A Biomechanical Comparison of Locked Unicortical with Non-Locking Bicortical Screws for Metacarpal Shaft Fractures in a Randomized Human Cadaveric Model.

Background: Locking plate fixation is widely used in large long bone fixation and is now available for small "long" bones in the hand. Potential advantages of unicortical locked fixation are reduced risk of over-drilling and therefore reduced risk of damage to surrounding structures and reduced risk of irritation from proud screws. Furthermore, unicortical fixation may be used where bicortical fixation is technically impossible. Our aim was to compare fixation strength of unicortical locked plate fixation with bicortical non-locked fixation in a human cadaveric model, by assessing strength under cyclical loading conditions and load to failure (LTF). Methods: 16 matched pairs of embalmed and refrigerated human cadaveric metacarpals were randomly allocated to either unicortical locked or bicortical non-locked plate and screw fixation. A transverse osteotomy was made. Fractures were stabilized with 2.0 mm self-tapping locking or cortical screws. Each metacarpal was then loaded with a 3-point cantilever testing using a 100 N cell on an Instron materials testing device, cyclically loading them at 1,000 repetitions of 30 N and 50 N. If there was no visible failure of the fixation from cyclical loading they were then loaded to failure with a 1 kN cell. Results: There was a significant difference of average LTF between the bicortical non-locking and unicortical locking of 38.07-59.95 N (p < 0.01). However, both groups showed no statistically significant difference when comparing their performance under cyclical loading. Conclusions: The authors regard unicortical locked fixation as a useful adjunct to standard plating technique.

In vitro and ex vivo characterisation of an in situ gelling formulation for sustained lidocaine release with potential use following knee arthroplasty.

Sustained lidocaine release via a thermoresponsive poloxamer-based in situ gelling system has the potential to alleviate pain following knee arthroplasty. A previously developed formulation showed a promising drug release profile in synthetic phosphate-buffered saline (PBS). To support the translation of this formulation, ex vivo characterisation was warranted. This study therefore aimed (1) to modify the previously developed formulation to reduce the burst release, (2) to compare the release behaviour into ex vivo human intra-articular fluid (IAF) and PBS and (3) to determine the formulation spread in an ex vivo human knee using magnetic resonance imaging (MRI). All formulations provided sustained release out to 72 h; polyvinyl pyrrolidone was the most effective additive yielding a small yet significant decrease (p < 0.05) in the burst release. Release of lidocaine from the formulation occurred significantly faster into IAF compared to PBS (1.4 times greater release in the first 24 h), correlating with faster rates of gel erosion in IAF. Injection was easily achieved through a 21-gauge (G) needle into the synovial space of a human cadaveric knee, and MRI scans revealed effective spreading of the formulation throughout the joint cavity. The pattern of spread is promising for the drug to reach the widespread nerve endings in the joint capsule; the effect of this spread on release in an in vivo setting will be the subject of future studies. The demonstrated properties indicate that the in situ gelling formulation has the potential to be used clinically to treat post-operative pain following knee arthroplasty.

Inter-observer validation study of quantitative CT-osteodensitometry in total knee arthroplasty.

INTRODUCTION: Proximal tibial bone quality is an important factor in implant mechanical stability following total knee arthroplasty. Quantitative computed tomography (CT) osteodensitometry has been used to measure the change in bone density post-operatively. We sought to validate the inter-observer reliability of these measurements. METHODS: Sixteen CT scans were obtained on cadaveric lower limbs. Two observers independently obtained cortical and cancellous bone mineral density measurements from these scans. Eight CT scans were performed with prosthesis in situ and eight without. Results were compared using correlation coefficient and Bland-Altman analysis. RESULTS: The study showed a high correlation coefficient of greater than 0.990 for all slices. The mean difference between observers falls within two standard deviations of the mean as seen on a Bland-Altman plot. INTERPRETATION: Quantitative CT-osteodensitometry is a reproducible method to measure bone mineral density changes about the knee and shows little variation between observers.

A novel in vivo model to study endochondral bone formation; HIF-1alpha activation and BMP expression.

Numerous growth and transcription factors have been implicated in endochondral bone formation of the growth plate. Many of these factors are up-regulated during hypoxia and downstream of Hypoxia-Inducible Factor (HIF)-1alpha activation. However, the specific function of these factors, in the context of oxygenation and metabolic adaptation during adult periosteal endochondral bone formation, is largely unknown. Here, we studied HIF-1alpha and the possible roles of (HIF-1alpha related) growth and transcription factors in a recently developed in vivo model for adult periosteal endochondral bone formation. At different phases of periosteal endochondral bone formation, mRNA levels of Transforming Growth Factor (TGF)-beta1, Bone Morphogenetic Proteins (BMP)-2, -4, and -7, Indian Hedgehog (Ihh), Parathyroid Hormone-related Protein (PTHrP), Sox9, Runx2, HIF-1alpha, Vascular Endothelial Growth Factor (VEGF), periostin (POSTN), and Glyceraldehyde-3-Phophate Dehydrogenase (GAPDH) were evaluated with RT-real time-PCR. Also protein levels of TGF-beta1, BMP-2, -4, and -7, HIF-1alpha, and POSTN were examined. During the chondrogenic phase, the expression of Sox9, Ihh, and HIF-1alpha was significantly up-regulated. TGF-beta1 mRNA levels were rather constant, and the mRNA levels of BMPs were significantly lower. Immunohistochemical detection of corresponding gene products, however, revealed the presence of the proteins of TGF-beta1, BMP-2, -4, and -7, HIF-1alpha, and POSTN within the chondrocytes during chondrogenesis. This discrepancy in gene expression between mRNA and protein level for TGF-beta1 and the different BMPs is indicative of post-transcriptional regulation of protein synthesis. HIF-1alpha activation and up-regulation of GAPDH support a hypoxia-induced metabolic shift during periosteal chondrogenesis. Our model recapitulates essential steps in osteochondrogenesis and provides a new experimental system to study and ultimately control tissue regeneration in the adult organism.

Appropriate use of pagers in a New Zealand tertiary hospital.

AIMS: To identify the appropriateness of calls to on-call house officers in a major tertiary teaching hospital. METHODS: A prospective observational study was conducted at Auckland City Hospital over the months of June, July, and August 2004. Fourteen house officers from a range of medical and surgical services categorised calls received while on-call after-hours into one of three groups: 'appropriate and urgent'; 'appropriate but not urgent'; and 'inappropriate'. RESULTS: 844 calls were recorded and categorised, with approximately even distribution between medical services (431 calls) and surgical services (413 calls); 30% of calls were deemed clinically appropriate and required a response within 1 hour; 53% of calls were deemed clinically appropriate but did not require a response within an hour; while 17% of calls were deemed inappropriate. CONCLUSIONS: The most important function an on-call house officer performs is responding to urgent medical situations. Frequent interruptions mean that house officers may become less efficient and more prone to making mistakes. The majority of calls received by on-call house officers did not need immediate responses and would have been better communicated via a less intrusive system such as text-messaging or the keeping of a non-urgent jobs list. If house officers were paged more appropriately then they would be interrupted less frequently and would be able to provide safer, more efficient, and timelier patient care.

Computer-assisted osteodensitometry following total hip arthroplasty.

Several factors, including polyethylene wear debris, implant micromotion and stress shielding, can cause bone loss and fixation failure following total hip arthroplasty. Various techniques have been utilized in an effort to detect bone density loss in vivo with varying success. Quantitative computed tomography (qCT)-assisted osteodensitometry has been shown to be useful in assessing the in vivo structural bone changes after total hip arthroplasty. It has high resolution, accuracy and reproducibility, making it a useful tool for research purposes. qCT osteodensitometry is able to differentiate between cortical and cancellous bone structures, and to assess the bone/implant interface. It provides valuable information about the pattern of stress shielding that occurs around the prosthesis. qCT-assisted osteodensitometry can show early bony changes, which may provide information about the quality of implant fixation and surrounding bone adaptation. In conjunction with finite-elements analysis, qCT is able to generate accurate patient-specific meshes on which to model implants and their effect on bone remodeling. This technology can be useful in order to predict bone remodeling and quality of implant fixation using prostheses with different design and/or biomaterials. In future, this tool could be used for preclinical validation of new implants before their introduction in the marketplace.