Development of an equation for calculating vertebral shear failure tolerance without destructive mechanical testing using iterative linear regression

Equations used to determine vertebral failure tolerances without the need for destructive testing are useful for scaling applied sub-maximal forces during in vitro repetitive loading studies. However, existing equations that use vertebral bone density and morphology for calculating compressive failure tolerance are unsuitable for calculating vertebral shear failure tolerance since the primary site of failure is the pars interarticularis and not the vertebral body. Therefore, this investigation developed new equations for non-destructively determining vertebral shear failure tolerance from morphological and/or bone density measures. Shear failure was induced in 40 porcine cervical vertebral joints (20 C3-C4 and 20 C5-C6) by applying a constant posterior displacement to the caudal vertebra at 0.15 mm/s. Prior to destructive testing, morphology and bone density of the posterior elements were made with digital calipers, X-rays, and peripheral quantitative computed tomography. Iterative linear regression identified mathematical relationships between shear failure tolerance, and morphological and bone density measurements. Along with vertebral level, pars interarticularis length and lamina height from the cranial vertebra, and inferior facet height from the caudal vertebra collectively explained 61.8% of shear failure tolerance variance. Accuracy for this relationship, estimated using the same group of specimens, was 211.9 N or 9.8% of the measured shear failure tolerance.     

An aid to drug dosing safety in obese children: development of a new nomogram and comparison with existing methods for estimation of ideal body weight and lean body mass

The risk of accidental over‐dosing of obese children poses challenges to anaesthetists during dose calculations for drugs with serious side‐effects, such as analgesics. For many drugs, dosing scalars such as ideal body weight and lean body mass are recommended instead of total body weight during weight‐based dose calculations. However, the complex current methods of obtaining these dosing scalars are impractical in the peri‐operative setting. Arbitrary dose adjustments and guesswork are, unfortunately, tempting solutions for the time‐pressured anaesthetist. The study's aim was to develop and validate an accurate, convenient alternative. A nomogram was created and its performance compared with the standard calculation method by volunteers using measurements from 108 obese children. The nomogram was as accurate (bias 0.12 kg vs ?0.41 kg, respectively, p = 0.4), faster (mean (SD) time taken 2.8 (1.0) min (vs 3.3 (0.9) min respectively, p = 0.003) and less likely to result in mistakes (significant errors 3% vs 19%, respectively, p = 0.001). We present a system that simplifies estimation of ideal body weight and lean body mass in obese children, providing foundations for safer drug dose calculation.     

Systematic Review of Literature of Cemented Femoral Components: What Is the Durability at Minimum 20 Years Followup?

Background

Cemented femoral total hip arthroplasty may be one of the most successful surgical interventions of all time. However, although results are very encouraging over the early to mid-term followup, relatively few studies have analyzed the durability of these implants beyond 20 years followup. To evaluate the performance of contemporary implants, it is important to understand how previous implants perform at 20 or more years of followup; one way to do this is to aggregate the available data in the form of a systematic review.

Questions/purposes

(1) How durable is cemented femoral fixation in the long term (minimum 20-year followup) with respect to aseptic loosening? (2) Is the durability of cemented femoral fixation dependent on age of the patient? (3) Are the long-term results of the cemented femoral fixation dependent on any identifiable characteristics of the prosthesis such as surface finish?

Methods

A systematic review was performed to identify long-term studies of cemented femoral components. After application of inclusion and exclusion criteria to 1228 articles found with a search in PubMed and EMBASE, 17 studies with a minimum of 20-year followup on cemented femoral components were thoroughly analyzed in an attempt to answer the questions of this review. The quality of the studies reviewed was assessed with the Methodological Index for Nonrandomized Studies (MINORS) instrument. All studies were case series and cohort sizes ranged from 110 to 2000 hips for patients older than 50 years of age and 41 to 93 hips for patients younger than 50 years at the time of surgery.

Results

Among the six case series performed in patients older than 50 years of age, survivorship for aseptic loosening of the femoral component ranged from 86% to 98% at 20 years followup. There were no obvious differences for younger patients when analyzing the five studies in patients younger than age 50 years in which survivorship free from aseptic loosening for these studies ranged from 77% at 20 years in one study and 68% to 94% at 25 years in the other studies. Although data pooling could not be performed because of heterogeneity of the studies included here, it appeared that stems with a rougher surface finish did not perform as well as polished stems; survivorship of stems with rougher surface finishes varied between 86% and 87%, whereas those with smoother finishes ranged between 93.5% and 98% at 20 years.

Conclusions

Excellent long-term fixation in both older and younger patients can be obtained with cemented, polished femoral stems. These results provide material for comparison with procedures performed with newer cementing techniques and newer designs, both cemented and cementless, at this extended duration of followup.     

Cyclin-dependent kinase 5 is a mediator of dopaminergic neuron loss in a mouse model of Parkinson's disease

Recent evidence indicates that cyclin-dependent kinases (CDKs, cdks) may be inappropriately activated in several neurodegenerative conditions. Here, we report that cdk5 expression and activity are elevated after administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a toxin that damages the nigrostriatal dopaminergic pathway. Supporting the pathogenic significance of the cdk5 alterations are the findings that the general cdk inhibitor, flavopiridol, or expression of dominant-negative cdk5, and to a lesser extent dominant-negative cdk2, attenuates the loss of dopaminergic neurons caused by MPTP. In addition, CDK inhibition strategies attenuate MPTP-induced hypolocomotion and markers of striatal function independent of striatal dopamine. We propose that cdk5 is a key regulator in the degeneration of dopaminergic neurons in Parkinson's disease.     

Sebaceous carcinoma of the lip: Comparing normal lip and cheek anatomy with the imaging features of a rare cutaneous malignancy

Sebaceous carcinoma is a rare cutaneous malignancy, commonly affecting the eyelids. This case highlights a patient who presented with sebaceous carcinoma of the right upper lip with extensive involvement of the soft tissues of the head and neck. As part of the initial investigation, ultrasound was requested. This case demonstrates the ultrasound features of sebaceous carcinoma as well as revising the normal ultrasound anatomy of the upper lip and muscles of the cheek.     

A 3-base pair deletion,c.9711_9713del,in DMD results in intellectual disability without muscular dystrophy

We have identified a deletion of 3 base pairs in the dystrophin gene (DMD), c.9711_9713del, in a family with nonspecific X-linked intellectual disability (ID) by sequencing of the exons of 86 known X-linked ID genes. This in-frame deletion results in the deletion of a single-amino-acid residue, Leu3238, in the brain-specific isoform Dp71 of dystrophin. Linkage analysis supported causality as the mutation was present in the 7.6 cM linkage interval on Xp22.11–Xp21.1 with a maximum positive LOD score of 2.41 (MRX85 locus). Molecular modeling predicts that the p.(Leu3238del) deletion results in the destabilization of the C-terminal domain of dystrophin and hence reduces the ability to interact with β-dystroglycan. Correspondingly, Dp71 protein levels in lymphoblastoid cells from the index patient are 6.7-fold lower than those in control cell lines (P=0.08). Subsequent determination of the creatine kinase levels in blood of the index patient showed a mild but significant elevation in serum creatine kinase, which is in line with impaired dystrophin function. In conclusion, we have identified the first DMD mutation in Dp71 that results in ID without muscular dystrophy.     

Variation of Medicare Payments for Total Knee Arthroplasty

We analyzed the 2009 Medicare inpatient claims data and other databases to estimate Medicare payments for primary or revision total knee arthroplasty (TKA). The average Medicare hospital payment per procedure was $13,464 for primary TKA (n = 227,587) and $17,331 for revision TKA (n = 18,677). For both primary and revision TKAs Medicare payments varied substantially across patients, hospitals and healthcare markets. Less than one percent of primary TKA cases but seven percent of revision TKA cases triggered Medicare “outlier” payments, which were $10,000 or higher per case beyond regular diagnosis-related-group payments. Urban and major teaching hospitals were more likely to treat these unusually expensive cases. Hospitals in the Northeast and West regions tended to receive higher Medicare payments than hospitals in the Midwest.