We thank Dr. Konstantoulakis and his colleagues for their observations and comments regarding the pediatric pelvis patient xrays depicted in our manuscript. Frankly, we had not previously noted the acetabular dysplasia which you have astutely described in your letter. This may in part be because the patient’s followup was performed by traumatologists who rarely treat pediatric hip dysplasia and because the patients subsequent symptoms did not correspond with hip pain. However, our measurement of the CE angles confirms your observations. Reexamination of the xray also confirms the other findings of dysplasia which you mentioned. Reexamination of coronal, axial and sagital CT scans taken at the time of injury show no evidence of an acetabular fracture or triradiate cartilage injury. The medical record confirms that the patient was not treated with any type of traction, either perioperatively or intraoperatively. Re-contact with the patient since receipt of your letter also confirms that there is no known history of hip dysplasia within this family.

We conclude that the finding of dysplasia must be related to either the initial injury or to the subsequent change in mechanics following an asymmetric reduction. There is a residual external rotation deformity from the pelvic malreduction which may contribute to the aymmetrical appearance of the acetabulum when compared to the other side. There is also a pelvic obliquity with an adduction contracture on the right uninjured side making the amount of femoral head uncovered look worse than it really is. However, without a followup CT scan it is difficult to estimate the degree to which this contributes to the xray finding of asymmetry.

Fortunately, the patient in question has no current evidence of hip pain or dysfunction. However, with the paucity of data regarding traumatic acetabular dysplasia in the child, it is difficult to prognosticate her future functional outcome.

Your observations point to the need for pediatric pelvic fractures to be treated in a multidisciplinary fashion. Orthopaedic trauma surgeons generally have the most experience and training in handling the initial management and reconstruction but pediatric orthopaedic surgeons are the experts in child and adolescent developmental issues. Traditionally, these injuries have often been cared for by whomever saw them first, with little thought to consultation because children “always remodel.” Given the importance of accurate fracture reduction as well as long term followup, we believe injured children with pelvic fractures are best served by systems which permit and encourage ongoing collaboration between subspecialty groups. Thank you for your interest.

To The Editor:

We read with great interest the article by Smith, et al, (1) in which the authors demonstrated the need for accurate reduction to deliver excellent long term results.. We would like to raise a question regarding the illustrated case labelled as Figs 2a, 2b and 2c.

The AP x-ray of the pelvis showed that the hip on the uninjured side is developing normally. It has good containment, there is a normal acetabular index (AI) of 20 to 22 degrees and there is a normal Center-Edge angle of 20 degrees. A sourcil is well formed and is horizontal offering good coverage of the head (10% uncovered). On the immediate postoperative x-ray the configuration of the hip remains unchanged. However on the x-ray taken 2 years post surgery the same hip appears to demonstrate acetabular dysplasia and the saurcil is now thicker and has a steeper inclination whilst the head is 30% uncovered. The AI measures 30 degrees and the CE angle 8 to 10 degrees. (2,3)

These findings raise a number of questions: Was there an occult injury to the acetabulum on the unaffected side which subsequently caused early growth plate closure of the acetabular tri- radiate cartiladge or the acetabular edge epiphysis? In the Dysplastic hip when lateral sourcil thickening occurs this generally represents an increased focal loading due to underlying mal- alignment. Post traumatic dysplasia in children has been described by Trousdale and Ganz (4) as having a number of distinctive features including widening of the teardrop and the inner wall and lateralization of the femoral head. These x-rays demonstrate a number of these findings, including lateralisation of the head, a difference in the appearance of the triradiate cartilage and under-development of the acetabular lip.

We will be interested to know the authors' opinion as to the reasons for the development of dysplasia on the contra-lateral side and whether they believe there was an unrecognised injury to the apparently unaffected hip. If not, are there any other reasons as to why this hip became dysplastic?

References:

1. Smith W, Shurnas P, Morgan S, Agudelo J, Luszko G, Knox EC, Georgopoulos G. Clinical outcomes of unstable pelvic fractures in skeletally immature patients. J Bone Joint Surg Am. 2005 Nov;87(11):2423- 31.

2. Than P, Sillinger T, Kranicz J, Bellyei A. Radiographic parameters of the hip joint from birth to adolescence. Pediatr Radiol. 2004 Mar;34(3):237-44.

3. Tonnis D. Normal values of the hip joint for the evaluation of X-rays in children and adults. Clin Orthop Relat Res. 1976 Sep;(119):39-47.

4. Trousdale RT, Ganz R. Posttraumatic acetabular dysplasia. Clin Orthop Relat Res. 1994 Aug;(305):124-32.