CORRInsights®: Is Increased Acetabular Cartilage or Fossa Size Associated With Pincer Femoroacetabular Impingement?

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Pincer-type femoroacetabular impingement (FAI) is defined as either a focal or global overcoverage of the femoral head by the acetabulum [2]. This pathoanatomy is thought to cause impingement and injury to the acetabular labrum, resulting in secondary injury to the articular cartilage and in some patients, osteoarthritis (OA) [4]. On the other end of the spectrum is acetabular dysplasia, where the femoral head is undercovered by the acetabulum leading to a decrease in the amount of weight bearing articular cartilage. Subsequently, increased forces across the joint can, in some patients, lead to OA [3, 8, 12].
Pincer FAI has been defined variably, including a lateral center-edge angle (LCEA) over 40° or 45° and/or an anterior center-edge angle (ACEA) over 40°. Acetabular profunda, acetabular protrusion, or the presence of a crossover sign are also used to describe pincer FAI [2].
There has been little consensus regarding a radiographic definition of pincer FAI [6]. In a cross-sectional study, Gosvig and colleagues [5] reported a relationship between pincer morphology and radiographic OA [5]. Conversely, one prospective study [11] reported no relationship between pincer FAI and OA development, while another prospective study reported a protective effect of pincer FAI on the development of OA [1]. Acetabular dysplasia is more-consistently associated with the development or presence of OA [1, 11]. In one of those studies [1], patients with an LCEA over 40° and an ACEA over 40° had a relative risk of developing incident OA over a 5-year period of 0.34 compared to the rest of the cohort, meaning they were three times less likely to develop OA.
In turn, pincer treatment with acetabuloplasty has been associated with poorer outcomes of hip preserving surgery when compared to other indications [7, 9]. This makes furthering our understanding of pincer FAI a critical focus of research in the field of hip preservation surgery. Pun and colleagues have reported on a measure of pincer FAI looking at acetabular fossa size and size of the weight bearing cartilage that is present in the acetabulum. This adds to prior work by Steppacher and colleagues [10], who similarly identified that patients with different morphologies of pincer FAI have differing amounts of weight-bearing cartilage in their acetabulum.
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