Use of adhesive cranial bone flap fixation without hardware to improve mechanical strength, resist cerebrospinal fluid leakage, and maintain anatomical alignment: a laboratory study

OBJECTIVE

Titanium plates and screws (TPS) are the current standard of care for fixation of cranial bone flaps. These materials have been used for decades but have known potential complications, including flap migration, bone resorption/incomplete osseous union, hardware protrusion, cosmetic deformity, wound infection/dehiscence, and cerebrospinal fluid (CSF) leakage. This study evaluated the efficacy of a novel mineral-organic bone adhesive (Tetranite) for cranial bone flap fixation.

METHODS

Craniotomy bone flaps created in human cadaveric skulls were tested under quasistatic and impact loading in the following conditions: 1) uncut skull; 2) bone flaps fixated with TPS alone; and 3) bone flaps fixated with bone adhesive alone. All fixative surgical procedures were performed by a group of 16 neurosurgeons in a simulated surgical environment. The position of adhesive-fixated cranial bone flaps was measured using computed tomography and compared with their original native location. The resistance of adhesive-fixated cranial bone flaps to simulated CSF leakage was also evaluated. Because there was a gap around the circumference of the TPS-fixated specimens that was visible to the naked eye, pressurized CSF leak testing was not attempted on them.

RESULTS

Adhesive-fixated bone flaps showed significantly stiffer and stronger quasistatic responses than TPS-fixated specimens. The strength and stiffness of the adhesive-fixated specimens were not significantly different from those of the uncut native skulls. Total and plastic deflections under 6-J impact were significantly less for adhesive-fixed bone flaps than TPS. There were no significant differences in any subthreshold impact metrics between the adhesive-fixed and native specimens at both 6-J and 12-J impact levels, with 1 exception. Plastic deflection at 6-J impact was significantly less in adhesive-fixated bone flaps than in native specimens. The energy to failure of the adhesive-fixated specimens was not significantly different from that of the native specimens. Time since fixation (20 minutes vs 10 days) did not significantly affect the impact failure properties of the adhesive-fixated specimens. Of the 16 adhesive-fixated craniotomy specimens tested, 14 did not leak at pressures as high as 40 mm Hg.

CONCLUSIONS

The neurosurgeons in this study had no prior exposure or experience with the bone adhesive. Despite this, improved resistance to CSF egress, superior mechanical properties, and better cosmetic outcomes were demonstrated with bone adhesive compared with TPS.

Impact of capacity reductions in acute public-sector inpatient psychiatric services

OBJECTIVE

This study tested the hypothesis that reductions in acute public-sector psychiatric inpatient capacity in a major urban area would be associated with negative impacts on patients and the community.

METHODS

The impact of two discrete service changes that reduced acute inpatient capacity by 50% in a single public-sector general hospital setting was examined. Indicators of impact were obtained from existing administrative databases for a 33-month period. Indicators included measures of utilization and case mix on the acute inpatient and psychiatric emergency services, suicides among community mental health clients, and psychiatric evaluations conducted in county jails.

RESULTS

Reductions in inpatient capacity were not associated with hypothesized negative impacts, such as increased demand for psychiatric emergency services, decreased access to emergency or inpatient services, or increased recidivism to inpatient care. Similarly, neither the number of suicides among community mental health clients nor the number of jail psychiatric evaluations increased after capacity reduction.

CONCLUSIONS

Data from a single urban public-sector setting suggest that acute inpatient psychiatric capacity may be reduced without negative impacts on patients or the community. In this setting, collaboration between inpatient and outpatient providers to speed discharge facilitated reductions in inpatient length of stay that made it possible to serve the same number of patients with fewer resources. Other service system adjustments may be more appropriate in other settings, and alternative approaches to reducing utilization of high-cost inpatient care warrant examination.

Stretch-associated injury in cervical spondylotic myelopathy: new concept and review

The simple pathoanatomic concept that a narrowed spinal canal causes compression of the enclosed cord, leading to local tissue ischemia, injury, and neurological impairment, fails to explain the entire spectrum of clinical findings observed in cervical spondylotic myelopathy. A growing body of evidence indicates that spondylotic narrowing of the spinal canal and abnormal or excessive motion of the cervical spine results in increased strain and shear forces that cause localized axonal injury within the spinal cord. During normal motion, significant axial strains occur in the cervical spinal cord. At the cervicothoracic junction, where flexion is greatest, the spinal cord stretches 24% of its length. This causes local spinal cord strain. In the presence of pathological displacement, strain can exceed the material properties of the spinal cord and cause transient or permanent neurological injury. Stretch-associated injury is now widely accepted as the principal etiological factor of myelopathy in experimental models of neural injury, tethered cord syndrome, and diffuse axonal injury. Axonal injury reproducibly occurs at sites of maximal tensile loading in a well-defined sequence of intracellular events: myelin stretch injury, altered axolemmal permeability, calcium entry, cytoskeletal collapse, compaction of neurofilaments and microtubules, disruption of anterograde axonal transport, accumulation of organelles, axon retraction bulb formation, and secondary axotomy. Stretch and shear forces generated within the spinal cord seem to be important factors in the pathogenesis of cervical spondylotic myelopathy.

Rotational stability of a spinal pedicle screw/rod system

Although the geometry of spinal instrumentation constructs may significantly affect efficacy, the variation in biomechanical data may not assist the clinician in an appropriate selection. The purpose of the present study was to quantify the effects of transverse fixators on rotational strength of a common pedicle-screw-with-rods system. Pedicle screws were mounted in blocks of polymethyl-methacrylate at angles to reproduce the configuration of placement in the human lumbar spine. Twenty cycles of +/- 12 N-m axial rotation moment was applied, and the steady-state response was used in the analysis. Configurations tested included both medial and lateral placement of longitudinal rods as well as the addition of one or two transverse rods. Up to a 20% difference in stiffness was noted between medial and lateral placement of longitudinal rods when no transverse rods were mounted. A maximum difference in flexibility of 6% was noted between the use of one and two transverse rods. For medially placed rods, a single transverse connector will add significant rotational stiffness even for shorter rod lengths; for laterally placed longitudinal rods, only the longer rod lengths need a transverse connector.

Role of catecholamines in regulating ovine median eminence blood flow

Blood flow was measured in the ovine median eminence and neural lobe before and after the intravenous infusion of dopamine (n = 7), the D1 agonist SKF 38393 (n = 4), the D2 agonist bromocriptine (n = 4), and the dopamine antagonist haloperidol (n = 5). It was also measured before and after the intracarotid infusion of dopamine into eight naive sheep and seven sheep pretreated with phenoxybenzamine. Radiolabeled microspheres were used to determine regional cerebral and regional neurohypophysial blood flows (RNHBF) in these 35 adult female sheep anesthetized with pentobarbital sodium. Samples for serum prolactin measurement by radioimmunoassay were obtained before and after drug infusion. Intravenous dopamine infusion did not change median eminence or neural lobe blood flow (RNHBF) but increased renal and choroid plexus blood flow. Intravenous haloperidol caused a significant fall in RNHBF and blood flow in choroid plexus, caudate nucleus, and kidneys. Intracarotid dopamine infusion decreased RNHBF but increased choroid plexus blood flow. RNHBF was significantly greater in the seven sheep pretreated with phenoxybenzamine than in the eight naive sheep. These findings do not support a role for dopamine in the regulation of median eminence blood flow. The last observation does add support to the hypothesis that norepinephrine or epinephrine interaction with alpha-receptors plays a role in the control of ovine median eminence blood flow and hence in the regulation of delivery of humoral messages from the brain to the anterior pituitary gland.

Breast cancer among women given X-ray therapy for acute postpartum mastitis

Acute postpartum mastitis (APM) is an inflammatory-infectious condition of the breast, occurring commonly at childbirth or during lactation. A series of 601 women who received x-ray therapy for APM during the 1940's or 1950's have been followed up by mail questionnaire, with medical verification of pertinent conditions, to ascertain their incidences of breast cancer. Control subjects consisted of a series with APM who did not receive irradiation, plus the female siblings of both the APM groups, for a total of 1,239 controls. The groups have been followed up to 45 years; the average was 29 years. The relative risk (RR) for breast cancer, adjusted for age and interval since irradiation (or an equivalent entry definition for controls), was 3.2 for the irradiated breasts; the 90% confidence interval (CI) was 2.3-4.3. For a linear multiplicative model, the risk increased by 0.4% per rad (90% Cl of 0.2-0.7). The dose-response curve appeared to be essentially linear, except for a diminution of risk at high doses (greater than or equal to 700 rad). The fact that there were no treated breasts with doses between 0 and 60 rad, however, means that it was not possible to evaluate the curvature with the maximum contrast between low and high doses. The dose fractionation analyses showed that neither the number of dose fractions, the number of days between fractions, nor the dose per fraction had any apparent effect on breast cancer risk when the variables were analyzed separately. Similarly, when the fractionation variables were considered jointly in a Cox regression analysis, none was significant once total breast dose was controlled for. Analyses of age at irradiation did not show appreciable differences between age groups, although the numbers were too small to be clear-cut (only 64 women greater than 34 yr old at irradiation). Other studies have shown diminished risk associated with an older age at irradiation. The lack of diminished risk in this study may occur because during pregnancy and lactation the breasts are under increased proliferative stimulation by hormones, by comparison with the normal condition of breasts at older ages. An analysis of the temporal relationship of radiation to breast cancer showed that the RR did not vary systematically with interval since irradiation, but the absolute risk increased over time. This finding agrees with other studies that have also suggested a better fit for the multiplicative model.

Thyroid tumors following thymus irradiation

About 2,650 persons who received X-ray treatment for purported enlarged thymuses in infancy and 4,800 sibling controls have been followed by mail questionnaire for an average of 29 years to observe their incidence of thyroid tumors. The follow-up rate in the latest survey was 88% in both groups. The radiation doses to the thyroid gland ranged from 5 to over 1,000 rad, with 62% receiving less than 50 rad. To date 30 thyroid cancers and 59 benign thyroid adenomas have been detected in the irradiated group, as compared with 1 thyroid cancer and 8 adenomas in the control group. The relative risks in the irradiated group were about 45 for thyroid cancer and 15 for benign thyroid adenomas. The dose-response curve for thyroid cancer was essentially linear, although a linear-quadratic curve could not be ruled out. For thyroid adenomas the risk per rad was somewhat greater at lower doses than at high doses. For both thyroid cancers and adenomas the absolute excess risk per rad was two to three times as great in females as males. Within the limitations imposed by the treatment regimens and the sample size, there was no indication of a "sparing" effect due to dose fractionation for either thyroid cancers or adenomas. There was an excess risk for both malignant and benign thyroid tumors for at least 40 years post irradiation. For thyroid cancer the radiogenic risk appeared to be additive with respect to time, rather than the age-specific natural rates of cancer being multiplied.

The pathology of breast cancer in women irradiated for acute postpartum mastitis

The gross and microscopic pathology of breast cancers in women irradiated for acute postpartum mastitis was compared to the breast cancers found in the sisters of the irradiated women. Fifty-one cancers in 50 irradiated women and 25 cancers in 24 nonirradiated women were examined. In considering the lesions in the two populations, the size, location, histologic type, histologic grade, inflammatory response, lymphatic and blood vascular invasion, nipple involvement, axillary lymph node metastases, and menopausal status at the time of diagnosis were statistically indistinguishable. The only parameter that was different in the two populations was the desmoplastic response to the malignant lesion (P = 0.04). The control population had more marked fibrosis within the cancers compared with the irradiated women. With the exception of stromal response, this study shows that breast cancer in irradiated women is similar in the parameters evaluated to breast cancer in a control population.

Morbidity and mortality among recipients of blood from preleukemic and prelymphomatous donors

The present investigation was designed to test the admittedly speculative hypothesis that a factor involved in the etiology of human lymphatic and hematopoietic neoplasms may be transmitted by blood transfusion prior to the clinical onset of illness in the donor. One hundred and five New York State residents, who received blood from donors who subsequently developed neoplasms of the lymphatic or hematopoietic tissues, were identified and followed for an average period of 7.05 years. No recipient was found to have developed a leukemia or lymphoma following receipt of blood from a preleukemic or prelymphomatous donor. The results of this study should be considered priliminary because the small size of the recipient group might mask even a large increase in risk among the recipients.