Timing for Closed Reduction of Developmental Dysplasia of the Hip and Failure Analysis

Background It remains controversial whether the older age at closed reduction (CR) of developmental dysplasia of the hip (DDH), the higher incidence of complications. The aim of this study is to evaluate the Mid-term outcome of CR for DDH among difference age groups, and to analyze and identify risk factors for the failure of this procedure. Methods Clinical data of DDH patients, who received CR, were retrospectively reviewed. Hips were divided into three groups according to initial age (Group I: <12 months; Group II: 12 months to ≤ 18 months; Group III: >18 months). The presence of avascular necrosis (AVN), residual acetabular dysplasia (RAD), re-dislocation, further surgeries (FS) and failure of CR were observed. The risk factors were identied for those outcomes abovementioned. Receiver operating characteristics (ROC) curve analysis based on age, pre-op AI and post-op AI for failure was conducted.

Conclusions RAD is a complication that must be carefully considered for severe patients older than 18 months before CR. Re-dislocation is associated with pre-op IHDI IV and walking. Patients, who are older than 12.5 months or have a pre-op AI of 38.7° or a post-op AI of 26.4°, are more likely fail of CR.

Background
Developmental dysplasia of the hip (DDH) is the most common developmental malformation affecting children's hips. The principle of management for DDH has been widely adopted that a concentric reduction should be obtained and maintained through the intervention as early as possible [1,2]. Closed reduction (CR) of the hip is indicated in patients who failed to achieve stable reduction with Pavlik harness, and or as the primary treatment option for patients with late diagnosis [3,4]. Although this procedure has achieved satisfactory outcomes, CR may also lead to a number of adverse complications, including iatrogenic avascular necrosis (AVN), re-dislocation and residual acetabular dysplasia (RAD), which might need further surgeries (FS) to address. Since, several articles reported that increased age at the time of CR predicted a higher rate of complications or further corrective surgeries [5][6][7], while others not [8,9]. Moreover, it still remains controversial whether CR or open reduction (OR) should be adopted for children approaching or older than 18 months at the rst time, especially for the severe dislocated cases.
Balancing advantages and disadvantages of treatment options, and evaluating the risks of complications, will help in bringing to a better outcome. The aim of this present study was to evaluate the effect of CR among different age groups, to identify the risk factors of complications of CR and to discuss the indications for unsuccessful CR, especially in controversial age abovementioned.

Materials And Methods
After institution Ethics Committee approval (XHEC-D-2020-014), a retrospective review was performed in 107 patients with the diagnosis of DDH from January 2011 to December 2013 successfully undergoing CR and cast xation. The inclusion criteria were: 1) At least 36 months follow-up time and complete medical records. 2) Diagnosed with unilateral or bilateral DDH with International Hip Dysplasia Institute (IHDI), III, IV grade, or Tönnis III, IV grade, without any treatment before. 3) Successful CR at initial attempt. Patients were excluded if their follow-up time less than 36 months, pathological or other secondary hip dislocation, dysplasia of the hip without hip dislocation or unsuccessful CR initially (postoperative MRI indicating dislocation of the hip, including 11 patients).
CR under uoroscopic guidance was performed under general anesthesia in all cases. After the percutaneous adductor tenotomy, close reduction was performed according to a routine manipulation.
Namely, the hip was reduced by placing it in exion nearly 100 degrees and gradually abducting it on the position of stability (nearly 45 to 65 degree). Then a hip spica cast was xed in a human position with a gentle posterior mold. MRI examination was carried out under sedation within 24 hours postoperatively. The spica cast maintained 3 months. Plain radiography of the pelvis was taken every month. After threemonth immobilization, the cast was removed and changed to application of an adjustable abduction orthosis for 7 months. The orthosis contained four holes with cap nuts and adjusted timely according to our protocol of 1-2-2-2-month (Fig. 1).
The medical data of patients were collected. Anteroposterior x-ray lms were obtained pre-and postoperatively till the nal follow-up. Radiological data were evaluated and included the ossi cation centers of femoral heads, AI and Tönnis and IHDI grade; Complications included re-dislocation, RAD and AVN. Redislocation: hip dislocated on MRI during casting time or on X-ray when nished the CR. RAD: evaluated by AI (AI > 28° 1 year following CR or > 25° two to four years after CR [10]).The presence or absence of AVN based on the nal follow-up was determined by Salter et al. [11], with a simple "yes" versus "no" to reduce subtype variability. FS of open reduction (OR) and osteotomy were warranted when RAD or redislocation exist. Failure was de ned as either an open reduction at any time and/or AVN at the nal follow-up. All measurements and evaluations were made by 2 observers (HL and ZQZ) who didn't get involved in the clinical care without knowing the outcome of the treatments.
Continuous variable was analyzed by Kolmogorov-Smirnov test to assess for normality. Comparisons of 3 groups in terms of AI, time of splint immobilization and follow-up time were performed by using ANOVA. The chi-squared test was used to compare categorical variables (i.e. walking, ossi c nucleus, Tönnis and IHDI grade, AVN rate, RAD rate, re-dislocation rate and FS rate). Furthermore, univariable logistic regression was performed to evaluate the relationships among the prereduction factors, including age groups, walking, ossi c nucleus, preoperative AI, Tönnis and IHDI grades. We then calculated the sensitivity and speci city of parameters (age, pre-op AI and post-op AI) based on thresholds detected for the ROC curve. An alpha level of 0.05 was used in all tests. The analysis would be done by hip affected. A p value < 0.05 was considered signi cant. Statistical analysis was performed using SPSS 19.0 (IBM, America).

Results
Total 107 children (95 girls and 12 boys) with DDH had been successfully received CR followed by plaster and splint xation. There were 58 unilateral DDH patients and 49 bilateral DDH patients who at least present with one side hip dislocation. Mean age at initial treatment was 13.0 months, ranging from 4 to 28 months. Mean follow-up time in this study was 6.7 years (range, 3-8 years

CR of DDH at Different Age Groups
The in uence of age at the beginning of treatment for DDH with CR is presented in Table 1. There was no signi cant difference in the general characteristic (including sex, side, femoral head, splint time and Tönnis grade) among 3 groups. Compared with Group I, the pre-op IHDI grade was signi cantly difference with other Groups, while the pre-op Tönnis grade was not. However, postoperatively, no signi cant difference was found between IHDI and Tönnis grade. As for pre-op AI, there was no statistically difference, preoperatively, while post-op AI was signi cantly higher in comparison with Group I. Among the observed complications, only RAD in Group III was signi cantly higher than the other Groups. Moreover, signi cant difference was found between Group III and other groups in FS rate.

Univariable Logistic Regression of Prognostic Factors for Different Outcomes
Univariable logistic regressions were used to develop models predicting the potential Odds Ratio (OR) (   (Fig. 3).

Discussion
The principle of the treatment for DDH is to establish a stable, concentric reduction of the hip to enable the subsequent hip development as early as possible, given the well-established correlation between residual dysplasia and the age of reduction. CR plays an essential role during the process of DDH treatment, especially the young children, with high success rate and low complications. It has drawn more attention, in recent years, with various studies and researchers focusing on the topic that how to make a proper intervention strategy for DDH patients who are approaching or older than 18 months old, treatment could be CR followed by plaster casting, or performing OR as soon as possible once the diagnosis was established, since several articles indicated that older age might indicate poor outcome [5][6][7]. It is still a controversial issue among pediatric orthopedists. This study enrolled 107 children (156 hips) with DDH in a single center from 2011 to 2013 in order to evaluate the effect of CR among different age groups, to identify the risk factors of complications of CR and to discuss the possible indicators for failure of CR, especially in controversial age abovementioned.
Compared with Group II and III, Group I showed signi cant difference about IHDI grade, but not Tönnis grade. Moreover, the ossi c nucleus was not present in 34% hips. Comparing IHDI classi cation to Tönnis classi cation, Both Miao and Brandon et al [12,13] concluded that IHDI classi cation can be applied more exibly which can better re ect the severity of the conditions, especially for those cases without ossi c nucleus of the femoral head.
Postoperatively, for all the measurements, the difference between Group I and Group II III were statistically signi cant among post-op AI, which revealed that the older the child, the lower the potential for the normalization of AI. The decrease of AI indicated a sign of gradual normalization of acetabular morphological structures under the condition of concentric reduction of the affected hip. Shin et al [14] considered that an AI > 32° and CEA < 14° at the age of three years could serve as a guideline for osteotomy. Correspondingly, our results showed that if the post-op AI > 26.4°, CR was more likely to fail (84.1%). Pre-op AI also manifested with an obvious tendency to be fail if the value larger than 38.7°( 68.8%). The ROC curve also showed that the predictor of failure DDH treated by CR was the initially age > 12.5 months (65%).
Several articles reported older age at the time of CR showing a higher rate of complications or further corrective surgeries [5][6][7], while others not [8,9,15]. RAD in group III was found to be signi cantly high, compared with Group I and II. Moreover, the result of univariable logistic regression manifested that age ≥ 18months was the only risk factor for the happening of RAD (OR: 4.000; p = 0.012). That is to say the prevalence of RAD increases with the age of hip reduction. Other researches have indicated that in the case of lateral hip subluxation, the pressure on the femoral head becomes concentrated along the medial aspect of the head as the hip hinges along the edge of the acetabulum. The acetabular growth cartilage lls the acetabular oor and arrests its lateral growth, forming a progressively shallower and more oblique acetabulum [16,17]. Therefore, we thought that, for the dislocation patients, RAD was a complication that must be carefully considered for children older than 18 months, which might require FS to correct.
Although there was no in uence of age at initiation of outcomes on AVN and re-dislocation in our study, some researches granted age as risk factor of AVN [11,18,19]. Similar to our results, age was not found to be the risk factor of AVN after CR also reported in other literatures [9,15,20]. The rate of AVN (18.6%) in this present study was similar to previously reported studies (10%-33%) [7] [21][22][23][24]. The most common cause is the immobilization in a position that places excessive pressure on the femoral head. Thus, Ramsey et al. [25] recommended creating a "safe zone" to prevent AVN. In certain situation, an adductor tenotomy will increase the safe zone by allowing for a wider range of abduction, especially for patients with high Tönnis grade. Madhu et al [26] collected nine articles and analyzed the data, found out the most critical element of AVN was extreme abduction angle, and the ossi cation of the femoral head was not associated with AVN, which was similar to this our result and other studies [7,27]. AVN was not associated with age or other factors (sex, side, ossi c nucleus etc.) in our cohort, but the IHDI IV was found to be the risk factor for AVN and re-dislocation resulting from univariable logistic regression (OR: 2.524, p = 0.033; OR: 4.211, p = 0.004). For severe patients, CR was di cult to perform when extreme abduction was warranted to stable reduction, which AVN might occur. The incidence of re-dislocation after CR was 23.1% in this study, which was similar to Sankar's study [7]. Except from IHDI IV, the walking experience was also a risk factor about re-dislocation (OR: 2.524, p = 0.033). As the time went on, especially after independent walking, a series of pathological changes of the affected hip would make CR more di cult, which, certainly, lowered the e ciency of CR [28,29]. This is consistent with results in our present study, namely, walking ability should be an important evaluation at the time of treatment.
This study has a number of limitations. First, a longer follow-up until adult is necessary, which may lead to different results of AVN and FS rate. Second, all the included cases had successful CRs at the initial attempt, which might bring to a selection bias. Third, the study was retrospective and more randomized controlled trials or large-scale case-control studies are required for further validation.

Conclusion
In summary, treatment initiated > 18 months of age produced higher rate of RAD and FS. Re-dislocation is associated with pre-op IHDI IV and walking. Pre-op IHDI IV was also found to be the risk factor of AVN. The threshold age, pre-op AI and post-op AI values associated with an increased risk of failure are older than 12.5 months and lager than 38.7° and 26.4° and more, respectively. The parents of such children should be informed about the high risk of treatment failure and further surgeries.