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What is Perthes?

Perthes, also known as Legg-Calve-Perthes, is a hip condition that occurs in children under 10 years old, most commonly in boys ages 4-8 .  Very generally, Perthes is a condition where the hip collapses due to poor blood supply.  There is a lot of variability in severity, and most kids recover well, but we will discuss most aspects of the condition below.

You may be wondering what blood flow has to do with our hip bones.  Bones are just blocks of calcium right?  Actually,  our bone might be covered by calcium but they aren't a simple block because there are living cells and constant changes occurring within the bone.  Our bones are more like trees, which are very strong but need nutrients to survive.  Our bones similarly need nutrients from our blood to keep them strong.  If they dont get the nutrients they need, the bone will scrivel up like a plant that hasnt been watered. 

In Perthes, a disruption in blood flow causes the hip bone to schrivel up and die (medically called "avascular necrosis" or "osteonecrosis").

To better understand the condition, lets quickly review the anatomy of our hip.  

The hip is a “ball-and-socket” joint where your thigh bone (the femur) joins with the pelvis (the acetabulum).  The femur is the “ball” while the pelvis is the “socket”.  Perthes affects the "ball" portion of the hip, which is part of the femur bone, called the "femoral head".  A normal femoral head is a nice circle which allows our hip to glide smoothly as you flex and rotation your leg.  In Perthes, once the femoral head loses its blood supply, it begins to wither away and the nice circular shape starts to flatten like a pancake.  This is known as the hip collapsing.

Perthes occurs in 3 phases.  The Initial Phase occurs when the blood supply is lost and the bone is unhappy but the femoral head is still a nice circle.  The bone doesnt schrivel up immediately, and this Initial Phase lasts about 4 - 6 months.  Phase 2 is called the Fragmentation Phase, which lasts about 18 months.  This is when the bone actually collapses. Phase 3 is the Re-ossification and Remodeling Phase, where the body recovers and does its best to reform a normal hip.

How is Perthes diagnosed?

A child with Perthes will report hip and groin pain and will often walk with a limp.  Initially the limp is caused by pain, but if the condition progresses, and the hip collapses, the hip muscles (called the hip abductors, specifically the gluteus minimus and medius muscles) are not under normal tension and cannot function normally, so the limp is actually caused by weakened hip muscles.  

When a doctor sees a young child limping from a painful hip, they think of many things that could cause these symptoms.  An inflammatory reaction, a broken bone, an infection, or Perthes are all possible causes.   Blood tests and an x-ray help to rule out other conditions and focus a doctors attention on the diagnosis of Perthes. 

In the Initial Phase, the femoral head has a normal shape on x-ray, but it will still show some signs that things in the bone aren't normal.

In later phases the diagnosis is more apparent.

How is Perthes treated?

Perthes is a complicated condition and therefore treatment depends on a few variables.  Firstly it depends on the severity of femoral head collapse.  But It also depends on how young this affect child is, and which phase of Perthes the child is in.

Overall, the key for the collapsed bone grow back to re-form a circle.  The bone will almost always grow back, but it wont always reform into a circle: this is the challenge of treatment, and it can be a especially difficult when the femoral head has collapsed into a pancake.  Getting the new bone to grow into a circle is like pouring jelly into a mold.  The hip socket acts as a mold, and the "ball" will reform inside that mold, so its key to contain the femoral head within the socket, which can be hard when the hip collapses. The worst the hip collapse (especially in the lateral pillar of the hip as measured by a Herring Classification) the more challenging the treatment.

In the initial phase the shape of the hip hasnt changed so the child can continue walking on the affected leg to the best of their ability.  The collapse will be monitored closely with x-rays. The biggest problem for doctors is the inability to predict the severity of the next phase (where you see actual collapse).  There is a wide spectrum of severity yet doctors have to wait until the next phase (which can be months later) to determine how treatment needs to proceed.  There is a lot of promising research focusing on this aspect of the condition. 

Treatment in the fragmentation phase depends on degree of collapse (remember that we want to maintain the normal "ball and socket" shape as a mold for new bone ingrowth).

If the collapse is minor, kids can continue walking but some activities, like running, needs to be restricted.  They are essentially allowed to be normal kids, and are watched closely with x-rays of their hip every few months, until the condition goes always. 

If however the collapse is significant then kids should have surgery to re-shape the "ball and socket" so that the new bone will form a circle.  

What is the long term outcome?  

The good news is that kids are growing and their bone wants to grow, so new blood vessels will form and provide nutrients to allow the bone to grow (in contrast to adults, where the bone doesnt grow back once it dies...even in kids, the younger they are, the more growth potential they have, and so the younger kids have better recovery).  One of the most important predictors of long term outcome, is the amount of residual of joint congruity (how well does the ball and socket match up after the hip has fully healed and stopped growing).  This is called the Stulberg Classification, which looks at x-rays of the hip and describes the hip as having (1) spherical congruity (type I and II where the ball is round and it matches the socket), (2) aspherical congruity (type 3 and 4, where the ball is not perfectly round, but it still matches up well with the socket); and (3) aspherical incongruity (type 5 and 6, where the ball is not round at all, and it doesnt sit centrally in the socket).  The higher the type of Stulberg Classification, the greater risk of future arthritis. 

Kids with moderate collapse (Lateral Pillar B group, and Pillar B/C group) will really benefit from surgery if they are over 8 years old, so their bone will grow back in a circle (as measured by the Stalburg Criteria).  This will lead to less pain and less risk for arthritis in the future.

Kids with the same amount of collapse, but under 8 years old, have good outcomes regardless (surgery is not required). Kids with severe collapse (Lateral Pillar C group) have high risk for future pain, decreased hip motion and early onset arthritis, regardless of treatment.  This is therefore an area of significant research to improve these outcomes. 

Future Directions

There have been recent studies looking into the use of bisphosphonates injected directly into the hip to prevent the bone from collapsing (even if the cells have died) which allows the hip architecture to remain intact until this calcium skeleton is re-filled with bone cells.  Another study is looking at the use of MRI to visualize the degree of decreased blood flow during the initial phase of the condition (before collapse) to start treatment earlier in kids that have a high risk of collapse.  




1) Herring JA, Kim HT, Browne R. Legg-Calve-Perthes disease. Part II: Prospective multicenter study of the effect of treatment on outcome. JBJS 2004; 86:2121-34. full articleage and severity based outcomes.

2) Sponseller PD, Desai SS, Millis MB. Comparison of femoral and innominate osteotomies for the treatment of Legg-Calves-Perthes disease. JBJS 1988; 70: 1131-9. full article. compare femur vs pelvic osteotomy

3) Grzegorzewski A et al. Treatment of the collapsed femoral head by containment in Legg-Clave-Perthes disease. J Ped Ortho 2003; 23: 15-9. full article

4) Wiig O, Terjesen T, Svenningsen S. Prognostic factors and outcome of treatment in Perthes' disease: a prosepctive study of 368 patients with five-year follow-up. JBJS Br 2008; 90: 1364-71. full article

5) Herring JA, Kim HT, Browne R. Legg-Calve-Perthes disease. Part I: Classification of radiographs with use of the modified lateral pillar and Stulberg classifications. JBJS 2004; 86: 2103-20. full article. classification system.

6) Stulberg SD, Cooperman DR, Wallensten R. The natural history of Legg-Calve ́- Perthes disease. J Bone Joint Surg Am. 1981;63:1095-108. see paper.  original stulberg classification system to predict future arthritis.  

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