Metal-on-metal retrieval studies indicated that MOM wear-rates could rise as high as 60–70mm3/year in short-term failures (Morlock, 2008). In contrast, some MOM and ceramic-on-ceramic (COC) devices of 1970's era performed admirably over 2–3 decades (Schmalzreid, 1996; Shishido, 2003). While technology has aided analysis of short-term MOM and COC failures (Morlock 2008; Lord 2011), information on successful THA remains scant. Lack of long-term data creates difficulties in setting benchmarks for simulator studies and establishing guidelines for use in standards. In this study we compared clinical and wear histories for a 30-year MOM and a 32-year COC to establish such long-term, wear-rates.

The McKeeTM retrieval was cemented and made 100% of CoCr alloy (Fig. 1a). This patient had a right femoral fracture at 47 years of age, treated by internal-fixation, which failed. Her revision with a Judet implant also failed, leaving her right hip as a Girdlestone. At the age of 68, she had a McKee THA implanted in left hip, and used it until almost 98 years of age (Campbell, 2003). The COC case was a press-fit AutophorTM THA, head and cup made of alumina ceramic, with the only metal being the CoCr stem (Fig. 1c). This was implanted in a female patient 17-years of age active in sports (water-skiing). This modular THA was revised 32-years later due to hip pain from cup migration. Wear on these implants was identified by stereomicroscopy and stained red for photography (Fig. 1). Cup-to-neck impingement was denoted by circumferential neck notching, roughness was assessed by interferometry, and wear determined by CMM (Lord, 2011).

McKee head wear covered 1092mm2 area (Figs. 1a, 2: hemi-area ratio 58%). There was no stripe wear and head roughness was 36nm (Ra). Cup wear covered an area of 1790mm2 (hemi-area 63%). Circumferential damage was noted on the supero-posterior femoral neck with scuff marks also on posterior collar (Fig. 2c). Head and cup wear amounted to 37.7 and 25.2mm3, respectively. Total MOM wear was 62.9mm3, indicating a wear-rate of 2.1mm3/year.

Ceramic head wear consisted of two circular patterns (Fig. 1c), the major one of area 1790mm2 (hemi-area 79%). No wear stripes were identified. Non-worn and extensively worn surfaces had roughness (Ra) 17nm and 123nm, respectively. The cup showed 360o circumferential arc of rim wear with a small, non-wear zone inferiorly (Fig. 1c). Gray metallic transfer was evident, EDS revealing Co and Cr (Fig. 3a). Head and cup wear volumes were 77.2 and 54mm3, respectively. Total COC wear amounted to 131.2mm3 indicating a wear-rate of 4.1mm3/year.

These two THA functioned successfully over 3 decades. The McKee retrieval had minor signs of impingement but no adverse “stripe wear”. This MOM performed satisfactorily due to good positioning and patient's advanced age (68 to 98Yrs of age). The COC patient was 17 years of age at index surgery and active. The ceramic cup showed 360o of edge wear, CoCr transfer and a COC wear-rate double that of the MOM retrieval. Thus the high ceramic wear-resistance protected this youthful patient.

INTRODUCTION

Deformation of modular acetabular press-fit shells is of much interest for surgeons and manufacturers. Initial fixation is achieved through press-fit between shell and acetabulum with the shell mechanically deforming upon insertion. Shell deformation may disrupt the assembly process of modular systems and may adversely affect integrity and durability of the components and tribology of the bearing. The aim of the study was to show shell deformation as a function of bone and shell stiffness.

INTRODUCTION

Deformation of modular acetabular press-fit shells is a topic of much interest for surgeons and manufacturer. Such modular components utilise a titanium shell with a liner manufactured from metal, polyethylene or ceramic. Initial fixation is achieved through a press-fit between shell and acetabulum with the shell mechanically deforming upon insertion. Shell deformation may disrupt the assembly process of inserting the bearing liner into the acetabular shell for modular systems. This may adversely affect the integrity and durability of the components and the tribology of the bearing.

Background

Hemiarthroplasty of the hip involves the replacement of the femoral side of the joint with a metal prosthesis, resulting in metal-on-cartilage articulation. The two most common types of hemiarthroplasty used are the Austin Moore and the Thomson, both of which are available in either Titanium (Ti) or cobalt chromium (CoCr). Hemiarthroplasty may be more cost effective in elderly patients who have lower life expectancy and are less active.