Prominent Anterior Inferior Iliac Spine Morphologies Are Common in Patients with Acetabular Dysplasia Undergoing Periacetabular Osteotomy

Abstract

Background The anterior inferior iliac spine (AIIS) prominence is increasingly recognized in the setting of femoroacetabular impingement (FAI). The AIIS prominence may contribute to decreased hip flexion after acetabular reorientation in patients with acetabular dysplasia. AIIS morphologies have been characterized in numerous populations including asymptomatic, FAI, and athletic populations, but the morphology of the AIIS in patients with symptomatic acetabular dysplasia undergoing periacetabular osteotomy (PAO) has not been studied. In acetabular dysplasia, deficiency of the anterosuperior acetabular rim is commonly present and may result in the AIIS being positioned closer to the acetabular rim. Understanding morphological variation of the AIIS in patients with symptomatic dysplasia, and its relationship to dysplasia subtype and severity may aid preoperative planning, surgical technique, and evaluation of postoperative issues after PAO. Questions/purposes In this study, we sought to determine: (1) the variability of AIIS morphology types in hips with symptomatic acetabular dysplasia and (2) whether the differences in the proportion of AIIS morphologies are present between dysplasia pattern and severity subtypes. Methods Using our hip preservation database, we identified 153 hips (148 patients) who underwent PAO from October 2013 to July 2015. Inclusion criteria for the current study were (lateral center-edge angle [LCEA] < 20°), Tönnis Grade of 0 or 1 on plain AP radiographs of the pelvis, preoperative low-dose CT scan, and no prior surgery, trauma, neuromuscular, ischemic necrosis, or Perthes-like deformity. A total of 50 patients (50 hips) with symptomatic acetabular dysplasia undergoing evaluation for surgical planning of PAO remained for retrospective evaluation; we used these patients’ low-dose CT scans for analysis. The median (range) age of patients in the study was 24 years (13 to 49). Ninety percent (45 of 50) of the hips were in female patients, whereas 10% (5 of 50) were in male patients. The morphology of the AIIS was classified on three-dimensional CT reconstructions according to a previously published classification to define the relationship between the AIIS and the acetabular rim. The morphology of the AIIS was classified as Type I (AIIS well proximal to acetabular rim), Type II (AIIS extending to level of acetabular rim), or Type III (AIIS extending distal to acetabular rim). Acetabular dysplasia subtype was characterized according to a prior protocol as either predominantly an anterosuperior acetabular deficiency, a posterosuperior acetabular deficiency, or a global acetabular deficiency. Acetabular dysplasia severity was distinguished as mild (LCEA 15° to 20°) or moderate/severe (LCEA < 15°). To answer our first question, regarding the proportions of each AIIS morphology in the dysplasia population, we calculated proportions and 95% CI estimates. To answer our second question, regarding the proposition of AIIS type between subtypes of dysplasia type and severity, we used a chi-square test or Fisher’s exact test to compare categorical variables. A p value of < 0.05 was considered significant. Results Seventy-two percent (36 of 50; 95% CI 58% to 83%) of patients had a Type II or III AIIS morphology. Type I AIIS morphology was found in 28% of patients (14 of 50; 95% CI 18% to 42%), Type II AIIS morphology in 62% (31 of 50; 95% CI 48% to 74%), and Type III AIIS/morphology in 10% (5 of 50; 95% CI 4% to 21%). A Type I AIIS was seen in seven of 15 of patients with anterosuperior acetabular deficiency, three of 18 of patients with global deficiency, and four of 17 patients with posterosuperior deficiency (p = 0.08). There was no difference in the variability of AIIS morphologies between the different subtypes of acetabular dysplasia pattern and no difference in AIIS morphology variability between patients with mild versus moderate/severe dysplasia. Conclusions The morphology of the AIIS in patients with acetabular dysplasia is commonly prominent, with 72% of hips having Type II or Type III morphologies. Clinical Relevance The AIIS is often prominent in patients with acetabular dysplasia undergoing PAO, regardless of dysplasia pattern or severity. Prominent AIIS morphologies may affect hip flexion ROM after acetabular reorientation. AIIS morphology is a variable that should be considered during preoperative planning for PAO. Future studies are needed to assess the clinical significance of a prominent AIIS on intraoperative findings and postoperative status after PAO.

Comparison of Anterior Center-Edge Angle Measured From the Acetabular Sourcil Versus the Anterior Bone-Edge of the Acetabulum: A Descriptive Laboratory Study

“…A previous study has indicated that patients with acetabular dysplasia often have a prominent AIIS. 25 In our clinical practice, our patients have consistently shown, as supported by this study, that for most hips, the bone-edge ACEA is significantly larger than the true ACEA because of the effect of the AIIS. In this study, the bone-edge ACEA was 16.8°± 10.4° larger than the true ACEA, with only a moderate correlation between the 2 ( r = 0.57).…”

Shelf acetabuloplasty may inhibit range of motion: A computer simulation analysis

“…On the other hand, it should be noted that iatrogenic anterior impingement can occur after PAO 15 . Nestorovski et al reported that the morphology of the anterior inferior iliac spine in patients with acetabular dysplasia is commonly prominent 16 ; therefore, the possibility of iatrogenic impingement should be considered after PAO. Over‐coverage of the acetabulum certainly inhibits ROM after osteotomy 17 .…”

CORR Insights®: Prominent Anterior Inferior Iliac Spine Morphologies Are Common in Patients with Acetabular Dysplasia Undergoing Periacetabular Osteotomy

“…In this CT imaging–based paper, Nestorovski et al [4] found that the morphology of the AIIS could potentially cause impingement in 72% (36 of 50) of patients undergoing Bernese PAO for symptomatic residual dysplasia. In light of this finding, I believe surgeons should focus on the shape and size of the AIIS while evaluating the most appropriate correction of acetabular deformities.…”