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  • Summary
    • ACL tears are common athletic injuries leading to anterior and lateral rotatory instability of the knee.
    • Diagnosis can be suspected clinically with presence of a traumatic knee effusion with increased laxity on Lachman's test but requires MRI studies to confirm diagnosis.
    • Treatment involves ligamentous reconstruction utilizing a variety of techniques and graft choices depending patient age and activity levels. 
  • Epidemiology
    • Incidence
      • common
        • ~400,000 ACL reconstructions / year
        • account for half of all knee injuries
    • Demographics
      • more common among female athlete (4.5:1 ratio)
        • females sustain 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
    • Risk factors
      • female participation in soccer, male participation in basketball
      • valgus moment at knee and adduction moment at hip upon landing
      • previous concussion
  • Etiology
    • Pathophysiology
      • pathoantomy
        • non-contact pivoting injury
          • tibia translates anteriorly while knee is in slight flexion and valgus
        • blow to the lateral aspect of the knee
        • common activities are soccer, basketball, skiing, and football
        • pre-ponderance for females due to landing biomechanics and neuromuscular activation patterns (quadriceps dominant) play the biggest role
    • Associated conditions
      • meniscal tears
        • lateral meniscal tears in 54% of acute ACL tears, medial in chronic cases
      • PCL, LCL/PLC injuries
      • chronic ACL deficient knees associated with
        • chondral injuries
        • complex, unrepairable meniscal tears and bucket handle medial meniscus tears  
  • Anatomy
    • Anatomy
      • two bundles measuring combined 32mm length x 7-12mm width
      • bundles named for tibial attachment
        • anteromedial bundle
          • more isometric
          • tightest in flexion
          • primarily responsible for restraining anterior tibial translation (anterior drawer test)
          • greater length changes
          • tightest in extension
          • 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
    • Composition
      • 90% Type I collagen
      • 10% Type III collagen
    • Blood supply
    • Innervation
      • posterior articular nerve (branch of tibial nerve)
    • Biomechanics and 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
      • 2200 N strength (anterior)
  • Presentation
    • History
      • felt a "pop"
      • pain deep in the knee
      • immediate swelling (70%) / hemarthrosis
    • Symptoms
      • generalized knee pain
      • feelings of instability preventing return to sport
      • difficulty weightbearing
    • Physical exam
      • inspection
        • effusion
        • quadricep avoidance gait (does not actively extend knee)
        • coronal or sagittal plane deformity
          • varus deformity increases risk for ACL re-rupture
      • motion
        • lack of full extension secondary to meniscal injury or arthrofibrosis
        • evaluate for meniscal or concomitant ligamentous injuries (McMurray, Dial test, varus/valgus stress)
    • Neurovascular
      • evaluate peroneal function following high energy mechanisms and suspicion for multi-ligamentous injury pattern
    • Provocative tests
      • 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
        • knee brought from extension (anteriorly subluxated) to flexion (reduced) with valgus and internal rotation of tibia
          • reduces at 20-30° of flexion due to IT band tension
        • patient must be completely relaxed (easier to elicit under anesthesia)
        • mimics the actual giving way event (see pathoanatomy section)
      • KT-1000
        • useful to quantify anterior laxity
        • measured with the knee in slight flexion and externally rotated 10-30°
  • Imaging
    • Radiographs
      • recommended views
        • AP, lateral, sunrise/merchant/skyline view
      • findings
        • often 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
      • indications
        • to confirm clinical diagnosis of ACL rupture and evaluate for concomitant pathology
      • findings of torn ACL
        • sagittal view
          • ACL fibers
            • discontinuity of fibers on T2
              • normal ACL fibers appear steeper than the intercondylar roof and in continuity of fibers all the way from the tibia to femur
            • 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, may contribute to long-term chondral damage
          • tibial spine avulsion fracture
        • coronal view
          • discontinuity of fibers (do not reach the femur)
          • fluid against the lateral wall ("empty notch sign")
      • sensitivity and specificity
        • 97% and 100% respectively
    • CT scan
      • indications
        • revision setting to evaluate for bone loss
      • sensitivity and specificity
        • most sensitive and specific test for bone loss associated with osteolysis and tunnel widening
  • Treatment
    • Treatment individualized to patient based on activity level, age, demands, and concomitant pathology
    • Nonoperative
      • physical therapy, lifestyle modifications
        • indications
          • low demand patients with decreased laxity
          • recreational athlete not participating in cutting/pivoting activities
        • outcomes
          • 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
          • must have full motion of knee restored following injury (unless meniscal tear causing mechanical block)
            • lack of pre-operative motion risk factor for post-operative arthrofibrosis
          • younger, more active patients (reduces the incidence of meniscal or chondral injury)
          • children (activity limitation is not realistic)
          • older active patients (age >40 is not a contraindication if high demand athlete)
          • partial/single bundle tears with clinical and functional instability
          • prior ACL reconstruction failure
        • outcomes
          • return to play largely influenced by psychological, demographic and functional outcomes
      • ACL repair
        • indications
          • previously abandoned but increased interest recently in pediatric populations and avulsion rupture patterns
            • femoral or tibial-sided ACL avulsions without mid-substance rupture 
            • low risk of growth disturbance or angular deformity with transphyseal suspensory fixation if approaching skeletal maturity
        • outcomes
          • previously abandoned due to high failure rates
          • arthroscopic bridge-enhanced ACL repair (BEAR) trial with a bridging scaffold is ongoing
            • 2 year results show comparable results
      • ACL revision reconstruction
        • indications
          • failure of prior ACL reconstruction with instability during desired activities
    • Concurrent pathology
      • MCL injury
        • indications
          • if low grade MCL injury amenable to non-operative treatment, allow MCL to heal prior to ACL reconstruction
          • if high grade MCL injury necessitating repair/reconstruction, may be done concurrently with ACL
        • outcomes
          • failure to address valgus instability can jeopardize ACL graft with higher re-rupture rates
      • meniscal tears
        • indications
          • perform meniscal repair or meniscectomy at time of ACL reconstruction
        • outcomes
          • increased meniscal healing rate when repaired at the same time as ACL
      • chondral injuries
        • indications
          • partial- or full-thickness chondral injury may be treated at time of ACL reconstruction in staged fashion if injury necessitates
        • outcomes
          • presence of chondral defects consistently lowers long-term patient-reported outcomes following ACL reconstruction
      • posterior cruciate ligament and posterolateral corner injuries
        • indications
          • may reconstruct concurrently with ACL reconstruction or as staged procedure
        • outcomes
          • failure to recognize and address PCL/PLC injuries will lead to varus instability and ACL graft overload
      • high tibial osteotomy or distal femoral osteotomy
        • indications
          • limb malalignment in both the coronal and sagittal plane must be addressed before or at the same time as ligament reconstruction
            • lateral closing wedge osteotomy is more effective at addressing posterior tibial slope than medial opening wedge osteotomy
        • outcomes
          • high ACL failure rates in unaddressed limb malalignment
  • Techniques
    • Physical therapy, lifestyle modifications
      • technique
        • early symptomatic treatment followed by 3 months of supervised physical therapy
        • physical therapy focusing on range of motion and progressing to quad, hamstring, hip abductor and core strengthening
        • re-evaluation at conclusion to assess progress
        • functional braces demonstrate no added functional stability
    • ACL reconstruction
      • goal is to anatomically reconstruct ligament to restore anterior and rotational stability
      • approach
        • arthroscopic assisted
      • technique
        • clear out remnant ACL fibers to visualize native bone landmarks
          • in cases of single bundle ACL tears, no difference whether removal remnant ACL or remove all fibers prior to reconstruction
        • no patient-reported differences between single or double-bundle reconstructions
          • single bundle most common
          • double bundle may better restore native knee kinematics with less laxity
        • femoral tunnel placement
          • may be drilled trans-tibial or independent of the tibia (inside-out or outside-in)
          • proper placement
            • sagittal plane
              • 1-2 mm rim of bone between the tunnel and posterior cortex of the femur
            • coronal plane
              • tunnel should be placed on the lateral wall at 2 o'clock for left knee or 10 o'clock for right knee
              • creates a more horizontal graft (and reduce rotational laxity)
              • anteromedial and far medial drilling portals may enhance ability achieve these tunnel locations
                • no difference in clinical outcomes between trans-tibial and anteromedial drilling techniques
          • drilling tunnel in over 70 degrees of flexion will prevent posterior wall blowout
        • 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, 6mm anterior to the median eminence, 9mm posterior to the inter-meniscal ligament
            • 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 pre-conditioning can reduce stress relaxation up to 50%
          • graft tensioning at 20N or 40N had no clinical outcome effects in a level 1 study
          • fix the graft in 20-30° of flexion
        • graft fixation
          • various options for graft fixation, dictated by graft selection and surgeon preference
          • can be used alone (i.e. all-inside suspensory fixation) or in combination (i.e. interference screw with screw and washer post)
            • interference screws (aperture/compression fixation)
            • cortical buttons (suspensory fixation)
            • screw and washer post (suspensory fixation)
            • staple (suspensory fixation)
    • Revision ACL reconstruction
      • approach considerations
        • cause for prior ACL failure
        • concomittant pathology
        • prior graft selection
        • careful assessment of the underlying cause of re-rupture
      • technique
        • high strength grafts (quad tendon, hamstring, allograft)
          • allograft use has >2x increased risk of re-rupture compared to autograft for revision cases
        • dual or back-up fixation (suspension + interference screws)
        • bone grafting and reconstruction in cases of previous tunnel dilation (15mm) or if interfering with anatomic tunnel creation
        • addition of anterolateral ligament/ALL reconstruction (lateral extra-articular tenodesis) controversial
        • re-harvesting BPTB is contraindicated
      • postoperative
        • conservative rehab
  • Graft Selection
    • Bone-patellar tendon-bone (BPTB) autograft
      • advantages of all autografts
        • 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 leads to faster incorporation time
        • ability to rigidly fix the joint line (screws)
        • the highest incidence of anterior knee pain (up to 10-30%) and kneeling pain
        • 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
    • Quadrupled 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
        • maximum load to failure is approximately 4000 Newtons
        • decreased peak flexion strength at 3 years compared to BPTB
        • 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
        • parasthesias due to injury to saphenous nerve branches during harvest
          • oblique or horizontal incisions lessen this risk
    • Quadriceps tendon autograft
      • pros & cons
        • small incision in area that does not see pressure during kneeling
        • does not involve physis
        • maximum load to failure 2185 Newtons
        • similar patient-reported and functional outcomes as other autografts
        • may include bone block or completely soft tissue
        • less commonly used so is often available in revision setting
        • same disadvantages as hamstring autograft with suspensory fixation
    • Allograft
      • pros & cons
        • useful in revisions
        • no harvest site morbidity
        • longer incorporation time
        • more expensive than autograft
        • risk of disease transmission (HIV is < 1:1.6 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
        • fresh-frozen grafts lower re-rupture rates compared with chemically treated or irradiated
          • supercritical CO2: decreases the structural and mechanical properties
          • radiation
            • > 3 Mrads is required to kill HIV (this 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
  • 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
    • Operative Techniques
      • intra-articular
        • physis-sparing (all intra-epiphyseal)
        • trans-physeal 
        • partial trans-physeal
          • 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 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)
        • Bone-patellar tendon-bone autograft 
        • Quadriceps tendon or hamstring autograft 
    • Graft Selection
      • trans-physeal 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 post-operative
      • 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)
        • no long-term differences found between accelerated and non-accelerated protocols
      • 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
            • core and gluteal strengthening incorporated throughout therapy
            • emphasize closed chain (foot planted) exercises
              • i.e. squats or leg-press
          • avoid
            • isokinetic quadricep strengthening (15-30°) during early rehab
            • open chain quadriceps strengthening
              • i.e. leg extensions mimic anterior drawer and Lachman maneuvers
    • Return to play
      • no widely accepted criteria supporting clearance or timing to return to sport
        • previously held consensus is no sooner than 9 months following surgery
        • patient should pass series of functional tests that replictae sport-specific activities
          • various single- and double- leg hopping and jumping
          • dynamic valgus shown to increase risk of ipsilateral and contralateral rupture
          • higher rates of re-rupture following early return to sport prior to clearance
        • clearance for return to play should be made between surgeon and patient
        • psychological factors play large role in timing of return and should not be overlooked
    • 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
    • Intra-operative complications
      • graft-tunnel mismatch
        • BPTB graft total length greater than combined length of femoral tunnel, tibial tunnel, and intra-articular distance connecting them
          • leads to prominent tibial bone plug and inadequate fixation
        • risk factors
          • BPTB allograft
          • patella alta
          • non-transtibial drilling techniques
        • treatment
          • precise intra-operative measuring of tunnels and graft
          • twisting graft tendon on itself to effectively shorten graft length
      • posterior wall blowout
        • cortical breach of posterolateral cortical wall of lateral femoral condyle
        • risk factors
          • inadequate exposure of posterior wall prior to drilling
          • failure to evaluate tunnel walls after drilling
          • drilling femoral tunnel while knee flexed less than 70-90 degrees
        • treatment
          • if minimal defect at notch opening (3-5mm)
            • can re-drill tunnel deviating anteriorly and proceed with prior intended fixation method
          • if substantial cortical defect
            • keep previous tunnel but graft fixed with suspensory fixation (screw and washer post, cortical button, or staple) and/or interference screw fixation
              • intereference screw fixation may be added to supplement suspensory device
    • Graft failure due to tunnel malposition
      • incidence
        • graft failure for any cause approximates 5%
        • is the most common cause of ACL failure, attributed to 70% of failures
      • 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 (10 o'clock)
            • will cause continued rotational instability which can be identified on physical exam by a positive pivot shift
            • restores the anterior-posterior stability (i.e. normal anterior drawer), fails to restore rotational stability (i.e. abnormal 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 roof impingement in extension
        • posterior misplacement
          • leads to an ACL that will impinge with the PCL
    • Graft failure due to other causes
      • inadequate graft fixation or hardware failure
        • can be caused by graft-screw divergence >30 degrees
      • attritional graft failure
        • graft less then 8mm in width
      • intra-articular femoral bone plug dislodgement
        • treatment
          • requires revision surgery
      • missed diagnosis of concomitant ligamentous injuries or bony malalignment
        • in combined ACL and PLC injuries, failure to treat the PLC will overload graft lead to failure
      • over-aggressive or improper rehab
        • open-chain exercises
      • preoperative factors
        • young age
        • higher level of activity
        • posterior tibial slope >12 deg 
    • Infection and septic arthritis
      • incidence
        • less than 1% of all ACL reconstructions
        • most commonly superficial
          • coagulase negative Staph (S. epidermidis) most common organism
          • Staph aureus 2nd most common
          • routine soaking graft intra-operative in vancomycin solution may lower risk of infection
      • risk factors
        • graft contamination during routine intra-operative handling
        • graft dropped on floor
      • presentation
        • pain, swelling, erythema, and increased WBC at 2-14 days postop
      • diagnosis
        • joint aspiration with gram stain and cultures
      • treatment
        • intra-operative
          • routine soaking of graft in various antibiotic solutions before placement
          • sequential washing in various antibiotic solutions showed no increase in infection risk for dropped grafts
        • post-operative
          • immediate arthroscopic I&D
          • often can retain graft with multiple I&Ds and antibiotics (6 weeks minimum)
            • more likely to be successful with S. epidermidis, less likely with S. aureus
    • Loss of motion & arthrofibrosis
      • incidence
        • most common complication following ACL reconstruction
      • risk factors
        • lack of pre-operative motion
      • presentation
        • loss of patellar translation
      • treatment
        • pre-operative prevention
          • 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 critical to have a full range of motion
        • post-operative prevention
          • aggressive cryotherapy (ice)
        • < 12 weeks, aggressive PT and serial splinting
        • > 12 weeks, lysis of adhesions/manipulation under anesthesia
    • Infrapatellar contracture syndrome
      • incidence
        • an uncommon complication which results in knee stiffness
        • 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
      • BPTP and quadriceps grafts w bone block implicated
      • most fractures occur 8-12 weeks post-op
    • Tunnel osteolysis
      • treatment
        • observation unless graft laxity and knee instability
    • Late osteoarthritis
      • related to meniscal integrity
      • increased rates noted in patients > age 50 at the time of ACL reconstruction
    • Local nerve irritation
      • incidence
        • saphenous nerve due to hamstring autograft harvest
    • Cyclops lesion
      • fibroproliferative tissue blocks extension
      • "click" heard at terminal extension
  • Prognosis
    • Natural history
      • ACL deficient knees believed to lead to an accelerated progression of arthritis
    • Survival with treatment
      • near complete restoration of native kinematics following reconstruction
      • high level of return to sport at all levels of competition
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