The long bone of the thigh is called the femur. The upper portion of the femur bone contains a round, dome-shaped structure known as the head of the femur. The head of the femur articulates with a concave cavity (the acetabulum) on either side of the hip bone and forms the hip joint. It is a ball and socket type of joint surrounded by muscles, ligaments, and tendons. The hip joint's main function is to support the weight of the body. In addition, it helps with the wide range of movements of the lower limb.
What Is Perthes Disease?
Perthes disease is a hip disorder affecting the hip joint. The disease was initially thought to be associated with tuberculosis (TB). It was in 1910 that the disease was recognized as a separate entity by three physicians working independently. Their names were Arthur Legg, Jacques Calve, and Georg Perthes. Hence, this disease is also called Legg-Calve-Perthes disease, named after these three physicians.
Perthes disease is most common in children aged five to ten years. Boys are more prone to develop this condition, but the severity of the disease is high in girls. In a few cases, both the hip joints are affected. The other names of Perthes disease are coxa plana, pseudocoxalgia, osteochondritis deformans coxa juvenilis, and osteochondrosis capital femoral epiphysis.
Which Bones Are Affected by Perthes Disease?
The femur (thigh bone) is the only bone affected by Perthes disease. In children with Perthes disease, the round spherical head of the femur, which articulates with the hip socket, stops growing. This is due to the disruption of blood supply to the femur head, and as a consequence, the bone cells die (avascular necrosis) by the lack of oxygen supply.
Over the course, the healing of the bone occurs by new penetrating blood vessels which remove the dead bone cells. As a result, there is a loss of bone mass and weakening of the femur head. Ultimately the bone loss leads to the collapse of the femur head with permanent deformity in the shape of the bone.
What Are the Causes of Perthes Disease?
The exact cause of the disease is idiopathic (unknown reason). Both the developmental and environmental factors contribute to disease development. Some proposed hypotheses are,
Another most accepted theory says that the femoral head blood supply is compromised after the age of 5 years. Normally, the femoral head is supplied by three arteries and in natural course of development, one of the arteries get subdued after the age of 5 years. The blood supply is restored after the age of 10 years. Hence, the child is most prone to develop Perthes between 5 to 10 years of age.
What Are the Stages of Perthes Disease?
The condition can be categorized into four stages depending on the evolution of the disease. They are;
This is the initial stage of the disease. There is a lack of blood supply to the femur head, and the upper-end part of the bone is necrosed (dead). The space between the femur head and the hip bone socket is increased. This stage may last for several months.
In this stage, there is ingrowth of new blood vessels and tissues. The dead bone cells are removed and replaced by immature bone tissues. Thus, the bones are very weak in this phase. It is at this stage that there is collapse and loss of structural integrity of the femoral head leading to deformation. The femoral head may extrude from the hip socket.
New bone starts forming in this stage. The re-ossification stage is the longest stage that may exist for a few years.
During this stage, complete healing is done, and depending on the severity of the disease, the residual shape of the femur head may be spherical or distorted.
What Are the Symptoms of Perthes Disease?
Characteristic presentations of Perthes disease are:
Limping but without pain.
Pain may be present along with limp in some cases.
Difficulty in spreading the legs away.
Altered walking style.
How to Diagnose Perthes Disease?
Clinical Examination: Physicians may check the movements of the hip joint.
Imaging Studies: An X-ray of the pelvis which includes both hips is the most appropriate view. The opposite hip is required for comparison. A lateral view should also be obtained to look for the position of the femur head in the acetabulum. With the easy availability of magnetic resonance imaging (MRI), early diagnosis of Perthes disease is possible even when X-rays are normal.
How to Treat Perthes Disease?
The goal of Perthes disease treatment is to prevent deformation of the femoral head, prevention of stiffness and maintenance of a good range of movements, and prevent or correct the growth disturbances.
Containment of the femoral head within the hip socket helps to prevent deformation as the socket acts as a mold to keep the head spherical. This can be done in two methods,
Medication: Painkillers are recommended to reduce the pain.
Rest and Weight Relief: This method was primarily directed at avoiding weight by bed rest for a prolonged period (up to two years).
Supporting Devices: Casting and bracing are used to temporarily contain the femur head within the hip socket until definitive treatment is undertaken. During the developmental stage, the casting helps to mold the femur head to a normal position. Petri cast is a type of casting that has two long leg cats that hold the legs apart and are supported by a bar in the middle. The application of the cast can be performed under the guidance of an arthrogram (a small amount of dye is injected into the hip joint, and a series of special X-rays are made).
Osteotomy is the most common and preferred surgical procedure to treat after effects or deformity caused due to Perthes disease, where the bone is cut and realigned or repositioned such that the femur head fits within the acetabulum.
Femur Osteotomy: A piece of bone is removed from the femoral shaft, and the bone is pushed into the hip socket minimizing the shortening of the bone.
Pelvic Osteotomy: In this method, the hip bone is altered to reorient the socket or create a bony shelf for the femur head.
Perthes disease can affect the child’s normal living. The treatment outcome depends on the age of the patient, the severity of the condition, and the extent of movement at the hip. In most cases, the treatment outcome is good, and children may have normal adulthood without further hip problems. In a few cases, there will be persistent hip pain and a high risk of developing arthritis during adulthood.
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