Screw angulation affects bone-screw stresses and bone graft load sharing in anterior cervical corpectomy fusion with a rigid screw-plate construct: a finite element model study

Background contextAnterior corpectomy and reconstruction with bone graft and a rigid screw-plate construct is an established procedure for treatment of cervical neural compression. Despite its reliability in relieving symptoms, there is a high rate of construct failure, especially in multilevel cases.PurposeThere has been no study evaluating the biomechanical effects of screw angulation on construct stability; this study investigates the C4–C7 construct stability and load-sharing properties among varying screw angulations in a rigid plate-screw construct.Study designA finite element model of a two-level cervical corpectomy with static anterior cervical plate.MethodsA three-dimensional finite element (FE) model of an intact C3–T1 segment was developed and validated. From this intact model, a fusion model (two-level [C5, C6] anterior corpectomy) was developed and validated. After corpectomy, allograft interbody fusion with a rigid anterior screw-plate construct was created from C4 to C7. Five additional FE models were developed from the fusion model corresponding to five different combinations of screw angulations within the vertebral bodies (C4, C7): (0°, 0°), (5°, 5°), (10°, 10°), (15°, 15°), and (15°, 0°). The fifth fusion model was termed as a hybrid fusion model.ResultsThe stability of a two-level corpectomy reconstruction is not dependent on the position of the screws. Despite the locked screw-plate interface, some degree of load sharing is transmitted to the graft. The load seen by the graft and the shear stress at the bone-screw junction is dependent on the angle of the screws with respect to the end plate. Higher stresses are seen at more divergent angles, particularly at the lower level of the construct.ConclusionThis study suggests that screw divergence from the end plates not only increases load transmission to the graft but also predisposes the screws to higher shear forces after corpectomy reconstruction. In particular, the inferior screw demonstrated larger stress than the upper-level screws. In the proposed hybrid fusion model, lower stresses on the bone graft, end plates, and bone-screw interface were recorded, inferring lower construct failure (end-plate fractures and screw pullout) potential at the inferior construct end.     

Changes in spinal cord injury-induced gene expression in rat are strain-dependent.

BACKGROUND AND CONTEXT: The functional recovery of animals subject to experimental spinal cord injury (SCI) is dependent on the injury model as well as the species and strain of animal used. Previous studies have shown differences in rates and degree of recovery between rats of different strains. PURPOSE: We sought to explore the hypothesis that differences in gene expression are associated with differences in functional recovery. STUDY DESIGN/SETTING: Laboratory study involving cohorts of three different strains of rat. METHODS: We used the Impactor device to produce identical spinal cord contusion injuries in groups of Long Evans, Sprague-Dawley, and Lewis rats (10 each). The functional recovery of animals was assessed using the Basso, Beattie, and Bresnahan rating scale. Six weeks after injury, rats were killed and the spinal cords were harvested for deoxyribonucleic acid microarray analysis. Changes in gene expression compared with intraspecies controls (3 each) were assessed at the region of injury and at a rostral segment of the spinal cord. Selected genes were also studied with real-time polymerase chain reaction. RESULTS: We found that different strains tended to exhibit different patterns of functional recovery. There were differences between the strains in terms of gene expression. CONCLUSIONS: These results emphasize the importance of testing novel therapies for SCI in a variety of animal species before introduction into human trials. Further research into the influence of several gene products on functional recovery is needed.     

Perioperative effects of oral ketorolac and acetaminophen in children undergoing bilateral myringotomy

Prophylactic administration of analgesics before surgery can decrease the intraoperative anaesthetic requirement and decrease pain during the early postoperative period. In a double-blind, placebo-controlled study involving 90 healthy ASA physical status I or II children undergoing bilateral myringotomy, we compared the postoperative analgesic effects of oral acetaminophen and ketorolac, when administered 30 min before induction of anaesthesia. Patients were randomized to receive saline (0.1 ml.kg-1), acetaminophen (10 mg.kg-1) or ketorolac (1 mg.kg-1) diluted in cherry syrup to a total volume of 5 ml. Anaesthesia was induced and maintained with halothane and nitrous oxide via a face mask. Postoperative pain was assessed by a blinded observer using an objective pain scale. The three study groups were similar with respect to demographic data, duration of anaesthesia and surgery, induction behaviour, oxygen saturation, incidence of postoperative emesis and, recovery times. The ketorolac group had lower postoperative pain scores and required less frequent analgesic therapy in the early postoperative period compared with the acetaminophen and placebo groups. In contrast, there were no differences in pain scores or analgesic requirements between the acetaminophen and the placebo groups. We conclude that the preoperative administration of oral ketorolac, but not acetaminophen, provided better postoperative pain control than placebo in children undergoing bilateral myringotomy.     

Mutational screening of the RB1 gene in Indian patients with retinoblastoma reveals eight novel and several recurrent mutations

Retinoblastoma is the most common primary intraocular malignancy in children, caused by inactivation of the RB1 gene on chromosome 13. We carried out a mutational screen of the exons and promoter of the RB1 gene in Indian patients with retinoblastoma in order to determine the range of mutations giving rise to disease. Forty-seven patients were screened for mutations in all exons and promoter of the RB1 gene by single strand conformation polymorphism followed by sequencing. Tumors were available from 27 patients (12 bilateral and 15 unilateral retinoblastoma) while only peripheral blood was available from 20 patients, all with bilateral disease. Mutations were found in 22 patients, 9 from the analysis of tumors and 13 from peripheral blood. Eight novel mutations were identified, including 4 single base changes, 2 small deletions and 1 duplication. These are g.64365T>G (Tyr325Ter), g.78131G>A (Trp515Ter), g.150061G>T (Glu587Ter), g.170383C>G (S834X), g.41924A>C (IVS3-2A>C), g.150064ins4, g.160792del22, and g.76940del14 (IVS15 del +20-33). Almost all mutations produced nonsense codons or frameshifts. Recurrent mutations, especially at CpG sites were seen predominantly. Detectable mutations in exons were found in 46% of patients tested. Large deletions, epigenetic changes as well as mutations in non-coding regions may be the cause of disease in the remainder of patients. Knowledge of the full range of mutations can aid in the design of screening tests for individuals at risk.