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Biomedical subjects

C E Johnston

Publications and source records attributed to C E Johnston.

At least 19 recordsLinked to original sources
PubMed1995

Effect of spinal construct stiffness on short segment fusion mass incorporation.

STUDY DESIGN: Three segment (L3-L5) pedicle screw constructs were implanted in caprine spines, and the resulting ankylosis evaluated mechanically and compared 12 weeks after surgery. OBJECTIVES: To determine if a construct of maximal stiffness could impair the biologic process of spinal arthrodesis by "stress-shielding." SUMMARY OF BACKGROUND DATA: Fusion mass stiffness is believed to be enhanced by increasing construct stiffness, although previous studies have used semirigid, nonconstrained constructs, which lose stiffness through cyclical loading. Device-related osteoporosis, reported to occur with stiff, constrained implants, may be more related to the presence of fusion induced by the implants rather than the implants themselves. METHODS: In 15 goats, L3-L5 segments were instrumented with pedicle screws, and four different diameters of rods (3.2 cm, 4.8 cm, 6.4 mm, and no rods) were implanted as longitudinal connections to vary the stiffness of the constructs. After 12 weeks, animals were killed and the segments were tested to determine their stiffness. RESULTS: In lateral bending, spines "fused" with rods (any size) were significantly stiffer (P = 0.03) than nonrodded spines. There was a trend toward stiffer segments with larger rods (4.8 cm or 6.4 mm) compared with 3.2 mm or no rods. There was a highly significant (P < 0.0001) increase in stiffness of all operated (rodded or nonrodded) segments compared with unoperated controls. CONCLUSIONS: The enhancement of segmental stiffness by stiffer constructs was confirmed, suggesting a beneficial effect on spinal arthrodesis by increasing stiffness. Stress shielding could not be shown.

Animals↗
PubMed1995

Three-dimensional analysis of clubfoot deformity by computed tomography.

The bony pathoanatomy of clubfoot has been assessed by a three dimensional reconstruction of transverse CT images obtained from 27 feet in children aged 3-10 years. Principal axes of the bones were determined to quantitate interosseous deformity, while visual inspection of the reconstructed images demonstrated intraosseous deformity. "Medial spin" and midfoot adduction were analyzed on the AP view of the foot ("top" view), while hindfoot pronosupination was analyzed on the AP view of the ankle (posterior view). This technique allows visualization of deformities which normally cannot be analyzed on plain radiographs, and also shows that a variety of interosseous relationships make up the clinical entity known as clubfoot. Abnormal talar pronation ("intorsion") was an unexpected finding of this three dimensional analysis.

Child↗
PubMed1995

Isolated effects of peripheral arm and central body cooling on arm performance.

BACKGROUND: Whole body cooling impairs manual arm performance. The independent contributions of local (peripheral) and/or whole body (central) cooling are not known. Therefore, a protocol was developed in which the arm and the rest of the body could be independently cooled. METHODS: Biceps temperature (Tmus), at a depth of 20 mm, and esophageal temperature (Tes) were measured. Six subjects were immersed to the clavicles in a tank (body tank) of water under 3 conditions: 1) cold body-cold arm (CB-CA); 2) warm body-cold arm (WB-CA); and 3) cold body-warm arm (CB-WA). In the latter two conditions, subjects placed their dominant arm in a separate (arm) tank. Water temperature (Tw) in each tank was independently controlled. In conditions requiring cold body and/or cold arm, Tw in the appropriate tanks was 8 degrees C. In conditions requiring warm body and/or warm arm, Tw in the appropriate tanks was adjusted between 29 and 38 degrees C to maintain body/arm temperature at baseline values. A battery of 6 tests, requiring fine or gross motor movements, were performed immediately before immersion and after 15, 45, and 70 minutes of immersion. RESULTS: In CB-CA, Tes decreased from an average of 37.2 to 35.6 degrees C and Tmus decreased from 34.6 to 22.0 degrees C. In WB-CA, Tmus decreased to 18.1 degrees C (Tes = 37.1 degrees C), and in CB-WA, Tes decreased to 35.8 degrees C (Tmus = 34.5 degrees C). By the end of immersion, there were significant decrements (43-85%) in the performance of all tests in CB-CA and WB-CA (p < 0.0002); scores for each test were similar in these two conditions. There was no significant change in scores throughout the CB-WA condition. In both conditions with arm cooling (i.e., WB-CA and CB-CA), Tmus accounted for 85-98% of the variance in all tests. When the core was cooled in the CB-WA condition, Tes was significantly correlated to scores in only two tests (accounted for 90 and 93% of the variance) although the actual effect was small. In the CB-CA condition, partial correlations indicated that Tes accounted for 4-10% of the variance in scores of 4 tests. CONCLUSIONS: We conclude that cooling of the body and/or the arm elicits large decrements in finger, hand and arm performance. The decrements are due almost entirely to the local effects of arm tissue cooling.

Adult↗
PubMed1994

Treatment of adolescent idiopathic scoliosis using Texas Scottish Rite Hospital instrumentation.

STUDY DESIGN: To determine the effectiveness of posterior TSRH instrumentation for the treatment of idiopathic scoliosis, 103 patients with a 2-year minimum followup were retrospectively studied. METHODS: Patients who underwent operations between October 1988 and April 1991 were evaluated for curve correction, spinal balance, and complications. Age at surgery averaged 14.3 years. Follow-up averaged 2.5 years. RESULTS: Thoracic curve correction averaged 65% in those with King Type III/IV curves and 54% in those with Type II curves. With follow-up, correction loss averaged approximately 13% for each group. Lumbar curve correction after instrumentation in Type I and II curves averaged 48% postop but lost approximately 20% with follow-up. Trunk balance improved 77% toward midline after surgery in those with Type III/IV curves. Improvement in trunk balance was less impressive in patients with Type II curves, particularly after selective thoracic fusions. Thoracic sagittal contour improved 43% for hypokyphotic (< 20 degrees) patients but, in the remainder, no significant radiographic change was evident. No neurologic complications occurred. Delayed deep infections developed in ten patients (10%) between 11 and 45 months postoperative. Cultures eventually grew Propionibacterium acnes, staph epidermidis, or staph coagulase negative in eight patients. Two patients had pseudarthroses. CONCLUSIONS: Frontal and sagittal thoracic curve correction can be satisfactorily obtained using TSRH instrumentation. Continued efforts are being made to improve lumbar hook patterns and technique to achieve and maintain better lumbar curve correction.

Adolescent↗
PubMed1993

Anterior correction of idiopathic scoliosis using TSRH instrumentation.

The first 14 consecutive patients with idiopathic lumbar scoliosis treated by anterior Texas Scottish Rite Hospital (TSRH) instrumentation are reported. Frontal curve correction averaged 76%, with a 5 degrees (9%) loss of correction in the follow-up period, which averaged 17.6 months (range, 12-29). Spinal balance was improved an average of 1.8 cm toward the center sacral line, and apical vertebral rotation was corrected an average of 49%. Instrumentational kyphosis was minimal, with total L1-S1 lordosis decreasing an average of 1 degree, and no measured compensatory hyperlordosis caudal to the instrumented segment. One hundred percent of disc spaces were radiographically fused by 8 months. There were no neurologic, septic, or implant complications. The contoured solid rod used in this construct provides the same frontal and rotatory correction as previous systems, and minimizes instrumentational kyphosis. Fusion occurs rapidly and reliably because of the stiffness of the construct, which also may eliminate the need for postoperative immobilization.

Adolescent↗
PubMed1993

Intraosseous infusion of prostaglandin E2 in the caprine tibia.

We evaluated the effects of intraosseously administered prostaglandin E2 (PGE2) within the proximal metaphysis of the goat (caprine) tibia under intraosseous normotensive and hypertensive conditions. PGE2 was administered at 0.5 or 1.0 mg (1 ml vol) twice daily for 10 days via an Osteoport which had been surgically implanted within the proximal tibial metaphysis. Intraosseous hypertension was produced when venous outflow obstruction (VOO) was created by ligation of the popliteal vein, which drained the proximal tibia, and occlusion of the diaphyseal medullary space distally with bone cement. After VOO, the intraosseous pressure measured at the metaphysis increased significantly (p < 0.05) from a baseline mean of 14.9 +/- 4.2 mm Hg to 28.6 +/- 5.3 mm Hg. Serum radioimmunoassays indicated that VOO prolonged the venous drainage of PGE2 from the tibia after an infusion. Static histomorphometric analysis indicated a marked dose-dependent increase in new bone formation in all PGE2 groups at 30 days after the PGE2 infusion. Significant (p < 0.05) formation of new bone occurred, primarily at the subperiosteal and endocortical surfaces, and moderately increased the marrow cavity of cancellous new bone as compared with the VOO-only group and the controls. Bone remodeling indices were also increased by PGE2. The PGE2 infusion, combined with VOO, produced significantly more new bone formation than the PGE2 infusion alone. Intensive marrow fibrosis was associated with the active bone remodeling.

Animals↗
PubMed1993

Bone changes associated with intraosseous hypertension in the caprine tibia.

We investigated the effects of increased intraosseous pressure on new-bone formation in the proximal metaphysis of the caprine tibia. Intraosseous hypertension was produced by obstruction of venous outflow by ligation of the popliteal vein draining the proximal aspect of the tibia and occlusion of the medullary space with bone cement (groups 1 and 2). After the obstruction of venous outflow (day 0), the intraosseous pressure measured at the proximal tibial metaphysis increased significantly from a mean of 15.5 millimeters of mercury before the obstruction to a mean of 28.7 millimeters of mercury in groups 1 and 2. In group 1, obstruction of venous outflow was combined with intraosseous infusion of autogenous whole blood under pressure to maintain the intraosseous pressure between thirty and forty-five millimeters of mercury during days 0 through 5. The time for venous drainage was still prolonged and intraosseous pressures were still increased on days 5 and 10 (means, 26.8 and 26.2 millimeters of mercury, respectively) in groups 1 and 2. The intraosseous hypertension produced in group 1 was associated with a significant increase in periosteal (138 per cent), endocortical (369 per cent), and cancellous new-bone formation (889 per cent) at the tibial metaphysis compared with control values. Osseous necrosis within the metaphysis was not observed.

Animals↗
PubMed1993

Progression of the curve in boys who have idiopathic scoliosis.

The prevalence of curve progression was evaluated in 210 boys who had idiopathic scoliosis. A minimum age of eight years, a deformity of at least 10 degrees, and radiographic follow-up of one year or progression of the curve within the first year of follow-up were the criteria for inclusion in the study. Of the 210 patients, sixty-eight (32 per cent) had progression of 10 degrees or more. Four of the five patients who had had an initial curve of 50 degrees or more subsequently had a spinal arthrodesis. The risk of progression was significantly greater for patients who were at an earlier Risser stage (p < 0.002) and for those who were younger (p < 0.005). The risk of progression was also greater for patients who had had a larger curve at the time of presentation; of the sixty-three boys for whom the Risser grade was 1, 2, 3, 4, or 5 when they were first seen and who had a curve of 25 degrees or more, twenty (32 per cent) had progression, compared with only two (5 per cent) of the thirty-eight who had a Risser grade of 1, 2, 3, 4, or 5 and a curve of 24 degrees or less. Of the thirty-four patients for whom the Risser grade was 4 when they were first seen, five (15 per cent) had progression.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Intraosseous infusion using the osteoport implant in the caprine tibia.

We evaluated the in vivo animal tolerance to intraosseous infusion via the Osteoport pediatric implant (model 2005PSO, Lifequest Medical, San Antonio, TX, U.S.A.) into the proximal tibia of immature goats and investigated the osseous effects of intermittent and sustained increases in intraosseous pressure (IOP). In group 1 (n = 3) autogenous whole blood was continuously infused (CI) for 5 days at flow rates producing an IOP of 30-45 mm Hg. Group 2 animals (n = 3) underwent a 5-s high-pressure infusion (HPI) of lactated Ringer solution (LRS) producing an IOP of 90-125 mm Hg twice daily for 10 days. In group 3, the Osteoports were left in place 5 (n = 2) or 10 days (n = 2) and evaluated for patency at 72-h intervals. An IOP > 35 mm Hg produced clinical evidence of bone pain. Bone mineral density was significantly increased (p < 0.05) in all implanted tibias (mean 1.04 g/cm2; range 0.87-1.21 g/cm2) compared with controls (mean 0.67 g/cm2; range 0.65-0.71 g/cm2). A nonsignificant increase (+9% to +31%) in periosteal new bone formation occurred in all implanted tibias. In the continuously infused group, there was a significant increase (p < 0.05) in cancellous new bone formation (+483%), percentage eroded bone surface (+143%), and osteoclast covered bone surface (+255%) compared with controls. HPI of LRS did not produce significant bone changes. Seemingly, the Osteoport provided a ready means of intraosseous infusion and may be associated with less complications than current methods of continual vascular access. Bone changes correlated more with the duration than the magnitude of increased intraosseous pressures.

Absorptiometry, Photon↗
PubMed1990

Effect of spinal construct stiffness on early fusion mass incorporation. Experimental study.

The relationship between initial spinal construct stiffness and the stiffness of the resulting fusion mass was studied by performing standardized 10-segment posterior spinal fusions in goats. Animals were divided into 5 groups based on type of spinal construct, using rods of different diameters (3.2 mm, 4.8 mm, 6.4 mm) with or without rigid crosslinking to produce constructs of different stiffnesses. Stiffness data on 28 animals were obtained by removing the spines en bloc, at 6 or 12 weeks postoperatively, and performing load-deformation testing in axial and torsional loading to determine the stiffness of the fusion masses (rods removed). The initial construct stiffnesses were also compared by ex vivo testing on spine specimens to correlate initial construct stiffness with eventual fusion mass stiffness. In axial testing, results showed stiffer fusion masses from larger diameter rod constructs compared with smaller rod constructs. This was similar to results of control testing on spine specimens ex vivo. Rigid crosslinking did not produce stiffer fusions in axial testing, due to a technical limitation of the button-wire implants used to segmentally fix the rods at each vertebra. In torsional testing, stiffer fusion masses resulted from using larger rods, and rigid Crosslinking also produced the stiffest fusion masses, which was consistent with ex vivo testing. In general, larger diameter (stiffer) rods produced stiffer fusion masses, and no evidence of stress shielding was found.

Animals↗
PubMed1990

Use of the Pavlik harness in congenital dislocation of the hip. An analysis of failures of treatment.

In twenty-five patients, the Pavlik harness failed to obtain or maintain reduction in thirty of thirty-five congenital dislocations of the hip. All of the patients had met the clinical criteria for use of the harness in our institution: they were less than seven months old, the femoral head pointed to the triradiate cartilage on anteroposterior radiographs that were made with the child wearing the harness, and they had no evidence of neuromuscular disease or teratological dislocation. These patients were compared with seventy-one patients (eighty-one dislocations) who had also been treated with the Pavlik harness and in whom a stable reduction was obtained and maintained. Statistically significant risk factors for failure of the harness included an absent Ortolani sign at the initial evaluation, bilateral dislocation, and an age of more than seven weeks before treatment with the harness was begun. All thirty hips in which the harness failed to obtain or maintain reduction had a subsequent attempt at closed reduction after preliminary Bryant traction. Fifteen of these hips were successfully reduced closed, but two later redislocated and needed an open reduction. The remaining fifteen hips needed an open reduction, and two redislocated and needed a second open reduction.

Age Factors↗
PubMed1990

Infantile tibia vara.

Infantile tibia vara is a developmental condition producing progressive varus deformity of the knee in young children. It appears to have a worse prognosis in the predominantly nonwhite population seen with this condition in the United States than previous studies from Scandinavia would suggest. Early roentgenographic diagnosis is critical, since toddlers can have infantile tibia vara at an early stage instead of physiologic genu varum. Aggressive bracing is appropriate treatment until age three years. Correction to valgus alignment with upper tibial osteotomy predictably can produce complete resolution of the condition if performed by age four years. After that age, the procedure becomes less effective. Prognosis for Langenskiold Grade IV disease is guarded at best, regardless of age, because the physis behaves as if effective growth arrest has already occurred. Young patients with Grade IV or greater lesions should have corrective osteotomy combined with a physeal procedure to attempt restoration of growth in the medial physis. Early effective treatment can prevent permanent intraarticular incongruity.

Age Factors↗
PubMed1989

Frontal plane and sagittal plane balance following Cotrel-Dubousset instrumentation for idiopathic scoliosis.

Postoperative decompensation has been reported following Cotrel-Dubousset instrumentation for right thoracic idiopathic scoliosis. The authors examined balance in the frontal and sagittal planes in 53 patients to determine optimal levels for fusion. King et al Type II curves, particularly larger ones, shifted to the left when the thoracic curve was fused to the stable vertebra or just below. Most Type III curves balanced well regardless of the levels fused. One-third of all patients developed mild radiographic junctional kyphosis at the lower level instrumented, more commonly when instrumentation ended at or above T12. The authors recommend fusing one segment short of the stable vertebra in most Type II curves. Large Type II curves need both curves fused for optimal balance. Type III curves can be fused short of the stable vertebra.

Adolescent↗
PubMed1989

Biomechanical analysis of pedicle screw instrumentation systems in a corpectomy model.

Five different spinal implants, all using pedicle screw attachment to vertebrae, were examined in a one above/one below corpectomy model, to determine 1) the relative stiffness of each construct, 2) the stresses generated in the implant during loading, and 3) the relative fatigue susceptibility of each implant. Results indicated that the relative axial and torsional stiffnesses were similar for all the implants tested (DKS/Zielke, VSP/Steffee, AO Fixator Interne, Luque plate, AO Notched plate). Hence, each of the devices impart approximately the same stability to the spine in this highly unstable model. Stresses measured at the root of the pedicle screws were found to exceed the endurance limit of stainless steel in those systems in which the pedicle screws were attached rigidly to the plates (VSP/Steffee, AO Fixator Interne). Good agreement was found between the measured stresses and stresses derived from static calculations. Comparisons between the stresses from each implant gave a relative measure of fatigue susceptibility that was validated by in vitro cyclic testing. Implants with stresses exceeding the endurance limit failed during the cyclic test.

Biomechanical Phenomena↗