Rehabilitation for Anterior Cruciate Ligament Injury

Like all ligaments, the anterior cruciate ligament (ACL) is composed of type I collagen. The ultrastructure of a ligament is close to that of tendons, but the fibers in a ligament are more variable and have a higher elastin content. Ligaments receive their blood supply from their insertion sites. The vascularity within a ligament is uniform, and each ligament contains mechanoreceptors and free nerve endings that are hypothesized to aid in stabilizing the joint. Avulsion of ligaments generally occurs between the unmineralized and mineralized fibrocartilage layers. The more common ACL tear, however, is a midsubstance tear. This type of tear occurs primarily as the ligament is transected by the pivoting lateral femoral condyle.

Frequency

United States

Epidemiologic studies estimate that approximately 1 in 3000 individuals sustains an ACL injury each year in the United States. This figure corresponds to an overall injury rate approaching 200,000 injuries annually.[4] This estimate is low for women, because ACL injury rates are estimated to be 2-8 times higher in women than in men participating in the same sports.

International

In a study of 101,125 ACL reconstructions in Denmark, Luxembourg, Norway, Sweden, the United Kingdom, and the United States, Prentice et al found that soccer injuries were the most common cause of these procedures, with the rate ranging from 14.1-42.3%.[5]

Mortality/Morbidity

Not a single report of mortality was found in 6 different studies examining the morbidity and mortality of anterior cruciate ligament repair. The total number of patients in these combined studies was 363. Morbidity was divided into 5 classes. The first class included patients who were symptomatic with activities of daily living (ADL). The second class included patients who were able to perform all ADL. Patients in the third class were able to perform mildly stressful sports (eg, jogging, swimming, biking, cross-country skiing). The fourth class included patients who were able to perform moderately stressful sports, including baseball, alpine skiing, racquet sports, dance, and lacrosse. The last class included patients who returned to perfect health and were capable of performing very stressful sports, such as soccer, basketball, football/rugby, volleyball, gymnastics, and hockey. Postsurgery status of patients was as follows:

• Remained class 1 - 3.3%

• Remained class 2 - 1.4%

• Attained class 3 - 11.8%

• Attained class 4 - 17%

• Returned to class 5 - 66.5%

Race

No known correlation exists between race and occurrence of ACL injuries.

Sex

According to numerous studies, female athletes sustain a greater number of anterior cruciate ligament (ACL) injuries than do male athletes. These results are well supported in 2 different papers. The first paper, by Arendt and Dick, showed that female athletes sustained significantly higher incidences of ACL injuries than their male counterparts did when competing in collegiate soccer and basketball.[6] The authors' data demonstrated that women have a 2.4 and a 4.1 times greater chance of incurring ACL injury when compared with males in soccer and basketball, respectively. A second paper, by Hutchinson and Ireland, reported that female athletes competing in the 1988 Olympic basketball trials sustained 81% of ACL injuries during the trials.[7]

Age

Anterior cruciate ligament injuries occur most commonly in individuals aged 14-29 years. These years correspond to a high degree of athletic activity.

Obtain as much information as possible directly from the patient. The important facts can be clarified by asking questions about the following:

• Mechanism of injury

• Pain

• Feeling/hearing a pop

• Feeling knee give out

• Ability to continue playing sport

• Swelling

• Loss of knee motion

• History of previous knee injury

Up to 50% of patients with acute knee injuries who report feeling or hearing a snapping or popping sound are found to have an anterior cruciate ligament (ACL) injury. A hemarthrosis almost always is present because of the vascular supply to the ACL. When a complete ligamentous tear occurs, pain may begin immediately, followed by resolution. Immediately following injury, minimal effusion or spasm is present, so ACL injury usually can be identified easily. Several hours after injury, effusion and spasm make diagnosis of an ACL tear more difficult.

To determine the patient's normal amount of laxity, examine the uninjured knee first.

Many diagnostic tests exist (eg, Slocum test, pivot-shift test), but the Lachman and anterior drawer tests are used most commonly.

Lachman test

The Lachman test is performed with the knee in 30° of flexion, with the patient lying supine.

Using one hand on the anterior aspect of the distal femur and a second hand behind the proximal tibia, attempt to displace the tibia forward from the femur.

A positive Lachman occurs when no endpoint is encountered. The degree of excursion may also indicate an ACL tear.

Anterior drawer test

Another test to detect ACL tears is the anterior drawer.

Perform this test with the knee at 90° of flexion, with the patient lying supine.

Place both hands behind the proximal tibia and attempt to displace the tibia forward from the femur.

If there is more than 6 mm of tibial displacement, an ACL tear is suggested.

The anterior drawer test is not very sensitive and has been found to be positive in only 77% of patients with complete ACL rupture.

Anterior cruciate ligament (ACL) injuries have no single cause. ACL injuries can be related to extrinsic factors and intrinsic factors. Numerous studies document the fact that poor levels of conditioning correlate directly with increased levels of injury. Research also has demonstrated that improved conditioning results in reduced numbers of injuries.

Body and movement factors

The first 2 factors, body movement and positioning, play a big role in ACL injuries.[8]

Noyes and colleagues demonstrated that most ACL injuries (ie, 78%) occur without contact.[9] Most of these injuries occur upon landing after a jump. The Noyes study involved only female basketball players, but the capacity of the knee to plant and turn or to absorb the shock of a jump is relevant to men and women in all sports.

Muscle strength

Muscle strength is the last of the extrinsic factors that affect the ACL. The hamstring is an ACL agonist working in concert with the ACL to prevent anterior tibial translation. Conversely, the quadriceps acts as an antagonist to the ACL, generating force that promotes anterior tibial translation. Ideally, a balance exists between these opposing forces to protect the knee; however, the quadriceps averages 50-100% greater muscle strength than does the hamstring.

Strength coaches often emphasize quadriceps strengthening and ignore hamstring strengthening, further exacerbating the inequality.

Other factors

Several intrinsic factors can contribute to ACL injuries.

Joint laxity is one such factor. Significant controversy surrounds this topic, because published studies are contradictory about whether or not increased laxity contributes to ACL injuries. Acasuso-Diaz and colleagues concurred with Kibler and coauthors that a strong relationship exists[10, 11] ; however, reports by Godshall and by Jackson and colleagues maintained that ACL laxity does not predispose to ACL injury.[12, 13]

The Q angle is the acute angle between the line connecting the anterior superior iliac spine, the midpoint of the patella, and the line connecting the tibial tubercle with the same reference point on the patella. Theoretically, larger Q angles signal increases in the lateral pull of the quadriceps muscle on the patella and put medial stress on the knee. Shambaugh and colleagues studied 45 athletes and found that the average Q angles of athletes sustaining knee injuries were significantly larger than were the average Q angles for players who were not injured.[14] Because lower extremity alignment cannot be altered, no recommendation can help to minimize the athlete's risk of ACL rupture; however, the dynamic position of the tibia can be improved with internal rotation exercises for the tibia (eg, medial hamstrings).

A narrow intercondylar notch may be a predictive factor for ACL rupture. According to various reports, athletes who sustain ACL injuries often have narrow notch widths compared with fellow athletes with uninjured knees. The notch width index (NWI), defined by Souryal and colleagues, is "the ratio of the width of the intercondylar notch to the width of the distal femur at the level of the popliteal groove on a tunnel view radiograph."

Another study by Souryal and coauthors established that NWI measurements fall along a Gaussian curve, indicating that measurement is reproducible.[15, 16] Results showed that athletes sustaining noncontact ACL injuries had the lowest NWIs. The critical NWIs were calculated as being 1 standard deviation below the gender-dependent mean. Athletes falling into this critical range, according to reported data, are 26 times more susceptible to ACL injuries than are other athletes.

Laboratory studies are not indicated in the evaluation and diagnosis of anterior cruciate ligament injuries.

Magnetic resonance imaging (MRI) of the knee usually is recommended prior to surgery for evaluation of the other ligaments and the menisci, because findings can influence the treatment plan.

MRI helps the surgeon to have the correct equipment at hand prior to beginning the surgery.

The sensitivity of MRI has been shown to be greater than 95% and the specificity to be approximately 98%, with a positive predictive value of 95% and a negative value of nearly 99% with fast spin-echo techniques.

Perform aspiration of any large hemarthrosis, if indicated, under aseptic conditions, to alleviate patient discomfort. The presence of fat globules suggests an intra-articular fracture. Radiographs may demonstrate an avulsed fragment just lateral to the tibial plateau. This type of fracture, referred to as a Segond fracture, represents an avulsion of the middle third of the lateral capsule from the tibial plateau; it is also known as a lateral capsule sign.

Physical Therapy

The primary goals in the treatment of anterior cruciate ligament (ACL) rupture are restoration of function in the short term and the prevention of long-term pathologic changes in the knee. Nonoperative treatment is a reasonable approach in patients who are not athletically active.

Research has demonstrated that the natural history of untreated complete injuries of the ACL consists of the progression of symptomatic instability to recurrent injuries. These injuries damage the menisci and the articular cartilage, eventually leading to osteoarthritis and osteoarthrosis.[17]

The key to successful treatment of an ACL tear is proper and early rehabilitation. Preoperative and postoperative rehabilitation programs are similar initially. Swelling control and restoration of motion and strength are the goals of each.

A study by Łyp et al indicated that following rupture of the ACL, the degree of rehabilitation success is inversely related to the length of time between reconstruction and the start of rehabilitation but is not associated with the amount of time passing between ACL rupture and reconstruction.[18]

The postoperative rehabilitation program begins as soon as the patient awakens from anesthesia, especially because patients are discharged earlier now than they were in previous years. Quadriceps co-contractions make up the first exercise that patients should be taught for the maintenance of terminal extension.

Passive motion is emphasized, with active flexion and assisted extension in the sitting or prone position to ensure good leg control (ie, ability to flex the hip and lift the leg against gravity without assistance). A continuous passive motion machine can be used to establish 0-30° of motion immediately postoperatively and to progress to 60° of knee flexion by the morning following the operation. The patient then begins gait training with crutches (weight bearing as tolerated), with the knee in an immobilizer. The patient usually can be discharged on the first postoperative day and should be encouraged to avoid crowds, keep the leg elevated when not ambulating, use the crutches at all times for protection, and continue frequent icing.

A number of different programs are used by different physical therapists. The therapy program chosen depends on the activity level of the patient and the type of surgery performed, coexistent injuries (meniscal or other ligamentous injury), the surgeon, the insurance policy, and time constraints.

Goal-oriented rehabilitation for patellar tendon grafts

The following rehabilitation program is an accelerated program for patellar tendon grafts. Note that the other grafts rehabilitate slightly differently. This rehabilitation program is classified as a goal-oriented approach. The dates listed are not meant to be followed strictly and can be varied by a day or 2, depending on the physician or the patient's schedule.

On day 3 following surgery, have the patient return to the surgeon for evaluation. Begin therapy on an outpatient basis, concentrating on gait training and other ambulation-oriented activities. The goal is to maintain terminal knee extension and progression toward 90° of flexion. The therapist emphasizes a normal heel-to-toe gait pattern, and the patient may weight bear as tolerated on the involved leg. Continue passive flexion ROM exercises. Have the patient increase quadriceps activity, introducing the partial squat with progression from bilateral to unilateral, placing increased body weight on the extremity involved at no more than 45° of flexion. Continue these exercises for 1 week. Continue the knee immobilizer when ambulating and continue regular icing of the knee.

On day 10 following surgery, have the patient return to the surgeon for evaluation. Advance therapy to include wall slide-squats and a stationary bike as tolerated. Place emphasis on terminal extension, progressive flexion, and full weight-bearing ambulation with normal heel-to-toe mechanics. In a controlled environment (no pets, children, or distractions), have the patient begin practicing crutch ambulation while out of the knee immobilizer. The patient should achieve full terminal knee extension and approximately 90-100° of knee flexion.

Three to 4 weeks after the surgery, the aggressive patient is ambulating with normal gait mechanics. At this point, the knee immobilizer can be removed. Advance the patient's activity to include loaded squats, swimming, eccentric quadriceps strengthening, bridging with a physioball, and a stair stepper. During this time, if the therapist is not observant, the patient can develop tendonitis of the quadriceps tendon or other repetitive use injuries of the lower extremity. Application of ice after each therapy session is very important.

Six weeks after surgery, release the patient to light jogging or bicycling. If the patient is older and has concomitant degenerative joint disease, encourage bicycling. The graft is still very weak at this stage, so advise the patient that it is important not to fall. The patient should jog only on a track or other flat protected surface. At this point, active ROM should be approaching 0-125° with minimal or no joint effusion. Work on balance and proprioception with activity drills.

At 3 months, recommend that the patient begin a gradual return to normal activities. At this point, most people do not require bracing, but occasionally, some athletes request a brace to increase their own comfort level when competing.

Open kinetic chain (OKC) and closed kinetic chain (CKC) exercises

Significant discussion surrounds the difference between OKC and CKC exercises during ACL rehabilitation. The difference concerns the assumption that CKC exercises are safer than OKC exercises because they place less strain on the ACL graft, producing less patellofemoral pain. The second assumption is that CKC exercises are more functional and are equally effective in improving quadriceps muscle force production.

A study by Beynnon and colleagues showed no difference in ACL strain characteristics between OKC and CKC exercises.[19, 20] A report by Fleming and coauthors argues that, with improved anatomical placement of the ACL graft, the graft may respond more like the intact ACL during OKC and CKC exercises. Therefore, these 2 articles argue that both types of exercise can be performed safely.

With regard to safety, OKC and CKC exercises can be applied in a manner that minimizes the risk of excessive graft strain and patellofemoral compression. Using different knee joint motion excursions for each type of exercise is the key to risk reduction. When OKC knee extensions are performed, limit knee joint motion to more flexed positions. During CKC lower extremity exercises, limit knee joint motions to more extended positions.

Nonoperative treatment

Patients may for a variety of reasons—if, for example, they are not highly active or athletic or are minimally symptomatic—opt for nonoperative treatment. In these cases, after initial control of pain and effusion, start hamstring and quadriceps activation/disinhibition and protected weight bearing in a hinged brace. As swelling and pain slowly resolve, ROM should return to normal, or nearly normal, parameters. Start exercises that take place in an anterior/posterior plane (eg, stationary cycling). Exercises need to be nonballistic.

Several options exist for the patient who elects to have surgery. For complete rupture, no local healing response is detectable at the injury site, and a graft must be used to replace the ACL.[1] Today, 4 options are used. The first 3 types are autografts using the central one third of the patellar tendon (considered a bone-tendon-bone graft), the quadruple semitendinosus/gracilis tendon, or the quadriceps tendon.[2, 3] The fourth type of graft is a cadaveric allograft.

Autografts

The patellar tendon with its bony ends has been a popular ACL replacement because of its high ultimate tensile load (~2300 N), its stiffness (~620 N/mm), and the possibility for rigid fixation with its attached bone graft.

By comparison, the dimensions of a round, 10-mm quadruple semitendinosus/gracilis tendon graft (hamstring graft) are more comparable to those of the intact ACL, and its ultimate tensile load has been reported to be as high as 4108 N. The quadruple tendon graft also may provide a multiple bundle replacement graft that better approximates the function of the 2-bundle ACL. Disadvantages of this soft-tissue graft include concern over tendon healing within the osseous tunnels and a lack of rigid bony fixation. A 1998 study from Japan suggests that aggressive early rehabilitation after an ACL reconstruction using the hamstring graft has more risk for residual laxity than does the patellar tendon graft.[21]

The quadriceps tendon graft has been shown to have an ultimate tensile load of as high as 2352 N. This graft has become an alternative replacement graft, especially for revision ACL surgeries and for patients with multiple ligament injuries in the knee.

In patients who are very skeletally immature, an iliotibial band autograft may be used, with the graft “attached over the top of the lateral femoral condyle and over the front of the tibia.”[22]

Cadaver studies have shown that the strength of fixation between the patellar tendon graft and the hamstring graft is equal to approximately 450 N, but the patellar graft can achieve fixation strength of as high as 1000 N. Grafts fixed to bone close to the articular surface (ie, patellar tendon grafts) undergo less strain and are stiffer than are those grafts fixed outside of drill holes (ie, hamstring grafts).

Allograft

Allograft tissues are harvested from human donors and typically include either the patellar tendon or the Achilles tendon.

Allografts are used for multiple ligament reconstructions and revisions of ligament reconstructions, as well as for the treatment of patients who are not high-performance athletes. However, the reduction of tensile strength that occurs with sterilization is a concern, as is the risk of inflammatory reactions.

Choice of graft type

In a prospective comparative 9-year follow-up study by Wipfler et al, the authors review the innovative technique of implant-free press-fit ACL reconstruction with bone–patellar tendon or quadrupled hamstring tendon grafts. This technique saves the cartilage and meniscal status of the knee, leaving little long-term differences between the operated and nonoperated knee. No significant differences, between the two groups, were found with range of motion, pivot-shift test, or quadriceps strength. Anterior knee pain was considerably less when kneeling and knee walking for those who underwent quadrupled hamstring tendon grafts, but hamstring strength was decreased.[23]

Ultimately, the decision as to which graft is best is still a matter of contention. The agreement is that the patellar and hamstring grafts are superior to the quadriceps graft and the allograft; however, the decision as to which is the better of the patellar and hamstring grafts depends on which surgeon is operating.

With regard to osteoarthritis, hamstring grafts have shown a lower rate of radiological osteoarthritis than patellar grafts at 15 years postsurgery.[24] In spite of the type of graft, some patients will develop osteoarthritis in the reconstructed knee, especially patients with concomitant or subsequent meniscectomy.

Prognosis

A prospective study by Müller et al indicated that results from the single-hop test for distance and the Anterior Cruciate Ligament-Return to Sport After Injury Scale (ACL-RSI) are significant factors in predicting whether an athlete will return to a preinjury level of sport after ACL reconstruction.[25]

In the study, 40 patients who underwent semitendinosus tendon autograft for an ACL rupture were assessed 6 months postoperatively with a variety of tools—including four single-leg hop tests, the ACL-RSI, the 2000 International Knee Documentation Committee (IKDC) Subjective Knee Evaluation Form, the Tampa Scale of Kinesiphobia-11 (TSK-11), and evaluation of knee extensor and flexor strength—to determine which of these could most effectively predict whether a patient was likely to return to his/her preinjury level of sport. Patients were then interviewed at 7 months postoperatively to identify which of them could be classified as “return to sport” (RS) or “non-return to sport” (nRS).[25]

The investigators found that the single-hop-for-distance limb symmetry index value, with a cutoff point of 75.4%, and the ACL-RSI, with a cutoff point of 51.3 points, had sensitivities of 0.74 and 0.97, respectively, and specificities of 0.88 and 0.63, respectively, for predicting which patients would fall into the RS or nRS group.[25]

A study by Villa et al found that the following factors had a positive influence on recovery in patients following ACL reconstruction: age younger than 20 years, a higher preinjury Tegner activity scale score, professional-level sports practice, an absence of concurrent capsular lesions and of postoperative knee bracing, a higher percentage of on-field rehabilitation sessions during patients’ customized rehabilitation protocol, and a deficit in knee flexor and extensor strength of less than 20% at the first isokinetic knee test.[26]

A study by Paterno et al indicated that when a 90% threshold is used, current criteria for RS fail to determine whether a high risk for a second ACL injury exists in active, skeletally mature adolescent and young adult athletes following ACL reconstruction. The criterion level for passing any of the six RS tests in the study was 90% limb symmetry. However, the investigators found that at 2 years post RS, in athletes who passed all six tests, the rate of second ACL injury (28.6%) did not significantly differ from that (19.7%) of athletes who failed at least one of the tests. The evaluation measures included the International Knee Documentation Committee Subjective Knee Evaluation Form score, the quadriceps limb symmetry index, the single-leg hop for distance, the triple hop for distance, the crossover hop for distance, and the 6-meter timed hop.[27]

In anterior cruciate ligament injury cases, presurgical consultations with other services generally are needed only in connection with surgical clearance. After surgery, it is important to consult with a specialist in physical medicine and rehabilitation (PMR) for initiation of a program to facilitate the patient's rehabilitation.

Some patients, especially those who are minimally involved in sports, elect not to have surgery and instead choose bracing. Several custom and off-the-shelf, anterior cruciate ligament–specific braces are available. For patients who are involved in vigorous sports, the use of braces without surgical stabilization is not recommended.

The goal of pharmacotherapy is to reduce morbidity.

Class Summary

These agents have analgesic, anti-inflammatory, and antipyretic activities. Their mechanism of action is not known, but they may inhibit cyclooxygenase activity and prostaglandin synthesis. Other mechanisms may exist as well, such as inhibition of leukotriene synthesis, lysosomal enzyme release, lipoxygenase activity, neutrophil aggregation, and various cell-membrane functions.

Ibuprofen (Motrin, Ibuprin)

DOC for patients with mild to moderate pain. Inhibits inflammatory reactions and pain by decreasing prostaglandin synthesis.

Class Summary

Pain control is essential to quality patient care. If nonsteroidal anti-inflammatory drugs (NSAIDs) are not sufficient, then narcotics may be given. Analgesics ensure patient comfort, promote pulmonary toilet, and have sedating properties, which are beneficial to patients who have sustained trauma or injuries.

Acetaminophen and codeine (Tylenol #3)

Indicated for the treatment of mild to moderate pain.

Class Summary

These drugs can be used as an alternative if the patient has GI upset or a history of GI bleeding with NSAID use. Because of the cost, these medications are not always a first-line choice.

Celecoxib (Celebrex)

Inhibits primarily COX-2. COX-2 is considered an inducible isoenzyme, being induced during pain and inflammatory stimuli. Inhibition of COX-1 may contribute to NSAID GI toxicity. At therapeutic concentrations, COX-1 isoenzyme is not inhibited; thus, GI toxicity may be decreased. Seek the lowest dose of celecoxib for each patient.

See Causes .

In a paper published by Hewett and coauthors, a jump training program was recommended strongly.[28] Another paper, by Wojtys and colleagues, showed that plyometrics and exercises requiring agility, such as running through cones, figure eights, and single leg jumps, are proven methods to improve muscle reaction time significantly.[29]

Ultimately, physical conditioning and balanced knee strengthening (hamstrings as well as quadriceps) are the keys to reducing the risk of an ACL tear.

Complications from ACL surgery generally arise during surgery (see Allograft Reconstruction, ACL-Deficient Knee). Complications include the following:

• Extravasation of irrigation fluid during arthroscopy

• Posterior femoral cortex compromise during endoscopic reaming of the femoral tunnel

• Paresthesias along the lateral aspect of the knee

• Improper handling of the graft (eg, dropping it on the floor)

• Bruising and/or hematoma formation

• Blood loss

• Improper alignment of the tunnels, causing graft impingement

• Improper graft placement, making the graft too short and thus not allowing the knee to reach full terminal extension

The main complication of ACL surgery during the postoperative period is rupture of the graft. Careful and conservative physical therapy (PT) during the first 8-12 weeks is important (see Physical Therapy).

Another complication that can develop after surgery is failure to achieve full knee extension (see Physical Therapy).

Most patients achieve good health and mobility after treatment for ACL injury. More than 75% of all patients who undergo ACL repair return to their previous level of functioning. They perform ADL without difficulty and return to participation in their previous sporting or recreational activities.

See the list below:

• See Physical Therapy.