Resurfacing arthroplasty of the hip enjoyed a resurgence of enthusiasm. A recent article has documented that the media played a significant role in its popularity, making claims that were not substantiated in scientific literature. Proponents of resurfacing arthroplasty state that it is bone conserving, provides greater stability, enhances range of motion, leads to a more normal gait, facilitates increased activity levels, decreases risk of dislocation, decreases the risk of leg length discrepancy and find that it is easier to insert in the face of deformity or retained hardware. The naysayers state that it is a more difficult operative procedure associated with a higher learning curve. They note that there are few patients who meet the selection criteria and there is an increased risk of fracture of the femoral neck. Finally, there is concern over metal ion toxicity and adverse tissue reaction. Furthermore, as we explore the literature, several studies have observed that resurfacing requires a bigger cup and results in a significantly higher volume of normal bone reamed from the acetabulum. Other studies note decreased range of motion with resurfacing compared with total hip arthroplasty (THA) secondary to an unfavourable head to neck ratio resulting in increased impingement. While resurfacing is purported to enhance functional outcomes, one randomized trial of 48 patients, 24 each resurfacing and large head THA, compared with 14 healthy control subjects found no difference in gait speed and postural balance evaluations, functional test, and clinical data at 3, 6 and 12 months post-operative. In another study comparing 337 resurfacings with 266 ceramic-on-ceramic THA, at 24 months there was no difference in Harris hip score, pain score or function score, but a statistically greater improved Harris hip range of motion score in THA. In a large meta-analysis study comparing 3269 hip resurfacings (3002 patients) with average follow-up of 3.9 years to 5907 cementless THA (5907 patients) with average follow-up of 8.4 years, the observed rate of femoral revision due to mechanical failure was 2.6% for resurfacing versus 1.3% for THA, yielding annualized rates of 0.67% and 0.15% respectively. An analysis of hip resurfacing data from national joint registries found that hip resurfacing demonstrates an overall increased failure rate compared with THA, except in males younger than 65 years old having a diagnosis of primary osteoarthritis and except with head diameters larger than 50 mm, which may be especially relevant as a contraindication for use of the procedure in female patients

The aim of this study was to analyze in human macrophages the effects of Co. 2+. and Cr. 3+. ions on the activity of caspase-8 and caspase-3, initiator and executioner of apoptosis, respectively. Caspase-3 and -8 activities were measured by colorimetric assays. Results show that Co. 2+. ions induced caspase-3 activity in a time-dependent manner. Co. 2+. had no effect on caspase-8 activity. The activation of caspase-3 by Cr. 3+. was time-dependent while caspase-8 activity reached a maximum after eight hours and decreased thereafter. Since caspase-8 is primarily activated by membrane-associated events, our results suggest that Cr. 3+. interacts with cell membrane components to induce macrophage apoptosis, whereas Co. 2+. seems to stimulate apoptosis most likely through intracellularly located mechanisms. Because of their potential for improved wear performance, there has been a revived interest in metal-metal bearings, made of cobalt-chromium-molybdenum alloys, as an alternative to the use of conventional metal-polyethylene bearings. However, metal ion toxicity remains a major cause for concern. Previous studies suggested that both cobalt (Co. 2+. ) and chromium (Cr. 3+. ) ions induce macrophage apoptosis. The interest in apoptosis lies in the fact that it offers specific targets for therapeutic intervention. The aim of this study was to analyze the effects in human macrophages of Co. 2+. and Cr. 3+. ions on the activity of caspase-8 and caspase-3, initiator and executioner of apoptosis, respectively. U937 human macrophages were exposed to 0–10 ppm Co. 2+. (CoCl. 2. ) and 0–500 ppm Cr. 3+. (CrCl. 3. ). Caspase-3 and caspase-8 activities were measured by colorimetric assays based on the recognition of specific amino acid sequences (DEVD and IETD, respectively). Results show that Co. 2+. ions induced caspase-3 activity with a significant increase after four hour incubation and a maximal 2.65-fold increase reached after twenty-four hour with 10 ppm. Co. 2+. had no effect on caspase-8 activity. Cr. 3+. ions significantly stimulated caspase-3 activity after four hours with a maximal 1.75-fold stimulation reached after twenty-four hours, reaching only 50% of that observed with Co. 2+. Caspase-8 activity was significantly increased after two hours incubation, peaking at eight hours with a 2.2-fold increase, and decreasing thereafter. Since caspase-8 is primarily activated by membrane-associated events, our results suggest that Cr. 3+. interacts with cell membrane components to induce macrophage apoptosis. On the other hand, Co. 2+. seems to stimulate caspase-3 activity and apoptosis most likely through intracellularly located mechanisms

The purpose of this study is to evaluate short to mid-term clinical and radiological results of metal on metal resurfacing arthroplasty in osteonecrosis of the femoral head (ONFH). 185 hips of 169 patients who underwent metal on metal resurfacing arthroplasty using Birmingham Hip Resurfacing system (Midland Medical Technololgies, Birmingham, UK) between December 1998 and May 2005 were available for this study and all cases were followed up over 3 years. All preoperative diagnoses were ONFH. The extents of necrotic area were analyzed by preoperative MRI scanning. Their mean age at the time of operation was 37.7(range, 16–67) years old and mean period of follow-up was 88(range, 36–113) months. For the clinical assessments, Harris hip scores, UCLA activity scores, pain and ROM were evaluated. Radiological changes such as radiolucencies around the stem, impingement sign, neck narrowing, osteolysis around head and neck junction, loosening of implants, heterotopic ossifications were evaluated in the serial antero-posterior, translateral radiographs of the hip joint. Preoperative necrotic area was average 42.7(range, 11.5–60) %. Clinically, the average Harris hip score was improved from 85.2 points to 97.1 points at final follow-up. Average UCLA activity scores at the last follow-up was 8.8 and almost of the patients showed high activity and returned to their original job. ROM were very satisfactory. Radiologically, the mean inclination of acetabular component was 48.0°. There were no radiolucent lines around the acetabular components, but 3 cases showed radiolucent lines around the stem of femoral components. Osteolytic lesions were noticed in 10 cases around head-neck junction. Nine hips had impingement signs around the head-neck junction. There was no case which showed evidence of stress shielding. Moderate neck narrowing were shown in 3 cases. There were 6 cases of heterotopic ossification. One hip had a revision surgery to a total hip arthroplasty using big metal ball because of loosening of acetabular component. There was no patient complained limb length discrepancy and no infection, dislocation, thigh pain. The midterm performance of metal on metal resurfacing arthroplasty in ONFH was very excellent in the aspects of pain relief, ROM of hip joints, rehabilitation and return to preoperative activity and minimization of common complications of conventional total hip arthroplasty. There was no mechanical failure related to the osteonecrosis and we can conclude that performing resurfacing arthorplasty in osteonecrosis less than 50% of extent can be justified. However, performing resurfacing arthroplasties in osteonecrosis of femoral heads needs meticulous surgical techniques and longer learning curve to prevent early failure. Even though our midterm follow-up study revealed excellent results, more long-term follow-up studies are mandatory to determine the survivorship and to verify the problems related to the increased serum metal ion and metal ion toxicity after resurfacing arthroplasty