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Using Imaging Studies to Sort Out Taumatic Hip Injuries in Children
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Posted on: 02/28/2013
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Hip pain in growing children isn't always from "growing pains." Children and young teens active in sports training and competition who have not completed their growth often develop hip pain. They will need some special consideration when being evaluated because the bones are not fully formed yet.
For example, when the hip socket (known as the acetabulum) is still more cartilage than bone, X-rays may falsely show what looks like a rotated angle of the hip. It is easy to mistake the hip pain as coming from a problem known as femoroacetabular impingement when that's not it at all.
In another example, X-rays and CT scans looking for a fracture of the backside of the acetabulum may not show a torn labrum (fibrous rim of cartilage around the hip socket) or a loose piece of cartilage in the joint. Only an MRI will show that.
So when should an X-ray versus CT scan versus MRI be ordered for a child with hip pain associated with trauma (accident, injury, or sports overuse)? That's what the orthopedic surgeons from the Hospital for Special Surgery in New York City try to sort out in this article.
They found medical records for 180 patients between the ages of four and 15 with hip pain who were evaluated by X-ray and MRI. They compared the findings and results. In the process of collecting this information, they were able to determine the order, speed, and age(s) at which the backside and rim of the acetabulum (hip socket) develops.
Up until now, no one has really known for sure how and when the bone develops in that particular location. And this piece of information is important because this portion of the hip socket is located at the juncture where three other bones meet (the ilium, the ischium, and the pubis). So the pattern of development of the posterior acetabulum depends on the coordination and timing of development of these three bones as well.
They found that the posterior (back) wall of the hip socket (acetabulum) develops in four distinct phases. At first (in the young child before age eight), the acetabulum is made up of 100 per cent cartilage. Around age eight or nine, the cartilage starts to turn to bone. That process is called ossification. MRI images showed a cobblestone formation with islands of bone ringed by areas of cartilage.
By age 12 or 13, the three bones (ilium, ischium, pubis) that join together to form the acetabulum have met together and fused. At this point, there is still a rim of bone forming (ossification) around the upper back (posterior) portion of the acetabulum. This is referred to as the posterior rim sign. The final step is closure of the cartilage between the three bones called the triradiate cartilage. This last phase occurs in girls by age 12 and in boys by age 14.
As a result of this study, it is clear that the posterior aspect of the acetabulum (hip socket) develops and progresses in an orderly fashion. It goes from cartilage to bone more slowly (and after) the same process takes place in the front (anterior) portion of the socket. But it is a predictable series of four phases. Boys tend to complete this ossification process later than girls (one to one and a half years later).
If a surgeon needs to know the shape and developmental phase of the acetabulum before that final phase (before closure of the triradiate cartilage), then an MRI (not X-rays or CT scans) will be needed. Children younger than eight won't need an MRI since it is known the socket is all cartilage. Children between nine and 14 must be evaluated on an individual basis keeping their gender in mind (remember, girls complete the fusion process at a younger age than boys).
Using only X-rays during phases two and three (ossification and fusion but before closure of the cartilage) can lead to problems. There can be false positives for femoral anteversion (twist in the angle at the top of the femur or thigh bone) and false negatives for damage to the posterior wall of the acetabulum from acute traumatic injury. Misjudging either of these signs can cause delays in diagnosis and treatment for these children.
In conclusion, the authors suggest surgeons should NOT rely on anything but MRIs when evaluating the hip socket in older children and young teens who do not have a fully closed triradiate cartilage.
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References:
Peter D. Fabricant, MD, et al. A Radiographic Study of the Ossification of the Posterior Wall of the Acetabulum: Implications for the Diagnosis of Pediatric and Adolescent Hip Disorders. In The Journal of Bone and Joint Surgery. February 6, 2013. Vol. 95A. No. 2. Pp. 230-236.
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*Disclaimer:*The information contained herein is compiled from a variety of sources. It may not be complete or timely. It does not cover all diseases, physical conditions, ailments or treatments. The information should NOT be used in place of visit with your healthcare provider, nor should you disregard the advice of your health care provider because of any information you read in this topic. |
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