What causes knee pain in teens?

Knee pain in adolescents is an increasingly common condition, especially in those who play sports and those who start playing sports at a young age. However, there are multiple different causes for knee pain in teens, which is why it's important to see a doctor for a thorough examination. 

Getting a diagnosis 

Getting a diagnosis for knee pain is based on taking a detailed medical history and performing a physical examination of the knee. The doctor will look for four key symptoms: pain, swelling, instability when bearing weight and locking. 

It is important to determine where the knee pain is focused ie the front, side or back of the knee. 

Further investigations may also be needed, such as X-ray and/or MRI scan. 

Common causes of knee pain in teens

Overuse injuries 

The most common cause of knee pain in teens is overuse, usually as a result of spending more time playing sports and/or not warming up or stretching properly beforehand. 

A particularly common overuse injury is jumper’s knee, also known as Sinding-Larsen-Johannson syndrome. This causes pain in the bottom part of the kneecap (patella) due to the patellar tendon being repeatedly strained at the point where it is attached to the patella. 

In some cases, a large strain placed on the patellar tendon results in the lower part of the patella becoming chipped (patella sleeve fracture).

Jumper’s knee is diagnosed with a physical examination and sometimes with an X-ray. It is treated with rest, physiotherapy and a gradual return to activity. Three-quarters of children respond well to this treatment, while the remaining quarter may need further treatment.

In the case of a patella sleeve fracture, the knee will need to be immobilised with a cast and in very rare cases, surgical treatment will be needed.

Osgood-Schlatter disease 

Around one in 10 adolescents aged 12 to 15 years have Osgood-Schlatter disease (OSD). It causes pain, redness and swelling at the point where the patellar tendon attaches to the shinbone (tibia) — this point is called the tibial tuberosity. Sometimes a bony bump forms on the tibial tuberosity too. 

OSD tends to occur in adolescents during the growth spurt around puberty as this is when the bones and tendons undergo bursts of growth, which can cause the patellar tendon to pull on the tibial tuberosity. Playing sports that involve a lot of running and/or jumping is associated with higher rates of Osgood-Schlatter disease.

OSD is diagnosed by a physical examination and X-ray, although in some cases an MRI scan will be needed to help rule out a tibial tuberosity fracture. With a tibial tuberosity fracture, it isn’t possible to actively fully straighten the leg, while with OSD, it’s usually possible. 

OSD is treated with rest, immobilising the knee joint, wearing Osgood-Schlatter bands over the knee and physiotherapy.

In severe cases, where treatment over a long period is not successful, surgery may be recommended as a last resort. However, surgery comes with several risks, including the risk of recurvatum deformity of the knee. 

Chondromalacia patella

Also known as runner’s knee, chondromalacia patella causes constant pain at the front of the knee, around and behind the patella. This pain is often aggravated by going up and down the stairs, and getting up after sitting for a long time. 

It is more common in adolescent girls and is diagnosed through a physical examination. Treatment involves rest, physiotherapy and wearing support braces or taping around the knee. 

Patellofemoral instability

This refers to pain at the front of the knee due to an unstable patella. The patella can partially dislocate from the groove at the end of the thigh bone (femur) where it sits (trochlea of the femur). 

The risk of developing patellofemoral instability is higher in those with knock-knees (genu valgum), an undeveloped or shallow trochlea of the femur, a stretched or torn medial patellofemoral ligament, or a femur and tibia that are malrotated ie the femur is turned in and the tibia is turned out (miserable malalignment syndrome). Patellofemoral instability can also result from a traumatic event. 

After the first episode of patellofemoral dislocation, treatment involves physiotherapy and strengthening of the quadriceps. However, if episodes persist, surgery may be needed. Surgery corrects the anatomical factors contributing to the instability. 

It is important to address limb malalignment that may be responsible for lateral forces acting on the patella. A common approach in children who have genu valgum is guided growth surgery, where surgery blocks one area of the growth plate while the other area continues to grow; this gradually corrects the deformity over 12–18 months.

If the patella remains unstable after correcting the limb malalignment, further surgery is needed, namely medial patellofemoral ligament (MPFL) reconstruction. This involves using a tendon from elsewhere in the body (eg a hamstring graft) or artificial ligament material to replace the torn ligament in the knee. 

Discoid meniscus 

The meniscus of the knee refers to two C-shaped pieces of cartilage — the lateral meniscus and medial meniscus — that sit between the tibia and femur and act as shock absorbers. However, in some children, the meniscus develops into a discoid shape. 

A discoid meniscus doesn’t usually cause any symptoms or problems and can remain asymptomatic for life. However, it is more prone to injuries and in some cases, children do present with knee pain. As it is more common to have a discoid lateral meniscus, this pain is usually on the outer side of the knee. 

A discoid meniscus is diagnosed via an MRI scan. If the knee pain is caused by a tear in the discoid meniscus, surgery can be performed to repair the tear and trim the discoid meniscus into a more regular shape. 

Anterior cruciate ligament injury 

Anterior cruciate ligament (ACL) injuries in children and adolescents often occur when playing sports due to sudden slowing down or changing direction, pivoting, landing awkwardly after a jump or a direct blow to the knee. This causes knee pain, swelling and instability. 

An ACL injury usually needs to be treated with surgery to avoid further injury to the meniscus or cartilage lining of the knee. As the bones are still growing in children and adolescents, surgery particularly focuses on minimising any damage to the growth plates of the bones (physis). In younger children, this involves physeal-sparing ACL reconstruction surgery.

Osteochondritis dessicans

This disorder involves the cartilage that lines the bony surfaces of your knee (articular cartilage). The exact cause of osteochondritis dessicans is currently unclear, although several causes have been suggested, including trauma, metabolic factors and genetics. 

The condition most often causes episodic pain and swelling of the knee. Diagnosis usually involves an X-ray, which can show the cartilage loss, followed by an MRI scan to confirm the diagnosis. 

Osteochondritis dessicans is initially treated with rest, avoiding physical activity, wearing off-loading braces and physiotherapy. Occasionally, surgery may be needed if these initial measures fail or if a piece of your cartilage comes off and floats around in your joint.  

Other causes of knee pain in teens

When investigating knee pain in teens, it is always important to keep the big three causes in mind: infection, inflammatory conditions (eg juvenile inflammatory arthritis) and tumours, particularly when other anatomical causes can’t be found. This often involves an MRI scan or in the case of inflammatory conditions, blood tests.