Back-side wear in HexLoc cups clinico-radiological, immunohistopathological, finite element, and retrieval analysis studies.
The HexLoc locking system was designed to prevent back-side wear of the polyethylene liner in the modular cementless metal-backed acetabular cup, but failed. Back-side wear was analyzed using clinico-radiological data, immunohistopathology, finite element modeling (FEM, and retrieval analysis. Screw holes allowed entry of titanium oxide and exit of polyethylene particles. Birefringent polyethylene wear particles were found behind the metal cup in macrophages containing pro-inflammatory tumor necrosis factor-α and interleukin-1β, whereas fibroblast-like cells stained for osteoclastogenic receptor activator of nuclear factor kappa B ligand (RANKL). Computerized tomography revealed granulomas (83% versus 17 %) and cortical destruction (50% versus 5%) better than radiographs. In FEM, a change of the abduction angle from 45 to 60 deg, and liner thickness from 4.8 mm to 2.5 mm, increased the back-side wear by 90% and 120%, respectively. Screw holes were stress concentration areas; their removal decreased wear by 40%. Modeling results were validated in retrieved implants, which demonstrated extensive back-side wear damage of liners with a high abduction angle. Combined clinico-radiological, immunohistopathological, FEM, and retrieval analysis disclosed that back-side wear in the HexLoc design is sensitive to the abduction angle, liner thickness, and presence of screw holes.
Department of Medicine, University of Helsinki and Helsinki University Central Hospital, 00029 HUS, Helsinki; Department of Applied Physics, University of Eastern Finland, Kuopio, 70210 Kuopio, Finland; Department of Orthopedic Surgery, Yamagata Universi.
Hiroyuki
H
Kawaji
Department of Applied Physics, University of Eastern Finland, Kuopio, 70210 Kuopio, Finland.
Arto
A
Koistinen
Department of Applied Physics, University of Eastern Finland, Kuopio, 70210 Kuopio, Finland.
Rami
R
Korhonen
Department of Applied Physics, University of Eastern Finland, Kuopio, 70210 Kuopio, Finland.
Reijo
R
Lappalainen
Department of Radiology, Peijas Hospital, 00029 Helsinki University Central Hospital, Espoo, Finland.
Martina
M
Lohman
ORTON Orthopedic Hospital, ORTON Foundation, 00280 Helsinki, Finland.
Antti
A
Soininen
Bone and Joint Research Laboratory, Fundacion "Jimenez Diaz" Hospital, Universidad Autonoma de Madrid, Madrid, 28040, Spain.
Enrique
E
Gomez Barrena
Department of Clinical Medicine, University of Helsinki and ORTON Orthopaedic Hospital of the Invalid Foundation, Helsinki, Finland.
Yrjo T
YT
Konttinen
ORTON Orthopedic Hospital, ORTON Foundation, 00280 Helsinki, Finland.
Pekka
P
Ylinen
ORTON Orthopedic Hospital, ORTON Foundation, 00280 Helsinki, Finland.
Kaj
K
Tallroth
D000328:Adult; D019644:Arthroplasty, Replacement, Hip; D005260:Female; D020342:Finite Element Analysis; D015743:Giant Cells, Foreign-Body / Q000378:metabolism; D006099:Granuloma / Q000473:pathology; D006622:Hip Prosthesis / Q000009:adverse effects*; D006801:Humans; D007150:Immunohistochemistry; D008264:Macrophages / Q000378:metabolism; D008297:Male; D008855:Microscopy, Electron, Scanning; D008875:Middle Aged; D011475:Prosthesis Failure