Special modes of corrosion under physiological and simulated physiological conditions.

The aim of this article is to review those aspects of corrosion behaviour that are most relevant to the clinical application of implant alloys. The special modes of corrosion encountered by implant alloys are presented. The resistance of the different materials against the most typical corrosion modes (pitting corrosion, crevice corrosion and fretting corrosion) is compared, together with observations of metal ion release from different biomaterials. A short section is dedicated to possible galvanic effects in cases when different types of materials are combined in a biomedical device. The different topics covered are introduced from the viewpoint of materials science, and then placed into the context of medicine and clinical experience.

Long-term survival of a cemented titanium-aluminium-vanadium alloy straight-stem femoral component.

We present a retrospective series of 170 cemented titanium straight-stem femoral components combined with two types of femoral head: cobalt-chromium (CoCr) alloy (114 heads) and alumina ceramic (50 heads). Of the study group, 55 patients (55 stems) had died and six (six stems) were lost to follow-up. At a mean of 13.1 years (3 to 15.3) 26 stems had been revised for aseptic loosening. The mean follow-up time for stable stems was 15.1 years (12.1 to 16.6). Survival of the stem at 15 years was 75.4% (95% confidence interval (CI) 67.3 to 83.5) with aseptic failure (including radiological failure) as the end-point, irrespective of the nature of the head and the quality of the cement mantle. Survival of the stem at 15 years was 79.1% (95% CI 69.8 to 88.4) and 67.1% (95% CI 51.3 to 82.9) with the CoCr alloy and ceramic heads, respectively. The quality of the cement mantle was graded as a function of stem coverage: stems with complete tip coverage (type 1) had an 84.9% (95% CI 77.6 to 92.2) survival at 15 years, compared with those with a poor tip coverage (type 2) which had a survival of only 22.4% (95% CI 2.4 to 42.4). The poor quality of the cement mantle and the implantation of an alumina head substantially lowered the survival of the stem. In our opinion, further use of the cemented titanium alloy straight-stem femoral components used in our series is undesirable.

Treatment of infected retained implants.

We have prospectively studied the outcome of infections associated with implants which were retained and treated using a standardised antimicrobial protocol. Over a period of four years, we studied 24 consecutive patients who had symptoms of infection for less than one year, a stable implant, no sinus tract and a known pathogen which was susceptible to recommended antimicrobial agents. The infections involved hip prostheses (14), knee prostheses (5), an internal fixation device (4), and an ankle prosthesis (1). Twenty patients had a successful outcome at a median follow-up of 3.7 years (1.8 to 4.7); four had failure of the implant after a median follow-up of 1.2 years (0.3 to 2.5). The probability of survival without failure of treatment was 96% at one year (95% confidence interval (CI) 88 to 100), 92% at two years (95% CI 80 to 100) and 86% at three years (95% CI 72 to 100). Patients with a short-term infection but with a stable implant, no sinus tract and a known pathogen may be successfully treated by retention of the implant and the use of a standardised regimen of antimicrobial treatment.

Chondroblastoma of the patella associated with an aneurysmal bone cyst.

Chondroblastoma is a rare, benign tumor of bone, accounting for about 1% of all bone tumor cases. It tends to affect the epiphyseal ends of long bones, most often in males during the first and second decades of life. It has well-characterized radiographic and histologic features but despite its histologically benign appearance a few cases of metastases have been reported. Local recurrences after curettage and bone grafting occur in 11% to 25% of cases. The features of a patellar chondroblastoma are the same as for other locations. In reviewing the literature we found an unusually high male-to-female ratio. It is interesting that the usual treatment of the patellar chondroblastoma has been patellectomy, whereas curettage and bone grafting has predominated in the other locations. We present a computer tomography and magnetic resonance imaging study of a case of chondroblastoma of the patella associated with an aneurysmal bone cyst. To our knowledge, it is the seventh case reported and the second with computer tomography and magnetic resonance imaging studies. We also review and discuss in detail all the cases of patellar chondroblastoma that we found in the literature.

Characteristics of prosthetic joint infections due to Enterococcus sp. and predictors of failure: a multi-national study.

The objective of this study was to review the characteristics and outcome of prosthetic joint infections (PJI) due to Enterococcus sp. collected in 18 hospitals from six European countries. Patients with a PJI due to Enterococcus sp. diagnosed between January 1999 and July 2012 were retrospectively reviewed. Relevant information about demographics, comorbidity, clinical characteristics, microbiological data, surgical treatment and outcome was registered. Univariable and multivariable analyses were performed. A total of 203 patients met the inclusion criteria. The mean (SD) was 70.4 (13.6) years. In 59 patients the infection was diagnosed within the first 30 days (29.1%) from arthroplasty, in 44 (21.7%) between 31 and 90 days, in 54 (26.6%) between 91 days and 2 years and in 43 (21%) after 2 years. Enterococcus faecalis was isolated in 176 cases (89%). In 107 (54%) patients the infection was polymicrobial. Any comorbidity (OR 2.53, 95% CI 1.18-5.40, p 0.01), and fever (OR 2.65, 95% CI 1.23-5.69, p 0.01) were independently associated with failure. The only factor associated with remission was infections diagnosed later than 2 years (OR 0.25, 95% CI 0.09-0.71, p 0.009). In conclusion, prosthetic joint infections due to Enterococcus sp. were diagnosed within the first 2 years from arthroplasty in >70% of the patients, almost 50% had at least one comorbidity and infections were frequently polymicrobial (54%). The global failure rate was 44% and patients with comorbidities, fever, and diagnosed within the first 2 years from arthroplasty had a poor prognosis.