Perthes disease, more formally known as Legg-Calvé-Perthes Disease, is a condition that affects growing children, most commonly boys between 5 and 7 years old, in which there is a decrease in the circulation of blood to the head of the femur (the thighbone), which acts as the ball that normally sits in the socket of the hip joint. When the femoral head does not receive enough blood in this manner, it becomes susceptible to collapse or small fractures, which can deform its normal spherical shape.
The clinical course of the condition is varied and somewhat unpredictable. Affected children may experience pain in the hip, the upper leg, or the knee, and can develop a limp. Full range of motion of the upper leg often becomes limited, and a child may have difficulty raising the thigh to the side, or rotating the leg inward. Alternatively, the condition may develop asymptomatically, in which a child experiences no pain or limp, and Perthes disease is only detected on x-rays. While most children, including those that experience symptoms, end up with healthy joints and recover normal hip function, in some children the process of collapse in the femoral head leads to a misalignment of the ball in the socket and causes joint problems, such as arthritis, later in a child’s life.
The hip has a unique combination of structural features that permit the transmission of tremendous forces (including the weight of the body) between the pelvis and the thigh, while still allowing for an extensive range of motion. The largely spherical head of the femur sits in an area of the pelvis bone called the acetabulum, which acts as a smooth, cup-shaped socket. There is a joint capsule that sits around the joint and is made up of a series of ligaments, thick fibrous structures found throughout the musculoskeletal system that attach bones to other bones. This capsule surrounding the joint insures that the ball remains snugly in the socket, throughout the movements of the upper legs. Smooth, slippery cartilage at the center of the socket and at the tip of the ball, as well as a thin layer of the body’s natural lubricating material, called synovial fluid, allow the two bones to slide past each other, much like a well-greased ball bearing.
Like all long bones in the human body, the femur does most of its growing not in the middle but at the ends of the bone during childhood, in a region of the bone known as the epiphysis. The bones of children also have a large component of cartilage, which is slightly softer connective tissue that slowly gets replaced by calcified bone. Because the bone and cartilage cells in the epiphysis are constantly dividing and regenerating in a young child, this area critically depends on a steady supply of oxygen and nutrients from the blood that runs through tiny vessels and channels in the bone.
As previously mentioned, a decrease in circulation to the femoral head is generally what leads to injury to the hip in Perthes disease. However, it remains unclear why, exactly, the circulation is affected this way, making the true cause of the disease unknown.
The progressive stages of the condition have begun to be characterized, however. The first phase is called the ischemic phase, which means that the bone cells are not receiving enough blood, in particular the cells in the epiphyseal region, the critical region of growth described above (in ‘The normal hip’ section). This results in a process called avascular necrosis in the epiphysis, in which the bone and cartilage cells gradually die from a lack of oxygen and nutrients. Over a period of weeks or months, circulation usually increases again in a phase known as revascularization, and the bone and cartilage cells become replenished and attempt to regenerate the surrounding bone. However, during this period, the femoral head becomes soft and therefore prone to small fractures, collapse and deformation. When the spherical head of the femur becomes deformed in this way, it may become misplaced from its normal location in the socket. Because so much force is transmitted over the hip joint, over time even a small amount of misalignment between the ball and the socket can lead to excess wear and tear in the cartilage of the joint, which causes arthritis, and possibly chronic pain and stiffness.
There is also scientific evidence that a genetic defect, most likely in the genes that code for cartilage cells in the epiphysis, is a contributing factor to Perthes disease. The simple fact that Perthes disease is more common in people whose family members had the condition lends support to this theory.
Because the condition is relatively common, but its precise precipitating factors remain a mystery, there is ongoing research at various medical centers in the U.S. devoted to identifying these causes and improving the treatment and prevention of the condition.
Perthes disease is almost always diagnosed with x-rays of the hip, usually performed after a child is brought to the doctor with complaints of hip or leg pain or is noticed to have a limp when walking. Because the x-ray appearance is quite specific for this condition, diagnosis is usually made fairly easily on this basis. Occasionally, MRI of the hip is used as a compliment to x-rays because of its enhanced ability to show the femoral head and the extent of collapse that may have occurred. In some instances, bone scans are also useful.
There are several different ways to treat Perthes disease, ranging from simple observation to active treatments, such as surgery. For many children, particularly those younger than 6 years old, regular checkups with diagnostic x-rays are the best way to manage the condition. The older a child develops symptoms or is diagnosed with the condition, the more likely he or she is to require additional forms of treatment. If x-rays demonstrate that the small fractures or collapse of the hip causes it to become misaligned or has dislocated from the socket, casting or bracing is often employed to provide joint stability while still allowing weight-bearing in the walking child. The Scottish Rite brace and the Petrie cast are two commonly utilized devices, and are usually worn for 1 to 2 years. Severity of pain and hip stiffness are other important indicators of the need for treatment. Mild pain killers, such as Advil, Motrin, or other NSAIDs (non-steroidal anti-inflammatory drugs) are often prescribed, and crutches—to reduce the amount weight placed on the hip—are commonly utilized, effective measures for relieving symptoms. If the movement of the thigh is significantly restricted, admission to the hospital may be appropriate to place a child in traction, which means that the joint is gently stretched over time by a device with straps that attach to the legs or feet, and physical therapy is concurrently initiated. However, if such measures do not enhance the flexibility of the hip, the best treatment may be surgery, in which the muscular structures surrounding the joint are released, so as to correct alignment of the bones and promote normal growth of the joint into adolescence and adulthood. Another operation that may need to be performed is a pelvic osteotomy, in which the bony socket of the hip joint is made more stable for containing the head of the femur. In general, both conservative methods of treatment and the various forms of active treatment have high rates of favorable outcomes, and long-term disability from Perthes disease remains relatively rare.
Perthes disease can present a difficult challenge for some children and their parents. Hip pain and the development of a limp can temporarily affect a child’s ability to play normally like other children. In addition, treatment of the condition, including casts, braces, and surgical procedures, may require a period of recuperation before resumption of full activity. However, children with Perthes disease, whether they receive active treatment or simply get observed, do remarkably well down the line, and very few suffer lasting disability. With few exceptions, parents can expect their kids to have a future filled with a full range of activities, from casual walking to competitive sports. Managing the condition may require some adjustments early on, but seeking continued medical guidance from your orthopaedic surgeon and maintaining a positive outlook is the best way for parents to help their children. For the vast majority of children with Perthes disease, a normal, healthy adolescence and adulthood lies ahead.
Naturally, you may have other questions about Perthes disease that are not answered in the above summary. As your orthopaedic surgeons, we welcome any and all questions you may have, which we urge you to pose during your next office visit. We have listed several additional websites below that further explain Perthes disease and some of the services and support groups available to children with the disease and their parents: