Summary

Comparison of AIIS between FAI and DDH

Abstract

Background

Anterior inferior iliac spine (AIIS) morphology has been defined as one of the common causes of extra-articular hip impingement and failed hip arthroscopy for femoroacetabular impingement (FAI). Thus, the AIIS classification by Hetsroni is popular in clinical practice, and surgeons should pay attention to extra-articular hip impingement in cases of type 3. Many previous studies have shown the AIIS morphology in patients with FAI, patients with labral tears or asymptomatic populations. However, there are a few studies about AIIS morphology in developmental dysplasia of the hip (DDH).

Purpose

The purpose of this study was to compare the AIIS morphology between FAI and DDH.

Methods

Four hundred twenty-three hips of 374 patients who underwent primary hip arthroscopic surgery from January 2015 to March 2019 were retrospectively reviewed. The inclusion criteria in this study were labral tears with FAI or DDH. Finally, 359 hips of 310 patients were included in this study. Preoperative demographics and imaging variables of patients in the FAI and DDH groups were compared. For demographic evaluation, age at surgery, sex, and body mass index (BMI) were assessed. For imaging evaluation, LCE angle, sharp angle, vertical center anterior (VCA) angle, alpha angle, Tönnis angle and AIIS were assessed. AIIS morphology was classified according to the Hetsroni’s classification. Statistical analysis was performed to compare the AIIS morphology between the FAI and DDH groups.

Results

Of 359 hips in 310 patients, FAI cases involved 241 hips (148 males, 93 females), and DDH cases involved 118 hips (34 males, 84 females) in this study. In FAI group, AIIS type 1 included 45 hips (18.7%), type 2 included 286 hips (77.2%), and type 3 included 10 hips (4.1%). In the DDH group, AIIS type 1 included 4 hips (3.4%), type 2 included 93 hips (78.8%), and type 3 included 21 hips (17.8%). The proportion of AIIS type 3 in the DDH group was significantly higher than that in the FAI group (chi-squared test, p <0.001). In the FAI group, there were no significant differences in demographic and radiographic parameters between AIIS type 1 or 2 and type 3. In the DDH group, there were significant differences in LCE, VCA and Tönnis angle between AIIS type 1 or 2 and type 3. The LCE angle was 19.0 ± 4.0 in type 1 or 2 and 13.0 ± 6.0 in type 3 (Mann-Whitney U test, p = 0.003). The VCA angle was 20.3 ± 9.3 in type 1 or 2 and 11.1 ± 10.0 in type 3 (Mann-Whitney U test, p = 0.011). The Tönnis angle was 12.5 ± 5.1 in type 1 or 2 and 16.8 ± 6.3 in type 3 (Mann-Whitney U test, p = 0.014). These results indicated that DDH with AIIS type 3 tends to be more severe dysplasia than that with type 1 or 2.

Conclusions

AIIS type 3 was more common in DDH than FAI. In DDH, AIIS type 3 tends to be more severe dysplasia than AIIS type 1 or 2.