What is an anterior cruciate ligament Tear?

Arguably, the most common season- and potentially career-threatening injury to the athlete’s knee, anterior cruciate ligament (ACL) injury occurs in an estimated 250,000 people annually (Figure 1).

About the ACL

The ACL is one of two cruciate ligaments (the other being the posterior cruciate ligament or PCL) of the knee, named for their "crucial" role in maintaining normal joint alignment.· The ACL is like a short rope composed of a thick bundle of collagenous (fibrous) tissue, which connects the tibia (leg bone) to the femur (thigh bone) (Figure 2).· The ACL maintains normal alignment between the femur and tibia, particularly during rotational (twisting, pivoting, cutting) activities.· When torn, the knee surfaces are no longer properly constrained, leading to potentially injurious shear stresses to the joint surfaces (articular cartilage) and menisci (shock-absorbing cartilage pads).· Recurrent such episodes may result in cumulative damage and eventually degenerative arthritis.· Like any ligament injury, the ACL may be partially (Grade I), significantly (Grade II), or completely (Grade III) torn.

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How common are ACL injuries?

ACL injuries are very common.· In fact, they are the most common season- and in some cases career-threatening injuries to threaten the athletes’ (and non-athletes’) knee (Figure 1).· They are not common in golfers, however.· The amount of torque generated, even in a swing as powerful as Tiger Woods’, is insufficient to cause tearing of the knee.

But when injured, as Woods was when running near his home in Orlando, an ACL-insufficient knee can be vulnerable to the rotational stresses imposed during the golf swing, particularly on the lead foot.·Fortunately for Woods and for all ACL-injured patients and their treating orthopaedic surgeons, this injury can be treated successfully, with the vast majority able to return to their previous level of activity. We have learned an extraordinary amount about this small but important ligament over the past few decades. Imaging studies such as MRI and technological advances in arthroscopic surgery have combined to make reconstruction a common and predictable procedure.

How does it occur?

Virtually all ACL injuries occur from a discrete traumatic event.· The exact mechanism varies according to the sport, but most occur when the athlete plants his/her foot and then cuts or pivots.· Typically, the knee is felt to shift out of place, often accompanied by considerable pain, a “popping” sensation and inability to continue playing.

Common sports in which this injury is likely to occur include football, soccer, lacrosse or rugby.· In skiing, the ski tip may get caught in the snow when turning; if the binding fails to release, an ACL tear may occur··At the moment of injury, a force which exceeds the strength of the normal ACL, results in some fiber failure, stretching and, if sufficient, complete ligament tearing.· In Woods’ case, he has indicated that he injured his knee while running near his home in Orlando.· Injury of the ACL in golf is extremely uncommon. Unless the foot remains fixed and with a particularly vigorous swing, the player rotates around his fixed foot (one might see such a move in Happy Gilmore), there is not enough torque to cause a torn ACL.

Most injuries involve contact or collision sports, but do not always involve actual contact during the injury.· Examples include the soccer player whose cleat gets stuck when cutting back across the field, or a basketball player landing awkwardly from a rebound.

What increases risk?

• Sports involving pivoting, cutting or jumping (such as basketball, soccer, football, rugby, lacrosse, or volleyball)
• Contact/collision sports (football, rugby, lacrosse or baseball)

• Gender:· A number of well-designed studies have shown that female athletes have a disproportionate risk of ACL injury compared to their male counterparts. This is particularly true in younger populations (high school and college athletes).· This risk increase varies from 4-10 times higher.· Despite considerable investigations, no single explanation has been accepted.· Theories include differences in gender muscle balance and proprioception (the perception of where a joint/extremity is spatially located), size of the ACL or intercondylar notch (the space through which the ACL travels within the knee), or variability due to hormone differences.

What are the symptoms of an ACL tear?

• Acute knee pain
• Many note an audible or· “pop” at the time of injury
• Many have difficulty weight-bearing on the knee
• Most athletes are unable to continue play
• Significant knee swelling within 24 hours after the injury (often within 3 hours)
• Inability to straighten knee
• Knee giving way or buckling, particularly when trying to pivot, cut (rapidly change direction) or jump
• Swelling with repeated giving way
• Occasionally, locking when there is concurrent injury to the meniscus cartilage
• Patients with chronic ACL instability may have “giving way” or the feeling of instability with pivoting or cutting activities.· They may also note pain and swelling, though this may be associated with other knee damage (injury to the articular cartilage (joint surface) or menisci (cartilage pads between the joint surfaces).

How is an ACL tear diagnosed?

The typical history of acute injury at the time of pivoting or cutting, pain, swelling and/or inability to continue to play, is compelling and usually associated with an ACL tear. Physical examination at the time of injury is especially helpful, prior to the onset of swelling, pain and reflex guarding that make laxity assessment more difficult.

Crutches are usually necessary for the first week or 10 days following injury. The effusion (swelling within the joint) may preclude them from completely straightening their knee on the examining table.

Some patients have little to no swelling.· This is more common in patients with mild recurrent instability episodes and those with no associated ligament or cartilage injury.

Lachman test

The hallmark physical examination test for ACL integrity is the “Lachman” test, named for the physician who first described this exam technique (Figure 3).· This exam relies on manually assessing the amount of translation (movement) between the tibia and the femur.· With the patient supine (lying flat on their back with their head supported by a pillow to encourage them to relax), the knee is gently positioned between 15 - 30 degrees of flexion (knee bending).· The thigh is firmly held by one hand of the examiner.· The other hand grasps the upper leg (proximal or upper part of the tibia), just below the knee joint, and attempts to gently translate it anteriorly.·Comparison to the opposite knee permits distinguishing normal from abnormal. When examined at the time of injury and swelling is minimal, laxity is easily detected.· However, within several hours, the onset of swelling (due to bleeding within the knee joint known as ahemarthrosis) and guarding (due to pain) make this exam more difficult.· Because injury to the menisci and other knee ligaments often occur in association with an ACL injury, the knee is examined to assess for these associated injuries.

X-ray: X-rays are usually normal.· Occasionally a small fragment of bone is avulsed (pulled away) from the lateral (outside) aspect of the tibia, known as a “Segond” fracture. This sign is specific for an ACL injury. In skeletally immature individuals, an ACL tear may occur by pulling off its attachment site on the tibia rather than tearing within its substance.· This finding is also seen on X-rays.

Differential Diagnosis: An acute patellar dislocation will lead to pain, swelling, guarding and a similar clinical picture.· However, this injury is accompanied by tenderness along the medial retinaculum (the soft tissue adjacent to the inside of the patella), and the Lachman exam will be negative. Acute injury can cause damage to any of the ligaments about the knee, most commonly the medial collateral ligament (MCL). This injury is detectable by palpating (feeling) for tenderness along its course over the inside of the knee joint, as well as applying stress to assess abnormal laxity due to loss of normal ligament integrity.· An MCL injury or injury to any other ligament (the PCL or lateral collateral ligament (LCL), may occur in isolation or in association with an ACL tear· Therefore, careful exam is necessary to best determine the nature and extent of ligament involvement.

Are there any special tests?

Several tests have been described to facilitate the diagnosis of ACL tear.· In the pivot shift test, the tibia and femoral articular surfaces shift relative to one another when subjected to a provocative physical examination maneuver.· With the patient supine (on their back) the knee flexed, and the foot internally rotated, a valgus stress (force is applied to the outside of the knee trying to bend the knee inward) is applied to the knee, as it is slowly extended.· At approximately 30 degrees of knee flexion, the tibia will often shift or “jump,” confirming instability due to ACL injury.· A positive pivot shift is specific for an ACL injury.· However, this test is not very reliable in the acute setting because of guarding and pain.

KT-1000

Another diagnostic tool to help assess ACL integrity is known as the KT-1000. Studies have shown that a side-to-side difference of 3mm or more reflects ACL injury.· Patients with less than 5mm have been shown to be better able to “cope” with chronic ACL insufficiency than those with more than this amount of instability. However, with the advent of sophisticated imaging techniques, specifically MRI, the use of KT-1000 has been relegated to use as a research tool for outcome assessment.

The most definite non-invasive diagnostic test is an MRI, which is virtually 100 percent sensitive to ACL injury (Figure 4A, B).· A downside of this test is that it is so sensitive that even a partial injury shows considerable abnormality within the ligament. In the patient with a typical history and obvious physical examination findings, MRI adds little to the diagnosis and does not usually influence treatment decision-making. However, the prevalence of MRI and the opportunity to evaluate other structures (ligaments, menisci, articular cartilage) the de facto standard of today’s sports medicine environment.

Infrequently, the ACL may only be partially torn.· ·A force great enough to cause the ligament to tear is typically sufficient to cause a complete rupture, usually in the ligament’s mid-substance.· However, the ligament is not completely compromised and only partially injured in some situations.· Such injuries may show no evidence of laxity on physical exam and MR imaging will reveal signal abnormality within the ligament.· In such situations, diagnostic evaluation may require an examination under anesthesia and arthroscopic evaluation.

How will my doctor treat my ACL tear or injury?

Historically, the standard treatment for an ACL tear was non-operative, relying on strengthening exercises, activity modification and use of a brace. Natural history (no treatment) studies of patients with ACL-deficiency however, combined with the advent of sophisticated minimally invasive surgical techniques, have changed this perspective.· Basic science studies have demonstrated that the ACL has poor inherent healing potential because of its intra-articular location, where synovial fluid interferes with normal fibrin clot formation and organization.· Failed healing leads to residual laxity, and in the active individual, recurrent instability is the likely sequela. Repeat episodes of instability further compromise the knee’s function by injury to the menisci and articular surfaces with each episode.·Cumulative injury is thought to eventually lead to the development of degenerative changes and arthritis. Thus, most individuals suffering an ACL injury are surgical candidates with the intention of preventing the athletic disability and further injury, particularly in the young, active population in which this injury most commonly occurs.

Non-operative Treatment

Non-operative treatment: Initial treatment consists of medications and ice to relieve pain and reduce the swelling of the knee. Walking with crutches until it is possible to walk without a limp is often recommended.

Range-of-motion, stretching and strengthening exercises may be carried out at home, although referral to a physical therapist or athletic trainer is recommended.

Occasionally your physician may recommend a knee brace, especially if other ligaments are injured along with the ACL. For those patients who do not perform sports that require pivoting, cutting, jumping, and landing frequently, surgery is usually not required and rehabilitation is recommended. Individuals who usually exercise by jogging, cycling or swimming only may not require ACL surgery.

Rehabilitation of ACL tears usually concentrates on reducing knee swelling, regaining knee range of motion, regaining muscle control and strength, functional training, bracing (occasionally), and education, such as avoiding sports that require pivoting, cutting, changing direction and jumping and landing.

Some less active, lower demand patients may elect a trial of non-operative treatment.· This approach relies on physical therapy to decrease swelling, restore motion, normal gait and, with time, strength. Once these goals have been reached, patients undergo agility drills in preparation for return to activity. Most patients who receive non-operative treatment will also require activity modification to eliminate more aggressive pivoting and cutting sports (such as football, rugby, downhill skiing, volleyball or tennis).

Patients unwilling to accommodate to their injury are at risk of re-injury and eventual surgery, so an attempt is made to encourage them to substitute previous activities for less demanding straight-line type of sports, such as cycling, swimming, running, cross-country skiing, rollerblading, etc.· Some patients will be fitted with a functional brace to be worn during athletic activity, but the literature has not demonstrated that this approach prevents recurrent instability.

Operative treatment

Surgery restores knee stability through reconstruction of the torn ACL arthroscopically.· In this procedure, small incisions permit use of an arthroscope (joint camera) and small instruments to debride (surgically remove) the torn ligament and implant substitute tissue which will become the new ACL (Figure 5). Operative treatment may be necessary for:

• Athletes who regularly perform sports that require pivoting, cutting and jumping and landing
• Patients with recurrent giving way or knee instability, despite 3 to 6 months of an adequate rehabilitation program

• 6A 6B Figure 6:· Meniscus tears are very common in both acute and chronic ACL insufficiency.·In (A) note the probe on the torn fragment of the medial meniscus. In (B) the torn mensiscus has been removed, leaving a small rim of remnant meniscus. Reconstruction of the ACL is intended to avoid recurrent injury to and loss of the important shock-absorbing menisci.

  Patients with an ACL tear and a reparable meniscus tear or articular cartilage injury requiring treatment (Figure 6,7)
• Patients with an ACL tear and other ligament injuries in the same knee

Surgery is delayed until the injured knee has full range of motion and muscle control of the thigh (usually three or more weeks following injury). In surgical repair of an ACL tear, the torn ligament is replaced because the ligament, when torn, usually cannot be repaired, and historically have shown poor results.

Goal of ACL surgery

The goal of surgery is to restore the knee to normal function, permitting the athlete to return to sports that require pivoting, cutting, change of direction, and jumping and landing. ACL grafts undergo a remodeling process over many months, and thus a period of recovery before re-engaging in stressful activities is warranted.

Surgery is usually performed with the assistance of an arthroscope on an outpatient basis. The torn ACL is replaced by a graft. Many graft substitutes have been described, but the most common include

(1)· Patellar tendon autograft (autograft means from the patient) from the same or opposite knee

(2)· Autograft hamstring tendon (usually from the same knee);

(3)· Autograft quadriceps tendon

(4)· Allograft (graft tissue from a cadaver) patellar tendon or Achilles tendon.

Each graft has its benefits and risks, and the type used for your graft is determined based on a discussion between you and your surgeon.

When the torn ACL is removed, some bone in the knee is shaved to help the surgeon see where the graft goes and to help reduce pressure on the graft. Other structures in the knee are examined at the time of reconstruction, including the meniscus and articular cartilage. Bone tunnels are drilled in the tibia (leg bone) and the femur (thigh bone) to place the ligament in almost the exact same position as the torn ACL was. The graft is held in position with screws, heavy sutures (stitches), spiked washers or posts. The devices used to hold the graft in place usually do not need to be removed.

Graft Alternatives

Several graft alternatives are available for use as a substitute, including the patient’s own tissue (autograft) or donor tissue from a cadaver (allograft).· No synthetic graft substitutes have been designed or are currently available that can withstand the repetitive stresses imposed during normal knee function.

Traditionally, autograft tissue (most commonly the patellar tendon) has been favored.· Advantages have included the fact that there is no risk of disease transmission, the tissue is incorporated more readily, and the patient is permitted to return to activity earlier.· Disadvantages however, have also been recognized, including pain at the site of graft harvest site, and a more difficult early recovery (longer dependency upon crutches, more swelling and longer time to regain motion).

Alternative autograft alternatives

Several autograft alternatives have been described, including the patellar tendon (from the same or opposite knee), hamstring tendons (the semitendinosis and gracilis) and quadriceps tendon.·· Historically, the first and most commonly used reconstructive graft has been the patellar tendon (Figure 8).· In this procedure, an incision is made in the anterior (front) aspect of the knee, and the central third (approximately 9-12mm wide) portion of the patellar tendon is harvested, along with small bone blocks to which the tendon is attached above (the patella) and below (the tibial attachment) (Video 1). Advantages of this graft are its long track record with predictably good outcomes, regeneration of the patellar tendon harvest site, and a strong viable graft that develops into an excellent substitute ACL (Figure 9).

8A 8B Figure 8:· The most common graft is the patellar tendon, harvested from the patient’ own knee tissue.· A strip of patellar tendon, along with a small fragment of bone from the patella side and the tibia (leg bone) side are harvested. (A) shows the artists’ illustration of harvesting, and (B) shows an actual intra-operative photo of a graft. The blue due stain demonstrates the junction of the bone plug and the tendon tissue.

Contralateral patella tendon graft, in which the patellar tendon is harvested from the opposite (good) knee, has also been described as an excellent alternative graft source in patients who have failed a previous ACL.·Observation that patients recovered even more quickly when the opposite knee was used as a graft source led to consideration of the opposite knee tissue even in primary cases (cases in which the patient was undergoing ACL reconstructive surgery for the first time).·Intuitively, this strategy made sense because it permits focusing efforts on restoring motion and function in the ACL reconstructed knee and emphasizing restoration of strength in the donor knee.

Donor site morbidity, such as anterior knee pain, has led to interest in alternative autograft sources, including use of the hamstrings and distal (towards the knee) quadriceps tendon.·Hamstring advocates have emphasized decrease in pain at the harvest site, decreased risk of anterior knee pain, and better cosmesis (smaller incision away from the front of the knee) (Video 2).· Advances in soft tissue fixation have further encouraged use of hamstring grafts as a good alternative to the patellar tendon.· Post-operative studies have found little difference in outcome between use of hamstring and patellar tendon.

Patellar tendon allograft tissue has also proven a good substitute, with comparable results to autograft tissue (Video 3). The single greatest advantage of using allograft is that it does not require any additional surgery on the knee, thus making early recovery easier.· It is especially relevant in those patients whose work demands emphasize early return to responsibilities.· In the over-35 patient group, allograft reconstruction may be preferable.· Although there is a risk of disease transmission, current testing and graft treatment techniques render this risk extremely low. An additional disadvantage of cadaver tissue is that it is slower to incorporate into the body.· So despite the typically earlier clinical recovery and patient interest in returning to sports earlier than their autograft counterparts, allograft patients are discouraged from returning to pivoting or cutting until the 6-month mark to minimize the risk of recurrent injury. Approximately 90% of patients undergoing ACL reconstruction can expect to return to activity following a post-operative rehabilitation program.

What are the treatment complications?

Possible complications of non-operative treatment include:

• Recurrent instability, damage to the articular cartilage, menisci and eventual arthritis
• Athletic impairment with inability to participate in pivoting/cutting activities

Possible complications of operative treatment include:

• Risks associated with any surgery, such as pain, bleeding, infection, nerve injury
• Risks specific to ACL surgery, which include stiffness, pain at the site of graft harvesting, DVT (deep venous thrombosis) and recurrent instability
• Risk of recurrent instability is about 3-5%, irrespective of graft choice

When can you return to your sport/activity?

Return to sport depends upon many variables, but requires resolution of pain, restoration of normal motion, strength and stability.· Timing can also be influenced by graft type, as autograft tissue permits earlier incorporation than allograft.· Generally, four to six months is a realistic time frame for return to pivoting and cutting activities, though full remodeling and knee function probably takes a year to complete.

How can an ACL tear be prevented?

• Appropriately warm up and stretch before practice and competition
• Maintain appropriate conditioning:
  • Thigh, leg, and knee flexibility
  • Muscle strength and endurance
  • Cardiovascular fitness
• Use proper technique.· Some studies have demonstrated that instruction in proper landing techniques and emphasis on muscle balance exercises may decrease the risk of ACL injury.
• Use proper equipment (appropriate length of cleats for surface)