Quality of motion considerations in numerical analysis of motion restoring implants of the spine

BACKGROUND: Motion restoring implants function in a dynamic environment that encompasses the full range of spinal kinematics. Accurate assessment of the in situ performance of these devices using numerical techniques requires model verification and validation against the well-established nonlinear quality of motion of the spine, as opposed to the previous norm of matching kinematic endpoint metrics such as range of motion and intervertebral disc pressure measurements at a single kinematic reference point. METHODS: Experimental data was obtained during cadaveric testing of nine three-functional spinal unit (L3-S1) lumbar spine segments. Each specimen was tested from 8 Nm of applied flexion moment to 6 Nm of applied extension moment with an applied 400 N compressive follower preload. A nonlinear kinematic curve representing the spinal quality of motion (applied moment versus angular rotation) for the index finite element model was constructed and compared to the kinematic responses of the experimental specimens. The effect of spinal soft tissue structure mechanical behaviors on the fidelity of the model's quality of motion to experimental data was assessed by iteratively modifying the material representations of annulus fibrosus, nucleus pulposus, and ligaments. FINDINGS: The present work demonstrated that for this model, the annulus fibrosus played a small role in the nonlinear quality of motion of the model, whereas changes in ligament representations had a large effect, as validated against the full kinematic range of motion. An anisotropic continuum representation of the annulus fibrosus was used, along with nonlinear fabric representations of the ligaments and a hyperelastic representation of the nucleus pulposus. INTERPRETATION: Our results suggest that improvements in current methodologies broadly used in numerical simulations of the lumbar spine are needed to fully describe the highly nonlinear motion of the spine.     

An open-label pilot study of naltrexone in childhood-onset trichotillomania

OBJECTIVE: This pilot open study evaluates the safety and efficacy of naltrexone in the management of patients with childhood onset trichotillomania (TTM). METHODS: A total of 14 patients with childhood-onset TTM were treated with naltrexone (25-100 mg/day) and were assessed at each visit for frequency of hair pulling, urge to pull hair, and symptom severity. Liver function was monitored during the treatment. The duration of the study was 10 months. RESULTS: A mean dose of 66.07 +/- 22.23 mg/day naltrexone was well tolerated and 11 out of 14 subjects showed a positive response. The mean age of the children was 9 +/- 1.88 years. The mean age of onset of symptoms in the group was 7.07 +/- 0.91 years. No abnormality in liver function was noted in the study. No adverse effects were reported by the children. CONCLUSIONS: This encouraging pilot open study has promising findings suggesting the use of naltrexone in childhood-onset TTM. However, results are needed from larger and more definitive trials before any conclusions are made.     

Comparison of a novel FiberWire-button construct versus metallic screw fixation in a syndesmotic injury model

BACKGROUND: There is minimal experience with less rigid syndesmotic fixation devices which may approximate the normal distal tibio-fibular mechanics during healing. This study evaluates the ability of a FiberWire-button implant (Arthrex, Naples, FL) to maintain syndesmotic reduction as compared with a metallic screw. METHODS: Ten matched fresh-frozen cadaveric ankle pairs with intact ligaments were tested (12.5 Nm external rotation force) to establish physiologic syndesmotic diastasis. The same force was applied to the ankles after sectioning of the syndesmotic and deltoid ligaments. Within the pairs, each limb was randomized to receive a FiberWire-button implant or a metallic screw (Synthes, Paoli, PA); the ankles were tested for syndesmotic diastasis with progressive external rotation force, from 2.5 Nm to 25 Nm (or failure). RESULTS: There was no significant difference in diastasis amongst pairs with intact or sectioned syndesmosis (p=0.64 and p=0.80, respectively). There was a significantly greater diastasis in the FiberWire-button group at all external rotation loads (p<0.0001). Nine of the ten pairs failed (all through fracture of the distal fibula). There were no hardware failures. The metallic screw group failed at a lower load (mean 15 Nm) compared to the FiberWire-button group (mean 18 Nm, p=0.0004). The metallic screw group maintained syndesmotic reduction up to 5 Nm of force. CONCLUSIONS: The FiberWire-button was unable to maintain syndesmotic reduction of the ankles at any of the forces applied. The ankles fixed with the FiberWire-button demonstrated significantly greater widening of the syndesmosis compared to the screw, at all loads. CLINICAL RELEVANCE: The FiberWire-button implant may not maintain adequate ankle syndesmotic reduction in the immediate post-operative period relative to a metallic screw.     

Multiple prethymic defects underlie age-related loss of T progenitor competence

Aging in mice and humans is characterized by declining T-lymphocyte production in the thymus, yet it is unclear whether aging impacts the T-lineage potential of hematopoietic progenitors. Although alterations in the lymphoid progenitor content of aged mouse bone marrow (BM) have been described, irradiation-reconstitution experiments have failed to reveal defects in T-lineage potential of BM hematopoietic progenitors or purified hematopoietic stem cells (HSCs) from aged mice. Here, we assessed T-progenitor potential in unmanipulated recipient mice without conditioning irradiation. T-progenitor potential was reduced in aged BM compared with young BM, and this reduction was apparent at the earliest stages of intrathymic differentiation. Further, enriched populations of aged HSCs or multipotent progenitors (MPPs) gave rise to fewer T-lineage cells than their young counterparts. Whereas the T-precursor frequency within the MPP pool was unchanged, there was a 4-fold decline in T-precursor frequency within the HSC pool. In addition, among the T-competent HSC clones, there were fewer highly proliferative clones in the aged HSC pool than in the young HSC pool. These results identify T-compromised aged HSCs and define the nature and cellular sites of prethymic, age-related defects in T-lineage differentiation potential.     

Outcome of neonates requiring assisted ventilation

Over a two-year period, we studied a total of 100 newborns delivered in our hospital, needing ventilation. The indications for ventilation, complications, outcome, and factors influencing outcome were analyzed. Of the 100 babies, 54 were preterm, 44 term and 2 post-term. Overall survival was 58%. The commonest indication for ventilation was meconium aspiration syndrome in term babies and hyaline membrane disease in preterms. Babies ventilated for pneumonia had the best outcome, while the poorest outcome was in sepsis. Survival increased significantly with increasing birth weight and gestational age. Downes score, Apgar score and pH at birth did not correlate significantly with outcome. The maximum peak inspiratory pressure requirement was significantly higher in the non-survivors. In pneumonia and sepsis, increased FiO2 requirement significantly impaired survival. The commonest complication was shock. Incidence of disseminated intravascular coagulation, pulmonary hemorrhage and pneumothorax was significantly higher in non-survivors; however, none of these factors was independently predictive of mortality.