What is it?

Sinding-Larsen Johansson Disease (SLJ) is a possible cause of knee pain in 8-to-13-year-old active individuals. Children often complain of pain and swelling at the bottom of the knee cap that may be worsened by climbing stairs, running, jumping, deep bending of the knee, or kneeling. Children may develop pain during periods of increased activities (such as the beginning of the season or a sports camp), or periods of rapid growth.

SLJ is a painful irritation of the growth plate (apophysis) at the bottom of the knee cap (patella). This type of irritation is sometimes called an apophysitis. Children have open growth areas on their bones that are made of cartilage where muscles and tendons attach. These growth areas can become irritated with repetitive stress or a sudden blow to the area.

Causes

The knee cap attaches to the shin bone or tibia through the patella tendon. The quadriceps or large muscle of the thigh pulls on the knee cap and patellar tendon to straighten the leg. Each time the leg is straightened, the patellar tendon is subjected to tension and the cartilage growth plates on both the shin bone and the knee cap are pulled on. Repeated tension and pulling on these regions may lead to cracks or small areas of trauma in the cartilage of the growth plate, resulting in pain and irritation. Apophysitis can also occur when someone kneels or falls on the growth area. With rapid bone growth, tendons may put increased tension on the growth areas as the tendons and muscles become tight.

Risk Factors

• Repetitive running and jumping activities
• Increase in training (for example, in the beginning of the season, summer camp, increased running mileage, overlapping sport seasons)
• Sport specialization - Doing the same sport year round without adequate breaks places stress on the same areas of the body
• Fall on the front of the knee
• Improper training technique, including poor form for conditioning, running, and/ or jumping.
• Improper foot wear
• Muscle tightness in the leg
• Weak hip or core muscles

Symptoms

Athletes complain of a dull, aching pain at the bottom of the kneecap. This pain may become worse when walking up stairs, kneeling or squatting, running or jumping. They may have swelling or a bump at the bottom of the kneecap.

Sports Medicine Evaluation

A sports medicine physician will ask the athlete questions about symptoms and perform a careful physical examination. The physician will ask about the athlete’s training program, changes in exercise routine, and prior injuries that might lead to changes in how the athlete runs or jumps. The physician will examine the knee to determine the location of the pain, test strength to identify deficits in strength or flexibility. They may watch the athlete walk, run, jump, or balance to evaluate for problems with leg alignment or form. 

X-rays may be ordered to ensure that there is not a fracture or cartilage injury, however it is not necessary for the diagnosis. Sometimes x- rays show cracks or fragmentation of the knee cap. Magnetic resonance imaging (MRI) is not typically ordered unless the diagnosis is not clear, or there are concerns regarding possible complications.

Treatment

Symptoms can be managed with ice and anti-inflammatory medications which include non-steroidal anti-inflammatory medications such as ibuprofen or naproxen. Sometimes, a brace or a patellar tendon strap can be helpful. In activities such as volleyball or basketball, where hitting the irritated area is common, wearing a protective pad can be helpful.
If the athlete is limping, he/she should rest completely from activities that make his/her pain worse, until a doctor states that he/she is able to return to his/her activities. Sometimes, when the pain is not severe, a doctor may allow the athlete to play but may discuss reducing activities that put strain on their knee, including reducing mileage, reducing the number of sports the athlete participates in, or the number of teams that they play for. 

Physical therapy or home exercises are an important part of treatment. Exercises will be aimed at stretching of the quadriceps and hamstrings, as well as strengthening of the core, hip, and leg muscles. Improving strength and flexibility decreases the stress put on the patella tendon and its attachments. It is important that athletes do the exercises at home and not just at therapy sessions, and that they continue the exercises after therapy is complete, to prevent further episodes of knee discomfort. 

It sometimes can be helpful to discuss the injury with coaches to assess if there are any correctable form issues that can be changed to prevent further injuries.

Prevention

As an overuse injury in children, gradually increasing exercise when a new activity is started can prevent this injury. The general rule is to increase intensity, duration, or volume by no more than 10% a week to avoid injury. Early sport specialization may lead to a greater chance of having overuse knee pain, as children do not have a break from the repetitive motions that cause it. Ensuring children have a break from a specific sport for at least one month a year, and that they only play on one team during a season, can help prevent overuse knee pain. Diversifying their activities, as well as ensuring periodic rest, may help prevent overuse injuries. Additionally, minimizing the amount of activities that strain the knee can help prevent overuse knee pain; these include minimizing unnecessary running, jumping and/ or squatting. Active children should incorporate core work and stretching into their activities to minimize overuse injuries. It can also be helpful to periodically look at children’s form during their activities.

Return to Play

Athletes can continue to play if they have minimum discomfort. They should continue symptomatic care and modify their activity to minimize any unnecessary jumping or running. If an athlete is limping, favoring his/her knee, or has knee swelling, rest may be necessary; the athlete should be removed from the game immediately. Playing through limping or severe pain may result in a complete tear of the tendon off the growth plate (avulsion), or could result in another injury. If a doctor recommends that an athlete rest, it is important to follow his/ her instructions until the athlete is cleared. Typically, an athlete must have full strength and range of motion to return to activity. He/she also should be able to play limp-free. SLJ is a self- limited condition. When the athlete is done growing and the growth plate closes, the pain from SLJ should resolve.

AMSSM Member Authors
Caitlyn Mooney, MD and George Pujalte, MD

References
Anderson, S.J., Harris, S.S. & editors., 2009. Care of the young athlete, United States: American Academy of Pediatrics.
Houghton, K.M., 2007. Review for the generalist: evaluation of anterior knee pain. Pediatric Rheumatology, 5(1).
Medlar, R.C. & Lyne, E.D., 1978. Sinding-Larsen-Johansson disease. Its etiology and natural history. JBJS, 60.
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