To the Editor:
We would like to thank Dr. Kocher for his fine work(1) in response to
our decision analysis on prophylactic pinning of slipped capital femoral
epiphysis(2). This is an important and controversial topic that warrants
thoughtful, scientific debate prior to adopting generalized standards of
care.
Although it may appear that the conclusions of our studies are vastly
different, the reality is the treatment options re: observation vs.
prophylactic pinning are very nearly equivalent in statistical probability
of outcome. In fact this is, in part, why decision modeling is such a
powerful tool which allows one to create models for predicting outcome
based on multiple probabilities that we otherwise could not compute.
The major differences in our studies relate to different probability
data used in the two studies. The most obvious of these is the
probability of late contralateral slip. This is a controversial subject
and some authors feel that it is a leading cause of degenerative arthritis
of the hip in older patients(3). Hagglund’s data suggest that the rate of
unrecognized mild slips is very high(4,5). Anthropometric skeletal studies
confirm this finding(3), but it is difficult to say with certainty if the
anatomic changes seen are the result of a primary slip or secondary
changes of degenerative arthritis.
We also have concerns about the probabilities of complications. Most
of these data were taken from isolated case reports. It is not clear from
your paper (1) where the denominator comes from to arrive at these numbers and
provide probabilities. In the Greenough paper(6) which was cited as one
source of probability data the complications were seen with pins that are
no longer in widespread clinical use today or viewed as standard of care(7).
In addition, recent studies suggest that avascular necrosis is a
phenomenon almost exclusive to unstable slips and not an iatrogenic
phenomenon(8). With the advent of computer assisted technology the
probabilities for iatrogenic complications related to hardware placement
may even be further reduced(9).
Dr. Kocher is absolutely correct in his explanation of decision
analysis. We chose to perform what is more appropriately termed an
“expected value analysis” for several reasons. First, utility analysis is
a challenging and difficult task in the adult population and virtually
impossible in the pediatric population. A true utility is not obtained
from a visual analogue scale because there is no relative quantification
of the value of a particular health state. Standard gamble and time trade
off methods are required to obtain true utility values. Both methods
require abstract thought, usually beyond the facility of the subjects
studied in this model.
We chose, instead, to assume the perspective of a person at middle
age that would have experienced the long-term outcomes of a slipped
epiphysis. We believe this is essential to the reasoning behind
performing these operations in children - for long-term gain. To bring
short-term complications into the model distorts the results of the model.
Many of these short-term complications are reversible and do not result in
long-term disability.
If short-term complications are to be considered then one must
perform Markhov modeling(10) within the decision analysis. This allows time
in a particular health state to be considered. One cannot compare
utilities for temporary health states such as superficial infections or
even fracture with utilities for long-term health states such as
degenerative arthritis of the hip. In a perfect model we would be able to
calculate the utility associated with short-term and long-term
disabilities and the different treatment options would accumulate utility
based on time spent in that particular health state – essentially Quality
Adjusted Life Years(QALY’s).
This type of model is achievable and may provide us with the most
accurate assessment of the benefits associated with each treatment option
but the major obstacle will remain the assessment of utility in the
pediatric population using traditional utility assessment tools (time
trade off or standard gamble).
It is still our opinion that long-term disability remains the
overriding concern when treating children with Slipped Capitol Femoral
Epiphysis and we stand by our assertion that prophylactic pinning provides
superior probability of better hip function over the long term.
Sincerely,
W. Randall Schultz MD, MS
James N. Weinstein, DO, MS
Stuart L. Weinstein, MD
Brian G. Smith, MD
References:
1. Kocher, M. S.; Bishop, J. A.; Hresko, M. T.; Millis, M. B.; Kim,
Y. J.; and Kasser, J. R.: Prophylactic pinning of the contralateral hip
after unilateral slipped capital femoral epiphysis. J Bone Joint Surg Am,
86-A(12): 2658-65, 2004.
2. Schultz, W. R.; Weinstein, J. N.; Weinstein, S. L.; and Smith, B.
G.: Prophylactic pinning of the contralateral hip in slipped capital
femoral epiphysis: evaluation of long-term outcome for the contralateral
hip with use of decision analysis. J Bone Joint Surg Am, 84-A(8): 1305-14,
2002.
3. Goodman, D. A.; Feighan, J. E.; Smith, A. D.; Latimer, B.; Buly,
R. L.; and Cooperman, D. R.: Subclinical slipped capital femoral
epiphysis. Relationship to osteoarthrosis of the hip. J Bone Joint Surg
Am, 79(10): 1489-97., 1997.
4. Hagglund, G.; Hannson, L. I.; and Sandstrom, S.: Slipped capital
femoral epiphysis in southern Sweden. Long-term results after
nailing/pinning. Clin Orthop, (217): 190-200., 1987.
5. Hagglund, G.; Hansson, L. I.; Ordeberg, G.; and Sandstrom, S.:
Bilaterality in slipped upper femoral epiphysis. J Bone Joint Surg Br,
70(2): 179-81., 1988.
6. Greenough, C. G.; Bromage, J. D.; and Jackson, A. M.: Pinning of
the slipped upper femoral epiphysis--a trouble-free procedure? J Pediatr
Orthop, 5(6): 657-60., 1985.
7. Kenny, P.; Higgins, T.; Sedhom, M.; Dowling, F.; Moore, D. P.; and
Fogarty, E. E.: Slipped upper femoral epiphysis. A retrospective, clinical
and radiological study of fixation with a single screw. J Pediatr Orthop
B, 12(2): 97-9, 2003.
8. Tokmakova, K. P.; Stanton, R. P.; and Mason, D. E.: Factors
influencing the development of osteonecrosis in patients treated for
slipped capital femoral epiphysis. J Bone Joint Surg Am, 85-A(5): 798-801,
2003.
9. Perlick, L.; Tingart, M.; Wiech, O.; Beckmann, J.; and Bathis, H.:
Computer-assisted cannulated screw fixation for slipped capital femoral
epiphysis. J Pediatr Orthop, 25(2): 167-70, 2005.
10. Weinstein, M. C.: Clinical decision analysis. Edited, xiv, 351
p., Philadelphia, Saunders, 1980.
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