Primary stability of the Fitmore® stem: biomechanical comparison

Purpose

After clinical introduction of the Fitmore® stem (Zimmer), we noticed the formation of cortical hypertrophies in a few cases. We questioned whether (1) the primary stability or (2) load transfer of the Fitmore® stem differs from other stems unassociated with the formation of hypertrophies. We compared the Fitmore® stem to the well-established CLS® stem.

Methods

Four Fitmore® and four CLS® stems were implanted in eight synthetic femurs. A cyclic torque around the stem axis and a mediolateral cyclic torque were applied. Micromotions between stems and femurs were measured to classify the specific rotational implant stability and to analyse the bending behaviour of the stem.

Results

No statistical differences were found between the two stem designs with respect to their rotational stability (p = 0.82). For both stems, a proximal fixation was found. However, for the mediolateral bending behavior, we observed a significantly (p < 0.01) higher flexibility of the CLS® stem compared to the Fitmore® stem.

Conclusion

Hip stem implantation may induce remodelling of the periprosthetic bone structure. Considering the proximal fixation of both stems, rotational stability of the Fitmore® stem might not be a plausible explanation for clinically observed formation of hypertrophies. However, bending results support our hypothesis that the CLS® stem presumably closely follows the bending of the bone, whereas the shorter Fitmore® stem acts more rigidly. Stem rigidity and flexibility needs to be considered, as they may influence the load transfer at the implant–bone interface and thus possibly affect bone remodelling processes.     

Wear in total knee arthroplasty—just a question of polyethylene?: Metal ion release in total knee arthroplasty

Purpose

Biological reactions against wear particles are a common cause for revision in total knee arthroplasty. To date, wear has mainly been attributed to polyethylene. However, the implants have large metallic surfaces that also could potentially lead to metal wear products (metal ions and debris). The aim of this study was to determine the local release of cobalt, chromium, molybdenum and titanium in total knee arthroplasty during a standard knee wear test.

Methods

Four moderately conforming fixed-bearing implants were subjected to physiological loadings and motions for 5×10⁶ walking cycles in a knee wear simulator. Polyethylene wear was determined gravimetrically and the release of metallic wear products was measured using high resolution-inductively coupled plasma-mass spectrometry.

Results

A polyethylene wear rate of 7.28 ± 0.27 mg/10⁶ cycles was determined and the cumulative mass of released metals measured 1.63 ± 0.28 mg for cobalt, 0.47 ± 0.06 mg for chromium, 0.42 ± 0.06 mg for molybdenum and 1.28 ± 0.14 mg for titanium.

Conclusion

For other metallic implants such as metal-on-metal total hip arthroplasty, the metal wear products can interact with the immune system, potentially leading to immunotoxic effects. In this study about 12 % by weight of the wear products were metallic, and these particles and ions may become clinically relevant for patients sensitive to these materials in particular. Non-metallic materials (e.g. ceramics or suitable coatings) may be considered for an alternative treatment for those patients.     

Phagocytosis and killing of Brucella by human polymorphonuclear leukocytes

Although cellular immunity involving activated macrophages is important in resistance to Brucella, serum factors and polymorphonuclear leukocytes (PMNLs) play some role in the initial response to infection. The interaction between human PMNLs and virulent and attenuated strains of Brucella abortus and Brucella melitensis was studied by in vitro techniques. Virulent and attenuated strains of both species were rapidly phagocytosed after opsonization with normal human serum (NHS); nonopsonized bacteria were not phagocytosed. In contrast, NHS devoid of detectable antibodies was bactericidal for strains of B. abortus but not of B. melitensis. In addition, intracellular killing of ingested bacteria was shown for virulent B. abortus but not for B. melitensis. Ultrastructural studies revealed morphological alterations in about one-half of phagocytosed B. abortus and B. melitensis after incubation for 10 min; thereafter, nearly 100% of B. abortus showed some degree of degeneration, whereas B. melitensis remained intact during 120 min of observation.     

Environmental factors and refractive error in Chinese schoolchildren

We surveyed and assessed 2,323 schoolchildren aged seven to 17 years from four schools in China, two in the city of Tianjin and the other two in a neighbouring rural village, Ban Chau, to investigate the prevalence of refractive error and its relationship with environmental factors. Every child from each of the participating classes was recruited in this study to avoid self-selection. A questionnaire was issued which queried some aspects of the child's visual habits and home. Refraction was canied out using the Canon R-22 autorefractor. The degree and frequency of myopia in these children increased almost linearly from age seven to 17 years. There was little difference between the urban and rural groups. Of the factors explored, the number of hours spent on near work showed the best correlation with the degree of myopia, albeit only weakly.     

Amniotic cavity cultures, blood cultures, and surface swabs in preterm infants--useful tools for the management of early-onset sepsis?

AIMS: To evaluate the potential benefit of amniotic fluid and amniotic/placental membrane cultures for the management of early-onset sepsis in preterm infants. METHODS: The results of amniotic cavity cultures obtained during cesarean section and of peripheral blood cultures and surface swabs obtained from the preterm infant at the time of admission were analyzed with respect to the diagnosis of clinical sepsis in 221 preterm infants <34 weeks of gestation. RESULTS: 136 (61.5%) patients had negative amniotic cavity culture results or growth of contaminants, 56 (25.3%) had growth of Ureaplasma urealyticum, and 29 (13.1%) of other pathogens. The corresponding numbers for surface swabs were 82.8%, 11.6%, and 5.6%. A positive blood culture was found in only two neonates. Fifty-four patients (24.4%) had clinical early-onset sepsis. Patients with amniotic cavity culture results that were positive for other pathogens were significantly more likely to experience clinical sepsis than patients with negative culture results (51.7% vs 15.1%, OR 6.1, p<0.0001). Regarding surface swabs, this correlation did not reach statistical significance. CONCLUSION: The strong association between positive amniotic cavity culture results and clinical early-onset sepsis supports the existence of a causal relation and provides evidence for the potential value of amniotic and/or placental membrane sampling in the management of early-onset sepsis in preterm infants. Surface swabs add no additional information and hence should not be performed routinely.     

Evaluation of a netilmicin-loading dose in very low birthweight infants

BACKGROUND: The bactericidal efficacy of aminoglycosides is directly related to maximum serum concentrations, particularly the initial one. Therefore, several groups have recommended an aminoglycoside loading dose. Our goal was to develop a simplified dosage regimen for preterm infants which would result in therapeutic maximum serum concentrations early in the course of therapy. METHODS: Open, noncomparative study during November 2000 to April 2001. The modified netilmicin-dosing protocol included a loading dose of 5 mg/kg in the first week of life, followed by a maintenance regimen of 3.5 mg/kg every 24 h. After the first week of life the corresponding doses were 6 (loading) and 5 mg/kg (maintenance). A peak level was measured 30 min after the second dose, and a trough level immediately before the third dose. RESULTS: Thirty-five very low birthweight infants (mean birthweight 876 +/- 170, range 536-1,385 g; mean gestational age 26 +/- 1.8, range 23-30 weeks) who had 46 episodes of netilmicin treatment were included in the analysis. Mean netilmicin peak and trough values were 15.9 +/- 3.7 (range 8.9-28.9) and 3.4 +/- 1.3 (range 1.0-7.8) micromol/l, respectively. Ninety-one percent of all peak levels were within the targeted range of > or =10 micromol/l. Eleven trough values (24%) were > or =4 micromol/l: in 7 instances netilmicin was administered within the first week of life, 5 of these patients had concomitant indomethacin treatment. Only 1 of the 35 neonates had a rise in serum creatinine of > or =0.5 mg/dl during netilmicin therapy. Hearing evaluations were performed in 25 of the 29 surviving infants at discharge home, all of which gave normal results. CONCLUSIONS: The new netilmicin-dosing protocol yielded therapeutic maximum serum concentrations in 91% of cases after the second dose. However, a significant number of very low birthweight infants had elevated trough levels, particularly when netilmicin was administered in the first week of life with concomitant indomethacin treatment. We speculate that a longer interval between the loading dose and the first maintenance dose would result in fewer elevated trough levels with a similarly high number of therapeutic peak levels.     

Edwardsiella tarda isolated in Israel between 1961 and 1980

Edwardsiella tarda was isolated from patients, water tortoises (Clemmys caspica), and samples of water from Lake Kinnereth, the river Jordan, well water, and sewage water. Of the 53 isolates, 35 belonged to completely identified serotypes, among them 7 new ones. Fourteen cultures had O antigens, and one had an H antigen, different from those previously described. Three serotypes isolated from patients were also found in other sources: water tortoises, lake water, or both.