Successful long-term fixation and progression of osteolysis associated with first-generation cementless acetabular components retrieved post mortem

Abstract

Background: Primary cementless acetabular reconstruction has shown durable long-term fixation. Late failures secondary to aseptic loosening are rare but may occur in patients with previously well-fixed components. In the present study, the histopathological characteristics of postmortem specimens were correlated with wear damage and radiographic data in an attempt to better understand the long-term events in the periacetabular tissue around well-functioning devices.

Methods: Seventeen primary cementless Harris-Galante I acetabular components with adjacent tissues were harvested after a mean of eleven years (range, four to twenty-five years) from patients whose implants were well functioning at the time of death. Undecalcified and paraffin sections were used to quantify the extent of bone and soft tissues within the porous coating and at the interface between the coating and the surrounding bone. Wear particles were identified with use of polarized light microscopy and energy-dispersive x-ray analysis. Bearing-surface volumetric wear and backside wear damage of the polyethylene liner were assessed.

Results: All of the components were fixed by bone ingrowth (mean extent, 33% ± 21%). Particle-induced granulomas were present in the porous coating and along the interface and progressed through screw holes, ballooning into the retroacetabular bone in the longer-term specimens. Particles of femoral and acetabular origin were identified in the granulomas. Bearing-surface volumetric wear (mean, 41.6 mm3/year) increased with duration and correlated with increasing extent of granuloma in the porous coating and the increasing size of pelvic granulomas. Radiolucencies on radiographs correlated with the extent of bone and fibrous tissue ingrowth. Of the six pelvic granulomas that were identified histologically, only one was apparent on routine radiographs.

Conclusions: Acetabular fixation by bone ingrowth can be successful into the third decade after implantation. Osteolysis and secondary replacement of bone with particle-induced granuloma are commonly seen in the presence of excellent clinical function. Strategies designed to minimize bearing-surface wear and backside damage are important to maintain long-term bone ingrowth fixation.

Fig. 1

Graph showing the extent of granuloma in the porous coating and the maximum dimension of pelvic granulomas versus the time since arthroplasty.

Fig. 2

Plastic-embedded ground sections of Specimen 7 at 12.4 years, stained with basic fuchsin and toluidine blue (left, ×60; right, ×300). In most of the longer-term specimens, the granulomas in the porous coating appeared to be associated with resorption of the ingrown bone. Left: Particle-induced granulomas (asterisks) expanded into the retroacetabular bone and infiltrated the porous coating adjacent to screw holes. Right: Granulomas consisting of macrophages laden with polyethylene particles filled the spaces between the titanium fibers replacing bone (arrows), marrow, or fibrous tissue that normally occupied the pores. The central globular spaces are a result of residual lipids from previous marrow.

Fig. 3

Figs. 3-A, 3-B, and 3-C Decalcified paraffin sections stained with hematoxylin and eosin. Fig. 3-A Specimen 3 at eighteen years. Wear damage to the backside of the polyethylene liners was primarily abrasive in nature, resulting from contact with the relatively rough concave surface of the metal shell and the sharp edges of the screw holes (*). Scale bar = 1 mm. Fig. 3-B Specimen 14 at five years. Scratching of the backside of the polyethylene liner was among the dominant features of wear damage and often included third-body metal particles. Scale bar = 1 mm. Fig. 3-C Specimen 7 at 12.4 years. Abrasive wear mechanisms on the backside of the polyethylene liner produced shreds of polyethylene 5 to 40 μm long, which were observed intracellularly in screw hole and pelvic granulomas. Scale bar = 25 μm.

Fig. 4

Graph showing maximum dimension of pelvic granulomas versus backside wear damage score and volumetric wear of the polyethylene (PE) bearing surface.

Fig. 5

Pelvic granulomas that were identified histologically were not visualized on the radiographs of five of the six hips in which pelvic granulomas were present. In the sixth specimen (Specimen 5), a small osteolytic area was noted on the clinical radiographs, greatly underestimating the actual the size of the lesion. Left: Contact radiograph of the cross-section of Specimen 5 at fourteen years, showing a retro-acetabular lesion due to a wear particle-induced granuloma. Right: The lesion was poorly visualized on this anteroposterior clinical radiograph of the same hip (Specimen 5), made one year before the patient’s death.