Neonatal Hip Instability: A Prospective Comparison of Clinical Examination and Anterior Dynamic Ultrasound

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1 ORIGINAL ARTICLE ACTA RADIOLOGICA Neonatal Hip Instability: A Prospective Comparison of Clinical Examination and Anterior Dynamic Ultrasound T. FINNBOGASON, H.JORULF, E.SÖDERMAN &L.REHNBERG Department of Pediatric Radiology and Department of Pediatric Orthopedics, Astrid Lindgren Children s Hospital, Karolinska University Hospital, Stockholm, Sweden; Department of Woman and Child Health, Karolinska Institute, Stockholm, Sweden Finnbogason T, Jorulf H, Söderman E, Rehnberg L. Neonatal hip instability: a prospective comparison of clinical examination and anterior dynamic ultrasound. Acta Radiol 2008;49: Background: Ultrasound is increasingly being used to complement the clinical examination in assessing neonatal hip instability. The clinical examination, although highly sensitive in detecting hip instability, can lead to considerable overtreatment. Purpose: To compare anterior dynamic ultrasound and clinical examination in the assessment of neonatal hip instability and regarding treatment rates. Material and Methods: 536 newborn infants (out of a population of 18,031) were selected, on the basis of a combination of risk factors, clinical signs of hip instability or ambiguous clinical findings, to undergo an anterior dynamic ultrasound examination of the hip, by a method developed by our group. This examination, performed by one out of seven experienced examiners, was compared with the standard clinical hip examination conducted by one of four pediatric orthopedic surgeons. The clinical examination was carried out both prior to and within a few hours after the ultrasound examination. Results: The clinical examination diagnosed 81.7% of the hips as normal, 14.5% as unstable, and 3.8% as dislocatable or dislocated. With the dynamic ultrasound method, the corresponding figures were 87.8%, 10.4%, and 1.8%, respectively. Use of the criteria of the clinical examination resulted in treatment of 147 infants. Using the dynamic ultrasound examination as a criterion meant that 87 infants would receive treatment. The calculated treatment rate was 0.85% when based on the clinical stress test and 0.49% when based on the dynamic ultrasound. Conclusion: The dynamic ultrasound results reduced the treatment rate by over 40% when used as a basis for the decision regarding treatment. Key words: Comparative studies; hip; pediatrics; skeletal, appendicular; ultrasound Thröstur Finnbogason, Department of Pediatric Radiology, Astrid Lindgren Children s Hospital, Karolinska University Hospital Solna, SE Stockholm, Sweden (tel / , fax , . throstur.finnbogason@ karolinska.se) Accepted for publication October 11, 2007 At our hospital, all newborn infants undergo clinical hip screening by the maternity unit pediatrician, in most cases within 24 hours after birth. Infants with risk factors for developmental dysplasia of the hip (DDH), hip instability or dislocation, or ambiguous clinical findings are referred for orthopedic consultation. The clinical findings at this consultation, using the Barlow and Ortolani maneuvers, determine the treatment or further management. The clinical hip screening program at our institution corresponds to the general situation in Sweden, where neonatal hip screening has been in practice for approximately 50 years (1 4). This clinical screening has formed the basis of the management of neonatal hip instability (NHI) and DDH. The overall treatment rate in Sweden has circulated around 1.0%, with local variations. The overall rate of treatment for DDH at our hospital has varied in recent years, between 0.8 and 1.0%. The prevalence of late-detected DDH has been 0.003% during the last 7 years. We defined late-detected DDH as all cases of DDH missed by the neonatal clinical screening. The reliability of the clinical test for hip instability with the Barlow and Ortolani maneuvers has been questioned (5). Since the early 1980s, ultrasonography has complemented DOI / # 2008 Informa UK Ltd. (Informa Healthcare, Taylor & Francis AS)

2 Clinical Examination and Anterior Dynamic US in Neonatal Hip Instability 213 the clinical diagnosis to an increasing extent, and in many cases has resulted in an increased treatment rate (6 10). The true prevalence of NHI or DDH in need of treatment is unclear, with varying figures in the literature, ranging up to several percent, and it appears to depend on the definition and the time and method of diagnosis (11 13). One Swedish study has shown a frequency of DDH needing treatment of around 0.2% (14). Before the advent of clinical screening in Sweden, the reported prevalence of DDH was below 0.1% (15). We have previously introduced an anterior dynamic ultrasound method (16) that is a modification of the method described by DAHLSTRÖM and coworkers (17) in The original method of DAHLSTRÖM et al. required two examiners, but with our method the combined ultrasound examination and the Barlow stress test can be performed by a single examiner by using a special transducer fixation device. The aim of this study was to compare our dynamic ultrasound method with the clinical hip examination in a prospective study of infants born at our hospital. We hypothesized that the ultrasound examination would lower the treatment rate. Material and Methods Patients All infants born at the maternity unit of this hospital during the study period, between September 2001 and March 2005, underwent clinical hip screening by an experienced pediatrician within 24 hours after birth. This included the Barlow and Ortolani tests (2, 18). Infants with confirmed hip instability, hip dislocation, or ambiguous findings, and those with risk factors such as breech delivery, foot deformity, neck deformity, or a history of a parent, grandparent, or sibling having been treated for DDH were referred for pediatric orthopedic consultation. The selection for the study was made at the orthopedic consultation. The inclusion criteria were: clinical signs of hip instability or dislocation, ambiguous clinical findings by the pediatric orthopedist, and risk factors (heredity, foot deformity, torticollis, and breech delivery). Four senior pediatric orthopedists participated in the study. The orthopedist carried out a standard clinical hip examination based on the Barlow and Ortolani maneuvers, and graded the hip into three categories as a) normal, b) unstable, or c) dislocatable or dislocated. Based on the hip with the worst outcome, a grading of unstable was equivalent to treatment with a Frejka pillow, and a grading of dislocatable or dislocated meant treatment with a von Rosen splint. After the first clinical orthopedic examination, the infants who were selected to enter the study were referred to the ultrasound section of the pediatric radiology department, on the same day, in most cases within 2 3 hours. Two ultrasonographic examinations were performed, as explained in detail below. The first was a static ultrasound examination according to the Graf method (19), and the second was the anterior dynamic ultrasound method developed at the radiology department. The ultrasound examiners were blinded to the results of the clinical orthopedic examination. The ultrasound examinations were performed either by an experienced pediatric radiologist or by a sonographer who, prior to the study, had received special training in examining newborn hips. A total of six pediatric radiologists with many years of experience in pediatric ultrasound participated in the study. Before the study, all ultrasound examiners were trained in both the dynamic ultrasound method and the Graf method by one of the authors (T.F.). The examiner made a primary assessment of hip stability, and graded the hips into three categories as stable, unstable, or dislocatable/dislocated. Hip morphology was classified into types as described by Graf, and the alpha angle was measured. This was included in a report that accompanied the patient to the second orthopedic examination. The ultrasound report was written directly after the ultrasound examination and reflected the subjective perception of the examiner, including visual impact and how the stability was sensed with the hands during the maneuver. Following the ultrasound examination, the infant was returned to the orthopedic clinic, where a second clinical hip examination was performed by the pediatric orthopedist, with the same classification criteria as at the first examination, i.e., normal, unstable, or dislocatable/dislocated hip. After this second examination, the orthopedist made a decision regarding further management, based on the combined findings at the second orthopedic examination and the ultrasonography. Based on the hip with the worst grading, instability resulted in treatment with a Frejka pillow, and hips graded as dislocatable or dislocated were treated with a von Rosen splint. Whenever possible, the two orthopedic examinations and the ultrasound examinations were performed on the same day. The flow of the study is explained in Fig. 1. The study was approved by the local ethics committee, and informed consent was obtained. All statistical analyses were done with SPSS for Windows, version (SPSS Inc., Chicago, Ill.,

3 214 T. Finnbogason et al. Fig. 1. The flow of the study. The 536 patients included were selected from 18,031 infants born at the hospital during the study period. USA). Cohen s kappa was used to measure the agreement between the dynamic ultrasound and the clinical examination. Ultrasound examinations First, a static ultrasound examination by the Graf method was performed by the radiologist or the sonographer. A 5- or 7-MHz linear transducer was used with Acuson Sequoia ultrasound equipment (Siemens Medical Solutions, Mountain View, Calif., USA). The examination was carried out in a standard manner, as described in the literature, with the infant lying on its side. Images of the acetabulum in the standard plane were acquired (Fig. 2). This was documented with at least two images of each hip; the hips were graded according to Graf (19), and the alpha angle was measured. Fig. 2. Graf s examination. Standard plane type I hip.

4 Clinical Examination and Anterior Dynamic US in Neonatal Hip Instability 215 The anterior dynamic ultrasound examination (Fig. 3) was based upon a method originally introduced by DAHLSTRÖM and coworkers in 1986 (17), with modifications involving a specially designed examination table with a probe fixation device (16). This allowed the examiner to use both hands freely for the Barlow stress test. The aim was to copy the clinical examination technique as closely as possible. With the infant lying supine, the examiner used one hand to stabilize the pelvis while applying a posterior force to the femoral head with the other. Thus, to examine the left hip, provocation was made with the right hand, and the pelvis was stabilized with the left hand, and vice versa. A 5-MHz sector transducer was used with Acuson128XP ultrasound equipment (Siemens Medical Solutions, Mountain View, Calif., USA). The dynamic ultrasound examination was documented with cineloops directly to the hospital PACS system and was also video recorded. During the dynamic ultrasound examination, the radiologist or the sonographer made an assessment of the stability of the hip based on the visual information from the ultrasound together with the tactile perception. The findings were graded into three groups: normal, unstable, and dislocatable/dislocated. These findings were included in the report to the orthopedic surgeon. Results From a total population of babies delivered at the maternity unit during the study period, 538 infants met the inclusion criteria and were recruited to the study. Two infants were excluded from statistical analysis because of missing clinical data. The study thus comprised 536 infants (1072 hips). The mean gestational age at birth was 39.0 weeks (SD 1.8, range weeks). The mean birth weight was 3375 g (SD 608). There were 342 (63.8%) girls and 194 (36.2%) boys. The mean age at the time of the dynamic ultrasound examination was 12.2 days (SD 4.8, range 2 30 days). In the majority of cases, the ultrasound examinations were performed within a few hours after the first orthopedic examination. However, 53 infants (9.9%) were examined 24 hours Fig. 3. Anterior dynamic ultrasound. A sagittal sonogram of the right hip parallel to the femoral neck with the anterior approach. The hip is imaged during Barlow s maneuver. A. Stable hip with the femoral head in the acetabulum. B. Unstable hip with posterior subluxation of the femoral head. C. Dislocatable femoral head; the arrowhead indicates the anterior acetabular rim, and the arrow indicates the posterior acetabular rim. d: femoral neck/diaphysis; h: femoral head.

5 216 T. Finnbogason et al. Table 1. The first orthopedic examination compared with the dynamic ultrasound (n51072 hips) Dynamic ultrasound First orthopedic examination Stable Unstable Dislocatable or dislocated Total Stable * 876 Unstable Dislocatable or dislocated Total * This hip was revised to dislocatable at the second orthopedic examination. or more after the orthopedic examination, including 14 infants with an interval of more than 7 days. There were three separate diagnostic occasions on which the stability of the hips was assessed: 1) the first orthopedic clinical examination, 2) the dynamic ultrasound examination, and 3) the second orthopedic clinical examination. At all assessments, the hips were allocated to three groups as stable, unstable, or dislocatable/dislocated. First orthopedic examination versus dynamic ultrasound In Table 1, the outcome of the first orthopedic examination is compared with that of the dynamic ultrasound examination. The first orthopedic examination resulted in a considerably larger number of abnormal hips as compared to the dynamic ultrasound: 196 and 131 hips, respectively. The two were in agreement concerning 867 out of 1072 hips (kappa 0.284). In addition to the dynamic ultrasound method, all hips were also examined with a static ultrasound method, the Graf method. Of the 125 hips that were stable according to dynamic ultrasound and unstable or dislocatable according to the first orthopedic examination, 93 were judged as normal (type I) on the basis of Graf s classification and 32 as type IIa, i.e., borderline or immature. None proved to be pathologic (type IIc or worse). Second orthopedic examination versus dynamic ultrasound The second orthopedic examination was performed after and in the light of the dynamic ultrasound examination. The results are shown in Table 2. The agreement between the orthopedic examination and dynamic ultrasound increased from 867 hips (80.9%) to 897 hips (83.7%) (kappa 0.375), but there were still 107 hips that the orthopedist considered unstable, dislocatable, or dislocated but were classified as stable on the dynamic ultrasound. Table 2. The second orthopedic examination compared with the dynamic ultrasound (n51072 hips) Dynamic ultrasound Second orthopedic examination Stable Unstable Dislocatable or dislocated Total Stable Unstable Dislocatable or dislocated Total Fifty hips that were classified as unstable on dynamic ultrasound were considered stable at the orthopedic examination. The outcome of and interrelations between the three diagnostic tests are illustrated in detail in Fig. 4. The two orthopedic examinations were in agreement in 96.8% of examinations (kappa 0.878; Table 3). Thirty-four hips were revised at the second orthopedic examination; 22 of these being judged as unstable or dislocatable at the first orthopedic examination were given a normal rating, which was in agreement with the dynamic ultrasound examination in all but one. Twelve hips received a worse rating, which was in accordance with the dynamic ultrasound in 10 cases. Impact on treatment All in all, 144 patients received treatment: 111 a Frejka pillow and 33 a von Rosen splint. Nine patients were treated with a Frejka pillow despite being classified as stable in both hips after the first and even after the second clinical orthopedic examination. Four of these were found on dynamic ultrasound to be unstable in at least one hip, and the remaining five had one hip categorized as immature (type IIa) with the Graf method. Twelve patients with clinically determined instability in at least one hip were not treated. In 10 of these, both hips were judged to be stable on dynamic ultrasound. Nine were graded as normal on Graf s examination, two had unilateral type IIa, and one had bilateral type IIa. The female/male ratio of infants who received treatment was approximately 2.5:1. With the dynamic ultrasound method, the ratio of females to males among those with instability was approximately 3.5:1, and among those assessed as dislocatable/dislocated, 4:1. During the study period, infants were born at this hospital. The treatment rate was calculated under the assumption that all infants with instability would be treated with a Frejka pillow, and that

6 Clinical Examination and Anterior Dynamic US in Neonatal Hip Instability 217 Fig. 4. Detailed outcome of and interrelations between the three diagnostic tests for hip instability (n51072 hips). those with at least one hip dislocatable or dislocated would be treated with a von Rosen splint, which is the routine at our hospital. Table 4 shows the treatment rates calculated for the different methods of diagnosis. Discussion This study showed that the number of hips with instability was considerably reduced when dynamic ultrasound was used as compared to the clinical Table 3. The first and second orthopedic examinations compared (n51072 hips); the number of pathologic hips has decreased from 196 to 188 Second orthopedic examination First orthopedic examination Stable Unstable Dislocatable or dislocated Total Stable Unstable Dislocatable or dislocated Total examination. The number of hips requiring treatment was reduced by 33.2%, and the number of infants requiring treatment by 42.2%. No case of late-detected DDH was recorded at our institute among the infants born at the maternity ward during the study period of more than 4 years, which meant a rate of late-detected DDH of below 0.006%. The study was closed in March The treatment Table 4. The theoretical treatment rates calculated for the different methods of diagnosis, based on the hip with the worst score. Instability test Instability based on the hip with the worst outcome in the test Normal Unstable Dislocatable or dislocated Treatment rate First orthopedic test % Second orthopedic test % Dynamic ultrasound % The difference in treatment rate between the first and second orthopedic examination was not statistically significant, but the difference in treatment rate between the dynamic ultrasound and each of the first and second orthopedic examinations was highly significant. The actual treatment rate during the study period was 0.8% (144 infants).

7 218 T. Finnbogason et al. rate during the study period was 0.8%. This implies that, at our institute, the clinical examination is successful in identifying DDH but less successful in identifying normal hips. The design of the study, however, has limitations. It involved three diagnostic tests of instability: the first orthopedic clinical examination, the dynamic ultrasound, and the second orthopedic examination. The second orthopedic examination served as the endpoint at which the final diagnosis and decision about treatment was made. Owing to the lack of a gold-standard diagnostic test for DDH, it is difficult to evaluate the rate of false-negative ultrasonographic instability. We reasoned that this could partly be compensated for by applying a second ultrasound method, the Graf method. Both the dynamic ultrasound method and the clinical hip examination rely upon the clinical skills of the examiner performing the stress test. The clinical examinations were all performed by experienced pediatric orthopedists, and the dynamic ultrasound was conducted by experienced pediatric radiologists or a pediatric sonographer specially trained in hip examination with the Barlow method. However, the number of examiners involved four orthopedists and seven ultrasound examiners is a possible source of bias. Another limitation is the subjective nature of the instability diagnosis. The line of demarcation between normal subtle instability and pathologic instability requiring treatment is indistinct. Potential risks with clinical hip stress tests have been addressed to only a limited extent in the literature, but a few reports have been published indicating risks with repeated stress tests (8, 20 22). Owing to the possible risks, the hip stress test in the present study was limited to three occasions: the two orthopedic examinations and the dynamic ultrasound. The question of a second dynamic ultrasound and a dynamic ultrasound examination carried out together with the orthopedist in consensus was considered, but decided against for this reason. The point of time for the tests was set at days of age. This has support in the literature as being the optimal time to investigate hip instability, as normal physiological instability will have settled (18, 23 25). In most instances, the orthopedic and ultrasound tests were done on the same day. The mean time delay between these two examinations in the whole study was 0.68 days. For the 125 hips that the orthopedic examination classified as unstable, dislocatable, or dislocated, and the ultrasound classified as stable, the mean time delay was 0.26 days. At the first orthopedic examination, 196 hips out of 1072 (18.3%) were considered in need of treatment. This was reduced to 131 hips (12.2%) by dynamic ultrasound. The second orthopedic examination was in greater agreement with the dynamic ultrasound, and reduced the number of hips that should receive treatment from 196 to 188. However, the clinical examination still diagnosed 43% more hips as unstable, dislocatable, or dislocated than the dynamic ultrasound. There was a large difference between the dynamic ultrasound and the clinical orthopedic examination regarding the treatment rate, as follows from Table 4. If the decision to treat were based on the dynamic ultrasound, the treatment rate would be reduced by a factor of more than 40%, from 0.85% to 0.49%. We believe that our dynamic ultrasound method has a definite role in the selective screening of neonatal hip instability as a complement to or replacement for the clinical examination. The method combines the standard clinical examination (Barlow s maneuver) with ultrasound visualization. The extra time needed to accomplish this is minimal. We consider two factors to be most important in diagnosing hip instability. First, the clinical stress test, the Barlow maneuver, must be correctly performed in order to displace the femoral head, and second, the displacement must be perceived. The method of stress testing is identical to the standard clinical examination, and the perception of the displacement is augmented by adding the visual information from the ultrasound to the tactile and proprioceptive feeling of instability. In conclusion, the limited impact of the dynamic ultrasound examination on the orthopedist s decision about treatment in this study reflects a lack of confidence in the ultrasound method. However, with increasing confidence, our anterior dynamic ultrasound method has the potential to lower the treatment rate to a significant extent. References 1. Duppe H, Danielsson LG. Screening of neonatal instability and of developmental dislocation of the hip. A survey of 132,601 living newborn infants between 1956 and J Bone Joint Surg Br 2002;84: Ortolani M. Congenital hip dysplasia in the light of early and very early diagnosis. Clin Orthop 1976;121: von Rosen S. Early diagnosis and treatment of congenital dislocation of the hip joint. Acta Orthop Scand 1956;26: von Rosen S. Instability of the hip in the newborn. Fifteen years experience in Malmo. Acta Orthop Scand Suppl 1970;130:13 24.

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