing (shown to reduce patellofemoral pain)
      • emphasize early full passive extension (especially if associated with MCL injury or patella dislocation)
    • early rehab
      • focus rehab on exercises that do not place excess stress on graft 
        • appropriate rehab  
          • eccentric strengthening at 3 weeks has been shown to result in increased quadriceps volume and strength  
          • isometric hamstring contractions at any angle
          • isometric quadriceps, or simultaneous quadriceps and hamstrings contraction
          • active knee motion between 35 degrees and 90 degrees of flexion
          • emphasize closed chain (foot planted) exercises
        • avoid
          • isokinetic quadricep strengthening (15-30°) during early rehab
          • open chain quadriceps strengthening   
  • Injury prevention
    • female athlete
      • neuromuscular training/plyometrics (jump training)
      • land from jumping in less valgus and more knee flexion
      • increasing hamstring strength to decrease quadriceps dominance ratio
    • skier training
      • teach skiers how to fall
    • ACL bracing
      • no proven efficacy except for ACL-deficient skiers
Complications
  • Failure due to Tunnel Malposition
    • overview
      • is the most common cause of ACL failure    
      • improper tunnel placement causes failure in 70% 
    • femoral tunnel malposition
      • coronal plane
        • vertical femoral tunnel placement 
          • cause by starting femoral tunnel at the vertical position in the notch (12 o:clock) as opposed to lateral wall (9 o: clock)
          • will cause continued rotational instability which can be identified on physical exam by a positive pivot shift    
      • sagittal plane
        • anterior tunnel placement    
          • leads to a knee that is tight in flexion and loose in extension
          • occurs from failure to clear "residents ridge"
        • posterior misplacement (over-the-top)
          • leads to a knee that is lax in flexion and tight in extension
    • tibial tunnel malposition
      • sagittal plane
        • anterior misplacement
          • leads to knee that is tight in flexion with impingement in extension 
        • posterior misplacement
          • leads to an ACL that will impinge with the PCL
  • Other cause of failure
    • inadequate graft fixation
      • can be caused by graft-screw divergence >30 degrees 
    • missed diagnosis
      • in combined ACL and PLC injuries, failure to treat the PLC will lead to failure of ACL reconstruction
    • overaggressive rehab
  • Infection
    • septic arthritis
      • coagulase negative Staph (S. epidermidis) most common
        • Staph aureus 2nd most common
      • presentation
        • pain, swelling, erythema, and increased WBC at 2-14 days postop
      • treatment
        • perform immediate joint aspiration with gram stain and cultures 
    • treatment
      • immediate arthroscopic I&D
      • often can retain graft with multiple I&Ds and antibiotics (6 weeks minimum)
        • graft retention more likely to be successful with S. epidermidis
        • graft retention less likely to be successful with S. aureus
  • Loss of motion & arthrofibrosis 
    • preoperative prevention
      • be sure patient has regained full ROM before you operate ("pre-hab")  
      • wait until swelling (inflammatory phase) has gone down to reduce the incidence of arthrofibrosis
    • operative prevention
      • proper tunnel placement is critical to have a full range of motion
    • postop prevention
      • aggressive cryotherapy (ice)
    • treatment
      • < 12 weeks, then treat with aggressive PT and serial splinting
      • > 12 weeks, then treat with lysis of adhesions/manipulation under anesthesia
  • Infrapatellar contracture syndrome
    • an uncommon complication following knee surgery or injury which results in knee stiffness
    • the physical exam will show decreased patellar translation    
  • Patella Tendon Rupture
    • will see patella alta on the lateral radiograph 
  • RSD (complex regional pain syndrome)
  • Patella fracture
    • most fx occur 8-12 weeks postop
  • Hardware failure
  • Tunnel osteolysis
    • treat with observation
  • Late arthritis
    • related to meniscal integrity 
  • Local nerve irritation
    • saphenous nerve  
  • Cyclops lesion
    • fibroproliferative tissue blocks extension
    • "click" heard at terminal extension
 

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