Osgood-Schlatter disease is the result of inflammation of the patellar tendon where it attaches to the lower leg. As children grow, it takes time for the tendons (tissues that attach muscle to bone) to become firmly attached to the bone. During periods of rapid development, such as from nine to fifteen years of age, children's muscles often strengthen more rapidly than the tendon-bone attachment does. Running and kicking, such as while playing sports, leads to repeated pulling on the tendon where it attaches to the bone, and the child develops inflammation at that spot. As a result, the anterior tibial tubercle (the bump just below the knee) becomes swollen and tender (Fig. 3-1).
The pain in Osgood-Schlatter disease is brought on by activity and relieved by rest. It is never associated with stiffness or swelling of the knee itself, only the bump below the knee. It does not cause pain when children wake up in the morning, and it does not wake children up from sleep. The key to diagnosing Osgood-Schlatter disease is to realize that the pain is not in the knee (although that is how the children usually describe it). On careful examination, the knee is entirely normal. The pain is reproduced by pressing on the anterior tibial tubercle (the prominent bump just below the knee). Most often the tenderness is present on both sides, but it may be only the dominant side (e.g., the right if the child is right-handed). The key to treatment is rest, so the inflamed tendon and bone can heal and the tendon-bone attachment can become stronger and withstand the pulling by the muscles.
Sinding-Larsen-Johansson disease is similar in its cause to Osgood-Schlatter disease. This condition is common in the early teenage years as well as among teenagers who are doing a lot of jumping in sports such as basketball and volleyball. Jumping increases stress on the knee, with sudden pulling on the tendon that attaches to the bottom of the kneecap (patella). As a result, these children complain of knee pain whenever they jump. On examination, they have pain when the bottom of the kneecap is pressed (see Fig. 3-2). This condition should be treated by resting the knee and avoiding jumping activities. Jumper's knee is a more severe injury occurring in older children, though the mechanism of the injury is the same. In jumper's knee there is a deep tear of the tendon itself that may ultimately require surgery to relieve the pain.
Chronic knee pain can be caused by a number of mechanical conditions that primarily result from excessive wear and tear on the knee and surrounding tissues. Chondromalacia patella or patellofemoral dysfunction causes knee pain that is much worse when going downhill or downstairs. Despite the large number of children and young adults who suffer from this condition, it is poorly understood. Although there are many proposed treatments for patellofemo-ral dysfunction, only two are generally agreed upon. The first is to avoid the activities that aggravate the condition. The second is a program of exercises that involve lifting the leg as it is held straight, which increases the strength of the muscles around the knee without bending it. Osteochondritis dissecans is the development of a dense area of damaged bone along the edge of the joint line. This may be the result
of direct trauma or overuse. It is a common injury in children who have continued running and jumping activities despite pain. It may respond to extended immobilization, but in some cases the fragment of damaged bone will fall into the joint. If this happens, the knee may lock and surgery may be required to remove the fragment. Finally, iliotibial band syndrome can cause pain along the thigh and the outer edge of the knee. It is caused by tightening of a band of tissue that runs along the outside (lateral) edge of the leg and anchors to the knee. The pain comes on with running, but only after an extended period. It is often aggravated by climbing stairs, in contrast to chon-dromalacia patella, which is made worse by going downstairs. A program of stretching and leg-strengthening exercises is often sufficient to correct this problem.
Osteoid osteomas are benign tumors of the bone, much like knots in wood. Often they never cause difficulty. However, in some children they cause pain. Most often the pain occurs in the middle of the night and is sufficiently severe to wake the child. They occur in boys more often than girls and frequently become symptomatic during the teenage years. They are most common in the region of the hip (see "Hip Pain") but may occur either above or below the knee. Osteoid osteomas around the knee are usually easily diagnosed on routine X-rays, but sometimes a CAT scan is required to recognize them. The pain from an osteoid osteoma is usually easily relieved by acetaminophen or ibuprofen. All children in whom there is any possibility that the lesion may be a serious bone tumor and all children whose pain is not easily relieved by these medications require careful evaluation by an orthopedist with extensive experience in these lesions.
Plicae are folds of synovial tissue that may be seen in the knee on MRI. They are a normal finding and not usually a cause of pain. If a child has vague unexplained knee pains and a plica is noted on MRI, orthopedists may suggest arthroscopic surgery. However, there is a good chance that the plica is not the cause of the pain. Proper treatment of children with plicae centers on excluding other causes of the pain. Once that has been done, most children are advised to avoid the activities causing pain. If the pain persists despite these measures or the activity cannot be reasonably avoided, the family may wish to consider surgery. Since early arthritis is accompanied by thickening of the synovium, it is not rare for a child with arthritis to be misdiagnosed as having plicae.
Plant thorn synovitis is an arthritis that occurs in children who have fallen on a palm frond, cactus thorn, or similar piece of sharp plant material and a part of the plant has broken off inside the knee. The knee is usually red and hot with no history of injury. The key to recognizing plant thorn synovitis is a proper history. Usually the child lives someplace warm (e.g., Florida, the Caribbean, southern California) or traveled there several weeks before the problem started. The child is typically four to six years old—just old enough to get out of sight and fall down. He or she had a small cut on the knee that healed quickly. No one remembers this cut when the knee is hot and swollen weeks later. It is important to recognize plant thorn synovitis because it will not respond to antibiotics or nonsteroidal anti-inflammatory drugs (NSAIDs). Proper treatment requires a synovectomy (cleaning out all of the inflamed tissue lining the knee). When this is done, the diagnosis of plant thorn synovitis can be confirmed by looking at the tissue under polarized light. This will show starch granules from the plant material that broke off inside the knee.
Blount's disease refers to bowing of the legs (genu varum). Young children may develop Blount's disease without any apparent explanation. There is a sudden shift in growth of the tibia (the main bone in the lower leg) and the inner edge no longer grows as well as the outer edge. With progressive growth of the outer edge the legs are forced to bow. In small children, this is most often painless and it affects both sides. In teenagers, Blount's disease is often associated with obesity. In these children, it is suspected that the excessive weight puts too much stress on the inner side of the tibia and the growth plate is damaged. Under these circumstances, one side may be affected and not the other. Blount's disease in teenagers may be associated with progressive pain. At first the pain may be intermittent and relieved by acetaminophen or other pain relievers, but over time it may steadily worsen. If it is left untreated, the pain will continue and the damage to the joint may result in the premature development of mechanical arthritis. An orthopedic surgeon should monitor children of all ages with Blount's disease. Bracing and surgical intervention are sometimes necessary.
There are two types of infection that must be considered in a child with knee pain. Septic arthritis is an infection in the joint itself. Osteomyelitis is an infection in the bone. In the knee, osteomyelitis is more common than septic arthritis. Often osteomyelitis occurs near the ends of the bones and produces pain in the joint near the infected bone. The pain of osteomyelitis may wax and wane, but the child is never free of pain. In children with osteomyelitis, the pain usually gets steadily worse over a few days at most. These children often have fevers and look ill, but occasionally the child looks well and is only limping. If the infection has been present for a period of time, it should be easy to see on X-rays. However, during the first few days after an infection begins, the X-ray may not show changes. Bone scans and MRIs will demonstrate infections in the bone even at the earliest stages.
A sympathetic effusion has its cause elsewhere in the leg but produces symptoms in the knee. In this situation, there may be an infection or a tumor (even leukemia) in the bone. At the same time the child will complain of pain and have an obviously swollen knee. Aspiration of the knee will show fluid that suggests arthritis and not an infection. The key to suspecting this situation is that these children are in more pain than would be expected from arthritis. In addition, careful examination will indicate that they are very tender in the shaft of the bone, not just in the joint itself.
Unicameral bone cysts are large cystic malformations of the bone that may occur in the femur (also in the humerus, the bone of the upper arm). They usually are entirely asymptomatic unless there is a fracture, in which case the child should be cared for by an experienced orthopedist. Following healing of the fracture, the orthopedist may choose to treat the lesion by direct injections of corticosteroids or curettage. Aneurismal bone cysts differ in having a significant blood vessel component in the cyst. They tend to grow more rapidly than unicameral bone cysts and are more likely to be discovered because they are causing pain. Like unicameral bone cysts, they are easily found by routine X-ray. The majority of bone cysts are minor. However, because they can be associated with more serious problems, children with bone cysts should be referred to an experienced orthopedist for evaluation.
While many bone tumors are benign, some are malignant and life-threatening. A full discussion of the types of bone tumors and their treatment is far beyond the scope of this book, but like tumors elsewhere, bone tumors begin very small and grow relatively slowly. Often they are easily visible on routine X-ray by the time they are producing pain.
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