Knee

The knee is a joint where the large femur (thigh bone) connects to the tibia (leg bone). It’s very vulnerable to injury, especially in children and adolescent athletes.

Bony knee anatomy

The knee joint is made of three bones: the femur, tibia and fibula. The fibula is on the outer portion of the leg bone. Many ligaments and muscles attach here, but it doesn’t contribute much to the knee otherwise.

The patella (knee cap) rests on the lower end of the femur bone and is embedded in the quadriceps tendon, making it stronger.

There are bony outgrowths of the tibia that deserve special attention. The first is the tibia spines, which serves as the attachment site of the anterior cruciate ligament (ACL). While adolescents and adults tend to get ACL ruptures, younger children are more likely to break the bone than tear the ligament.

The second bony outgrowth is the tibia tubercle. This is the bump that resides on the front of the tibia bone approximately one to two inches below the knee cap. The large patella tendon inserts into this outgrowth and is very vulnerable to both fractures as well as chronic pain due to overuse, such as with running and jumping.

Knee Fractures and Sprains

The knee is a common place for injury in children, adolescents and athletes. Commonly injured parts of the knee include:

  • The femur physis (growth area)
    • The distal femur: the end of the femur bone near the knee.
  • The tibia physis (growth area)
    • The proximal tibia: the top portion of the tibia bone close to the knee. 

Medial collateral ligament (MCL) sprains 

A sprained medial collateral ligament (MCL) is a common football injury. It usually occurs when a player receives a direct hit to the outside of their knee while their foot is planted. There may be “popping” sound in the knee at the time of injury, followed by pain on the inner-side of the knee. Swelling and knee weakness is possible.

Surgery is usually not needed to treat an MCL sprain. Icing the knee and elevating the leg can reduce swelling, and crutches may be needed to allow the knee to rest. X-rays are usually taken to rule out a fracture. Athletes should begin a rehabilitation program within a few days of the injury. 

Tibial tubercle fractures

These fractures occur when a child lands on a straight knee, such as when they are jumping while playing basketball. The tibia tubercle is the bump under the knee cap. When this bump breaks, it often needs to be fixed surgically to ensure the knee can continue to be straightened. The fracture is typically repaired with a few screws and your child is immobilized in either a cast or a knee brace for approximately six weeks. Once the cast is removed, physical therapy is often necessary to help strengthen the quadriceps muscle.

Tibial spine fractures

A knee injury common in active, growing children, adolescents and teens is a tibial spine fracture. It happens when the anterior cruciate ligament (ACL) is stretched and it pulls the tibial spine (a bony ridge at the top of the tibia, or shin bone) away from the rest of the bone.

This fracture can happen when the knee is extended too far or twisted. It is more common in children because a child’s ACL is stronger than the still-growing tibia.

How to spot a tibial spine fracture

  • Pain
  • A popping sensation in the knee
  • Swelling
  • Inability to put weight on the knee
  • Inability to straighten the knee completely
kid on bike illustration showing broken shin bone

How we diagnose a tibial spine fracture

An X-ray or magnetic resonance imaging (MRI) scan can help diagnose the fracture properly. This is the best way to make sure your child gets the right treatment.

How we treat a tibial spine fracture

The common complications of a tibial spine fracture are knee stiffness or instability. These complications resemble those of an ACL tear or knee sprain.

  • If the tibial spine is not displaced, or separated from the rest of the bone, the fracture can be treated non-surgically by lining up the bone correctly and casting it.
  • If the fracture is more severe, surgery is needed to ensure proper healing. In many cases, an arthroscopic (minimally invasive) procedure can be used to put the fracture fragment back into place and secure it appropriately. This procedure involves placing two pins into the knee. The pins pull a suture over the tibial ridge to pull it into the right position. By treating the fracture this way, the surgeon can properly repair the fracture and avoid damaging t the nearby growth plate.
illustration of tibial spine knee repair

ACL Tears

What are Anterior Cruciate (ACL) Tears?

The ACL, or anterior cruciate ligament, is one of the four main knee ligaments. Even though it is only about an inch long, it functions as the main stabilizer of the knee. The ACL protects the shinbone (tibia) from sliding forward on the thighbone (femur) during sudden decelerations. It also stabilizes the knee during rotational motions, such as landing from a jump or during a sudden change of direction. Sports requiring sudden stops and changes of direction, like basketball and soccer, carry the highest risk for ACL injury. 

Girls are four- to eight-times more likely to suffer an ACL tear than boys because their body mechanics are different. Some of these differences include:

Hips

Girls have wider hips than boys, which increases the angle on the knee joint. The knee was designed as a hinge that’s supposed to rock forward and backward. With wider hips, there is an inward-directed angle on the knee that causes it to roll side-to-side. This puts increased stress on the ACL, especially during landing and cutting movements.

Knees

Girls have a narrower notch in the inside of their knee that leaves their ACL more susceptible to getting pinched or frayed during sudden stops or direction changes.

Quadriceps

Hamstrings (muscles in the back of the thigh) protect the ACL. Quadriceps (muscles in the front of the thigh) put stress on the ACL. Girl’s quadriceps are typically stronger than their hamstrings, which leaves their ACL vulnerable to injury.

External rotators

The gluteus muscles, or external rotators of the hip, fire differently in males and females. In boys, the hip muscles fire a split second before landing, stabilizing the hips and core. In girls, the muscles remain idle throughout the landing cycle, which allows the hips to rotate in and the knee to buckle, putting stress on the ACL.

How we treat ACL tears

Most of the time when the ACL is injured, it is completely torn. The two ends of the ACL shrivel up and will not grow back together. A torn ACL leaves the knee unstable and at risk for further shifting and damage to the cartilage, which will eventually cause arthritis.

The recommended treatment for an ACL tear is surgical reconstruction. Since the two ends of the torn ligament curl up, it would be difficult to sew them back together. Even if it could be sewn together, a “repaired” ACL would not hold up under the amount of stress sports puts on the ligament. ACL reconstruction involves creating a new ligament and putting it where the old one used to be. The new "ligament" can be made with a tendon from another part of your child’s leg or from a donor. The new ACL graft is anchored to the thigh and shin. Surgery is done through a tiny incision and usually takes less than two hours.

How do to prevent ACL tears

The best way to prevent ACL tears in young athletes is to identify and correct biomechanical "risk factors," such as balancing the hamstring to quadricep strength ratio and helping female athletes train their hip and glute muscles to fire prior to landing.

Learn more about how to prevent ACL injuries with our ACL Injury Prevention Program

Discoid Meniscus

A discoid meniscus is an abnormality of the structure of the meniscus. Instead of the meniscus having its typical "C" shape, the center of the cartilage is filled in to varying degrees.  The cause of these abnormalities is unknown. It’s thought that genetic reasons could play in role in causing the meniscal cartilage to develop abnormally. It’s estimated that discoid menisci occur in three to five percent of people. The more abnormal the shape, the less normal the function—increasing the risk of injury. Discoid menisci can be thick and round, which causes them to snap when the knee performs a range of motions. They can also tear spontaneously in very young children. Typically, only one knee is affected. Discoid menisci are seen in both knees only about fifteen percent of the time. Discoid menisci almost always occur on the outer side of the knee, but in very rare cases can occur on the inner side.

Meniscus Tear

What is a torn meniscus? 

A meniscus is a rubbery tissue in the knee that serves as a cushion between the thigh (femur) and the shin (tibia). A meniscus can tear when a child twists their knee, squats or sustains significant trauma. Since a meniscus is made of specialized cartilage, injuries to it are commonly referred to as "torn cartilage."

A meniscus:

  • Cushions and protects the knee joint

  • Assists the ligaments in providing stability to the knee joint

Tearing of a normal meniscus rarely occurs in kids under 12 years old. Most of the time, if a child sustains a meniscus tear, it’s from a significant trauma. However, it can also occur if your child has abnormal cartilage.

How to spot a torn meniscus

Symptoms of a torn meniscus include pain, limited motion and swelling of the joint. The knee may occasionally lockup or become stuck in place. An MRI scan is used to confirm the diagnosis and other radiology tests may be done to rule out additional injuries.

How we treat a torn meniscus

In most cases, it’s best to have a torn meniscus treated since this injury rarely heals on its own. Left untreated, there can be further damage or tearing of the remaining meniscus, or even worse, to the joint surface (articular cartilage).

Treatment for a torn meniscus typically includes:

  • Ice
  • Rest, including the use of crutches
  • Surgery, depending on the type of tear

Treatment of meniscus tears depend on the type of tear:

  • Incomplete tear: If the tear involves only a portion of the meniscus, an incomplete or partial thickness tear, it may not need treatment. These are commonly seen in association with ligament injuries.
  • Inner tear: If the meniscus tear occurs in the inner two-thirds of the cartilage, where there is no blood supply, it will not heal. So, the tear is treated by trimming away the torn portion and leaving as much of the normal meniscus behind as possible.
  • Outer tear: If the tear is in the outer third of the meniscus, where there is a naturally occurring blood supply, it has the potential for healing. In many of these cases, the meniscus can be sutured or "tacked" together.

Overuse Injuries

Overuse injuries can happen with repetitive motions and are often seen in athletes. Some common types of overuse injuries include: 

Patella (Kneecap) Instability

What is patella instability?

The patella (kneecap), which rests in a groove at the end of the femur (thigh bone), protects the knee joint and helps with knee extension.

Patella dislocations usually happen when the knee is extended and twisted. Direct collisions to the knee (such as in football) can also cause a dislocation.

How to spot patella instability

Symptoms of a patellar dislocation include pain and swelling in the front of the knee. You may also notice your child’s patella is positioned on the outside of the knee, or the knee has an abnormal appearance.

How we diagnose patella instability

During an examination, your physician will assess range of motion, check stability and mobility and pinpoint any tender areas. X-rays of your child’s knee will be taken to show the alignment of the patella and to check for fractures of the patella or femur. Additional imaging, including MRI or CT scan, may be used to check for injuries to the bone or cartilage, tears of the medial patellofemoral ligament or to measure overall limb alignment.

How we treat patella instability 

After a dislocation, the patella may spontaneously go back to its normal position, or your doctor may need to put it back in place.

Treatment Options

Initial treatment usually includes over-the-counter anti-inflammatory medications (such as aspirin or ibuprofen), restricting activity and immobilization or bracing. Physical therapy is also prescribed to strengthen quadriceps as well as hip and core mechanics.

If your child injures the cartilage over the knee joint (articular cartilage), which can cause loose fragments of bone or cartilage within the joint, surgery may be recommended. Children with recurrent patellar dislocations may need surgery to repair structures (bone, muscle, tendons, or ligaments) on the inside of the knee, release tight structures on the outside of the knees, or modify the alignment of the leg.

Recurrent patellar dislocations occur more commonly in children than in adults. This is often a result of abnormal anatomy that increases the likelihood for children to dislocate the patella.

Unlike adults, children have open growth plates to allow for continued bone growth. When considering surgical options for recurrent patellar dislocations, treatment options and timing may vary based on whether the child has open or closed growth plates.

Growth Plate Knee Trauma

Symptomatic Plica

What is a plica?

A plica is a naturally occurring fold in the joint lining. It rarely causes symptoms unless it sustains a direct trauma.

There are several naturally occurring plicae (plural of plica) of the knee, including:

  • Suprapatellarplica
  • Medial patellar plica
  • Infrapatellarplica

How to spot plica

Plicae rarely cause symptoms, except for medial parapatellarplica. Typically, plicae cause symptoms after young athletes sustain a direct blow to the area. Although not proven, it’s believed that the plica and overlying connective tissue become thickened and begin to catch or impinge after trauma.

Symptoms can occur suddenly (acute) or over time (chronic). Persistent pain during activity is the most common symptom, but sometimes athletes will also experience a "locked" knee.

It’s not uncommon for symptomatic plica to occur at the onset of a new sport’s season or with a sudden increase of training levels. Athletes in track, cross-county, soccer, football and cycling are especially vulnerable.

How we diagnose plica

There is no one test that conclusively diagnoses symptomatic plica. A doctor will need to examine your child to confirm the diagnosis and rule out other possible problems.

Exams may include:

  • Medical history review
  • Physical exam
  • Radiology tests

How we treat plica

Most symptomatic plica can be treated without surgery. Physical therapy may be recommended to help regain strength and mobility, as well as prevent future injury.