Practice Essentials of Imaging in Early Diagnosis of DDH

Abstract

Introduction

Developmental dysplasia of hip joint (DDH) is a dynamic progressive pathology which can tilt either way. The term strictly applies to primary dysplasia, where etiology is not clearly known. Secondary dysplasia can be due multiple causes, such as neuromuscular disorders, connective tissue disorders or skeletal syndromes.

Methods

The etiology being multifactorial, it needs a multidisciplinary team to address the issue at hand. The management starts antenatally with a detailed history of any risk factors and a dedicated ultrasound of the foetus, since forewarned is forearmed. At birth, a paediatrician having a keen sense of DDH will perform Barlow’s or Ortolani’s manoeuvre and can be the first one to sound the alarm in the event of positive findings. How and when a Radiologist needs to step in will depend on inter-departmental discussions between the paediatrician and the orthopedician.

Results

In the presence of positive clinical screening tests, and non-availability of ultrasound, a preliminary X ray pelvis AP view including both hip joints should be the requisitioned in a child of any age, particularly, if belonging to the high-risk group. If ultrasound is available, a screening exam till 6 months of age is recommended to rule out DDH.

Discussions

India is known for its vast numbers and little babies with occult diseases are the first to bear the brunt of conditions which have very few symptoms to start with. DDH is one such condition which most unfortunately expresses itself as a symptom only when it’s too late, i.e., most often when the child begins to walk. Ultrasound is the modality of choice in neonates; however, since India is a country of modest means, in majority of the regions, radiographs still remain the first line of investigation.

Section I Radiographic Evaluation of DDH

Introduction

Developmental dysplasia of the hip (DDH) is a multifactorial derangement of the femoral head and acetabular relationship starting in-utero [1]. Femoro-acetabular relationship works in a synergistic manner, that is, a well-placed femoral head within the acetabulum helps the acetabulum to develop optimally and vice versa. DDH encompasses a wide spectrum of clinical presentations which include acetabular dysplasia, subluxation of the femoral head or complete dislocation of femoral head from the true acetabulum. DDH is a common musculoskeletal disorder in the paediatric population, with an incidence of approximately 3–4 per 1000 live births [2]. In India, the incidence has been reported to be 1.0–9.2 per 1000 in various studies, with the incidence being higher in northern region [3–5]. Despite the fact that these numbers look small, the end result of missed or neglected cases is a big let-down, since the disability resulting from DDH is preventable [6–8]. The treatment of DDH is most effective and remains non-surgical if the diagnosis is made early. Left untreated beyond a certain age, such as when the child begins to walk, leads to an increase in surgical interventions and high probability of sub-optimal results [9]. Complications, such as an abnormal gait, leg-length discrepancy, early adult-hood osteoarthritis and rarely avascular necrosis can ensue [10]. Majority of the medical centres do not have an access to a trained ultrasonologist or a Radiologist to evaluate DDH by ultrasound. However, X-ray facilities are quite well established across the nation with the presence of qualified radiologists to interpret DDH findings. The average age of presentation in India is about 1–2 years, depending upon the gender of the child, astuteness of the parents and the stage at which the child begins to stand or walk [11]. Lack of awareness and understanding of DDH amongst general population is an important factor that leads to late presentations and an increase in morbidity. Hence it becomes a joint responsibility of all concerned including the obstetricians to keep the high-risk population appropriately counselled about the need for an early surveillance. Public awareness programs can help disseminate information about the role of ultrasound and radiographs in the management of DDH at various ages. Ultrasound loses its efficacy after 6 months of age. Thus, radiographs become the strength in evaluation of DDH at an older age. CT and MRI are reserved for problem-solving during the course of treatment and in the follow-up of cases. For the purpose of routine screening, CT is falling into disrepute due to the radiation related adverse effects on growing immature skeleton and on the gonads [12].

Indications

Physical examination of a newborn is usually a part of screening for DDH. Static ultrasound combined with dynamic study (Harcke’s method) is the modality of choice [13] in infants younger than 6 months of age, while X-ray pelvis including both hip joints is more useful in older children.

Plain radiographs are of a limited value in evaluation of DDH in a new born, because unossified femoral head and partly cartilaginous acetabulum are not visible on the X rays. Yet, radiography can be performed at any age and is the standard imaging modality after 6 months, the only limitation being radiation safety in an immature skeleton. After 6 months of age, ultrasound is rendered ineffective, because the developing ossific nucleus in the femoral head epiphysis starts obscuring ileum and triradiate cartilage which form important sono-landmarks for a diagnosis. [14]. Following the As Low As Reasonably Achievable (A.L.A.R.A) principle, indications for requisitioning a radiograph in DDH evaluation are as follows:

Before 6 months of age:

• In the absence of ultrasound availability

• For children in high-risk group

• Positive clinical exam

• In the presence of other congenital skeletal abnormalities

• For evaluation during conservative management—with Pavlik’s Harness

After 6 months of age:

• Assessment at the time of first presentation

• After Closed or Open reduction

• For evaluation with hip spica

• During follow-ups

Definition of High-Risk Group viz-a-viz DDH [15]

There are multiple factors which may cause or predispose to DDH in a child.

A positive family history of DDH, if the child is a first born, a girl child, h/o multiple gestation, prematurity, breech presentation (with knees extended), oligohydramnios and a history of improper swaddling, are important risk factors which may contribute to DDH in a child.

Basic X-ray Projections and Technique:

1. The most important projection is the Antero-posterior (AP) or Frontal view of the pelvis with both hip joints, in neutral position. The patient is supine with both lower limbs stretched symmetrically and both patellae facing forwards (Fig. 1a).

   For achieving symmetry of the pelvis and accommodating femoral anteversion, internal rotation of the feet by 15°–20° is recommended.

   Advantages:

   • It is the basic view for all the lines and angle measurements in DDH assessment.
   • The two important classifications of DDH are based on AP view of the pelvis only.
   • The position for AP view can be achieved easily.
   • Some of the radiographic signs of DDH, e.g., the asymmetry between the ossific nuclei of both proximal femoral epiphysis of the hip joints, can be interpreted just by eyeballing this view.

2. A supplementary view is the frog leg lateral view (Fig. 1b) Both hip joints are taken together in a landscape film orientation. The patient is supine with both hips abducted, mildly flexed and externally rotated by 25°–30°. The knee joints are flexed at 30° and both plantar surfaces of the feet touch each other.

   Advantages:

   • This view helps to assess femoral head coverage by the acetabulum, specially, supero-laterally.
   • It helps to assess reducibility of the femoral head on manipulation.

3. Von Rosen view This view is not a very popular view with the orthopaedic surgeons, yet, it can assist in the evaluation of dislocatibility more precisely as compared to the frog leg lateral view. The patient is supine with legs extended and abducted to 30° and feet internally rotated by 15°–20°. This view is specific for the paediatric population in the evaluation of DDH.

   Interpretation: In a normal infant hip, a line drawn along the long axis of the femoral shaft should touch the lateral sourcil (supero-lateral edge of acetabulum) indicating that the femoral head is enlocated. If this line touches the anterior superior iliac spine (ASIS) instead of lateral sourcil, it suggests an acetabular dysplasia with dislocation. Presence or absence of ossific nucleus does not affect the strength of interpretation with this view.

Fig. 1.

a AP view frontal view in neutral position, measurements made on PACS. b Frontal radiograph of pelvis both hip joints in frog leg position

Lines Drawn to Evaluate DDH on AP View Pelvis Including Both Hip Joints

In infants, the femoral head is not ossified and most of the acetabulum is still cartilaginous. There are several classic lines that are helpful in evaluating an immature hip. These lines help in localization of the femoral head, in assessing femoro-acetabular congruency and in documenting acetabular roof flattening or concavity.

All measurements are made on PACS (Picture Archiving and Communication Systems) for standardization of calculations and interpretation.

1. Hilgenreiner line (H-Line) (Fig. 2a) Hilgenreiner line is a horizontal line drawn touching lower ends of iliac bones while passing through the centre of the triradiate cartilages of both hip joints [16].

   Importance:

   • It serves as a reference line to draw the next line, called the Perkin’s line.
   • Helps in calculating the acetabular angle.
   • Is the most specific landmark line in IHDI classification of DDH.

2. Perkin’s line (P-Line) (Fig. 2a) Perkin’s line is a vertical line drawn perpendicular to the H line (Hilgenreiner line) touching the supero-lateral edge of acetabular roof also called as the lateral sourcil [17].

   Importance:

   In conjunction with H-line, Perkin’s line divides the hip region into four quadrants (superior—medial and lateral; inferior—medial and lateral). This helps in accurate mapping the position of the unossified or partially ossified femoral head for the ease of description in classifying DDH .

3. Shenton’s line (Fig. 2b) Shenton’s line is a smooth uninterrupted arc that is drawn connecting the inferior margin of femoral neck and superior margin of obturator foramen in one continuous sweep [18].

   Importance An interrupted arc or an arc with a step off indicates dislocation in DDH.

   Limitation In neonates, Shenton’s line has a lower sensitivity due to sub-optimal positioning of the lower limbs, since hip joints in neonates show physiological abduction and flexion (frog-leg position). Shenton’s line has a higher sensitivity in children of walking age group.

4. Superior Margin of Acetabulum line (SMA Line) (Fig. 2a) SMA line is a horizontal line which connects the lateral sourcils of both hip joints.

   Importance It serves as the most important line for Grading of DDH by Tonnis classification.

   Limitations It is difficult to draw this line in presence of rounding or flattening of the acetabular roof, in the presence of pelvic asymmetry or in the presence of a pelvic tilt.

5. Diagonal line (D-Line) (Fig. 2a) Diagonal line is an oblique line drawn from the confluence of H- and P-lines and bisecting the infero-lateral quadrant at 45°. D-line should always be drawn at both hip joints for side-to-side comparison.

   Importance A specific line for IHDI classification of DDH (Table 1).

Fig. 2.

a Important lines for radiographic interpretation of DDH. b Broken Shenton line of dislocated femoral head on the right (IHDI Grade III) with smaller ossific nucleus. Left hip joint is normal with continuous Shenton line from the inferior surface of neck of femur to the superior margin of obturator foramen in a child presenting with DDH at 2 years of age

Table 1.

Earliest signs of DDH on radiograph AP (frontal) view

Loss of acetabular concavity

Flattening or increased obliquity of the acetabular roof

Broken Shenton’s line

Absent or smaller ossific nucleus

Acetabular superior margin irregularit

Angles Drawn to Evaluate DDH on AP View of Pelvis (Including Both Hip Joints)

1. Acetabular Index (Acetabular angle of Hilgenreiner/Tonnis angle/AI) (Fig. 3a): AI is measured on AP view of the pelvis in neutral position, assuring symmetrical positioning of both hip joints. The primary reference line is the H-line. The angle is drawn with the medial end starting from the H-line at the triradiate cartilage and extending laterally to touch the lateral sourcil (the supero-lateral end of acetabular roof).

   Importance:

   • AI helps to quantify the acetabular depth and in turn predict the development of acetabulum.
   • Its’ greatest help is in the post reduction follow-up of patients, indicating the success or failure of the treatment.
   Interpretation:

   • Normal angle— < 30° in a neonate, keeps decreasing to < 22° at and beyond 1 year of age [19].
   • Post reduction if AI is > 35°, it predicts hip replacement in early adulthood [20].

   Limitation: AI is a useful predictor only up to 5–6 years of age.

2. Centre Edge angle of Wiberg (Fig. 3b) Centre edge angle of Wiberg is drawn on an AP view of the pelvis with legs in neutral position and assuring a symmetrical position of both hip joints. A best fit circle of the ossific nucleus is drawn touching the lateral and inferior margins of the ossific nucleus. Taking the centre of the ossific nucleus as the reference point for the angle calculation, a vertical line is drawn extending cranially along the long axis of iliac bone. The angle is drawn from the reference point (centre of the ossific nucleus) and extending laterally so that it touches the lateral sourcil. Comparison with contralateral hip helps in increasing the diagnostic confidence.

   Importance:

   • It helps to assess the femoral head coverage, specifically supero-laterally.
   • It is an important measurement in the follow-up cases, post conservative or surgical management and in prognostication of any residual disability.
     Interpretation: Normal angle is > 25° [19]. Angle less than 20°, indicates severe dysplasia and early development of osteoarthritic changes in adults.
     Limitation: Presence of ossific nucleus (ON) is essential for its calculation. Hence it is a value-added information only after 5 years of age.

Fig. 3.

a Acetabular angle (AI) Yellow line—H-line/Hilgenreiner line, blue line—from the medial end at triradiate cartilage extending laterally touching lateral sourcil subtending the angle with H-line. b Centre edge angle of Wiberg (red oval ossific nucleus to identify centre of ON), green line vertical line from the centre of ossific nucleus, blue line from the centre of the ON extending laterally touching the superior edge of acetabulum, the lateral sourcil

For a subtle and very early diagnosis of femoro-acetabular incongruency, assessment of proximal femoral epiphysis displacement is a sensitive index. Its’ evaluation can be done in the following ways:

1. When the ossific nucleus (ON) is not visualized, Proximal–lateral migration (Fig. 4) of the femoral epiphysis is assessed. H-line and P-lines are drawn as primary reference lines on both hip joints. A side-to-side comparison is mandatory for a confident diagnosis. A vertical line is then dropped from the H line to touch the medial metaphyseal ends on each side. The side with a shorter line, indicates presence of a subtle proximal migration of the femoral epiphysis. For the lateral migration evaluation, a horizontal line is drawn parallel to the H-line, connecting the P-line and the medial metaphyseal beak, on each hip joint. The side with a longer line suggests having a lateral migration of the proximal femoral epiphysis.

2. When ossific nucleus is visualized, Reimer migration Index [21] is calculated which is also called the Femoral extrusion index. It is calculated if hip dysplasia is suspected or to assess for hip dislocation. To calculate this index, the horizontal distance (a line drawn parallel to the Hilgenreiner line) between the Perkin line and the lateral border of the ossification centre of the femoral head is measured, and then divided by the horizontal width of the ossification centre. The Reimer migration index is normally less than 25% by most sources [21], but 25–30% have also been suggested [22].

Fig. 4.

Proximal–lateral migration. Yellow line—H (Hilgenreiner) line, Red lines—P (Perkin) lines, blue lines—distance of medial epiphyseal peak from H-line to indicate superior migration if shorter than asymptomatic side, Black line—distance of medial epiphyseal beak from P line indicating lateral migration if shorter than the asymptomatic side

Classifications

Having observed that DDH in India majorly presents at an age when the ossific nucleus has significantly developed, diagnosis of DDH comes literally written on the radiographs. No radiologist or orthopaedic surgeon would really need the lines or the angles to make a diagnosis at this stage. The importance of the lines and angles, however, lie in classifying the degree of severity in neonates, where ossific nucleus is yet to appear or in the post-reduction assessment of the follow-up cases. Two classifications have been in practice and in both the classifications, the grading of DDH is performed on AP view X-ray of pelvis which includes both hip joints, in supine neutral position. The two most important factors in prognosticating the treatment outcome of DDH rests on the severity of acetabular dysplasia and the position of the proximal femoral epiphysis with respect to the true acetabulum.

The first classification to emerge was, The Tonnis classification [23] (Fig. 5a). Not only was this classification useful in primary assessment of the severity of DDH but was also helpful in prognosticating the success of closed reduction in the walking age group patients. It also helped define radiographic evidence of complications, such as an avascular necrosis (AVN), or the need for subsequent surgical procedures, such as pelvic osteotomy.

Fig. 5.

a Lines and landmarks for Tonnis classification of DDH Grading severity: White dot (O point)—centre of ossific nucleus, white line—SMA (Superior Margin of Acetabulum) line, red line—P (Perkin) line. b Tonnis classification—yellow horizontal line—SMA (Superior Margin of Acetabulum) line, vertical red line—P(Perkin) line, Black asterix—(O point) centre of ossific nucleus

Important bony landmark for Tonnis classification Centre of the ossific nucleus (O-point).

Age when best suited > 4–6 months or after, when the ossific nucleus can be seen.

Important lines for Tonnis classification Superior margin of acetabulum line (SMA line) and Perkin’s line (P-line).

Limitations: This classification is not useful, where ossific nucleus is either yet to develop, or is delayed in appearing, is eccentric in location so that the visualization is difficult, when centre of the ON cannot be clearly identified, because it is very small, or, when the acetabular dysplasia is so advanced that the lateral sourcil is difficult to identify due to blunting or rounding.

Grading of DDH severity by Tonnis classification: Having drawn the SMA and the P line, centre of the ossific nucleus (ON) is taken as the reference point (O-point) (Fig. 5b). For the grading, the relative position of the ossific nucleus is defined with respect to the lines drawn do indicate the severity of the disease.

Grade I O-point medial to the P-line and inferior to SMA line.

Grade II O-point lateral to the P line and inferior to SMA line.

Grade III O-point lateral to P-line and closer to or lying on the SMA line.

Grade IV O-point above the SMA line.

Note: If the O-point falls on the SMA line, it is given a Grade III and not Grade IV.

Grade I is physiologically normal hip in both Tonnis and IHDI classifications.

Tonnis classification continued to be useful, but only in those children in whom the ossific nucleus could be seen. Hence there arose a need for a more comprehensive classification for defining the severity of DDH in children in whom the ossific nucleus could not be seen. A newer classification was developed by the International Hip Dysplasia Institute (IHDI) task force group which gained a stronger acceptance in grading severity of DDH, even in the absence of ossific nucleus.

International Hip Dysplasia Institute Task Force Group (IHDI classification) This classification focussed on the proximal femoral metaphysis instead of the ossific nucleus (ON) for the grading of severity of dysplasia and the primary landmark defined was the centre of metaphysis called the H-Point [24]. This made IHDI classification universally applicable to children of all age groups with suspect DDH (Fig. 6a).

Fig. 6.

a Lines and landmarks for IHDI classification of DDH severity grading: yellow line—H (Hilgenreiner) line, red line—P (Perkin) line, blue line—D (Diagonal) line, black dots at the centre of metaphysis—H-Point. b IHDI classification: Horizontal yellow line—H (Hilgenreiner) line, vertical red line—P (Perkin) line, Black asterix—centre of metaphysis (H-Point), Diagonal blue line—D (Diagonal) line

Important lines for IHDI classification:

Hilgenreiner line (H-line), Perkin line (P-line), Diagonal (D-line) line.

Important bony landmark for IHDI: H-point.

Age at which useful: From any time after birth till proximal femoral epiphyseal fusion is seen.

Grading of severity of DDH by IHDI classification (Fig. 6b).

Grade I H-point medial to the P-line and below H-line.

Grade II H-point lateral to P-line, medial to D-line below H-line.

Grade III H-point lateral to D-line and below or overlying H-line.

Grade IV H-point above the H-line.

Remarks:

The primary intent of the IHDI classification was to overcome the limitations of Tonnis classification, that is in cases, where ossific nucleus could not be clearly defined. The IHDI and Tonnis classifications are both efficient radiographic methods of DDH assessment; however, the former classification shows a better reliability, particularly in evaluating DDH when ossific nucleus is visualized. The IHDI classification is useful in evaluating DDH regardless of the appearance of the ossific nucleus. Therefore, the IHDI classification seems to be the upgraded version of Tonnis classification [24].

Radiation Risks

1. Routine pelvic radiographs pose negligible radiation risk. It is not a matter of great concern if ten X-rays are being taken in a year or two. What matters most is the intensity of the radiation dose delivered at any point of time [25].

2. Gonadal protective lead shields—Recent studies recommend the use of gonadal shields for pelvic radiography in children, which are now customized. It’s a matter of debate whether the gonadal shield leads to multiple exposures, since a child may not find it comfortable and become irritable. This can lead to undue movement and an increase in delivery of radiation to the patient. Developing restraining contraptions, soothing techniques such as soft low lights, a warm comfortable room and the presence of parents can help minimize the movement and hence repeated exposures [26].

3. Radiation effective dose can be calculated using PCXMC software—The radiation effective dose of < 0.01 mSv for the combined 6- and 12-months single-view anteroposterior radiographs of the pelvis is recommended.

4. The risk of radiation-induced cancer (following two pelvic X-rays) compared to naturally occurring cancer appears to be less than 1 per million. However, a few studies recommend implementation of X-ray controls after the second year of life to reduce the radiation exposure [27].

Follow-ups: Radiographic and clinical follow-up.

The length of radiographic and clinical follow-up is still a point of contention that has not been definitely addressed. For all the patients diagnosed with DDH in infancy and were treated with closed reduction and a harness, Sarkissian et al. utilized follow-up radiographs at 6 months, at 12 months or up until when the child was ambulatory [25]. This view is in contrast to Dornacher et al. who delayed radiographic examination until 2 years of age to avoid radiation exposure to the immature acetabulum and proximal femoral epiphysis [1].

• Every 3 months till the baby stands, followed by at 6 monthly intervals until the baby starts walking (i.e., up to 2 years of age) [25].

• In high-risk cases and late detected cases, i.e., at < 3 years of age, follow-up suggested up to 10–12 years of age [28].

Limitations of Radiography

1. Plain radiography has lower sensitivity in early cases.

2. Exposes the infant to ionizing radiations.

3. Does not provide dynamic information.

4. Radiographs are difficult to interpret before the ossific nucleus is seen.

5. Plain radiographs in neonates obtained with the hip in the neutral position may fail to show DDH, since some hips may be subluxable only and do not frankly dislocate [29].

Section II: Role of Ultrasound in Management of Developmental Dysplasia of Hip Joint

Introduction

Ultrasound examination of the hip started in the early 1980s when Prof. Graf showed how useful it was in evaluating neonatal hips for dysplasia. Later, with the advancement in machine technology and better transducers, sonography of other joints and soft tissues developed both in adults and children.

Ultrasound is commonly used for neonates and infants less than 6 months of age for diagnosing and following up hip dysplasia. Ultrasound can accurately evaluate the unossified femoral head in the acetabulum which is also partly cartilaginous. In addition, the dynamic examination (Harcke’s method) has an added advantage of testing hip for subluxation or dislocation.

Examination Technique

Static (Graf technique):

Ultrasound of infant hip is done with the baby lying in lateral decubitus position. A high frequency 12 MHz linear probe can be used for a newborn but as the child grows, a 7 MHz lower frequency probe will be required to achieve an adequate penetration.

A coronal scan of the hip joint is done from the posterolateral approach with knees flexed, hip positioned in neutral or slight internal rotation (Fig. 7a). A coronal long axis section is taken through the triradiate cartilage. Neither the pubis nor ischium should come in the view. In this image (Fig. 7b), we see the bony ilium and acetabulum. The deepest point of bony acetabulum joins the hypoechoic triradiate cartilage. The cartilaginous femoral head is located in the acetabulum which is hypoechoic with a stippled appearance. Lateral to the bony acetabulum at the site of promontory (junction of ilium and acetabulum) is the acetabular cartilage which is hypoechoic and further lateral is the echogenic acetabular labrum. The gluteal muscles and the underlying joint capsule are located lateral to the femoral head inserting on the greater trochanter.

Fig. 7.

a Probe positions for the ultrasound of hip joint in DDH (reproduced with permission from the co-author). b Coronal long axis image of pediatric hip joint posterolateral approach. FH—femoral head, AC—bony acetabulum, P—promontory, C—acetabular cartilage, L—acetabular labrum, FH—femoral head, GT—greater trochanter. Three lines as described

Based on the standard coronal plane, Graf described two angles formed by intersection of three lines (Fig. 8). The iliac line (baseline), tangential to the iliac wing; the acetabular roof line, which joins the promontory with the deepest edge of the acetabulum; and the labral line, drawn from the promontory to the middle of the fibrocartilaginous labrum [30, 31]. The intersection of the first two lines forms the α angle (acetabular inclination angle), which reflects the depth of the bony acetabular roof and the coverage of the femoral head. This angle correlates with hip maturity: the wider the angle, the more mature the hip; the smaller the angle, the greater the degree of dysplasia. The α angle should be ≥ 60°. A second angle, the β angle (cartilage roof angle) is obtained from the intersection of the baseline and the labral line. It indicates the superior displacement and lateralization of femoral head.

Fig. 8.

Coronal long axis image of pediatric hip joint posterolateral approach for Graf angles

Graf’s classification of hip dysplasia derives from the combined measurements of these angles [32].

Graf type I hips have an alpha angle of more than 60⁰ and is reflective of normal mature hips. Although there is a distinction between types Ia and Ib, it is not very clinically relevant.

Type Ia

Type I a classification signifies a good morphology of the bony acetabular roof with a sharp angular bony rim (promontory). There is optimal coverage of the femoral head by the cartilaginous roof and the labrum. The alpha angle is more than 60⁰ and the beta-angle is stays less than 55°.

Type Ib

This is also a normal hip. There is adequate coverage of the femoral head. The only difference with the type Ia-hip is that there is a blunted bony rim (promontory) in Type 1b. As a result of this, the alpha-angle becomes mildly steeper than in type Ia, but still remains within a normal range. The beta angle is more than 55º. These hips are normal and follow-up is not needed.

Type II

Type IIa

If a child is less than 3 months of age, an alpha angle of 50–59° is considered an immature hip. The bony acetabular roof is less well-formed and there is a rounded acetabular bony rim. Hence between the age group of 6–13 weeks, a distinction has to be made whether a suspect immature hip will develop and be categorized age appropriate as (IIa+) or inappropriate as (IIa−).

Type IIa+ 

The maturation process to type IIa+ hip is considered within acceptable limits of maturity for the age.

Type IIa–

A type IIa– hip is at risk to develop dysplasia.

So an alpha angle of 55° at 7 weeks of age is called type IIa+ , while at 10 weeks is called a type IIa–.

Type IIb

If a child is older than 3 months or 13 weeks, an alpha angle of 50°–59° is considered a sign of dysplasia, i.e., type IIb.

Type IIc

The bony acetabular roof is severely deficient with a round to almost flat bony rim.

The alpha angle is 43°–49°. The femoral head is still covered with the cartilaginous roof and the labrum.

Type D

A type D hip is much like a type IIc hip, but the important difference between the two is a decentred unossified proximal femoral epiphysis with a displaced cartilaginous roof in Type D.

Type III

In type III hips, the femoral head is dislocated. The α angle is < 43° and the labrum has been pushed upwards (everted).

Type IV

In Graf type IV, the α angle is < 43° and there is a severe dislocation of the femoral head which obscures most of the bony roof. The cartilaginous roof is compressed between the femoral head and the bony acetabular rim. The labrum is dislocated downwards and interposed between the femoral head and the lateral acetabular edge.

Simplified Graf’s Classification for Selective DDH Screening Programme

Graf’s method is widely accepted for static anatomic assessment of DDH. However, it has its’ limitations by virtue of being very exhaustive and hence having questionable applicability for universal screening. Subjecting all neonates at birth to ultrasound screening and rule out DDH becomes a non-viable option. That the neonates at risk should be screened at birth for DDH and that the Graf’s technique is the foundation for classifying and charting out further management, is an important protocol which needs a serious thought [33].

For the purpose of screening, a shorter version of Graf’s classification can be adopted, where only the alpha-angle is considered. Alpha-angle is the measure of the bony roof of the acetabulum and forms the basis for hip subtype in Graf’s method of classification. The age of the child indeed is an important factor and cannot be ignored when performing an ultrasound. Up to 12 weeks, an alpha angle of 50°–60° is acceptable, provided it shows a steady increase through interval scanning, reaching 60° or more at 12 weeks [34] (Table 2).

Table 2.

A proposed simplified version of Graf’s classification based on alpha angle only for quicker interpretation of hip subtype

Type I	Normal	Alpha angle >60°
Type II	a, b, c	Alpha angle 43°–60°
Type III		Alpha angle < 43°
Type IV		Dislocated

Note: Beta angle is useful in distinguishing Sub-type II—55°–77° is normal

Dynamic Evaluation (Harcke’s Method)

In this technique, a four-step scanning protocol is followed at rest and during stress of hip joint, utilising coronal and transverse planes, in both neutral and flexion positions. Posteriorly directed stress along the femoral shaft, which is held at 90° of flexion and maximum adduction at hip joint, is also known as the Barlow manoeuvre.

On coronal neutral view, general morphology of hip is studied without any angle measurements. This followed by coronal flexion view, where the probe is placed slightly posterior to the standard coronal plane over the triradiate cartilage. A stress manoeuvre is performed provocating subluxation, by holding the knee and adducting the thigh as well as pushing it posteriorly, simulating a Barlow manoeuvre. The femoral head should not be visible in the posterior hip on stress. If visible, then it indicates subluxation. In transverse flexion view, the femoral head is between bony ischium and medial acetabulum [35]. Using Harcke’s technique, the hips are grouped as either normal, lax under stress, subluxable or dislocated [36].

Another technique for assessing the lateralisation of femoral head is the femoral head coverage technique proposed by Morin et al. [37] and then modified by Terjesen et al. [38]. From the Baseline as drawn for Graf’s technique for static assessment, a vertical line is drawn to the medial aspect of femoral head annotated as (d). The second vertical line is referred to as (D), which is the maximum diameter of femoral head. The percentage of femoral head coverage by bony acetabulum is given by the equation (d/D) × 100. Values of < 50% are considered abnormal (Fig. 9a, b) [38].

Fig. 9.

a Normal femoral head coverage of > 50%. b Abnormal femoral head coverage of < 50%

Selective Ultrasound Screening Program Recommendations of the American Academy of Paediatrics (AAP) and Paediatric Orthopaedic Society of North America (POSNA)

Universal screening for DDH by ultrasound is not recommended by any Society or the fear of high false positive results. Ultrasound hence is an optional investigation in infants younger than 6 months with suspicious or inconclusive findings on physical examination. The AAP recommends against universally screening for DDH with ultrasound; however, it can be selectively performed in infants 6 weeks to 6 months of age who have normal findings on physical examination, but are considered high risk [39].

Selective ultrasonographic screening is recommended either to clarify suspicious findings on physical examination after 3–4 weeks of age or to detect clinically silent DDH in the high-risk infant from 6 weeks to 4–6 months of age [40] (Fig. 10).

Fig. 10.

Diagnostic Imaging algorithm for ultrasound in DDH (US—ultrasound; N.A.—not available; FU—follow-up)

Conclusion

DDH is an orthopaedic condition with spectrum of disorders, usually encountered first by the paediatrician. A timely diagnosis and prompt management can prevent long term morbidity associated with DDH. Radiography and ultrasounds are the basic imaging modalities, and form the primary investigative tools for selective screening, which assist in early diagnosis and management of DDH. Screening programs relying primarily on physical examination techniques for the early detection and treatment of congenital hip abnormalities have not been as consistently successful as expected. Since the 1980s, increased attention has been given to ultrasound imaging of the hip in young infants (less than 6 months of age) as a possible tool for improving patient outcomes. Although ultrasound examination may not provide advantages over careful repeated physician examination for universal screening, a growing body of evidence indicates that ultrasound surveillance of mild abnormalities can reduce the need for bracing without worsening outcomes. Simplification of Graf’s method by focussing on the alpha angle can help in faster surveillance of DDH. Radiographic documentation of hip normality after the femoral nucleus of ossification has appeared (at 3–5 months of age) is still appropriate to rule out hip dysplasia.

Author Contributions

AA and NB conceptualised and designed the study. The first draft of the manuscript was written and compiled by NB and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Funding

Nil.

Declarations

Conflict of Interest

The authors declare that they have no conflict of interest.

Ethics Approval and Consent to Participate

No ethics approval was required for this study.

Informed Consent

For this type of study informed consent is not required.