Specific Hip Conditions

Toxic synovitis is an inflammation of the hip that typically occurs in children from four to six years of age. Although it often occurs in children with evidence of a viral respiratory infection, its cause is unknown. Children with toxic synovitis have a very characteristic story. Most often the child went to bed well or with a slight sniffle the night before. In the morning the child has severe hip pain and is unable to walk. Because the symptoms are so dramatic, the children are immediately brought to the doctor. Often there is a low-grade fever and blood tests may show an elevated white blood cell count and slight elevation of the erythrocyte sedimentation rate. The immediate concern is to exclude a bacterial infection of the hip, which can worsen dramatically over a period of only a few hours, and so these children are often referred to an orthopedist, who may remove fluid from the hip to look for signs of infection. In contrast, I have often seen children with toxic synovitis who are already improving by the time they reach my office. Ultrasound is increasingly being used to differentiate bacterial infection from toxic synovitis. However, if there is any doubt, aspiration of fluid from the hip, hospitalization, and antibiotic therapy are appropriate until the possibility of an infection has been excluded.

Once the diagnosis of toxic synovitis has been made, children may be treated with NSAIDs and rest. They usually recover completely within a few days, though there may be some residual irritability of the hip for several weeks. The prognosis for these children is very good.

A diagnosis of recurrent toxic synovitis should be regarded with suspicion, since true toxic synovitis is not a recurrent condition. Some children have Legg-Calve-Perthes disease (see below) that has not been recognized. In other children, recurrent episodes of synovitis in the hip may be the first manifestation of what will ultimately become obvious spondyloarthropathy. Any child diagnosed with recurrent synovitis should have a thorough evaluation by a pediatric rheu-matologist if possible. Also, toxic synovitis should never be diagnosed in a child over nine years of age, in whom isolated synovitis of the hip is usually the initial manifestation of a spondyloarthropathy (though other causes of hip inflammation must be excluded).

Legg-Calve-Perthes disease (LCP) results from softening of the head of the femur (the long bone of the leg), which gradually becomes distorted and may flatten or crumble (see Fig. 3-3). It is thought that this results from problems with the blood supply to the head of the femur, which may be caused by an injury or congenital abnormality. One report has suggested that LCP occurs far more frequently in the children of parents who smoke. However, problems with the environment or blood supply cannot be the whole answer, since LCP occurs four times more often in boys than in girls.

LCP usually begins in young children (commonly four to six years of age), who are most often noticed to be limping before there is any complaint of pain. Over time, the limp becomes more noticeable and the child may begin to complain of pain. At the earliest stages an MRI may be required to diagnose LCP. However, if the symptoms have been present for more than several weeks, it should be possible to make the diagnosis with a regular X-ray of the hip. This will show flattening of the head of the femur. Most cases of LCP involve only one hip, but in a few children both hips are involved. Premature birth and problems during the newborn period increase the risk of LCP, as does a family history of the disease.

FIG 3-3 Changes in the head of the femur resulting from Legg-Calve-Perthes disease.

Children diagnosed with LCP should be under the care of an orthopedist. Treatment often consists initially of traction followed by casting. Once the cast is removed, physical therapy is important to restore strength and range of motion. The purpose of the traction and casting is to keep the femur properly seated in the hip while decreasing the pressure on the femoral head. Often this allows the bone to reestablish its blood supply and begin to repair itself. The precise details of treatment will depend on the age of the child and the degree of damage to the bone at the time the problem is discovered.

Children with bilateral LCP should be thoroughly evaluated. In some instances, this is a sign of an underlying condition such as hyperthyroidism or sickle-cell disease. In others, the deformed head of the femur may be the result of more widespread conditions, such as multiple epiphyseal dysplasia or spondy-loepiphyseal dysplasia tarda. These orthopedic conditions are recognized by the presence of abnormal epiphyses (the ends of the bone that insert into the joints) in multiple joints, as seen on a complete set of X-rays. The long-term prognosis for children with LCP who are diagnosed early is good. If the disease has been present for a long time, the bone may already have begun healing itself by the time the disease is recognized. In many children, this healing is adequate and things go well. However, in some children, there may be permanent damage to the bone. There is also concern that children with residual damage from LCP may have persistent mechanical problems that will cause them to have mechanical arthritis of the hip, leading to problems when they become adults.

Sickle-cell anemia may cause pain in the bones because of blood vessels being blocked by abnormally shaped red blood cells. This may occur in the blood vessels that supply the hip and result in damage to the femur. When it does, it looks exactly like—and essentially is—LCP. In children with severe sickle-cell anemia, other bones may be damaged also and there may be widespread joint problems. Usually a child with these problems will have been recognized to have sickle-cell disease long before the bone problems begin.

There are two basic types of infections that must be considered in children with hip pain. Septic arthritis is an infection in the joint itself, whereas osteomyelitis is an infection in the bone. In the hip, septic arthritis is more common than osteomyelitis.

For many years Haemophilus influenzae was the bacterium responsible for most septic infections of the hip, but now most children are vaccinated against this infection and it has become rare. Staphylococcal and streptococcal infections of the hip do still occur. It is also possible to have a tuberculosis infection in the hip. At present, Lyme disease may be the most common cause of infectious arthritis involving the hip for people living in endemic areas of the United States (see Chapter 8).

Most infections in the hip are sudden in onset and associated with rapidly worsening symptoms of pain, fever, and difficulty in walking. A child with these symptoms should be seen by a physician as soon as possible. Tuberculosis may cause slowly worsening symptoms of hip pain. A child with an acutely painful hip should be seen by an orthopedist. Although there may be some initial confusion between children with infections and those with toxic synovitis, children with toxic synovitis usually improve rapidly without treatment. If there is serious concern that the joint may be infected, it should be aspirated for appropriate studies, including bacterial cultures. Chronic hip pain associated with stiffness is more likely to be the result of enthesitis-associated arthritis involving the hip (see Chapter 7), but the possibility of an infection should always be given careful consideration.

Osteomyelitis often occurs near the ends of the bones and produces pain in the joint near the infection. The pain of osteomyelitis may wax and wane, but the child is never free of pain and the pain usually gets steadily worse over a period of a few days. Children with osteomyelitis often have fevers and look ill, but occasionally the child looks well and is only limping. If the infection has been present for more than a few days, it should be easy to detect 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 at the earliest stages when pain is present.

Pain in the lower abdomen near the hip may be a cause of confusion. When dealing with younger children, it can be difficult to know exactly where the pain is coming from. Children with severe lower abdominal pain may walk with an abnormal gait, suggesting arthritis or an infected hip. A ruptured appendix should always be considered in children with pain in the right side of the pelvis without an obvious explanation.

Osteoid osteomas are benign tumors of the bone. See the section on these tumors under "Knee Pain," above.

Slipped capital femoral epiphysis (SCFE) is an injury to the growth plate of the femur (the bone in the upper leg) that results in the epiphysis, the growing end of the bone, slipping off the shaft (see Fig. 3-4). This injury occurs most

FIG 3-4 This is the characteristic appearance of a slipped capital femoral epiphysis. The epiphysis is the roundedportion of the bone in the hip joint. It has literally slipped off the end of the long bone (femur). Compare this with Fig. 3-3, where the epiphysis has crumbled but remains in the proper position.

often in boys between the ages of ten and fifteen years but may occur in girls and occasionally is seen in younger children. It occurs more often in African Americans and in children who are overweight. The most dramatic cases of SCFE occur as an injury with sudden slipping of the epiphysis. This produces acute hip pain and inability to walk. X-rays to confirm the diagnosis should include both standard views and "frog leg" views in which the child is instructed to bend the knees and spread them apart. SCFE may be missed on standard views of the hips, but the slippage is usually obvious on the "frog leg" views.

Some children develop SCFE on a more gradual basis. No one is sure why this happens. These children will have progressive onset of pain and stiffness in the involved hip. SCFE may also occur in children with hypothyroidism and other growth problems. In about one-third of children, the disease is bilateral. The slip on the opposite side may be present when the first SCFE is noted or may occur later.

Because deep pain may be difficult to localize, the child may describe the pain as coming from the groin, the thigh, or the knee instead of the hip. Children with a chronic slip usually have an obvious limp. The changes in the bone may force the hip on the affected side to rotate outward. The abnormal alignment of the bones that results triggers muscle spasm. This muscle spasm causes children with chronic SCFE to report stiffness with rest and increased pain with activity, symptoms that suggest arthritis. The chronic slippage should be evident on X-ray. In uncertain or difficult cases, an MRI may be useful to confirm the diagnosis.

Orthopedists treat SCFE by putting a pin in the bone to hold the epiphysis in place while the bone heals. If detected and treated early, children with SCFE usually do well. Chronic SCFE that is not promptly treated may result in damage to the head of the hip bone (femur). This can result in a permanent limp, difference in the length of the two legs, and early onset of arthritis due to mechanical damage.

Iliotibial band syndrome, discussed above under "Knee Pain," may also produce pain at the hip. In these cases, children typically complain of a snapping sensation with certain movements. Often this is associated with trochanteric bursitis (see Fig. 3-5 and the next section), which may be the result of excessive activity. Iliotibial band syndrome may also occur in children with a spondyloarthropathy (see Chapter 7). Iliotibial band syndrome itself is a benign condition that does not normally require therapy. However, if the snapping is associated with a sensation of pain, further evaluation is warranted.

The greater trochanter is the large bump that sticks out on the side of the femur where it turns toward the knee. Because this protrusion is just under the skin at the side of the hip, it is protected by a bursa. The bursa is a small sac of fluid that allows easy movement of the tissues over the bone (see Fig. 3-5). With excessive running or other activities, this bursa may become inflamed, a condition called trochanteric bursitis. Typically, this is a problem of teenagers or adults and not younger children. The classic complaint is pain along the side of the leg that can be reproduced by pressure over the greater trochanter. The pain

FIG 3-5 Trochanteric bursitis results from irritation in the fluid-filled sacs (bursas) that are located just under the skin and over the greater trochanter.

often is described as moving both up and down the side of the leg. Trochanteric bursitis is treated with ice, stretching exercises, and in more severe cases NSAIDs. In rare cases, children require injection of steroids into the bursa for relief.

The hip and pelvis may be the site of avulsion fractures, in which a tendon pulls off its attachment to the bone. These injuries are usually associated with the sensation of a snap or pop and immediate pain. X-rays typically confirm the diagnosis. Stress fractures in the femur or pelvis may come on more slowly. Children who participate in athletics may complain of progressively increasing groin pain with activities. Although stress fractures in the femur are not always evident on X-rays, most often they are obvious on bone scan. MRIs may also be helpful to confirm the diagnosis.

Congenital hip dislocation results from improper formation of the acetabulum, the socket on the pelvis into which the head of the hip bone inserts. This condition should be diagnosed in early childhood. Often it is first suspected when the pediatrician notices a "hip click" in the nursery. This is a sensation of clicking when the hip is moved in what is called the Ortolani maneuver. In most children, the hip click will go away after a period of observation and perhaps "double diapering" (the bulk of an extra diaper forces the legs into a frog leg position, which helps keep the head of the femur properly positioned). However, if it persists, orthopedic evaluation is needed.

Children with congenital hip dislocation walk with a waddling gait that is obvious to a trained observer but may be overlooked by parents. If the hip dislocation is present on only one side, it may be suspected when the parents or physician notice that the line under the curve of the buttock is not in the same position on both sides (asymmetric gluteal folds). The child will have decreased range of motion of the hips and abnormal X-rays. However, because the condition has always been there, the child may never have complained of pain.

Congenital hip dislocation is easily diagnosed if appropriate X-rays are done. It is treated by orthopedists. Cases detected in early life can often be managed without surgery. However, in severe cases surgical correction is necessary. If it is not detected and corrected, the hips may become severely damaged because of mechanical damage leading to degenerative arthritis. It is important that any child who walks with a waddling gait be appropriately evaluated.

The hip joint is rarely the first joint involved in children with juvenile arthritis (see Chapter 5), but it may become involved over time. In contrast, the hip is commonly the first joint involved in children with spondyloarthropathies (Chapter 7). These children often begin with complaints of stiffness in the hip or lower back when they wake up in the morning. Over time, they develop symptoms in other joints. However, they often have to be asked about and examined carefully for evidence of pain or limitation in the back, wrists, knees, or ankles, as they will not associate the complaints in other joints with their hip pain. Since spondyloarthropathies rarely begin in children before the age of ten, younger children with hip pain must be carefully evaluated to exclude other causes.

Mechanical arthritis may occur in children who have had damage to the bones of the hip from SCFE, congenital hip dislocation, or previous infection. These conditions and the mechanical cause of the arthritis are often evident on routine X-rays. If the routine X-rays do not provide an explanation for the pain, an MRI may be necessary.

Some children with muscle or systemic diseases will experience significant pain in the muscles in the front of the thigh. This pain may be mistakenly reported as coming from the hip or the knee (and in fact, hip and knee problems may cause pain in those muscles). Whenever a child complains of chronic pain and disability without obvious findings in the bones or joints, a careful evaluation for muscle or systemic diseases should be performed, including blood tests to measure muscle enzymes, thyroid function studies, a complete blood count, and appropriate MRIs and X-rays.

Unicameral bone cysts are large cystic malformations of the bone that may occur in the femur or the humerus. They usually do not produce any symptoms unless there is a fracture. Like bone cysts near the knee, they should be cared for by an experienced orthopedist. Bone tumors should be considered in the evaluation of children who initially have pain in the hip as well.

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