Missed low-grade infection in suspected aseptic loosening has no consequences for the survival of total hip arthroplasty.

BACKGROUND AND PURPOSE: Aseptic loosening and infection are 2 of the most common causes of revision of hip implants. Antibiotic prophylaxis reduces not only the rate of revision due to infection but also the rate of revision due to aseptic loosening. This suggests under-diagnosis of infections in patients with presumed aseptic loosening and indicates that current diagnostic tools are suboptimal. In a previous multicenter study on 176 patients undergoing revision of a total hip arthroplasty due to presumed aseptic loosening, optimized diagnostics revealed that 4-13% of the patients had a low-grade infection. These infections were not treated as such, and in the current follow-up study the effect on mid- to long-term implant survival was investigated. PATIENTS AND METHODS: Patients were sent a 2-part questionnaire. Part A requested information about possible re-revisions of their total hip arthroplasty. Part B consisted of 3 patient-related outcome measure questionnaires (EQ5D, Oxford hip score, and visual analog scale for pain). Additional information was retrieved from the medical records. The group of patients found to have a low-grade infection was compared to those with aseptic loosening. RESULTS: 173 of 176 patients from the original study were included. In the follow-up time between the revision surgery and the current study (mean 7.5 years), 31 patients had died. No statistically significant difference in the number of re-revisions was found between the infection group (2 out of 21) and the aseptic loosening group (13 out of 152); nor was there any significant difference in the time to re-revision. Quality of life, function, and pain were similar between the groups, but only 99 (57%) of the patients returned part B. INTERPRETATION: Under-diagnosis of low-grade infection in conjunction with presumed aseptic revision of total hip arthroplasty may not affect implant survival.

Incidence of low-grade infection in aseptic loosening of total hip arthroplasty.

PURPOSE: We investigated the hypothesis that many total hip arthroplasty revisions that are classified as aseptic are in fact low-grade infections missed with routine diagnostics. METHODS: In 7 Dutch hospitals, 176 consecutive patients with the preoperative diagnosis of aseptic loosening of their total hip arthroplasty were enrolled. During surgery, between 14 and 20 tissue samples were obtained for culture, pathology, and broad-range 16S rRNA PCR with reverse line blot hybridization. Patients were classified as either not being infected, suspected of having infection, or infected according to strict, predefined criteria. Each patient had a follow-up visit after 1 year. RESULTS: 7 patients were classified as infected, 4 of whom were not identified by routine culture. 15 additional patients were suspected of having infection. 20 of these 22 patients received a cemented prosthesis, fixated with antibiotic-loaded bone cement. All 22 patients received prophylactic systemic antibiotics. 7 of them reported complaints one year after surgery, but only one showed signs of early loosening. However, additional surgery was not performed in any of the patients. INTERPRETATION: Although the proportions were not as high as previously reported in the literature, between 4% and 13% of patients with the preoperative diagnosis of aseptic loosening were infected. However, as thorough debridement was performed during surgery and prophylactic antibiotics were used, the diagnosis of infection did not have any obvious clinical consequences, as most patients performed well at the 1-year follow-up. Whether this observation has implications for long-term implant survival remains to be seen.

Factors associated with reduced early survival in the Oxford phase III medial unicompartment knee replacement.

The aim of this study was to determine the prognostic value of preoperative patellofemoral osteoarthritis, BMI and age for implant survival of unicompartmental knee arthroplasty (UKA) performed in patients meeting strict admission criteria. The data and radiographs of 437 unilateral Oxford phase III procedures (Biomet, Bridgend, UK) were analysed. All procedures were carried out or supervised by 13 specialised knee surgeons in three different hospitals. The study group comprised 437 patients with a median follow of 2.6 years (0.1-7.9). The cumulative standard case survival rate at 5 years, when there were still 101 patients at risk, was 84.7% (CI-95%: 80.1-89.3%). Young age (<60 years) was associated with a 2.2-fold increased adjusted risk of revision (CI: 1.08-4.43; p=0.03). The preoperative presence of radiological features of patellofemoral osteoarthritis was associated with a 0.3-fold reduced adjusted risk of revision (CI: 0.11-0.89; p=0.03). BMI>30 kg/m(2), gender, the surgeon performing the operation (either as an individual or categorised by annual surgical UKA caseload, i.e., more or less than 10 UKAs) and the hospital in which surgery took place did not predict implant survival of UKA. We conclude that young patients (<60 years) experience an increased early risk of revision for UKA when compared to older patients (>60 years). Obesity (BMI>30 kg/m(2)) and preoperative patellofemoral osteoarthritis are not associated with a decreased implant survival and therefore should not be considered risk factors in this context.

In vivo pharmacokinetics of a gentamicin-loaded collagen sponge in acute periprosthetic infection: serum values in 19 patients.

BACKGROUND: The in vivo pharmacokinetics of gentamycin- loaded collagen fleeces in humans have not been described in the current literature. We therefore analyzed in vivo pharmacokinetics of these fleeces when used in the treatment of periprosthetic infections. PATIENTS AND METHODS: Gentamycin concentrations were measured in 19 consecutive patients with an acute periprosthetic infection. Each patient received 2-5 fleeces (130 mg gentamycin/fleece). RESULTS: Initially, the blood concentration increased to 3.2-7.2 mg/L, depending on the number of fleeces that were applied. The serum peak concentrations resulted in peak/MIC ratios of 2.5-36 for P. aeruginosa, S. aureus,and Klebsiella spp. Subsequently, the serum values decreased almost linearly below 0.3 mg/L in 18 to 62 hours. After 24 hours, the serum levels of gentamicin dropped below 2 mg/L, the toxicity threshold. INTERPRETATION: The application of 2 to 5 130-mg gentamycin-loaded collagen fleeces may be useful as an adjuvant treatment for implant-related infections, since no toxic concentrations were measured 24 hours postoperatively.

Toxic serum gentamicin levels after the use of gentamicin-loaded sponges in infected total hip arthroplasty.

BACKGROUND: At our clinic, total hip arthroplasties with an acute postoperative infection are treated with surgical debridement and application of several gentamicin-loaded sponges, each with an equivalent of 130 mg gentamicin. We studied the possible systemic effect of this local application of gentamicin. PATIENTS AND METHODS: All 12 patients treated during 1997-2001 were included. 4-6 sponges were used in each case. We measured the serum gentamicin levels daily, from the first postoperative day until gentamicin was no longer measurable. The creatinine levels were monitored daily and the creatinine clearance was calculated according the Cockcroft-Gault formula. RESULTS: In 7 of the 12 patients, we found toxic serum levels of gentamicin (range 2-13 mg/L). In 3 cases there was a significant drop in renal clearance, which persisted. In 3 other cases there was a temporary decrease in renal clearance. INTERPRETATION: We found toxic serum levels after local administration of gentamicin. We even found a persistent decrease in renal clearance in some patients. Because of the alarming results, we have reduced the number of sponges used for this purpose.