Anterior Cruciate Ligament Injury

Background

Based on statements found in the Orthopaedic Knowledge Update 7 regarding the increased incidence of knee ligament injuries, the author proposes that this incidence may be associated with the current emphasis on fitness. These injuries are most often a result of low-velocity, noncontact, deceleration injuries and contact injuries with a rotational component. Contact sports also may produce injury to the anterior cruciate ligament (ACL) secondary to twisting, valgus stress, or hyperextension all directly related to contact or collision.

When matched for activities, a greater prevalence for ACL injury is found in females compared with males. Approximately 50% of patients with ACL injuries also have meniscal tears. In acute ACL injuries, the lateral meniscus is more commonly torn; in chronic ACL tears, the medial meniscus is more commonly torn. The only study on the prevalence of ACL injuries in the general population has estimated the incidence as 1 case in 3,500 people, resulting in 95,000 new ACL ruptures per year.

The importance of the ACL has been emphasized in athletes who require stability in running, cutting, and kicking. The ACL-deficient knee has also been linked to an increased rate of degenerative changes and meniscal injuries. For these reasons, approximately 60,000-75,000 ACL reconstructions are performed annually in the United States.

For restoration of activity and stability, the expected long-term success rate of ACL reconstruction is between 75-95%. The current failure rate is 8%, which may be attributed to recurrent instability, graft failure, or arthrofibrosis.

Treatment options must be tailored to a patient's preoperative level of activity. The following activity levels are based on the International Knee Documentation Committee:

• Level I includes jumping, pivoting, and hard cutting.

• Level II is heavy manual work or side-to-side sports.

• Level III encompasses light manual work and noncutting sports (eg, running, cycling).

• Level IV is sedentary activity without sports.

Nonsurgical treatment may be considered for patients who participate in level III or IV activities; all others should be considered as candidates for surgery. In addition, consider surgical consultation on any young athlete due to potential complications from recurrent instability.

Frequency

United States

An estimated 200,000 ACL-related injuries occur annually in the United States, with approximately 95,000 ACL ruptures. Approximately 100,000 ACL reconstructions are performed each year. The incidence of ACL injury is higher in people who participate in high-risk sports such as basketball, football, skiing, and soccer. When the frequency of participation is considered, a higher prevalence of injury is observed in females over males, at a rate 2.4-9.7 times greater for females.

International

No international incidence is reported in the literature.

Functional Anatomy

The knee joint develops as a cleft between mesenchymal rudiments of the femur and the tibia. This occurs around the eighth week of fetal development. The cruciate ligaments appear as condensations of vascular synovial mesenchyme at the same time.

By fourteen weeks gestation, the ACL and posterior cruciate ligament have divided; both have a functional blood supply, which is mainly derived from the middle geniculate artery. The inferomedial and lateral genicular arteries also provide blood supply through the fat pad.

The ACL is composed of densely organized, fibrous collagenous connective tissue that attaches the femur to the tibia. The ACL is composed of 2 groups, the anteromedial and posterolateral bands. During flexion the anterior band is taught while the posterior is loose; during extension, the posterolateral band is tight, while the anterior band is loose.

The ACL attaches to bone through a transitional zone of fibrocartilage and mineralized cartilage. On the femur, the ACL is attached to a fossa on the posteromedial edge of the lateral femoral condyle. The tibial insertion is located in a fossa that is anterior and lateral to the anterior tibial spine. The tibial attachment is noted to be somewhat wider and stronger than the femoral attachment.

The ACL is intracapsular and extrasynovial. It courses anteriorly, medially, and distally as it runs from the femur to the tibia.

The ACL receives nerve fibers from the posterior branch of the posterior tibial nerve. The main function is believed to be proprioception, providing the afferent arc for postural changes during motion and ligament deformation.

Sport Specific Biomechanics

The ACL is the primary (85%) restraint to limit anterior translation of the tibia. The greatest restraint is in full extension.

The ACL also serves as a secondary restraint to tibial rotation and varus/valgus angulation at full extension. Since the relationship between the tibia and femur provides little bony stability, the ligamentous structures must provide stability. When the ACL is injured, a combination of anterior translation and rotation occurs.

The average tensile strength for the ACL is 2160 N. This is slightly less than the strength of the posterior cruciate ligament and approximately half as strong as the medial collateral ligament (MCL).

Treatment

Acute Phase

Rehabilitation Program

Physical Therapy

Before any treatment, encourage strengthening of the quadriceps and hamstrings, as well as ROM exercises. Performance of ROM helps reduce the amount of effusion and regain motion and strength.

Surgical Intervention

When deciding whether to perform reconstructive surgery, the physician should consider the following factors:

• Preinjury activity level

• Desire to return to high-demand sports (eg, basketball, football, soccer)

• Associated injuries

• Abnormal laxity

• Patient's expectations

Generally, the recommendation is that surgical intervention be delayed at least 3 weeks following injury to prevent the complication of arthrofibrosis. The methods of surgical repair may be categorized into 3 groups, primary repair, extra-articular repair, and intra-articular repair.

• Primary repair is not recommended except for bony avulsions, which are mostly seen in adolescents. Because the ACL is intra-articular, the ligamentous ends are subjected to synovial fluid, which does not support ligamentous healing.

• Extra-articular repair generally involves a tenodesis of the iliotibial tract. This may prevent a pivot shift but has not been shown to decrease anterior tibial translation.

• Intra-articular reconstruction of the ACL has become the criterion standard for treating ACL tears.

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• • Bone-patella-bone autografts are currently popular because they yield a significantly higher percentage of stable knees with a higher rate of return to preinjury sports. The major pitfall of these grafts is their association with postoperative anterior knee pain (10-40%).

• • Hamstring tendon grafts are associated with a faster recovery and less anterior knee pain. Critics believe that these are more susceptible to graft elongation.

• • Recent literature has supported a greater tensile strength with the use of braided quadruple hamstring grafts. However, this finding has not been confirmed in vivo, and the graft may be limited by the type of fixation.

• • Allografts have also been very popular because of their efficiency, their ability to provide bony fixation, and the lack of associated patella morbidity. However, they are associated with a risk of viral transmission. Allografts are best used in revisions. These have also fallen out of favor by some because several deaths linked to clostridial infections from inadequate sterilization techniques have been reported, which led to increased research into sterilization techniques to ensure safety. In addition, concerns exist regarding what effects the immunologic response and delayed revascularization and remodeling may have on clinical outcomes. Although allografts are generally accepted as having less associated morbidity, no proof of this is present in the literature.

• • Synthetic grafts and ligament augmentation devices have also been used. Synthetic grafts are no longer acceptable, because of their high rate of complications, including failure and aseptic effusions.

• • Intra-articular reconstruction may be performed through a 2-incision technique or a single-incision endoscopic technique; the latter is currently more popular. This procedure requires graft stabilization with some type of fixation hardware for all of the graft options. The stabilization may be performed with metal interference screws, bioabsorbable screws, endobuttons, and cross pins. Each device has its own benefits.

• • Double-tunnel ACL reconstructions attempt to reproduce stability in internal rotation and valgus torque applied to the knee. Investigations into the benefits of such surgical treatment versus the increased level of difficulty and operative time are currently ongoing. Studies at this time have been limited to animal models.

Other Treatment

Nonoperative treatment may be considered in elderly patients or in less active athletes who may not be participating in any pivoting type of sports (eg, running, cycling). The goal is to obtain a full ROM and strength compared with the uninjured knee. This modality of treatment requires modification of activity levels and avoidance of physically demanding occupations. Arthroscopy may also be considered for persons who are poor candidates for reconstruction but have a mechanical block to ROM. The goal of this procedure is to debride the remaining stump to increase motion. Patients with significant arthritis are also thought to be poor candidates unless they are experiencing recurrent instability. See below for bracing information.

Recovery Phase

Rehabilitation Program

Physical Therapy

Postoperative treatment is discussed.

• Closed-chain exercises are used to emphasize early and long-term maintenance of full extension.

• Therapy protocols may be divided into the following 4 categories per Shelbourne and Nitz:

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• • Phase I: This is the preoperative period when the goal is to maintain full ROM.

• • Phase II (0-2 wk): The goal is to achieve full extension, maintain quadriceps control, minimize swelling, and achieve flexion to 90^o.

• • Phase III (3-5 wk): Maintain full extension and increase flexion up to full ROM. Stair-climbers and bicycles may be used.

• • Phase IV (6 wk): Increase strength and agility, progressive return to sports. Return to all sports without activity may take 6-9 months and should be closely monitored by the surgeon and physical therapist.

Other Treatment (Injection, manipulation, etc.)

The use of knee braces remains a highly controversial topic; braces are well accepted by patients, but most biomechanical studies do not support their use. Studies have shown that functional bracing can limit anterior translation of the tibia at low loads. Furthermore, most braces have been found to decrease the reaction time of the hamstring muscles.

Maintenance Phase

Rehabilitation Program

Physical Therapy

Open-chain exercises are initiated. The patient's timeframe for returning to sports depends on his/her strength, ROM, and the type of fixation that was performed.

Medication

Medication for ACL injuries mainly consists of analgesics. Preoperative drugs may include cyclooxygenase-2 (COX-2) inhibitors and opioid analgesic agents. Postoperatively, the patient may obtain pain relief through nonsteroidal anti-inflammatory drugs (NSAIDs) and opioid analgesics. NSAIDS have been shown to decrease bone formation in spine fusions and rotator cuff surgery. Although this has not been seen clinically in ACL reconstructions with bone-patella tendon-bone grafts, it is plausible to think that this may be the case. Therefore, long-term postoperative use may not be beneficial.

Drug Category: Nonsteroidal anti-inflammatory drugs

Have analgesic and anti-inflammatory activities. Their mechanism of action is not known, but 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.

Drug Name	Ketorolac (Toradol)
Description	Inhibits prostaglandin synthesis by decreasing the activity of the enzyme, cyclo-oxygenase, which results in decreased formation of prostaglandin precursors. Used in postoperative pain control.
Adult Dose	10 mg PO q6h for 5 d (requires IM/IV loading dose) Alternatively, 15-30 mg IM/IV q6h for 5 d
Pediatric Dose	Not established
Contraindications	Documented hypersensitivity; peptic ulcer disease; recent GI bleeding or perforation; renal insufficiency; high risk of bleeding; do not administer into CNS
Interactions	Coadministration with aspirin increases risk of inducing serious NSAID-related adverse effects; probenecid may increase concentrations and, possibly, toxicity of NSAIDs; may decrease effect of hydralazine, captopril, and beta-blockers; may decrease diuretic effects of furosemide and thiazides; monitor PT closely (instruct patients to watch for signs of bleeding); may increase risk of methotrexate toxicity; phenytoin levels may be increased when administered concurrently
Pregnancy	C - Safety for use during pregnancy has not been established.
Precautions	Category D in third trimester of pregnancy; acute renal insufficiency, hyperkalemia, hyponatremia, interstitial nephritis, and renal papillary necrosis may occur; increases risk of acute renal failure in patients with preexisting renal disease or compromised renal perfusion; low WBC counts (rare) usually return to normal during ongoing therapy; discontinue therapy if persistent leukopenia, granulocytopenia, or thrombocytopenia occur

Drug Category: Cyclooxygenase-2 inhibitors

Although increased cost can be a negative factor, the incidence of costly and potentially fatal GI bleeds is clearly less with COX-2 inhibitors than with traditional NSAIDs. Ongoing analysis of cost avoidance of GI bleeds will further define the populations that will find COX-2 inhibitors the most beneficial.

Drug Name	Celecoxib (Celebrex)
Description	Inhibits primarily COX-2. COX-2 is considered an inducible isoenzyme, 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 lowest dose of celecoxib for each patient. Used for postoperative pain control.
Adult Dose	100 mg PO bid or 200 mg PO qd
Pediatric Dose	Not established
Contraindications	Documented hypersensitivity to drug or sulfa
Interactions	Coadministration with fluconazole may cause increase in celecoxib plasma concentrations because of inhibition of celecoxib metabolism; coadministration of celecoxib with rifampin may decrease celecoxib plasma concentrations
Pregnancy	C - Safety for use during pregnancy has not been established.
Precautions	May cause fluid retention and peripheral edema; caution in compromised cardiac function, hypertension, conditions predisposing to fluid retention; severe heart failure and hyponatremia, because may deteriorate circulatory hemodynamics; NSAIDs may mask usual signs of infection; caution in the presence of existing controlled infections; evaluate symptoms and signs suggesting liver dysfunction, or in abnormal liver lab results