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Scientific Articles   |    
Evaluation of Dynamic Instability of the Dysplastic Hip with Use of Triaxial Accelerometry
Akira Maeyama, MD1; Masatoshi Naito, MD1; Shigeaki Moriyama, PhD2; Ichiro Yoshimura, MD1
1 Department of Orthopaedic Surgery, Fukuoka University, 7-45-1 Nanakuma, Jonan-ku, Fukuoka 814-0180, Japan. E-mail address for A. Maeyama: akira.maeyama0713@joy.ocn.ne.jp. E-mail address for M. Naito: mnaito@cis.fukuoka-u.ac.jp. E-mail address for I. Yoshimura: ichiroy@cis.fukuoka-u.ac.jp
2 Department of Mechanical Engineering, Faculty of Engineering, 8-19-1 Nanakuma, Jonan-ku, Fukuoka 814-0180, Japan. E-mail address: moriyama@fukuoka-u.ac.jp
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Disclosure: The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.
Investigation performed at the Department of Orthopaedic Surgery, Fukuoka University, Fukuoka, Japan

The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2008 Jan 01;90(1):85-92. doi: 10.2106/JBJS.G.00029
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Abstract

Background: Dysfunction of the hip secondary to dysplasia is a complex problem that includes excessive stresses on the articular cartilage, dynamic hip instability, and muscular fatigue, eventually leading to degenerative arthritis if left uncorrected. Mechanical stress on the dysplastic hip has been widely described, but dynamic instability requires further evaluation. The purpose of this study was to investigate dynamic instability of the dysplastic hip with use of triaxial accelerometry.

Methods: We evaluated forty-eight hips of twenty-four patients with unilateral hip dysplasia (a center-edge angle of <25°). All contralateral hips were disease-free with normal radiographic findings. An accelerometer was used to record triaxial acceleration while the patient was walking (x-axis: superoinferior direction, y-axis: anteroposterior direction, and z-axis: mediolateral direction). Sensors were attached to the skin, with adhesive tape, over the greater trochanter and the anterior superior iliac spine bilaterally. The time of heel-strike was confirmed visually and by superoinferior acceleration. The averages of the peak values of the middle three gait cycles were used for data analysis. The overall magnitude of acceleration was calculated to evaluate hip instability. The overall magnitudes of acceleration of the dysplastic and contralateral, normal hips were compared with the radiographic data.

Results: The three directions of acceleration were the same in all cases. The overall magnitude of acceleration of the dysplastic hips was significantly larger than that of the contralateral, normal hips (p < 0.0001). There was a negative correlation between the overall magnitude of acceleration and both the center-edge angle and the acetabular head index, and there was a positive correlation between the overall magnitude of acceleration and both the acetabular roof angle and the Sharp angle.

Conclusions: Hip instability is increased in proportion to the degree of dysplasia. Triaxial accelerometry is helpful in the evaluation of dynamic instability of the dysplastic hip. The center-edge angle can be used as an indicator of hip instability.

Level of Evidence: Diagnostic Level III. See Instructions to Authors for a complete description of levels of evidence.

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    Accreditation Statement
    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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