For a comparison of independent measures, such as body mass index, age at the time of the index operation, and the Oxford and WOMAC scores, the Student t test was used to compare group means.
Sixty of the seventy-six patients in the original cohort were traced, and the cases of these patients were reviewed, for a follow-up rate of 79%. There were sixty-three hips in forty-seven women and seventeen hips in thirteen men. The average length of follow-up for patients surviving to the end of the study was 43.3 years (range, forty to forty-eight years) from the time of the index operation. The average age of the patients was 2.8 years (range, 1.5 to five years) at the time of the index operation and 45.8 years (range, forty-two to fifty-one years) at the time of the latest follow-up.
Twenty-four hips in nineteen patients (eighteen female and one male) had undergone a total joint replacement (see Appendix). Three patients had died of unrelated causes without a hip replacement during the study. They were included in the survival analysis only. Thus, the rate of joint replacement was 31% in the seventy-seven hips of patients surviving beyond forty years from the index procedure. The rate of postoperative complications had been 46% in the hips that had a joint replacement compared with 15% in the hips that had not been replaced (see Appendix). The postoperative complications included recurrent dislocation requiring revision open reduction, residual subluxation requiring abduction casting or revision innominate osteotomy, and supracondylar femoral shaft fracture. Overall, the complication rate for the entire study group was 25%.
The occurrence and the description of osteonecrosis were poorly documented in the patient records. Most archived radiographs from that period had been destroyed so that contemporary classifications could not be applied retrospectively. This study group forms the greater part of 110 dislocations that had the operation as a primary procedure and were reviewed at an average of 5.5 years postoperatively16. The additional nine dislocations included then were managed operatively after 1965. The rate of osteonecrosis at that time was 5.7%, on the basis of the delayed appearance or mottling of the ossific nucleus and subsequent flattening of the femoral head or coxa magna33.
Of the sixteen patients (twenty-one hips) lost to followup, five had bilateral involvement. The average age at the time of the index operation was 2.7 years (range, 1.9 to 4.6 years), and the postoperative complication rate was 33%. These figures are similar to those of the study group.
Fifty-three hips (69% of all hips in the surviving patients) in thirty-eight patients (twenty-seven female and eleven male) had not been replaced at the end of the study. The average Oxford hip score was 16.4 (range, 0 to 82), and the average WOMAC score was 16.3 (range, 0 to 71).
The control group comprised seventy-five hips in fifty women and twenty-five men whose average age was 45.4 years (range, forty-two to fifty years). Chosen at random, thirty-eight patients were asked to complete the questionnaires for their right hip and thirty-seven for their left. They had an average Oxford hip score of 2.9 (range, 0 to 26) and an average WOMAC score of 4.1 (range, 0 to 49). The differences in scores between the study and control groups were highly significant (p < 0.0001). In studies of patients who had a hip replacement, the average preoperative scores were 67.7 with the Oxford hip-scoring system34 and 59 with the WOMAC35 system.
The original22 and modified8 Harris hip scores were an average of 88 points (range, 30 to 100 points) and 89 points (range, 27 to 100 points), respectively, for the study group.
Fifty-one of the fifty-three surviving patients who had not had a hip replacement had radiographs made for this study (Figs. 1-A, 1-B, 1-C, 2-A, 2-B, 2-C and 2-D). Thirty-eight of them had a minimum joint space width of >2.0 mm, and thirteen had definite osteoarthritis on the basis of thiscriterion. Twenty-nine hips had no or doubtful signs of osteoarthritis (grade 0 or 1) according to the Kellgren and Lawrence score (Figs. 2-A, 2-B, 2-C and 2-D). Seven hips had mild osteoarthritis (grade 2), but only two of them had substantial symptoms on the pain domain of the WOMAC questionnaire. The remaining fifteen hips had moderate or severe osteoarthritis (grade 3 or 4, respectively), although two patients with hips categorized as grade 3 had a minimum joint space width of >2.0 mm.
The average center-edge and acetabular angles were 40° (range, 0° to 61°) and 32° (range, 20° to 43°), respectively. Nine hips had a center-edge angle of ≤30°, while six had an acetabular angle of >38°. Nine hips were graded as Severin Class I, thirty-three, as Class II; eight, as Class III; and one, as Class IV.
Two female patients (three hips) had rheumatoid arthritis develop. All three hips were involved. One hip had been replaced; one had severe, symptomatic arthritis; and one had mild signs with no symptoms.
The survival rates for all hips are plotted in Figure 3. The first failure occurred thirty years after the index procedure. The data become unreliable after forty-five years, when there are fewer than ten patients in the tail of the survival curve36. Until that time, the survival rates at thirty, forty, and forty-five years after reduction are 99% (95% confidence interval, ±2.4%), 86% (95% confidence interval, ±6.9%), and 54% (95% confidence interval, ±16.4%), respectively.
Association of Risk Factors for a Poor Outcome
The patients who had a hip replacement or had definite development of osteoarthritis, according to joint space width, by the end of the study and those who had not were compared with respect to their mean age at the time of the index surgery. The mean ages were 3.05 and 2.65 years, respectively, and the difference was four months, which failed to reach significance (p = 0.07). Body mass indices in these same groups were almost identical (28.59 and 28.57, respectively).
With use of the Cox proportional-hazards regression model, the hips in the patients who had undergone surgery bilaterally were at 2.9 times greater risk of a subsequent hip replacement compared with the hips in patients with unilateral involvement (p = 0.02)
The present investigation is a retrospective study without controls, either untreated or managed with isolated steps of the protocol. The data cannot therefore identify whether, for example, capsulorrhaphy37 was important in the outcome or whether innominate osteotomy was required in every patient within this age-range. The timing of and indications for intervention to improve acetabular dysplasia in all forms of developmental dysplasia of the hip are highly controversial13,20. The senior author believed that the normal osseous development of the acetabulum could no longer be ensured even after successful reduction beyond the age of eighteen months, and so all children with late-presenting developmental dislocation of the hip underwent innominate osteotomy with open reduction after this age. Our data can be used to predict the outcome of children managed in this way.
The Severin classification of developmental dysplasia of the hip is historically popular despite concerns for its reliability38. At an average of 5.5 years after the index operation, 96% of the hips in this group were Class I or II. However, at the time of the latest follow-up, twenty-four hips (31%) had undergone joint replacement and thirteen (17%) had definite osteoarthritis. Thus, a good Severin grade approaching skeletal maturity did not guarantee a good outcome into middle age.
Perhaps uniquely in a series with this duration of followup, the operative technique has not been altered. The main change in protocol concerns preoperative traction, which is generally no longer practical. All of the children in this study had a minimum period of two weeks of traction, to stretch the soft tissues and decrease joint pressure after reduction, but our subsequent experience has shown that this may not be essential for a safe reduction in younger children. In older children, instead of prolonged traction in the hospital, we currently recommend femoral shortening, which we believe may decrease the rate of osteonecrosis. Radiographic archives for this group, for the period from the time of the operation to adolescence, had been destroyed, and the rate of osteonecrosis quoted in the present study is from a study that predates contemporary classifications39,40. This invalidates any comparison of the rates of osteonecrosis after traction in the present study with those in more recent series of femoral shortening.
Otherwise the methodology is robust and was designed to eliminate potential bias in the interpretation of outcomes. Survival analysis was based on the objective end point of total hip replacement, and we used validated, self-administered outcome questionnaires. The WOMAC index assesses three domains—pain, disability, and joint stiffness—in patients with arthritis of the hip. The Oxford hip score is similar but is designed specifically to assess patients undergoing hip replacement. Both demonstrate a ceiling effect for patients without arthritis, manifested in a relatively high prevalence of hips with a score of 0. We included the Oxford score to establish what proportion of the surviving hips had scores close to those of patients requiring replacement. This identifies the patients who satisfy the criteria for this intervention but do not reach the end point for survival analysis, perhaps because they are on a waiting list or are delaying surgery because of their relatively young age. In the series, two surviving hips reached the age-matched reference value of the Oxford score35 for joint replacement and four more were within 10 points of it. This indicates failure, impending or actual, in 39% of the hips at the end of the study.
Our definition of osteoarthritis as radiographic evidence of a minimum joint space width is objective and validated28,29. We included the Kellgren and Lawrence score26 although it is more subjective. A recent longitudinal cohort study followed 1904 men and women with osteoarthritis of the hip who were fifty-five years of age or older at baseline for five years41. The Kellgren and Lawrence score was by far the strongest predictor of all determinants studied for progression of hip arthritis. We can use it to examine the decrease in survival from 86% at forty years to 54% at forty-five years, which could be an anomaly of the low numbers in the tail of the curve36. At the end of the study, fifty-one of the fifty-three surviving hips had radiographs, which demonstrated a low risk for the development or progression of osteoarthritis (a Kellgren and Lawrence grade of 0 or 1 or grade 2 without pain) within the next five years in thirty-four hips (67%) and a high risk of progression or joint replacement (grade 3 or 4 or grade 2 with pain) in seventeen hips (33%). Thus, 55% of all seventy-five surviving hips with radiographs available had either been replaced or were likely to progress to this step within five years, while the remaining 45% had an excellent radiographic outcome and were at low risk for deterioration. These figures are similar to those in the tail of the survival curve.
There are few studies of intervention for this condition with comparable follow-up. Angliss et al. reported the results of the so-called direct method of treatment for late-presenting developmental dislocation of the hip42,43. The majority of 191 hips underwent preoperative traction with progressive abduction followed by open reduction with limbusectomy44,45 and staged femoral derotation osteotomy. The median age at the time of the index operation was two years (range, 0.75 to 7.9 years) with follow-up to a median of thirty-three years (range, twenty-five to forty-eight years). Forty percent had moderate or severe arthritis (50% in the open reduction group), and there was a 14% rate of hip replacement or arthrodesis. Twenty-six percent remained in Severin Class I or II at the time of the final follow-up. The replacement rate in our group at thirty-three years was 3.8% (95% confidence interval, ±4.2%). Eighty-two percent (forty-two) of the fifty-one surviving hips (or 53% of the original cohort of hips) were Severin Class I or II with additional years of follow-up at the end of our study.
Malvitz and Weinstein reported on 152 hips in patients who were an average of 1.75 years old (range, 0.8 to eight years) at the time of closed reduction46. They were followed for an average of thirty years (range, fifteen to fifty-three years). The Harris hip score was an average of 90 points for the surviving hips (compared with an average of 88 points in our series with an additional ten to eighteen years of follow-up), and there was an 11% rate of joint replacement (compared with 1.2% [95% confidence interval, ±2.4] in our series at thirty years).
Comparison of retrospective case series is inherently unsatisfactory. Nonetheless, we feel justified in recommending this operative protocol for late-presenting developmental dislocation of the hip on the basis of these results. We accept that preoperative traction can probably be safely omitted in younger children, in whom the dislocated femoral head has not migrated a substantial distance proximally, or traction can be replaced with femoral shortening osteotomy in older children.
Even in this series, however, the rate of hip replacement, prevalence of osteoarthritis47, and functional outcomes compared with those for age-matched controls demonstrate that some of the involved hips have residual abnormalities. Bilateral hip dislocation and postoperative complications are poor prognostic factors, but it is otherwise unclear why some hips fare better than others into middle age. Given the association between obesity and osteoarthritis48, it is surprising that body mass was not related to outcome and this may simply be a Type-II statistical error. The failure to detect a significant association between the age at the time of surgery and the outcome could have the same explanation. Albinana et al. demonstrated a substantial increase in the prevalence of residual acetabular dysplasia with increasing age at the time of reduction13. From two to seven years after reduction in their series, an increased acetabular index was the strongest indicator for failure to achieve a satisfactory Severin grade at maturity. An alternative explanation, therefore, is that the addition of innominate osteotomy in all late presentations brings the risk profile for subsequent failure toward that associated with a dislocation that is treated earlier. If this inference (that redirecting the acetabulum in older children with reduced remodeling capacity ameliorates the negative effect of increased age) is correct, then it would seem appropriate to perform the innominate osteotomy at the time of open reduction.
In summary, this method of open reduction and innominate osteotomy for developmental dislocation of the hip presenting after eighteen months of age can be expected to result, on the basis of data derived from validated and reliable measures, in the following outcomes at forty-five years after the index procedure. The failure rate (with joint replacement as the end point) is 46% (95% confidence interval, ±16.4), with definite osteoarthritis in 25% of the surviving hips. Two-thirds of the surviving hips are able to function at a high level up to and well beyond forty-five years, on the basis of predictive data from well-designed population studies. The potentially modifiable risk factors of body mass and age at the time of index surgery do not appear to affect outcome for children between eighteen and sixty months old, but bilateral dislocation of the hip is a poor prognostic factor. Even in the face of postoperative complications, failure after the use of this procedure to treat late-presenting dislocation of the hip is unlikely for the first thirty years after surgery.
Tables showing clinical details on all study patients are available with the electronic versions of this article, on our web site at jbjs.org (go to the article citation and click on “Supplementary Material”) and on our quarterly CD-ROM (call our subscription department, at 781-449-9780, to order the CD-ROM). ▪
NOTE: The authors thank Dr. James Wright, Dr. Andrew Howard, and Dr. William Cole for their peer review throughout this study and Derek Stephens for performing the statistical analyses. They are also grateful to their research assistants Laura Sutton and Mauro Barillas and to Sam Donaldson for her advice and assistance during this project.
Disclosure: In support of their research for or preparation of this work, one or more of the authors received, in any one year, outside funding or grants in excess of $10,000 from Physicians Services Incorporated and the Research Institute of the Hospital for Sick Children, Toronto, Ontario, Canada. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.
A commentary is available with the electronic versions of this article, on our web site (www.jbjs.org) and on our quarterly CD-ROM (call our subscription department, at 781-449-9780, to order the CD-ROM).
Investigation performed at The Hospital for Sick Children, Toronto, Ontario, Canada
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