Encompassing a spectrum from mild dysplasia to frank dislocation, developmental dysplasia of the hip (DDH) is one of the most common developmental deformities of the lower extremities and one of the leading causes of future osteoarthritis and hip arthroplasty.1,2 The goal of treatment is to achieve a stable, concentric reduction to facilitate normal femoral head development and continued acetabular growth and remodeling.2–4 For those infants who fail initial nonsurgical management, or those who present late, treatment often involves closed reduction (CR) and spica casting.2,5 Although this procedure is generally successful,2 concerns persist about the risk for iatrogenic avascular necrosis (AVN) of the femoral head and its associated impact on long-term outcomes and function.3,6–8 Other adverse outcomes may include redislocation and the need for further corrective surgery to address residual dysplasia.2,5
Although a variety of demographic and baseline characteristics have been proposed to influence outcomes, conflicting reports have often been described for each. Because of the mixed results following a failure of reduction, as well as the long-term negative impact of AVN, the role of CR in the management of DDH is increasingly being questioned. There is, however, a relative dearth of prospectively collected data guiding such decision-making. Therefore, the purpose of this multicenter study group was to establish a representative cohort of dislocated hips that may be followed prospectively to ascertain accurate long-term success and complications rates following CR for infantile DDH. For this investigation, the authors sought to determine early-term outcomes following CR, as well as potential risk factors for failure of therapy and the future development of AVN.
The data for this study were queried from a prospectively collected database of a multicenter, international study group [International Hip Dysplasia Institute (IHDI)]. Institutional review board approval was obtained by all sites before patient enrollment. At each encounter, contributing surgeons collected and uploaded all relevant patient information and pertinent clinical details to a central database, including most recent hip radiographs. This deidentified database was then queried between 2009 and December 2014 to identify all patients below 18 months of age at initial diagnosis who were treated with CR for DDH. All hips were frankly dislocated by ultrasound (≤35% femoral head coverage)9,10 and/or radiograph (IHDI grade ≥3)11 at the time of CR. Bilateral hips were counted separately. Fourteen hips were excluded for <12 months radiographic follow-up postreduction. As demonstrated in Figure 1, patients treated with open reduction at any time following the index CR were noted and separated from the final cohort
The database was designed to collect patient information and clinical details for each included hip from the time of initial consultation through most recent follow-up. All radiographic measurements, except AVN, were utilized as originally entered by the treating surgeon. The presence or absence of AVN by most recent follow-up was determined by independent, blinded assessment of follow-up radiographs by 3 authors from 3 different institutions (W.N.S., K.M., C.T.P.); group consensus was reached for any discrepancies. Each reviewer based their designations on the Salter criteria,12–14 but for the purposes of this manuscript each hip was only classified with a simple “yes” versus “no” for radiographic evidence of AVN to reduce subtype variability (Figs. 2A–C). Secondary outcomes included residual dysplasia (acetabular index and IHDI grade11), redislocation rate, and the need for further corrective surgery. Failure of CR was defined as either an open reduction at any time following the index reduction and/or an IHDI grade 3 or 4 hip at most recent radiographic follow-up.
Comparative analyses were performed using the Fisher exact/χ2 tests, Student t tests/Mann-Whitney U test, or ANOVA. Multivariate regression was used to assess outcomes when controlling for given patient characteristics and/or clinical details. Categorical variables are reported as frequency and percentage; continuous variables are presented with a measure of central tendency (mean or median) and spread (SD or range). All comparative analyses were 2-tailed with α set at 0.05. Statistical analysis was performed using Stata (StataCorp, College Station, TX).
A total of 78 patients (87 hips) across 7 institutions were evaluated. Median age at initial CR was 8 months (range, 1 to 20 mo; Fig. 1). Of these, 8 hips (9%) could not be successfully closed reduced on initial attempt. Hips that were irreducible on clinical and/or ultrasonographic exam were more likely to have an unsuccessful initial CR. We found no other significant differences between those that were and were not able to be successfully closed reduced (Table 1).
Among infants with an initially successful CR (n=79; 91%), 34% were previously treated in brace (Pavlik harness and/or rigid abduction orthosis) for a median of 3 weeks (range, 1 to 25 wk). An adductor tenotomy was performed in 85% of infants, a psoas release in 14%, and prereduction traction in 13%. When used, prereduction traction was for an average duration of 1 week. For those with preoperative ultrasound (n=32, 41%), median femoral head coverage was 10% (range, 0% to 40%), and median α angle was 48 degrees (range, 22 to 60 degrees). For those with preoperative radiographs (n=57, 72%), the proportion of infants with a prereduction IHDI grade of 1, 2, 3, or 4 was 0%, 12%, 56%, and 32%, respectively. An ossific nucleus was present in 56% of hips. Following the initially successful CR, 90% of hips were placed into a hip spica cast (median 12 wk; range, 4 to 30 wk), and 10% were placed directly into a Denis Browne splint (median 26 wk; range, 9 to 53 wk). Of those treated with spica casting, 68% of hips were treated to some extent with a postcasting abduction orthosis (eg, Rhino cruiser, broomsticks, Denis Browne splint, etc.).
At most recent follow-up (median 22 mo; range, 12 to 36 mo), 7/79 initially successful CRs (9%) went on to fail (6 requiring open reduction; 1 with an IHDI grade of 3) (Table 2). The failures occurred at a median of 4 months (range, 1 to 6 mo) following the index reduction. Within our limited numbers, the likelihood of failure was unaffected by initial clinical reducibility of the hip (P=0.434), age at initial CR (P=0.897), or previous treatment in brace (P=0.222). There was a nonsignificant trend toward fewer adductor releases (57% vs. 88%, P=0.065) and higher initial IHDI grades in hips that failed initial reduction.
At most recent follow-up, 67/72 (93%) hips were IHDI grade 1 and 5/72 (7%) were grade 2. According to consensus review of the radiographs, 18/72 (25%) of hips developed radiographic evidence of AVN (Table 3). The risk of osteonecrosis was unaffected by prereduction reducibility of the hip (P=0.586), age at CR (P=0.745), presence of an ossific nucleus at the time of reduction (P=0.496), previous treatment in brace (P=0.662), or prereduction traction (P=1.000). Hips that developed AVN had a significantly longer duration of postreduction spica casting (median 15 wk vs. 12 wk, P=0.011). There was a nonsignificant trend toward increased AVN with higher initial IHDI grade.
At latest follow-up, mean acetabular index was 25 degrees (±6 degrees), and was unaffected by any baseline characteristics or treatment details, including the presence of AVN on final radiographs (P=0.220). The Spearman correlations revealed no statistically significant linear association between age at CR and final acetabular index (P=0.553). During the follow-up period, 8/72 successfully reduced hips (11%) underwent acetabular and/or femoral osteotomy for residual dysplasia (Supplementary Table 1, Supplemental Digital Content 1, http://links.lww.com/BPO/A87). Hips treated with further corrective surgery were older at the time of CR (median 14 mo vs. 8 mo, P=0.003), more likely to have an ossific nucleus present (100% vs. 52%, P=0.017), and less likely to have been treated with a prereduction brace (0% vs. 36%, P=0.049). Hips with AVN were not more likely to undergo further corrective surgery (P=1.000). Increasing severity of initial disease as measured by IHDI grade did not appear to affect the rate of further corrective surgery for residual dysplasia (P=0.362).
As one of the primary treatment options for infants with DDH, CR typically includes examination under anesthesia, arthrogram with/without an adductor tenotomy, and postreduction immobilization of the affected hip (eg, spica cast). Although largely successful, CR may also lead to a number of adverse complications, including AVN and loss of reduction. Most outcome data for CRs, however, are based on retrospective series. Specifically, a systematic review by Novais et al15 evaluating both open and closed management of DDH noted that “the majority of studies included were rated as being of poor methodologic quality” and that “higher quality evidence is needed to better understand” the potential risk factors for future AVN.
In addition to establishing a representative multicenter cohort that can be followed prospectively, the purpose of this investigation was to report early outcomes following CR for DDH. At early-term follow-up (median 22 mo; range, 12 to 36 mo), our cohort had a 91% initial success rate with a 25% incidence of AVN, a 9% incidence of redislocation following an initially successful CR, and an 11% incidence of further corrective surgery. Interestingly, the likelihood of either loss of reduction or the development of AVN was unaffected by a number of characteristics frequently cited to negatively influence early outcomes, including femoral head reducibility before CR, previous orthotic bracing, age, or presence of the ossific nucleus at the time of reduction. Conversely, infants that were older at the time of CR were more likely to need further corrective surgery. Importantly, this study’s multicenter design and primary analysis by investigators not affiliated with the treating institutions limited the publication bias inherent to any single-center, self-authored cohort.
Osteonecrosis is one of the most concerning complications following CR. In recent studies (published since 2000), the incidence of AVN following CR varies widely between 2% and 36%,4,5,13,14,16–27 with Cooper et al2 noting that this disparity is “largely caused by differences in the definitions of AVN and the timing of follow-up.” Comparing closed versus open treatment, Novais et al15 reported in their recent meta-analysis an incidence of significant AVN (grade ≥2) of 8% following CR versus 19% following OR, with Clarke et al19 reporting a similar pattern of 7% and 14%, respectively. Here, our reported incidence of AVN was 25% at a median follow-up of approximately 2 years. Although some have suggested that prolonged follow-up for 10 to 12 years is necessary to ascertain the true incidence of AVN,3,6,7 others argue that follow-up beyond 2 years will not identify additional cases.14,28–30 A variety of classification criteria have also been used, and many authors differentially include low-grade changes.2 This variation in AVN definitions and lengths of follow-up highlight the importance of establishing a prospective cohort that can be followed longitudinally to determine accurate data.
Multiple potential risk factors for AVN have been reported, with the presence of the ossific nucleus at the time of reduction remaining one of the most controversial. Although some authors argue that the ossific nucleus is protective against AVN,17,19,27,31 others note no such effect.18,23,24,26,29 Relatedly, whereas some have linked older age at reduction to a higher incidence of AVN but a lower rate of severe disease,3,7,18,32 others have noted that age at reduction has no effect on AVN risk.4,6,15,24,29,31 In this cohort, neither age at reduction nor the presence of an ossific nucleus was associated with the presence of AVN. Consistent with prior studies, sex, bilateral disease, family history, previous treatment with Pavlik harness/abduction orthosis, and the performance of an adductor tenotomy also did not impact disease frequency.3,6,13,17,21,29,31 Although a trend was appreciated, the limited number of patients with prereduction radiographs may have constrained our findings regarding the severity of initial dislocation (as measured by IHDI grade), which prior reports suggest may influence AVN risk.3,18,32 We did note an increased length of spica cast immobilization following CR in those who developed AVN versus those who did not. Whereas this difference was statistically significant, its clinical significance is unclear. It is possible that longer periods of casting were an indirect reflection of greater disease severity, or that there is an intrinsic ill effect on perfusion from prolonged immobilization of an infantile hip.
Achieving, and maintaining, a concentric reduction of the hip is one of the primary drivers of future acetabular growth and development.4,33,34 Although potential overlap is likely, rates of failed initial reduction across the literature vary between 6% and 25%,2,13,16,20,25,35,36 and rates of loss of reduction from 0% to 18%.5,13,16,20,23–25,35–37 In this cohort, 91% of hips were successfully reduced on the initial attempt, with 9% going on to fail CR at latest follow-up. Importantly, however, rates of failed initial reduction are likely to vary considerably based upon the treating surgeon’s threshold for proceeding directly to open reduction. Nevertheless, our results fall within the lower half of the previously reported ranges, suggesting reasonable success may be achieved following CR.
Several factors have been proposed to increase risk of residual dysplasia following CR. In this study, we chose to measure residual dysplasia in 2 ways: objective acetabular measurements (acetabular index and IHDI grade) and the incidence of further corrective surgery. Regarding the former, no patient-specific factors in this cohort were predictive of worsened acetabular index, including prereduction IHDI grade, age at reduction, or final AVN status. Regarding the latter, 11% of hips in this study were treated with a subsequent acetabuloplasty and/or femoral osteotomy, although that rate will likely rise with continued follow-up. In comparison, rates of further corrective surgery across the literature range as high as 57% to 100%,19,22,38 with the majority of published studies identifying a frequency ≤35%.5,16,21,23,25,36,37,39 In contrast to the acetabular index, we did observe that increased age at the time of CR predicted a higher rate of further corrective surgery, which is consistent with Luhmann et al’s37 observation that delaying CR may increase the need for later intervention.
This study has a number of limitations. First, longer follow-up may lead to different values for AVN, acetabular dysplasia, and further corrective surgery. The purpose of this study was to report early results from a prospective cohort of infants undergoing CR. Certainly, we aim to follow this cohort longitudinally to provide long-term success and complication rates. Second, AVN is difficult to unilaterally define, as there are a variety of different classification systems in use across the literature. Given the potential for these variations to impact the reported frequency of AVN within our database, we chose to retrospectively assess AVN using a blinded panel of surgeons each applying the Salter criteria in a yes/no manner, a step the authors felt was imperative to improve the accuracy and consistency of our findings. Third, due to the large number of surgeons contributing to the database, there is considerable variation in treatment practices. Regardless, the authors view this heterogeneity as a strength in that it more accurately reflects real-world practice. Fourth, given the smaller number of hips with certain conditions and/or outcomes, the P-values in our tables should be interpreted with caution. Fifth, we did not measure abduction angle in postreduction immobilization, which has been suggested to influence AVN rates,26,40 as practice variation in postoperative imaging and treatment limited the availability of such data. Finally, the quality of our results is dependent on the completeness and accuracy of data reporting by the individual centers, which is a limitation of any multicenter database study.
In conclusion, this prospective, multicenter cohort of infants undergoing CR for DDH demonstrated a 9% failure rate after initially successful reduction and a 25% rate of AVN at early-term follow-up. In this study, older age at the time of CR and longer immobilization in a spica cast were predictive of needing further corrective surgery for residual dysplasia and developing osteonecrosis, respectively. No other patient-specific factors related to history, treatment, or outcome were associated with the future development of either AVN, residual dysplasia, or failed reduction. Further follow-up of this cohort will be necessary to establish accurate long-term success and complication rates following CR for infantile DDH.
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