CORRInsights®: Complete Circumferential Osseous Extension in the Acetabular Rim Occurs Regardless of Acetabular Coverage

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Acetabular labral ossification, a condition resulting from labral damage, is not generally well-known among orthopaedic surgeons. From what I found, Ninomiya and colleagues [4] first described a patient with enchondral ossification of the labrum in 2000. More than a decade later, Corten and colleagues [2] postulated in a case series that this rim ossification was bone apposition in the presence of preexisting pincer impingement in which ossification began in the subperiosteal region, subsequently either displacing or encasing the labrum. Recently, my colleagues and I reported on the demographics and outcomes of patients with femoroacetabular impingement (FAI) associated with labral ossification compared to FAI cases in which no ossification was present [1].
Patients with labral ossification generally are older and tend to be female with slightly inferior outcome scores compared to patients with FAI in absence of ossification. We postulated that this was due to enchondral ossification as documented by a sample of histologic evaluations. Additionally, we believed that the subset of pincer FAI with labral ossification probably still represented a heterogeneous population with subgroups of differing causes [1]. In a separate study, Ferguson and colleagues (which included myself) [3], identified an association between labral ossification and sacroiliac (SI) disease. Since SI disease is sometimes associated with autoimmune disorders, perhaps there is a link between labral ossification and an autoimmune etiology. Overall, there is a distinct deficit in the understanding of the etiology of labral ossification.
Although the research is limited, understanding labral ossification is important because, as the authors of the current study show, the frequency of the condition is probably much greater than is commonly thought. In addition, the etiology is poorly understood, and the disorder may have negative implications on current treatment strategies.
In the current study, Watari and colleagues examine the prevalence of circumferential osseous extension of the acetabular rim and indirectly provide some etiological evidence. Osseous extension occurred in only 6% of hips, and the frequency was not different among patients with dysplasia, normal hips, or acetabular overcoverage. However, osseous extension was present bilaterally among 89% of the patients who had it. Equal prevalence, regardless of coverage, suggests that variations of acetabular coverage are not an etiological factor; but the high presence of bilaterality suggests that some other physiological or metabolic process may be at work.
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