Dysplasia of the hip frequently leads to early asymptomatic and symptomatic hip degeneration. The goal of contemporary joint-preserving hip surgery is to correct the anatomic abnormalities leading to early degeneration ideally to prevent or at least retard the development of secondary OA. The goal of the Bernese PAO is to specifically correct deficient acetabular coverage in hips with developmental dysplasia to prevent secondary osteoarthrosis. We raised the following questions: (1) what is the 20-year cumulative survivorship of hips that had the Bernese PAO?; (2) will the clinical scores and (3) the radiographic measures be maintained with time?; (4) do any demographic (age, gender, body mass index), clinical (hip pain, ROM, walking ability, pain provocation tests), radiographic (osteoarthrosis, femoral head morphology, acetabular coverage and orientation), or surgery-related factors (concomitant intertrochanteric osteotomy [IO] or previous surgeries) predict a poor outcome? Finally, we compared our outcomes with the natural history and with the results of other osteotomies.
In additional to the lack of a control group, there are three other limitations to our study. First, clinical parameters of all patients were assessed by different observers at each followup. This is unavoidable for a longitudinal study design spanning more than 20 years. In the literature, substantial interobserver agreement and intraobserver agreement have been reported for the Merle d’Aubigné and Postel score [20
], limp [4
], and ROM, particularly flexion [14
], internal [14
] and external [14
] rotation, and abduction [14
]. Most of these parameters differed between the preoperative and 20-year followup status and therefore we believe these limitations do not influence the results of this study to a large extent. We identified no publication about the reliability and correlation with morphologic findings intraoperatively or in MRIs of the anterior impingement test. This should be considered when comparing the rates of positive anterior impingement tests at the different followups or interpreting the anterior impingement test as a predictive factor. Second, this series of patients reflects the learning curve and the first experiences of a new surgical technique that could be associated with a higher rate of complications [40
]. Third, there was considerable heterogeneity in terms of indications, varying degrees of dysplasia [44
], OA grade, high number of previous operations, and additional underlying diseases. Although these variations likely reduced the overall 20-year survivorship results, these variations allow an analysis of factors predicting long-term survival.
The surgical technique underwent some minor modifications since the first case in April 1984 (Fig. ). The supraacetabular osteotomy is now placed more cranially from the anterior-inferior to the anterior-superior iliac spine to preserve vascularity of the acetabular fragment [2
] and to improve the hold of the Schanz screw for reorientation (Fig. ). In addition, since the introduction of the femoroacetabular impingement concept, more emphasis was put on avoiding anterior and lateral overcorrection or retroversion, which could be associated with an unfavorable outcome [34
]. For approximately 10 years now, an additional arthrotomy is performed routinely allowing for treatment of labral cysts, observation of range of internal rotation and flexion, and for correction of an aspherical portion of the femoral head-neck offset by osteochondroplasty to improve impingement-free ROM. Therefore, we believe the outcomes with the current technique (including the modifications) would be superior to those in our current study.
Fig. 6A–C The first Bernese PAO was performed in 1984 in a 13-year-old girl with a (A) subluxated femoral head articulating in a very shallow and retroverted acetabulum after proximal femoral focal deficiency. (B) The PAO was performed with a concomitant valgus (more ...)
We identified six factors predicting poor outcome (Table ). One was demographic, three were clinical, and two were radiographic factors. A substantial number of these factors were associated with an already advanced stage of joint degeneration at the time of surgery as could be proven for other types of acetabular reorientation procedures: the preoperative OA score [21
], a decreased preoperative Merle d’Aubigné and Postel score [58
], a preoperative limp, and a positive anterior impingement test indicating a labral lesion [18
]. In addition, advanced age [64
] was a risk factor for early conversion to THA. The only one of these parameters positively influenced by surgery was the postoperative extrusion index. An undercorrected hip with an extrusion index greater than 20% is prone to develop end-stage OA during the postoperative course. An aspherical femoral head could not be correlated with failure according to these data [30
]. Compared with the 10-year result of the same patient series reported earlier [47
], the Merle d’Aubigné and Postel score, preoperative positive anterior impingement test and limp, and postoperative extrusion index were new predictive factors. We could not confirm a diminished ACE or an acetabular index less than 0 or greater than 10° predicted poor outcome.
A comparison with the current literature on this topic is difficult. We considered these comparisons in three ways: with the natural course of dysplastic hips, with other acetabular reorientation techniques, and with alternative surgical treatments.
Describing the natural history of hips with dysplasia, Hartofilakidis et al. [12
] reported all referred dysplastic hips with a subluxation (ie, broken Shenton’s line) would undergo a THA by the age of 45. These authors would not, of course, be able to comment on asymptomatic patients with subluxation or those who were not symptomatic enough to warrant a referral; many of these patients might undergo THA at a later age or not at all. Others [59
] suggest an “inevitability of disabling coxarthrosis” in patients with recognized subluxation. In our study cohort, 54% of all hips with preoperative subluxation (Severin Grade 4 and higher) did not have additional surgery at a mean age of 41 years with a mean Merle d’Aubigné score of 16 points. Murphy et al. [31
] reported that all hips with an LCE angle less than 16° or an acetabular index greater than 15° ultimately would develop end-stage OA. In our symptomatic patient cohort, 54% with these radiographic characteristics had no additional surgery at the latest followup (mean age, 44 years). Given more than half of our patients with subluxation did not have additional surgery, we suggest the PAO provides outcomes superior to the natural history in symptomatic patients.
Comparing our results with those of other acetabular reorientation procedures, various studies are available with different followups, treatment in much younger patients before closure of the triradiate cartilage [3
], or strong inclusion or exclusion criteria (Table ). We found two studies for other periacetabular osteotomies with a followup of 20 years [43
]. Schramm et al. [43
] reported a slightly higher survivorship of 68% for the first 22 cases of spherical periacetabular osteotomy over two decades. However, their patients had a distinctly higher percentage of hips with no signs of preoperative osteoarthritis (77%). Takatori et al. [50
] reported a 100% survivorship of dysplastic hips after a rotational acetabular osteotomy at 15 to 22 years followup. However, their study was comprised of a highly selected patient population with a low number of patients (n = 15), no consecutive patient series, exclusively young patients (age younger than 29 years), no preoperative advanced stages of OA, no previous surgeries, and no concomitant femoral osteotomies. Furthermore, the high rate of patients lost to followup (32%) might bias survivorship. Comparing our results with those of other pelvic osteotomies (eg, Chiari, Salter, or triple osteotomy), higher survival rates are reported for a similar followup but in a considerably younger patient group [3
] with followup rates of only 60% [61
]. Our findings do confirm a worse outcome with increasing age at surgery [61
] and with preoperative signs of OA [61
]. Additionally, in all of the cited studies [3
] the patients had no previous surgical attempts to achieve better acetabular coverage or the series were selected with exclusion of patients with reoperation [3
] or neuromuscular disorders [61
Selected middle and long-term followups
Good results have been reported with isolated femoral varus ostetotomies [17
] or for patients treated with open or closed reduction [1
]; however, the patients reported in these series do not represent those in our series.
Despite the fact that our series represents the learning curve of a technically demanding procedure in an inhomogeneous patient group with various previous surgical attempts to achieve sufficient coverage and several concomitant IO, we believe the 20-year results of the first 75 hips are promising. Based on the predictive factors we identified, we suggest the ideal patient for this surgical procedure is young (younger than 30 years) with no or slight preoperative OA (OA score 0 or 1) and no severe hip pain. A positive anterior impingement test suggests an anterior labral lesion and therefore a worse prognosis. A major surgical difficulty is to find the correct balance between undercorrection and overcorrection of the acetabular fragment and to restore correct anteversion. Undercorrection should be avoided because a postoperative extrusion index less than 20% predicts worse outcome. However, overcorrection with acetabular retroversion may cause subsequent painful femoroacetabular impingement [34
], which also predicts a worse outcome. We believe these long-term results show PAO is an effective technique for treating symptomatic DDH in selected patients and can maintain the natural hip for at least 19 years in most patients.