Copyright © 2009 by The Journal of Bone and Joint Surgery, Inc.
Commentary & Perspective
Commentary & Perspective by
Reinhold Ganz, MD*,
University of Bern, Bern, Switzerland
Posted September 2009
With regard to the papers by Troelsen et al. and Matheney et
al., both try to identify factors predicting failure after a periacetabular
osteotomy. The osteotomy was basically executed according to the same
technique, while the approach to the bone was slightly different. The overall
study protocol, the parameters that were evaluated, and the selected statistical
methods differ in several aspects and therefore do not allow direct comparison;
however, these papers demonstrate how different methodology can lead to
different information, although the goal is identical and both studies are
based on a comparable starting point, equal treatment, and the same end point.
The paper by Troelsen et al. reports retrospectively on 116
periacetabular osteotomies that were performed as treatment for residual
acetabular dysplasia; however, in fourteen hips the etiology was Legg-Calvé-Perthes
disease and in seven hips the underlying disease was a neuromuscular disorder.
The average age at the time of surgery was approximately thirty years, and the
follow-up time averaged 6.8 years. Seventeen hips had to be converted to a
total hip replacement; this group, however, was not analyzed separately. With conversion
to total hip replacement as the end point, Kaplan-Meier survival reached 81.6%
at 9.2 years. Complications are not reported except for dysesthesia of the
lateral femoral cutaneous nerve in 48% of the hips. Of the seventy-seven hips that
were available at the time of follow-up, twenty-six (34%) were associated with
groin pain and fourteen (18%) had a positive impingement test. There are no
data describing the preoperative clinical situation. There are also no
preoperative scores, a fact that makes the available postoperative scores less
meaningful.
Radiographic parameters included measurement of the width of
the sclerotic acetabular zone, which, in comparison with the lateral center-edge
angle, offers a more realistic quantification of the cartilage roof. Preoperative
data on acetabular version came from an assessment of the computed tomographic
scans, but it is not clear whether tilt and rotation of the pelvis were taken
into consideration. Furthermore, angles were measured at the center of the
femoral head, although measuring at this level may not reveal all cases of
retroversion. The crossover sign was not identified on the preoperative
radiographs. After surgery, 26% of the hips had a positive crossover sign but,
again, no information is given about the control of pelvic rotation and/or
tilt. Furthermore, no attempt was made to quantify retroversion.
Only radiographic parameters were used to analyze possible
predictors of failure. Seven factors and Tönnis grades 2 and 3 were identified
as high-grade predictors. It is not surprising that the postoperative width of
the sclerotic wall reached a higher grade than the center-edge angle, and one
may speculate that this would also be true for the same preoperative parameter.
The os acetabuli as a predictor is a special form of labrum avulsion, an aspect
which previously has been identified as a factor for a less favorable outcome.
A low angle of anteversion as a predictor may point toward retroversion;
however, the retroversion data are not very precise in this paper. All in all,
this paper confirms well-known factors that are predictive of failure of a
periacetabular osteotomy and discusses some new aspects of potential interest.
The paper by Matheney et al. is also based on a
retrospective study and reports on a nine-year follow-up of periacetabular
osteotomy in 135 hips with developmental dysplasia only. The average patient
age at surgery was 26.7 years. Sixty-one percent of the hips had an additional
arthrotomy, and, in 27% of this group, labral pathology was found.
Complications occurred in twenty hips. Seventy-six percent of the hips were
preserved at nine years, and 24% (thirty-three hips) met the failure criteria
(total hip arthroplasty or a high pain score); seventeen of the thirty-three
underwent a total hip arthroplasty at an average of 6.1 years after the
osteotomy, and sixteen had a pain score of 10 or more (maximum possible score,
20) at the time of follow-up. Two independent predictors of failure could be
identified: an age at the time of surgery of more than thirty-five years, and
poor or fair preoperative joint congruency. The probability of failure was 14%
for hips that had no predictors of failure; this rose to 36% for hips that had
one predictor and to 95% for hips that had both predictors.
Age at the time of surgery is a factor that is discussed in
nearly all follow-up papers about joint-preserving surgery, but not with any
consistent conclusions being drawn. There is little question that the
biological potential to recover decreases with age; however, a "normal joint"
lasts longer than thirty-five years. Intuitively, one may postulate that other
factors may be present. Because it is known that even advanced and extended
cartilage destruction—which fulfills the definition of arthritis—is not
necessarily visible on standard radiographs, one may speculate that, for most
older patients, the most important factor behind the term age is, in fact, undiagnosed arthritis. Joint congruency, at least as it is understood in this article, is a concept that is composed of different
aspects, mainly, malformation, subluxation, and arthritis.
In conclusion, both articles offer interesting information,
but they also highlight the problem of comparability. It is time now for a
prospective study with a design that includes a full clinical evaluation before
surgery and at the time of follow-up as well as the use of high-quality
magnetic resonance imaging to better classify the amount of arthritis and
completely characterize the three-dimensional position of the acetabulum both
before and after surgery. Ideally, we should be able to create a consensus
regarding the methodology of examination so that we can make a true step
forward in decision-making regarding this disease.
*The author did not receive any outside funding or grants in support of his research for or preparation of this work. Neither he nor a member of his immediate family received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity.
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