Your baby's ultrasound report is full of numbers and letters that nobody explains at the appointment. Understanding them makes every follow-up less frightening, because you can see progress rather than waiting to be told.
Here is what each measurement means in plain language.
Why ultrasound, not X-ray
Under about six months the femoral head is mostly cartilage, which X-rays cannot see. Ultrasound images cartilage directly, involves no radiation, and can be repeated as often as needed. After six months the head begins to ossify and X-ray becomes the more useful test.
The alpha angle
The alpha angle measures how deep and steep the bony socket is. It is the single most important number on the report.
Above 60 degrees is a mature, normal hip. 50-59 degrees is immature or mildly dysplastic. 43-49 degrees indicates significant dysplasia. Below 43 degrees means the hip is severely dysplastic or dislocated. Rising alpha angles across successive scans are exactly what successful harness treatment looks like.
The beta angle and femoral head coverage
The beta angle measures the cartilage roof over the head; lower is better, with under 55 degrees considered normal. Femoral head coverage is the percentage of the ball sitting inside the socket — above 50 percent is normal, and it is often the number a sonographer will quote to you verbally.
Graf types in plain language
- Type I — normal, mature hip. No treatment.
- Type IIa — immature for age, common in babies under three months. Usually watched with a repeat scan.
- Type IIb / IIc — delayed or deficient socket. Harness treatment typically starts here.
- Type D — the head is beginning to displace. Harness treatment.
- Type III / IV — the head is out of the socket. Harness first if it reduces; otherwise reduction under anaesthetic.
What to ask at the scan
- What is the alpha angle today, and what was it last time?
- Is the hip reduced while the harness is on?
- Which Graf type are we, and has it changed?
- Is the socket deepening at the rate you expect?
- What would make you change the treatment plan?
Timing of scans
A typical schedule is a scan at diagnosis, a confirmation scan one to two weeks after the harness is fitted, then every two to four weeks until the alpha angle normalises, then a final scan before weaning. Many surgeons add an X-ray around six to twelve months and again at walking age.
Frequently asked questions
What is a normal alpha angle for a baby's hip?
Above 60 degrees is considered a mature, normal hip. Between 43 and 59 degrees indicates varying degrees of dysplasia, and below 43 degrees is severe dysplasia or dislocation.
How fast should the alpha angle improve?
Most hips show measurable improvement within three to six weeks of consistent full-time harness wear. No improvement by three to four weeks usually prompts a change of plan.
Can I get a copy of the report?
Yes — ask for it. Keeping your own record of alpha angles over time is the clearest way to see progress.