Evaluation of pediatric surgery information on the Internet.

BACKGROUND/PURPOSE: Increasing numbers of parents use the Internet to obtain information about their child's medical diagnosis. Unfortunately, this information is not screened or regulated. The authors sought to evaluate the information available on the Internet regarding intersex anomalies as a representative pediatric surgical diagnosis. METHODS: Six search engines were searched for ambiguous genitalia. The first 30 sites on each search engine were reviewed. Sites were reviewed to identify information that did not conform to accepted recommendations for evaluation and treatment. RESULTS: Searches for ambiguous genitalia and synonyms found 0 to 44,471 sites per search engine. Of the 300 sites reviewed, only 45 represented 8 unique sites offering medical information. Five of these sites conformed to recommendations in 2 standard pediatric surgery texts, whereas 3 offered misleading information or information that did not conform to text recommendations. Of the total 300 sites, only 5 (1.6%) of accessible pages offered appropriate medical information to parents. CONCLUSIONS: Parent-oriented information regarding intersex anomalies is difficult to find on the Internet. Over one third of sites containing medical information failed to conform to standard pediatric surgical recommendations for treatment. Pediatric surgeons should help parents effectively use Internet information.

The New Injury Severity Score and the evaluation of pediatric trauma.

BACKGROUND: To compare the effectiveness of the Injury Severity Score (ISS) and New Injury Severity Score (NISS) in predicting mortality in pediatric trauma patients. METHODS: NISS, the sum of the squares of a patient's three highest Abbreviated Injury Scale scores (regardless of body region), were calculated for 9,151 patients treated at four regional pediatric trauma centers and compared with previously calculated ISS values. The power of the two scoring systems to predict mortality was gauged through comparison of misclassification rates, receiver operating characteristic curves, and Hosmer-Lemeshow goodness-of-fit statistics. RESULTS: Although there were significant differences in mean NISS and ISS values for each hospital, differences in the predictive abilities of the two scoring systems were insignificant, even when analysis was restricted to the subgroup of patients with severe or penetrating injuries. CONCLUSION: The significant differences in the predictive abilities of the ISS and NISS reported in studies of adult trauma patients were not seen in this review of pediatric trauma patients.

Car surfing: an underreported mechanism of serious injury in children and adolescents.

BACKGROUND: Car surfing, in which participants stand on top of a moving vehicle as though it were a surfboard, has been reported as a cause of traumatic injury in only 5 cases in the literature. Over the last 8 years, however, the authors have treated 26 children, primarily adolescents, for injuries resulting from car surfing. This report describes the injuries and outcomes of this potentially underreported mechanism of injury. METHODS: Medical records of 26 patients treated for car surfing injuries between 1991 and 1999 were reviewed. Demographics, hospital course, and type and severity of injuries were analyzed. RESULTS: Eighteen boys (69%) and 8 girls (31%) with an average age of 15.7+/-3.4 years (range, 6 to 22) have presented with injuries related to car surfing. All patients had fallen from the hood, roof, or trunk of a moving motor vehicle, the majority falling from the hood (n = 13; 50%). Injury severity was evaluated using the Injury Severity Scores (ISS; 12.4+/-6.5), Revised Trauma Score (RTS; 7.5+/- 1.1) and Glasgow Coma Score (GCS; 13.5+/-3.2). Injury severity was equivalent between boys and girls (P>.05). Central nervous system injuries predominated, with closed head injuries occurring in 22 (85%) and loss of consciousness in 10 (39%). Skull fractures occurred in 11 (42%) and intracranial bleeding in 9 (35%). Long-term cognitive rehabilitation was necessary in 22 (85%) patients. Three patients (12%) had spinal column fractures, with 2 (8%) suffering permanent paralysis. Two extremity (8%) and 3 (11.7%) pelvic fractures occurred. Most patients (73%) suffered significant skin and soft tissue injuries. Two patients (8%) presented with solid visceral injuries, and 1 child died. CONCLUSIONS: Car surfing is an extremely high-risk behavior in children and adolescents that leads to significant morbidity, long-term disability, and is potentially fatal. The incidence of car surfing may be greater than has been reported previously; therefore, prevention programs aimed at discouraging this high-risk behavior in children and adolescents should be considered.

Historical changes in the postoperative treatment of appendicitis in children: impact on medical outcome.

BACKGROUND/PURPOSE: The introduction of managed care in the 1980s caused increased pressure to reduce costs for hospitalized patients. The authors hypothesized that these market forces have resulted in a decreased hospital stay and utilization of sophisticated diagnostic testing in children treated for appendicitis. If true, the impact of this paradigm shift on patient outcome is unknown. METHODS: Hospital records for 913 pediatric patients treated for appendicitis from 1974 to 1998 were reviewed retrospectively. Patients were stratified into those with perforated appendicitis (PA) and nonperforated appendicitis (NPA). Demographics, perioperative hospital course, diagnostic testing, complications, and long-term outcomes were analyzed after stratification into time intervals. RESULTS: Over time, children with NPA were treated with shorter antibiotic courses (P<.05) and were placed on a regular diet earlier (P<.05). These changes in treatment resulted in an earlier discharge (P<.05). The amount of time to become afebrile with a normal white blood cell count (WBC) did not change over time. Children with PA exhibited similar results with shorter antibiotic courses (P<.05), earlier dietary intake (P<.05) and earlier hospital discharge (P<.05) over time. In all children with appendicitis there was no significant difference in the rate of wound infections, abscesses requiring drains, readmission, or reoperations overtime. The utilization of abdominal radiographs (83%) and ultrasonography (USN; 40%) was high and remained unchanged over time. Utilization of computed tomography (CT scan) was low (4.3%) in the early decades and was not used as a preoperative test from 1991 to 1994. Given the high diagnostic accuracy of a pediatric surgeon for this disease, Bayesian analysis indicates that USN utilization rates should be 15%. CONCLUSIONS: The market pressures of managed care have resulted in a new treatment paradigm with an earlier discharge of all children with appendicitis. There has been no concomitant increase in the complication rate in either group as a result of this paradigm shift. Bayesian analysis indicates that USN and abdominal radiographs are overutilized in our institution.

Specialty networking in pediatric surgery: a paradigm for the future of academic surgery.

OBJECTIVE: To review retrospectively a 4-year experience with pediatric surgical networking at a major academic medical center in the Midwest. BACKGROUND: The growth of managed care in the United States during the past decade has had a major impact on the practice of medicine in general, but especially on academic medicine. In some academic medical centers, the loss of market share has not only affected clinical activity but has also compromised the educational and research missions of these institutions. METHODS: At the authors' institution, a networking strategy in pediatric surgery was established in 1993 and implemented on July 1, 1994. In 1994, one new satellite practice was established; over the next 4 years, four additional practices were added, including one in another state. To assess the impact on financial status, clinical activity, education, and academic productivity, the following parameters were analyzed: gross and net revenue, surgical cases, clinic visits, ranking of the pediatric surgery residency, publications, grant support, and development and endowment funds. RESULTS: Gross and net revenue increased from $3,273,000 and $302,000 in 1993 to $10,087,000 and $2,826,000, respectively, in 1998. Surgical cases and clinic visits increased from 1240 and 3751 in 1993 to 5872 and 11,604, respectively, in 1998. At the medical center's children's hospital, surgical cases and clinic visits increased from 1240 and 3751 to 2592 and 4729 during the same time period. During this 4-year period, the faculty increased from 4 to 11. Since 1997, the National Resident Matching Program has provided data on how pediatric surgery residency candidates ranked a training program. In 1997, this program received the second-most one to five rankings; in 1998, it tied for first. This exceeds the faculty's perception of previous years' rankings. Publications increased from 26 in 1993 to a peak number of 62 in 1996; in 1997 and 1998 the publications were 48 and 37, respectively. External grant support increased from $139,882 in 1993 to a total of $6,109,971 in 1998. Development and endowment funds increased from $103,559 in 1993 to $2,702,2777 in 1998. CONCLUSIONS: Pediatric surgical networking at the authors' institution has had a markedly positive impact on finances, clinical activity, education, and academic productivity during a 4-year period. The residency training program appears to have improved in popularity among candidates, probably because of the increased referral of complex cases to the medical center from the various networking satellites. External grant support and basic laboratory research significantly increased, most likely because of the greater number of faculty with protected time for research recruited. Development and endowment funds dramatically grew because of the excellent fiscal health of the pediatric surgical program. This experience may serve as a model for other academic surgical specialties.

ATP converts necrosis to apoptosis in oxidant-injured endothelial cells.

Cell death due to necrosis results in acute inflammation, while death by apoptosis generally does not. The effect of adenosine triphosphate (ATP) on the pattern of cell death induced by oxidants was examined in bovine endothelial cells. ATP levels were altered by hydrogen peroxide (H2O2), glutamine (Gln), and metabolic inhibition (MI), to determine if necrosis can be shifted to apoptosis during oxidant injury. The form of cell death was determined by fluorescence microscopic techniques and the pattern of DNA degradation on agarose gels. ATP levels were measured using the luciferase-luciferin assay. Apoptosis occurred with 100 microM H2O2 without an alteration in ATP levels. ATP was significantly lowered with 5 mM H2O2, and necrosis occurred. MI, in combination with 100 microM H2O2, decreased ATP and resulted in necrosis. MI alone, however, did not cause cell death. Gln partially restored ATP levels in cells injured with 5 mM H2O2 and resulted in a significant increase in apoptosis. DNA laddering on agarose gels confirmed the apoptotic changes seen by fluorescence microscopy. In summary, a threshold level of ATP 25% of basal levels is required for apoptosis to proceed after oxidant stress, otherwise necrosis occurs. Agents like glutamine that enhance ATP levels in oxidant-stressed cells may be potent means of shifting cell death during inflammation to the noninflammatory form of death--apoptosis.

The lateral approach for open splenectomy.

BACKGROUND: Laparoscopic splenectomy (LS) has been used increasingly to treat children with hematologic disorders and has been reported to have advantages over open splenectomy performed through a standard vertical or subcostal incision. The authors perform open splenectomy (OS) through a lateral, muscle-splitting approach, and believe their approach is more reasonable in comparison with LS. METHODS: Thirty-nine consecutive open splenectomies performed between 1991 and 1995 were reviewed retrospectively and compared with recent reports of LS. The series included 24 boys and 15 girls with an average age of 9 years and average weight of 37.5 kg. Indications included immune thrombocytopenic purpura (n = 20), hereditary spherocytosis (n = 18), and sickle cell anemia (n = 1). The operation was performed with the child in the lateral decubitus position through a left upper abdominal muscle-splitting incision (off the 11th rib), sparing the rectus muscle. RESULTS: All 39 cases were completed without intraoperative complications with an average surgical time of 98.0 minutes (range, 30 to 302). The average surgical blood loss was 89 mL (range, 10 to 300). The children started feeding an average of 1.2 days (range, 0 to 4) postoperatively, were on a regular diet at an average of 2.0 days (range, 1 to 6) postoperatively, and had an average length of stay of 2.7 days (range, 1 to 6). There was no mortality or morbidity. CONCLUSIONS: Open lateral splenectomy is performed with shorter surgical times, less blood loss, an excellent cosmetic result, no complications, and a length of stay comparable to any of the published series on laparoscopic splenectomy in children. This approach provides a reasonable basis for comparison with laparoscopic splenectomy.

Efficacy of the straight endorectal pull-through in the management of familial adenomatous polyposis--a 16-year experience.

From 1979 to 1995, 27 patients who had familial adenomatous polyposis (FAP) were treated at the authors' institution. Most patients (n = 23) presented as a result of a previous family history of FAP. Eighteen patients presented with symptomatic colonic disease that included bloody stools (n = 14), diarrhea (n = 10), and abdominal pain (n = 6). Treatment consisted of a total colectomy, rectal mucosectomy, and straight endorectal pull-through (ERPT) in 26 of 27 patients. One patient preferred to undergo an ileoanal J pouch reconstruction. A temporary diverting loop ileostomy was performed in 25 patients and closed at an average of 100 days after the ERPT. Follow-up has been achieved in 100% of the patients and ranges from 6 to 182 months with an average of 48 months. Postoperative complications included partial bowel obstruction (two patients, one requiring enterolysis); and mild pouchitis (one patient). Two of the 27 patients required proctectomy and permanent ileostomy procedures, one for rectal cancer that was present microscopically in the initial rectal specimen from the ERPT and the other because of recurrent anastomotic complications. No patient required revision of the straight pull-through to a pouch or takedown of the pull-through as a result of persistent diarrhea or dissatisfaction. All of the patients are continent, and 80% deny any soiling during bouts of gastroenteritis. The mean number of bowel movements reported was 10 per day at the first postoperative clinic visit with a gradual decreased to six per day after 2 years. Initial use of bulking (62%) and antimotility agents (88%) decreased significantly over the course of follow-up to 29% and 67%, respectively at the most recent follow-up (average, 48 months) of each patient. Pelvic sepsis, which occurs in 8% of most series of patients who have pouches, did not occur in any of our patients. Pouchitis, a common complication with pouches (23%), occurred in only one of the patients and was mild and easily treated medically. This series demonstrates that total colectomy with rectal mucosectomy and straight ERPT eliminates the risk of colorectal cancer and achieves continence with a low complication rate and excellent functional results and patient satisfaction.

Efficacy of the transthoracic modified Heller myotomy in children with achalasia--a 21-year experience.

From 1974 to 1995, 19 children with achalasia of the esophagus have been treated at our institution. Presenting symptoms included vomiting (n = 14), dysphagia (n = 13), failure to thrive (n = 6), and odynophagia (n = 1). Diagnosis was established by a barium swallow in 19, with eight also undergoing esophageal manometry. Six boys and 13 girls with an average age of 10 years (range, 1.3 to 17.6) underwent a transthoracic, modified anterior Heller esophagomyotomy (HM). Five underwent a concomitant, modified, Belsey fundoplication (BF). Follow-up ranging from 6 months to 21 years (mean, 9 years) was accomplished in all 19 patients by both office visits and telephone interviews. Early postoperative follow-up showed initial swallowing difficulty in two (14%) patients with a HM alone and in four out of five (80%) patients treated with a HM and BF. All patients (n = 5) with a HM and BF and one with a HM alone required one esophageal dilation during the first postoperative year. These initial swallowing difficulties resolved in all six patients during this first postoperative year. Late postoperative follow-up, however, indicates occasional, mild dysphagia in two out of five with an HM and BF resulting in complete relief of presenting symptoms in 17 of the 19 patients (90%). All patients rated their overall result as either excellent (68%) or good (32%) with none rating it as fair or poor. None of the 19 patients had clinical evidence of gastroesophageal reflux, although five patients had evidence of nonpathologic reflux noted during upper gastrointestinal x-ray. Recurrent vomiting, asthma, wheezing, or esophagitis symptoms have not been reported by any patients. No patients required reoperation, and there were no deaths or postoperative complications. Modified Heller esophagomyotomy is safe (0% mortality) and effective (90% relief of symptoms) in children with achalasia. A concurrent modified Belsey fundoplication results in early and late mild postoperative dysphagia that was responsive to esophageal dilation. The transthoracic, modified Heller esophagomyotomy without a fundoplication is currently our treatment of choice for achalasia in children.

Sulfur mustard induces apoptosis and necrosis in endothelial cells.

Sulfur Mustard (SM) is a vesicant or blistering chemical warfare agent, for which there still is no effective therapy. Endothelial cells are one of the major cellular targets for SM. The mechanism of endothelial cell death during SM injury is poorly understood. We studied the effect of exposure of endothelial cells to 0-1000 microM SM over the time course of 2-24 hr to determine the role of apoptotic and necrotic patterns of cell death in endothelial injury induced by SM. SM concentrations < or = 250 microM induced exclusively apoptosis which was observed after 5 hr in 30% of endothelial cells. Exposure to SM concentrations > or = 500 microM caused apoptosis and necrosis to the same extent in 60-85% of all cells after 5 to 6 hr. Necrosis was accompanied by a significant (approximately 50%) depletion of intracellular ATP, while in apoptotic cells ATP remained at the level similar to healthy cells. Interestingly, disruption of the long actin filament stress fibers and rounding of cells preceded other features of apoptosis--DNA fragmentation, membrane budding, and apoptotic body formation. In apoptotic cells, microfilaments formed constricted perinuclear bands, which were not observed in necrotic cells. Pretreatment with 50 mM N-acetyl-L-cysteine (NAC), a sulfhydryl donor and antioxidant, nearly eliminated the apoptotic features of cell death but did not prevent necrosis in response to SM. NAC pretreatment alone induced reorganization of actin filaments into an enhanced network of long stress fibers instead of a dominant cortical band of actin. NAC pretreatment prevented loss of cell adherence and cell rounding following exposure to 250 microM SM. The effect of NAC on cytoskeletal organization and its ability to eliminate SM-induced apoptosis suggests that actin filament organization may be an important element in cellular susceptibility to apoptotic stimuli.

Actin polymerization and depolymerization during apoptosis in HL-60 cells.

Little is known about the biochemical "machinery" responsible for the morphological features of apoptosis, although the cytoskeleton is presumed to be involved. Using flow cytometry, polyacrylamide gel electrophoresis, and fluorescence microscopy, we show that apoptosis induced by ultraviolet (UV) irradiation or 80 micrograms/ml etoposide correlates with early transient polymerization and later depolymerization of filamentous (F)-actin and dramatic changes in visible microfilament organization. Depolymerization of F-actin began before the formation of apoptotic bodies and was ultimately composed of decreases in both the detergent-insoluble (40%) and detergent-soluble (50%) pools of F-actin. Dihydrocytochalasin B (H2CB), which blocked apoptotic body formation, depolymerized F-actin in the detergent-insoluble pool only. Visually, H2CB treatment disrupted microfilament organization, resulting in short, brightly stained microfilaments dispersed throughout the cytoplasm. In contrast, apoptotic cells contained a network of fine microfilaments with bright staining concentrated at the site of apoptotic body formation. Together, these results suggest that reorganization of the microfilament network is necessary for the formation of apoptotic bodies and that depolymerization of F-actin may also be a necessary component of the process of apoptosis.

Effect of very delayed repair of congenital diaphragmatic hernia on survival and extracorporeal life support use.

BACKGROUND: Since November 1992, operative repair in neonates with congenital diaphragmatic hernia (CDH) at this institution was delayed until respiratory insufficiency had resolved. METHODS: A retrospective analysis was performed (n = 33) comparing delayed repair with our previously reported institutional experience with immediate repair from January 1988 to October 1992 (n = 66). Infants with severe genetic defects or moribund conditions or who were premature were not considered candidates for repair or extracorporeal life support (ECLS), but they were included in the survival analysis. Survival was defined as hospital discharge. Data were compared with an independent t test or Pearson chi-squared test. RESULTS: Mean age at repair was 8.9 +/- 4.5 days (range, 3 to 20 days). Eleven infants in the study group were placed on ECLS (33% versus 68% in the comparison group; p = 0.001). Six of these infants survived (55% versus 58% in the comparison group; p = 0.846). Of these survivors, one patient was repaired while on ECLS, and the remainder underwent repair after decannulation from ECLS. All 20 of the remaining candidates for repair survived without need for ECLS. Overall survival was 79% versus 56% in the comparison group (p = 0.027). CONCLUSIONS: Our current data suggest that very delayed repair of newborns with CDHs is associated with an increase in the overall survival and a decrease in the use of ECLS when compared with previous experience at this institution.

Gastroesophageal reflux.

GER is a major pediatric disease. The respiratory, nutritional, and inflammatory complications of this disease process, invisibly hidden in the gastroesophageal junction, have a profound effect on the quality and sometimes the very life of infants and children. The astute pediatrician and surgeon should always keep this disease process in mind when dealing with these problems of children. Having a high suspicion of GER is often necessary to find this hidden enemy. The Nissen fundoplication and the Thal fundoplication are equally successful in the treatment of GER in children. However, the complication rate with the Nissen fundoplication is higher than with the Thal. We feel that the Thal does an outstanding job of treating GER while maintaining normal gastroesophageal function in the developing child, and is therefore our operation of choice for GER.

Effects of coenzyme Q10 on the mediator cascade of sepsis.

Coenzyme Q10 (CoQ) has been promoted as an effective agent for reducing the deleterious effects of septic shock by acting as an oxygen free radical scavenger and thus stabilizing mitochondrial membranes and by inhibiting the arachidonic acid metabolic pathway and the formation of various prostaglandins. This study was undertaken to evaluate the effect of CoQ in a live Escherichia coli model of canine septic shock. Group I (E. coli, n = 5) animals received an LD100 dose of 10(9) live E. coli/kg and were given no further treatment. Group II (CoQ, n = 5) animals received a 20-mg/kg bolus of CoQ without further treatment. Group III (CoQ + E. coli, n = 5) animals received a 20-mg/kg bolus of CoQ 10 min prior to a bacterial infusion as in group 1. Mean arterial pressure stabilized at 70% of baseline levels (P < .002), while cardiac output remained near 50% of baseline levels (P < .053) in group III compared to group I dogs. The arachidonic acid metabolites, prostaglandin E2, Thromboxane B2, and leukotriene B4 were significantly elevated in groups I and III (vs. group II) (P < 0.05). The catecholamines, tumor necrosis factor (TNF) and interleukin 6 (IL-6) were significantly elevated in groups I and III (vs. group II) (P < 0.05). Fluorescent products (lipid peroxidation activity) were elevated in group I (vs. groups II and III) at 120 and 180 min (P < 0.05). We conclude that CoQ supports cardiovascular hemodynamics and prevents free radical mediated lipid peroxidation during live E. coli septic shock, and its effect is not due to altered levels of humoral or cytokine mediators.

Prevention of postischemic injury in immature intestine by deferoxamine.

Free radical-mediated reperfusion injury has been demonstrated in ischemic neonatal bowel necrosis, but the mechanism of injury remains elusive. To determine whether such an injury can be prevented, 76 weaning rats were studied to test the effects of deferoxamine, an iron chelator, in postischemic injury. Group I (N = 20) had a sham laparotomy without vascular occlusion. Group II (N = 21) was subjected to 90 min of superior mesenteric artery occlusion prior to reperfusion. Group III (N = 35) received deferoxamine 15 mg/kg intravenous prereperfusion, in addition to ischemia and reperfusion as in group II. Survival profiles for each group were determined and a scale of pathologic severity was applied and compared. Group I had 100% long-term survival and group II, 14%. Group III had an overall survival of 28% and demonstrated a prolonged postreperfusion survival profile (P < 0.002) compared to group II. Histology was nearly identical to human necrotizing enterocolitis in degrees of bowel wall destruction and relative paucity of neutrophils. Group III showed a significant reduction in severity of injury compared to group II (P < 0.003). We conclude that neonatal bowel ischemia conditions such as necrotizing enterocolitis may be reperfusion injuries wherein free iron plays an important role in tissue injury. Administration of an iron chelating agent under such conditions has a beneficial effect on survival and histology.

Silastic catheterization of the axillary vein in neonates: an alternative to the internal jugular vein.

The axillary vein is a suitable alternative to the jugular venous system for tunnelled silastic catheterization in neonates, and should be included in the armamentarium of the surgeon who treats neonates. It is technically easy and is comparable to the internal jugular vein in terms of complications. Proper positioning of the catheter tip can sometimes be problematic, but without a resultant increase in morbidity or mortality.

Hypoxia-induced bacterial translocation in the puppy.

Because hypoxia is one of the most common major stresses to which a neonate is exposed, we postulated that it alone might be the cause of intestinal bacterial translocation, which could be the underlying etiology of neonatal sepsis. An animal model, in which hypoxia is the sole stress, was developed in our laboratory and tested in 18 puppies to determine the effect of hypoxia and reoxygenation on intestinal bacterial translocation. In group I (n = 8), following laparotomy and cannulation of the superior mesenteric vein (SMV), the FIO2 was decreased from 21% to 9% for 90 minutes followed by reoxygenation at 21% for 120 minutes. The abdomen was closed and the animals were allowed to recover. After 24 hours the mesenteric lymph nodes (MLNs), spleen, and liver were harvested for bacterial determination and the ileum and jejunum for histological evaluation. Group II (n = 7) was treated the same as group I with the FIO2 maintained at 21%. Group III (n = 3) animals were killed, without intervention, for bacterial analysis. In group I, the systemic PO2 decreased by 75%, SMV PO2 decreased by 64%, and oxygen delivery to the small bowel decreased by 80% in comparison with group II. The mean arterial pressure and cardiac output were not significantly different between group I and group II; however, the mucosal blood flow was decreased by 60% (P less than .001) in group I. Arterial and SMV blood lactic acid levels were unchanged in group I in comparison with group II, suggesting that anaerobic metabolism was not initiated in the splanchnic circulation during hypoxia.(ABSTRACT TRUNCATED AT 250 WORDS)

Monitoring the healing of a tibial osteotomy in the rabbit treated with external fixation.

Fracture site axial rigidity was monitored non-destructively at weekly intervals during healing of tibial osteotomies in adult rabbits. Two groups of 20 rabbits each were treated with external fixators of two different rigidities. Four animals from each group were killed at 3, 5, 6, 7, and 8 weeks to determine the bending moments at failure of the healing fractures. Normal fracture healing was accompanied by characteristic phases in the development of fracture site axial rigidity. From 0 to 3 weeks there was a period of low and approximately constant rigidity, followed by a linear increase during 3 to 5 weeks to an approximately three to four times greater rigidity. The maximum average normalized axial rigidities were reached at 6 weeks and were 57% (high rigidity group) and 77% (low rigidity group) of the untreated contralateral controls. The maximum average normalized failure moments occurred at 8 weeks and were 48% (high rigidity) and 44% (low rigidity) of controls. The differences due to fixator rigidity were not statistically significant except for a large increase in failure moments at 3 weeks for the low rigidity group. Axial rigidities were correlated (r2 = 0.74 and 0.53, respectively) with failure moments, but only during the first 6 weeks. The monitoring technique provides a nondestructive means for following the biomechanical progress of fracture healing in an animal model. The occurrence of the characteristic increase in fracture site axial rigidity at 3 to 5 weeks can also be used to distinguish between normal and abnormal healing.