Building a Better Forecast: Reformulating the Ensemble Kalman Filter for Improved Applications to Volcano Deformation.

As the volume of data collected at monitored volcanoes continues to expand, researchers will need quick, reliable, and automated methods of inverting those data into useful models of the underlying magma systems. Recently adapted from other fields for use in volcanology, the Ensemble Kalman Filter (EnKF) is one such inversion technique that has been used to produce several successful forecasts and hind-casts of volcanic unrest, correlating geodetic deformation with mechanical stresses around the magma reservoir. However, given the similarity in which changes to a reservoir's size and pressure are expressed at the surface, the filter can have trouble fully resolving magmatic conditions. In this study, we therefore test several different published variations of the EnKF workflow to produce an optimal configuration for use in future forecasting efforts. By generating synthetic observations of ground deformation under known conditions and then assimilating them through different implementations of the EnKF, we find that many variants favored in other fields underperform for this specific application. We conclude that correlations between model parameters that develop within the EnKF's Monte Carlo ensemble distort the filter's ability to correctly update the model state, causing the filter to systematically favor changes in some parameters over others and ultimately converge to a partially inaccurate solution. This effect can be somewhat mitigated by interrupting these parameter correlations, and the filter remains sensitive to many aspects of the magma system regardless. However, further research and novel approaches will be needed to truly optimize the EnKF for use in volcanology.

Use of carbon fibers for repair of abdominal-wall defects in rats.

Carbon in the form of 8-micron fibers induces growth of connective tissue. The purpose of this study was to measure and histologically characterize tissue ingrowth occurring in carbon fibers implanted for up to 12 months in abdominal-wall defects in rats, compared with polypropylene mesh. Carbon fibers induced significantly more tissue ingrowth than polypropylene mesh at 6 to 12 months postoperatively. The predominant tissues associated with carbon fibers and polypropylene mesh were dense connective tissue and fat, respectively. Fragmentation of the implants did not occur, and implant debris was not found in the regional lymph nodes. Carbon fibers are potentially useful for reinforcing abdominal-wall defects.

The use of one compared with two distal screws in the treatment of femoral shaft fractures with interlocking intramedullary nailing. A clinical and biomechanical analysis.

The torsional and compressive biomechanical characteristics of a system for intramedullary fixation with a slotted locking nail and either one or two distal locking screws were evaluated in sixteen femora obtained from eight cadavera. No significant difference was found in the torsional rigidity or axial load to failure when one as opposed to two distal screws had been used. We also managed twenty-seven patients who had a fracture of the femoral shaft with interlocking fixation, using only a single distal screw for distal fixation. The average duration of follow-up was nine months (range, three to twenty-five months). The average time to radiographic healing was three months (range, two to six and one-half months). There were no non-unions or failures of the implant. Clinically unimportant migration of the distal screw occurred in five patients. We concluded that one distal screw provides adequate distal fixation of fractures of the femoral shaft treated with interlocking intramedullary nailing.

Atlanto-axial fusion for instability.

The problem of how best to treat a patient with instability of the atlanto-axial complex is still somewhat controversial. In this follow-up study of fifty-nine patients, nineteen were treated by a plaster jacket and brace; eleven, by single midline wiring and onlay bone grafts; and thirty, by four circumferential wires around the posterior elements of the axis and atlas with two bone grafts wedged between these elements on each side according to the method described by Brooks and Jenkins. (One patient had both types of fusion.) Although direct comparison of the results of treatment in three groups was not possible because of the many variables that may have influenced the results, the incidence of solid fusion was distinctly higher after the Brooks fusions despite less postoperative immobilization.

Cervical facet fusion for control of instability following laminectomy.

Cervical laminectomy may compromise the stability of the spine. Posterolateral facet fusion can be used to stabilize the spine after laminectomy and prevent progressive deformity. The procedure includes passing wires through drill holes in the articular processes and binding two longitudinal struts of bone to the posterior columns of the articular processes. Sixty-three p atients with cervical laminectomy and facet fusion were reviewed, and fifty-two of them were followed for one to seventeen years. The reasons for fusion were to control overt spinal instability and deformity or to eliminate motion which may contribute to spondylosis. Solid fusion occurred in fifty of fifty-two patients at a mean of 6.5 months and provided continuing stability without progressive deformity. Although facet fusion is a complex procedure, it provides secure stabilization, does not interfere with decompression, and permits early mobilization of the patient.

Biomechanical study of C1-C2 posterior arthrodesis techniques.

Fifteen cervical spines from cadavers were used to compare the rotational and translational stability of the Brooks fusion, a fusion construct using Halifax interlaminar clamps, and the Gallie fusion. The Brooks and Halifax clamp constructs exhibited significantly greater rotational and translational stiffness than the Gallie construct (P < 0.001). The Halifax clamp construct exhibited greater rotational stiffness and equal translational stiffness when compared with the Brooks construct (P < 0.05). The Brooks and Halifax fixation constructs provided superior fixation but presented technical challenges. The Gallie construct is less technically demanding but provides less stable fixation.

Anterior screw fixation of type II odontoid fractures. A biomechanical study.

STUDY DESIGN: This study examined the torsional and shear stiffness of Type II odontoid fractures that were stabilized with two 3.5-mm cannulated AO screws or a single 4.5-mm cannulated Herbert screw. OBJECTIVE: To determine the stability of a commonly used two-screw method versus a single-screw fixation method. Insertion of a single screw could make the procedure technically easier. SUMMARY OF BACKGROUND DATA: Biomechanical studies have shown the 4.5-mm Herbert screw to generate greater compressive forces than 3.5-mm cannulated screws, which are commonly used to anteriorly stabilize Type II odontoid fractures. No previous biomechanical studies have compared the shear or torsional stiffness of Type II odontoid fractures stabilized with these screws. METHODS: Twelve cadaver C2 vertebrae were harvested and an osteotomy was performed to simulate a Type II fracture pattern. Six were stabilized with two 3.5-mm cannulated screws, and the remaining were stabilized with a single 4.5-mm cannulated Herbert screw. Each specimen then was tested in torsion through +/- 0.75 degrees, +/- 1.25 degrees, and +/- 1.75 degrees for 10 cycles each. Shear forces then were applied from an anterior to posterior direction to a maximum load of 44.48 N. RESULTS: The mean torsional stiffness for the Herbert screw was 1196 N.m/deg, which was significantly greater than the mean stiffness of the 3.5-mm screw fixation, which measured 434 N.m/deg. The mean shear stiffness for the Herbert screw fixation was 106.9 kN/m, compared to 86.1 kN/m for the 3.5-mm cannulated screw. This was not statistically significant. CONCLUSIONS: The biomechanical properties of the 4.5-mm cannulated Herbert screw suggest it may lend itself for use in fixation of Type II odontoid fractures. With only a single screw to insert, this technically demanding procedure may be less daunting.

Mechanical stability of thoracolumbar pedicle screw fixation. The effect of crosslinks.

STUDY DESIGN: Pedicle screw fixation for unstable thoracolumbar spine injuries is relatively new. The effect of one or two crosslinks on rotational and lateral bending stiffness was studied. OBJECTIVE: To determine the rotational and bending stiffness values of thoracolumbar fractures fixed by the AO's internal fixation system with zero, one, or two crosslinks. METHODS: Eight embalmed thoracolumbar spine segments. (T12-L2) were instrumented at T12 and L2 with a pedicle screw-rod system. Rotational stiffness was determined for 10 cycles to 2.5 degrees, 3.5 degrees, and 5 degrees of rotation, with and without one or two crosslinks, and lateral bending stiffness for 10 cycles to 0.25, 0.40, and 0.50 inch. The results showed a clear trend toward increased stiffness with crosslinks. RESULTS: The stiffness values of the two-crosslink construct at 2.5 degrees and 3.5 degrees of rotation were significantly higher than those of the zero-crosslink system. Also, the bending stiffness of the two-crosslink construct was significantly higher than that of no-crosslink system at all of the displacements. CONCLUSIONS: Rotational stiffness values of the two-crosslink construct were significantly higher than those of the zero-crosslink system, at 2.5 degrees and 3.5 degrees of rotation. Lateral bending stiffness of the two-crosslink system was higher than that of the zero-crosslink system at all levels of displacement.

Modification of the L'Episcopo procedure for brachial plexus birth palsies.

We reviewed 19 children who had undergone a new modification of the L'Episcopo procedure for obstetric brachial plexus palsy. Through an axillary approach the latissimus dorsi tendon was re-routed anteriorly to the humerus and then anastomosed to the teres major tendon routed posteriorly. At an average follow-up of four years two months, the mean increase in shoulder abduction was 26 degrees and the mean increase in external rotation was 29 degrees. No neurovascular injury or postoperative infection occurred. Two patients had complications, and five did not gain from the procedure. The modified operation was relatively easier to perform and provided excellent cosmesis.

Biomechanical study of atlantoaxial arthrodesis: transarticular screw fixation versus modified Brooks posterior wiring.

OBJECTIVE: The purpose of the present study was to compare the biomechanical stability of C1 and C2 vertebrae after treatment of ligamentous instability by either modified Brooks posterior wiring (MB) or transarticular screw (TAS) techniques. We hypothesized that the TAS technique would be more stable because of direct fixation through the facet joints. STUDY DESIGN: We studied the in vitro stability (arthrodesis) of TAS fixation of C1 and C2 versus that of MB. TAS fixation involves placing screws across the facets from posteriorly at C2 to the anterior surface of C1, plus a bone graft and posterior wiring of C1 and C2. METHODS: Cervical spines from nine individuals with an average age of sixty-two years (range 51 to 71 years) were harvested from cadavers (six male, three female). C1 and the segment from C2 to C5 were potted to allow motion only at the C1-C2 articulation. The specimens were destabilized by cutting the transverse ligament on both sides of the odontoid and the tectorial membrane between C1 and C2. The MB and TAS techniques were performed by methods similar to those described in the literature. The stiffness of the C1-C2 articulation of each specimen was tested under rotation, lateral bending, flexion, and anterior translation in random order. Intact and destabilized specimens fixed with either MB or TAS were tested in sequence. RESULTS: Significantly higher stiffness values in the elastic zone were obtained with the TAS technique than with the MB technique for all modes of testing (p < 0.002, t test). Values for the neutral zone (the region where minimal loads produce displacement) were not significantly different between the MB and TAS techniques (p > 0.1, t test). CONCLUSION: We conclude that stability is significantly enhanced by use of the TAS construct for treatment of ligamentous instability at the atlantoaxial joint for all motions tested in the present study.

Regulation of osteoblast levels during bone healing.

OBJECTIVE: To confirm the occurrence of programmed cell death of osteoblasts during bone healing and to evaluate the role of interleukin-1beta (IL-1beta) in regulating osteoblast concentration. STUDY DESIGN: Electron microscopic study of the response of rats to a controlled bone injury, and a randomized controlled study of the effect of IL-1beta administered continuously for three days. METHODS: A standardized defect (1.1 millimeter in diameter, 0.5 millimeter deep) was created unilaterally on the anteromedial surface of the tibia. In some animals, the injury site was recovered five days after operation and processed for ultrastructural evaluation of osteoblasts in the callus. In another group, IL-1beta was delivered to the bone defect using micro-osmotic pumps (0.5 nanograms/hour); control rats received vehicle only. The bones were recovered one to fourteen days after injury, and concentrations of proliferating cells, osteoblasts, and apoptotic bodies were determined. The amount of callus that formed in the defect was measured. RESULTS: Osteoblasts in the callus exhibited ultrastructural changes characteristic of cells undergoing apoptosis, including condensation of chromatin, membrane blebbing, formation of apoptotic bodies, and phagocytosis by nearby osteoblasts. Addition of IL-1beta significantly increased the number of osteoblasts at the injury site and significantly decreased the number of apoptotic bodies in relation to the number of osteoblasts. The amount of callus in the bone defect was not affected by IL-1beta treatment. CONCLUSION: The role of programmed cell death of osteoblasts as a normal concomitant of bone healing was confirmed. Evidence was found suggesting that IL-1beta mediated the appearance and disappearance of osteoblasts, possibly by affecting the rates of differentiation and apoptosis, respectively. Understanding these mechanisms conceivably could lead to the ability to control osteoblast levels at an injury site.

Autogenous bone grafting in clinical osteomyelitis and septic nonunion (the papineau technique).

The technique of extensive wound debridement and secondary use of autogenous cancellous bone chips can be used to salvage both septic nonunions and chronic osteomyelitis. The same technique may also be used to bridge large bony defects of traumatic origin. With time, the cancellous bone becomes completely incorporated and strengthens, allowing full use of the limb. There are few complications with the procedure. Nonunion may develop on occasion and require a closed bone graft once the wound is free of infection and closed. The major surgical principles are: 1) adequate debridement with removal of all infected tissue, 2) a viable base to support the graft, 3) the use of autogenous cancellous bone, 4) adequate immobilization, and 5) delayed wound closure.1-5.

Anatomic variations of the blood supply of the soleus muscle.

A total of 36 cadaver and fresh amputation specimens were studied by dissection. Two vascular patterns were identified--a segmental posterior tibial artery (Type 1) and a proximally dominant posterior tibial artery (Type 2). Type 1 was seen in 77.8% of cases, and Type 2 in 22.2%. Injection studies in five fresh specimens demonstrated numerous cross-connections between the two halves of the muscle. A distally based hemisoleus flap should not be performed when a Type 2 vascular pattern is encountered. Also, vascular cross-connections between the two halves of the soleus muscle should be preserved, when possible.

The effect of isometric graft posterior cruciate ligament reconstruction on anterior tibial translation.

Eight fresh-frozen cadaver knees were studied to evaluate whether an isometrically placed posterior cruciate ligament (PCL) graft restores normal posterior tibial translation without overconstraining anterior tibial translation. Each knee was tested with a three-axis load cell in the intact state, after PCL sectioning, and after PCL reconstruction. After PCL reconstruction, posterior tibial displacement was restored to values observed in the intact state for all flexion angles except 60 degrees and 90 degrees. Anterior tibial translation was not significantly changed for any of the three states. These results indicate isometric reconstruction of the PCL significantly reduces posterior tibial translation without overconstraining anterior tibial translation.