clinical practice
This Journal feature begins with a case vignette highlighting a common clinical problem. Evidence supporting various strategies is then presented, followed by a review of formal guidelines,
when they exist. The article ends with the authors’ clinical recommendations.
Anterior Cruciate Ligament Tear
Kurt P. Spindler, M.D., and Rick W. Wright, M.D.
From Vanderbilt Sports Medicine, Vander-bilt University Medical Center, Nashville (K.P.S.); and the Department of Orthope-dic Surgery, Washington University School of Medicine at Barnes–Jewish Hospital, St. Louis (R.W.W.). Address reprint re-quests to Dr. Spindler at Vanderbilt Sports Medicine, 4200 Medical Center E., South Tower, 1215 21st Ave. S., Nash-ville, TN 37232-8774, or at kurt.spindler@ vanderbilt.edu.
N Engl J Med 2008;359:2135-42.
Copyright © 2008 Massachusetts Medical Society. A female high-school soccer athlete reacts to a defender, plants her leg, cuts to the left
without contact, feels her leg give out, hears a pop, and has acute pain. She is unable to walk off the field or return to play. That evening her knee progressively swells. The next day she presents for evaluation. How should her case be managed?
The Clinical Problem
The passage in 1972 of Title IX legislation, which guarantees equal access to athletic programs for both sexes at any high school or college receiving federal funds, has led to an exponential rise in the number of female participants in sports. Although this has resulted in many benefits, including the promotion of physical fitness and the foster-ing of team-buildfoster-ing behavior, it has also led to an increase in sports-related injuries among female athletes, particularly tears in the anterior cruciate ligament (ACL).
The ACL is the most commonly injured ligament in the body, for which surgery is frequently performed. It is estimated that 175,000 ACL reconstructions were per-formed in the year 2000 in the United States at a cost of more than $2 billion.1
This number continues to increase. Incidence rates for tears are difficult to assess because some injuries remain undiagnosed. A recent study at West Point, where injuries are consistently reported, showed an incidence of ACL tears of 3.2% for men and 3.5% for women during a 4-year period.2 When considering sports or
activities in which both sexes participate, women had a significantly higher rate of ACL tears than men (incidence ratio, 1.5; 95% confidence interval [CI], 1.3 to 2.2).3
The majority of ACL tears (67% in men and almost 90% in women) occurred with-out physical contact. In other studies, the injury rate in female athletes has ranged from two to six times the rate in male athletes, depending on the sport studied.4-7
The increased risk of an ACL tear in female athletes remains incompletely under-stood but has been attributed to several factors, including sex differences in leg alignment, with an increased rate of valgus deformity (knock-knee) among women; in notch width, with possibly less space for the ACL in women; in hormonal factors, including an increased risk during the preovulatory stage of the menstrual cycle8;
and in neuromuscular control.6,9
Besides the immediate associated morbidity and costs, an ACL tear significantly increases the risk of premature knee osteoarthritis.3,10 It is estimated that
osteoar-thritis develops in 50% of patients with ACL tears 10 to 20 years after the injury, while they are still young.3,11,12
S tr ategies and Ev idence Diagnosis
Careful history taking and physical examination will frequently allow an accurate diagnosis of an ACL tear without the need for additional testing or evaluation. An
isolated ACL tear occurs less than 10% of the time, and assessment is needed for associated injuries; the prevalence of associated meniscus injuries is 60 to 75%7,13,14; articular cartilage injuries, up to
46%7,13-15; subchondral bone injuries (i.e., “bone
bruises”), 80%16-18; and complete collateral
liga-ment tears (medial or lateral), 5 to 24%.14,16,19
Table 1 and Figure 1 summarize the functions of the three major intraarticular knee structures (ACL, meniscus, and articular cartilage) and mani-festations of injury to these structures.
Key points of the history suggesting ACL tear include a noncontact mechanism of injury, the identification of an audible popping sound, the early occurrence of swelling as a result of bleed-ing (hemarthrosis) from the rupture of the vascu-lar ACL, and an inability to continue to partici-pate in the game or practice after the injury. Collateral ligament tears usually do not result in swelling, and frequently patients with partial posterior ligament tears can continue to play. Meniscus tears are associated with a delayed on-set of swelling (commonly the next day).
During the physical examination, two maneu-vers — the Lachman test and the pivot shift test — are useful in the assessment of an ACL tear. The Lachman test is shown in Figure 2; the pivot shift test assesses whether there is a sudden sub-luxation of the lateral tibial condyle on the distal femur when the knee is extended. In a recent meta-analysis of 28 studies, the pooled sensitivity and specificity of the Lachman test for an ACL tear were 85% and 94%, respectively.20 For the
pivot shift, the specificity was high (98%), but the sensitivity was low (24%).
Magnetic resonance imaging (MRI) is often used to confirm the diagnosis of an ACL tear, although it is not needed before proceeding to ACL reconstruction in an athlete when the diagnosis is clear from the history and physical examination. According to a systematic review, MRI had a sen-sitivity of 86%, a specificity of 95%, and an ac-curacy of 93% for an ACL tear, as confirmed by arthroscopy.21
Treatment
The majority of patients with a torn ACL can walk normally and can perform straight-plane activi-ties, including stair climbing, biking, and jog-ging. Surgical treatment is indicated if the patient has a sensation of instability in normal activities
of daily living or wants to resume activities that involve cutting and pivoting, including football, soccer, basketball, lacrosse, singles tennis, and mogul skiing. Occupations such as firefighting, law enforcement, and some construction jobs also require an ACL-stabilized knee.
Regardless of whether surgical intervention is pursued, the short-term management of an ACL tear should focus on the reduction of hemar-throsis with rest, ice, compression, and elevation (RICE); the administration of nonsteroidal anti-inflammatory agents; and the regaining of a normal range of motion, the reinitiation of quad-riceps control, and the restoration of a normal gait. A delay of 2 to 4 weeks between the acute injury and surgical correction is common.
Surgical Approaches
The surgical approach to ACL tears for the past two decades has involved the reconstruction of the ACL with the use of a graft (a piece of tendon) passed through tunnels drilled into the tibia and femur at insertion points of the ligament to ap-proximate normal anatomy, with the goal of elim-inating ACL instability. Reconstruction is indicat-ed rather than repair, since randomizindicat-ed trials have shown that ACL repair is no better than nonoperative treatment22 and that ACL
reconstruc-tion significantly improves knee stability and the likelihood of return to preinjury activity over re-pair alone or rere-pair with augmentation (insertion of a tendon graft or synthetic graft).23 In addition,
randomized trials of ACL reconstruction have shown significantly fewer subsequent meniscus tears requiring surgery at 2 years than in nonop-erative management,24 whereas the addition of
augmentation to ACL reconstruction offered no benefit over reconstruction alone.
A systematic review of four randomized trials has demonstrated similar outcomes using endo-scopic (single-incision) versus rear (two-incision) entry.25 Either patellar tendon or hamstring
ten-don may be used. A systematic review of nine randomized, controlled trials involving autografts found that these approaches yielded similar re-sults, including anterior–posterior laxity, isoki-netic quadriceps and hamstring strength, anterior knee pain, and clinical outcome or rating scores,26
although the four trials that evaluated pain on kneeling found an increase in pain in procedures harvesting the patellar tendon, as compared with
the hamstring. Meta-analyses of trials comparing patellar tendon and hamstring autografts27,28
showed no significant differences in the rates of restoring a “normal” knee, categorized as group A by the International Knee Documentation Com-mittee (41% and 33%, respectively), and of a re-turn to preinjury activity (76% and 67%, respec-tively). Patients with patellar tendon grafts had a significantly lower rate of positive results on the Lachman test (30% vs. 34%) but a significantly higher rate of anterior knee pain (22% vs. 13%) and extension deficit (9% vs. 6%). However, vali-dated scales were not used to assess anterior knee pain, activity level, or overall knee rating, and validated patient-reported outcomes have not been compared between these grafts.
There is a lack of randomized trials to inform the choice of allograft versus autograft for ACL reconstruction. The best available evidence is from seven observational studies29-35 showing no
significant differences in patient-reported out-comes, instrumented laxity, and donor-site symp-toms. However, the failure rate after 2 years was significantly higher for patients receiving allo-grafts (9 of 158) than for those receiving auto-grafts (2 of 167) (P = 0.03). Thus, the avoidance of allografting is prudent when possible in young athletes. The means of graft fixation (i.e., the technique or device used to secure the graft into the tibial and femoral tunnels) has not affected outcomes, including stability, range of motion, strength, and clinical assessments.
Immediate complications of ACL
reconstruc-tion are uncommon but include infecreconstruc-tion, deep venous thrombosis, and nerve injury.26 Graft
failure has been reported in 3.6% of patients at 2 years, with no significant differences noted between grafting of a hamstring tendon and grafting of a patellar tendon. Additional arthro-scopic surgery was necessary in 14.7% of patients in one series, including the débridement of scar tissue and treatment of meniscus and articular cartilage. In a prospective cohort study, the risk of tearing an ACL reconstruction graft was the same as the risk of tearing the contralateral nor-mal ACL (3.0% for each).36
Associated Injuries
The presence of other knee injuries may adversely affect outcomes after ACL reconstruction. The risk of osteoarthritis appears to be increased in pa-tients who have had an associated meniscal tear or cartilage injury. Detailed discussion of the techniques to treat these associated injuries is beyond the scope of this article, but case series indicate high success rates for treating meniscal injuries. Longitudinal tears in the vascular zone (the peripheral third of the ligament) undergo repair, which has been reported to result in an 87% success rate (defined as the absence of a need for reoperation for clinical symptoms) with the use of current techniques.37 Tears in the
avas-cular zone (the central two thirds of the ligament) are treated with partial meniscectomy. There is currently no effective treatment for articular car-tilage injuries that do not penetrate subchondral Table 1. Function, Type of Injury, and Initial Evaluation of Commonly Injured Knee Structures.
Knee Structure Biomechanical Function Clinical Function Injury Type Symptoms* Signs
Anterior cruciate
ligament Prevents anterior and rotational motion of tibia relative to femur
Stabilizes knee for
cut-ting and pivocut-ting Tear (primarily rupture) “Giving out” while cut-ting and pivoting Positive Lachman test and pivot shift test Meniscus (medial
and lateral) Decreases force per unit area on articular car-tilage (distributes load)
Protects articular carti-lage from prema-ture degeneration or osteoarthritis
Tear (both partial
and complete) Mechanical symptoms (e.g., catching, locking)
Joint-line pain, effusion
Articular cartilage Allows for nearly fric-tionless gliding sur-face and impact dis-sipation
Allows for painless and nearly effort-less active motion and impact
Focal defect or
osteoarthritis† Focal defect: no symp-toms or possible pain; osteoarthritis: pain, stiffness, swelling
Focal defect: no symp-toms or loose piece of cartilage; osteo-arthritis: joint-line pain, effusion * Symptoms that are most specific for the diagnosis are listed.
† Focal defects are those isolated to a small area, such as the femoral condyle. Focal defects are believed to be predictive of osteoarthritis, which is characterized by a regional loss of structure and function of the articular cartilage.
bone, other than débridement of unstable pieces. In patients in whom a lesion extends to bone, a variety of restorative procedures are available.
Rehabilitation
A recent systematic review38,39 of 54 randomized
clinical trials evaluated a variety of rehabilitation techniques and “assistive devices.” Among its conclusions were that immediate postoperative
weight bearing does not adversely affect subse-quent knee function; that in a motivated patient, a self-directed home-therapy program with ini-tial education and monitoring is as effective as regular physical therapy visits; that the use of continuous passive-motion machines does not im-prove outcome, as compared with no use of such machines; that the use of postoperative function-al bracing versus no bracing does not improve
33p9 B Meniscus C Articular cartilage A Anterior cruciate ligament AUTHOR: FIGURE: JOB: 4-C H/T RETAKE SIZE ICM CASE EMail Line H/T Combo Revised
AUTHOR, PLEASE NOTE:
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REG F Enon 1st 2nd 3rd Spindler 1 of 2 11-13-08 ARTIST: ts 35920 ISSUE:
outcome; that closed-kinetic-chain exercises (i.e., leg press or squat) result in better stability than open-chain exercises (i.e., knee extensions); and that an accelerated rehabilitation program with a goal of returning to a sport after 6 months re-sults in no increase in knee laxity, as compared with a delayed rehabilitation program.
Prevention
The recognition of the disproportionate risk of ACL tears among female athletes who participate in the same sports as male athletes at similar competition levels has led to the development of prevention strategies for female athletes. Modifi-able factors that are associated with injury (in both men and women) include the nature of the sport, the competition level, the level of contact, and the types of footwear and playing surfaces. Primary prevention strategies that were evaluated in controlled trials involving female athletes have
focused on a comprehensive program that includ-ed neuromuscular training (with plyometrics, the use of muscle stretching just before rapid con-traction), balance, and strengthening exercises performed more than once a week for a minimum of 6 weeks. Three of six trials of such interven-tions in one meta-analysis9 showed a
significant-ly reduced risk of ACL tears, with an overall odds ratio for an ACL tear of 0.40 (95% CI, 0.26 to 0.61) among the six trials.
The identification of patients with an ACL de-ficiency who can function normally without re-construction may provide insights into neuro-muscular adaptation patterns, which may have potential to improve prevention strategies.39-41
Ar e as of Uncertaint y
The optimal treatment of patients who have a partial ACL tear, who are skeletally immature and have an ACL tear, or whose ACL graft has failed remains unclear; multicenter observational studies of such patients are ongoing. The risk of future osteoarthritis associated with ACL tears and potential modifiers of this risk (including me-niscus and articular cartilage injuries and their treatments) remain incompletely understood, and it remains unclear how best to minimize this risk. Further studies are needed to define appro-priate nonoperative treatment of ACL tears, the optimal time to return to sports, and the influ-ence of hormones on the risk of such injuries. The potential role of tissue engineering to enable successful repair of associated injuries (including avascular-zone meniscus tear and articular carti-lage injuries) is unclear.
Guidelines
To our knowledge, there are no published profes-sional guidelines for the management of ACL tears.
Conclusions and R ecommendations
An athlete’s injured knee should be evaluated by a thorough physical examination when an ACL tear is suspected on the basis of a history of an audible popping sound, a noncontact pivoting mechanism, or immediate swelling, as in the case described in the vignette. A positive Lachman test Figure 1 (facing page). Biomechanical Function
of the Anterior Cruciate Ligament, Meniscus, and Articular Cartilage, Diagnosis of Injury on MRI, and Appearance during Surgery.
Panel A shows normal biomechanical function of the anterior cruciate ligament (ACL), as seen on magnetic resonance imaging (MRI, arrows). The MRI scan of the injury shows the ACL tear as a disruption of the normal straight, black contour of the ligament. An intraopera-tive photograph indicates a completely torn ACL bunched in the front of the notch. Panel B shows the medial and lateral menisci on MRI in the coronal plane (front view) as triangular black structures in between the femoral condyles above and the tibial plateau below, distribut-ing loads between the meniscus and articular cartilage. Meniscus tears include a “bucket handle” tear, in which a large portion of the ligament is displaced into the notch, as seen on MRI (upper panel, arrows), an injury that locks the knee. The corresponding intraoperative photograph shows the displacement of a large piece of ligament that is blocking the medial compartment. The lateral view (lower panel, arrows) shows one of the most common acute tears of the meniscus as a white line straight through the posterior horn of the lateral meniscus. In the intraoperative photograph, the arrows indicate the tear. Panel C shows articular cartilage, the thin avascular covering over the femur and tibia. This surface is nearly frictionless by design to dissipate im-pact loads. Injury to the articular cartilage can be either a focal defect (upper panels on MRI and arthroscopy) or a degenerative defect or arthritis (lower panels on MRI and arthroscopy). For the focal defect, treatments are available for restoring short-term function. Howev-er, once degenerative arthritis develops, as shown by the abnormal signal on MRI and fibrillation during sur-gery, there are no effective surgical treatments.
or pivot shift test is consistent with the diagno-sis, although such tests (particularly the pivot shift test) may be equivocal even when a tear is pres-ent. If the diagnosis is uncertain or associated injuries are suspected, then an MRI is indicated. Indications for ACL reconstruction include a de-sire for future participation in sports and insta-bility in activities of daily living. Randomized trials support the use of either a single-incision or double-incision surgical approach and the use of an autograft from either the hamstring or pa-tellar tendon with an appropriate fixation system for the chosen autograft. Rehabilitation should be supervised by a professional in the field and should include initial weight bearing with crutch-es and a closed-chain–based exercise program,
with a typical aim of returning the patient to sports activity in 6 months. Neuromuscular train-ing programs may reduce the risk of ACL tears in female athletes and other high-risk populations.
Supported by a Kenneth D. Schermerhorn Endowed Chair (to Dr. Spindler) and by a grant (R01-AR053684-01-A1) from the National Institute of Arthritis and Musculoskeletal and Skin Diseases.
Dr. Spindler reports receiving grant support from Smith and Nephew and holding two patents related to biologic replacement for fibrin clots (U.S. patent application numbers 10/378,285 and 11/092,992). No other potential conflict of interest relevant to this article was reported.
We thank Frank E. Harrell, Jr., Ph.D., and Michelle Shepard, M.S., for their review of the manuscript; Lynn S. Cain for assis-tance in the preparation of the manuscript; and Alex Bottiggi for assistance with Figure 1.
An audio version of this article is available at www.nejm.org.
2
Solomon
10/23/08
AUTHOR PLEASE NOTE:
Figure has been redrawn and type has been reset Please check carefully
Author Fig # Title ME DE Artist Issue date COLOR FIGURE Draft 4 Spindler Knoper
Knee anatomy and lachman test
11/13/08 Knee with torn anterior cruciate ligament
20-to-30-degree knee flexion Tibia Fibula Anterior cruciate ligament Medial meniscus Lateral meniscus Lachman test
Tibia pulled anteriorly while femur is stabilized
Figure 2. Lachman Test for the Diagnosis of a Torn Anterior Cruciate Ligament (Inset).
The most popular variation of the Lachman test requires that the patient be relaxed in a supine position. The examiner places one hand on the outside of the thigh, just above the knee, stabilizing the femur in slight external rotation and elevated off the bed to produce a knee flexion angle of 20 to 30 degrees. The second hand is placed on the anteromedial tibia with the thumb on the flat, bony border of the tibia. Once the patient is relaxed, the hand on the tibia attempts to displace the tibia anteriorly in relation to the stabilized femur. First, the normal knee is examined as a control, with a positive test on the injured knee categorized as the absence of sensation of a sol-id stop (“end point”) to anterior displacement of the tibia (called “soft end point”). Additional supporting information is an increased displacement of the tibia anteriorly, as compared with the contralateral normal knee. The pivot shift test has many variations but repro-duces the subluxation of the tibia on the femur that the athlete feels clinically.
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