Accuracy of arthroscopic fluid pump systems in shoulder surgery: a comparison of 3 different pump systems.

BACKGROUND: Extra-articular fluid extravasation is a known complication during shoulder arthroscopy. The risk and amount of extravasation to a large degree is dependent on the fluid pressure delivered to the surgical site. Accurate measurement, knowledge, and control of the pressure delivered is thus important to surgeons, anesthetists, and the patient. The purpose of this study was to compare the pressure measurement accuracy of 3 arthroscopic fluid pumps, with 2 of them having 2 different settings. METHODS: Twenty-five patients (n = 5 per group) undergoing shoulder arthroscopy were selected. Three different arthroscopic fluid pumps (ConMed 24K, Stryker Crossflow, Arthrex Dual Wave) were tested in 5 different operational settings (Stryker, standard and dynamic mode; ConMed, with and without TIPS; Arthrex Dual Wave). In each operation, the set pump pressures and the subsequently delivered intra-articular surgical site fluid pressures were measured by a spinal needle connected to an anesthetic standard pressure transducer attached to the anesthetic machine. Independent measures of the surgical site pressures were obtained before multiple portals were created or extravasation had occurred. Measurements were taken at the beginning of surgery. RESULTS: Measurements of the mean intra-articular pressure were found to not be significantly different from the set pressure for the ConMed 24K with TIPS (0.98 ± 0.02-fold) and Stryker Crossflow in standard mode (0.98 ± 0.02-fold). However, actual pressure was significantly greater than the set pressure for the ConMed 24K without TIPS (by 1.30 ± 0.13-fold), Stryker Crossflow in dynamic mode (by 1.82 ± 0.08-fold), and Arthrex Dual Wave (by 2.19 ± 0.06-fold). CONCLUSION: Independently measured intra-articular pressure can be more than double the set pressure for some arthroscopic pumps. Measuring intra-articular pressure can thus aid in adjusting the set pressure. This could minimize the risk of intraoperative complications.

A Biomechanical Comparison of Different Suture Materials Used for Arthroscopic Shoulder Procedures.

PURPOSE: To evaluate the viscoelastic properties of 4 commercially available cord-like sutures and 2 commercially available suture tapes when subjected to physiological loads, as well as to compare them with each other and to identify the clinically most desirable combination of suture material properties. METHODS: Six suture materials (Ethibond, FiberWire, FiberTape, Orthocord, Ultrabraid, and Ultratape) underwent creep testing (n = 7, 60 N, 10 minutes) to determine specimen stiffness, initial elongation at 60 N of load, static creep (during 10 minutes of loading), and relaxed elongation (material recovery 3 minutes after removal of load). Furthermore, cyclic testing (n = 7, 10-45 N, 0.5 Hz, 500 cycles) was carried out to determine dynamic creep, peak-to-peak displacement, and relaxed elongation. Mechanical testing was conducted on a material testing machine in 37°C phosphate-buffered saline solution. RESULTS: FiberTape showed the greatest stiffness (23.9 ± 3.2 N/mm, P < .001), the smallest amounts of static (0.38 ± 0.10 mm, P < .001) and dynamic (0.16 ± 0.09 mm, P = .003) creep, and the smallest peak-to-peak displacement (0.20 ± 0.02 mm, P < .001). FiberTape and FiberWire showed the smallest initial elongation (1.17 ± 0.17 mm and 1.63 ± 0.25 mm, respectively; P < .001). Ultrabraid showed the greatest relaxed elongation, both statically (4.73 ± 0.73 mm, P < .001) and dynamically (4.18 ± 0.83 mm, P = .002). CONCLUSIONS: FiberTape consistently displayed less creep, greater stiffness, and less extensibility than the other suture types. Ultrabraid showed the largest amount of relaxed elongation on both static and dynamic testing. CLINICAL RELEVANCE: When considering high stiffness in combination with low initial extension and low static creep to be ideal parameters to achieve optimal initial construct stability and considering low dynamic creep in combination with low peak-to-peak displacement to be ideal conditions for the repetitive loading of the construct during the healing process, tapes seem to be superior to cord-like sutures for performing rotator cuff repair.

A novel fracture mechanics model explaining the axial penetration of bone-like porous, compressible solids by various orthopaedic implant tips.

Many features of orthopaedic implants have been previously examined regarding their influence on migration in trabecular bone under axial loading, with screw thread design being one of the most prominent examples. There has been comparatively little investigation, however, of the influence that implant tip design has on migration under axial loads. We present a novel fracture mechanics model that explains how differences in tip design affect the force required for axial penetration of porous, compressible solids similar to trabecular bone. Three tip designs were considered based on typical 5 mm diameter orthopaedic locking screws: flat and conical tip designs, as well as a novel elastomeric tip. Ten axial penetration trials were conducted for each tip design. In order to isolate the effect of tip design on axial migration from that of the threads, smooth steel rods were used. Tip designs were inserted into polyurethane foam commonly used to represent osteoporotic trabecular bone tissue (ASTM Type 10, 0.16 g/cc) to a depth of 10 mm at a rate of 2 mm/min, while force and position were recorded. At maximum depth, elastomeric tips were found to require the greatest force for axial migration (mean of 248.24 N, 95% Confidence Interval [CI]: 238.1-258.4 N), followed by conical tips (mean of 143.46 N, 95% CI: 142.1-144.9 N), and flat tips (mean of 113.88 N, 95% CI: 112.2-115.5 N). This experiment was repeated in cross-section while recording video of material compaction through a transparent window. Strain fields for each tip design were then generated from these videos using digital image correlation (DIC) software. A novel fracture mechanics model, combining the Griffith with porous material compaction, was developed to explain the performance differences observed between the three tip designs. This model predicted that steady-state stress would be roughly the same (~ 4 MPa) across all designs, a finding consistent with the experimental results. The model also suggested that crack formation and friction are negligible mechanisms of energy absorption during axial penetration of porous compressible solids similar to trabecular bone. Material compaction appears to be the dominant mechanism of energy absorption, regardless of tip design. The cross-sectional area of the compacted material formed during migration of the implant tip during axial penetration was shown to be a strong determinant of the force required for migration to occur (Pearson Coefficient = 0.902, p < .001). As such, implant tips designed to maximize the cross-sectional area of compacted material - such as the elastomeric and conical tips in the present study - may be useful in reducing excessive implant migration under axial loads in trabecular bone.

What is the underlying mechanism for the failure mode observed in the proximal femoral locking compression plate? A biomechanical study.

PURPOSE: Recently, several cases of clinical failure have been reported for the Proximal Femoral Locking Compression Plate (PF-LCP). The current study was designed to explore biomechanically the underlying mechanism and to determine whether the observed failure was due to technical error on insertion or to implant design. METHODS: A foam block model simulating an unstable intertrochanteric fracture was created for 3 study groups with 6 specimens each. Group C was correctly instrumented according to the manufacturer's guidelines. In Group P and Group A, the first or second proximal screw was placed with a posterior or anterior off-axis orientation by 2° measured in the transversal plane, respectively. Each construct was cyclically tested until failure using a test setup and protocol simulating complex axial and torsional loading. Radiographs were taken prior to and after the tests. Force, number of cycles to failure and failure mode were compared. RESULTS: A screw deviation of 2° from the nominal axis led to significantly earlier construct failure in Group P and Group A in comparison to Group C. The failure mode was characterised by loosening of the off-axis screw due to disengagement with the plate, resulting in loss of construct stiffness and varus collapse of the fracture. CONCLUSIONS: In our biomechanical test setup, the clinical failure modes observed with the PF-LCP were reproducible. A screw deviation of 2° from the nominal axis consistently led to the failure. This highlights how crucial is the accurate placement of locking screws in the proximal femur.

The direct anterior approach in hemiarthroplasty for displaced femoral neck fractures.

PURPOSE: Hip replacement is the most common treatment for displaced femoral neck fractures in the elderly, and minimally invasive surgery is popular in the field of orthopaedic surgery. This study evaluated the outcome of monopolar hemiarthroplasty by the direct anterior approach over a postoperative period up to 2.5 years. METHODS: A total of 86 patients with displaced femoral neck fractures were included (mean age of 86.5 years). Surviving patients were reviewed three months (retrospectively) and one to 2.5 years (prospectively) after surgery. One-year mortality was 36 %. RESULTS: For all stems, implant positioning with respect to stem alignment, restoration of leg length and femoral offset was correct. Acetabular protrusion was observed in 55 % of the patients one to 2.5 years postoperatively. Subsidence and intraoperative periprosthetic fractures occurred in three patients (3 %) each. All revision stems for postoperative periprosthetic fractures could be implanted using the initial surgical technique without extension of the previous approach. The mean Harris hip score was 85 points at the one to 2.5-year follow-up; 85 % of the patients were satisfied with their hip and 57 % returned to their preoperative level of mobility. CONCLUSION: Based on these findings, hemiarthroplasty for hip fractures can be performed safely and effectively via the direct anterior approach with good functional outcome and high patient satisfaction.

Synthesis and bio-functionalization of magnetic nanoparticles for medical diagnosis and treatment.

The synthesis of multifunctional magnetic nanoparticles (NPs) is a highly active area of current research located at the interface between materials science, biotechnology and medicine. By virtue of their unique physical properties magnetic nanoparticles are emerging as a new class of diagnostic probes for multimodal tracking and as contrast agents for MRI. Furthermore, they show great potential as carriers for targeted drug and gene delivery, since reactive agents, such as drug molecules or large biomolecules (including genes and antibodies), can easily be attached to their surface. On the other hand, the fate of the nanoparticles inside the body is mainly determined by the interactions with its local environment. These interactions strongly depend upon the size of the magnetic NPs but also on the individual surface characteristics, like charge, morphology and surface chemistry. This review not only summarizes the most common synthetic approaches for the generation of magnetic NPs, it also focuses on different surface modification strategies that are used today to enhance the biocompatibility of these NPs. Finally, key considerations for the application of magnetic NPs in biomedicine, as well as various examples for the utilization in multimodal imaging and targeted gene delivery are presented.

Human cytomegalovirus impairs the function of plasmacytoid dendritic cells in lymphoid organs.

Human dendritic cells (DCs) are the main antigen presenting cells (APC) and can be divided into two main populations, myeloid and plasmacytoid DCs (pDCs), the latter being the main producers of Type I Interferon. The vast majority of pDCs can be found in lymphoid organs, where the main pool of all immune cells is located, but a minority of pDCs also circulate in peripheral blood. Human cytomegalovirus (HCMV) employs multiple mechanisms to evade the immune system. In this study, we could show that pDCs obtained from lymphoid organs (tonsils) (tpDCs) and from blood (bpDCs) are different subpopulations in humans. Interestingly, these populations react in opposite manner to HCMV-infection. TpDCs were fully permissive for HCMV. Their IFN-alpha production and the expression of costimulatory and adhesion molecules were altered after infection. In contrast, in bpDCs HCMV replication was abrogated and the cells were activated with increased IFN-alpha production and upregulation of MHC class I, costimulatory, and adhesion molecules. HCMV-infection of both, tpDCs and bpDCs, led to a decreased T cell stimulation, probably mediated through a soluble factor produced by HCMV-infected pDCs. We propose that the HCMV-mediated impairment of tpDCs is a newly discovered mechanism selectively targeting the host's major population of pDCs residing in lymphoid organs.

Diagnostic value of reverse transcription-PCR for detection of cytomegalovirus pp67 in samples from solid-organ transplant recipients.

We evaluated a highly sensitive quantitative real-time one-step reverse transcription-PCR (RT-PCR) for detection of human cytomegalovirus pp67 transcripts in monitoring of solid-organ transplant recipients. Results were compared with those of pp65 antigen testing and quantitative DNA-PCR. Due to a low clinical sensitivity, the pp67 RT-PCR was not able to replace these assays.

Interaction of severe acute respiratory syndrome-associated coronavirus with dendritic cells.

Severe acute respiratory syndrome (SARS) of humans is caused by a novel coronavirus of zoonotic origin termed SARS-associated coronavirus (SARS-CoV). The virus induces severe injury of lung tissue, as well as lymphopenia and destruction of the architecture of lymphatic tissue by as-yet-unknown mechanisms. In this study, the interaction of SARS-CoV with dendritic cells (DCs), the key regulators of immune responses, was analysed. Monocyte-derived DCs were infected with SARS-CoV and analysed for viability, surface-marker expression and alpha interferon (IFN-alpha) induction. SARS-CoV infection was monitored by quantitative RT-PCR, immunofluorescence analysis and recovery experiments. SARS-CoV infected both immature and mature DCs, although replication efficiency was low. Immature DCs were activated by SARS-CoV infection and by UV-inactivated SARS-CoV. Infected DCs were still viable on day 6 post-infection, but major histocompatibility complex class I upregulation was missing, indicating that DC function was impaired. Additionally, SARS-CoV infection induced a delayed activation of IFN-alpha expression. Therefore, it is concluded that SARS-CoV has the ability to circumvent both the innate and the adaptive immune systems.