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ACL Injury and Rehabilitation

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DOI: 10.1007/s40141-013-0036-8

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Curr Phys Med Rehabil Rep (2014) 2:35–40
DOI 10.1007/s40141-013-0036-8

MUSCULOSKELETAL REHABILITATION (NA SEGAL, SECTION EDITOR)

ACL Injury and Rehabilitation

Edward R. Laskowski

Published online: 27 November 2013

 Springer Science + Business Media New York 2013

Abstract The anterior cruciate ligament (ACL) is a primary knee stabilization [1]. The ACL contributes in a significant
restraint to anterior tibial translation and a significant contrib- way to knee stability, especially with respect to dynamic cut/
utor to both static and dynamic knee stability, especially for pivot and deceleration movements. Activities that involve
sports and activities that require deceleration and aggressive cutting and pivoting movements or sudden deceleration with
cutting and pivoting movements. ACL injuries have a signifi- change of direction account for approximately 70 % of acute
cant impact on individual function and on the health care ACL injuries [2]. Most ACL injuries are noncontact in nat-
economy, and continue to be prevalent and disproportionate, ure, and most tears are complete tears of the ligament [3].
affecting more women than men. Factors have been identified
which can help predict success in non-operative treatment, and
surgical procedures have advanced to the point of ensuring a ACL Anatomy and Biomechanics
reliable outcome with respect to joint stability. Rehabilitation
interventions focus on enhancing lower extremity strength, The ACL is a collagenous ligament that originates on the
stability, and neuromuscular control. Both operative and non- anterior intercondylar region of the tibia and inserts on the
operative treatment options, however, have been associated posteromedial aspect of the lateral femoral condyle.
with an increased risk of later osteoarthritis. ACL prevention Although it functions as a single ligament, it contains two
programs have attempted to correct flaws in movement patterns main bundles: an anteromedial bundle, which is rigid in
and neuromuscular control, but long-term data on the efficacy flexion, and a posterolateral bundle, which is rigid in
of these programs and of specific interventions are lacking. extension [1]. Forces on the ACL are highest in the final
30 of the knee extension and also with knee hyperexten-
Keywords Anterior cruciate ligament
ACL
sion. The ACL provides rotary control and limits internal
ACL injury
ACL rehabilitation tibial rotation. It also functions as a secondary restraint to
valgus and varus stressors throughout the range of motion
[4]. The main blood supply of the ACL arises from the
Introduction middle geniculate artery, and innervation is via a branch of
the tibial nerve, the posterior articular nerve [5]. In addition
The anterior cruciate ligament (ACL) is the primary restraint to static stability, the ACL contributes proprioceptive
to anterior tibial translation. It is a collagenous structure feedback, which is thought to enhance dynamic control.
approximately four times as long as it is wide, and has two Studies have shown persistent proprioceptive deficits even
major bundles that function as a unit to provide isometric in a knee that has undergone ACL reconstruction [6, 7].

E. R. Laskowski (&) Epidemiology of ACL Injury

Department of Physical Medicine and Rehabilitation, Mayo
Clinic Sports Medicine Center, Mayo Clinic Rochester, 200 First
Street SW, Rochester, MN 55905, USA In the United States, there are approximately 100,000 ACL
e-mail: laskowski.edward@mayo.edu injuries (estimated to be 1 in 3,000 individuals) each year.

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36 Curr Phys Med Rehabil Rep (2014) 2:35–40

Estimated annual surgical costs are nearly US$1 billion [3, isolated ACL injuries is reported to be lower than in
8–11]. It is estimated that over 2 million ACL injuries combined ACL and meniscal injuries (0–13 vs. 21–48 %)
occur each year worldwide [12]. A National College Ath- [22••, 23, 24]. ACL reconstruction is not associated with
letic Association (NCAA) survey reported ACL injury to significant reduction in the prevalence of knee osteoar-
be the second most common injury of the lower extremity thritis [22••, 23, 24]. Meniscal injury is commonly asso-
[3]. A 3- to 7-times greater injury incidence has been ciated with ACL injury and is a risk factor for the
observed in women [3, 8–10, 13]. Noncontact ACL injuries development of osteoarthritis in the future [22••, 25, 26].
have multiple risk factors, and it is difficult to determine Non-operative treatment of ACL tears without associated
the relative contributions of various factors. Factors pos- meniscal injury reveals no or very little osteoarthritic
tulated as influencing injury risk include biomechanical, change after 15 years [27]. Quadriceps weakness, which
anatomic, environmental, neuromuscular, and hormonal [8, may be due to muscle inhibition or impaired neural acti-
14–16]. Hormonal factors have been postulated to con- vation, has been documented after ACL injury, and is also
tribute to the increased incidence of ACL injuries in thought to be a contributing factor to the development of
females, but research has not proven this to be an inde- osteoarthritis [28]. Proprioceptive deficits which persist
pendent risk factor. Narrow intercondylar notch dimen- after ACL injury, and even after surgical ACL recon-
sions have been associated with an increased risk of ACL struction, may also contribute to an increased risk of knee
injury, with a lower intercondylar notch width index and instability and subsequent chondral injury [8, 22••, 29].
intercondylar notch width stenosis predisposing to ACL
injury [17]. Neuromuscular control patterns and biome-
chanical patterns have been found to be amenable to spe- ACL Injury Assessment
cific prevention programs [8]. ACL injuries appear to occur
more commonly on artificial turf [18]. They are common in History
sports that require rapid deceleration, change of direction,
and impact absorption, such as basketball, volleyball, and An accurate history is one of the essential components of a
soccer [8, 18]. They are also common in downhill snow diagnosis of ACL injury, and an accurate history and
skiing due to the long lever arm of the ski and the rigid ski physical exam can diagnose a great majority of ACL
boot which transmits significant rotational and translational injuries. The patient will usually relate a history of feeling
forces to the knee [2]. a ‘‘pop’’ or ‘‘give-way’’ of the knee during an aggressive
cut, pivot, or deceleration movement [5]. Landing awk-
wardly from a jump or ‘‘knee hyperextension’’ are other
Pathophysiology mechanisms of injury. The patient usually experiences
rapid swelling of the knee, and usually will be unable to
Acute ACL injury is associated with a high incidence of return to sport or activity due to pain, swelling, and a
lateral meniscal tears. Chronic ACL injury is associated feeling of instability. Acute hemarthrosis is associated with
with medial meniscal tears and articular cartilage injury ACL injury a high percentage of the time, and ACL injury
[19]. An ACL-deficient knee is susceptible to instability should be a prime consideration in any individual with
events (subluxations) if the person returns to aggressive ‘‘at acute traumatic knee swelling.
risk’’ activities, which usually involve rapid deceleration
and rapid change of direction. Repeated episodes of Physical Examination
instability are thought to lead to meniscal and articular
cartilage injury, and compromise ability to return to high The diagnosis of ACL injury can be assessed by per-
demand athletic activity. A smaller percentage of ACL- forming the Lachman test, which challenges the ACL’s
injured individuals may experience ‘‘functional’’ instabil- ability to control anterior tibial translation in 20–30 of
ity, with give-way episodes occurring during activities of knee flexion with the femur stabilized. The Lachman test is
daily living. A large segment of persons with ACL injuries the ‘‘gold standard’’ physical exam assessment for ACL
can function well, and limit or prevent subluxation events disruption, and is more sensitive than the Anterior Drawer
by avoiding high-risk activities [20]. test as menisci and condylar containment are not as much a
The development of osteoarthritis in an ACL-injured factor in 30 of flexion [30–34]. Increased tibial excursion
knee is caused by both intra-articular processes initiated at without an end point indicates ACL disruption. Hamstring
the time of injury combined with changes in joint loading relaxation is essential to accurately performing the Lach-
over time. ACL injuries combined with a meniscus tear man test, as the hamstrings are antagonists of anterior tibial
increase the risk of subsequent x-ray-appreciated osteoar- translation. A thorough examination of the knee for asso-
thritis [21, 22••]. The development of osteoarthritis in ciated meniscal or other injury should be performed,

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Curr Phys Med Rehabil Rep (2014) 2:35–40 37

though muscle guarding, effusion, and limited and painful also reached good functional status [42]. Many factors can
motion may make examination difficult. influence an operative or non-operative decision. In addi-
tion, ACL injury can be devastating to the athlete, since it
Imaging creates the loss of ability to perform an activity. Significant
changes in mood state have been measured after injury,
Knee radiographs are usually obtained to assess osseous including grief and depression [2]. A support structure
status and to detect evidence of other injuries. Radiographs entailing family, friends, and the medical team is important
can also detect associated findings, such as lateral tibial for successful outcome of both surgical and nonsurgical
plateau (Segond) fracture or avulsions of the tibial spine treatments.
[5]. Ultrasound evaluation can be used as a screening tool
when physical exam assessment is uncertain [35]. An MRI ACL Rehabilitation
evaluation is the gold standard imaging study used to
confirm ACL injury and to evaluate for associated meni- Initial treatment for an ACL injury aims to reduce pain and
scal, ligament, and articular cartilage injury [36, 37]. swelling in the knee, regain normal joint movement, and
strengthen the musculature around the knee. Regaining full
Supplemental Assessment knee extension is critical to a successful outcome, espe-
cially after reconstruction surgery. After acute injury,
Ligament arthrometry (KT-1000, KT-2000) can be used to individuals will likely require assisted ambulation with
objectively measure and compare anterior tibial translation crutches until weight-bearing pain resolves and gait
[2]. Functional testing (distance hops, vertical jump) can be mechanics normalize. A medial/lateral support brace may
used to assess dynamic knee stability, and is also used to be used for combined medial collateral or lateral collateral
assess return to play readiness after surgical or nonsurgical injuries. Acute ACL injury treatment begins with institu-
treatment; however, despite a significant amount of tion of PRICE principles: Protection of the injured limb
research, there is no true single functional test that will with crutches, Relative rest from at risk activity while
objectively determine when an athlete is ready to return to maintaining aerobic conditioning as much as possible, and
play [38, 39]. use of Ice, Compression, and Elevation. Bone bruises
characteristic of ACL injury may initially make weight
Operative Versus Non-operative Treatment bearing painful, and studies indicate that these initial bone
injuries may contribute to long-term damage to articular
The goal of treatment of ACL injury is to prevent episodes cartilage that predisposes to arthritis [36, 37]. If significant
of recurrent knee instability and, theoretically, to protect bone bruise involvement is seen on MRI, it seems prudent
the meniscus and articular cartilage from further trauma. to limit weight bearing after injury, though the optimal
This can be accomplished in two ways: nonsurgical treat- time period for modified weight bearing has yet to be
ment involving activity modification, lower extremity determined.
strength, and stability training and appropriate bracing, or Progressive weight bearing and weight shifting can help
surgical reconstruction of the ligament. If meniscal repair to maintain neuromuscular activation patterns, and isolated
is performed, ACL reconstruction is the option of choice to and integrated lower extremity strengthening can be started
protect the meniscal repair [40]. ACL reconstruction is also as joint motion permits. In both post-surgical and non-
preferable in cases of functional instability with activities surgical programs, isolated (open kinetic chain) and inte-
of daily living, in most cases of combined and multi-liga- grated (closed kinetic chain) strength training can be uti-
ment injuries, and in patients with significant meniscal lized and advanced along with low impact aerobic
involvement that contributes to knee instability or that conditioning [43••]. Proprioceptively enriched exercises
results in a mechanical block to knee motion [40]. Recent and stability training are introduced early and are advanced
studies have reinforced the need for individualized as status permits. Function-based movements are empha-
assessment and treatment options. Many ACL injury sized, along with sport-specific movements as applicable
‘‘copers’’ can do well with a program of non-operative later in the course of rehabilitation [43••]. After the acute
management emphasizing lower extremity strength and phase, rehabilitation after ACL injury can progress to
stability training [41]. One study evaluated non-opera- recovery and functional phases. Recovery includes
tively-treated ACL-injured individuals and found that 60 % modalities as needed for pain, progressive strengthening,
of these individuals managed as well as ACL-reconstructed and sports-specific movement pattern progression. Func-
individuals in the short term. Of those who did not have tional phase activities include power and endurance of
initial reconstruction, 40 % eventually had arthroscopic lower extremities, diagonal and multiplanar movements,
intervention for meniscal involvement, but subsequently increased neuromuscular and proprioceptive training, and

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38 Curr Phys Med Rehabil Rep (2014) 2:35–40

return to sport training [43••]. Neuromuscular training is an prevention of ACL injury, and on whether programs
essential component of a rehabilitation program to opti- emphasizing enhanced neuromuscular control of the lower
mize performance after ACL injury. Surgical reconstruc- limb, especially in female athletes, (i.e. correcting dynamic
tion provides static stability, but dynamic stability is medial valgus) can prevent injury if incorporated into a
provided by muscle strength and coordinated muscle firing preseason or in-season prevention program.
patterns [2]. Suboptimal neuromuscular patterns contribute
to movement flaws, such as dynamic medial knee valgus, Education and Comprehensive Treatment of ACL
which can increase the risk of ACL injury, especially in Injury
female athletes. Correction of these flaws is associated with
a reduced incidence of ACL injury [44, 45]. Education regarding surgical and nonsurgical treatment
ACL prevention interventions can also be used in options for ACL injury is essential in order for the patient
rehabilitation, as many of the same factors that contribute to make a well-informed decision. ACL injury can be
to ACL injury can be modified in an attempt to optimize associated with significant changes in mood state, includ-
status and protect against future injury. ‘‘Ligament domi- ing depression and grief over loss of sport or functional
nance’’ is a term used by Hewett to define the neuromus- status. Sports psychology is often useful to provide edu-
cular imbalance responsible for valgus collapse [44, 46••]. cation regarding coping strategies. The long-time course of
In this condition, ground reaction forces are not adequately rehabilitation after surgical or nonsurgical treatment
absorbed during impact activities, and more force is requires motivation and dedication. Preoperative education
imparted to the static restraints, including the ACL. Glu- of both patient and family can contribute to improved
teal, hamstring, and gastrocsoleus groups theoretically postoperative compliance [2].
have a significant role in the prevention of ACL injury, as
suboptimal recruitment of these groups during landing Surgical Treatment
increases load transmission to the ACL. Hewett also uses
the term ‘‘quadriceps dominance’’ to describe the female Surgical reconstruction with the ‘‘double bundle’’ tech-
preference for preferentially activating their quadriceps nique has been advocated by some as being more ‘‘physi-
muscles more than males when landing from impact [45, ologic’’ and similar to the native ACL. Studies suggest that
46••]. Studies show that females who have not sustained the double bundle technique provides improved control of
ACL injuries have decreased quadriceps strength compared knee rotation in a laboratory setting, but other studies have
to the hamstrings [46••, 47]. It appears that rehabilitation shown that a single bundle ACL reconstruction can restore
focused on increasing hamstring strength can modify one anteroposterior and rotational laxity as well as double
factor which can contribute to ACL injury. bundle reconstruction [50, 51]. In addition, no significant
Suboptimal core strength, reliance preferentially on one outcome difference has been found when comparing single
leg, and fatigue have also been shown to ne risk factors for bundle and double bundle reconstruction techniques [51].
ACL injury and should be addressed in rehabilitation Many seasoned sports orthopedists feel that, rather than the
programs as well as preventive programs [45, 46••, 48]. It double or single bundle techniques, the experience of the
is also important to remember that the treatment of ACL ACL reconstruction surgeon should be considered [52•]
injury is inherently multidisciplinary. A coordinated team
of physiatrists, orthopedic surgeons, physical therapists,
athletic trainers, and, in select cases, sports psychologists, Conclusion
is essential to ensure optimal outcomes.
Most individuals return to sports activities approxi- ACL injury is common, especially in sports involving
mately 6–9 months after ACL reconstruction. The criteria sudden deceleration and cutting/pivoting, and a greater
for return to sports after ACL injury involves many dif- incidence of this injury has been observed in women. The
ferent parameters, including both objective and functional decision of whether to pursue surgical or non-surgical
performance measures, such as single and triple leg hops treatment of ACL injury needs to be individualized to the
for distance. The Lysholm knee score and Tegner activity person, and activity goals as well as associated injury
scales can be used as patient-administered means of func- should be considered in the decision. Further research is
tional assessment after ACL injury [38, 39]. needed to better define who will benefit most from ACL
Shorter rehabilitation periods after surgical reconstruc- reconstruction, who will best be able to ‘‘cope’’ with the
tion may help to improve patient compliance, and studies injury, and which functional tests are the best predictors of
show similar outcomes between accelerated versus non- good outcome. Operative procedures for ACL reconstruc-
accelerated rehabilitation programs [49]. A significant tion focus on obtaining as anatomic a repair as possible,
amount of research currently is focusing on primary and both single bundle and double bundle techniques have

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Curr Phys Med Rehabil Rep (2014) 2:35–40 39

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Arthrosc. 2013;21(4):804–15.
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