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The crescent sign: dissociation of the polyethylene liner from a modular acetabular component in total hip
1Avon Orthopaedic Centre, Bristol, United Kingdom. simonpwhite@blueyonder.co.uk
Insights
Late polyethylene liner dissociation in hip arthroplasty presents with mobility reduction, groin pain, and limp. A characteristic "crescent sign" on X-rays aids diagnosis, enabling timely intervention to prevent further damage.
Area of Science:
- Orthopaedic Surgery
- Biomaterials Science
Background:
- Polyethylene liner dissociation is a complication of cementless acetabular components.
- Identifying a common pattern of presentation can aid in early diagnosis and management.
Purpose of the Study:
- To identify common clinical, radiographic, and symptomatic patterns associated with polyethylene liner dissociation.
- To investigate potential causes for these observed features.
Main Methods:
- Retrospective review of revision hip arthroplasty cases for polyethylene liner dissociation.
- Analysis of clinical notes, radiographs, and patient-reported symptoms for the cementless Harris-Galante I acetabular component.
Main Results:
- Nine cases of late polyethylene liner dissociation were identified.
- Common symptoms included reduced mobility, groin pain, limp, and audible noise on movement.
- Radiographs revealed a characteristic "crescent sign" indicating an eccentrically placed femoral head and metal shell contact.
Conclusions:
- A distinct clinical and radiographic pattern exists for polyethylene liner dissociation.
- "Crescent sign" on anteroposterior pelvic radiographs is diagnostic, differentiating it from polyethylene wear.
- Early surgical revision is recommended to prevent further damage and simplify revision procedures.
Objective:
To study whether there was a common pattern of clinical symptoms, signs and radiographic features for the dissociation of the polyethylene liner from an acetabular component and to postulate reasons for these features.
Design And Patients:
Retrospective study of notes and radiographs of cases of revision hip arthroplasty for polyethylene liner dissociation of the cementless Harris-Galante I porous-coated acetabular component (Zimmer Inc, Warsaw, IN) at the Avon Orthopaedic Centre, Bristol, UK and St. Mary's Hospital, Bristol, UK between 1995 and 2004. Patients were contacted to confirm preoperative symptoms.
Results:
Nine cases of late polyethylene liner dissociation of this prosthesis have been revised in these institutions. All patients presented with a reduction in mobility, groin pain and limp. Eight patients reported an audible noise on hip movement. In all cases, radiographs showed radiolucency medial to the femoral neck in association with an eccentrically placed femoral head showing contact with the acetabular metal shell, which we have termed the "crescent sign."
Conclusions:
There is a typical clinical presentation in this study. The diagnosis can be made from a single anteroposterior pelvic radiograph without the need for previous films for comparison, or the need for arthrography. Clinicians should look specifically for the crescent sign when an eccentrically placed femoral head has been noted, in order to differentiate the more unusual diagnosis of dissociation from that of polyethylene wear. Early revision surgery can prevent damage to the femoral head and metal acetabular shell, thus reducing the complexity of revision surgery.