Perthes 101

Perthes 101

Everything you need to know about Perthes

Intro to Perthes

Roughly 5 in 100,000 people have Legg Calve Perthes Disease, or simply Perthes. Perthes, most often affects children 4-6 and is more common in boys. Know one knows the exact cause of Perthes but the damage is due to osteonecrosis. The blood supply to the hip is temporarily interrupted causing bone and tissue damage. Without sufficient blood and nutrients, the bone begins to collapse and die.

Perthes occurs gradually. In the beginning Perthes may cause no pain at all or appear as a painful limp. Regularly monitoring progression with x-rays allows specialists to categorize disease progression in stages. Perthes is a variable process. Each child appears differently and responds to differently to treatment.

A mainstay of treatment is activity restriction including bracing or casting and wheelchair restriction to more invasive treatments such as surgery. Early diagnosis and treatment by a Pediatric Orthopaedic Surgeon is associated with positive outcomes. While bone deterioration eventually stops and blood supply is restored, Perthes survivors often experience early onset arthritis, gait abnormalities, muscle weakness, and decreased range of motion in adulthood.

How Bones Grow

Bones are constantly changing and growing, especially in childhood. In fact, bone strength and density peaks in a person’s late twenties. Blood supplies vital nutrients like Calcium and Vitamin D. When blood flow is disrupted, so is the remodeling of the bone.

But bones don’t grow like you might expect; it’s a process called “remodeling.” Remodeling involves the removal of old bone and creation of new bone, carefully monitored by specialized cells that react to stress on that bone.  During childhood bone is deposited at a more rapid rate than it is resorbed causing the bone to grow in both size and density until skeletal maturity.

Children’s bone age may differ from their numerical age but generally follows a predictable pattern. Bones are considered “immature” until they are done growing. This is important because an immature bone has a much greater ability to heal or remodel, than an adult.

For this reason treatment of Perthes is frequently classified by a patient’s age. This may mean a child who is younger at time of Perthes diagnosis is treated with a longer period of initial observation than an older child who is closer to skeletal maturity. This is just one way to classify the extent of Perthes; the extent of bone damage must also be taken into consideration.

Perthes by Age

0-6 Children that are under 6 at onset can expect observation and treatment of symptoms such as pain, limping, decreased range of motion. Typically, this involves rest, activity restriction, anti-inflammatory medications and wheelchairs or crutches as needed.

6-8 Children that are between 6 and 8 at onset have variable presentations which makes the disease stage a very important consideration. Many can be treated non-surgically, similar to those under 6 with the addition of bracing or traction. Others will require surgery.

8-11 For children between 8 and 11 at onset pelvic or femoral surgery is generally recommended to ensure proper containment of the femoral head within the acetabulum and prevent further damage.

Over 11 Children who are over 11 at onset typically do not respond as favorably to pelvic or femoral surgeries. Osteotomy and hip distraction with external fixation are newer surgical treatments which may be provided to these candidates.

For all ages, containment of the femoral head and preserving range of motion through physical therapy are cornerstones of care.

Adapted with permission from International Perthes Study Group,, Texas Scottish Rite Hospital, 2016.

Perthes by Stage

Age is not the only means by which Perthes disease is classified. Children with less damage are generally treated more conservatively.  Conversely, more extensive damage at any age may require more aggressive treatment.

The Waldenstrom Scale is commonly used to stage progression based on the radiographic findings on x rays. The Waldenstrom Scale includes 4 stages: Initial or Avascular Necrosis stage, the Fragmentation or Resorptive stage, the Re-ossification stage, and the final Healed stage.

Stage 1 Initial Stage may last less than a year. The diminished blood flow to the femoral head produces a smaller, more dense, (whiter) appearance of the affected bone on x-ray. The femoral head may appear flattened and the joint space may appear widened.

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Stage 2 Fragmentation Generally lasts between a year to a year and a half. The femoral head begins to fragment or dissolve because of the remodeling process. This results in collapse and even flattening of the femoral head. On x rays the changes noted in Stage 1 may be more severe. The bone appears mottled, or both black and white, on x ray due to the cycle of destruction and regrowth. During this stage the Lateral Pillar, or Herring, classification is used.

Stage 3 Re-ossification This is often the longest stage and can last 2-3 years. New bone fills in areas of necrosis and appears as increased density, which is white on x-ray. Additionally, the shape of the femoral head is more defined on radiographically.

Stage 4  Healed The femoral head continues to remodel until skeletal maturity is reached. The pattern of bone is almost identical to the unaffected side. At this point, the final shape of the femoral head can be evaluated. as well as its position inside the acetabulum, (or socket). At the Healed  stage, the Stulberg system is used to classify prognosis.

Not all patients progress through all stages, particularly patients older than 11 at onset.  Additionally, each stage takes a variable amount of time with stage 3 being the longest. However, patients younger than 6 at onset tend progress through the stages more rapidly.

The Lateral Pillar, or Herring, Classification

There are several methods of classifying the fragmentation stage of Perthes including the Caterall and Salter-Thompson classification systems. However, the Herring classification system is widely used and studies have shown it to be the most accurate.

The Herring classification is used during the fragmentation phase and is based on the height of the lateral pillar of the capital femoral epiphysis on AP imaging of the pelvis.

In layman’s terms, using x-ray the shape, size, and density of the femoral head is measured. A bone that appears whiter, or more dense on x-ray is a bone with less necrosis or destruction. The goal is to provide early prognostic information.

Group A: The lateral pillar maintains full height with no density changes. This is associated with a positive outcome.

Group B: The lateral pillar maintains greater than 50% height. This is associated with poor outcomes in patients >6 years of age.

Group C: The lateral pillar maintains less than 50% height and is associated with poor outcomes across all age groups.

Therapy and Non Surgical Treatment

The Legg Calve Perthes Foundation supports patient centered care. There is no “one size fits all” treatment for Perthes disease. Similarly, we believe you cannot successfully treat Perthes when you treat the hip alone. A well rounded treatment plan includes family counseling, physical and occupational therapy, diet and nutrition considerations, as well treatments to treat the hip targeted at containment and supporting range of motion. Here we focus on some of the common non-surgical medical interventions. Click on our Perthes Toolkit for more information on therapies and resources.

The first step may be activity restriction to minimize weight-bearing and protect the hip joint. This involves substituting running, jumping, and other high impact activities for low impact activities such as swimming. Crutches and wheelchairs may also be recommended. Non-steroidal anti-inflammatory drugs (NSAIDs) or pain relievers such as Motrin, Naprosyn, or Tylenol can be used to alleviate pain. Avoid aspirin, particularly in children under 2. Massage and counseling are also great pain management tools.

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Bed rest and traction may be periodically recommended to decrease pain and strain on the affected joint. Casts and bracing are also used to keep the femoral head contained. The cast is often used for one to two months and maintains the leg in a wide spread abduction. The hip-spica cast and petrie cast are commonly used and keep the legs spread, resembling the letter “A.” Night bracing can be also used to maintain hip flexibility.

It is important to note that these interventions require a lot of adaptation both physical and psychological. Children often experience difficulty accomplishing everyday tasks such as showering, getting out of bed, using the bathroom, or getting in cars. Your child may find it difficult to fit through doors in a petrie cast. Adaptive clothing may be required in a cast and stairs in the home may pose a challenge in casts or wheelchairs.

When so much emphasis is placed on physical restriction, it may be hard to find something your child enjoys doing. Adapting activities to meet new requirements may take some creativity but the reward is great, physically and psychologically. To paraphrase Issac Newton, a body in motion stays in motion. Physical therapy promotes range of motion and muscle tone which can lessen the overall damage of Perthes after the healed stage.



Surgical Treatment

To protect the hip more invasive intervention may be necessary. As with other treatments and approaches to Perthes, this requires expertise and individual evaluation by a pediatric orthopedic surgeon. Some surgeries include:

Arthroscopy Some children experience painful, restricted motion during the active disease phase. Repairing damaged cartilage and removing fragmented pieces of bone within the joint space can help decrease pain and increase range of motion. Small incisions are made at the hip joint to allow for removal of bone fragments, spurs, and repair.

Osteotomy For older children, joint realignment may restore the natural shape of the hip joint. Surgical cuts are made to the pelvis and/or femur and these bones are placed in a more natural anatomical alignment. In some cases the bone is internally fixed with a plate to maintain alignment.

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Contracture release Children with Perthes may hold their affected leg across the body. Over time, this can shorten the muscles and tendons in the leg causing inward strain or contracture. Lengthening the tendons surgically may ease pain and increase flexibility.

New Surgeries are promising and include:

  • Hip Distraction, where pins are temporarily placed through the skin into the pelvic and femur bones to increase the space in the hip joint allowing the femoral head to heal with a more rounded shape.
  • Core decompression involves drilling a hole into the femoral head, removing the dead bone, and allowing the space to relieve pressure on the damaged joint while encouraging revascularization.
  • Femoral neck tunneling, multiple epiphyseal drilling and are concepts of drilling small hole(s) to act as a pathway for new blood vessels to enter the femoral head.
  • Bone marrow Aspirate concentrate (BMAC) injection involves concentrating the child’s bone marrow cells and injecting the cells into the femoral head through core decompression. Potentially these cells differentiate into blood, bone, and fibrous cells.



The long-term prognosis for children with Perthes is good in most cases. After 2-5 years of treatment, most children return to daily activities without major limitations. There is a correlation of the extent of deformity of the femoral head and potential problems in adulthood such as pain and early onset arthritis.

The shape of the femoral head (ball) is largely influenced by the acetabulum (socket) while the bone is healing. This is why “containment” is so important in Perthes treatment. When the ball can sit in the socket, with good joint space, the head can regenerate to a natural shape. When both femoral head and acetabulum (ball and socket) articulate well, the joint operates well reducing risk of arthritis, impingement, subluxation into adulthood.

The Stulberg classification system is used to measure the degree of damage to femoral head by x-rays taken in the healed stage. There are 5 classes of the Stulberg system:


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Classes I and II describe a rounded femoral head with less than 2 mm loss of shape and may have an enlarged femoral head, shortened neck, or steep acetabulum. This is associated with a good prognosis.

Classes III and IV describe a aspherical congruency and a loss of shape up to 2mm. The femoral head is non-spherical to flat, ovoid, or mushroom shaped and may display enlargement of head, shortening of neck, a markedly steep or flat acetabulum. This is associated with mild to moderate arthritis in adulthood.

Class V describes an aspherical incongruency and a flattening of the femoral head. This is associated with severe early arthritis.

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