Percutaneous epiphysiodesis using transphyseal screws for limb-length discrepancies: high variability among growth predictor models.

PURPOSE: Percutaneous epiphysiodesis using transphyseal screws (PETS) was developed as a minimally invasive outpatient procedure to address limb-length discrepancy (LLD) that allowed immediate postoperative weight bearing and was potentially reversible by removing the screws. The aims of our study were to report our results using PETS for LLD and evaluate the accuracy of three growth predictor models. METHODS: Sixteen patients with an average age of 14 years were treated for LLD using PETS. Thirteen patients had screws inserted in a parallel fashion and 3 had crossed screws. We compared the predicted LLD at skeletal maturity using the three growth predictor methods with the actual LLD at skeletal maturity and preoperative LLD with the final LLD at skeletal maturity. RESULTS: The mean LLD at skeletal maturity between the predicted and final measurements was 0.2 cm using the Green-Anderson method, 1.4 cm using the Moseley method, and -0.1 cm using the Paley method. The mean preoperative LLD of 3.1 cm was corrected to 1.7 cm at skeletal maturity (p < 0.001). Six patients complained of pain over the screw heads; however, no patient developed an infection or angular deformity. CONCLUSIONS: The three growth predictor methods predicted the final LLD within an average of 1.4 cm, but there was high variability. Although PETS improved the LLD by a mean of 1.4 cm, we believe the results would have been better if PETS was performed at an earlier skeletal age.

What is the best material for molding casts in children?

BACKGROUND: Casts are used to treat clubfeet, developmental dysplasia of the hip (DDH), forearm fractures, and femur fractures. The ability of a cast to maintain a desired shape is termed moldability. Clinicians use plaster, fiberglass, and soft casts. To our knowledge the biomechanical molding characteristics of these 3 materials have never been reported. We hypothesized that moldability of plaster would be better than fiberglass and fiberglass would be better than soft cast. METHODS: We compared 12.7 cm wide casts of plaster, fiberglass, and soft cast. Casts were 5 layers thick, prepared in 40°C water, and placed over 2 layers of cotton padding on 5.1 cm and 15.2 cm diameter foam cylinders. A loading device simulated loads applied by clinicians when molding casts for 4 conditions: clubfoot (thumb-shaped 50 N load on 5.1 cm model), DDH (thumb-shaped 100 N load on 15.2 cm model), forearm fracture (palm-shaped 50 N load on 5.1 cm model), and femur fracture (palm-shaped 100 N load on 15.2 cm model). The loading device applied molding for 7 minutes. Five casts of each material were made for each model. Casts were removed, photographed, and the area of maximal deformation was compared with an unmolded cast. A large area of maximal deformation meant that the deformation was spread out over a large area, less precise molding. RESULTS: In the clubfoot model, plaster was more precise than fiberglass (P=0.002) and soft cast (P<0.0001). In the DDH model, plaster was more precise than fiberglass (P<0.0001) and soft cast (P<0.0001) and fiberglass was more precise than soft cast (P<0.0001).In the femur fracture model, plaster was more precise than fiberglass (P=0.001) and soft cast (P=0.001). CONCLUSIONS: The moldability of plaster is better than fiberglass and soft cast and fiberglass is better than soft cast. CLINICAL RELEVANCE: If precise molding is required, plaster has the best moldability. In cases not requiring precise molding, fiberglass and soft cast are lightweight, waterproof, and available in child-friendly colors.

Metabolic Effects of Angulation, Compression, and Reduced Mobility on Annulus Fibrosis in a Model of Altered Mechanical Environment in Scoliosis.

STUDY DESIGN: Comparison of disc tissue from rat tails in 6 groups with different mechanical conditions imposed. OBJECTIVES: To identify disc annulus changes associated with the supposed altered biomechanical environment in a spine with scoliosis deformity using an immature rat model that produces disc narrowing and wedging. BACKGROUND: Intervertebral discs become wedged and narrowed in a scoliosis curve, probably partly because of an altered biomechanical environment. METHODS: We subjected tail discs of 5-week-old immature Sprague-Dawley rats to an altered mechanical environment using an external apparatus applying permutations of loading and deformity for 5 weeks. Together with a sham and a control group, we studied 4 groups of rats: A) 15° angulation, B) angulation with 0.1 MPa compression, C) 0.1 MPa compression, and R) reduced mobility. We measured disc height changes and matrix composition (water, deoxyribonucleic acid, glycosaminoglycan, and hyaluronic acid content) after 5 weeks, and proline and sulphate incorporation and messenger ribonucleic acid expression at 5 days and 5 weeks. RESULTS: After 5 weeks, disc space was significantly narrowed relative to internal controls in all 4 intervention groups. Water content and cellularity (deoxyribonucleic acid content) were not different at interventional levels relative to internal controls and not different between the concave and convex sides of the angulated discs. There was increased glycosaminoglycan content in compressed tissue (in Groups B and C), as expected, and compression resulted in a decrease in hyaluronic acid size. We observed slightly increased incorporation of tritiated proline into the concave side of angulated discs and compressed discs. Asymmetries of gene expression in Groups A and B and some group-wise differences did not identify consistent patterns associating the discs' responses to mechanical alterations. CONCLUSIONS: Intervertebral discs in this model underwent substantial narrowing after 5 weeks, with minimal alteration in tissue composition and minimal evidence of metabolic changes.

Contributions of Remodeling and Asymmetrical Growth to Vertebral Wedging in a Scoliosis Model.

STUDY DESIGN: We performed a laboratory study of rats of 3 different ages with imposed angulation and compressive loading to caudal vertebrae to determine causes of vertebral wedging. OBJECTIVES: The purpose was to determine the percentage of total vertebral wedging that was caused by asymmetric growth, vertebral body, and epiphyseal wedging. Approval from the Institutional Animal Care and Use Committee, the University of Vermont, was obtained for the live animal procedures used in this study. BACKGROUND SUMMARY: Vertebral wedging from asymmetrical growth (Hueter-Volkmann law) is reported to cause vertebral wedging in scoliosis with little attention to the possible contribution of bony remodeling (Wolff's law). METHODS: In our study, an external fixator imposed a 30° lateral curvature and compression of 0.1 megapascal (MPa) in 5- and 14-week-old animals (Groups 1 and 2) and 0.2 MPa in 14- and 32-week-old animals (groups 3 and 4). Total vertebral wedging was measured from micro CT scans. Wedging due to asymmetrical growth and epiphyseal remodeling was calculated from fluorescent labels and the difference was attributed to vertebral body wedging. RESULTS: Total vertebral wedging averaged 18°, 6°, 10° and 5° in Groups 1, 2, 3, and 4, respectively. Metaphyseal asymmetrical growth averaged 8°, 1°, 4°, 0° (44%, 17%, 40% and 0% of total). Epiphyseal wedging averaged 9°, 0°, 3°, and -1°. The difference (vertebral body) averaged 1°, 5°, 3°, and 7° (6%, 83%, 30% and 140% of total). The growth of the loaded vertebrae as a percentage of control vertebrae was 56%, 39% and 25% in Groups 1, 2 and 3; negligible in Group 4. Vertebral body cortical remodeling, with increased thickness and increased curvature on the concave side was evident in young animals and 0.2 MPa loaded older animals. CONCLUSIONS: We conclude that asymmetrical growth was the largest contributor to vertebral wedging in young animals; vertebral body remodeling was the largest contributor in older animals. If, conversely, vertebral wedging can be corrected by appropriate loading in young and old animals, it has important implications for the nonfusion treatment of scoliosis.

Ankle fractures in children.

Computed tomography is useful for preoperative planning and postreduction assessment for intra-articular pediatric ankle fractures. Nondisplaced pediatric ankle fractures can be effectively managed with cast immobilization and close radiographic follow-up evaluation. Physeal ankle injuries in younger children with considerable growth remaining should be followed closely for at least one year after injury as growth arrest may result in substantial angular deformity. Open reduction and internal fixation should be strongly considered when an articular step-off of <2 mm cannot be maintained by closed means for Salter-Harris type-III and IV and transitional ankle fractures.

Intervertebral disc changes with angulation, compression and reduced mobility simulating altered mechanical environment in scoliosis.

PURPOSE: The intervertebral discs become wedged and narrowed in scoliosis, and this may result from altered biomechanical environment. The effects of four permutations of disc compression, angulation and reduced mobility were studied to identify possible causes of progressive disc deformity in scoliosis. The purpose of this study was to document morphological and biomechanical changes in four different models of altered mechanical environment in intervertebral discs of growing rats and in a sham and control groups. METHODS: External rings were attached by percutaneous pins transfixing adjacent caudal vertebrae of 5-week-old Sprague-Dawley rats. Four experimental Groups of animals underwent permutations of the imposed mechanical conditions (A) 15° disc angulation, (B) angulation with 0.1 MPa compression, (C) 0.1 MPa compression and (R) reduced mobility (N = 20 per group), and they were compared with a sham group (N = 12) and control group (N = 8) (total of 6 groups of animals). The altered mechanical conditions were applied for 5 weeks. Intervertebral disc space was measured from micro-CT images at weeks 1 and 5. Post euthanasia, lateral bending stiffness of experimental and within-animal control discs was measured in a mechanical testing jig and collagen crimp was measured from histological sections. RESULTS: After 5 weeks, micro-CT images showed disc space loss averaging 35, 53, 56 and 35% of the adjacent disc values in the four intervention groups. Lateral bending stiffness was 4.2 times that of within-animal controls in Group B and 2.3 times in Group R. The minimum stiffness occurred at an angle close to the in vivo value, indicating that angulated discs had adapted to the imposed deformity, this is also supported by measurements of collagen crimping at concave and convex sides of the disc annuli. CONCLUSION: Loss of disc space was present in all of the instrumented discs. Thus, reduced mobility, that was common to all interventions, may be a major source of the observed disc changes and may be a factor in disc deformity in scoliosis. Clinically, it is possible that rigid bracing for control of scoliosis progression may have secondary harmful effects by reducing spinal mobility.

Nonfusion treatment of adolescent idiopathic scoliosis by growth modulation and remodeling.

BACKGROUND: Adolescent idiopathic scoliosis (AIS) is a common disorder in which the spine gradually develops a curvature that is first detected in patients between 11 and 17 years of age. The only accepted treatment methods are bracing and surgery. Whether brace treatment alters the natural history is being questioned, and patient compliance is low. Surgery usually includes a spinal fusion that creates a rigid spine and concentrates stresses at the ends. METHODS: This study focuses on correlating the laboratory results with clinical reports for treating patients with AIS. In the laboratory, scoliosis with vertebral wedging has been created by asymmetric mechanical loading and has been corrected by reversing the loading. In the clinic, bracing and derotational casting have been successful in some reports, but compliance has been a problem with bracing and derotational casts have mainly been used in young children. Operative treatment has been successful, but a nonfusion operation remains elusive. FINDINGS AND RESULTS: In the laboratory, axial loading of growth plates altered growth according to the Hueter-Volkmann law, which states that compression decreases and distraction increases growth. Asymmetric loading of the spine caused asymmetric growth resulting in scoliosis with vertebral wedging. Asymmetric loading of tail vertebrae created vertebral wedging according to Wolff's law, which states that the bone remodels over time in response to prevailing mechanical demands. In the clinic, studies have shown that bracing may work if patients wore the brace as prescribed. Derotational casting in young children has been shown to prevent progression and even correct the scoliosis in some patients. Convex vertebral stapling has been successful in mild curves, but the results in larger curves have been disappointing. Anterolateral tethering has been successful in mild curves in young patients, but there is limited experience with this technique in patients with large curves. CONCLUSIONS: A brace that applies the appropriate loading and is worn as prescribed may dramatically improve the results of brace treatment. A procedure using external fixation or adjustable anterolateral tethering may achieve a nonfusion correction of AIS. LEVEL OF EVIDENCE: Level II.

The role of remodeling and asymmetric growth in vertebral wedging.

BACKGROUND: Scoliosis with vertebral wedging is thought to be caused by asymmetric growth (Hueter-Volkmann law), but vertebral diaphyseal remodeling (Wolff's law) may also contribute to the deformity. We investigated whether vertebral wedging in scoliosis might involve both mechanisms. METHODS: An external fixator was used to impose a 30 degrees scoliosis and compression of 0.1 or 0.2 MPa to the tails of 10 5-week-old and 20 14-week-old Sprague-Dawley rats for 6 weeks. The rats were divided into three groups of 10 animals each: Group 1: 5-week-old animals with 0.1 MPa compression; Group 2: 14-week-old animals with 0.1 MPa compression; Group 3: 14-week-old animals with 0.2 MPa compression. Vertebral wedging and diaphyseal curvature were measured from micro CT scans performed at weeks 1, 3, and 6. Wedging due to asymmetrical growth and remodeling was calculated from a Calcein label administered at week 3 and a Xylenol label at week 6. RESULTS: The growth rate of the loaded vertebrae as a per cent of control vertebrae was 60% in Group 1, 40% in Group 2, and 30% in Group 3. The growth rate of control vertebrae in 14-week-old animals was 16% that of 5-week-old animals. The animals in all 3 groups developed a scoliosis with vertebral wedging that averaged 18.7 degrees in Group 1, 8.2 degrees in Group 2, and 10.1 degrees in Group 3. Asymmetric growth was much greater in Group 1 (5-week-old) animals. The ossified epiphyses became wedged and diaphyseal remodeling occurred in all groups. CONCLUSIONS: The major contribution to the vertebral wedging was asymmetric growth in the 5-week-old animals and diaphyseal remodeling in the 14-week-old animals. The results support the concept that if appropriate loads can be applied to human vertebrae through minimally invasive techniques, scoliosis and vertebral wedging can be corrected without a spinal fusion in both adolescents and adults.

Slipped capital femoral epiphysis.

Slipped capital femoral epiphysis (SCFE) is a common adolescent hip disorder. The etiology of SCFE includes biomechanical and biochemical factors. SCFEs are classified as stable and unstable and are more common in boys than girls and in certain racial groups; most children with SCFEs are obese. Bilateral SCFEs may have a simultaneous or sequential presentation. Imaging studies show a posterior slip of the epiphysis relative to the metaphysis, seen early on lateral radiographs. The most common and effective initial treatment for stable SCFEs is in situ central single-screw fixation; other options include epiphysiodesis, and osteotomy with or without surgical dislocation of the hip. Later reconstruction options, typically reserved for the child with functional abnormalities, include proximal femoral osteotomy, or surgical dislocation of the hip with removal of metaphyseal prominent bone to remove the source of femoroacetabular impingement. Unstable SCFEs have an increased risk of osteonecrosis; the role of reduction, methods of fixation, and decompression are controversial. The natural history of untreated SCFEs is associated with the risk of progression and later degenerative joint disease. Based on treatment methods of 30 to 40 years ago, in situ fixation provided the best long-term function with the lowest risk of complications and the most effective delay of degenerative arthritis regardless of the severity of the SCFE. Newer technologies and techniques are allowing the reevaluation of the role of either acute or later reconstructive osteotomy. It has not yet been determined if these improved techniques will result in better outcomes than in the past. Surgical dislocation of the hip with epiphyseal orientation is a considered treatment option for those technically adept at the procedure; however, the long-term outcome compared with in situ fixation is still unknown.

Alterations in the growth plate associated with growth modulation by sustained compression or distraction.

Sustained mechanical load is known to modulate endochondral growth in the immature skeleton, but it is not known what causes this mechanical sensitivity. This study aimed to quantify alterations in parameters of growth plate performance associated with mechanically altered growth rate. Vertebral and proximal tibial growth plates of immature rats and cattle, and rabbit (proximal tibia only) were subjected to different magnitudes of sustained loading, which altered growth rates by up to 53%. The numbers of proliferative chondrocytes, their rate of proliferation, and the amount of chondrocytic enlargement occurring in the hypertrophic zone were quantified. It was found that reduced growth rate with compression and increased growth rate with distraction were associated with corresponding changes in the number of proliferative chondrocytes per unit width of growth plate, and in the final (maximum) chondrocytic height in the hypertrophic zone (overall correlation coefficients 0.38 and 0.56 respectively). According to multiple linear regression coefficients for these two variables (0.72 and 1.39 respectively), chondrocytic enlargement made a greater contribution to altered growth rates.

Intervertebral disc adaptation to wedging deformation.

UNLABELLED: Although scoliosis includes wedge deformities of both vertebrae and discs, little is known about the causes of the discal changes, and whether they result from mechanical influences on growth and/or remodelling. METHODS AND MATERIALS: An external apparatus attached to transvertebral pins applied compression and 15 degrees of angulation to each of two adjacent young rat caudal intervertebral discs for 5 weeks (four animals), or for 10 weeks (four animals). Each week, micro-CT scanning documented the in vivo discal wedging. After euthanasia, tail segments (three vertebrae and the 2 angulated discs) were excised and their flexibility was measured over a range of lateral bending. The angle of maximum flexibility was recorded. Then discs were fixed in situ (with the external apparatus in place) and sectioned for polarized light microscopy. RESULTS: The disc-wedging deformity averaged 15 degrees initially, it averaged 20 degrees after 5 weeks, and then reduced to 10 degrees (in 10 week animals). The lateral bending flexibility showed a distinct maximum at an average of 1.1 degrees from the in vivo position in the 5-week animals, indicating structural remodeling of the discs almost to the deformed geometry. The 10-week animals had maximum flexibility at 1.4 degrees from the in vivo position (no significant difference between 5 and 10-week animals.) Collagen crimp angles [Cassidy et al., Conn Tiss Res 1989, 23:75-88] were not significantly different between convex and concave sides, again suggesting that remodeling had occurred. CONCLUSIONS: In a mechanically induced scoliosis deformity in skeletally immature rats, the intervertebral discs underwent remodeling within 5 weeks. This indicates that this animal model is suitable for studying adaptive wedging changes in human scoliosis.

Slipped capital femoral epiphysis: current concepts.

Slipped capital femoral epiphysis is a common hip disorder in adolescents, with an incidence of 0.2 (Japan) to 10 (United States) per 100,000. The etiology is unknown, but biomechanical and biochemical factors play an important role. Symptoms at presentation include pain in the groin, thigh, or knee. Ambulatory patients also may present with a limp. Nonambulatory patients present with excruciating pain. The slipped capital femoral epiphysis is classified as stable when the patient can walk and unstable when the patient cannot walk, even with the aid of crutches. Because the epiphysis slips posteriorly, it is best seen on lateral radiographs. The treatment of choice for stable slipped capital femoral epiphysis is single-screw fixation in situ. This method has a high probability of long-term success, with minimal risk of complications. In the patient with unstable slipped capital femoral epiphysis, urgent hip joint aspiration followed by closed reduction and single- or double-screw fixation provides the best environment for a satisfactory result, while minimizing the risk of complications.

Endochondral growth in growth plates of three species at two anatomical locations modulated by mechanical compression and tension.

Sustained mechanical loading alters longitudinal growth of bones, and this growth sensitivity to load has been implicated in progression of skeletal deformities during growth. The objective of this study was to quantify the relationship between altered growth and different magnitudes of sustained altered stress in a diverse set of nonhuman growth plates. The sensitivity of endochondral growth to differing magnitudes of sustained compression or distraction stress was measured in growth plates of three species of immature animals (rats, rabbits, calves) at two anatomical locations (caudal vertebra and proximal tibia) with two different ages of rats and rabbits. An external loading apparatus was applied for 8 days, and growth was measured as the distance between fluorescent markers administered 24 and 48 h prior to euthanasia. An apparently linear relationship between stress and percentage growth modulation (percent difference between loaded and control growth plates) was found, with distraction accelerating growth and compression slowing growth. The growth-rate sensitivity to stress was between 9.2 and 23.9% per 0.1 MPa for different growth plates and averaged 17.1% per 0.1 MPa. The growth-rate sensitivity to stress differed between vertebrae and the proximal tibia (15 and 18.6% per 0.1 MPa, respectively). The range of control growth rates of different growth plates was large (30 microns/day for rat vertebrae to 366 microns/day for rabbit proximal tibia). The relatively small differences in growth-rate sensitivity to stress for a diverse set of growth plates suggest that these results might be generalized to other growth plates, including human. These data may be applicable to planning the management of progressive deformities in patients having residual growth.

Computer-assisted algorithms improve reliability of King classification and Cobb angle measurement of scoliosis.

STUDY DESIGN: Interobserver and intraobserver reliability study of improved method to evaluate radiographs of patients with scoliosis. OBJECTIVE: To determine the reliability of a computer-assisted measurement protocol for evaluating Cobb angle and King et al classification. SUMMARY OF BACKGROUND DATA: Evaluation of scoliosis radiographs is inherently unreliable because of technical and human judgmental errors. Objective, computer-assisted evaluation tools may improve reliability. METHODS: Posteroanterior preoperative radiographic images of 27 patients with adolescent idiopathic scoliosis were each displayed on a computer screen. They were marked 3 times in random sequence by each of 5 evaluators (observers) who marked 70 standardized points on the vertebrae and sacrum in each radiograph. A computer program (Spine 2002;27:2801-5) that identified curves, calculated Cobb angles, and generated the King et al classification automatically analyzed coordinates of these points. The interobserver and intraobserver variability of the Cobb angle and King et al classification evaluations were quantified and compared with values obtained by unassisted observers. RESULTS: Average Cobb angle intraobserver standard deviation was 2.0 degrees for both the thoracic and lumbar curves (range 0.1 to 8.3 degrees for different curves). Interobserver reliability was 2.5 degrees for thoracic curves and 2.6 degrees for lumbar curves. Among the 5 observers, there was an inverse relationship between repeatability and time spent marking images, and no correlation with image quality or curve magnitude. Kappa values for the variability of the King et al classification averaged 0.85 (intraobserver). CONCLUSIONS: Variability of Cobb measurements compares favorably with previously published series. The classification was more reliable than achieved by unassisted observers evaluating the same radiographs. The same principles may be applicable to other radiographic measurement and evaluation procedures.

Demographic predictors of severity of stable slipped capital femoral epiphyses.

BACKGROUND: The outcome of stable slipped capital femoral epiphysis is directly related to the severity of the slip. If it is assumed that the slip will be less severe if it is diagnosed early, then early diagnosis should improve the prognosis. It was our purpose to determine demographic predictors of the severity of a slipped capital femoral epiphysis. METHODS: A retrospective study of 243 children with a total of 328 stable slipped capital femoral epiphyses was performed. Gender, race, age, and symptom duration were noted. Slip severity was classified as mild (<30 degrees ), moderate (30 degrees to 50 degrees ), or severe (>50 degrees ). Statistical analyses included bivariate, multivariate, linear correlation, and logistic regression techniques. RESULTS: There were 159 boys and eighty-four girls; 149 children had unilateral and ninety-four had bilateral slipped capital femoral epiphysis. Of the bilateral slips, forty-two were simultaneous and fifty-two were sequential. The mean age (and standard deviation) was 12.6 +/- 1.8 years, the mean duration of the symptoms was 5.2 +/- 7.4 months, and the mean slip angle was 29 degrees +/- 20 degrees . There were 199 mild, sixty-eight moderate, and forty-five severe slips. The mean duration of symptoms was 3.5 +/- 5.0 months for the mild slips, 7.7 +/- 9.0 months for the moderate slips, and 8.8 +/- 10.6 months for the severe slips (p < 0.0001). Older children had more severe slips: the average age was 12.3 +/- 1.8 years for the children with a mild slip, 13.0 +/- 1.6 years for those with a moderate slip, and 13.8 +/- 1.8 years for those with a severe slip (p < 0.0001). Multivariate analyses demonstrated that, among the factors studied, only the age of the patient and the duration of the symptoms were associated with the slip severity. Symptom duration and patient age were used as predictors of slip severity in a logistic regression analysis, with > or =30 degrees and <30 degrees used as the categories for slip severity, older than 12.5 years old compared with 12.5 years old or younger used as the categories for age, and more than 2.0 months compared with 2.0 months or less used as the categories for symptom duration. This model predicted the probability of a slip with confidence (p < 0.0001). The odds ratios (with 95% confidence intervals) for age and symptom duration were 2.0 (1.15 to 3.53) and 4.1 (2.34 to 7.12), respectively. Thus, a child with a stable slipped capital femoral epiphysis is 2.0 times more likely to have a moderate or severe slip if he or she is older than 12.5 years of age at the time of the diagnosis and 4.1 times more likely to have a moderate or severe slip if the duration of symptoms was longer than two months. CONCLUSIONS: The only two known significant predictors of the severity of a slipped capital femoral epiphysis are age at diagnosis and symptom duration. For any individual child, slip severity and symptom duration are unique; in a large population, there is a general correlation between slip severity and increases in patient age and increases in the duration of symptoms.

Modulation of vertebral and tibial growth by compression loading: diurnal versus full-time loading.

PURPOSE: This study was designed to determine whether the amount of endochondral growth response to mechanical compression and the underlying growth mechanism differed with night-time or day-time loading, relative to full-time loading. METHODS: Mechanical compression (nominally 0.1 MPa stress) was applied across tibial and tail vertebral growth plates of growing Sprague-Dawley rats. Four groups of animals (five per group) were used: 24/24 h (full-time loading); 12/24 h (day-loading); 12/24 h (night-loading); and 0/24 h (sham instrumented). Contralateral tibiae and adjacent vertebrae served as within-animal controls. The animals were euthanized after eight days. Growth plates were processed for quantitative histology to measure 24-h growth, total and BrdU-positive proliferative zone chondrocyte counts, and hypertrophic chondrocytic enlargement in the growth direction. RESULTS: Growth as a percentage of within-animal control averaged 82% (full-time); 93% (day-loading); 90% (night-loading); 100% (sham) for vertebrae. For proximal tibiae it averaged 70% (full-time); 84% (day-loading); 86% (night-loading); 89% (sham). Reduced amount of hypertrophic chondrocytic enlargement explained about half of this effect in full-time loaded growth plates, but was not significantly altered in half-time loaded growth plates. The remaining variation in growth was apparently explained by reduced total numbers of proliferative zone chondrocytes. These findings indicate that sustained compression loading suppressed growth more than intermittent loading at both anatomical locations.

Ischemic necrosis following clubfoot surgery: the purple hallux sign.

Ischemic necrosis, which develops rarely after clubfoot surgery, may have a vascular etiology, since many idiopathic and neurogenic clubfeet have congenital deficiency of the anterior tibial and dorsalis pedis arteries. Dorsalis pedis deficiency is demonstrated more frequently in those clubfeet showing greater deformity. Substantial hypoplasia of the profunda femoris and posterior and anterior tibial arteries was evident in the affected limb of a patient in this series who underwent postoperative arteriography. Herein, we report massive necrosis in seven limbs of six patients after clubfoot surgery and have combined this series with seven previously published cases. Additional cases support our hypothesis that arterial deficiencies put some postoperative clubfeet at risk of perioperative ischemic necrosis. Necrosis occurs in those regions supplied by the congenitally diminished anterior tibial and dorsalis pedis arteries. Knowing that children with congenital vascular deficiency are at risk for ischemic necrosis, surgeons should be alert to the subtle, early signs of ischemia and be prepared to prevent or ameliorate the consequences of this condition. Since hypoperfusion in these postoperative feet is a surgical emergency, we propose clinical guidelines for treatment for this phenomenon, which we have named the purple hallux sign.

Identifying sources of variability in scoliosis classification using a rule-based automated algorithm.

STUDY DESIGN: Use of a rule-based automated algorithm to determine sources of variability in radiographic classification. OBJECTIVES: To determine whether unambiguous rules encoded in a computer program would ensure reliable classification. SUMMARY OF BACKGROUND DATA: Reliability problems have been identified in classifications used in surgical planning for patients with thoracic idiopathic scoliosis, but the sources of unreliability are not understood. METHODS: Objective classification methodology was tested on the King et al (1983) scheme. There were two novel components: 1) positions of the corners of vertebrae in radiographs were digitized relative to a defined axis system and used in automated evaluation of spinal shape parameters required for classification; and 2) the assignment of a classification was done with a rule-based algorithm. The algorithm was implemented after some ambiguities and absence of precise definitions in the King et al classification scheme had been resolved. The algorithm was tested with radiographs of patients having adolescent idiopathic scoliosis. RESULTS: The automated procedure could encounter reliability problems in cases in which a lumbar curve was very close to crossing the midline, thoracic and lumbar curves were of approximately equal value, when the apex level in the thoracolumbar region was ambiguous, when a Cobb angle was close to 10 degrees, or when the flexibility index was close to unity. CONCLUSION: Objective measurements and rule-based algorithms can eliminate some sources of interobserver and intraobserver errors in classification of spinal deformity. When classification parameters fall close to the boundaries for classification, reliability problems will persist.

Enlargement of growth plate chondrocytes modulated by sustained mechanical loading.

BACKGROUND: Mechanical compression and distraction forces are known to modulate growth in vertebral growth plates, and they have been implicated in the progression of scoliosis. This study was performed to test the hypothesis that growth differences produced by sustained compression or distraction loading of vertebrae are associated with alterations in the amount of increase in the height of growth plate chondrocytes in the growth direction. METHODS: Compression or distraction force of nominally 60% of body weight was maintained for four weeks on a caudad vertebra of growing rats by an external apparatus attached, by means of transcutaneous pins, to the two vertebrae cephalad and caudad to it. Growth of the loaded and control vertebrae was measured radiographically. After four weeks, the animals were killed and histological sections of the loaded and control vertebrae were prepared to measure the height of the hypertrophic zone (average separation between zonal boundaries), the mean height of hypertrophic chondrocytes, and the amount of increase in cell height in the growth direction. RESULTS: Over the four weeks of the experiment, the growth rates of the compressed and distracted vertebrae averaged 52% and 113% of the control rates, respectively. The reduction in the growth rate of the compressed vertebrae was significant (p = 0.002). In the compressed vertebrae, the height of the hypertrophic zone, the mean chondrocyte height, and the amount of increase in cell height averaged 87%, 85%, and 78% of the control values, respectively, and all were significantly less than the corresponding control values. In the distracted vertebrae, these measurements did not differ significantly from the control values. The height of the hypertrophic zone and the mean chondrocyte height correlated with the growth rate (r (2) = 0.29 [p = 0.03] and r (2) = 0.23 [p = 0.06], respectively), when each variable was expressed as a proportion of the control value. The percentage changes in the measurements of the chondrocytic dimensions relative to the control values were smaller than the percentage changes in the growth rates, a finding that suggested that the rate of chondrocytic proliferation was also modulated by the mechanical loading. CONCLUSIONS: Mechanical loading of tail vertebrae in rats modulated their growth rate, which correlated with changes in the height of hypertrophic chondrocytes. The effects of compression were greater than those of distraction. CLINICAL RELEVANCE: Information about the growth rate and chondrocytic response to mechanical loads in rat vertebrae undergoing mechanically modulated growth will be helpful in determining how human vertebral growth might respond to altered loading states during progression or treatment of scoliosis and other growth-related angular skeletal deformities.

Rule-based algorithm for automated King-type classification of idiopathic scoliosis.

Recent studies have demonstrated poor reliability of the King et al. classification of idiopathic scoliosis. The purpose of the present work was to determine whether the reliability of the King classification would be improved by employing unambiguous rules for classification encoded in a computer program. Thus the only possible source of variability in classifying a given radiograph would be variable landmark identification on the radiograph. Coordinates of the four comers of each thoracic and lumbar vertebra were obtained by digitizing radiographs, using the central sacral line to define the y-axis. A computer algorithm located curve apices as the most laterally deviated vertebra in a range of two above to two below a change in the sign of vertebral tilt. End vertebrae of each curve were located as those with the greatest tilt of the superior (proximal end vertebra) or inferior (distal end vertebra). In a lumbar curve, the apical vertebra was defined as 'crossing the midline' if all four corners laid on one side of the vertical central sacral line. Curves were defined as in Table I in King et al., except that curve flexibility data were not used. The algorithm was verified on the five examples in King et al. It then classified the six examples in Lenke et al. and Cummings et al. which were classified unreliably by human observers. The algorithm was also tested on 33 radiographs of 17 patients with AIS, 8 radiographs were repeat marked by two observers. The algorithm overcame accuracy and reliability problems, except in rare cases when it was borderline whether or not a lumbar curve crossed the midline, when the apex level was ambiguous, or when a Cobb angle was close to 10 degrees.