Mechanical behaviour of standardized, endoskeleton-including hip spacers implanted into composite femurs

Two-stage reconstruction using an antibiotic loaded cement spacer is the preferred treatment method of late hip joint infections. Hip spacers maintain stability of the joint and length of the limb during treatment period. However, as the material strength of bone cement (PMMA) is limited, spacer fractures led to serious complications in the past. This study investigated the load capacity of custom made hip spacers, developed at the 'Klinik für Orthopädie und Orthopädische Chirurgie' (Universitätsklinikum des Saarlandes, Homburg/Saar, Germany), and implanted into composite femurs. In a quasi-static test, non-reinforced spacers tolerated hip joint loads of about 3000 N, whereas reinforced spacers with titanium-grade-two endoskeletons doubled this load up to 6000 N. Even for cyclic loading, endoskeleton-including hip spacers tolerated loads of >4500 N with 500,000 load cycles. Thus, an endoskeleton-including spacer should provide a mobile and functional joint through the treatment course. A generated FE-model was used to determine the fracture stresses and allows for further sensitivity analysis.

Development of a reinforced PMMA-based hip spacer adapted to patients' needs

Two-stage reimplantation using an interval hip prosthesis (spacer) of antibiotic-impregnated bone cement has become a well-accepted method to eradicate infection and prevent limb shortening. However, custom made as well as prefabricated spacers share a weakness of limited strength and hence several fractures of spacers have been observed, even for partial weight bearing. The purpose of this study was therefore to improve the strength of the custom made spacer, used at the Orthopaedic Department of the Saarland University Hospital (Germany). As the material strength of bone cement is limited, several reinforced spacers with a metal core consisting of titanium grade two have been developed and investigated. Loading procedure was close to the ISO 7206/4, though small adaptation was made. An inserted rod of titanium grade two increased the collapse load up to 1000-1300 N, but considering a maximum expected load of about three times the body weight, still below the required value. A "full-stem" reinforced spacer, i.e. spacer with a titanium endoskeleton and a minimum of 2-3mm PMMA-coating in order to assure drug release, provides a mobile and functional joint through the treatment course. Those with 8mm thickness of titanium endoskeleton endured up to one million load cycles in a load range of 300-2300 N. To give further support for individual cases a meaningful S-N curve for this device was determined.

Left ventricular hypertrophy in ascending aortic stenosis mice: anoikis and the progression to early failure

BACKGROUND

To determine potential mechanisms of the transition from hypertrophy to very early failure, we examined apoptosis in a model of ascending aortic stenosis (AS) in male FVB/n mice.

METHODS AND RESULTS

Compared with age-matched controls, 4-week and 7-week AS animals (n=12 to 16 per group) had increased ratios of left ventricular weight to body weight (4.7+/-0.7 versus 3.1+/-0.2 and 5. 7+/-0.4 versus 2.7+/-0.1 mg/g, respectively, P<0.05) with similar body weights. Myocyte width was also increased in 4-week and 7-week AS mice compared with controls (19.0+/-0.8 and 25.2+/-1.8 versus 14. 1+/-0.5 microm, respectively, P<0.01). By 7 weeks, AS myocytes displayed branching with distinct differences in intercalated disk size and staining for beta(1)-integrin on both cell surface and adjacent extracellular matrix. In vivo left ventricular systolic developed pressure per gram as well as endocardial fractional shortening were similar in 4-week AS and controls but depressed in 7-week AS mice. Myocyte apoptosis estimated by in situ nick end-labeling (TUNEL) was extremely rare in 4-week AS and control mice; however, a low prevalence of TUNEL-positive myocytes and DNA laddering were detected in 7-week AS mice. The specificity of TUNEL labeling was confirmed by in situ ligation of hairpin oligonucleotides.

CONCLUSIONS

Our findings indicate that myocyte apoptosis develops during the transition from hypertrophy to early failure in mice with chronic biomechanical stress and support the hypothesis that the disruption of normal myocyte anchorage to adjacent extracellular matrix and cells, a process called anoikis, may signal apoptosis.

Intrathecal thyrotropin-releasing hormone therapy of amyotrophic lateral sclerosis

Six patients with amyotrophic lateral sclerosis were given from 800 to 4000 micrograms of thyrotropin-releasing hormone (TRH) intrathecally for a period of 2-6 months. The progressive course of this disease, manifested by increasing atrophy, paralysis and disability score, was not altered. This supports the hypothesis that the decrease in TRH content in the anterior horn region is secondary to the cellular destruction. TRH appears to play no significant role in the pathogenesis of amyotrophic lateral sclerosis.