Radiographic Evaluation Of Dynamic Hip Instability In Lequesne s False Profile View

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1 Radiographic Evaluation Of Dynamic Hip Instability In Lequesne s False Profile View Ryo Mori 1, Yuji Yasunaga 2, Takuma Yamasaki 1, Michio Hamanishi 1, Takeshi Shoji 1, Sotaro Izumi 1, Susumu Hachisuka 1, Mitsuo Ochi 1. 1 Department of Orthopaedic Surgery,Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima, Japan, 2 Department of Artificial Joints and Biomaterials, Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima, Japan. Disclosures: R. Mori: None. Y. Yasunaga: None. T. Yamasaki: None. M. Hamanishi: None. T. Shoji: None. S. Izumi: None. S. Hachisuka: None. M. Ochi: None. Introduction: The purpose of this study was to evaluate hip instability in Lequesne s false profile view (FPV) [1] in patients with acetabular dysplasia. Methods: Patients We reviewed standard antero-posterior (AP) pelvic view and Lequesne s FPV [1] of 27 hips in 19 patients with acetabular dysplasia, obtained during preoperative examinations for rotational acetabular osteotomy (RAO) between July 2011 and June Acetabular dysplasia was defined as a lateral center-edge (CE) angle [2] less than 20º, based on measurements of AP radiographs. All hips were classified as Grade 0 or 1 according to the Tönnis classification [3] and as type 1 according to the classification system of Crowe et al. [4] The mean age of these patients at the time of examination was 40.2 years (range, years). The study subjects were disproportionately all females, because acetabular dysplasia is common in females in Japan. Therefore, to eliminate the effect of differences between genders in hip instability, we also included only female subjects in the control group described later.the control group included 20 patients (25 hips) without acetabular dysplasia (CE angle 20º). These subjects were obtained from patients who had no collapse of osteonecrosis of femoral head, or no dysplastic hip in contra-lateral side of study group. Also, these patients all were females with a mean age of 44.2 years (range, years). CE angle, Head lateralization index (HLI) [5], and vertical center anterior margin (VCA) angle [1] were evaluated on the AP view or FPV of radiographs (Fig. 1 and 4). These two groups were similar in terms of the age and body mass index (BMI), while there were statistical differences between two groups in terms of CE angle, HLI, and VCA angle (Table 1) Table 1. Demographic and radiographic parameters in dysplastic and control groups Parameters Dysplastic group (N=27) Control group (N=25) p Value ** Age (years) * 40.2 (21-61) 44.2 (14-67) p=0.17 Body mass index (kg/m 2 ) * 23.6 ( ) 21.9 ( ) p=0.12 Center-edge angle (º) * 8.3 (0-18) 25.9 (20-42) p<0.01 Head lateralization index* 0.61 ( ) 0.56 ( ) p<0.01 Vertical center anterior margin angle (º) * 2.7 (-12-27) 24.2 (12-48) p<0.01 Radius of femoral head (mm) * 23.5 (21-26) 23.2 (21-27) p=0.23 Radius of acetabulum (mm) * 28.9 (26-31) 27.0 (25-32) p<0.01

2 * The values are given as the mean, with the range in parentheses ** Mann-Whitney U test Statistical differences were considered significant for p values < 0.05 Assessment The standard FPV, which Lequesne proposed [1], was taken as follows; Subjects were placed in a standing position and each pelvis was rotated by 65º for the X-ray Film in the axial plane, while the axis of the ipsilateral foot in the hip of interest was parallel to the X-ray Film (Fig. 1). The standard FPV was taken, and subsequently the functional FPV was taken when the hip of interest was 90º of flexion (Fig. 2). At that time, the lower extremity of interest was put on a folding chair with an appropriate height. The axis of the ipsilateral foot was also parallel to the radiographic plate. The radiographs obtained from the two group were analyzed with Ortho Planner Pro (Toyo Corporation, Tokyo, Japan), which is mainly used digital preoperative templating of total hip arthroplasty. The evaluation of dynamic hip instability was carried out by measuring the above-mentioned standard and functional FPV as follows. Using the facility of image-relation in Ortho Planner Pro, overlay of weight bearing area in standard and functional FPV was carried out to confirm the most correspondences. In standard FPV, two circles were each drawn to best approximate the shape of weight bearing area and femoral head, and the centers of rotation in acetabulum and femoral head were each determined. Similarly, in functional FPV, the same method was carried out. The distance between the centers of femoral head (FHC) in the standard and functional FPV were analyzed. The sagittal direction of connecting line between FHC in the standard and functional FPV was also evaluated, and the x and y axes were defined as anterior and superior direction respectively. The distance between FHC in the standard and functional FPV was named translation-xy. In the x axis and y axis, translation of FHC was named translation-x, translation-y respectively, with the origin defined as FHC at the neutral position. CE angle, HLI, VCA, and radius of femoral head and acetabulum were also analyzed by Ortho Planner Pro. Statistical analysis The differences between the two means were calculated using the Mann-Whitney U test. Simple linear regression analyses in each group were carried out to evaluate relationships with translation-xy and age, BMI, CE angle, HLI, VCA angle, radius of femoral head, and radius of acetabulum. Multiple linear regression analysis was performed to assess independent relationship with translation-xy as criterion variable, and age, BMI, CE angle, HLI, VCA angle, radius of femoral head, and radius of acetabulum as explanatory variables. The selection criterion of variables for inclusion was forward-stepwise with entrance criterion of F-value 2 and an exit criterion of F-value < 2. The criterion values in the final model was checked in the multico-linearity. Statistical differences were considered significant for p-values <0.05. Results: In the radius of femoral head, there was no difference between dysplastic and control groups, while in the radius of acetabulum, there was difference between two groups (Table 1). FHC tended to translate postero-inferiorly for the dysplastic group, and antero-inferiorly or antero-superiorly for the control group (Fig. 5). The mean translation-xy was 2.9 mm (range; mm) for the dysplastic group, and 1.0 mm (range; mm) for the control group. The mean translation-x was -1.4 mm (range; mm) for the dysplastic group, and 0.7 mm (range; mm) for the control group. The mean translation-y was -2.0 mm (range; mm) for the dysplastic group, and -0.1 mm (range; mm) for the control group (Table 2). Table 2. Comparison of translation of center of femoral head in dysplastic and control groups Dysplastic group (N=27) Control group (N=25) p Value ** Translation-xy (mm) * 2.9 ( ) 1.0 ( ) p<0.001 Translation-x (mm) * -1.4 ( ) 0.7( ) p<0.001 Translation-y (mm) * -2.0 ( ) -0.1 (-0.8-1) p<0.001 X-axis and y axis pointed anteriorly and superiorly respectively.

3 * The values are given as the mean, with the range in parentheses ** Mann-Whitney U test Statistical differences were considered significant for p values < 0.05 There was difference between two groups in term of translation-xy (p < 0.001), translation-x (p < 0.001), and translation-y (p < 0.001). There was strong correlation between VCA angle and translation-xy (p < 0.001; R = 0.664), and between HLI and translation-xy (p < 0.001; R = 0.676) in the dysplastic group, while there was no correlation between morphological parameters and translation in the control group (Table 3). Table 3. Linear regression analysis in dysplastic and control group parameters Translation in Dysplastic group Translation in Control group Correlation coefficient p Value Correlation coefficient p Value Age Body mass index Center-edge angle p< Vertical center anterior margin angle p< Head lateralization index p< Radius of femoral head p< Radius of acetabulum p< Statistical differences were considered significant for p values < 0.05 In multiple linear regression analyses, translation-xy was independently correlated with HLI (β =0.484, p < 0.01). Adjust coefficient of determination was Discussion: Acetabular dysplasia shows deficiency of acetabular coverage, and has been considered that the femoral head have a tendency to migrate anterolaterally compared to normal hip. In dysplastic hip, functional pelvic view of radiograph, taken supine with the hips in maximum abduction, can demonstrate a medial reduction of subluxation. In the present study, functional FPV, taken at the position with 90º of flexion, demonstrated postero-inferior reduction of subluxation. Furthermore, there was a correlation between the translation of FHC obtained from standard and functional FPV, and the lateralization of femoral head obtaind from AP view of radiograph. These measures may be helpful in determining surgical indication of acetabular dysplasia. Significance: Radiographical hip instability in sagittal plane was increased in proportion to the severity of lateralization of femoral head in coronal plane.this measures performed by plain radiographs is less costly than those by multi-planar imaging such as CT or MRI, and dynamic hip instability can be easily identified on a standard and functional FPV. Acknowledgments: The authors would like to thank Michiko Takeuchi, M.D. for her help in this study. References: [1] Lequesne M et al. Rev Rhum Mal Osteoartic 1961; 28: [2] Wiberg G. Acta Chir Scand 1939; 83(suppl):58. [3] Crowe JF et al. J Bone Joint Surg Am. 1979; 61: [4] Tönnis D. Berlin, Springer-Verlag , [5] Ninomiya S. Clin Orthop. 1989; 247:

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9 ORS 2014 Annual Meeting Poster No: 0869

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