Dynamic Instability in Young Adults with Symptomatic Hip Dysplasia: Analysis using a Computer-Assisted Image-Matching Procedure

Abstract Background: Repeated microtrauma often causes damage to the periarticular soft tissues. This damage, together with the lack of acetabular bony coverage, such as developmental dysplasia of the hip (DDH), can contribute to various degrees of dynamic instability of the hip joint and cause progressive osteoarthritic changesThe purpose of this study was to use an image-matching procedure to compare dynamic instability of the hip joint in patients with DDH who did or did not undergo periacetabular osteotomy (PAO). Methods: Six patients (6 hips) with symptomatic DDH were enrolled. A 6-month trial of nonsurgical management was initiated at the first visit. PAO was performed in 3 patients who experienced persistent pain after conservative treatment. The dynamic instability of all 6 hips was evaluated. Results: Japanese Orthopaedic Association hip scores improved significantly in all hips regardless of PAO. At the first visit, the center-edge angle, Sharp angle, vertical-center-anterior angle, and acetabular head index were not significantly different between the PAO and non-PAO groups. Dynamic instability was defined as the 3D translation of the femoral head center for the acetabular center at hip abduction angles from 0° to 30°. In the non-PAO group, the mean sagittal, axial, and coronal translations were 2.4 mm, 2.2 mm, and 1.1 mm, respectively, and in the PAO group they were 2.4 mm, 7.2 mm, and 2.7 mm, respectively. There was a significant difference in axial translation between the 2 groups. Conclusion:Dynamic instability leads to periarticular soft tissue damage and insufficient bony coverage, and causes progressive osteoarthritic changes. Dynamic instability in the axial plane induces persistent hip pain after nonsurgical management. Affected patients should undergo PAO as soon as possible.