Anterior Cruciate Ligament Injury

DEFINITION

• A sudden or violent twist or wrench of the tibiofemoral joint results in the stretching or tearing of the anterior cruciate ligament (ACL).

• The ACL is a tough band of fibrous tissue that connects the bones of the upper and lower leg at the knee joint.

Ligament-Cruciate-Knee

• Like other types of sprains,knee sprains are classified according to the following grading system: 

• Grade I (mild): 

This injury stretches the ligament, which causes microscopic tears in the ligament. These tiny tears do not significantly affect the overall ability of the knee joint to support the body’s weight. 

• Grade II (moderate): 

The ligament is partially torn, and there is some mild to moderate instability (or periodic giving out) of the knee while standing or walking.

 • Grade III (severe): 

The ligament is torn completely or separated at its end from the bone, and the knee is more unstable.

Anterior-Ligament-Injury

SYNONYMS

• ACL tear

• ACL sprain

ETIOLOGY

• TheACL,like all other ligaments,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.

• No one single cause accounts for this injury. ACL injuries can be related to extrinsic and intrinsic factors. Numereous 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 movement and positioning play a big role in ACL injuries. Noyes et al demonstrated that most ACL injuries (78%) occur without contact, and most of these injuries occur on landing after a jump.The Noyes study involved only female basketball players, but the capacity of the knee to plant and turn or absorb the shock of a jump is relevant to both male and female athletes in all sports.

• Muscle strength is the last of the extrinsic factors that affects the ACL.The hamstring is an ACL agonist working in concert with theACL 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% to 100% greater muscle strength than the hamstring. Strength coaches often emphasiz quadriceps strengthening and ignor ehamstring strengthening, further exacerbating the inequality.

• Several intrinsic factors can contribute to ACL injuries, as follows:

• Joint laxity is one of these factors.Significant controversy surrounds this topic,since published studies are contradictory about whether increased laxity contributes to ACL injuries. Acasuso-Diaz et al and Kibler et al concurred that a strong relationship exists; however, Godshall and Jackson et al maintain that ACL laxity does not predispose to ACL injury.

• 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 et al studied 45 athletes and found that the average Q angles of athletes sustaining knee injuries were significantly larger than the average Q angles for players who were not injured. Because lower extremity alignment cannot be altered, no recommendation can help 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(e.g., 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 to fellow athletes with uninjured knees.The notch width index (NWI),defined by Souryal et al,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 et al established that NWI measurements fall along a gaussian curve, indicating that measurement is reproducible.Results showed that athletes sustaining ACL injuries had the lowest NWI. The critical NWIs were calculated as 1 standard deviation(SD) below the,genderdependent mean.Athletes falling into this critical range, according to data reported, are 26 times more susceptible toACL injuries than other athletes.

• Repetitive friction has been found to occur at the posterior edge of the band,which is felt to be tighter against the lateral femoral condyle than the anterior fibers. The friction causes a gradual development of a reddish brown bursal thickening at the lateral femoral condyle.

EPIDEMIOLOGY 

AND DEMOGRAPHICS

• ACL injuries occur most commonly in individuals aged 14 to 29 years. These years correspond to a high degree of athletic activity.

• Epidemiological studies estimate that approximately 1 in 3000 individuals sustain an ACL injury each year in the United States. This figure corresponds to an overall injury rate approaching 200,000 injuries annually.

• Female athletes are 2.4 to 9.5 times more likely to sustain anACL injury than male athletes.There have been studies correlating menstruation withACL tears in women.

• Estrogen and progesterone receptor sites have been reported in human ACL cells. It has been reported that levels of these hormones may have deleterious effects on the tensile strength of theACL.

• Female athletes are more susceptible to ACL injuries. Studies have shown a two-fold increase in female collegiate soccer players and a fourfold increase in female basketball players compared with their male counterparts.

Differences may be due to experience, differences in training, different strength to weight ratios, limb alignment, joint laxity, muscle recruitment patterns, and NWI, but further studies to document a definitive cause are ongoing. A recent study has determined that ACL laxity does not vary with the menstrual cycle, thus dismissing this possible etiology.

• Unlike ACL injuries, which occur at a higher rate in females, lateral collateral ligament (LCL) and medial collateral ligament (MCL) injuries occur at an equal rate in males and females.

MECHANISM OF INJURY

•The ACL and the posterior cruciate ligament (PCL) bridge the inside of the knee joint, forming an “X” pattern that stabilizes the knee against front-to-back and back-to-front forces.

• The ACL typically sprains during one of the following knee movements: A sudden stop; a twist, pivot, or change in direction at the joint; extreme over straightening (hyperextension); or a direct impact to the outside of the knee or lower leg.

• These injuries are seen among athletes in football, basketball, soccer, rugby, wrestling, gymnastics, and skiing.

• The ACL provides 85% of the total restraining force to anterior translation of the tibia. This injury usually occurs during a sudden cut or deceleration, as it typically is a noncontact injury. The patient states, " I planted, twisted, and then heard a pop."

• Often, the mechanism of injury results in injuries to multiple structures. The most common structures to be injured in association with the ACL are the MCL and the medial meniscus.

COMMON SIGNS 

AND SYMPTOMS

• Pain

• Feeling or hearing an audible pop

• Feeling the knee give out

• Inability to continue playing sport

• Swelling or large hemarthrosis

• Instability and giving away

• Loss of knee motion

AGGRAVATING ACTIVITIES

• Ambulation

• Going up and down stairs in a reciprocal pattern

• Returning to normal activities or sport

• Change of direction

• Cutting

• Pivoting

• Jumping

EASING ACTIVITIES

• Elevation

• Prescription anti-inflammatory medications, muscle relaxants, and pain medications.

• Ice

• Rest

24-HOUR SYMPTOM PATTERN

Within 1 to 2 hours, a large hemarthrosis may develop.

PAST HISTORY FOR THE REGION

• Patient may report prior history of knee injury that has affected the mechanics of the knee.

• Prior injuries to the ankle or hip may also predispose the patient to increased stresses at the knee.

PHYSICAL EXAMINATION

• Joint examination: Observe any gross effusion or bony abnormality

• Immediate effusion indicates significant intraarticular trauma.Effusion that takes many hours to accumulate usually indicates an extraarticular trauma or meniscal involvement

• The presence of bruising is also a good indicator of tissue injury. Extraarticular injured tissue, such as an MCL, results in visible bruising.Intra-articular injured tissue, such as the ACL, does not result in visible bruising.

• In the absence of bony trauma,an immediate effusion is believed to have a 72% correlation with an ACL injury of some degree.

• Ligamentous laxity

IMPORTANT OBJECTIVE TESTS

• Lachman’s test is the most sensitive test for acute ACL rupture.Sensitivity:0.82;specificity:0.97 (Katz et al).

• Pivot shift test Sensitivity:0.82;specificity:0.98 (Katz et al).

• Anterior drawer test Sensitivity:0.41;specificity:0.95 (Katz et al).

DIFFERENTIAL 

DIAGNOSIS

• Muscle strain

• Myofascial pain

• Patellofemoral stress syndrome

Pain-Meniscus-Ligament

• Early degenerative joint disease

• Popliteal or biceps femoris tendinitis

• Common peroneal nerve injury

• Tendinitis

• Referred pain from the lumbar spine or hip

• Femoral stress fracture

• Infection

• Neoplasm

• Tibial spine fracture

• Tibial plateau fractures

• Osteochondral fracture

• Knee dislocation

• Meniscal tear

• Multiligamentous injury

• Posterolateral instability

• Osteochondral fracture

• Extensor mechanism rupture

• Osteonecrosis of the femoral epicondyle

• Osteonecrosis of the tibial condyle

• Inflammatory conditions (systemic disease).

CONTRIBUTING FACTORS

• Football,baseball,soccer,skiing,and basketball account for up to 78% of sports-related injuries.

• 100-fold increase in the incidence of ACL injury in college football players when compared to the general population.

• Female athletes are more susceptible to ACL injuries

• Femoral notch stenosis (the ratio of the femoral notch width to the width of the femoral condyles). NWI <0.2 is defined as notch stenosis.

TREATMENT

SURGICAL OPTIONS

• Intraarticular reconstruction of the ACL

• Bone-patella-bone autografts

• Hamstring tendon grafts

• Allografts

• Surgical reconstruction

 Autograft

 Patellar tendon

 Quadriceps tendon

 Hamstring tendons

 Medial head of     gastrocnemius.

Reconstruction-Operation -Graft

• Allograft

 Achilles tendon

 Patellar tendon

 Quadriceps tendon

 Hamstring tendons

• Mid-patellar tendon graft had been the treatment of choice, but the recent trend has been to use arthroscopic techniques and reconstruct the ligament with an allograft. Rationales for this change are varied, but in general it is believed that use of the allograft minimizes the trauma to the knee extensor mechanism. Patellar tendon problems were common after the midpatellar tendon autograft technique.

• Allograft use

 Pros: Less invasive to patient, with a quicker return to function.

  Cons:Disease and infection (sterilized via gamma radiation and ethyleneoxide) and weaker than autografts (radiation decreases strength by 26%.

Autograft strength:

Normalized to the patellar tendon

 Normal ACL: 100%

 Bone–patellar tendon–bone: 175%.

 Semitendinosus: 75%

 Gracilis: 49%

 Iliotibial tract: 38%

 Tensor fascia lata (TFL): 36%

• Surgical indicators, as follows:

• Desire to return to high demand sports

• Associated injuries (e.g., MCL or meniscal involvement).

• Abnormal laxity.

REHABILITATION

• Rehabilitation of the ACL depends on whether surgery was performed. 

Rehabilitation-Exercises

In patients who underwent surgery, several factors need to be taken into consideration.They include the following:

 • Graft maturation and ligamentation process.

• Autographs are strong at implantation.

 • Autografts undergo “ligamentation,” which is a gradual biological transformation of tissue.

• Collagen forms,remodels,and matures for 1 to 2 years after surgery.

• The transplanted graft never obtains all of the cellular features of normal ACL tissue.

• Stages of ligamentation

1. Necrosis (1 to 3 weeks):

Cells of graft die because blood supply is interrupted. Collagen matrix remains intact.

2. Revascularization (6 to 8 weeks):

New blood vessels grow into graft. Process occurs from peripheral to central.

3. Cellular proliferation (8 weeks +): 

New cells can proliferate into graft as early as the first week. The cells are thought to arise from extrinsic sources (synovial fluid and bone marrow) and intrinsic sources (surviving original cells).

4. Collagen formation, remodeling, and maturation (8 weeks +):

 Cell proliferation takes place as a continuing process throughout the maturation process. New cells proliferate into graft from the new blood sources,as well as from synovium,ostium,and fat pads.

GENERAL ACL REHABILITATION 

GUIDELINES

Phase I:

Acute Inflammatory Phase (Days 0 to 14 after injury)

• When to progress to phase:Initial injury to the ligament

• Goals of phase

 • Maintain range of motion (ROM).

• Decrease inflammation and irritation and promote healing.

• Interventions :

 Medications: Anti-inflammatories and/or muscle relaxants.

 Modalities: Electrical stimulation for quadriceps contraction, ultrasound, ice after activity.

 Myofascial release to global muscles as needed.

 Lower extremity flexibility:Hamstrings,iliotibial band (ITB), and hip flexors

 Home exercise program: ROM exercises; lower extremity flexibility; hip strengthening; and rest, ice, compression, and elevation (RICE).

Phase 2: 

Reparative Phase (Days 15 to 21 after injury)

• When to progress to phase: Progress as pain allows

• Goals of phase

• Restore normal ROM.

• Achieve full extension ROM.

• Minimize swelling.

• Interventions :

 Medications as needed.

  Modalities as needed.

  Myofascial release to global muscles;progress as needed.

  Lower extremity flexibility: Hamstrings and hip flexors

 Home exercise program:Walking program, lower extremity flexibility, and strengthening.

Rehabilitation-Joint-Strength

Phase 3:

Remodeling Phase (Days 22 to 60 after injury)

• When to progress to phase

• Pain-free ROM

• No functional limitations

• Goals of phase

• Increase agility

• Progress to return to sports

• Address contributing factors

• Interventions : 

 Medications and myofascial release as needed.

 Home exercise program: Progress lower extremity flexibility and strengthening program.

 Other:Address contributing factors.

Phase 4: 

Remodeling Phase (Days 60 to 360 after injury)

• When to progress to phase: No functional limitations

• Goals of phase

• Correction of contributing factors that result in ligament injury

• Retraining muscle activity to account for functional activities.

• Interventions : 

 Medications and myofascial release as needed.

 Home exercise program: Progress lower extremity flexibility and strengthening program.

 Other: Address contributing factors, functional rehabilitation, and retraining.

PROGNOSIS

• Patients treated with surgical reconstruction of theACL have long-term success rates of 82% to 95%.

• Recurrent instability and graft failure is seen in approximately 8% of patients.

• Patients with ACL ruptures, even after successful reconstruction, are at risk for osteoarthrosis.

• The goal of surgery is to stabilize the knee, decrease the chance of future meniscal injury, and delay the arthritic process.

SIGNS AND SYMPTOMS 

INDICATING REFERRAL 

TO PHYSICIAN

• Constant unrelenting leg pain or pain that does not change with position may indicate infection or tumor.

• Significant and unexplained weight loss or nocturnal pain may indicate the presence of a tumor.

• Major trauma may necessitate radiographs to rule out the presence of a fracture.

• A history of cancer may indicate the need to rule out metastatic disease if all other musculoskeletal factors have been eliminated.