Common Knee Injury

Acute injuries - A sudden force that twists the knee or moves it beyond its normal boundaries can cause major damage to the knee. Common areas that are injured are.

Most acute injuries, including breaks in the bones, accumulation of joint fluid due to severe knee strain, infection, arthritis, or bleeding, or a severe torn cartilage or ligament rupture cause severe pain and swelling. However, more subtle injuries, such as partially torn cartilage or tendon, and ligament sprains cause less swelling, pain, and minimal functional loss. Overuse or excessive use of the knee, particularly when the muscles are "out of shape," can cause painful knee caps, arthritis flares, bursitis, or a knee strain and effusion.

Patellar tracking disorder - Patellar tracking disorder is a condition in which the kneecap (patella) shifts out of place as the leg bends or straightens. In most cases, the kneecap shifts too far toward the outside of the leg, although in a few people it shifts toward the inside. The kneecap can shift or rotate off track if the groove is too shallow or if the cartilage is damaged. Ligaments, tendons, or muscles that are too loose or too tight may also lead to a misaligned kneecap.

Excessive use and Overuse - Repetitive soft-tissue trauma and imbalanced knee muscles can result in tendonitis, bursitis, patellofemoral pain syndrome  and iliotibial band friction syndrome.

Wear and tear - Arthritis is a common cause of knee pain. Parts of the knees are vulnerable to wear and tear. One such area is the knee cartilage. The purpose of cartilage is to stop bones rubbing together and allow a smooth motion in the joints.

Meniscus Tears
The most common injury to the young athletic knee is a tear of the medial meniscus. There are two menisci within each knee and they function to distribute stress during weight-bearing activities. By distributing stress evenly, menisci can limit articular cartilage surface damage which is the beginning of arthritic degeneration. Menisci also function to help stabilize the knee and to increase the smooth motion of the knee joints.

Causes
Meniscal tears most often occur posteriorly in the knee. The tears occur as the knee is in a flexed weight-bearing position and then the knee is twisted. This creates a shear force on the meniscus, causing it to tear. Unfortunately, meniscal tears usually do not heal themselves once they have reached a substantial length (1 cm). When meniscal tears of this length or greater occur, mechanical problems and pains are caused, bringing the injured athlete to a physician’s office.

Meniscal tears often occur in association with other injuries to the knee. Perhaps the most common of these is an anterior cruciate ligament (ACL) tear. Interestingly, meniscal tears that occur in association with an ACL disruption occur on the lateral side more commonly than on the medial side while isolated and degenerative meniscal tears occur more commonly on the medial side.

Symptoms

• Pain along joint line, usually posteriorly
• Clicking and sometimes a locking with activities
• Mild swelling especially following activities
• Vague aching pain throughout day

Frequently Asked Questions
Anterior Cruciate Ligament (ACL) Injuries

Treatment
Meniscal tears occur in all age groups. Care of meniscal tears is dependent not only on the age of the patient, but also the size, length, and quality of the tear. As an athlete ages, the meniscus becomes less vascular and therefore less able to heal and/or be repaired. For this reason, degenerative meniscal tears usually occur in individuals aged 35 and over and they are commonly treated by surgical excision of the tear.

Non-operative
Many meniscal tears are small and will not become symptomatic. Tears that are big enough to cause symptoms can be treated non-operatively especially in older individuals. A course of activity modification followed by therapy and a gradual return to sports is successful in approximately 50% of these individuals. The tear itself does not heal but rather is ‘ground-down’ to a point where it is no longer symptomatic. When this does occur, a patient feels better within three weeks and is able to return to normal activities by six weeks.

N.B.: This form of treatment is not recommended in young, healthy individuals as this age group has a greater potential to worsen their tear by walking or playing on it. Further, younger individuals can often have their tear repaired surgically. This possibility decreases the longer surgical intervention is delayed.

Alternative Treatment Options

• Glucosamine
• Hyaluronic Acid
• Non-steroidal Anti-inflammatory Medications (NSAIDs)

Operative
Partial menisectomies (meniscal excisions) are done arthroscopically and as long as less then 20 percent of the meniscus itself is removed, little long-term detrimental effect to the knee is caused. Removing larger portions of the meniscus, however, can be a predecessor to progressive degenerative arthritis.

Meniscal tears in younger individuals often can be repaired. The repair process is more involved than removing the tear. However, provided the tissue that is torn is not itself damaged, the repair can be performed, saving the overall function of the meniscus. Ultimately this can lead to a longer, higher functioning ability of the knee and presumably less likelihood of post-traumatic arthritis. Unfortunately, in the United States only seven percent of all meniscal tears are repaired.

Rehabilitation following meniscal surgery is relatively straight forward with the reduction of swelling and effusion followed by establishing normal range-of-motion (ROM) and then strengthening. Menisectomies are minimally painful and normal functional ability returns to the knee usually within six weeks, post-operatively. When meniscal repairs are performed, the repair should be protected until the repair has healed. This process usually takes six weeks. Different protocols for protecting the knee during that time frame have been developed and vary from physician to physician.

In the knee there is an area called the meniscus which is C-shaped shown below.



Cartilage is also present in the  undersurface of the knee cap. Here it can become worn down, irritated, or irregular, a condition known as arthritis. Specialized "shock absorber" cartilage located between the thigh and leg bones (meniscal cartilage) can be damaged, a condition known as a torn meniscus.

Patellar Dislocation
Patellar (knee cap) dislocations occur with significant regularity, especially in younger athletes. Most of the dislocations occur laterally (outside). When these occur, they are associated with significant pain and swelling. Following a patellar dislocation, the first step must be to relocate the patella into the trochlear groove. This often happens spontaneously as the individual extends the knee either while still on the field of play or in an emergency room or training room as the knee is extended for examination. Occasionally relocation of the patella occurs spontaneously before examination and its occurrence must be inferred by finding related problems.

Associated problems normally occur with patellar dislocations, the most obvious of which is tearing of the ligaments that stabilize the kneecap itself. As is the case with all other joints, ligamentous disruption or tearing occurs to allow the joint to dislocate. In the case of patellar dislocation, the ligaments on the inside of the knee are the most commonly injured as the kneecap slides laterally. While tearing of these ligaments is unfortunate, they do have the potential to heal. Of much more concern, are the small fragments of cartilage and bone that often are knocked off of the kneecap or the lateral femoral condyle during the relocation of the kneecap. These fragments become loose bodies and usually require removal during an arthroscopic procedure. Patellar dislocations can cause significant quadriceps muscle injuries, which can be made worse due to the effusion within the knee or to early onset of exercises and premature return to play.

A condition referred to as patellar subluxation also exists. The problem exists on a continuum between patellofemoral malalignment and patellar dislocation. It can be sequelae of a traumatic dislocation or in situations where patellar hyperlaxity exists. A subluxation is a partial dislocation in which the patella attempts to dislocate but does not do so completely. Situations such as these are very disconcerting and often give the patients a sense of giving way or buckling. At a minimum, these situations should be treated with aggressive therapeutic intervention as the constant subluxation events not only will interfere with competition, but will also potentially cause repeated wear and discomfort within the patellofemoral joint.

Causes
Patellar dislocations can occur either in contact or non-contact situations. An athlete can dislocate his/her patella when the foot is planted and a rapid change of direction or twisting occurs. Usually a pre-existence ligamentous laxity is required to allow a dislocation to occur in this manner. Direct blows to a knee can cause dislocations as well. The force of these is obviously much greater and usually causes more severe damage especially to restraining ligaments.

Symptoms

• Rapid, acute swelling
• Extreme pain initially until relocation occurs
• Continued pain along medial (inside) ligaments
• Discoloration medially at site of ligament injury
• Sense of instability and apprehension that problem will recur

Treatment

Non-operative
Normal care of patellar dislocations, when a loose fragment has not been created is the immobilization of the knee for a short period of time (seven to 10 days). During this time, the swelling is reduced and the acute discomfort of the dislocation decreases. Slow mobilization of the knee and of the patellofemoral joint is then begun, and usually full recovery can be expected within a three to six week period. This period of time is significantly lengthened when the patellar dislocation is recurrent.

Unfortunately, once a patellar dislocation occurs, especially when it occurs in a situation where hyperlaxity of the ligaments exists, which is commonly the case, recurrent dislocations can be expected. These are significantly problematic for athletes as they often come in the midst of the season. Conservative management of these problems in season with appropriate rest, appropriate hip and thigh muscle strengthening, and perhaps the use of a patellar buttress brace is appropriate.

Alternative Treatment Options

• Glucosamine
• Hyaluronic Acid
• Non-steroidal Anti-inflammatory Medications (NSAIDs)

Operative
Some situations of patellar dislocation can and/or should be treated surgically. One situation is when recurrent dislocations occur. In these situations, to limit the amount of lost time in competition and to reduce the chances for cartilage lesions on the undersurface of the patella, which often are non-reparable, patellar stabilization procedures are appropriate. These procedures can be either soft tissue or bone procedures, or a combination thereof. First-time traumatic patellar dislocations can also be treated with procedures such as this, and in chosen situations doing so may be appropriate.

It has been found in retrospective studies that the incidence of recurrent dislocation after the first dislocation occurs can be as high as 40 percent. Surgically treating those dislocations by lessening lateral tension and tightening medial restraint could reduce this recurrence rate to below 10 percent.

Surgical procedures on the patella are usually done in the out-patient setting. Procedures limited to altering soft-tissue tension begin rehabilitation within a week and return to activity can be expected as early as six weeks. Procedures that require bone work (osteotomies) require a period of relative immobilization and need 10 to 12 weeks before a return to athletic activity is permitted.
 

Patellar Tendinitis (Jumper's Knee)
Patellar Tendinitis is also known as jumpers knee. It is an inflammation in the patellar tendon, the band of tissue that connects the kneecap (patella) to the shinbone (tibia).

It is diagnosed with a history and physical examination. X-rays or other tests may or may not be necessary.

Causes
The most common activity causing patellar tendinitis if jumping, hence it is commonly referred to as jumper’s knee. Activities that place repetitive stress on the patellar tendon may cause it to become inflamed. Other activities such as running, walking or bicycling may also cause patellar tendinitis. Most commonly, however, patellar tendinitis is caused by tightness of the quadriceps muscles.

Patellar tendinitis can be caused by problems with the way your hips, legs, knees or feet are aligned. Having wide hips, being knock-kneed, or having flat feet, can predispose you to patellar tendinitis because certain body mechanics will place more stress on this area with activity.

Symptoms

• Pain or tenderness around the patellar tendon, especially where it attaches to the patella
• Swelling around the patellar tendon
• Pain with activities, such as jumping, running, or walking
• Pain may be worse with downhill walking, or descending stairs

Treatment

Non-operative
The treatment of patellar tendinitis begins with rest, and avoiding activities that cause the discomfort. Any problems with body mechanics or alignment should be addressed, and corrected if possible. Icing is recommended. Bracing with a infrapatellar strap or a Cho-pat strap is common.

Operative
Operative treatment of patellar tendinitis is rarely necessary.

Altered mechanical loading of meniscal tissue occurs following various injuries and surgical treatments such as anterior cruciate ligament (ACL) transection and meniscectomy. The degenerative sequel of the joint following both ACL transection and partial meniscectomy is well documented. However, most studies have focused on the degradation of the articular cartilage of the joint. Few studies have focused on how the meniscal tissue responds to the altered loading. Other musculoskeletal tissues, such as cartilage and bone, have been shown to respond to altered loading with a biochemical response that in turn mediates tissue remodeling. The biochemical events resulting from altered loading of meniscal tissue have not been previously studied. Previous experimental data by others, suggests that both interleukin-1 (IL-1) and nitric oxide (NO) are important mediators in the degradation of musculoskeletal tissues such as articular cartilage and meniscus. Furthermore, NO has been shown to be upregulated in meniscal tissue following mechanical compression. Therefore, the first hypothesis of this study is that altered mechanical loading of meniscal tissue stimulates meniscal cells to produce IL- 1 and NO in a magnitude dependent fashion. The menisci are comprised of two geometrically distinct cell populations; elliptical fibroblast-like cells in the superficial zone, and spherical chondrocytic-like   cells in the deep zone. Following mechanical stimulation, only cells from the superficial zone showed an increase in NO levels. In contrast, cells from the deep zone were shown to produce NO following chemical stimulation, but no increase in NO was seen following mechanical stimulation. Therefore, the second hypothesis of this study is that elliptical shaped cells elicit a greater biochemical response when subjected to mechanical loading compared to spherical shaped meniscal cells. To test these hypotheses, a custom mechanical testing system will be built to compress meniscal explants to precise stresses and strains after which the biochemical response will be measured. Finite element modeling will be used determine the distinct mechanical environment of both elliptical and spherical shaped cells, and the cellular mechanical environment will be correlated to the biochemical response.

The knee can be a common area of joint pain in the body. It is a hinge joint which allows leg flexion and extension.

Muscle toning exercises — Rehabilitation of the knee begins with gentle toning exercises. Straight leg raising and leg extension exercises are used to strengthen the quadriceps and hamstring muscles, to provide support to the joint, and to counteract the giving out sensation caused by disuse or weakened ligaments. These muscle toning exercises are performed without bending the knee.

• To perform straight leg raises, sit on the edge of a chair or lie down with the opposite leg bent (show figure 3). Raise your leg 3 to 4 inches off the ground and hold for 5 seconds. Sets of 15 to 20 raises should be performed daily with the leg perfectly straight. As your condition improves, perform straight leg raises with weights at the ankle; begin with a two pound weight and gradually increase to a 5 to 10 pound weight (pennies or fishing weights in an old sock, 2 cans in an old purse, or Velcro ankle weights).

• To perform leg extensions, lie on your stomach or kneel on all fours (show figure 4). Raise your leg 3 to 4 inches off the ground and hold for 5 seconds. Sets of 15 to 20 extensions should be performed daily with the leg perfectly straight. As your condition improves, perform leg extensions with weights at the ankle; begin with a 2 pound weight and gradually increase to a 5 to 10 pound weight. Note that the exercise should be performed lying flat if the knee cap is the source of pain.

If the straight leg raising exercises do not aggravate the underlying condition, weighted leg lifts with a bent knee can begin. Initially these are performed with the legs bent to 30 degrees, using the same amount of weight and number of repetitions as with straight leg raises. The amount of bending is gradually increased as tolerated, in increments of 30 to 45 to 60 to 90 degrees of bending.

Advanced knee exercises and high impact sports can be attempted several months after full recovery of thigh and hamstring muscle tone. Tolerance of these exercises depends upon the underlying injury and the likelihood of recurrence. These exercises are not advised for people with moderate to severe arthritis of the main knee joint, in people who have had surgical removal of the shock absorbing meniscal cartilage, or in people with severe ligament injuries that have left the knee partially unstable. Advanced knee exercises include the following:

• Squats are excellent for the development of the quadriceps muscles and the gluteus muscles of the buttocks. However, the pressure created in the fully bent position is too high for an arthritic joint or for people with painful knee caps. It is safer to perform a half squat, bending the knee only half way to no greater than 45 degrees.

• Rope jumping, high impact aerobics, step aerobics, etc. may be acceptable for some but not all conditions. People with arthritis, torn cartilage, and fractures with improper bony alignment should not perform these types of exercises.

INTRODUCTION — There are several bursae surrounding the knee; two commonly become inflamed and cause knee pain [1]:

• The anserine bursa
• The prepatellar bursa

Bursitis typically has the following features:

• Exquisite local tenderness at the site of the bursa
• Pain on motion and at rest
• Occasional loss of active movement
• Swelling when bursitis occurs close to the body surface (eg, prepatellar bursitis)

PREPATELLAR BURSITIS — Acute prepatellar bursitis is an inflammation of the largest knee bursa, located between the patella and the overlying skin. It is most commonly caused by trauma, as a result of a fall or the direct pressure and friction of repetitive kneeling ("housemaid's knee"). The prepatellar bursa is one of two bursa in the body (the other is the olecranon bursa) that can become infected, most commonly by Staphylococcus aureus [2,3]. The prepatellar bursa also may be inflamed by urate crystals [4].

What is the medial collateral ligament?
The medial collateral ligament (MCL) is one of four ligaments that are critical to the stability of the knee joint. A ligament is made of tough fibrous material and functions to control excessive motion by limiting joint mobility. The four major stabilizing ligaments of the knee are the anterior and posterior cruciate ligaments (ACL and PCL, respectively), and the medial and lateral collateral ligaments (MCL and LCL, respectively).

How is the medial collateral ligament injured?
Because the medial collateral ligament resists widening of the inside of the knee joint, the MCL is usually injured when the outside of the knee joint is struck.

INTRODUCTION — The medial collateral ligament (MCL) extends from the medial femoral to the medial tibial condyle (show figure 1). It is the primary stabilizer to valgus (abductor) stress of the knee, and therefore the most vulnerable ligament following an injury associated with a valgus force. The anterior and posterior cruciate ligaments also provide support with valgus stress, and injuries to these ligaments may accompany a MCL injury.

MCL strain is an irritation, inflammation, or partial separation of the ligament. Ligaments that are irritated and inflamed but otherwise intact are classified as first-degree strains. A partially torn ligament is a second-degree separation. Third-degree separations are characterized by complete disruption of the ligament with gross knee instability.

PRESENTATION — The MCL is usually injured by a valgus force applied to the lateral aspect of a partially flexed knee with the foot fixed, or by twisting. This commonly occurs when skiers get caught on the inside edge of a ski, and in contact sports when a player is struck on the lateral side of the knee by another player.

Patients with an MCL strain complain of knee pain along the inner aspect of the knee joint. They often have difficulty walking, pivoting, and twisting, although most patients are able to ambulate after an acute injury. Patients with first and second degree injuries frequently continue with the activities that they were doing at the time of the injury. Instability and symptoms such as "locking" or "popping" are uncommon following an isolated MCL injury. Third degree MCL tears are commonly associated with a torn anterior cruciate ligament (ACL), which often produces instability [1].

DIAGNOSIS — The diagnosis of MCL injury is based upon an appropriate history, symptoms of pain crossing the medial joint line of the knee, and an examination showing local tenderness along the medial knee that is consistently aggravated by valgus stress testing. Regional anesthetic block is rarely used to differentiate this injury from an intraarticular process.

INTRODUCTION — A torn meniscus is a disruption of the fibrocartilage pads located between the femoral condyles and the tibial plateaus (show figure 1) [1]. The medial and lateral meniscus provide shock absorption and play a role in joint lubrication.

Tears are classified as partial or complex; anterior, lateral, or posterior; traumatic or degenerative; and horizontal, vertical, radial, parrot-beak, or bucket handle. Significant tears lead to loss of smooth motion of the knee (locking), knee effusion, and premature osteoarthritis. Meniscal tears may occur in isolation or in association with a medial collateral ligament (MCL) or anterior cruciate ligament (ACL) tear [2].

PRESENTATION — The most common cause of meniscal injury is a twisting injury with the foot fixed; this frequently occurs in football and basketball. Older individuals may have degenerative tear with a history of minimal or no trauma.

The degree of pain at the time of injury is variable; most patients can ambulate after a small tear occurs and may continue to participate in the activity that caused the injury. The acute event is then followed by an insidious onset of pain and swelling over 24 hours. The pain is exacerbated by twisting or pivoting movements. Severe tears are usually associated with more significant pain and early restriction of knee motion. Some patients describe a tearing or popping sensation at the time of injury.

Patients with untreated meniscal tears can present weeks after the injury complaining of popping, locking, catching, and the knee "giving out," or may simply report a vague sense that the knee is not moving properly. This feeling of instability is related to the proprioceptive misinformation that occurs when a fragment (eg, meniscal tear) floats between the two articular surfaces, creating the sensation that the knee is not in the position in which it was anticipated to be. "Locking" is not true locking in the sense of not being able to move at all, but rather reflects the inability to fully extend the knee because of interference from the torn meniscus.

INTRODUCTION — Running is one of the most popular forms of exercise, with approximately 30 to 40 million Americans participating regularly [1-3]. Benefits include improved cardiopulmonary function, reduced risk of obesity and osteoporosis, and enhanced mental health. (See "Overview of the risks and benefits of exercise" and see "Exercise and fitness in the prevention of cardiovascular disease").

Running is not without risk; approximately 35 to 45 percent of participants suffer a running-related injury every year [4]. Since the forces associated with running are largely absorbed by the lower extremity, the majority of injuries occur in the foot and leg. These include intra- and periarticular hip and knee injuries, stress fractures of the tibia, fibula and foot, tendonitis, heel pain, and plantar fasciitis. An overview of lower extremity injuries due to running is presented here.

GENERAL ISSUES — Most running injuries have an insidious onset and are not associated with specific trauma.

Risk factors — Some people beginning a conditioning program are at higher risk of injury. Army recruits represent one group that has been studied to identify potential risk factors. Poor physical fitness, extremes of flexibility (high or low), a prior sedentary lifestyle, and tobacco use are among the factors that increase the risk of exercise related injuries [5]. Malalignment problems such as genu varum, patellar deviations, tibial torsions, and foot pronation may result in overuse injuries.

Among female recreational runners, increasing age may be a risk factors for a new injury. This was illustrated in a study of 844 runners training for a 10 km race [6]. Age greater than 50 years in women was a risk factor and age less than 31 was protective against new injury.

INTRODUCTION — Patellofemoral pain syndrome (PFPS) can be defined as retropatellar or peripatellar pain resulting from physical and biochemical changes in the patellofemoral joint. It is one of the most common nonsurgical orthopedic conditions and a frequent cause of primary care office visits.

PFPS should not be confused with chondromalacia patellae, a pathological term that describes gross histological abnormalities of the patellar articular cartilage [1]. This distinction is important since the latter can be a more painful condition that is amenable to arthroscopic debridement of the patellar cartilage [2].

ETIOLOGY AND PATHOGENESIS — The patella is a sesamoid bone embedded in the quadriceps tendon that articulates with the trochlear groove of the femur. Its function is to increase the mechanical advantage of the quadriceps muscle. The patella moves up and down, tilts, and rotates; thus, there are various points of contact between the undersurface of the patella and the femur. Repetitive contact at any of these areas, sometimes combined with maltracking of the patella, is the likely mechanism of patellofemoral pain syndrome (PFPS).

The precise cause of PFPS is unknown, but is likely multifactorial. Any of the following factors may be involved [3]:

• Overuse or overload
• Biomechanical problems
• Muscular dysfunction

Overuse or overload — PFPS is often classified as an overuse injury because bending the knee increases the pressure between the patella and its various points of contact

Click on images for more info on the postures.

Ligaments are tough bands of fibrous tissue that connect two bones. The anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL) are inside the knee joint. These ligaments connect the thigh bone (femur) and the large bone of the lower leg (tibia) at the knee joint. The ACL and PCL form an "X" inside the knee that stabilizes the knee against front-to-back or back-to-front forces.

An ACL injury is a sprain, which is a tear of a ligament. In almost all cases, the ACL is torn during at least one of the following patterns of injury:

• A sudden stop, twist, pivot or change in direction at the knee joint — These knee movements are a routine part of football, basketball, soccer, rugby, gymnastics and skiing. For this reason, athletes who participate in these sports have an especially high risk of ACL tears.
  
   
• Extreme hyperextension of the knee — Sometimes, during athletic jumps and landings, the knee straightens out more than it should and extends beyond its normal range of motion, causing an ACL tear. This type of ACL injury often occurs because of a missed dismount in gymnastics or an awkward landing in basketball.
  
   
• Direct contact — The ACL may be injured during contact sports, usually during direct impact to the outside of the knee or lower leg. Examples are a sideways football tackle, a misdirected soccer kick that strikes the knee or a sliding tackle in soccer.

Like other types of sprains, ACL injuries are classified by the following grading system:

• Grade I — A mild injury that causes only microscopic tears in the ACL. Although these tiny tears may stretch the ligament out of shape, they do not affect the overall ability of the knee joint to support your weight.
  
   
• Grade II — A moderate injury in which the ACL is partially torn. The knee can be somewhat unstable and can "give way" periodically when you stand or walk.
  
   
• Grade III — A severe injury in which the ACL is completely torn through and the knee feels very unstable.

Overall, most ACL injuries are severe Grade IIIs, with only 10% to 28% being either Grade I or Grade II. Currently, between 100,000 and 250,000 ACL injuries occur each year in the United States, affecting approximately one out of every 3,000 Americans. Although most of these injuries are related to athletic activities, especially contact sports, about 75% occur without any direct contact with another player.

Women who play contact sports injure their ACLs about seven times more often than men who play such sports. So far, sports medicine experts have not been able to determine why women athletes have a higher risk of ACL injuries. Some researchers believe it's related to a slight difference in the anatomy of the knee in males and females. Others attribute it to the effects of female hormones on body ligaments. Still others point to differences between females and males in skill, training, conditioning or even athletic shoes.

Symptoms of an ACL injury can include:

• Feeling a "pop" inside your knee when the ACL tears
• Significant knee swelling and deformity within a few hours after injury
• Severe knee pain that prevents you from continuing to participate in your sport (most common in partial tears of the ACL)
• No knee pain, especially if the ACL has been completely torn and there is no tension across the injured ligament
• A black and blue discoloration around the knee, due to bleeding from inside the knee joint
• A feeling that your injured knee will buckle, "give out" or "give way" if you try to stand

In diagnosing an ACL sprain, your doctor will want to know exactly how you hurt your knee. He or she will ask about:

• The type of movement that caused the injury (knee twist, sudden stop, pivot, direct contact, hyperextension)
• Whether you felt a "pop" inside your knee when the injury happened
• How long it took for swelling to appear
• Whether severe knee pain sidelined you immediately after the injury
• Whether your knee immediately felt unsteady and could not bear weight

Also, if you are an athlete who hurt your knee while you were training or competing in a sport, your doctor may want to contact your coach or trainer to get an eyewitness account of your injury.

The doctor will examine both your knees, comparing your injured knee with your uninjured one. He or she will check your injured knee for signs of swelling, deformity, tenderness, fluid inside the knee joint, and discoloration. The doctor also may check your knee's range of motion if it's not too painful or too swollen, and will pull against the ligaments to check their strength. To do this, the doctor will ask you to bend your knee and he or she will gently pull forward on your lower leg. If your ACL ligament is torn, when your lower leg is moved it will create the appearance of an "underbite" or a protruding "lower lip" of the knee. The more your lower leg can be displaced forward from its normal position, the greater the amount of ACL damage and the more unstable your knee.

If your physical examination suggests that you have a significant ACL injury, your doctor may order a magnetic resonance imaging (MRI) scan of your knee joint or perform camera-guided surgery (arthroscopy) to inspect the damage to your ACL. For diagnosing partial ACL tears, arthroscopy is usually more efficient than MRI.

How long you have problems depends on the severity of your injury, your rehabilitation program and the types of sports you play. In most cases, full recovery takes 4 to 12 months.

To help prevent sports-related knee injures, you can:

• Warm up and stretch before you participate in athletic activities.
  
   
• Strengthen the muscles around the knee through an exercise program.
  
   
• Avoid sudden increases in the intensity of your training program. Never push yourself too hard, too fast. Increase your intensity gradually.
  
   
• Wear comfortable, supportive shoes that fit your feet and fit your sport. If you have problems in foot alignment that might increase your risk of a twisted knee, ask your doctor about shoe inserts that can correct the problem.
  
   
• If you play football, ask your sports-medicine doctor or athletic trainer about specific types of shoe cleats that may help to reduce your risk of knee injuries.
  
   
• If you ski, use two-mode release bindings that are installed and adjusted properly. Make sure that the binding mechanism is in good working order and that your boots and binding are compatible.

For Grade I and Grade II ACL sprains, initial treatment follows the RICE rule:

• Rest the joint
• Ice the injured area to reduce swelling
• Compress the swelling with an elastic bandage
• Elevate the injured area

Your doctor also may suggest that you wear a knee brace, and that you take a nonsteroidal anti-inflammatory drug, such as ibuprofen (Advil, Motrin and others), to relieve pain and ease swelling. As your knee pain gradually subsides, the doctor will have you start a rehabilitation program to strengthen the muscles around your knee. This rehabilitation should help to stabilize your knee joint and prevent it from being injured again.

Treatment depends on your activity level. Surgery may be used for those needing to return to sports that involve pivoting and jumping. Initially, Grade III injuries are also treated with RICE, bracing and rehabilitation. Once swelling subsides, the torn ACL may be reconstructed surgically using either a piece of your own tissue (autograft) or a piece of donor tissue (allograft). When an autograft is done, the surgeon usually replaces your torn ACL with a portion of your own patellar tendon (tendon below the kneecap) or a section of tendon taken from a large leg muscle. Currently, almost all knee reconstructions are done using arthroscopic surgery, which uses smaller incisions and causes less scarring than traditional open surgery.

Call your doctor immediately if your knee becomes swollen or deformed, even if it is not painful. This is especially important if you cannot bear weight on your injured knee or if the knee feels as if it will buckle or "give out."

Overall, about 90% of patients with ACL injuries fully recover, as long as they faithfully follow a good rehabilitation program. As a long-term complication, some patients with Grade III ACL injuries may eventually develop symptoms of osteoarthritis in the injured knee joint. According to one study, 50% to 60% of patients who suffered a severe ACL sprain showed X-ray evidence of knee osteoarthritis within 5 years after their ACL injury.

The anterior cruciate ligament (ACL) is probably the most commonly injured ligament of the knee. In most cases, the ligament is injured by people participating in athletic activity. As sports have become an increasingly important part of day-to-day life over the past few decades, the number of ACL injuries has steadily increased. This injury has received a great deal of attention from orthopedic surgeons over the past 15 years, and very successful operations to reconstruct the torn ACL have been invented.

This guide will help you understand

• where in the knee the ACL is located
• how an ACL injury causes problems
• how doctors treat the condition

Ligaments are tough bands of tissue that connect the ends of bones together. The ACL is located in the center of the knee joint where it runs from the backside of the femur (thighbone) to connect to the front of the tibia (shinbone).

The ACL runs through a special notch in the femur called the intercondylar notch and attaches to a special area of the tibia called the tibial spine.

The ACL is the main controller of how far forward the tibia moves under the femur. If the tibia moves too far, the ACL can rupture. The ACL is also the first ligament that becomes tight when the knee is straightened. If the knee is forced past this point, or hyperextended, the ACL can also be torn.

Ligaments of the knee may be injured when the knee is twisted. (ACL)  Anterior cruciate ligament injury occurs when the knee is twisted or hyperextended. Sudden force  and medial collateral ligaments (MCL) are the most commonly injured knee ligaments.

The ACL is responsible

 It is not uncommon to also see a tear of the medial collateral ligament (MCL) on the inside edge of the knee, and the lateral meniscus, which is the U-shaped cushion between the outer half of the tibia and femur bones.

How do ACL injuries occur?

The major cause of injury to the ACL is sports. The types of sports that have been associated with ACL tears are numerous. Those sports requiring the foot to be planted and the body to change direction rapidly (such as basketball) carry a high incidence of injury. Football is also frequently the source of an ACL tear. Football combines the activity of planting the foot and rapidly changing direction and the threat of bodily contact. Downhill skiing is another frequent source of injury, especially since the introduction of ski boots that come higher up the calf. These boots move the impact of a fall to the knee rather than the ankle or lower leg. An Many patients recall hearing a loud pop when the ligament is torn, and they feel the knee give way.

The number of women suffering ACL tears has dramatically increased. This is due in part to the rise in women's athletics. But studies have shown that female athletes are two to four times more likely to suffer ACL tears than male athletes in the same sports.

Recent research has shown several factors that contribute to women's higher risk of ACL tears. Women athletes seem less able to tighten their thigh muscles to the same degree as men. This means women don't get their knees to hold as steady, which may give them less knee protection during heavy physical activity. Also, tests show that women's quadriceps and hamstring muscles work differently than men's. Women's quadriceps muscles (on the front of the thigh) work extra hard during knee-bending activities. This pulls the tibia forward, placing the ACL at risk for a tear.

Meanwhile, women's hamstring muscles (on the back of the thigh) respond more slowly than in men. The hamstring muscles normally protect the tibia from sliding too far forward. Women's sluggish hamstring response may allow the tibia to slip forward, straining the ACL. Other studies suggest that women's ACLs may be weakend by the effects of the female hormone estrogen. Taken together, these factors may explain why female athletes have a higher risk of ACL tears.

What does a torn ACL feel like?

The symptoms following a tear of the ACL can vary. Usually, the knee joint swells within a short time following the injury. This is due to bleeding into the knee joint from torn blood vessels in the damaged ligament. The instability caused by the torn ligament leads to a feeling of insecurity and giving way of the knee, especially when trying to change direction on the knee. The knee may feel like it wants to slip backwards.

The pain and swelling from the initial injury will usually be gone after two to four weeks, but the knee may still feel unstable. The symptom of instability and the inability to trust the knee for support are what require treatment. Also important in the decision about treatment is the growing realization by orthopedic surgeons that long-term instability leads to early arthritis of the knee.

How do doctors identify ACL injuries?

The history and physical examination are probably the most important ways to diagnose a ruptured or deficient ACL. In the acute (sudden) injury, the swelling is a good indicator. A good rule of thumb that orthopedic surgeons use is that any tense swelling that occurs within two hours of a knee injury usually represents blood in the joint, or a hemarthrosis. If the swelling occurs the next day, the fluid is probably from the inflammatory response.

Placing a needle in the swollen joint and aspirating (or draining as much fluid as possible) gives relief from the swelling and provides useful information to your doctor. If blood is found when draining the knee, there is about a 70 percent chance it represents a torn ACL. This fluid can also show if the cartilage on the surface of the knee joint was injured.

During the physical examination, your doctor will determine how badly the ACL was injured and whether other knee ligaments or joint cartilage were injured.

Your doctor may order X-rays of the knee to rule out a fracture. Ligaments and tendons do not show up on X-rays, but bleeding into the joint can result from a fracture of the knee joint, or when portions of the joint surface are chipped off. Magnetic resonance imaging (MRI) is probably the most accurate test for diagnosing a torn ACL without actually looking into the knee. The MRI machine uses magnetic waves rather than X-rays to show the soft tissues of the body. This machine creates pictures that look like slices of the knee. The pictures show the anatomy, and any injuries, very clearly. This test does not require any needles or special dye and is painless.

In some cases, arthroscopy may be used to make the definitive diagnosis if there is a question about what is causing your knee problem.

How to prevent ACL injuries
Hip weakness can exacerbate the anatomical alignment problems. Additional internal rotation of the knee can occur too far and too fast if the hip abductors and hip external rotators are not functional. The static pelvic position has been shown to influence the rate of ACL injury. Weak lower abdominals and poor muscular control can lead to a forward pelvic tilt, or sway-back position. This forward pelvic tilt also allows more internal rotation than happens when the pelvis is held in neutral alignment. Strengthening the body core muscles, gluteus medius, external hip rotators, lower abdominals and obliques should increase stability and help control knee internal rotation, thus reducing ACL injury risks.

Strong quadriceps and hamstrings are also crucial for ACL injury prevention. Women are considered to be more ligament-dominant in stabilising the knee joint, whereas men are more muscle-dominant. Thus, it is essential that the quadriceps are strengthened so they are capable of eccentrically controlling rapid knee joint decelerations.

However, overtraining the quadriceps compared to hamstrings is detrimental, since the hamstrings must cooperate with the quads during knee joint decelerations to assist the stabilising role of the ACL. It has been shown that athletes with good hamstring/quadriceps strength ratios suffer fewer non-contact ACL injuries. Strong ankle and calf muscles also help control the knee joint decelerations and help provide more stability from the ankle.

Along with good all-round leg, hip and trunk strength, the coordination of the muscular recruitment is important for knee injury prevention. Neuromuscular coordination must occur optimally for the knee joint to be safely controlled. Thus coordination drills and proprioceptive training are equally as important as muscular strength training in preventing ACL injury. Sporting movements are very rapid. Landing and cutting movements involve little knee flexion movement but require large deceleration forces. Thus the hamstrings need to fire quickly on impact as the knee joint is decelerated, and this must be properly coordinated with a strong eccentric contraction from the quadriceps. In addition, the hip and ankle muscles must be active so that hip and ankle stability is maintained. For effective ACL injury prevention training, knee deceleration movements such as landing, cutting, hopping, etc., must be included as separate drills.
Teaching the correct techniques of these movements can also help prevent injury. The landing movement should involve an upright torso position, and increased knee flexion on impact should be encouraged. In addition, continuing to move after landing also helps because less deceleration is required. Unfortunately, in sports such as gymnastics, basketball and netball, this is not always possible. The cutting movement should be performed by lowering one's centre of gravity and increasing knee flexion. This allows for more stability and a more powerful quadriceps contraction. Trying to cut with a straight leg is ineffective as well as dangerous. Encouraging a less severe cut also helps, although again this is not always possible since it is a less effective movement.
Finally, using the correct footwear is essential. The athlete's shoes should always be stable to control any excess pronation. Prescribed orthotics may also help with this. The grip must always be suitable for the surface on which the game is being played. Gripping and not slipping is essential for ACL injury prevention

An anterior cruciate ligament injury is extreme stretching or tearing of the anterior cruciate ligament (ACL) in the knee. A tear may be partial or complete.

Alternative Names:

Cruciate ligament injury - anterior; ACL injury; Knee injury - anterior cruciate ligament (ACL)

Considerations:

The knee is essentially a modified hinge joint located where the end of the femur (thigh bone) meets the top of the tibia (shin bone). There are four main ligaments connecting these two bones:

• medial collateral ligament (MCL) -- runs along the inner part of the knee and prevents the knee from bending inward.
• lateral collateral ligament (LCL) -- runs along the outer part of the knee and prevents the knee from bending outward.
• anterior cruciate ligament (ACL) -- lies in the middle of the knee. It prevents the tibia from sliding out in front of the femur, and provides rotational stability to the knee.
• posterior cruciate ligament (PCL) -- works in concert with the ACL. It prevents the tibia from sliding backwards under the femur.

The ACL and PCL cross each other inside the knee forming an "X." This is why they are called the “cruciate” (cross-like) ligaments.

ACL injuries are often associated with other injuries. The "unhappy triad" is a classic example, in which the ACL is torn at the same time as the MCL and the medial meniscus (one of the shock-absorbing cartilages in the knee). This type of injury is most often seen in football players and skiers.

Women are more likely to suffer an ACL tear than men. The cause for this is not completely understood, but may have to do with differences in anatomy as well as muscular functioning.

Adults who tear their ACL usually do so in the middle of the ligament or pull the ligament off the femur bone. These injuries do not heal by themselves. Children are more likely to pull off their ACL with a piece of bone still attached -- these may heal on their own, or may require the bone to be fixed.

In cases of suspected ACL tear, an MRI may help to confirm the diagnosis, and to evaluate other injuries to the knee, such as to the other ligaments or cartilage.

Some people are able to live and function normally with a torn ACL. However, most people complain that their knee is unstable and may "give out" with attempted physical activity. Unrepaired ACL tears may also lead to early arthritis in the affected knee.

Causes:

ACL tears may be due to contact or non-contact injuries. A blow to the side of the knee, such as may occur during a football tackle, may result in an ACL tear.

Alternatively, coming to a quick stop, combined with a direction change while running, pivoting, landing from a jump, or overextending the knee joint, can cause injury to the ACL.

Basketball, football, soccer and skiing are common causes of ACL tears.