Summary

Evaluation of the frequency of ossific / calcific fragments adacent to the acetabular rim in patients with femoroacetabular impingement, fragments characteristics, and imaging modalities used to identify them.

Abstract

Introduction

Femoroacetabular impingement (FAI) is a cause of hip pain that results from abnormal conflict between the acetabulum and femoral head/neck. Associated bony morphologic abnormalities can contribute to symptoms of FAI. Para-acetabular ossific or calcific fragments have been described, and most often take the form of unfused acetabular physes (os acetabulum), labral ossification, or amorphous calcific densities at the acetabular labral junction. The purpose of this study was to define the prevalence of these ossific / calcific fragments in surgically treated patients with FAI, and further describe their characteristics.

Methods

A single surgeon’s case list was retrospectively reviewed to identify primary hip arthroscopy surgeries for treatment of FAI. All patients with preoperative 3D CT imaging of the hip were included. Patients with a distinct radio-opaque fragment adjacent to the acetabular rim were noted. The location of these fragments on the acetabular clock-face was noted. Patient factors including gender and age, as well as radiographic parameters including lateral center edge angle and alpha angle were recorded. Operative records were reviewed to classify the lesions as bony fragments or amorphous calcific densities. Treatment performed for associated labral injury (debridement vs repair) was recorded. Preoperative plain radiographs were reviewed to determine if the fragment was identifiable using this modality.

Results

204 patients were included in the study. 33/204(16.2%) had ossific/calcific para-acetabular fragments noted on 3D CT (mean age 33.7 years; 48.4% males, 51.65 females). The fragment was visible on plain radiographs in 23/33(69.7%) of patients. The mean location of the fragments was 12:32 on the acetabular clock-face. At the time of arthroscopy, 13(39.4%) of patients had a bony fragment; 12/(36.4%) had amorphous calcific densities; 3(9.1%) had an acetabular fibrous cleft; and 5(15.1%) had no bony or calcific fragment identified. The labrum was repaired in 31(93.9%) and debrided in 2(6.1%) patients.

Conclusion

This study reports the prevalence, typical location, and gross structural characteristics of bony & calcific para-acetabular densities in surgically treated FAI patients. Our findings suggest that many but not all of these fragments can be identified on plain radiographs. The majority of hips in this series were amenable to labral repair.