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) posterolateral bundle 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 middle geniculate artery 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 Pivot shift 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 lateral extra-articular tenodesis (LET) can decrease graft failure rates and persistent rotatory instability in young patients with non-modifiable risk factors 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 hyperextension 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