There are some limitations to our study. First, this is a relatively small population. However, compared with the available literature, it is the only population of this size with a homogenous series of patients (spherical femoral heads, congruent joints, limited or no OA), followed prospectively with 96% followup. Second, we did not analyze confounding factors and cannot know how they influence the VAS or Merle d’Aubigné-Postel score. However, because this is a series of 51 hips, dividing this population into smaller subgroups to evaluate certain confounding factors (such as age, gender, obesity, smoking, physical exercise) would lead to over-stratification, making it impossible to distinguish any reliable confounders. In addition, owing to the descriptive nature of the study design we decided not to include an analysis for confounding factors. Third, without a control group without surgery it is not possible to determine the natural course and subsequently impossible to determine the long-term effect of surgery. Developmental dysplasia of the hip occurs in one to two per 1000 births and, when left uncorrected, it may be associated with high long-term morbidity. Furnes et al.  reported an incidence of 9% dysplastic hips in patients having THAs and stated that as much as 1/3 of all patients undergoing THA before 65 years of age experience the consequences of developmental hip dysplasia. Surgical correction of residual dysplasia in adults can relieve pain and substantially improve function, but it has not been proven that it can improve the natural history of developmental dysplasia of the hip [7, 10, 12, 14, 17].
The mean VAS score deteriorated slightly with time, but remained higher than preoperatively. Kotz et al.  reported patients after Chiari osteotomy with a mean VAS score of 25 mm at an average followup of 32 years, which is comparable to the VAS score for our population.
Comparing the Merle d’Aubigné-Postel scores at 15 years followup with the results at 25 years followup, the following pattern was observed. Up to 15 years postoperatively, the clinical scores showed major improvement compared with preoperatively. However, at 25 years, the clinical scores showed deterioration of 1 point. Nevertheless, the results are better than the Merle d’Aubigné-Postel scores preoperatively. Nakamura et al.  described a population of 145 rotational osteotomies of the acetabulum at a mean followup of 13 years, and in this population, the clinical outcome based on the Merle d’Aubigné-Postel score was 15 to 18 in 90 (80%) of the 112 hips which had Stage I or II OA preoperatively and 15 to 18 for nine of the 33 hips which had Stage III or IV OA preoperatively. This shows that when degenerative changes have developed preoperatively, the clinical outcome of acetabular osteotomies and the postoperative Merle d’Aubigné-Postel score can be expected to be lower.
In this population, the development of symptomatic OA did occur with time and could not be avoided by performing triple osteotomies. At most, it was delayed. This also is reported in the literature [7, 10, 12-14, 17]. In the population described by Janssen et al. , six radiographs (18.8%) showed radiographic signs of progression of OA at the final followup. Nakamura et al.  also described an increase in OA with time, graded according to the Japanese Orthopaedic Association [15, 16]. Of the 112 hips with Grade I or II OA preoperatively, only 70% (79 hips) still had Grade I or II OA at the last followup, and the rest had progressive degenerative changes. The reason for this progression of OA despite an osteotomy may be that the acetabulum is reoriented to a more favorable position, reducing the shear forces in the joint by making the weightbearing zone more horizontal, but it is not enlarged and not normalized; it remains a shallow and suboptimal joint.
The rate of conversion to THA increased in this population after 15 years. Comparing the conversion rate of 31% for this population with the rates reported in the literature remains difficult. Most of the available studies describing results greater than 10 years describe different operative techniques [7, 10, 14, 17] with much lower followup rates (range, 15%-98%). Kotz et al.  reported the long-term followup for the Chiari osteotomy and showed a conversion rate of 40% to THA at an average followup of 32 years. However, their population had a followup of only 15% because for most of the patients, the records could not be identified. This makes their study of limited value and difficult to compare with ours because of the different operative technique and because the preoperative degree of OA generally was greater in their population . A major disadvantage of the Chiari osteotomy, compared with the triple osteotomy, is the difficulty it poses when performing a THA. A THA after a triple osteotomy is notably easier than after a Chiari osteotomy. Matheney et al.  reported 109 patients (135 hips) treated with a Bernese periacetabular osteotomy. At an average followup of 9 years, 17 hips were converted to THA. However, the preoperative radiographs showed a higher rate of patients with OA than in our population, thus making direct comparison difficult (Table 3).
We report a series of patients with 96% followup at 25 years after triple osteotomy of the pelvis for developmental dysplasia of the hip. In this population of selected patients with a congruent joint and limited preoperative OA (Grades 0-1), the triple osteotomy can provide substantial pain reduction and improved function at 25 years followup. There appeared to be a substantial increase in OA between 15 and 25 years after triple osteotomy and the subsequent number of patients requiring THAs increased to 32%. A triple osteotomy can improve a patient’s symptoms, but it cannot normalize the joint and prevent OA from developing with time. If THA is required, it can be performed uneventfully.
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