The Pavlik harness is a positioning device commonly

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1 RESEARCH PAPERS Ultrasound Evaluation of Hip Position in the Pavlik Harness Leslie E. Grissom, MD*, H. Theodore Harcke, MD*, S. Jay Kumar, MOt, George S. Bassett, MOt, G. Dean MacEwen, MOt Fifty infants undergoing treatment in the Pavlik harness for congenital hip dysplasia (CDH) were serially evaluated with ultrasound. Comparison with clinical and radiographic examinations showed sonography to be 100% sensitive and highly specific. Discrepancies between the studies are attributed to the greater sensitivity of the technique compared with the physical examination andfor radiographs. Using this method, it is possible to significantly reduce radiation exposure to the infant being treated for CDH. JCEY WORDS: congenital hip dysplasia; Pavlik harness; ultrasound evaluation. (/ Ultrasound Med 7:1, 1988) The Pavlik harness is a positioning device commonly used by orthopedic surgeons to treat con genital hip dysplasia (CDH) in infants when an unstable hip is easily reduced. The harness holds the hips in flexion and abduction with the femoral heads directed toward the triradiate cartilage, promoting acetabular development. It is a dynamic splint, permitting movement within a safe zone, but restricting extremes of motion that would allow subluxation or dislocation. 1 Infants remain in the harness for 6 weeks to 6 months, with periodic adjustments to ensure proper fit and position. Radiographs are obtained frequently during this period to monitor the hip position. From an anteroposterior (AP) view of the pelvis, it is possible to judge the relationship of the femur to the acetabulum in two di mensions; however, one cannot always diagnose posterior displacement. Because of this problem and because of the desire to reduce radiation exposure, we have used real-time ultrasound to evaluate hip position in the har ness. In this report, we describe our technique and present the results in 50 infants. Received March 19, 1987, from the Departments of Medicallmag ing and torthopedics, Alfred L dupont Institute, Wilmington, DeJa~ ware. Revised manuscript accepted for publication July 7, Address correspondenc and reprint requests to Dr, Grissom, Dept. of Medical Imaging, Alfred I. dupont Institute, 1600 Rockland Rd., Wilmington, DE MATERIALS AND METHODS We scan our patients with an ATL MK 100 real-time sector scanner, using the 7.5-MHz transducer in young infants and a lower-frequency transducer in patients over 3 months of age. Our examination consists of evaluation in two planes, transverse and coronal, while the hip is held in flexion and abduction in the harness. The sector passes from lateral to medial into the hip joint in both views and represents a variation of the technique we have described previously. 2-4 In our institution, the examination takes a total of 15 min from the time the patient arrives to the time he or she leaves. The transverse plane sonogram is illustrated in Figure 1. The cartilaginous femoral head is a sonolucent ball bounded anteriorly by the femoral metaphysis and shaft and posteriorly by the posterior margin of the acetabu lum. In the normal transverse/flexion view, the bony structures form a "U" or "V" configuration around the femoral head, and no echoes are seen between the femo ral head and the bony acetabulum in any position. This view may be better understood by comparing it with an axial computed tomography scan, as illustrated in Figure 2 With subluxation, the femoral head will ride up the posterior acetabular lip, with abnormal echoes seen in the acetabular fossa between the femoral head and the bony acetabulum. When the hip is dislocated, the 1988 by the American Institute of Ultrasound in Medicine J Ultrasound Med 7:1-6, /88/$3.50

2 2 ULTRASOUND EVAWATION OF HIP POSmON IN THE PAVUK HARNESS J Ultrasound Med 7:1-6, 1988 Figure 1 The normal transverse/flexion view shows the "U" created by the femoral metaphysis (closed arrow) and the posterior acetabulum (open arrow) surrounding the sonolucent femoral head. A, anterior; L, lateral; P. posterior. Figure 2 Computed tomography scan of the pelvis in the prone position indicates the scanning sector and bony landmarks of the transverse/flexion view. Note the posterior dislocation of the hip on the right with loss of the "U" configuration seen on the normal left side. Open arrow, acetabulum; closed arrow, femoral metaphysis. will not be resting against the posterior acetabulum and the "U" relationship will not be seen (Fig. 3). In the coronal plane, the sonolucent femoral head is surrounded by the bright, bony echoes of the acetabulum, with the linear echoes of the ilium seen superiorly (Fig. 4). The configuration of the hip resembles that seen on an AP radiograph (Fig. 5). With subluxation or dislocation, the head will be displaced away from the central portion of the acetabular fossa, often positioned over the posterior lip of the acetabulum, identified by the gap representing the posterior limb of the triradiate cartilage (Fig. 6). Finally, if the standard views show normal positioning and the patient has been in the harness for at least several weeks, we perform stress maneuvers, with adduction of the hip in the range of the harness and pistoning of the hip posteriorly. This is particularly done in the weaning period. In this real-time procedure,. the ab-

3 J Ultrasound Med 7:1-6, 1988 GRISSOM El' AL 3 Figure 3 Transverse/flexion view of a dislocated hip shows the sonolucent fem oral head bordered by the metaphysis (closed arrow) displaced laterally and posteriorly in relation to the posterior acetabulum (open arrow). L, lateral; P, posterior. Figure 4 Normal coronaljflexion view shows the fem oral head (curved arrow) surrounded by bony acetabu lum (white arrow) with ilium superiorly (open arrow). I, inferior; L, lateral; M, medial; S, superior.

4 4 ULTRASOUND EVAWATION OF HIP POSITION IN THE PAVUK HARNESS J Ultrasound Med 7:1-6, 1988 Figure 5 Anteroposterior view of the pelvis shows the scanning sector of the coronal/flexion view with the bony landmarks of the ilium and acetabulum outlined. Figure 6 Coronal/flexion view of the dislocated hip shows the femoral head resting on the posterior limb of the triradiate cartilage (arrow). The sector has been rotated from the usual orientation to enable comparison with the radiograph. L, lateral; S, superior.

5 J Ultrasound Med 7:1-6, 1988 GRISSOM ET AL 5 normal hip may show some laxity that was not seen on routine images without stress. RESULTS We reviewed the charts and studies of 50 infants who were identified as having CDH and were placed in our Pavlik treatment program. A total of 126 ultrasound ex aminations were performed in the harness (average, 25 per patient). We compared the results of these studies with clinical examinations and available radiographs. When all three examinations were not in agreement, the two in agreement were considered to be the accurate result. For this investigation, when there were only two examinations, the clinical examination was considered more accurate. Our results showed 100% sensitivity and 94% specificity. In 120 examinations, our study agreed with the clinical evaluation or radiographic results. Twenty nine showed dislocation, subluxation, or laxity with motion or stress (true-positive), and 91 were satisfactorily positioned (true~negative). In a total of six stud ies, in three patients, we identified abnormal hip positions not recognized clinically or radiographically. The conflicts typically occurred when the ultrasound examination showed the hip to be slightly subluxated (not dislocated) and the clinical examination and/or radiographs in the harness were thought to show satisfactory reduction. In the first patient, the harness was adjusted following both ultrasound examinations, and the patient was weaned from the harness 3 months later with a satisfactory clinical result. In the second patient, the family was not compliant in the use of the Pavlik harness, and a subsequent arthrogram showed capsular laxity on the abnormal side. In the third patient, there was no change in the treatment, and a follow-up ultra sound examination in 1 month showed satisfactory positioning. The patient was weaned from the Pavlik harness in 2 months with a satisfactory result. We believe that follow-up in at least the first two cases confirms the accuracy of sonography. For statistical purposes, however, these discrepancies must be deemed false-positives. There were no false-negative results. DISCUSSION When we look at the overall results of the Pavlik treatment program, 42 patients responded to Pavlik harness treatment and eight went on to closed or open reductions with casting. The ultrasound examination successfully identified all dislocations and significant instability and was therefore 100% sensitive. The specificity was 94% based on the six false-positive examinations described earlier. We believe that the occurrence of discrepancies or false-positive ultrasound studies can be explained. First, the ultrasound examination seems to be more sensitive than the physical examination, sometimes detecting minimal subluxation that is not normal but is not clini cally recognized. Second, the radiographic examination is two-dimensional and in only one position, and it may show apparent reduction of a hip that is actually posterior, or reduction that is not stable with motion on an ultrasound examination. Finally, the calculation of specificity based on a gold standard of radiographic and clinical findings, both of which are known to be inaccurate at times, should be recognized. Blank showed that a slight change in positioning of the infant pelvis can lead to misinterpretation of the hip position. 5 Even in a perfectly positioned film, the large proportion of cartilage in the immature pelvis can make it difficult to evaluate. 3 With regard to clinical examination, Barlow showed that several classic physical signs of instability or dislocation are not always reliable and that there are pitfalls to the physical examination even in experienced hands. 6 An important aspect of evaluation in the Pavlik harness is the assessment of stability. After an initial period in the harness, stability is one factor that determines the duration of treatment. It is particularly useful for the orthopedic surgeon to know when stability has been achieved so that weaning from the harness can be con sidered. Although we do not advocate elimination of all radio ~ graphs, we are able to use ultrasound successfully to reduce the number of radiographs for infants being treated. Typically, a patient suspected of having CDH will have sonography initially, and if the study is abnormal, a radiograph will be taken at the beginning of treatment. The patient is then followed with sonography throughout the treatment, and on completion of treatment, a final radiograph is obtained. CONCLUSION Real-time ultrasound is an effective alternative to radiography for assessing hip position in the Pavlik harness. It is able to identify positional abnormalitie:; not detected clinically or radiographically. Its use to monitor infants being treated for CDH also reduces exposure to radiation. With it, we are able to assess the hip position accu rately, at times identifying abnormalities not detected clinically or radiographically. REFERENCES 1. Ramsey PL, Lasser S, MacEwen GO: Congenital disloca tion of the hip: use of the Pavlik harness in the child during the first six months of life. J Bone joint Surg 58A:1000, 1976

6 6 ULTRASOUND EVALUATION OF HIP POSmON IN THE PAVUK HARNESS J Ultrasound Med 7:1-6, Harcke HT, Clarke NMP, Lee MS, eta): Examination of the hip with real-time ultrasound. J Ultrasound Med 3:131, Clarke NMP, Harcke HT, McHugh P, et al: Real time ultra sound in the diagnosis of congenital dislocation and dysplasia of the hip. J Bone Joint Surg 67B:406, Harcke HT, Grissom LE: Sonographic evaluation of Che infant hip. Semin Ultrasound Cf MR 7:331, Blank E: Some effects of position on the roentgenologic diagnosis of dislocation at the infant hip. Skeletal Radial 7:59, Barlow TQ Early diagnosis and treatment of congenital dislocation of the hip. J Bone Joint Surg 44B:292, 1962