Anatomical variations of hip acetabulum and femoral head-neck junction may predispose to clinical consequences: a case-based discussion of complex morphological interactions

BACKGROUND: Femoroacetabular impingement (FAI) morphology is defined by anatomical variants that may predispose to mechanical conflict between the bony structures of the acetabulum and proximal femur with underlying bony incongruence leading to damage of adjacent tissues. Repetitive abnormal contact in this region can contribute to the formation of herniation pits (HPs) in the anterosuperior femoral head-neck junction, which may exacerbate symptoms and complicate surgical management of FAI. CASE REPORT: This case report describes a 55-year-old male who underwent arthroscopic osteochondroplasty for mixed-type FAI morphology, combined with resection of a large HP and subsequent cavity filling using allogenic bone graft. Importantly, even though he did not have classic acetabular overcoverage, focal acetabular retroversion resulted in mechanical impingement when combined with anatomical variation of the femoral head-neck junction and patient's activity patterns. The postoperative course was uneventful, and graft incorporation was confirmed during the three-year follow-up. CONCLUSIONS: This case highlights the anatomical and surgical interplay between osseous morphology, soft-tissue integrity, and joint biomechanics in the setting of FAI. Importantly, the various FAI morphologies should be considered anatomical variants that, when combined with specific movement patterns or loading conditions, may predispose to impingement and subsequent clinical symptoms. Additionally, this case demonstrates that allogenic bone grafts used to fill the herniation pit cavity can successfully incorporate into the surrounding bone, even in the anterosuperior femoral neck - a region known for relatively limited vascular supply.