Biomechanical comparison of occipitoatlantal screw fixation techniques

OBJECT: The stability provided by 3 occipitoatlantal fixation techniques (occiput [Oc]-C1 transarticular screws, occipital keel screws rigidly interconnected with C-1 lateral mass screws, and suboccipital/sublaminar wired contoured rod) were compared. METHODS: Seven human cadaveric specimens received transarticular screws and 7 received occipital keel-C1 lateral mass screws. All specimens later underwent contoured rod fixation. All conditions were studied with and without placement of a structural graft wired between the skull base and C-1 lamina. Specimens were loaded quasistatically using pure moments to induce flexion, extension, lateral bending, and axial rotation while recording segmental motion optoelectronically. Flexibility was measured immediately postoperatively and after 10,000 cycles of fatigue. RESULTS: Application of Oc-C1 transarticular screws, with a wired graft, reduced the mean range of motion (ROM) to 3% of normal. Occipital keel-C1 lateral mass screws (also with graft) offered less stability than transarticular screws during extension and lateral bending (p < 0.02), reducing ROM to 17% of normal. The wired contoured rod reduced motion to 31% of normal, providing significantly less stability than either screw fixation technique. Fatigue increased motion in constructs fitted with transarticular screws, keel screws/lateral mass screw constructs, and contoured wired rods, by means of 19, 5, and 26%, respectively. In all constructs, adding a structural graft significantly improved stability, but the extent depended on the loading direction. CONCLUSIONS: Assuming the presence of mild C1-2 instability, Oc-C1 transarticular screws and occipital keel-C1 lateral mass screws are approximately equivalent in performance for occipitoatlantal stabilization in promoting fusion. A posteriorly wired contoured rod is less likely to provide a good fusion environment because of less stabilizing potential and a greater likelihood of loosening with fatigue.     

Biomechanical comparison of anterior cervical plating and combined anterior/lateral mass plating.

BACKGROUND CONTEXT: Previous studies showed anterior plates of older design to be inadequate for stabilizing the cervical spine in all loading directions. No studies have investigated enhancement in stability obtained by combining anterior and posterior plates. PURPOSE: To determine which modes of loading are stabilized by anterior plating after a cervical burst fracture and to determine whether adding posterior plating further significantly stabilizes the construct. STUDY DESIGN/SETTING: A repeated-measures in vitro biomechanical flexibility experiment was performed to investigate how surgical destabilization and subsequent addition of hardware components alter spinal stability. PATIENT SAMPLE: Six human cadaveric specimens were studied. OUTCOME MEASURES: Angular range of motion (ROM) and neutral zone (NZ) were quantified during flexion, extension, lateral bending, and axial rotation. METHODS: Nonconstraining, nondestructive torques were applied while recording three-dimensional motion optoelectronically. Specimens were tested intact, destabilized by simulated burst fracture with posterior distraction, plated anteriorly with a unicortical locking system, and plated with a combined anterior/posterior construct. RESULTS: The anterior plate significantly (p<.05) reduced the ROM relative to normal in all modes of loading and significantly reduced the NZ in flexion and extension. Addition of the posterior plates further significantly reduced the ROM in all modes of loading and reduced the NZ in lateral bending. CONCLUSIONS: Anterior plating systems are capable of substantially stabilizing the cervical spine in all modes of loading after a burst fracture. The combined approach adds significant stability over anterior plating alone in treating this injury but may be unnecessary clinically. Further study is needed to assess the added clinical benefits of the combined approach and associated risks.     

Endoscopic pelvic osteotomy for the treatment of hip dysplasia.

Adolescent and adult hip dysplasia can be surgically treated by rotating the acetabulum into a better weight-supporting position; however, open pelvic osteotomies are among the most invasive of all pediatric orthopaedic procedures. Endoscopic pelvic osteotomy offers the theoretical advantages of magnified visualization of the bone cuts, minimized surgical dissection, and rapid postoperative recovery. The technique of endoscopically assisted triple innominate osteotomy requires the combination of endoscopic skills and facility with more standard surgical approaches.     

Combination cisplatin, 5-fluorouracil and radiation therapy for locally advanced unresectable or medically unfit bladder cancer cases: a Southwest Oncology Group Study

PURPOSE: Patients with locally advanced bladder cancer or who are not medically fit for surgery are a therapeutic dilemma. Radiotherapy with or without single agent cisplatin has been the major therapeutic modality. A phase II Southwest Oncology Group trial investigated the efficacy and feasibility of 5-fluorouracil, cisplatin and radiation in this patient subset. MATERIALS AND METHODS: Eligible patients had muscle invasive bladder cancer (clinical stages T2-T4) with nodal involvement at or below the level of bifurcation of the iliac vessels, were medically or surgically inoperable, or refused cystectomy. Patients underwent pretreatment cystoscopy and detailed tumor mapping, and were treated with 75 mg. /m.2 cisplatin on day 1 and 1 gm./m.2 daily, 5-fluorouracil on days 1 to 4 and definitive radiotherapy. Chemotherapy was repeated every 28 days, twice during and twice after radiation. RESULTS: From October 1993 to April 1998, 60 patients were enrolled in study. Of the 56 eligible patients 34% had unresectable tumors, 21% were not medically fit for surgery and 45% refused cystectomy. Overall, 68% of the patients had clinical T3 tumors or greater and 22% had nodal metastasis. Treatment was completed as planned in 32 of 56 (57%) patients. The most frequent grade 3 or 4 toxicities were neutropenia, stomatitis or mucositis, diarrhea, neuropathy and nausea. There were 53 patients who were evaluable for response, although response was not determined for 18. The overall response rate was 51% (95% confidence interval [CI] 37 to 65) based on intent to treat with a complete response rate of 49% (95% CI 35 to 63). Estimated median survival of the 56 patients was 27 months (95% CI 21 to 40 months) with an overall 5-year survival of 32%. The 5-year survival of the 25 patients who refused surgery was 45%. CONCLUSIONS: Concurrent 5-fluorouracil, cisplatin and radiation therapy is feasible. Despite a promising complete response rate, the overall 5-year survival suggests the need for more effective systemic therapy. The 5-year survival of patients who refused cystectomy suggests that this combined modality may provide another alternative to cystectomy for these patients.     

Accelerating the washout of inhalational anesthetics from the Dräger Primus anesthetic workstation: effect of exchangeable internal components

BACKGROUND: To establish guidelines for the preparation of the Primus anesthetic workstation (Dr?ger, Lübeck, Germany) for malignant hyperthermia-susceptible patients, the authors evaluated the effect of replacing the workstation's exchangeable internal components on the washout of isoflurane. METHODS: Primus workstations were exposed to isoflurane, and contaminated internal components were replaced as follows: group 1, no replacement; group 2, new ventilator diaphragm; group 3, autoclaved ventilator diaphragm; group 4, autoclaved integrated breathing system; group 5, flushed integrated breathing system; group 6, autoclaved ventilator diaphragm and integrated breathing system. The fresh gas flow was set at 10 l/min, and subsequently reduced to 3 l/min when a concentration of 5 ppm was achieved. Isoflurane concentration was measured in the inspiratory limb of the circle circuit every minute. RESULTS: Washout times for isoflurane decreased in the following order: group 1 (67 +/- 6.5 min) > groups 2 and 3 (50 +/- 4.1 and 50 +/- 5.7 min, respectively) > group 5 (43 +/- 9.5 min) > group 4 (12 +/- 1.5 min) > group 6 (3.2 +/- 0.4 min). Isoflurane concentration increased approximately threefold when the fresh gas flow was reduced to 3 l/min. CONCLUSION: Washout of isoflurane increased 20-fold with the use of an autoclaved ventilator diaphragm and integrated breathing system. To prepare the Primus for malignant hyperthermia-susceptible patients, the authors recommend replacing the ventilator diaphragm and integrated breathing system with autoclaved components, flushing the workstation for 5 min at a fresh gas flow of 10 l/min, and maintaining this flow for the duration of anesthesia.     

The frequency and clinical significance of congenital defects of the posterior and anterior arch of the atlas

OBJECT: In this study the authors investigated the anatomical, clinical, and imaging features as well as incidence of congenital defects of the C-1 arch. METHODS: The records of 1104 patients who presented with various medical problems during the time between January 2006 and December 2006 were reviewed retrospectively. The craniocervical computed tomography (CT) scans obtained in these patients were evaluated to define the incidence of congenital defects of the posterior arch of C-1. In addition, 166 dried C-1 specimens and 84 fresh human cadaveric cervical spine segments were evaluated for anomalies of the C-1 arch. RESULTS: Altogether, 40 anomalies (2.95%) were found in 1354 evaluated cases. Of the 1104 patients in whom CT scans were acquired, 37 (3.35%) had congenital defects of the posterior arch of the atlas. The incidence of each anomaly was as follows: Type A, 29 (2.6%); Type B, six (0.54%); and Type E, two (0.18%). There were no Type C or D defects. One patient (0.09%) had an anterior arch cleft. None of the reviewed patients had neurological deficits or required surgical intervention for their anomalies. Three cases of Type A posterior arch anomalies were present in the cadaveric specimens. CONCLUSIONS: Most congenital anomalies of the atlantal arch are found incidentally in asymptomatic patients. Congenital defects of the posterior arch are more common than defects of the anterior arch.     

The influence of esmolol on the dose of propofol required for induction of anaesthesia

Cardiac output may be an important determinant of the induction dose of intravenous anaesthetic. Esmolol is known to reduce cardiac output, and we examined its effect on the propofol dose required for induction of anaesthesia. The size of the effect seen with esmolol was compared with midazolam co-induction. Sixty patients were randomly allocated to placebo (saline), esmolol (1mg x kg(-1) bolus, followed by an infusion at 250 microg x kg(-1)min(-1)) or midazolam (0.04 mg x kg(-1)) groups. Induction of anaesthesia commenced 3 min following the administration of the study drug, using a Diprifusor set to achieve plasma propofol concentrations of 10 microg x ml(-1) at 5 min. The primary end point used was the propofol dose per kg at loss of response to command. The mean (SD) propofol dose for each group was 2.38 (0.48) mg x kg(-1) for placebo, 1.79 (0.36) mg x kg(-1) for esmolol and 1.34 (0.35) mg x kg(-1) for midazolam (all means significantly different; p < 0.0005). We found that predosing with esmolol reduces the propofol requirements for induction of anaesthesia by 25%.     

Femoral component revision using an extensively hydroxyapatite-coated stem

Femoral component revisions with extensively coated stems have shown promising clinical results, although concerns over stress shielding still exist. We retrospectively reviewed 59 patients undergoing femoral component revision with an extensively hydroxyapatite (HA)-coated stem. The average length of follow-up was 3.3 years (range, 2-5 years). The average preoperative Harris Hip Score was 43 points, which improved to 86 points at the latest follow-up (P < .01). The overall mechanical failure rate was 2%. No evidence of stress shielding was seen in 78% of patients. The clinical results of this series using an extensively HA-coated stem are similar to those using an extensively porous-coated stem. Long-term follow-up is required to determine if an extensively HA-coated implant will be superior to an extensively porous-coated implant with regard to stress shielding.