James Aronson

The Histology of Distraction Osteogenesis Using Different External Fixators

The local biology of distraction osteogenesis using Ilizarov and Wagner external fixators was compared in unilateral tibial lengthenings in two groups of eight dogs. Serial roentgenograms with histological correlation revealed some basic similarities as well as distinct differences between the two groups. All dogs fully bridged the experimental gap by intramembranous ossification. Subtle histological changes in the alignment of collagen bundles and subsequent ossification reflected the mechanical configuration of each fixator. The multiplanar, full-pin Ilizarov system delivered concentric load to the site of osteogenesis, inducing perfectly parallel columns of new bone. The uniplanar, one-half pin Wagner system induced angulation of the collagen and subsequent bone columns on the basis of eccentric load to the osteogenic interface. Despite a significant difference in axial rigidity, the Ilizarov and Wagner external fixators induced osteogenesis of equal volume.

External Fixation of Femur Fractures in Children

Forty-two children (44 femur fractures) were treated by primary external fixation and early weightbearing (1984–1989), The fractures were reduced anatomically when possible. Average age at fracture was 9 years 7 months (range, 2 years 5 months to 17 years 8 months). Duration of external fixation averaged 70 days (range 42–117 days). Of 176 pins, 15 (8.5%) were inflamed and five (2.8%) required intravenous antibiotics; none resulted in osteomyelitis. Most patients returned to school by 4 weeks, and all had full knee motion 6 weeks after fixator removal. Of 16 patients with documented follow-up of at least 18 months, only six (38%) had overgrowth from 2 to 10 mm (average 5.8 mm).

Temporal and spatial increases in blood flow during distraction osteogenesis.

Ten adult mongrel dogs underwent left tibial lengthening at the proximal metaphysis. They were divided into three groups on the basis of distraction period: 14, 28, and 56 days. Quantitative technetium scintigraphy was used to measure regional blood flow within the tibiae during distraction, and periodically during consolidation, up to 17 weeks after operation. Blood flow was measured from regions of interest during the flow phase of the scan and expressed as a ratio of lengthened side to control side. At the distraction site, the flow increased to nearly ten times control, peaked at two weeks postoperatively, then decreased to four to five times the control for the remainder of the distraction period. During the consolidation period, significantly increased flow persisted at levels of two to three times control. The distal tibiae, away from the distraction gap, showed similar amplitude and temporal patterns of increased flow. No significant differences were found between the groups tested or when compared with similar fracture models. These findings lend credence to Ilizarovs hypothesis that distraction osteogenesis may contribute to healing of chronic osteomyelitis or hypovascular nonunions at distant sites by inducing a prolonged hypervascular state. Whether distraction osteogenesis transforms the normal reparative response of bone injury to a regenerative response remains conjectural.

Preliminary studies of mineralization during distraction osteogenesis.

Distraction osteogenesis by the Ilizarov method was performed on 20 dogs. Mineralization at the site of the left tibial metaphyseal lengthening was measured by weekly quantitative computer tomography (QCT) using the contralateral tibia as a control. Four dogs each were killed on Days 7, 14, 21, and 28 of distraction in order to correlate QCT with microradiology, nondecalcified histology, quantitative calcium analysis, and scanning electron microscopy. It was consistently found that intramembranous ossification proceeded centripetally from each corticotomy surface toward the central fibrous interzone. Bone columns crystallized along longitudinally oriented collagen bundles, expanding circumferentially to surrounding bundles. As the distraction gap increased, the bone columns increased in length and in diameter, while the fibrous interzone remained about 4 mm long. Histologically, the bone columns resembled stalagmites and stalactites, as seen by microradiography and scanning electron microscopy, that projected from each corticotomy surface toward the center. These cones reached maximum diameters of 150-200 mu at the corticotomy surfaces. Radiodensity (QCT) increased gradually from the central fibrous interzone toward each corticotomy surface. Mineral density, as determined by calcium quantification, reflected the microscopic geometry and radiographic polarity.

Deformity and disability from treated clubfoot.

To identify disability associated with treated unilateral, idiopathic clubfoot deformity, 29 patients and 23 controls were compared by morphometry, radiography, and performance testing. The average period following definitive treatment was greater than 10 years. Treatment regimens varied from prolonged casting to early posteromedial release. The most significant limitations in these treated clubfeet averaged (a) a 42% decrease in normal ankle motion, specifically lacking 65% of normal dorsiflexion, a consistent finding independent of treatment; (b) a 24% decrease in normal plantarflexor muscle strength, correlating directly to the number of heelcord lengthenings per foot; and (c) a noticeable 10% decrease in calf girth, unrelated to total time spent in cast.

External fixation of pediatric femur fractures.

One-hundred and thirty-two children with 139 femur fractures were treated with external fixation from 1984 to 1993. Average age at presentation was 8.97 years. All fractures were followed until union, with an average time of external fixation of 11.4 weeks. There were no nonunions. Of 18 patients with definitive radiographic measurements at 2-year follow-up, 15 patients developed overgrowth (average, 8.7 mm) and three demonstrated shortening (average, 7.7 mm). No patient required treatment for residual leg-length discrepancy. Although pin-tract inflammation was common, pin-tract infection requiring intravenous antibiotics occurred in only six patients (4.5%). No patient developed osteomyelitis. Two fractures (1.4%) were not healed at the time of elective fixator removal, necessitating additional time in the fixator. There were two refractures (1.4%) and one fracture through a healing pin tract after fixator removal (0.7%).

Preliminary Evidence for Effectiveness of a Stance Control Orthosis

Individuals with lower limb paresis or paralysis have traditionally had limited orthotic options to provide knee stability during walking. Recent developments have made available new “stance control” orthoses that provide stability in stance while allowing free knee motion during swing phase. The purpose of this study was to determine whether individuals with lower limb weakness walk more efficiently when using the Stance Control Orthotic Knee Joint (SCOKJ®) than when using a conventional knee-ankle-foot orthosis (KAFO) with the knee locked in extension. Data were collected on three male subjects with significant weakness in at least one lower limb. All subjects could walk independently, without walking aids, in the home and for short distances in the community. All three subjects exhibited increased speed and cadence, increased stride and step lengths, and fewer compensatory movements at the hip, pelvis, and trunk when walking with the SCOKJ®. Two subjects completed an obstacle course more quickly with the SCOKJ®. During 5 minutes of treadmill walking (comfortable speed), two subjects exhibited a lower heart rate response when wearing the SCOKJ®, suggesting lower energy requirements for walking with the SCOKJ®. In summary, the subjects used a more symmetric, more aesthetic walking pattern, maneuvered over and around obstacles more easily, and seemed to walk more efficiently when wearing the SCOKJ® than when wearing a KAFO with the knee locked in extension.

Experimental healing of distraction osteogenesis comparing metaphyseal with diaphyseal sites.

Distraction osteogenesis was performed on 32 adult dogs to compare bone healing at metaphyseal and diaphyseal sites. Sixteen dogs underwent proximal metaphyseal corticotomy and 16 dogs underwent middiaphyseal corticotomy of the left tibiae for gradual lengthening. Each major group was then divided into four subgroups of four dogs each on the basis of zero-, seven-, 14- and 21-day latency periods. The standard radiograph, quantitative computer tomography density, and bone-healing index were used to evaluate new bone formation and consolidation. A distraction rate of 1 mm per day for four weeks created an average elongation of 23.9 +/- 3.7 mm in the metaphyseal groups and 23.8 +/- 2.0 mm in the diaphyseal groups, excluding nine premature consolidations. In the 16 metaphyseal lengthenings, there were six premature consolidations (37.5%): four with a 21-day latency, two with a 14-day latency, and one nonunion (6.2%). In the 16 diaphyseal lengthenings, three fused prematurely (18.7%), two with a 21-day latency and one incomplete corticotomy with a seven-day latency. Three lengthenings of the diaphyseal group resulted in nonunion (18.7%). All animals, metaphyseal and diaphyseal, successfully bridged the distraction gap after a zero-day latency. The bone-healing index showed that new bone consolidation was best with a zero-day latency in metaphyseal (22 +/- 7.6 days/cm) and diaphyseal lengthening (26.5 +/- 6.5 days/cm). Comparing the minimum quantitative computer tomography density ratio of the experimental side with the contralateral side indicated a significant difference at the end of distraction (p = 0.001), at fixator removal (p = 0.001), and when the dogs were killed (p = 0.04).(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanical forces as predictors of healing during tibial lengthening by distraction osteogenesis.

Direct axial loads were measured weekly during a 15% left tibial lengthening in 21 skeletally mature dogs using three in-line load cells mounted between the rings of an Ilizarov external fixator. The loads increased linearly over time to a maximum at the end of distraction (Week 4). The metaphyseal lengthening sites (mean, 155 N) generated significantly higher loads than diaphyseal sites (mean, 111 N). Stress was calculated by dividing measured load by the computed tomographic-measured cross-sectional area of each distraction osteogenesis site; the metaphyseal and diaphyseal groups demonstrated equal stress at each time point with a maximum of 47 N/cm2 at the end of distraction. Six premature consolidations occurred that demonstrated loads significantly greater than 200 N by Week 2 of distraction. Three nonunions occurred that had significantly lower loads measured by Week 3 of distraction (mean, 60 N or 26 N/cm2).

Mechanical induction of osteogenesis: the importance of pin rigidity.

Eight dogs, divided into two groups of four by varying pin rigidity, underwent 15% left tibial lengthening by the Ilizarov method. In group I, “tensioned” 1.6-mm wires maintained a rigidity approaching that of 4.0-mm pins. In group II, the wires, maintained at half the tension, averaged 45% of the rigidity measured in group I. All dogs in group I filled the experimental gap with de novo osteogenesis, whereas all of the dogs in group II prematurely bridged the gap, arresting the process of osteogenesis. From these experimental results, clinical trials have been started using commercially available external fixation devices utilizing pins with equivalent rigidity.