Mesenchymal stromal cell implantation for stimulation of long bone healing aggravates Staphylococcus aureus induced osteomyelitis.

Large bone defects requiring long-term osteosynthetic stabilization or repeated surgeries show a considerable rate of infection. Mesenchymal stromal cells (MSCs) have been successfully used to enhance bone regeneration, but their powerful immunomodulatory effects may impose an enhanced risk for osteomyelitis development. In order to unravel whether implantation of MSCs aggravates a simultaneous bone infection, a hydrogel-supported osteomyelitis ostectomy model was developed in which rats received a femoral bone defect with rigid plate-fixation. After fibrin-assisted transfer of Staphylococcus aureus (SA), effects of MSC implantation on osteomyelitis development were quantified over 3-4 weeks. All SA-infected animals developed an acute local osteomyelitis with significantly increased blood neutrophil count, abscess formation and bone destruction. MSC-treatment of infected defects aggravated osteomyelitis according to a significantly elevated osteomyelitis score and enhanced distal bone loss with spongy alteration of cortical bone architecture. Increased attraction of macrophages, osteoclasts and regulation of pro- and anti-inflammatory mediators were potential MSC actions. Overall trophic actions of MSCs implanted into non-sterile bone defects may enhance an infection and/or exacerbate osteomyelitis. Studies on antibiotic carrier augmentation or antibiotic treatment are warranted to decide whether MSC implantation is a safe and promising therapy for orthopedic implant-stabilized bone defects at high risk for development of infection.

A vibrational technique for diagnosing loosened total hip endoprostheses: an experimental sawbone study.

Aseptic loosening of hip implants is a severe orthopaedic problem and a valid diagnosis is often difficult. A potential method to determine loosening of the prosthesis is a swing analysis of the bone-implant interface using a vibrational technique. In this study, hip models were constructed to assess the vibration behaviour of the stem and cup components. Four different states of implant loosening were simulated: (1) stem and cup stable, (2) stem loosened and cup stable, (3) stem and cup loosened, and (4) stem stable and cup loosened. The model was excited at the lateral condyle of the femur between 100 Hz and 2000 Hz. Resonance spectra were recorded using an optical laser vibrometer and an accelerometer-based system. Analysis of the spectra revealed shifts of the resonances towards lower frequencies, especially in the case of a loosened stem component. The integral value of the spectra was a second parameter that was sensitive to a stem loosening. In the case of a loosened cup, a peak count analysis resulted in a significantly higher number of counts. In our model, different states of implant loosening could be determined with a vibrational technique and the localisation of the loosened component could be distinguished as well.

In vivo failure analysis of intramedullary cement restrictors in 100 hip arthroplasties.

BACKGROUND: We occasionally noticed excessive distal plug position in our clinical routine of cemented hip arthroplasties. We therefore performed an analysis of risk factors for migration of a biodegradable intramedullary gelatine plug. PATIENTS AND METHODS: The performance of a cement restrictor was studied in 100 consecutive cemented total hip arthroplasties implanted with third-generation cementing techniques. In a radiographic analysis anatomical parameters, cement mantle quality, and mechanisms and factors for restrictor failure were evaluated. RESULTS: 40 restrictors showed inadequate performance: 5 cases of tilting, 22 cement leakages, 16 excessive migrations, 2 excessive migrations plus leakages, and 1 case of leakage plus tilting. excessive migration (< 5 cm) was more common in large intramedullary canals (p = 0.04) and cement leakage was more common in patients with a proximally located isthmus (p = 0.04). Half of the hips showed a complete or almost complete filling of the intramedullary cavity, which was more often found in operations carried out by experienced surgeons. INTERPRETATION: A more reliable plug design should be considered for patients with wide intramedullary canals and a high isthmus, to minimize the risk of plug migration and poor cement mantle quality.

Effects of vascular perfusion on coagulation size in radiofrequency ablation of ex vivo perfused bovine livers.

OBJECTIVES: A standardized perfused ex vivo bovine liver model was used to evaluate the effect of organ perfusion on coagulation size and energy deposition during radiofrequency ablation (RFA) procedures. MATERIALS AND METHODS: Bovine livers were perfused in a tank after rinsing the prepared liver vessels with anticoagulants. Tyrode's solution, oxygenated and heated to 36.5 degrees C, was used as perfusion medium. A flow and pressure controlled pump regulated Portal vein circulation; a dialysis machine provided pulsatile arterial circulation. Impedance-guided radiofrequency ablations were performed with 4-cm LeVeen electrodes with and without underlying liver perfusion. Two-dimensional diameters (Dv, Dh) of each ablation area were measured after dissecting the livers. RESULTS: In 4 bovine livers weighing 8.85 +/- 0.83 kg per organ (min, 7.7 kg; max, 9.7 kg) altogether 40 RF ablations were performed. A total of 20 ablations were generated with underlying liver perfusion (group 1) and 20 ablations with no liver perfusion (group 2). In group 1, Dv was 28.4 +/- 5.3 mm, Dh 38.6 +/- 7.8 mm, and energy deposition 36.9 +/- 18.0 kJ. The 20 ablation areas generated without liver perfusion displayed statistically significant differences, with Dv being 35.7 +/- 6.5 mm (P = 0.001), Dh 49.5 +/- 9.4 mm (P = 0.001), and energy deposition 25.5 +/- 13.0 kJ (P = 0.018). CONCLUSION: The model reproduced the cooling effect of perfused tissue during RFA. The ablation areas produced under perfusion conditions had smaller diameters despite longer exposure times and higher energy deposition.