Open versus closed halo rings: comparison of fixation strengths.

STUDY DESIGN AND OBJECTIVE: A mechanical skull model was used to compare axial loads to failure for three marketed and one experimental halo ring. SUMMARY OF BACKGROUND DATA: Open-back halo rings have become increasingly popular; however, to the authors' best knowledge the literature provides no comparison of the fixation strength of an open-back halo versus the traditional closed design. METHODS: A model biomechanically similar to a human skull was used to compare the axial force necessary to distract each of four halo rings to failure. Three clinically used halo rings were compared: a closed titanium ring, an open titanium ring, and an open graphite ring. One additional open titanium halo ring was constructed with an angular profile; this ring was compared with the clinically used halos. RESULTS: The mean force to failure for the closed titanium ring significantly exceeded that for the open rings (P < 0.005). No significant differences were noted among the open halo rings. DISCUSSION: The data obtained by use of this biomechanical model show that the closed halo ring provides distraction strength greater than that of the open rings, suggesting a more rigid system with the closed device. Use of an angular halo did not improve fixation strength in the open ring device. These findings may support use of a closed halo ring in cervical spine traction and immobilization, if this greater strength is shown to be sufficiently clinically important to offset any disadvantages of a closed ring.

Penetration of cranial inner table with Gardner-Wells tongs.

The compression force exerted by Gardner-Wells tongs was compared with the force necessary to penetrate the cranial inner table with a Gardner-Wells tong pin. Load cells measured the force exerted by the spring-loaded Gardner-Wells tong pin on fresh cadaveric skull samples. Increasing forces were exerted until penetration of the inner table occurred. At the manufacturer's recommended, 1 mm indicator stem protrusion an average of 30 pounds of compressive force was exerted by the spring-loaded pin. The average force necessary to penetrate the inner table with the cadaveric specimens with the tong pin was 162 pounds. The force necessary to penetrate the inner table of the skull well exceeds that exerted by properly applied tongs, suggesting that the risk of inner table penetration is low.

Early failure of Pavlik harness treatment for developmental hip dysplasia: clinical and ultrasound predictors.

A cohort of 93 patients with developmental dysplasia of the hip (DDH) treated with a Pavlik harness were evaluated to determine predictors of treatment failure. Failure was defined as failure to achieve or maintain hip reduction in the Pavlik harness. Of 93 patients (137 hips), 17 (26 hips) failed Pavlik harness treatment. Univariate risk factors for failure included bilaterality, initial clinical exam, and initial ultrasound (US) percent coverage. Clinical exam and initial percent coverage were multivariate risk factors for failure. Among initially clinically dislocatable hips, a low initial US alpha angle correlated with an increased likelihood of failure. All (6/6) patients with an initially irreducible hip and an initial coverage of <20% by US eventually failed treatment. Gender, side of pathology, and age at diagnosis and initiation of treatment did not correlate with failure. Irreducibility by physical exam combined with US coverage of <20% identified a patient group that uniformly failed Pavlik harness treatment. These patients may be candidates for alternative bracing, traction, or closed or open reduction.

A biomechanical comparison of Gardner-Wells tongs and halo device used for cervical spine traction.

SUMMARY OF BACKGROUND DATA: Unstable cervical spine fractures and dislocations are often reduced by the application of axial traction using a halo or Gardner-Wells tongs. Failure of tong or halo attachment can cause substantial morbidity and usually occurs at the pin-bone interface. Institutions commonly clean and reuse tongs. The effect of tong wear on pullout strength and the strength of the halo used as a traction device have not been documented. METHODS: A skull model biomechanically similar to human calvarium was used to compare the axial pullout strengths of four sets of new tongs, three sets of rarely used tongs, and one set of heavily used tongs, as well as a standard four-pin halo. RESULTS: The pullout strength of tongs tightened to the manufacturer's recommended level appeared to decrease with increased use. Measurement of the pin force generated by each set of tongs and of the spring constant of each spring, as well as inspection of the tongs after testing, suggested that the decrease in pull-out strength may be partly attributable to spring and/or pin wear. The pullout strength of the halo or of the new or slightly used tongs but not the heavily used tongs exceeded the maximum weight used clinically in cervical spine traction. CONCLUSION: The data suggest that consideration be given to replacement or recalibration of heavily used tongs.

The effects of bone cement powder on human adherent monocytes/macrophages in vitro.

This study reports the effects of Simplex bone cement powder (BC) on the proliferation and production of bone resorbing factors in vitro by human adherent monocytes/macrophages. Adherent peripheral blood cells were isolated from seven healthy individuals and exposed to a dispersion of BC powder (1 mg/mL), phytohemagglutinin (PHA, 40 micrograms/mL), or medium alone at different periods of cell incubation (days 0-2, 0-7, 5-7, or 10-12). Cell proliferation was quantified by incorporation of 3H-thymidine uptake. Culture supernatants were evaluated for levels of interleukin 1-like activity (IL-1) by murine thymocyte proliferation assay, prostaglandin E2 (PGE2) by radioimmunoassay, lysosomal enzyme activity (N-acetyl-beta-D-glucosaminidase and beta-glucuronidase using fluorometry, and collagen and casein degrading activity using radioactive substrates. Human adherent peripheral blood cells showed a proliferative response to PHA that coincided with cell maturation; BC did not inhibit PHA-induced cell proliferation of either adherent or nonadherent blood cells, indicating the non-toxic nature of these particles at the concentrations tested. BC stimulated increased release of the lysosomal enzyme N-acetyl-beta-D-glucosaminidase; the levels of PGE2, IL-1, collagenase, and caseinase were unchanged.

The effect of valvulotomy on the flow rate through the saphenous vein graft: clinical implications.

Potential differences in flow rates between reversed and in situ saphenous vein bypass grafts were evaluated. One hundred ten greater saphenous vein segments containing isolated valves were examined with fiber-optic angioscopy during pulsatile and nonpulsatile flow. Valve competency was determined, and the degree of luminal obstruction caused by the valve during reversed flow was calculated with caliper measurements of the video image. Flow measurements were obtained before and after valvulotomy, in reversed and nonreversed vein orientations. Increased flow rates occurred during pulsatile irrigation only, after valvulotomy in vein segments with diameters less than 2.5 mm (p less than 0.001, Bonferroni t test). In these small-diameter vein segments, the flow rate in reversed valve-intact vein was 94.4 +/- 28.9 ml/min (mean +/- 1 standard deviation), the flow rate in reversed valve-disrupted vein was 136.4 +/- 36.5 ml/min, and the flow rate in nonreversed valve-disrupted vein was 137.8 +/- 31.3 ml/min. In 22 vein segments, luminal obstruction caused by the intact valve was measured angioscopically. A small valve orifice was found to be related to a large increase in flow rate after valvulotomy (p less than 0.02, least-squares regression). In addition, veins with diameters less than 2.5 mm have significantly smaller valve orifices compared with veins with diameters greater than 2.5 mm. These results present important clinical implications as the number of distal extremity reconstructions increases.

The effects of buspirone on sleep in the rat.

Buspirone is a novel anxiolytic compound that does not produce the sedation often associated with the use of benzodiazepines. The present study evaluated the effects of this anxiolytic on sleep in rats surgically prepared for long-term recordings. Buspirone, at a dose of 3 mg/kg i.p., produced a significant increase in total wake time (P less than 0.05) compared with drug-free controls. At a dose of 10 mg/kg i.p., rats displayed altered sleep patterns with the most significant effects observed in the first third of recording period. These animals displayed increased wakefulness (P less than 0.001), decreased non-REM sleep (P less than 0.001), and an obliteration of REM sleep (P less than 0.02). These data support the suggestion that the clinically useful anxiolytic buspirone, unlike the benzodiazepines, does not induce sleep.