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Increased Diagnostic Information and Understanding Disease: Uncertainty in the Diagnosis of Developmental Hip Dysplasia¹

¹ From the Department of Orthopaedic Surgery, Great Ormond Street Hospital for Children, Great Ormond St, London WC1N 3JH, England (A.R.); Institute of Child Health, University College London, London, England (A.R.); Division of Orthopaedic Surgery, Child Health Evaluative Sciences Program, the Hospital for Sick Children, Toronto, Ontario, Canada (J.G.W.); and Departments of Surgery, Public Health, and Health Policy, Management and Evaluation, University of Toronto, Toronto, Ontario, Canada (J.G.W.). Received November 29, 2005; revision requested January 19, 2006; revision received January 28; final version accepted February 21. Address correspondence to A.R. (e-mail: a.roposch{at}ich.ucl.ac.uk).

	ABSTRACT

TOP ABSTRACT INTRODUCTION THE CONCEPT OF DISEASE THE CLINICAL PHENOMENON OF... US-BASED DIAGNOSIS OF DDH RECOMMENDATIONS References

 
Great advances have been made in developing strategies to improve the quality of medical care in the past decade; these advances include better diagnostic technologies, such as ultrasonography (US), computed tomography, and magnetic resonance imaging. Although these tests provide new information on many conditions, such as developmental dysplasia of the hip (DDH), the differentiation of what is normal, what is abnormal, and what is disease is no longer intuitive. Historically, the diagnosis of DDH was straightforward. The diagnosis was based primarily on clinical findings, which were often confirmed with radiography. Abnormal hips were either subluxated or dislocated and, if left untreated, adverse consequences were certain in either situation. Since the introduction of hip US, however, increased diagnostic sophistication has led to uncertainty as to how to interpret the continuous spectrum of acetabular morphology. There is no consensus on the degree of acetabular dysplasia that does or does not require treatment. Because not every abnormal finding may require treatment, the terms abnormality and disease are not synonymous.

© RSNA, 2007

	INTRODUCTION

TOP ABSTRACT INTRODUCTION THE CONCEPT OF DISEASE THE CLINICAL PHENOMENON OF... US-BASED DIAGNOSIS OF DDH RECOMMENDATIONS References

 
Consider a case in which an 8-week-old girl has a persistent click in the left hip. Ultrasonography (US) shows an angle of 50° and the hip is stable at dynamic evaluation. What is the diagnosis in this girl? Would you consider the finding to be within the normal range or to indicate a form of developmental dysplasia of the hip (DDH)? The diagnosis is important because it is used to determine if the patient requires no further assessment, continued follow-up, or immediate treatment. If the incorrect decision is made, the patient may experience (a) future consequences if left untreated when treatment was warranted or (b) complications of treatment if the patient would have done well without treatment. Continued but unnecessary follow-up adds a tremendous financial burden to society and stress to affected families.

Historically, such considerations were not part of the evaluation of an infant hip. In the practice of Perkins (1), evaluation was based entirely on the clinical examination, and the disease was the dislocated hip. New diagnostic tests contribute new information on the evaluation of medical conditions, and this information may change the way physicians think about a certain condition (2). For example, before US was used to evaluate the infant hip, radiography was the standard imaging technique, especially in an infant older than 6 months. With the addition of radiographs to the clinical examination, disease findings were classified as dysplastic, subluxated, or dislocated. With the use of US, the radiographic stage "subluxation" was further refined into various US stages (3). A neonatal hip may be unremarkable at clinical examination but at US may reveal remarkable findings if stress view images are obtained and unremarkable findings if static view images are obtained. Additional appraisals can include the shape of the roof of the acetabulum, the location of the labrum, the femoral head coverage, or a combination of these (4–6). New techniques, such as contrast material–enhanced US or high-spatial-resolution magnetic resonance imaging (7,8), will contribute additional variables that may create more uncertainty about the actual disease state in DDH.

Two decades after the introduction of hip US, there is no universal agreement in the evaluation of the neonatal hip for dysplasia: Some physicians rely on the clinical examination alone, whereas others rely exclusively on US, independent of the clinical findings (9). Some use both tools for evaluation. We suggest that this dilemma, which is typical of many clinical conditions, has occurred because the diagnostic information has superseded our understanding of disease.

	THE CONCEPT OF DISEASE

TOP ABSTRACT INTRODUCTION THE CONCEPT OF DISEASE THE CLINICAL PHENOMENON OF... US-BASED DIAGNOSIS OF DDH RECOMMENDATIONS References

 
Delivering the best quality of patient care is the absolute goal of clinical medicine. For the physician, this largely involves the processes of diagnosis and treatment. To improve treatment, one must first understand the disease that is being treated. To understand the neonatal hip, we suggest it is time to return to basic principles and consider the connotations of the term disease in the light of today's medicine, because the concept of disease is fundamental to medicine. Only by clarifying the definition of disease can we hope to sort through the information provided by new and advanced diagnostic studies.

There are three main approaches to the definition of disease: normativism, functionalism, and pragmatism. In defining disease, normativists argue that some conditions have undesirable outcomes, whereas the undesirability is socially constructed (10). This approach is evaluative, with a value-based perspective (it is the society that decides what is undesirable) on what constitutes a disease. For example, in the wide spectrum of DDH, only unilateral hip dislocation, and not acetabular dysplasia, might be regarded as a disease because it is considered that the first but not the latter is causally related with physical impairment of the affected individual and causes financial burden (hip surgery) to the society within a defined period.

Functionalists favor a descriptive approach—the concept of disease is defined descriptively in terms of those functions that are typically found within members of the same species. There is a physical basis for the disease without relying on a socially constructed evaluative element (11). In the context of neonatal hip dysplasia, this approach denotes that there is a need for valid and reliable measures of acetabular morphology to establish what is "typical." Any neonate whose condition was not identified as being typical would be labeled as having disease.

We favor a pragmatic theory of disease—that is, disease language is essentially connected to patient care, which fits the overall aim of clinical medicine. Disease, in this context, is a condition that places a patient at an increased risk for an adverse outcome (12). This definition seems closest to what physicians mean when they use the term disease. With the pragmatic theory of disease, labeling a phenomenon as a disease should help to differentiate unimportant from important clinical phenomena and to provide directions for therapeutic actions. These actions can include care, curing disease, or controlling disease.

While we focus on DDH, considerations on the concept of disease will foreseeably expand more and more into clinical research: Physicians order many more diagnostic tests now than they did in the past (13). In our environment of defensive medicine that aims for ever-increasing levels of diagnostic certainty, physicians may be required to more rigorously justify the benefit of tests for individual patients and how additional tests influence therapeutic actions. Society expects evidence of the physician's competence (14)—the process of making a diagnosis is a key competence of any physician.

	THE CLINICAL PHENOMENON OF DDH

TOP ABSTRACT INTRODUCTION THE CONCEPT OF DISEASE THE CLINICAL PHENOMENON OF... US-BASED DIAGNOSIS OF DDH RECOMMENDATIONS References

 
Neonatal hip dysplasia is one of many terms applied to the neonatal hip, and it indicates neonatal hip disease, congenital hip disease, congenital dysplasia of the hip, DDH, true dysplasia, serious dysplasia, or suspected dysplasia (15). DDH displaced the term congenital dysplasia of the hip because it was considered to be more appropriate, since a hip may be normal at birth but instability and subsequent dysplasia may develop (16). This great variety of terms used for a single phenomenon may reflect the uncertainty related with it. The term DDH covers a spectrum of different conditions, such as hip instability, anatomic dysplasia, and, the most severe form, dislocation (17).

Dysplasia is defined as an "abnormality in development, alteration in size, shape, and organization of adult cells" (18). DDH refers to a deficient or abnormal development of the acetabulum in the neonate or infant. In medicine, "abnormality" is often assumed to indicate that there is something wrong. Clouser et al (19) argued that abnormality is neither a necessary nor a sufficient feature of disease. According to Clouser et al, there must be an element that involves the incurring of harms—harms that every person acting rationally wants to avoid (eg, death, pain, disability). Thus, a hip that is not within the usual range of normality but that does not cause adverse consequences would not be considered diseased. Even if it does not cause any incurring of harms initially, neonatal hip dysplasia still may be regarded as a disease because it is associated with the predicted harm—neonates with DDH are generally believed to be at increased risk for harm in later years, such as that from residual dysplasia or early onset osteoarthritis, if left untreated. There is, however, no clear understanding on when this harm is substantial.

Radiographically, acetabular dysplasia can be subgrouped as subluxation (Shenton line broken, abnormal center edge angle) and anatomic dysplasia (Shenton line intact, abnormal center edge angle) (20). Subluxation eventually results in premature osteoarthritis (21,22), but there is limited evidence on the positive relationship between mild forms of acetabular dysplasia and the onset of osteoarthritis (23). In a community-based study of elderly white women (24), the odds ratio for the association of an abnormal center edge angle with incident hip osteoarthritis was 2.9 (95% confidence interval: 1.0, 8.3), and in another study that included both women and men (25), this odds ratio was 2.4 (95% confidence interval: 1.2, 4.7). In another study (26), in which a standardized radiographic ratio was applied for hip osteoarthritis, authors assessed the radiographs of 20–70-year-old men and women and found no relationship between acetabular dysplasia and risk for osteoarthritis. It remains controversial how often and at what age osteoarthritis develops in radiographically evident anatomic dysplasia (27).

Less understood is the relationship between forms of dysplasia seen at US and later pathologic conditions of the hip, such as adult radiographic dysplasia or osteoarthritis. However, if we follow the concept of Clouser et al (19), it is crucial to understand this relationship in order to distinguish between abnormality and disease when interpreting US findings. Defining those states seen at US that are associated with future harm would justify labeling them as disease because the affected patient is at risk for adverse consequences if left untreated.

	US-BASED DIAGNOSIS OF DDH

TOP ABSTRACT INTRODUCTION THE CONCEPT OF DISEASE THE CLINICAL PHENOMENON OF... US-BASED DIAGNOSIS OF DDH RECOMMENDATIONS References

 
The Graf index (28) is widely used in interpreting US findings. Hips are classified into one of 10 categories, each of which has specific treatment recommendations with the aim of avoiding residual acetabular dysplasia and, ultimately, premature osteoarthritis. There is substantial agreement that a dislocated hip (Graf types III and IV; angle of <43°) should be treated independently of the patient's age (20) and that hips with an angle of 60° or larger are considered normal, as are neonatal hips with an angle of 50° or larger. The interpretation of US findings between those two extremes and the determination of cutoff points remain controversial. The angle is regarded to be a continuous US measure of acetabular morphology. Thus, the normal range of this angle could be established by norm-referenced methods (29): A random sample of a large number of apparently normal individuals would have to undergo a standardized and reliable US assessment, and then the conventional statistical range of the 2.5–97.5 percentiles (± 2 standard deviations) would be established as the normal range. This approach, unless it ties to some meaningful outcome, is fundamentally limited because it does not help the affected individual. Clearly there is no general relationship between the degree of statistical abnormality and the clinical definition of a disease because there is no biologic standard for health or for the correct acetabular morphology at US—observations are empirical.

The situation becomes even more complicated if age is taken into account as another covariate, because the progression of the angle over time (and its predictive value) is poorly understood (30). Additional variables can be obtained from dynamic US—for example, the amount of femoral head displacement in relation to the acetabulum caused by applying transverse forces to the leg. While the Graf method uses dynamic US to refine static findings (28), other methods favor dynamic over static US scanning (31). However, the diagnostic accuracy of single methods of hip US is poorly established in general (32). This diagnostic accuracy involves both the reliability of image acquisition and the interpretation and validity of US findings. Studies on hip US screening for DDH do not provide more encouraging results: The lack of evidence for and against hip US screening for DDH was identified in a recent systematic review (33). Facing the poor evidence for both diagnostic accuracy and benefit of the test in terms of outcomes, we have to reevaluate the routine use of hip US in the diagnosis of DDH and find strategies to improve this test.

	RECOMMENDATIONS

TOP ABSTRACT INTRODUCTION THE CONCEPT OF DISEASE THE CLINICAL PHENOMENON OF... US-BASED DIAGNOSIS OF DDH RECOMMENDATIONS References

 
We believe there are four substantial problems in the current diagnosis of DDH: (a) the identification of disease state according to different diagnostic criteria, (b) the definition of and the unclear relationship with the adverse consequences, (c) the definition of appropriate cutoff points for dividing the continuous spectrum of acetabular morphology at US into prognostic subgroups, and (d) the disagreement on how to define substantial risk for the predicted harm.

In addressing these problems, an understanding of the concept of disease is essential. The process of labeling a clinical phenomenon as a disease always goes along with some clinical response. This response may cause burden to patients and society. For DDH, the response may include referral to other health care professionals, continued clinical and US examinations, harness treatment, radiographic follow-up for years, or surgical treatment. Any response must therefore be well justified. We believe that the disease label alone is not enough to justify medical interventions. An abnormality needs to be associated with a clinical meaningful departure from good health to be considered a disease. In neonatal hip dysplasia this may be the occurrence of later treatable hip disease, a loss of quality-of-life–related utility because of a symptomatic hip condition, or the age of onset of osteoarthritis.

The definition of disease states according to different diagnostic criteria, as well as the uncertainty of the relationship between those states, requires a specific use of terms. In particular, the terms sonographically depicted dysplasia and radiographically depicted dysplasia should be distinguished because they provide different information and their association is not fully understood.

The purpose of diagnostic information is to aid in the decision on the best further management. At present, the term disease in the context of DDH is understood with respect to range of normality. But there is scientific dispute about it, which mainly relates to two states: the neonatal hip and the infant hip with an angle of approximately 50°. The absence of true knowledge about the prognosis of these states inhibits us to reliably define where normality ends and disease begins. Thus, current classifications may need to include a third category, which we propose to call "uncertainty." The quality assessment of patient care has become an important issue among health authorities and policymakers. This assessment includes a thorough evaluation of medical interventions. According to Grol et al (34), "those delivering care no longer hold the monopoly of opinion on what constitutes good or best care." Thus, it is evidently appropriate to more credibly state what scientifically is known and what is uncertain.

For future research, it is essential to refine the predictive ability of current classification schemes (ie, define those patients with adverse outcomes and which states of DDH are associated with which risks and which outcomes). Adverse outcomes should be clearly defined and explored in the entire lineage of the condition (ie, from DDH to osteoarthritis). Long-term observational studies, with the use of surrogate outcomes such as radiographically depicted acetabular dysplasia in adolescence, are much needed to determine the degree of deviation from normality at US as a predictor of the risk for future adverse consequences. It would be desirable if the level of neonatal acetabular dysplasia (as expressed by means of the angle) in conjunction with other variables, such as age at assessment, could serve as a probability index for later radiographically depicted dysplasia or subluxation or even for osteoarthritis. The question as to whether the chosen cutoff points cause a desirable proportion of false-positive findings is crucial. The definition of what is desirable depends on the consequences of a mistake, and these consequences differ with each possible diagnosis. In our opinion, understanding the concept of disease is a key element directing this research. As long as there is a lack of good evidence on the long-term outcome of the many forms of DDH, we should be careful with the language we use and consider deliberately what we say is disease, what is normal, or what simply is uncertain.

	FOOTNOTES

 

Abbreviations: DDH = developmental dysplasia of the hip

Authors stated no financial relationship to disclose.

	References

TOP ABSTRACT INTRODUCTION THE CONCEPT OF DISEASE THE CLINICAL PHENOMENON OF... US-BASED DIAGNOSIS OF DDH RECOMMENDATIONS References

 

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