High Yield Topics

ACL Injuries

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Ovid: 5-Minute Sports Medicine Consult, The


ACL Injuries
Suraj A. Achar
Basics
Description
  • The anterior cruciate ligament (ACL) is a critical stabilizer of the knee.
  • The ACL provides stability against anterior translation of the knee.
  • The ACL has 2 important bundles: The posterolateral bundle is tight in extension, whereas the anteromedial bundle is tight in flexion.
  • The ACL is a secondary stabilizer of tibial rotation and provides some restraint to varus and valgus rotation if the primary lateral structures have been disrupted.
  • ACL tears can occur with trauma or noncontact hyperextension or twisting injuries.
Epidemiology
  • The ACL is the most commonly injured knee ligament.
  • An estimated 200,000 ACL injuries occur annually in the U.S.
  • ∼100,000 ACL reconstructions are performed each year.
  • The incidence of ACL injury is greater in active adults and children participating in cutting sports such as basketball, football, skiing, soccer, and gymnastics.
  • Noncontact ACL tears account for 2/3 of injuries.
  • Female gender confers higher risk. A meta-analysis in 2007 noted a roughly 3× greater incidence of ACL tears in female soccer and basketball players versus male athletes. Year-round female athletes who play soccer and basketball have an ACL tear rate approaching 5%.
Risk Factors
  • High-risk sports and female gender appear to be the most clear risk factors for ACL injuries:
    • ∼70% of ACL injuries occur in the high-risk sports, such as football (ie, soccer), American football, basketball, volleyball, gymnastics, and downhill skiing. Hewson and colleagues found a 100-fold increase in the incidence of ACL injury in college football players compared with the general population.
    • Female risk factors being evaluated include differences in training, different strength-to-weight ratios, limb alignment, joint laxity, muscle recruitment patterns, and notch index.
    • Kinematics and electromyography studies suggest that females prepare for landing with decreased hip and knee flexion, increased quadriceps activation, and decreased hamstring activation, which may result in increased ACL loading and the risk for noncontact ACL injury.
    • Data have shown that ACL laxity does not vary with the menstrual cycle, making hormonal differences a less likely etiology.
  • Factors that increase traction have been associated with a higher incidence of ACL tears:
    • Early studies of artificial turf (“Astroturf”) in the National Football League noted an increased risk.
    • Cleats that have a predominant grip on the periphery may also increase the risk, especially when used with artificial turf.
General Prevention
  • Neuromuscular training programs:
    • A meta-analysis of 6 prospective studies demonstrated a significant effect of neuromuscular training programs on ACL incidence in female athletes (p < .0001). One potential limitation of the meta-analysis is publication bias. The reviewers noted the following:
      • All 3 studies that incorporated high-intensity plyometrics reduced ACL risk, whereas the studies that failed to use this regimen did not reduce ACL injuries.
      • Training sessions need to be performed more than once a week.
      • Duration: Minimum of 6 wks
      • Plyometrics, balance, and strengthening exercises all need to be incorporated into a comprehensive training protocol.
    • A consensus statement issued by the American College of Sports Medicine and the American Academy of Orthopedic Surgeons supports the use of ACL injury prevention programs for female athletes.
  • Bracing:
    • Bracing has been used to reduce knee injuries in American football for many years. Studies on the use of prophylactic knee bracing have had mixed results. Early research in the 1980s revealed an increased number of ACL injuries during a prospective period of time that prophylactic braces were used.
    • A larger prospective study at West Point showed no difference in overall ACL injuries but showed a decrease in the severity of knee injuries overall.
    • As brace technology changes, new studies will be needed to access potential benefits and risks.
Commonly Associated Conditions
  • Injuries to the medial and lateral meniscus are commonly associated with an ACL tear.
  • ∼50% of ACL injuries are associated with meniscal tears.
  • Chondral and subchondral injuries are often noted.
  • These associated injuries can be identified on both physical examination and MRI.

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Diagnosis
History
  • Many patients with an ACL tear feel a “pop” in their knee, followed by an acute swelling of the knee within hours.
  • According to Noyes and colleagues, in the absence of bony trauma, an immediate effusion is believed to have a 72% correlation with an ACL injury of some degree.
  • Symptoms of an ACL-deficient knee include feeling of “giving out” and instability aggravated by squatting, pivoting, and stepping laterally or bearing the entire body weight when walking down stairs.
Physical Exam
  • If evaluated within 12 hrs of an acute injury, the athlete will have difficulty bearing weight and will have an effusion.
  • An athlete with an ACL injury likely will have difficulty achieving full knee extension because the ACL stump gets caught in the notch.
  • Other causes of loss of range of motion (ROM) are a possible associated bucket-handle meniscal tear or loose bony fragment.
  • Examination should begin with inspection to look for an effusion or bony abnormalities.
  • Palpation of bony structures is important to evaluate for associated tibial plateau fractures or growth plate injuries in the case of growing adolescents.
  • Palpation of the joint line is critical to evaluate for meniscal tears or medial collateral ligament (MCL) injuries.
  • Valgus stress testing can be of further help in evaluating the MCL.
  • Specific tests to determine an ACL tear include the Lachman test, the pivot shift, the anterior drawer test, and the flexion-rotation drawer examination:
    • The anterior drawer test was found to be only 50% positive, especially if the posterior horn of the medial meniscus is intact.
    • The flexion-rotation drawer examination is performed by cradling the calf and flexing the knee. A posteriorly directed force on the tibia will cause reduction of the tibia as the femur rotates from an externally rotated position.
    • The pivot shift test, although useful, is often painful and leads to guarding.
    • The Lachman test, performed under anesthesia, was 98% accurate in predicting anterior cruciate injury. The sensitivity of this test decreases with hemarthrosis, guarding, and experience of the performer but is still reported to have a sensitivity of 87%. One key to using the Lachman test is to 1st examine the uninjured side for comparison. Patients may have increased laxity that is not pathologic.
    • The Lachman test should be the 1st special test performed for evaluation of a possible ACL-injured athlete. Performance of the test is described below:
      • Allow the hip to rotate externally, and support the knee in slight flexion to facilitate relaxation.
      • One hand should firmly grasp the femur, while the other is positioned below the joint, grasping the tibia to allow anterior translation.
      • The knee should be flexed around 20–30 degrees.
      • A quick, firm motion pulling the tibia anteriorly while stabilizing the femur should be performed.
      • The examiner will appreciate the degree of translation and quality of endpoint.
      • A soft endpoint has a greater specificity for a positive ACL tear.
      • It is more important to interpret the Lachman test as positive or negative rather than to quantify the degree of laxity.
Diagnostic Tests & Interpretation
Imaging
  • Standard radiography:
    • Plain radiography should be performed on all patients suspected of acute ACL tears because of the risk of fractures.
    • X-ray studies have a pivotal role in the evaluation of adolescents and children because of the risk of growth plate fractures and tibial spine fractures.
    • In children, plain x-rays should be performed before aggressive maneuvers are performed, especially in the case of decreased active ROM or tenderness at the distal femoral physis.
    • X-rays should include anteroposterior (AP), lateral, and oblique views to better visualize fractures.
  • Advanced imaging:
    • MRI should be used to evaluate for other concomitant injuries and, in some cases, either to confirm the diagnosis or help to plan surgery.
    • The surgical consent and plan will depend on associated injuries, such as meniscal or MCL injuries.
    • MRI, if used for evaluation of a presumed ACL tear, should be non-contrast-enhanced.
    • The accuracy and sensitivity of MRI are excellent when compared with arthroscopic findings.
    • US is another modality that can be used to assess the ACL. Research in Europe and Australia shows US to have 88–91% sensitivity and 98–100% specificity when used to detect rupture of the ACL.
    • Sonography is a useful and inexpensive method of detecting the presence of rupture of the ACL in the clinical setting of a traumatic hemarthrosis.
    • Sonography has limited use in the US owing the widespread use of MRI in this setting.

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Treatment
  • Most patients who sustain an ACL injury are active in some type of sports. Expectations after injury vary, however, based on age and activity. Reconstruction is an elective procedure for most individuals. Many can maintain an active lifestyle with an ACL-deficient knee. High-level athletes and the young do the worst without surgery and have frequent episodes of instability.
  • The adolescent with open growth plates poses a significant challenge. There is some concern about damaging the growth plates in adolescents with tunnels. However, studies are ongoing, and more procedures on adolescents to reconstruct the ACL are being performed.
  • To date, there is a lack of evidence to support a protective role of reconstructive surgery of the ACL against osteoarthritis development. At 10–20 yrs, 50% of those diagnosed with an ACL tear have osteoarthritis and functional impairment—“the young patient with an old knee.”
  • No studies have shown that bracing an ACL-deficient knee will prevent episodes of instability when an athlete returns to cutting and pivoting sports. The data on bracing do show a decrease in anterior tibial translation at low levels of force. Activity modification provides the best method outside of surgery to prevent “giving way” episodes. If an athlete attains and maintains full ROM and at least 90% strength of the contralateral lower extremity, low-risk sports such as running, bicycling, and swimming can be performed.
  • Daniels and colleagues found that an athlete's inability to return to sports determines whether that athlete elects surgery. KT-1000 measurements of more than 5 mm have been shown in some studies to predict instability and the need for surgery. A positive pivot-shift test at 3 mos after injury in an awake patient is a strong predictor of the future need for reconstruction. Dynamic functional testing (a series of hopping tests) may be a useful adjunct to predict who may be a “coper” and can continue nonoperative treatment.
Surgery/Other Procedures
  • Operative treatment: The procedure selected for ACL reconstruction must restore normal stability and full ROM. Primary ACL suturing does not restore stability and has been abandoned. One exception to primary repair is a bony avulsion, seen mostly in adolescents.
  • Graft selection:
    • Autogenous tissue:
      • Patellar tendon (with bone attached both proximally and distally)
      • Hamstring tendons
    • Allograft tissue: The use of synthetic materials such as Dacron and Gore-Tex has been abandoned because of long-term failure and complications secondary to wear of the material.
  • Patellar tendon autograft: The patellar tendon autograft is an example of bone-to-bone ACL reconstruction and has been used more for high-demand athletes. Of all the procedures, it appears to have the least laxity on KT-1000 testing on follow-up. The potential bone-to-bone fixation promotes earlier graft fixation. Long-term follow-up shows no difference in return to full participation for either autograft procedure.
  • Hamstring tendon autograft: The hamstring graft has several advantages. Use of the hamstring tendon avoids patellar tendon morbidity. As of 2001, studies have shown a decrease in anterior knee pain among those who undergo a hamstring autograft compared with those undergoing bone-to-bone fixation (relative risk 0.49, 95% confidence interval 0.32–0.76, p = .001, I2 = 0%). Hamstring donor-site pain heals within 3 mos.
  • New techniques that go beyond the scope of this chapter, including double-bundle reconstruction, yield even greater stability.
  • Allografts: Allografts are used commonly for ACL reconstruction. These are often employed as 2nd-option surgeries in those who have already had a hamstring or bone-to-bone patellar graft.
    • The risks of infection are extremely low. The benefits of decreased surgical morbidity and easier rehabilitation must be weighed against the potential for greater failure of biologic incorporation, infection, and possibly slower return to activities.
    • The overall risk of infection is extremely low because donors are tested and the grafts are irradiated.
    • Significant bacterial infections occur in fewer than 1%, and no reports of HIV or hepatitis transmission have occurred after 2002.
    • Perhaps the newest and most concerning risk of allograft use is bone resorption noted on follow-up.
    • The significance of this resorption has yet to be completely understood.
    • New data now suggest increased failure rates with allografts compared with hamstring tendon or patellar tendon autografts.
  • Timing of surgery:
    • The timing of surgery is controversial because some surgeons perform surgery at the site where patients are injured, ie, the ski area.
    • Negative outcomes, especially arthrofibrosis, are not directly associated with surgical timing but rather with signs of inflammation marked by periarticular swelling, effusion, and hyperthermia.
    • Other factors that predict arthrofibrosis include decreased ROM and perioperative pain.
    • Surgery should be delayed until these factors are improved.
    • Early surgery is absolutely indicated only in bony avulsions.
  • Graft placement:
    • Placement of the grafts is critical because the ACL performs a role in rotatory stability and with valgus torque.
    • Double-tunnel ACL reconstructions have been postulated to improve this stability, but the early results are limited to animals.
    • Ongoing research may lead to improved placement of the graft and potential use of multiple bundles.

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Ongoing Care
  • Patients are now returning to activity sooner after reconstruction. Return to sport depends more on strength and proprioception than on time from surgery. Usual return to sport may fall between 6 and 12 mos or longer after surgery. Early return prior to full proprioception and strength may lead to prolonged instability and possible reinjury.
  • Therapy protocols may be divided into 4 categories, as per Shelbourne and Nitz:
    • Phase 1: Preoperative; maintain ROM.
    • Phase 2 (0–2 wks): Achieve full extension; maintain quadriceps strength, reduce swelling, and achieve flexion to 90 degrees.
    • Phase 3 (3–5 wks): Maintain full extension and increase flexion up to full ROM; stair climbers and exercycles may be used.
    • Phase 4 (6 wks–9 mos): Increase strength and agility; progressive return to sports.
  • The use of custom ACL bracing has also been controversial. A systemic review of several randomized, controlled trials (level I evidence, 12 trials) found no evidence that pain, ROM, graft stability, or protection from subsequent injury was affected by postoperative bracing.
Follow-Up Recommendations
  • If arthrofibrosis is evident after surgery, early surgical intervention (<1 yr) improves the outcome.
  • Full ROM should be achieved to prevent degenerative joint disease.
Prognosis
  • Most patients with ACL injuries do well with activities of daily living even after follow-up in the range of 5–15 yrs. Most can participate in some sports activity if they are inclined to do so, but most will have some limitations in vigorous sports, and only a few will be entirely asymptomatic.
  • The presence of clinically significant chondral and meniscal injuries that occur at the time of injury or after injury determines long-term prognosis more than the ACL injury itself. Over time, the prevalence of meniscal injuries increase, leading to increasing disability, surgery, and arthrosis in high-risk patients.
  • Ligament reconstruction has not been shown to prevent arthrosis, but in prospective studies, it appears to reduce the risk of subsequent meniscal injury, to improve passive AP knee motion limits, and to facilitate return to high-level sporting activities.
Additional Reading
Chappell JD, Creighton RA, Giuliani C, et al. Kinematics and electromyography of landing preparation in vertical stop-jump: risks for noncontact anterior cruciate ligament injury. Am J Sports Med. 2006;36:e3.
Daniel DM, Malcom LL, Losse G, et al. Instrumented measurement of anterior laxity of the knee. J Bone Joint Surg Am. 1985;67:720–726.
Daniel DM, Stone ML, Dobson BE, et al. Fate of the ACL-injured patient. A prospective outcome study. Am J Sports Med. 1994;22:632–644.
Fithian DC, Paxton LW, Goltz DH. Fate of the anterior cruciate ligament-injured knee. Orthop Clin North Am. 2002;33:621–636, v.
Guelich DR, Lowe WR, Wilson B. The routine culture of allograft tissue in anterior cruciate ligament reconstruction. Am J Sports Med. 2007;35:1495–1499.
Hewett TE, Ford KR, Myer GD. Anterior cruciate ligament injuries in female athletes: part 2, a meta-analysis of neuromuscular interventions aimed at injury prevention. Am J Sports Med. 2006;34:490–498.
Hewson GF, Mendini RA, Wang JB. Prophylactic knee bracing in college football. Am J Sports Med. 1986;14:262–266.
Huston LJ, Greenfield ML, Wojtys EM. Anterior cruciate ligament injuries in the female athlete. Potential risk factors. Clin Orthop Relat Res. 2000;372:50–63.
Kostogiannis I, Ageberg E, Neuman P, et al. Clinically assessed knee joint laxity as a predictor for reconstruction after an anterior cruciate ligament injury: a prospective study of 100 patients treated with activity modification and rehabilitation. Am J Sports Med. 2008;36:1528–1533.
Lohmander LS, Englund PM, Dahl LL, et al. The long-term consequence of anterior cruciate ligament and meniscus injuries: osteoarthritis. Am J Sports Med. 2007;35:1756–1769.
Mayr HO, Weig TG, Plitz W. Arthrofibrosis following ACL reconstruction—reasons and outcome. Arch Orthop Trauma Surg. 2004;124:518–522.
Miller SL, Gladstone JN. Graft selection in anterior cruciate ligament reconstruction. Orthop Clin North Am. 2002;33:675–683.
Noyes FR, Bassett RW, Grood ES, et al. Arthroscopy in acute traumatic hemarthrosis of the knee. Incidence of anterior cruciate tears and other injuries. J Bone Joint Surg Am. 1980;62:687–695, 757.
Poolman RW, Farrokhyar F, Bhandari M. Hamstring tendon autograft better than bone patellar tendon bone autograft in ACL reconstruction: a cumulative meta-analysis and clinically relevant sensitivity analysis applied to a previously published analysis. Acta Orthop. 2007;78:350–354.
Prodromos CC, Han Y, Rogowski J, et al. A meta-analysis of the incidence of anterior cruciate ligament tears as a function of gender, sport, and a knee injury-reduction regimen. Arthroscopy. 2007;23:1320–1325.e6.
Ptasznik R, Feller J, Bartlett J, et al. The value of sonography in the diagnosis of traumatic rupture of the anterior cruciate ligament of the knee. AJR Am J Roentgenol. 1995;164:1461–1463.
Rovere GD, Haupt HA, Yates CS. Prophylactic knee bracing in college football. Am J Sports Med. 1987;15:111–116.
Shelbourne KD, Nitz P. Accelerated rehabilitation after anterior cruciate ligament reconstruction. Am J Sports Med. 1990;18:292–299.
Sitler M, Ryan J, Hopkinson W, et al. The efficacy of a prophylactic knee brace to reduce knee injuries in football. A prospective, randomized study at West Point. Am J Sports Med. 1990;18:310–315.
Up-to-date
Wright RW, Fetzer GB. Bracing after ACL reconstruction: a systematic review. Clin Orthop Relat Res. 2007;455:162–168.
Codes
ICD9
  • 717.83 Old disruption of anterior cruciate ligament
  • 844.2 Sprain of cruciate ligament of knee
Clinical Pearls
  • Nearly all patients with an acute ACL tear have an effusion.
  • Noncontact injuries account for the majority of ACL tears.


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