Excessive polyethylene wear and acetabular bone defects from standard use of a hooded acetabular insert in total hip arthroplasty

Abstract

Purpose: In total hip arthroplasty (THA) the use of a polyethylene (PE) insert with a hooded rim can be considered to reduce dislocation risks. This benefit has to be balanced against the potential introduction of impingement of the femoral component on this rim. We present a case series of early acetabular revisions for excessive PE wear and acetabular bone defects from overuse of such a hooded rim insert.

Material and methods: Twenty-eight patients with 34 consecutive early acetabular revisions were evaluated on failure mechanism. One type of implant was used in all cases. Standard pelvic radiographs and pre-operative CT scans were used to quantify PE wear, implant positioning and acetabular bone defects.

Results: An acetabular revision with impaction grafting was performed in all cases with a mean cup survival of ten years (range 1.3-19.3). No concurrent stem revisions were necessary. Overall implant positioning was adequate with a mean cup inclination of 45° (range 39-57) and anteversion of 25° (range eight to 45). The mean PE wear was 0.24 mm/year (range 0.00-1.17). The mean acetabular bone defect on pelvic CT scans was calculated as 352 mm² (range zero to 1107) and 369 mm² (range zero to 1300) in the coronal and transversal planes, respectively. A hooded acetabular insert was retrieved in all cases and profound PE wear, typically from the posterior hooded rim, was encountered.

Conclusion: The use of hooded acetabular inserts may be considered to improve implant stability intra-operatively. This case series clearly presents that together with these devices, component impingement with concordant complications such as accelerated PE wear may be introduced. Standard use of these stabilizing inserts should thus be avoided.

Fig. 1

CT scans. Cup anteversion (a), the angle between the line bisecting the anterior and posterior part of the metal lamella cup and a perpendicular line towards the horizontal line connecting the posterior portions of the pelvis. Maximal pelvic bone defect in the transversal (b) and coronal (d) planes in square millimetres by using the software Ortho-toolbox. Cup inclination (c), the angle between the horizontal interteardrop line and the line bisecting the superior and inferior parts of the metal lamella cup

Fig. 2

PE-wear measurement on AP pelvic radiograph as the displacement distance between the centres of rotation of the prosthesis cup and head

Fig. 3

Typical example of intraoperatively encountered polyethylene wear. a Acetabular component intraoperative, impingement is visible at the hooded rim. b Retrieved acetabular component illustrating the damage due to neck impingement over the entire polyethylene insert rim. c Acetabular metal lamella cup