We appreciate Dr. Brannon's comments and questions. He raises several
necessary points of clarification.
First, he correctly emphasizes the limitations of citing the article by
Gregosiewicz and
Wosko4 pertaining to
the causation of osteonecrosis in children with known congenital hip
dislocation. His mention of the discrepancy regarding the age of the patients
in that series and the age of the patients in our report is indeed accurate.
We cited that article to demonstrate the paucity of literature regarding the
relationship between osteonecrosis and developmental dysplasia of the hip. The
primary utility that we found from that article was related to its postulation
that osteonecrosis tended to be more severe in hips with developmental
dysplasia than in those without dysplasia. Clearly, any additional
extrapolation from the article by Gregosiewicz and
Wosko4 would be
inaccurate because of the age and disease differences between their series of
patients and ours. The article by Hadley et
al.8, which was also
cited in our manuscript, was instead a more appropriate validation of our
hypothesis as it emphasized the increased contact stresses on the femoral head
in patients with developmental dysplasia of the hip.
The second point raised by Dr. Brannon pertained to the causative agent of
the poor outcomes for dysplastic hips as cited in our report. We certainly now
believe that the dysplastic acetabulum in itself portends a worse outcome for
hips with osteonecrosis that are treated with free vascularized fibular
grafting. We are not in a position to attribute the poor results to the free
vascularized fibular grafting treatment chosen as every patient in our study
had the same procedure and patients with an increased center-edge angle tended
to do quite well after the procedure. Furthermore, as Drs. Steinberg and
Steinberg1 point
out, the 39% overall rate of progressive collapse of the femoral head and
conversion to total hip arthroplasty that we found in our series compares
favorably with reports in the existing literature regarding non-arthroplasty
treatments of osteonecrosis of the femoral head. This is particularly striking
because 30% (sixty) of the 200 hips in our series demonstrated some degree of
developmental dysplasia (a center-edge angle of =25°). To investigate
this issue further, we would need to compare the rates of developmental
dysplasia of the hip in other series, which are not accessible because these
values have not been routinely recorded. It is our hope that some degree of
assessment of developmental dysplasia of the hip will be employed and recorded
in the future to further elucidate the role of this condition in the outcome
of osteonecrosis treatment and perhaps to devise a more refined treatment
strategy for these patients.
Dr. Brannon also questioned whether the core tract made during the free
vascularized fibular grafting procedure may potentiate collapse of dysplastic
hips. This is a distinct possibility, although we did not address this issue
in our study. Perhaps a lower-diameter threshold of core tract exists when the
presumed increase in contact force from a dysplastic acetabulum is at work? By
this rationale, smaller core tracts (such as those made during nonvascularized
fibular grafting), the use of porous tantalum
implants9, or core
decompression may play a larger role in the treatment of those patients.
Before those techniques can be recommended in this setting, however, basic
science studies evaluating the diameter threshold of core tracts in the
setting of developmental dysplasia of the hip would need to be performed.
A further point of desired clarification regarded our statement that
concluded the abstract: "An estimation of the degree of hip dysplasia
should be included in the preoperative assessment of patients with
osteonecrosis of the femoral head for prognostic and possibly surgical
planning purposes." Rather than planning a variation of the free
vascularized fibular grafting procedure, our intent with this statement is to
challenge future researchers and investigators to consider alternative
procedures in the setting of developmental dysplasia of the hip and
osteonecrosis. In particular, this pertains to procedures addressing the
deficient acetabulum.
Finally, Dr. Brannon questioned whether femoral heads may be better saved
with the use of avascular techniques that provide better subchondral support
after thorough débridement. This concern is quite valid and, although
theoretically accurate, will require further elucidation by obtaining a more
accurate assessment of critical thresholds of core tract and graft strength in
the setting of developmental dysplasia of the hip.
In conclusion, we appreciate the insightful questions and comments
expressed by Dr. Brannon regarding our study. After proposing that a
relationship exists between (a lack of) acetabular coverage and the outcomes
of free vascularized fibular grafting treatment for osteonecrosis of the
femoral head, our results pose many more questions regarding the optimal
treatment for these patients. We look forward to further research that
addresses this important problem.