What's New / Orthopedic Spotlight

ACL tames the Tiger, for now

Tiger Woods’ mental toughness is unquestioned. His conditioning and prowess on are well known. His triumph at this year’s US Open, in which he prevailed despite a painful and unstable knee, as well as accompanying stress fractures, was a courageous athletic performance. In the course of his phenomenal career, there doesn’t appear to be any limit to his abilities. So, it turns out that it is not his competitors, it is a mere, small ligament in the knee, the ACL, that , at least for now, has tamed Tiger. Instead of challenging himself at the British Open, PGA Championship, Ryder cup, and even his own signature AT&T classic here in DC, he instead will be calling upon his mental and physical strength to recover following reconstructive knee surgery.

Success following ACL reconstructive surgery is high, with better than 90% returning to their previous level of activity. Tiger is going to likely be in that group, not just because he has a skilled surgeon (Dr. Tom Rosenberg of Utah was one of the orthopaedic leaders who pioneered the way ACL reconstructions are currently performed), but because the same skill set required to rehabilitate following surgery, discipline and commitment and hard work, are his signature traits already. His tour competitors, sympathetic for his (and the tour’s) temporary loss, should be served notice. The window of competitive opportunity will not be open long.

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 in athletes.(Figure 1). However, the injury is seldom directly caused by the golf swing. But the resultant instability from the injury can have serious effects on performance. . The amount of torque generated, even in a swing as powerful as Tigers’, is insufficient itself to cause tearing of the knee. But when otherwise injured, as Tiger was when running near his home in Orlando, an unstable ACL insufficient knee can be vulnerable to the rotational stresses imposed during the golf swing, particularly on the leading leg.

Fortunately, 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.

What is an Anterior Cruciate Ligament Tear?

Anterior Cruciate Ligament (ACL) injury occurs in an estimated 250,000 people annually. The ACL is one of two cruciate ligaments (the other being the Posterior Cruciate Ligament or PCL) of the knee, named for their "crossed” configuration 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 resisting excessive, destructive degrees of rotation (twisting, pivoting, cutting). 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.

How does it occur?

Virtually all ACL injuries occur from a discrete traumatic event. The exact mechanism varies, ,but most occur when the athlete plants his/her foot, and cuts or pivots. Typically the knee is felt to shift out of place, often accompanied by considerable pain, a sensation of a “pop”, and inability to continue playing. Common sports in which this mechanism is likely to occur include football, soccer, lacrosse and rugby. In skiing, the ski tip may get caught in the snow when turning. 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. Though most ACL injuries occur during contact or collision sports, such as in New England Patriot’s Tom Brady they often do not result from an actual acute contact event. They may occur from a cleat getting stuck when making a cutting move in a field sport or a basketball player, gymnast or volleyball player landing awkwardly from a jump.

Risk Increases With:

• Sports involving pivoting, cutting, and jumping (such as basketball, soccer, football, rugby, lacrosse, volleyball
• Contact/collision sports (football, rugby, lacrosse, even baseball)
• Gender:  A number of well-designed studies have shown that female athletes have a disproportionate risk of ACL injuy compared to their male counterparts. This is particularly true in younger populations such as high school and college soccer and basketball athletes. This risk increase varies from 4 to 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?

• Acute knee pain
• Many note an audible or palpable “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
• Occasionally, locking when there is concurrent injury to the meniscus cartilage
• Patients with chronic ACL instability may have repeated episodes of “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 it diagnosed?

The typical history of acute injury at the time of pivoting or cutting, pain, swelling and/or inability to continue to play, is very suggestive of 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 prescribed for the first week or ten days following injury. The effusion (swelling within the joint) may preclude completely straightening the knee.

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.

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. . 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 a hemarthrosis)) and guarding (due to pain) make this exam more difficult. Another important diagnostic test is called the “pivot shift exam” which is done by applying a specific gentle twisting maneuver to the injured knee to produce a characteristic shifting phenomenom.

Because injury to the menisci and other knee ligaments often occur in association with an ACL injury, other tests are done to determine the presence of 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). In skeletally immature individuals, an ACL tear may occur by pulling off it’s bony attachment site on the tibia rather than tearing within its substance. This finding is also seen on X-rays.

Differential Diagnosis: Acute knee injury can also cause fractures or damage to any of the other ligaments or the menisci (cartilage),. most commonly the Medial Collateral Ligament (MCL) An MCL injury, or injury to any other ligament for that matter (the Posterior Cruciate Ligament (PCL) or Lateral Collateral Ligament (LCL), may occur in isolation, or in association with an ACL tear. Dislocation of the patella (kneecap) is also frequently confused wit ACL injury. Therefore, careful exam is necessary to best determine the exact nature and extent of overall involvement of the damage

Are there any Special Tests?

The most definite non-invasive diagnostic test is an MRI, which is virtually 100% 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 prevelance of MRI and the opportunity to evaluate other structures (ligaments, menisci, articular cartilage) the de facto standard of today’s sports medicine environment.

Uncommonly the ACL may only be partially torn. Such injuries are very infrequent. 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. . Such injuries may show no evidence of laxity on physical exam but do produce increased vulnerability to further injury if not recognized and appropriately treated. MR imaging will reveal this abnormality within the ligament. In this situation, depending on specific circumstances, an examination under anesthesia and arthroscopic evaluation may be indicated

How is it treated?

Historically, the standard treatment for an ACL tear was non-operative, relying on strengthening exercises, activity modification and use of a brace. Natural history 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 sequel. Repeat episodes of instability further compromise the knee’s function by causing injury to the menisci and articular surfaces. Cumulative injury is thought to eventually lead to the development of degenerative changes and premature arthritis. Thus, most healthy, active individuals suffering an ACL injury, who aspire to returning to athletic activites, are surgical candidates. This is particularly true in the younger 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 you 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 with the ACL. For those patients who do not perform sports that require pivoting, cutting, and 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.

Non-operative treatment: Initial treatment consists of medications and ice to relieve pain and reduce the swelling of the knee. Walking with crutches until normal gait is restored is often recommended. Range-of-motion, stretching, and strengthening exercises should be out at home, usually after instruction and rehearsal with an experienced physical therapist or athletic trainer. Continuing supervision, when possible, is recommended.

Occasionally your physician may recommend a knee brace, especially if other ligaments are injured with the ACL. For those patients who do not perform sports that require pivoting, cutting, and jumping or contact, surgery is usually not required but careful rehabilitation is essential.. Emphasis is on reducing knee swelling, regaining knee range of motion, regaining muscle control and strength, functional training, bracing (occasionally), and education. It is also important to counsel the patient to avoiding sports that require pivoting, cutting, jumping and contact.

Surgical Treatment Surgery restores knee stability through reconstruction of the torn Anterior Cruciate Ligament. The torn ligament cannot be repaired because of its anatomy and location. Instead, it is reconstructed using a substitute structure. 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
• Patients with an anterior cruciate ligament (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 3 or more weeks following injury). The surgery is usually performed 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; and (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 patients’ 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.)

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 w/ small bone blocks to which the tendon is attached above (the patella) and below (the tibial attachment) (Video 1). Advantages of this graft are it’s 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).

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, have 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 year old 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 6th 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.

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 of course, stability. Timing can also be influenced by graft type, as autograft tissue permits earlier incorporation than allograft. Generally, 4-6 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 Anterior Cruciate Ligament 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).

Additional Resources: