Intra-Articular Ossifications After Total Hip Arthroplasty: A New Pathology

Introduction Heterotopic ossification (HO) is a recognised complication following total hip arthroplasty (THA), frequently associated with pain and restriction of movement. Conventional HO typically develops within the soft tissues between the ilium and lesser trochanter, particularly around the rectus femoris, capsular reflection, and abductor insertions. In recent years, we have identified a distinct pattern of intraarticular ossification originating from the acetabular rim and extending along the cup surface towards the prosthetic femoral head, resulting in painful impingement of the femoral neck. To our knowledge, this pattern has not been previously described. The purpose of this study was to characterise this newly observed pathology. Methods Between 2023 and 2025, 12 patients presented with progressive hip pain and loss of flexion secondary to intraarticular ossifications. Demographic data, indication for THA, surgical approach, implant type, time to symptom onset, and ossification site were recorded. All patients underwent radiographic evaluation, with additional CT imaging in nine cases. The acetabulum was divided into four quadrants (anterosuperior, posterosuperior, posteroinferior, anteroinferior) for localisation. Seven patients underwent excision of the ossification via a direct anterior approach. Results There were nine women and three men, with a mean age of 41 years (range 16 to 58). THA was performed for primary osteoarthritis in nine hips and for sequelae of childhood hip disease in three. The mean interval between implantation and diagnosis was seven years (range two to 14). All cases demonstrated anterosuperior ossification, with additional posterosuperior (45%) and posteroinferior (33%) involvement. The ossifications were continuous with the acetabular rim, extending intraarticularly over the polyethylene liner towards the femoral head, causing impingement. Surgical excision relieved pain and improved range of motion in all cases. Conclusion Intraarticular ossification arising from the acetabular rim represents a previously undescribed cause of painful impingement following THA. CT scanning is essential for diagnosis, and surgical resection yields excellent symptomatic improvement.