Jumper’s knee, also known as patellar tendonitis, can cause pain and tenderness near the bottom of the kneecap. Jumper’s knee affects mostly children who participate in sports that require a lot of running, jumping and kicking. Performing these actions repetitively can cause pain in the tendon that stretches over the front of the kneecap.

At times, the bone growth centre at the bottom tip of the kneecap may cause pain and tenderness in the front of the knee. This is a condition called Sinding-Larsen-Johansson disorder. It occurs mainly during growth spurts. Pain and tenderness in the front of the knee is caused by disruption within the developing bone in the bottom tip of the kneecap. Thankfully, this condition is not severe. It is typically only temporary and improves with age.

In this article, we will cover:

• The part of the knee involved
• Causes of the condition 
• Available treatment options

Jumper’s knee affects the patellar tendon. The patellar tendon connects the sizeable and powerful quadriceps muscle in the front of the thigh to the tibia (shinbone). It wraps over the front of the patella (kneecap), its upper end connecting to the bottom tip of the patella. This area is known as the inferior pole of the patella. The lower end of the patellar tendon, on the other hand, connects to a small bump of bone on the front surface of the tibia. This bump is known as the tibial tuberosity.

Typically, jumper’s knee is caused by overuse of the patellar tendon. Children who participate in sports involving a lot of jumping and squatting are especially at risk. In order to squat and land softly from a jump, the quadriceps muscle must work extra hard to slow the body down and protect the knee. This is known as an eccentric contraction, where the quadriceps muscle lengthens as it works. This muscle action places abnormally high tension on the patellar tendon. When squatting and jumping are done repeatedly, the repetitive stress on the tendon causes injury to the individual fibres of the tendon. As a result, the tendon becomes painful and inflamed. This condition is known as jumper’s knee.

Another possible cause of jumper’s knee is an abnormal alignment of the lower limbs. Children who are knock-kneed or flat-footed may have a higher risk of developing this condition. These altered postures create a sharper angle between the quadriceps muscle and the patellar tendon. This angle is known as the Q-angle. A large Q-angle means there is already higher tension on the patellar tendon. As such, the risk of developing jumper’s knee is higher. A greater Q-angle also places unusually high tension on the bone growth plate of the inferior pole of the patella. Thus, the risk of developing Sinding-Larsen-Johansson disorder is increased. On top of that, a high-riding patella, known as patella alta, is also thought to be a cause of jumper’s knee in children and adolescents.

As for active children whose bones are not fully developed, patellar tendon pain has a slightly different cause. During growth spurts, there begins to be increased tension in the tendon. The patellar tendon is unable to keep up with the growth of the lower leg and as a result, is too short. This causes the tendon to pull on the bottom tip of the kneecap. Intense or repetitive sports activity can also cause further stress upon this area. Eventually, this increased tension can disrupt the normal growth of the bottom tip of the patella. This condition is called Sinding-Larsen-Johansson disorder.

Sinding-Larsen-Johansson is a unique condition, part of a category of bone development disorders called the osteochondroses. Osteo refers to bone and chondro means cartilage. In normal development, specialised bone growth centres, known as growth plates, change from cartilage to bone over time. Bone growth centres are located throughout the body. These growth plates expand and unite, which is how bones grow in length and width.

Children with bone development disorders in one area of their body may possibly develop similar problems in other areas. For example, children with Sinding-Larsen-Johansson disorder also have a small risk of bone growth problems where the lower end of the patellar tendon attaches to the tibial tuberosity. This is called an Osgood Schlatter lesion.

Normally, jumper’s knee produces tenderness and pain directly over the patellar tendon, right below the kneecap. At times, there may be a small amount of swelling. Kneeling on the sore knee can also hurt. In addition, activities where the quadriceps muscle works eccentrically can also cause pain. Such activities include jumping, squatting and going down the stairs. Movement such as running, walking and bending or straightening the leg can also be painful.

Children with Sinding-Larsen-Johansson disorder may experience similar symptoms along the top of the kneecap, where the quadriceps muscle meets the patellar tendon. At times, tightness may be felt in the area, particularly when one tries to fully bend the knee.

Normally, history and physical examination are enough to make a diagnosis of jumper’s knee. Information regarding the child’s age and activity level will be required. The doctor will press on and around the patella and patellar tendon to observe for any tenderness. The sore knee will then be compared to the healthy knee. The patient may also be asked to straighten the knee against resistance. This is to work the quadriceps muscle and put tension on the patellar tendon. The pain felt during this test can assist the doctor in the diagnosis of jumper’s knee.

If Sinding-Larsen-Johansson disorder is suspected, an X-ray may be ordered. The X-ray will be taken from the side of the knee. This view may show small fragments of bone where tension in the patellar tendon has disrupted the growth plate in the bottom tip of the patella. Additionally, the it may also show calcification or roughness around the bottom of the patella.

An X-ray will also be needed if the kneecap is painful from trauma such as a fall. In such cases, the X-day will help the doctor determine if a patellar fracture has occurred.

Certain times, a magnetic resonance imaging (MRI) scan may be able to produce more detail. The MRI can provide a clearer picture of any calcification in the patellar tendon where it attaches on the bottom tip of the kneecap. It can detect swelling and any injury or inflammation that is present within the patellar tendon.

Nonsurgical treatment

In certain cases of jumper’s knee, the patient may need to refrain from participating in sports activities for a while. This is to keep the pain and inflammation under control and does not need to happen for a long period of time.

For patients with Sinding-Larsen-Johansson disorder, time may be all that is required. It typically takes one or two years for the bone growth plates that form the inferior pole of the patella to grow together and combine into a single solid bone. By this time, pain and other symptoms would have normally faded away.

Additionally, anti-inflammatory medications may be prescribed to help reduce swelling. There is a wide range of knee straps and sleeves available to help minimise the pain. A physical therapist may also be suggested.

Physical therapy treatment may include ultrasound, heat or ice to subdue pain and inflammation. As symptoms ease, the physical therapist will work on strength, flexibility and muscle balance in the knee. Posture exercises may also be taught to improve knee alignment. In addition, special shoe inserts called orthotics may be designed to support flat feet or correct knock-kneed posture.

Although cortisone injections are typically used to control pain and inflammation in other kinds of injuries, they have not shown consistently good results and thus may not be appropriate for this condition. Furthermore, there is a high risk of the cortisone causing the patellar tendon to rupture.

Surgical treatment

It is unusual for jumper’s knee conditions to require surgery. In fact, it is not even considered for cases with Sinding-Larsen-Johansson disorder, unless bone growth is complete and symptoms have not gone away after nonsurgical treatment. Even then, the need for surgery is rare.

However, surgery may be considered if the issue involves only the tendon, not the growth plate, and if symptoms have not disappeared after other kinds of treatment. In such cases, the surgeon may perform an operation to strip away inflamed and damaged tissue on the surface of the patellar tendon.

In this procedure, the surgeon creates a small incision down the front of the knee below the patella. The skin is opened to expose the patellar tendon. Afterwards, the damaged tissue is carefully peeled off the surface of the tendon. Three to five thin lengths of the tendon are removed. In certain cases, tiny drill holes are created in the bottom tip of the patella. Drilling causes a small amount of bleeding, which signals the body to start healing the area. The surgeon then removes any damaged tissue nearby.

Lastly, the skin is stitched up and the area is wrapped with a bandage.

Nonsurgical rehabilitation

The goal of non-surgical rehabilitation is to reduce inflammation and pain. It is usually effective in easing symptoms of jumper’s knee. Some doctors may recommend a physical therapist. Treatments such as ultrasound, ice and heat may be used to ease swelling and pain.

In addition, therapists may work on the possible causes of the issue. For example, flexibility exercises for the hamstring and quadriceps muscles can help decrease tension in the patellar tendon where it attaches to the patella. At times, orthotics are issued to place the leg and knee in proper alignment. Furthermore, strengthening exercises to improve muscle balance can help the kneecap to move properly during activity. For patients who are athletes, therapists will help improve their form and reduce knee strain while doing sports. When symptoms are particularly bad, activities that aggravate the pain, including sports, may need to be avoided.

For cases with Sinding-Larsen-Johansson disorder, the symptoms tend to disappear gradually as time passes. Thus, non-surgical rehabilitation may not fix the issue. Treatments may only provide short-term relief.

Post-surgery

For a few weeks after surgery, the patient may be required to wear a hinged knee brace. This brace allows the knee to bend, but it does not allow the quadriceps muscle to fully straighten the knee. In addition, crutches may be needed for a few days after surgery until the patient is able to bear weight without any pain or issues.

Within 10 to 14 days after surgery, patients will need to visit their surgeon to remove their stitches. Patients are then encouraged to start actively bending and straightening the knee.

In addition, physical therapy may be recommended. Initial therapy treatments are designed to control the pain and swelling from surgery. Exercises will also be chosen to improve motion in the knee and tone the quadriceps muscle once again.

Patients will be able to resume their everyday activities gradually. However, they should refrain from high-intensity activities and exercise for at least six weeks. Athletes should also stop high-level sports for six months. Afterwards, it should be safe to resume their normal sports activities as long as the quadriceps muscle has regained normal strength.