A Condition More Common Than Many Realize
Developmental dysplasia of the hip (DDH) is a condition where the hip joint does not form properly before or shortly after birth. The ball of the hip joint sits too loosely — or not at all — in the socket. It affects about 1 in 1,000 babies, though milder forms are more common.
When caught early, DDH can often be managed with a brace. But in more severe cases, or when diagnosis comes later, surgery is needed to put the hip joint back in place. The operation works well for most children. The concern is a complication called avascular necrosis (AVN) — a condition where the blood supply to the femoral head (the ball part of the joint) is cut off. Without blood, bone tissue dies, and the hip can deform permanently.
Why Predicting Risk Has Been Difficult
For years, surgeons knew AVN was a possibility after DDH surgery, but pinpointing exactly which children were most at risk was difficult. Each hospital had its own experience, and individual studies were too small to draw firm conclusions.
But here's the shift — a new analysis pooled data from 16 different studies involving more than 1,600 children to identify the strongest predictors of AVN.
How Blood Supply Works — and Fails
Think of the femoral head like a plant in a pot. The blood vessels feeding it are the water pipes. When a hip is dislocated for a long time, those pipes are already stretched and strained. Surgery then repositions the ball into the socket, sometimes forcefully. If the blood supply was already fragile — or gets disrupted during the procedure — the "plant" can dry out and die.
Three factors appear to make this much more likely. The absence of the ossific nucleus (a small bone development marker visible on X-ray that signals how mature the hip bone is), a high-grade dislocation (meaning the hip was severely out of place), and the need for a second operation all independently raised the risk.
The Evidence Behind the Finding
Researchers conducted a systematic review and meta-analysis — a method that combines data from many studies to find patterns that individual studies might miss. They analyzed 16 studies covering 1,631 patients and 1,941 individual hips. Of those hips, 468 developed AVN after surgery.
Children without the ossific nucleus visible on imaging had 2.6 times the odds of developing AVN compared to children who did have it. A high-grade dislocation (classified as Grade III or IV on the IHDI scale) was associated with 2.4 times the risk. Children who needed a second surgical procedure faced 2.6 times the odds.
Each of these factors independently predicted AVN — meaning they were not just linked to each other. A child with all three risk factors stacks up significant added danger, and surgeons can now factor this into their planning before going into the operating room.
This is where things get interesting.
The Bigger Picture
This analysis matters because it gives surgeons a clearer checklist to work from. In the field of pediatric orthopedics, risk stratification — sorting patients by how much danger they face — has become increasingly important. Knowing preoperatively (before surgery) that a child has a missing ossific nucleus and a severe dislocation can shift the approach: closer monitoring, different surgical techniques, or early imaging after the operation to catch problems sooner.
Surgeons cannot yet prevent AVN entirely, but knowing who is at highest risk is the first step toward protecting those children.
What This Means for Parents
If your child has been diagnosed with DDH and surgery is being discussed, it is worth asking your child's orthopedic surgeon about their specific risk profile. The factors identified in this study — severity of dislocation, bone maturity on imaging, and history of prior procedures — are all things a surgeon can assess in advance. This research does not change the need for surgery, but it may shape how carefully your child is watched before and after.
What This Study Cannot Tell Us
Because this was a meta-analysis of existing studies, its conclusions are only as strong as the data those studies provided. Some studies used different methods to assess AVN or classify dislocation severity. The children in these studies came from different countries and healthcare settings, which can introduce variability. Larger, prospective studies with standardized methods would give cleaner answers.
Pediatric orthopedic researchers are now better positioned to design targeted studies that test whether early intervention — such as adjusting surgical timing or technique for high-risk children — can reduce AVN rates. The goal is not just to identify risk, but to act on it. Future trials may explore whether closer postoperative imaging or modified surgical approaches for children with these risk factors can change outcomes. That work has not yet been done, but this analysis sets a clear foundation for it.