Hellenic Journal οf Radiology

Introduction

Developmental dysplasia of the hip (DDH) is a condition that includes a wide spectrum of disorders, which share the potential of causing significant long-term compli­cations that may lead to severe disability during early adult life.

Most of the cases of DDH are potentially reversible if diagnosed and treated early. Therefore, the role of imag­ing, which is the mainstay of early diagnosis, is critical. Especially ultrasonography (US), the imaging modality of choice, has evolved to be the one-stop-shop imaging method for early diagnosis of DDH and the preferred tool for treatment evaluation and monitoring.

In this manuscript, we sought to review the published literature, focus on the pros and cons of US, present current clinical practice and propose an algorithm for screening.

Definition of DDH

DDH is the term which has replaced congenital disloca­tion of the hip in medical literature. This is mainly be­cause it covers a wider spectrum of disorders, ranging from maturation deficits to severe dysplasia or disloca­tion [1, 2]. Moreover, it better describes a condition with a poorly understood natural history, the origin of which is both congenital and developmental.

The existence of various approaches to infant hip as­sessment, some of them being clinical and others being imaging (mainly sonographic with various techniques), makes the effort of defining pathology even more com­plicated, leading to several variations [2]. Fortunately, with the use of US, the exact anatomy of the infant hip joint has nowadays been studied thoroughly, facilitating a systematic approach to the joint disorders.

The definition of DDH does not include hip joint dis­orders which are due to co-existing medical conditions (cerebral palsy, slipped capital femoral epiphysis, Legg- Calve-Perthes disease etc.), teratologic disorders and cases of traumatic hip dislocations [3, 4].

Epidemiology

Depending on whether we refer to the pre- or the post-sonographic screening era, prevalence of DDH in the lit­erature ranges from 0.07% to 0.15% and 0.25% to 2.5% (or even higher in certain geographic areas) respective­ly [3, 5, 6]. Significant geographic variability is due to true population differences, but also due to the defini­tion variations mentioned above [7-9]. In most DDH cas­es, up to 80% in published reports, the disorder affects the left hip joint. This has been attributed to fetal posi­tioning (left occiput anterior), with the left side of the fe­tus being more restricted and adducted as it is adjacent to the maternal sacrum, especially during the 3d trimes­ter of pregnancy [10]. More important than the exact prevalence of the disorder is the fact that almost 1/3 of total hip replacements in patients younger than 60 are due to undiagnosed or untreated cases of DDH [11], most of which (95-98%) might have the chance of being treat­ed if diagnosed earlier.

Risk factors

Risk factors according to the literature [12-15] include female gender, white race and positive family history of DDH. Mechanical restriction during pregnancy (oligo­hydramnios, breech presentation, macrosomic babies), during delivery (vaginal birth in breech presentation with extended legs) or after birth (swaddling), signifi­cantly contribute to morbidity. On the contrary, lack of mechanical charge explains lower incidence of DDH in premature babies. Presence of risk factors alerts the cli­nician to perform a thorough clinical/imaging exami­nation, although most of the DDH cases are diagnosed in babies without any identifiable risk factors. So, it is clear that DDH screening based solely on risk factor identifica­tion is not justified [2, 16].

Clinical vs. Imaging Examination

Physical examination of the hips is the initial step of hip assessment. It is usually carried out at birth by the neo­natologist and subsequently routinely by the paediatri­cian [17]. Clinical examination mainly consists of pro­vocative tests (namely Ortolani and Barlow (Fig. 1), assessment of joint motion range, measurement of leg length and assessment of skin fold symmetry.

Fig. 1.Barlow and Ortolani maneuvers consist part of the standard infant examination performed by the pediatrician in early infancy. Barlow maneuver aims to identify unstable hips and consists of the application of a posterior force with the hip adduct­ed, which produces a posterior dislocation of the joint (with a palpable clunk). On the contrary, Ortolani maneuver consists of the application of anterior traction on an abducted / flexed dislocated hip, which reduces (with a palpable clunk) the dislocation

Although it remains the mainstay of screening in several health systems and guidelines, it is neither specific nor sensitive and requires careful consideration and clinical experi­ence [18, 19]. Dysplastic hips may remain clinically silent when the femoral head is centered [20, 21]. Even cases of severe hip dysplasia may remain clinically obscure [12, 21, 22]. The combination of risk factors and clinical histo­ry may perform slightly better; however, it is still insuffi­cient to provide an effective screening method.

US offers us the opportunity to image the non-os­sific(-ied) parts of the hip joint very early in life. Carti­laginous structures (femoral head, cartilaginous roof, labrum), joint capsule and the muscles are adequately ex­amined with US, both in an anatomic and dynamic (when needed) way (Fig. 2).

Fig. 2.Cartilaginous structures (femoral head, cartilaginous roof, labrum), joint capsule and the muscles are adequately ex­amined with ultrasound (blue colour). FH: Femoral Head, FM: Femoral Metaphysis, L: Labrum, HC: Hyaline Cartilage, PP: Prox­imal Perichondrium, GM: Gluteal Muscles / Intermuscular Septa

At the same time, integrity and ade­quacy of the acetabular bony roof is assessed, both quali­tatively and quantitatively, and the position of the femoral head within the joint socket is documented. Several dif­ferent sonographic techniques have been developed and clinically assessed, a few of which are still in clinical prac­tice [23-27]. X-ray nowadays has a historical role in DDH screening and is preserved mainly for late presenting cas­es and treatment monitoring when US is no more techni­cally feasible [28]. CT and MRI still have a role when exam­ining the consequences of neglected or maltreated cases of DDH or when planning hip surgery [29].

Hip US

The era of hip US began in 1980 when Reinhard Graf pub­lished the original paper about hip US for the diagno­sis of congenital dislocation of the hip in infants [23]. Over the next years, several publications suggested modifications or advances of this technique, or differ­ent techniques altogether. Traditionally, examination techniques have been categorised according to their im­aging focus (acetabular morphology, femoral head cov­erage) or their technical approach (static vs. dynamic). It is beyond the scope of this paper to describe every dif­ferent sonographic technique that is or has been used or proposed. It is our aim to emphasise the main advan­tages and disadvantages of the most widely used ones and then conclude with evidence based conclusions / recommendations.

Femoral head coverage

Measuring the femoral head coverage (FHC), from a tech­nical point of view, seems to be the easiest and more re­producible way to assess a hip joint. On a standard coro­nal hip scan the percentage of the femoral head covered by the acetabular roof is calculated as demonstrated on the figure (Fig. 3).

Fig. 3.Assessment of Femoral Head Coverage (FHC). FHC (per­centage) is calculated in a standard coronal scan by diving ac­etabular width (distance a, measured from the medial part of the acetabulum to a line parallel to the iliac bone) by the fem­oral head diameter (distance b, measured between lines par­allel to the iliac line, the first from the medial part of the ace­tabulum as in distance a and the second from the outer part of the cartilaginous femoral head).FHC is calculated by the for­mula a/b x 100%

There are however certain method­ological problems that significantly reduce the value of the technique, which was originally proposed by Morin (USA) and Terjesen (Norway) [25, 26] and is still utilised in Northern Europe. Ovoid shape (and not spherical) of the femoral head [30], alongside with failure to define a standard plane for measurement, makes the meth­od vulnerable to rotational distortions. Furthermore, the classification scheme utilised for assessment has a wide “gray” zone (FHC<50% may be abnormal) and an unsound reasoning behind it. As a result, it is of limited use, restricted in certain geographic areas [31].

Hip Stability - Dynamic assessment

Dynamic assessment of the hip joint was introduced by Harcke and coworkers in USA and mirrored the hypoth­esis that correct development of the acetabulum was heavily dependent on the position of the femoral head [24, 32]. Examination includes static and dynamic eval­uation of hip stability in two examination planes (coro­nal and transverse) with the baby lying supine or lateral, and the hip in both neutral and flexed position (dynam­ic four-step method). A modified Harcke technique (in­cluding an optional rough assessment of the acetabular morphology and femoral head coverage) is the technique currently proposed by the American Institute of Ultra­sound in Medicine, developed in conjunction with the American College of Radiology, the Society for Paediat­ric Radiology and the Society of Radiologists in Ultra­sound [33].

The main drawbacks of the aforementioned “dynamic” examination techniques are the following: Examination methodology (free hand, not fixed baby position) may cause certain technical problems with image acquisition, consisting mainly of rotational / tilting effects that may remain undetected (due to limited scanning plane defi­nition) and may heavily affect image diagnostic quality and interpretation. Examination in a transverse plane does not offer any additional information and does not solve any diagnostic problems. Furthermore, qualitative interpretation of the examination results and the pro­posed simplified hip joint classification may be a cause of concern when following up hip treatment and a cause of subjectiveness of the results, especially when comparing the results of different examiners. Arbitrary (or on de­mand) addition of extra examination bits (including ac­etabular assessment and femoral head coverage) is not acceptable for a universal screening test which must fol­low a strict examination protocol. Finally, the dynam­ic part of the sonographic examination may be very un­comfortable and irritating for the baby (if not hazardous under certain circumstances), is not justified in the ma­jority of cases where acetabular morphology is normal (a high correlation has been shown between acetabular morphology and hip stability in several publications) and hip instability is not separated objectively from harm­less movements.

Graf’s technique

The technique that is utilised in most European coun­tries is Graf’s technique. The main advantage of this tech­nique is that it offers a well-structured anatomical ap­proach, based on the application of a stepwise, strictly defined protocol (Fig. 4).

The addition of specified check­lists for the examiner helps in avoiding certain techni­cal mistakes and further enhances correct interpretation and classification in certain categories. The examination is carried out in the lateral position using an examina­tion cradle with a fixed probe guide. This setting is con­sidered a necessary adjunct for correct image acquisi­tion and maintenance of a standard examination plane. Image acquisition is followed by anatomical identifica­tion. The acquired image is only acceptable for diagnosis if it depicts certain anatomic structures. If any of them is missing, then it is considered unacceptable and a new image must be acquired (Fig. 5).

Fig. 5.Right Hip, Coronal Plane – Anatomic identification: COB – ChondroOsseous Border, FH – Femoral Head, SF – Synovial Fold, JC – Joint Capsule, L – Labrum, HC – Hyaline Cartilage, BR – Bony Roof, LL – Lower Limb os ilium

Usability check follows anatomic identification. As already mentioned, it is ab­solutely necessary to define a standard plane of exami­nation, because only then can the examiner be confident that the image is correctly acquired, lines and angles can be drawn and the examination is appropriate for clinical judgment. For this purpose, a standardised approach is utilised (lower limb-plane-labrum) to define the correct scanning position and plane (Fig. 6).

Fig. 6.Defining the Standard Plane of examination. For this purpose, a standardised approach is utilised (lower limb-plane-la­brum) to define the correct scanning position and plane. The yellow triangle represents the labrum, the straight line the correct scan­ning plane and the yellow circle the lower limb of the os ilium

Provided that a correct image at a standard scanning plane has been acquired, morphological classification into four main categories (I to IV) is then performed and comprises the first step of the interpretation of the scan (Fig. 7a, b). It is mandatory that subjective morpholog­ical assessment is in full accordance with the objective classification with the use of measurements. Acetabu­lar morphology is described with the use of two angles, theαangle which is the angle of acetabular inclination (bony roof angle) and theβangle which is the cartilag­inous roof angle. Each hip is classified into one of four main types (nine subtypes) and clinical management is based on this classification (Table 1).

Fig. 7a (above), 7b (below).Provided that a correct image at a standard scanning plane has been acquired, morphological classification into four main categories (I to IV) is then performed. This comprises the first step of the interpretation of the scan

Table 1. Hip type classification according to Graf

Hip examination and type classification is performed in a resting position (without stress). A dynamic exam­ination is only preserved for a specific hip joint catego­ry(ΙΙc). In those cases, separating harmless movements from (pathological) instability is important for treat­ment decisions. The same examination protocol and hip type categorisation is also used for treatment monitor­ing. Strict adherence to the above-mentioned examina­tion steps (correct baby positioning, anatomic identifica­tion, usability check etc.) eliminates the risk of mistakes. However, there are cases where poor examination tech­nique, no usability check, wrong anatomic identification or incorrect measurements have led to misdiagnoses.

Graf’s examination technique’s main criticism is about its complexity. This is mainly due to the fact that it no longer uses the original clinical and x-ray classification of normal, dysplastic, subluxed and dislocated hip, but classifies hip joints according to the exact anatomic pa­thology which must be identified and treated appropri­ately. What is considered by many the main disadvantage of the technique is actually its main strength: on the ba­sis of this classification, treatment can be conducted ap­propriately according to the exact sonographic hip type. Monitoring of treatment is much easier and more objec­tive since evaluation is no longer qualitative [34].

Selective vs. Universal Screening

Although universal clinical screening has been common clinical practice for many decades, universal hip screen­ing has not gained general approval [2, 35]. The reason for this is mainly the fact that there is wide geograph­ic variation in screening policies, published literature is heterogeneous (screening methods and population com­position differ in different studies) and there are no ran­domised trials (it is not ethical to perform any). The fact that there are different diagnostic definitions for DDH further complicates the situation. Thus, at least at firstsight, it seems impossible to collect high quality evidence to support universal sonographic screening.

On the other hand, in Austria and Germany, universal population screening with US is being carried out since the 1990’s and there is sufficient epidemiological data to support it [35-37]. Dramatic decrease of treatment costs and surgical intervention rates in young patients with DDH were shown (Fig. 8, 9). The facts that most DDH cases affect low risk populations and that screen­ing performance based on clinical examination and risk factors, as mentioned above, is suboptimal, further en­hance the opinion that all infants should be sonograph­ically screened for DDH.

Fig. 8.Dramatic drop of surgical intervention rate in young children documented in Austria between 1991 and 2004 (used with per­mission: Graf R. The use of ultrasonography in developmental dysplasia of the hip.Acta Orthop Traumatol Turc 2007; 41 Suppl 1: 6-13)

Fig. 9.Dramatic drop of treatment costs of DDH in young chil­dren documented in Austria between 1991 and 2004 (used with permission: Graf R. The use of ultrasonography in developmen­tal dysplasia of the hip.Acta Orthop Traumatol Turc 2007; 41 Suppl 1: 6-13)

A significant number of publications which are critical of Graf’s technique, supporting clinical over sonographic screening for DDH, exhibit images which are suboptimal and thus non-diagnostic (according to the stepwise exam­ination protocol presented above). This further supports the attitude that high quality hip US is not always availa­ble and proves that training has not been as optimal as de­sired. Erroneous US diagnoses are common and are main­ly due to suboptimal technique. According to Graf, bedside teaching by non-authorized teachers must be rejected be­cause it promotes habitual faults being passed on [38, 39]. Continuous advancement of hip US necessitates extra tu­ition of instructors. Thus, it is mandatory, in parallel with the screening policy, to adequately train the examiners and maintain a high level of competence by a carefully de­signed certification and audit scheme.

Timing of Screening

Appropriate US screening time has been a matter of de­bate. Maturation of the hip joint (measured as an increase of theαangle), is more rapid during the first few months of life [40]. Therefore, scanning babies as early as possible is important in order to achieve the best results of treat­ment, if needed. To eliminate unnecessary re-examina­tions, it would be reasonable to perform US screening ear­ly enough to provide the best possible outcome in treated cases, while at the same time offering an appropriate time window for the spontaneous resolution of immature hips. Performing a scan during the first week of life in clinically unstable hips or high-risk cases and screening all babies between the fourth and sixth week might be an optimal screening protocol [41]. However, any policy that would involve universal US screening until the second month at the latest would be sufficient.

Selection of the appropriate screening scenario is heavily dependent on local or national circumstances [37, 38] and the aim would be to ascertain that all babies would be scanned at some time during the first weeks of life.

Management of DDH according to Graf[40]

DDH treatment aims at (1) centering the head within the acetabulum to facilitate correct development of the former, thus preventing future limping and (2) elimi­nating acetabular dysplasia, thus preventing early on­set of arthritis and the need of early arthroplasty in a young adult. Treatment algorithm consists of femoral head reduction, maintenance of head relocation (reten­tion) and correction of any residual acetabular dyspla­sia (maturation).

There is still some controversy about the correct tim­ing of initiation of treatment (especially head reduction). There is some concern that reduction maneuvers should be performed after the ossification nucleus appears, in order to avoid head necrosis. According to the majori­ty of published reports, early initiation of treatment is suggested.

The key in reduction technique is flexing the hips at 110owith a maximum abduction of 45o. Correct position­ing is of utmost importance, to avoid causing avascular necrosis of the femoral head due to exertion of excessive pressure on the centered head.

Treatment of dislocated or unstable dysplastic hips consists of:

femoral head reduction: in babies younger than 6 months, early (as soon as possible) closed reduction of the femoral head / in older babies, open reduction (ex­cept when the femoral head is relocating easily),

application of a spica cast for 4-6 weeks (retention), although in newborns some centers may use the Pav­lik harness,

depending on the age of the baby, a Pavlik harness is used until the hip joint turns to a Graf Type I hip (mat­uration) or until the baby is too old for a Pavlik or other flexion - abduction device (or plaster). If there is a resid­ual dysplasia, a pelvic osteotomy is arranged at the age of 2 years or later.

In stable (centered) dysplastic hips, therapy begins from the maturation step (c).

Conclusion

US offers an effective and accurate method for the early diagnosis of DDH. Among the most popular sonographic techniques, Graf’s technique is a powerful screening tool which is based on anatomical description of hip patholo­gy, and combines early diagnosis with effective monitor­ing of treatment. Its universal application for more than two decades in central European countries has been clin­ically useful and thus it is generally recommended. Tim­ing of screening should be modified according to region­al peculiarities. It is however mandatory that diagnosis should not be made later than eight weeks to ensure ear­ly initiation of treatment. The treatment algorithm con­sists of femoral head reduction, maintenance of head relocation (retention) and correction of any residual ac­etabular dysplasia.R

Conflict of interest:

The authors declared no conflicts of interest.

Figure Figure