Prevalence and characteristics of cam-type femoroacetabular deformity in 100 hips with symptomatic acetabular dysplasia: a case control study

Abstract

Background: Cam-type femoroacetabular deformity in acetabular dysplasia (AD) has not been well clarified. The primary purpose of this study was to determine the prevalence and characteristics of femoroacetabular deformity in symptomatic AD patients.

Methods: We retrospectively reviewed the cases of 86 women (92 hips) and eight men (eight hips) with symptomatic AD. The mean patient age was 37.9 (range, 14-60) years. All participants underwent lateral cross-table and lateral whole-spine radiographic examinations to measure the alpha angle and pelvic tilt. Pelvic computed tomography scans were used to measure femoral anteversion. The patients were classified into two groups: AD only group, containing hips with an alpha angle less than 55°; and AD with cam-type femoroacetabular deformity (AD + cam-type deformity) group, containing hips with an alpha angle greater than or equal to 55°.

Results: Of the patients with AD, 40 hips displayed additional radiographic evidence of cam-type morphology, while 60 hips had exclusive AD morphology. The patients in the AD + cam-type deformity group had significantly increased forward pelvic tilt in the standing position (p = 0.023) and decreased femoral anteversion (p =0.047) compared with the AD only group.

Conclusions: Our data revealed that 40% of patients with AD also had radiographic evidence of cam-type femoroacetabular deformity. Greater forward pelvic tilt in the standing position and decreased femoral anteversion seemed to be associated with the cam-type deformity in these patients. These results indicate the morphological features that are most likely to induce secondary symptoms to developmental hip dysplasia. It is suggested that the symptoms in the AD + cam-type deformity group could arise through femoroacetabular impingement (FAI) after periacetabular osteotomy, because a predisposition was present preoperatively.

Figure 1

Diagram showing the radiological indices of lateral whole-spine radiographs in the standing and decubitus positions. (A) The pelvic inclination angle was formed by the angle between a solid line connecting the promontorium and the upper edge of the symphysis pubis and a vertical line. (B) The pelvic angle was formed by the angle between a dotted line extending from the posterior side of the upper edge of the sacrum to the midpoint of a line connecting the central point of the left and right femoral heads and a vertical line. (C) The lumbar lordotic angle was formed by the angle between a dashed line extending from L1 to L5.

Figure 2

Examples of preoperative radiographs and three-dimensional computed tomography (CT). A 23-year-old woman with right hip pain presented with acetabular dysplasia and a non-spherical femoral head-neck junction. Radiographs and three-dimensional CT images were taken prior to curved periacetabular osteotomy. (A) The centre-edge angle and acetabular roof obliquity were 19.0° and 13.0°, respectively. (B) The alpha angle was 61°. (C) The pelvic angle was 16.4° in the standing position, as indicated by the dashed lines. (D) The arrow indicates cam-type femoroacetabular deformity on a three-dimensional CT image.

Figure 3

Example of postoperative radiographs and three-dimensional CT. A 23-year-old female presented with cam-type femoroacetabular deformity and acetabular hip dysplasia. Radiographs and three-dimensional CT images were taken 1 week after curved periacetabular osteotomy. (A) The centre-edge angle and acetabular roof obliquity were 33.0° and 0°, respectively. (B) The alpha angle was 40.0°. (C) The arrow indicates the spherical junction of the femoral head-neck on a three-dimensional CT image after curved periacetabular osteotomy and osteochondroplasty.