About the knee joint  

The other bone in the knee is the Patellla which is known as the kneecap. This bone is held in front of the knee joint by tendons and ligaments. Cartilage lines the underside of the knee and helps it slide along a groove at the end of the femur as the knee joint moves.

Anterior Cruciate Ligament
Rupture of the anterior cruciate ligament (ACL) is a serious injury, and the diagnosis may be missed.¹⁸ This type of injury can be produced by pure hyperextension or by a combination of valgus force and external rotation of the tibia relative to the femur.

More than 90 percent of ACL injuries can be detected based on the history and physical examination.¹⁷ However, even the best specialists may fail to recognize the joint laxity of an ACL injury. Therefore, radiographic signs are useful in making the diagnosis
 

Anterior Cruciate Ligament (ACL)
Perhaps the most publicized injury to the knee is that of an ACL tear. ACL tears unfortunately are very common and are devastating to most individuals who suffer them.

While not exclusively, most sporting ACL injuries occur in the non-contact mode and usually are caused during sports that require pivoting, twisting and rapid changes in direction such as basketball and soccer.

One of the unfortunate realities of ACL injuries in young athletes is that a return to pivoting, twisting sports is often not possible without reconstructive measures being performed. A return back to sports with an ACL deficient knee exposes that knee to further damage and sometimes permanent sequelae. It is for that reason that ACL injuries should not be taken lightly nor should they be disregarded even if an initial return to full activities is achieved or permanent activity modification is chosen as a method of treatment.

The ACL provides stability of the knee in a front to back fashion. To a lesser extent rotatory stability is also achieved by the ACL. Loss of this stability is most commonly felt by the patient and described as a recurrent buckling or a giving away sensation.

Causes
ACL injuries occur with sharp movements during athletic activities. Pivoting, twisting sports such as soccer, basketball, and lacrosse require activity that may lead to ACL injuries. Unfortunately, there are no completely successful ways to eliminate the risk of an ACL injury.

Diagnosis
Diagnosis of an ACL begins with a careful history of the injury mechanism. Usually ACL injuries are associated with a large amount of intra-articular swelling - known as an effusion. There is sometimes a large pop felt. When these two historical findings are present the diagnosis of an ACL injury is made 72% of the time.

Without the finding of intrarticular swelling or a pop, an injury can be confirmed on physical exam with the use of various techniques including Lachman’s and pivot shift maneuvers. The lack of these two findings, however, does not eliminate the possibility of an ACL injury. If suspicion is high, diagnosis can be assisted with the use of an MRI. MRI’s are commonly used in aiding the diagnosis of serious knee injuries especially to evaluate the knee for secondary injuries to the meniscus and articular cartilage.

Symptoms

• Large effusion after injury
• Moderate effusion for as much as a week thereafter
• Sense of weakness or rubbery legs
• Buckling or giving way sensation

Treatment

Non-operative
The options for treating ACL injuries in older individuals and those involved in less aggressive sports are many. Older individuals or those involved in life long sports can often develop compensatory strength about the knee and, with the use or not of a brace, can return to most activities. Unfortunately this fact is not well known and therefore ACL reconstruction is commonly sought before full evaluation and discussion about alternative options has been undertaken. If non-operative treatment is to be tried fully, full range-of-motion and strength with emphasis on the hamstring muscles is necessary. The use of a brace, while not proven, may help the sense of stability that the knee feels.

Operative
ACL reconstructions are performed more than 150,000 times per year in the US. This vast experience has allowed the technique to be well refined and results in experienced hands can now be expected to achieve 85 – 90% success rates. The process however is a lengthy one with a return to sports rarely recommended before 6 months of rehabilitation.

ACL injuries are often associated with other injuries to the knee. Meniscal tears (30-60%) and articular cartilage injuries (5-45%) should be noted and treated when present. In fact, there presence is often more devastating to the health of the knee in the long run then the ACL tear itself. Treatment of these injuries (meniscal repair or meniscus tear excision and articular debridement or preservation) can change the rehabilitation process as well as the long term success of ACL injuries.
 

Posterior Cruciate Ligament
Injuries of the posterior cruciate ligament (PCL) are relatively uncommon, apparently because this is the strongest major knee ligament. The mechanism of isolated PCL injury is blunt trauma to the anterior proximal tibia

Medial Collateral Ligament
Knee injuries involving valgus force, with or without a rotational element, are suggestive of MCL injury. The physical examination may demonstrate effusion or local soft tissue swelling and ecchymosis.¹⁸ Injuries to the MCL usually occur at the ligament's proximal origin. Therefore, tenderness is usually localized along the distal femur and extends to the joint line.

Lateral cCollateral Ligamentous Domplex
Injuries of the lateral collateral ligamentous complex (LCL) are estimated to account for only 5 percent of all knee ligament injuries.^18,23 Radiographic signs suggesting LCL injury include lateral joint space widening and medial tibial plateau fracture.¹⁸

The knee joint is cushioned by articular cartilage that covers the ends of the tibia and femur, as well as the underside of the patella. The lateral meniscus and medial meniscus are pads of cartilage that further cushion the joint, acting as shock absorbers between the bones.

Ligaments help to stabilize the knee. The collateral ligaments run along the sides of the knee and limit sideways motion. The anterior cruciate ligament, or ACL, connects the tibia to the femur at the center of the knee. Its function is to limit rotation and forward motion of the tibia. (A damaged ACL is replaced in a procedure known as an ACL Reconstruction.) The posterior cruciate ligament, or PCL (located just behind the ACL) limits backward motion of the tibia.

These components of your knee, along with the muscles of your leg, work together to manage the stress your knee receives as you walk, run and jump

 

Your knee is one of the most used and abused joints in your body. You use your knee joint over one million times per year and as a result it is one of the most injured joints in your body. Your knee is more vulnerable to injury because it is one of the most mobile and flexible joints in your body. The more mobile a joint is, the less stable the joint is and thus, the more vulnerable it is to an injury.

Your knee is made up of three bones carefully designed to provide smooth, stable motion. These bones are called the tibia (shinbone), the femur (thighbone) and the patella (kneecap). These bones are enclosed in the joint capsule lined with a special tissue called synovium, which produces a thick liquid called synovial fluid which is necessary to lubricate, protect and nourish your joints.

Your knee is kept in alignment by ligaments and tendons. There are two large ligaments in the center of your knee, which cross each other, thus they are called the cruciate ligaments. These ligaments prevent your shinbone ( the tibia) from moving forward and backward on your thighbone (the femur) The most famous of these is called the anterior cruciate ligament or ACL for short. This is called the anterior cruciate because it originates near the back of your thighbone and ends at the front or anterior part of your knee. The other ligament is called the posterior cruciate ligament or PCL for short. As you may have already guessed, this ligament starts from the front part of your thighbone and ends at the back of your knee called the posterior aspect of your knee.

On either side of your knee there are another set of stabilizing ligaments called the collateral ligaments. There are two major sets of these ligaments. On the inside part of your knee (the side closer to your other knee) this is called the medial collateral ligament ( MCL), the other is on the outside of your knee (the side closer to your hand) which is called the lateral collateral ligament (LCL). They supply stability when your knee moves from side to side or when you make any sharp cutting moves.

Between the thighbone (femur) and shinbone (tibia), there are two semicircular rings of cartilage which are called menisci ("MEN-NIS-KI"). These also supply more added stability to your knee when the knee twists or pivots. Just like the collateral ligament, the inside meniscus is called the medial meniscus. This meniscus is also partially attached to the medial collateral ligament. Thus sometimes, when one is injured, the other is also injured. The outside meniscus is called the lateral meniscus. Unlike the medial side, this lateral meniscus is not attached to the collateral ligament. Thus, there is a rare association of a meniscus and collateral ligament tear.

The major two tendons of your knee are connected to your kneecap (patella). The tendon below the patella is called the patellar tendon (but really is technically a ligament since it connects your bone to another bone). The tendon above your patella is called the quadriceps tendon.

The kneecap or patella moves between a specially designed groove on your femur called chondyles. Movement of your patella outside of these chondyles can result in a subluxation (when it just moves partially out of the groove) or a total dislocation when the patella moves completely out of the groove.

There are three compartments to the knee joint: an inner and outer compartment located between the thigh bone (femur) and the lower leg bone (tibia), and a knee cap compartment located between the knee cap (patella) and a special groove in the femur

The knee is lubricated by joint fluid that is produced by the lining of the joint and by six lubricating "bursa" sacks. The bursa sacks can become irritated from injury, excessive pressure, and overuse; inflammation of a bursa is called bursitis. Excessive production of joint fluid due to knee injury is called "water on the knee" or a joint effusion.

The knee contains two types of cartilage:

• The cartilage covering the ends of the bones and the undersurface of the knee cap (surface or articular cartilage) 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.

The knee joint is held tightly together by four ligaments the inner and outer fan-shaped hinge ligaments (medial and lateral collateral ligaments) and the crossing ligaments (the anterior and posterior cruciate ligaments). The collateral ligaments are firmly attached to the sides of the thigh and leg bones, hold the two bones together, and prevent side to side motion. The cruciate ligaments are firmly attached to the middle of the thigh and leg bones and prevent forward and backward motion. Irritation of these ligaments is called a sprain, and rupture is called a separation.

The quadriceps muscle in the front of the thigh and the hamstring muscles in the back of the thigh support and move the knee joint. Loss of muscle tone from injury or disuse causes instability of the knee joint. Significant loss of support can cause the knee to "give out," leading to a fall and further injury. Excessive use or rapid contraction (ie, from sprinting or jumping) can cause a quadriceps muscle strain or a hamstring pull.

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. Painful knee caps and arthritis are the two most common causes of knee pain in the noninjured knee.

There are three compartments to the knee joint: an inner and outer compartment located between the thigh bone (femur) and the lower leg bone (tibia), and a knee cap compartment located between the knee cap (patella) and a special groove in the femur

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

Physical therapy is essential to the treatment, rehabilitation, and prevention of many of the conditions that affect the knee joint and its surrounding supporting structures. You can enhance your recovery with the following:

• Physical therapy
• Activity limitations

PHYSICAL THERAPY — Physical therapy of the knee may include the following:

• Ice and elevation
• Muscle toning exercises

Ice and elevation — Ice is useful for the control of pain and swelling. It is applied to the knee for 15 to 20 minutes as often as every 2 to 4 hours, particularly after any physical activity. A bag of ice, frozen vegetables, or an iced towel cooled in a freezer work well. The acutely swollen knee should be elevated above the level of the heart while icing.

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.