https://doi.org/10.1177/1120700017752566 HIP International 1–6 © The Author(s) 2018 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/1120700017752566 journals.sagepub.com/home/hpi HIP HIP International Introduction The supraacetabular fossa (SAF) is a normal anatomic variant found in the weight bearing portion of the acetabu- lum. 1,2 It is typically located at the 12 o’clock position. SAF are classified into 2 types when viewed on magnetic resonance imaging (MRI): Type 1 are bony fossae that remain unfilled; Type 2 are fossae filled with cartilage. 2 Both types of SAF may or may not contain fibrous tissue. It has been hypothesised that the 2 types of SAF represent an age-dependent progression from unfilled fossae earlier in life to filled fossae with maturation. 3 On MRI, SAF generally have smooth edges and no underlying marrow edema. Acetabular chondral or osteochondral defects are typically associated with femoroacetabular impingement (FAI) (usually cam-type) and labral tears, located near the MRI prevalence and characteristics of supraacetabular fossae in patients with hip pain Nickolas Boutris 1 , Stephanie L Gardner 1 , Thomas R Yetter 1 , Domenica A Delgado 1 , Luis Pulido 1 and Joshua D Harris 1 Abstract Background: Supraacetabular fossae (SAF) are normal anatomic variants found at the 12 o’clock position of the acetabulum and can be mistaken for osteochondral defects. Purpose: Determine SAF prevalence on MRI of patients with hip pain. Characterise SAF by type, size, and location. Determine sensitivity of radiology reports and sensitivity of radiographs in SAF detection. Methods: MRIs performed over 1 year in patients with hip/groin pain were analysed for SAF. Measurements of SAF in the coronal and sagittal planes and location using clockface notation were recorded. Radiology reports were reviewed to determine if SAF were identified and radiographs were assessed for presence of SAF. Mean characteristics of type 1 and 2 SAF were compared using Student’s t-test. Results: 214 hips (mean age 35.9 ± 14.2 years; 66.8% female) were analysed. Twenty-seven hips (12.6%) had SAF. There were five type 1 SAF (mean age 16.8 ± 2.2 years) and 23 type 2 SAF (mean age 33.0 ± 16.3 years). Mean dimensions of type 1 and 2 SAF (coronal width × sagittal width × depth, in millimetres) were 7.1 × 6.5 × 3.4 and 6.1 × 5.9 × 2.8, respectively. Mean clockwise location in the coronal and sagittal planes (in minutes) was 1236 and 1212 for type 1 SAF and 1213 and 1207 for type 2 SAF. Radiology reports identified 7.1% of SAF identified on MRI. Plain radiographs demonstrated 67.9% of SAF identified on MRI. Conclusion: This study found a 12.6% prevalence of SAF in hips. Radiology reports had a 7.1% sensitivity in correctly identifying SAF on MRI. Keywords Acetabulum, hip, magnetic resonance imaging, OCD, osteochondral defect, supraacetabular fossa Date received: 28 March 2017; accepted: 27 October 2017. IRB: Pro00016584 1 Houston Methodist Orthopedics and Sports Medicine, Houston, Texas, USA Corresponding author: Joshua D Harris, Houston Methodist Orthopedics and Sports Medicine, 6445 Main St., Houston, TX 77030, USA. Email: joshuaharrismd@gmail.com 752566HPI 0 0 10.1177/1120700017752566HIP InternationalBoutris et al. research-article 2018 Original Research Article