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Journal of Long-Term Effects of Medical Implants
SJR: 0.332 SNIP: 0.491 CiteScore™: 0.89

ISSN Print: 1050-6934
ISSN Online: 1940-4379

Journal of Long-Term Effects of Medical Implants

DOI: 10.1615/JLongTermEffMedImplants.2014011940
pages 319-331

Back-Side Wear in HexLoc Cups Clinico-Radiological, Immunohistopathological, Finite Element, and Retrieval Analysis Studies

Hiroyuki Kawaji
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
Arto Koistinen
Department of Applied Physics, University of Eastern Finland, Kuopio, 70210 Kuopio, Finland
Rami Korhonen
Department of Applied Physics, University of Eastern Finland, Kuopio, 70210 Kuopio, Finland
Reijo Lappalainen
Department of Applied Physics, University of Eastern Finland, Kuopio, 70210 Kuopio, Finland
Martina Lohman
Department of Radiology, Peijas Hospital, 00029 Helsinki University Central Hospital, Espoo, Finland
Antti Soininen
ORTON Orthopedic Hospital, ORTON Foundation, 00280 Helsinki, Finland
Enrique Gomez Barrena
Bone and Joint Research Laboratory, Fundacion "Jimenez Diaz" Hospital, Universidad Autonoma de Madrid, Madrid, 28040, Spain
Yrjo T. Konttinen
Department of Orthopaedics, Teaching Hospital, Faculty of Medicine and Dentistry, Palacky University, Olomouc, Czech Republic; Department of Orthopaedics, ORTON Orthopaedic Hospital, 00280 Helsinki, Finland; COXA Hospital for Joint Replacement, 33520 Tampere, Finland
Pekka Ylinen
ORTON Orthopedic Hospital, ORTON Foundation, 00280 Helsinki, Finland
Kaj Tallroth
ORTON Orthopedic Hospital, ORTON Foundation, 00280 Helsinki, Finland

ABSTRACT

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.