Implementing the AAOS Guidelines for Screening of Developmental Dysplasia of the Hip Before the Age of 6 Months in Taiwan

Abstract

Background: 

The prevalence of developmental dysplasia of the hip (DDH) has been considered to be low in East Asia, but this may be incorrect because of inconsistent diagnostic definitions and testing criteria. In 2015, the AAOS released guidelines for systematic screening for DDH in newborns. We implemented these guidelines and compared DDH incidence and outcomes before and after their implementation.

Methods: 

We used a historic comparison cohort of newborns with DDH between July 2015 and May 2017 before guideline implementation (the preguideline group); their data were retrieved using electronic medical records. In this group, the newborns received general hip screening without systemic follow-up. The postguideline group included newborns who were screened for hip dysplasia and followed up per the AAOS guidelines between July 2017 and May 2019. Their data were prospectively collected. The primary outcome in the postguideline group was DDH incidence. Other outcomes included rates of referral, surgery, and complications, and DDH prognosis.

Results: 

The preguideline and postguideline groups included 3534 and 2663 newborns, respectively, of whom 49 (1.1%) and 225 (8.4%), respectively, were referred to the pediatric orthopaedic clinic enrolled. In the postguideline group, 35 patients were diagnosed as having DDH (incidence: 1.3%, 95% CI: 0.8%–1.9%). Both the incidence and referral rates were significantly higher in the postguideline group than in the preguideline group. Furthermore, the mean age at referral was 6.7±10.06 months and 0.9±0.25 months in the preguideline and postguideline groups, respectively, indicating a potential for early treatment in the postguideline group. Finally, the female sex was identified as a risk factor for residual hip dysplasia at 6 months of age.

Conclusion: 

DDH incidence in East Asia seems comparable to that in Western countries. Implementing the AAOS guidelines increased the diagnosis rate and opportunity for early treatment initiation, thus potentially avoiding surgical intervention. Nevertheless, residual DDH may be detected in some patients at 6 months of age, particularly in female infants.

Level of Evidence: 

Level IV.

Developmental dysplasia of the hip (DDH) has been considered to be 10 times less prevalent in East Asian people than in White people.¹ However, this finding was obtained in a study from Hong Kong in the 1980s, in which the participants were family physicians, obstetricians, and caregivers of newborn babies, and DDH was defined as the dislocation of the hip at birth.

DDH is currently considered a spectrum of disease and is defined as an abnormal relationship between the acetabulum and femoral head during development.^2,3 The spectrum includes hip dislocation or dislocatable hip, acetabular dysplasia, and hip subluxation and leads to a higher risk of early hip osteoarthritis, warranting further treatment.⁴

The first primary screening report in Taiwan was published in 1988,⁵ which indicated that the DDH incidence was 2.7 per 1000 births. It defined DDH as hip dislocation or dislocatable hip on physical examination. Universal neonatal hip screening with a physical examination was introduced in Taiwan in 2002, but no clear rules have been established for follow-up. Moreover, most physicians performing neonatal hip screening in Taiwan are residents whose relative lack of experience often causes negative or uncertain results. Follow-up studies on DDH incidence in Taiwan investigated based on Taiwan’s National Health Insurance Research Database have reported the incidence as 1.75 per 1000 newborns. In 2015, AAOS published a systematic screening guideline for DDH in newborns.⁶ However, Taiwan has not introduced systematic screening and tracking standards for DDH. Thus, DDH incidence in Taiwan remains unclear.

Compared with the AAOS guidelines, the current screening protocol for DDH in Taiwan lacks clear ultrasound examination time, a clear definition of risk factors, or a clear follow-up time course; moreover, most neonates with abnormal findings or risk factors cannot be tracked up to 6 months of age, and first-line pediatricians do not reach a consensus on physical examination findings. Therefore, we evaluated DDH incidence by using the 2015 AAOS guideline (Detection and Nonoperative Management of Pediatric Developmental Dysplasia of the Hip in Infants up to Six Months of Age).⁶ We also compared the outcomes after implementing this guideline with those before implementation.

METHODS

This is a historic comparison study performed in a single medical center in north Taiwan. The study protocol was approved by the local Institutional Review Board (TPEVGH IRB No. 2022-06-018AC, date of approval: July 11, 2022) and followed the Guideline for Good Clinical Practice.⁷

The study was divided into 2 groups: preguideline and postguideline. Data from the preguideline group were collected retrospectively from the hospital’s electronic medical records from July 2015 to May 2017. The postguideline group comprised neonates who underwent hip screening according to the AAOS guidelines and were followed up based on the guidelines until at least 6 months of age. The data of the postguideline group were collected prospectively from July 2017 to May 2019.

Description of the Preguideline Group

General hip screening for newborns was implemented in Taiwan in 2002. In common clinical conditions, screening is performed mostly by pediatric residents, and if problems are found, follow-up in the pediatric clinic is arranged.

However, the definitions of risk factors remain unclear, and no regulations or clear consensus on follow-up time and duration and referral to pediatric orthopaedics exist.

Screening Protocol in the Postguideline Group

The protocol in the postguideline group was performed by 2 pediatric orthopaedic surgeons. According to the guidelines, we designed a screening flowchart, which is a type of selective ultrasound screening for DDH (Fig. 1). Newborns were classified into the dislocated hip, dislocatable hip, unstable hip, and risk factor groups. Current evidence reveals that the risk factors for DDH are controversial and diverse. As the guideline recommends, we adopted breech and family history as 2 risk factors for DDH because the evidence of these 2 factors as the risk factors were the strongest.⁶

FIGURE 1: Flowchart of the screening protocol and follow-up results in the experimental group.

If the hip is dislocated or dislocatable, DDH is indicated, and we arrange Pavlik harness treatment immediately. In cases with unstable hips or risk factors, we arrange hip sonography at 6 weeks of age and follow-up every month; if the hip ultrasound indicates persistent dysplasia, corresponding treatment is initiated.⁸

We use the Graf classification to define and grade hip dysplasia,^9,10 with Graf 1 (α angle: 60°) indicating a normal hip; Graf 2a (α angle: 50°–59°) indicating borderline data, necessitating further follow-up; and Graf 2c or more (α angle <49°) indicating hip dysplasia, necessitating treatment.⁸ The relevant measurements for the Graf classification were undertaken by 2 pediatric orthopaedic surgeons. The Graf method has been reported to have moderate interrater and intrarater reliability (0.59 and 0.57, respectively).¹¹

During the screening protocol, we defined the patient as having DDH if they received treatment for DDH. In the current study, we followed up with all the patients with positive physical findings, abnormal sonographic findings, and risk factors until at least 6 months of age, as suggested by the guidelines⁶ (Fig. 1). At 6-month follow-up, we assess the single-view anteroposterior radiograph of the pelvis and use the acetabular index (AI) to discriminate hip dysplasia or normally developed hip. If AI >30°, residual hip dysplasia is diagnosed.¹²

Treatment Protocol in the Postguideline Group

The treatment protocol was designed according to DDH severity. In dislocatable or dislocated hips, immediate treatment with the Pavlik harness is initiated.^2,8 In patients with an unstable hip or having risk factors, treatment is determined based on the follow-up sonographic examination. If the sonography reveals hip dysplasia (Graf 2c or more), a Pavlik harness treatment is conducted. In patients with immature hips (Graf 2a), we perform further follow-up at a 1-month interval, and if persistent abnormal ultrasonic findings are noted, the Pavlik harness treatment was performed.

The duration of the Pavlik harness treatment is controversial.⁸ In our practice, the patients wear the Pavlik harness for 23 h a day, and the frequency of follow-up visits is based on severity, with visits continuing until the sonographic image shows classification as Graf I. Weekly follow-ups are arranged for newborns with hip dislocation or dislocatable and monthly follow-ups are scheduled for those with radiographic hip dysplasia. Our protocol does not involve the weaning of the Pavlik harness after normalization because the current evidence does not support this practice.¹³

Outcome Measurement

The primary outcome was DDH incidence in the postguideline group. Incidence is defined as the number of newborns who received treatment for DDH divided by the total number of newborns in the postguideline group during the study period. Moreover, we report the residual hip dysplasia rate at 6 months of age under the current screening protocol.

The secondary outcome was a comparison of the early diagnosis rate, refer rate, early treatment rate, surgical rate, and complications rate between the postguideline and preguideline groups.

Statistical Analysis

Descriptive data are reported as frequencies, percentages, and means. Continuous variables were analyzed using Student’s t test, and categorical variables were analyzed using the χ² test. Statistical significance was defined as a 2-sided P value of <0.05. All statistical analyses were performed using MedCalc v19.6.4 (MedCalc Software, Ostend, Belgium).

RESULTS

The preguideline group consisted of newborns who received routine hip screening between July 2015 and May 2017. A total of 3534 newborns were reported during this period. In the postguideline group, after the introduction of the AAOS guidelines, 2663 newborns born between July 2017 and May 2019 underwent screening based on the AAOS guidelines. A comparison of the basic demographics between the 2 groups is presented in Table 1. No significant difference was observed between the postguideline and preguideline groups.

TABLE 1 - Demographic Characteristics of the Preguideline and Postguideline Groups

Characteristic	Preguideline Group (n=3534)	Postguideline Group (n=2663)	P
Female, n (%)	1682 (47.6)	1263 (47.4)	0.861
Firstborn, n (%)	1342 (38.0)	1009 (37.8)	0.865
Multiparity, n (%)	123 (3.5)	105 (3.9)	0.379
Gestational weeks (SD)	38.6 (0.9)	38.7 (1.1)	0.216
Birth weight (g) (SD)	3077 (274)	3085 (326)	0.263
Apgar score (SD)	7.84 (0.47)	7.85 (0.40)	0.355

In the preguideline group, 49 patients were referred to the pediatric orthopaedic clinic, and the referral rate was ~1.1% (CI: 0.7–1.3%). Among the patients referred, no patient had a dislocated or dislocatable hip. The mean age at referral was 6.7 months (SD =10.06). Among these 49 patients, 27 were regarded as having normal hip development, and 22 were considered to have DDH; 12 of these 22 patients received early treatment (Pavlik harness). The other 10 underwent corrective osteotomy because they were older than the acceptable range for the harness, and 7 of them had to undergo multiple surgeries.

In the postguideline group, 225 patients were referred to the pediatric orthopaedic clinic; the referral rate was 8.4% (CI: 7.3–9.6%), and the mean referral age was 0.9 (SD =0.25) months. Of these 225 newborns, 3 were diagnosed as having hip dislocation and 13 had dislocatable hips; these 16 patients received Pavlik harness treatment immediately in the neonate room. The remaining 209 neonates with hip instability or risk factors were followed up in the clinic, and no delayed hip dislocation or dislocatable was found; ultimately, ultrasonography revealed hip dysplasia or persistent hip immaturity in 19 of them. These 19 patients were treated with the Pavlik harness until ultrasound morphology showed normal results (Graf I). A total of 35 patients in the postguideline group were diagnosed as having DDH and received Pavlik harness therapy before 6 months of age; therefore, the incidence of hip dysplasia was 1.3% (CI: 0.9–1.8%) in the postguideline group (Fig. 1).

Among the 35 patients who received harness treatment, 1 was converted to closed reduction due to the failure of Pavlik harness treatment, and the remaining 34 patients were successfully return to normal sonographic morphology under harness.

Compared with the preguideline group, the postguideline group had a higher referral rate (8.44% vs. 1.11%, P=0.001) and lower referral age (6.7 mo vs. 0.9 mo, P=0.002). In the preguideline group, due to the relatively high referral age, 10 neonates exceeded the age limit for Pavlik harness and required surgery.

In the preguideline group, complete dislocation of the hip joint or dislocatable hip was not found in neonates during general physical examination (Table 2).

TABLE 2 - Difference in Outcomes Between the Preguideline and Postguideline Groups

Outcomes	Preguideline Group (n=3534)	Postguideline Group (n=2663)	P
Referral numbers, n (%)	42 (1.11)	225 (8.44)	0.001*
Average referral age (mo) (SD)	6.7 (10.06)	0.9 (0.25)	0.002*
No. Pavlik harness, n (%)	12 (0.25)	34 (1.27)	0.001*
No. surgical treatment, n (%)	10 (0.2)	1 (0.03)	0.051
Severity of DDH	—	—	0.001*
Dislocated	0	3	—
Dislocatable	0	13	—
Unstable	20	55	—

^*P<0.05.

DDH indicates developmental dysplasia of the hip.

In the postguideline group, 119 patients finally completed the 6-month follow-up (Fig. 1). All 35 patients treated for DDH were followed up until 6 months of age, and the remaining 84 newborns had normal development on ultrasound examination during the screening process. At the final follow-up in the sixth month, 22 were diagnosed as having residual hip dysplasia through pelvic radiography. Of these 22 patients, 6 had DDH and were treated with a harness, and 18 were not identified as having DDH during the systemic screening.

Of the 34 patients with normalization of hip morphology after the Pavlik harness treatment, 6 exhibited residual hip dysplasia at the 6-month follow-up. The Pavlik harness treatment had an 80% (CI: 59%–92%) success rate. The risk factors for residual hip dysplasia are listed in Table 3. Female sex is the main risk factor for residual hip dysplasia at 6 months of age; no other risk factors for residual DDH have been observed (Table 3).

TABLE 3 - Characteristics of the Residual Hip Dysplasia at the 6-Month Follow-Up in the Postguideline Group

Characteristic	Normal hip morphology (n=97)	With residual hip dysplasia (n=22)	P
Female, n (%)	63 (64.9)	20 (90.9)	0.001*
First birth, n (%)	28 (35.0)	7 (31.8)	0.781
Multiparity, n (%)	6 (7.5)	0 (0)	0.187
Positive physical findings, n (%)	13 (13.4)	4 (18.2)	0.472
Breech position, n (%)	16 (16.5)	3 (13.6)	0.742
Positive family history, n (%)	15 (18.8)	2 (9.1)	0.284
Have had received Pavlik harness, n (%)	22 (22.7)	6 (27.3)	0.648

^*P<0.05.

Positive physical findings include dislocated, dislocatable, and unstable hips.

DISCUSSION

The study prospectively investigated DDH incidence under AAOS guidelines in Taiwan and reported the 6-month follow-up results. Moreover, we evaluate the impact of introducing AAOS guidelines in clinical practice by comparing the results obtained after implementation with the records before guideline implementation. To the best of our knowledge, this is the first study to evaluate the effect of applying AAOS guidelines in clinical practice. This is also the first study to prospectively evaluate DDH incidence in the Eastern Asian group based on modern DDH definitions.

A comparison of the 2 groups revealed that before implementing the guidelines, the overall referral rate was only 1.1%, and no newborn with hip dislocation or hip dislocation was found. In the preguideline group, the mean age of the referred patients was 6.7 months, which was past the optimal time for Pavlik harness treatment. As a result, approximately half of the infants diagnosed as having hip dysplasia in the preguideline group required osteotomy, and most of them required multiple surgeries.

By contrast, after the introduction of AAOS screening guidelines, the referral rate increased to 8.4%, and the mean age of referral was 0.9 months, making all patients eligible for Pavlik harness as first-line treatment. Moreover, patients with complete dislocation or dislocation of the hip joint were more frequently identified, thus facilitating early treatment.

The results of the postguideline group revealed that DDH incidence in Taiwan is 1.3% (95% CI: 0.9%–1.8%). The success rate of Pavlik harness treatment was 80% (95% CI: 59%–92%).

Even after systematic screening and ultrasonography, 22 infants were found to have radiologic hip dysplasia at 6 months of age, with female sex being the main risk factor. However, these 22 infants were treated with abduction brace and were found to return to normal development levels at follow-up, with none requiring surgery.

The DDH incidence reported in this study is 10 times higher than that in other reports in Asian countries.^1,14,15 However, the reported incidence is not higher than that in other regions from Europe and the Americas.¹⁶ Moreover, a cross-sectional study in China revealed that the DDH incidence in adults is 1.52%, which is similar to the incidence reported in our study.¹⁷ The low incidence of DDH in the Eastern Asian group may be due to the lack of sufficient awareness regarding DDH or the lack of a complete protocol to support DDH screening and follow-up in the public health policy in this region.

Even in the current screening protocol, a few patients showed residual DDH at the 6-month follow-up. This may be explained by the possibility of a false-negative result on sonographic examination.¹⁸ Moreover, selective ultrasound screening may not be sufficient to detect DDH.

The reliability of the AI remains controversial; sex has been demonstrated to have an effect on the AI.¹² Therefore, in our study, female babies accounted for the most cases of residual DDH. Although DDH may still be suspected at the 6-month follow-up, the AAOS guidelines enable patients and health providers to detect DDH early and thus avoid the need for surgical intervention.

Limitations

This study has some limitations. The study samples were collected from a single medical center; therefore, the results may not be generalizable to the general population. The data used in the preguideline group were retrospective in nature, and most hip examinations in the preguideline group were completed by resident physicians and interns, leading to possible false-negative results. Moreover, in the postguideline group, the procedures were performed by pediatric orthopaedic physicians, which may have caused observer errors. In addition, only 119 patients returned at the 6-month follow-up, resulting in missing values and false-negative errors.

CONCLUSION

The incidence of hip dysplasia before 6 months of age is 1.3%. The implementation of the AAOS guidelines presents the advantage of early referral age, which helps physicians provide timely treatment and thus avoid the need for surgical interventions. However, residual DDH may still be detected in some patients at 6 months of age, with the female sex being a major risk factor.