Christine L. Farnsworth

Etiology of supracondylar humerus fractures

The specific etiology of supracondylar humerus fractures in children is not well known. All supracondylar humerus fractures treated at Childrens Hospital and Health Center, San Diego (CHSD) over an 8-year period (n = 391) were reviewed to determine specific information about the manner in which the injury occurred. Girls tended to sustain these fractures more often, and the nondominant arm was more often injured. Falls from a height accounted for 70% of the fractures. Children < or = 3 years old tended to fall off of household objects (beds, couches, other objects 3-6 feet high), and children 4 years and older tended to fall from playground equipment such as monkey bars, slides, and swings. Safety precautions should be implemented in homes of young children and at playgrounds to avoid these fractures.

Asymmetrical flexible tethering of spine growth in an immature bovine model.

Study Design. A 12-week bovine survival study of tethering anterior spine growth that included untethered control subjects. Objective. To determine the effects that a flexible cable attached to the anterolateral aspect of the thoracic spine has on spine growth in rapidly growing calves. Summary of Background Data. The search for a way to correct scoliosis without the use of an arthrodesis continues in an attempt to maintain normal spine mobility. Experience in the hemiepiphyseal stapling of long bones has provided a background rationale for attempting growth modulation in the spine. It is postulated that a mechanical tether to the anterior and lateral growth of the spine in a growing child with scoliosis may allow spontaneous correction of sagittal and coronal plane deformity obviating the need for an arthrodesis. Methods. Eight calves (age, 3–4 weeks; weight, 47 ± 4.6 kg) underwent right-side thoracotomies exposing the thoracic spine. Laterally directed anterior vertebral body screws were placed into each body and two vertebrae, either T6 and T7 or T8 and T9, were tethered with a stainless steel cable. After 12 weeks, radiographs were obtained to evaluate the degree of deformity that had developed. In addition, biomechanical testing to determine the range of motion in the tethered and untethered segments was performed. Results. The calves increased their weight 153% during the 12-week postoperative period. The radiographic analysis demonstrated scoliosis of 11.6° ± 4.8° in the tethered levels, as compared with 0.3° ± 1.7° in the control segments (P < 0.0001). Similarly, kyphosis developed in the tethered segments (5.1° ± 5.8°), as compared with −1.8° ± 3.1° at the control levels (P = 0.01). There was a significant wedging of the disc in the tethered (6.8° ± 1.6°) as compared with the untethered (0.7° ± 2°) segments (P < 0.0001). There was a trend toward lower height of the vertebrae on the tethered right side, as compared with the left side in the tethered segments (P = 0.075), whereas no side-to-side difference was noted in the control subjects (P = 0.48). Biomechanical analysis showed that the tether did not affect the range of motion in axial rotation or flexion–extension. However, the tether did restrict lateral bending as compared with that of the control subjects. When the tether was cut, the range of motion returned to levels matching that of the untethered control subjects. Conclusions. Anterolateral tethering of the spine creates kyphosis and scoliosis in this rapidly growing bovine model. The spinal tether limited motion primarily in lateral flexion. However, total lateral bending motion returned to levels comparable with control motion segments after removal of the tether. This method of spine growth modulation may provide a possible treatment for the correction of spine deformities without arthrodesis in patients who are skeletally immature. The exact mechanisms of growth modulation and the effects of tethering on disc function and integrity are unknown and deserve further study.

Spinal growth modulation with an anterolateral flexible tether in an immature bovine model: disc health and motion preservation.

Study Design. An immature bovine model was used to evaluate multilevel anterolateral flexible tethering in a growing spine. Objective. To evaluate radiographic, biochemical, histologic, and biomechanical results of tethered spinal growth. Summary of Background Data. An anterolateral flexible tether has been shown to create a kyphotic and scoliotic spinal deformity in calves. Subsequent disc health and spinal motion has not been analyzed. Methods. Four consecutive thoracic vertebral bodies (T6–T9) were instrumented anteriorly in 36 1-month-old calves. Seventeen animals (Tether Group) were instrumented with a vertebral staple-two screw construct connected by 2 flexible stainless steel cables. Nineteen animals (Control Group) were instrumented with 1 vertebral body screw with no connecting cable. After a 6-month survival period, the spines were harvest en-bloc and underwent radiographic, computed tomography, biochemical, histologic, and biomechanical analysis. Results. On average, 37.6° ± 10.6° of coronal and 18.0° ± 9.9° of sagittal deformity was created in the Tether Group, with significant vertebral wedging toward the tether (P < 0.001). Disc thickness decreased significantly in the Tether Group (P < 0.001), however, disc wedging was not observed. There was no change in gross morphologic disc health or disc water content (P = 0.73). However, proteoglycan synthesis was significantly greater in the tethered discs compared with controls (P < 0.001), and collagen type distribution was different with a trend toward increased type II collagen present on the tethered side of the disc (P = 0.09). Tethers significantly increased spinal stiffness in lateral bending and in flexion/extension (P < 0.05) without affecting torsional stiffness, however, after tether removal range of motion returned to control values. Conclusion. Tethering resulted in vertebral wedging while maintaining spinal flexibility. Although changes in proteoglycan synthesis, collagen type distribution, and disc thickness were observed, the tethered discs had similar water content to control discs and did not demonstrate gross morphologic signs of degeneration. Growth modulation is an attractive treatment option for growing patients with scoliosis, avoiding multilevel fusions or brace wear. Strategies for fusionless scoliosis correction should preserve disc health, as adolescent patients will rely on these discs for decades after treatment.

Spinal growth modulation with use of a tether in an immature porcine model.

BACKGROUND Spinal growth modulation by tethering the anterolateral aspect of the spine, as previously demonstrated in a nonscoliotic calf model, may be a viable fusionless treatment method for idiopathic scoliosis. The purpose of the present study was to evaluate the radiographic, histologic, and biomechanical results after six and twelve months of spinal growth modulation in a porcine model with a growth rate similar to that of adolescent patients. METHODS Twelve seven-month-old mini-pigs underwent instrumentation with a vertebral staple-screw construct connected by a polyethylene tether over four consecutive thoracic vertebrae. The spines were harvested after six (n = 6) or twelve months (n = 6) of growth. Monthly radiographs, computed tomography and magnetic resonance imaging scans (made after the spines were harvested), histologic findings, and biomechanical findings were evaluated. Analysis of variance was used to compare preoperative, six-month postoperative, and twelve-month postoperative data. RESULTS Radiographs demonstrated 14 degrees +/- 4 degrees of coronal deformity after six months and 30 degrees +/- 13 degrees after twelve months of growth. Coronal vertebral wedging was observed in all four tethered vertebrae and progressed throughout each animals survival period. Disc wedging was also created; however, in contrast to the findings associated with vertebral wedging, the tethered side was taller than the untethered side. Magnetic resonance images revealed no evidence of disc degeneration; however, the nucleus pulposus had shifted toward the side of the tethering. Midcoronal undecalcified histologic sections showed intact bone-screw interfaces with no evidence of implant failure or loosening. With the tether cut, stiffness decreased and range of motion increased in lateral bending away from the tether at both time-points (p < 0.05). CONCLUSIONS In this porcine model, mechanical tethering during growth altered spinal morphology in the coronal and sagittal planes, leading to vertebral and disc wedging proportional to the duration of tethering. The resulting concave thickening of the disc in response to the tether was not anticipated and may suggest a capacity for the nucleus pulposus to respond to the compressive loads created by growth against the tether.

A Biomechanical Comparison of Open and Thoracoscopic Anterior Spinal Release in a Goat Model

Study Design. A biomechanical assessment of anterior release and discectomy in the thoracic spine was performed on an animal model using thoracoscopic and open thoracotomy techniques. Objectives. To compare the relative efficacy of these two techniques of release in achieving increased spinal mobility. Background Data. The clinical use of video‐assisted thoracoscopy in the correction of spinal deformity is increasing. The effectiveness of thoracoscopic anterior spinal release with discectomy has not been evaluated biomechanically. Methods. Anterior release with discectomy was performed on six midthoracic motion segments in five mature goats. The thoracoscopic technique was used for three levels on one side, and an open thoracotomy was used for the alternating three levels of the contralateral side. The duration of surgery for disc excision and the amount of blood loss for each technique were recorded. The intact cranial and caudal motion segments served as controls. The motion segments were individually subjected to nondestructive biomechanical testing. Torsional, sagittal, and coronal bending torques were applied, and the resulting angular displacement was measured. Results. The duration of surgery to remove a disc thoracoscopically decreased as experience was gained by the surgeon. The amount of intraoperative blood loss was comparable using the two methods. There was significantly increased flexibility in the released segments with both techniques, compared with the flexibility in the intact levels for all three loading directions. There was no difference in the motion obtained after release between the two techniques. Conclusion. Open and thoracoscopic anterior release and discectomy have been demonstrated, through biomechanical in vitro testing, to increase the flexibility of the spine to a similar extent.

Multilevel spinal growth modulation with an anterolateral flexible tether in an immature bovine model.

Study Design. A bovine model was used to evaluate the effects of a multilevel anterolateral flexible tether in a growing spine. Objective. To evaluate the radiographic changes in a growing spine with a multilevel anterolateral tether. Summary of Background Data. Spinal growth modulation has long been considered as a conceptually attractive and elegant possible alternative to arthrodesis in the treatment of idiopathic scoliosis. Although some experimental studies have described spinal growth modulation, few have described a purely mechanical tether. Clinical studies of spinal epiphysiodesis have described inconsistent curve stabilization and/or correction. Methods. A total of 33 one-month-old male calves underwent a single thoracotomy and placement of vertebral screws at T6–T9. In 11 animals, one screw per level was connected by a 3/16 in. stainless steel cable (single tether). In 11 animals, two screws per level were connected by two cables (double tether). In the remaining 11 animals, single screws in each level were left unconnected (control). After 6 months, the spines were harvested and underwent radiographic analysis. Results. In the control group, there was little change in the coronal and sagittal measurements during the survival period. In the single tether group, there was variable instrumentation fixation and inconsistent creation of coronal deformity, which ranged from 0° to 31°. The double-tether group had more consistent creation of deformity, ranging from 23° to 57°. Conclusions. Given adequate bony fixation, a flexible lateral spinal tether can affect growth modulation. This technique of growth modulation may serve as a future fusionless method of correction in a growing patient with scoliosis.

A comparison of early versus late conversion from intravenous to oral therapy in the treatment of septic arthritis

Background Clinical outcomes of children with bacterial septic arthritis, common in the pediatric age group, are often satisfactory with early recognition, prompt surgical drainage, and appropriate antibiotic therapy. However, the optimal duration and route of antibiotic administration for treatment of septic arthritis continues to be debated, as traditional treatment favored longer intravenous (IV) therapies yet oral regimens are increasingly available that are more cost effective, safe and produce satisfactory disease resolution. Methods Records of 186 patients from two childrens hospitals, one that was thought to convert from IV to oral antibiotic therapy considerably earlier than the other, treated between 1985 and 1995 for bacterial septic arthritis were reviewed. Patients with concurrent osteomyelitis were excluded. Results Patients at Hospital ♯1 were converted to oral antibiotics after 7.4±7.4 days of IV antibiotic therapy and at Hospital ♯2 after 18.6±13.6 (P<0.001) days of IV therapy. Both groups received an average of four weeks of total antibiotic treatment. There was similar time to defervescence (2.4±3.2 d vs. 2.4±3.8 d, P>0.05) and to normalization of erythrocyte sedimentation rate (35.7±19.7 d vs. 33.8±44.9 d, P>0.05) in the patients converted to oral therapy early compared to those converted late. One case of mild avascular necrosis with no clinical disability developed in a patient from Hospital ♯2. Conclusions We conclude that the clinical outcome in patients with septic arthritis converted to oral antibiotic therapy early in their treatment based on defined criteria was similar to those converted late.

Effects of Intraoperative Tensioning of an Anterolateral Spinal Tether on Spinal Growth Modulation in a Porcine Model

STUDY DESIGN in vivo analysis in an immature porcine model. OBJECTIVE to evaluate the effect of intraoperative tensioning of an anterolateral flexible spinal tether on growth modulation manifested as deformity creation, disc response, spinal motion, and screw fixation using radiographs, computed tomography, magnetic resonance imaging, biomechanical testing, and histology. SUMMARY OF BACKGROUND DATA spinal growth modulation using an anterolateral flexible tether has been proposed as a nonfusion surgical deformity correction strategy for idiopathic scoliosis and has been successfully demonstrated in a porcine model to create spinal deformity while maintaining disc viability. METHODS twelve 7-month-old mini-pigs were instrumented with a screw-staple and polyethylene tether construct over 4 consecutive thoracic vertebrae (T8-T11). Intraoperative tensioning of the tether (250 N) was performed in alternate pigs (Pretensioned and Untensioned groups, n = 6 per group). Screws were coated with hydroxyapatite in half of the animals in each surgical group. Preoperative, postoperative, and monthly radiographs were evaluated, comparing deformity creation, vertebral body wedging, and disc wedging between the groups. Vertebral body shape was evaluated by computed tomography. Magnetic resonance and histology evaluated disc health. Biomechanical testing was performed to determine the effect of tensioning the tether on spinal motion and screw fixation. RESULTS intraoperative tensioning produced immediate coronal deformity (8° ± 4° vs. 2° ± 1° in untensioned spines; P = 0.01) and apical disc (T9-T10) wedging, vertex on tethered side, (5° ± 2° vs. 2° ± 1°; P = 0.01). After 12 months, the groups were similar in coronal deformity (28° ± 18° pretensioned, 27° ± 11° untensioned, P = 0.88), sagittal deformity (25° ± 3° vs. 22° ± 3°; P = 0.14), vertebral body wedging (10° ± 5° vs. 8° ± 3°; P = 0.45), and disc wedging (-4° ± 1° vs. -4° ± 3°; P = 0.88). There was no radiographic evidence of screw loosening. One of the discs from each group had diminished T2 signal after 12 months of tethering. Tether pretensioning did not affect spinal stiffness or motion. Interestingly, screw fixation increased with pretensioning; however, there was no significant advantage with hydroxyapatite coating. Histology demonstrated normal-appearing discs. CONCLUSION pretensioning of the tether created immediate deformity without effecting ultimate vertebral or disc deformity creation. Spinal motion and stiffness were not altered by pretensioning; however, pretensioning increased the torque required for screw extraction.

Thoracic vertebral screw impingement on the aorta in an in vivo bovine model

Study Design. A bovine model was used to evaluate the effects of thoracic vertebral screw impingement of the aorta. Objectives. To evaluate the histologic and biomechanical changes in aortic wall tissue that was severely impinged by abutting instrumentation. Summary of Background Data. Case reports of vascular injury associated with spinal instrumentation generally describe intraoperative injury; some report delayed presentation of large vessel damage. Risks associated with placing instrumentation adjacent to large vessels are largely unknown. Methods. Six 1-month-old calves underwent left-sided thoracotomies, exposing the anterior thoracic spine and aorta. With the heads removed, screws were inserted in reverse fashion into T6 through T11, leaving the screw tips 1 cm proud and abutting the aorta. After 3, 6, or 12 months (2 calves each), the spines were resected with the adjacent aorta and underwent radiographic, histologic, and biomechanical testing. Results. Computed tomography revealed varying degrees of vessel impingement. Although there were no frank ruptures, 96% of aortic specimens showed histopathologic changes, including 52% with wall thinning; 43% were no longer impinged, yet 60% of these had increased collagen (scar). Biomechanical testing of screw-impinged aortas demonstrated a lower failure stress (1.2 ± 0.5 N/mm2 vs. 1.8 ± 0.4 N/mm2, P = 0.016) but no difference in failure strain (42 ± 9% vs. 32 ± 10%, P = 0.06) than controls. Conclusions. Major impingement of vertebral screws on the aorta caused acute and chronic histopathologic and biomechanical changes in the vessel wall. This model represents a severe form of vessel penetration by a screw that confirms such a “worst case” scenario results in marked compromise of the vessel wall integrity. The sequelae of less severe impingement are unknown.

Pedicle screw surface coatings improve fixation in nonfusion spinal constructs.

Study Design. Biomechanical and histologic analysis. Objective. To compare the strength of the bone-screw interface of standard uncoated pedicle screws with screws treated with hydroxyapatite (HA), titanium plasma spray (TPS), and a composite HA-TPS coating. Summary of Background Data. Transpedicular screw fixation has become the gold standard in the treatment of various thoracolumbar spinal conditions. Pedicle screw loosening, however, has been reported, especially in mechanically demanding constructs or in vertebrae with low bone mineral density. Methods. Six mature porcine were instrumented with 4 types of titanium monoaxial pedicle screws (uncoated, HA-only coated, TPS-only coated, and HA-TPS composite coated) in a systematically varied, single-blinded fashion. After a 3-month survival period, the spines were harvested en-bloc and “time zero” control screws were instrumented in adjacent vertebrae. Screw placement and bone mineral density were evaluated with a postharvest computed tomography, and the strength of the tissue-implant interface was evaluated with a torsional screw extraction analysis (60 screws) and a nondecalcified histologic analysis (16 screws). Results. At 3 months postoperative, peak torque increased for all 3 types of coated screws (increased fixation) and decreased significantly for the uncoated screws (P < 0.001). Although 3-month peak torque was not statistically different between the 3 screw coatings, 4 of 10 TPS-only coated screws had a peak torque that was nearly 0 (<0.1 N m) versus only 1 of 10 HA-only screws and 0 of 10 HA-TPS composite screws. Histologic analysis confirmed the biomechanical findings with improved osseointegration in the HA-only and HA-TPS composite screws. Conclusion. Pedicle screw coatings that promote mechanical interlocking, TPS, or direct osteoblast bonding(HA) increased screw fixation in this nonfusion model. More non-HA coated screws, however, were thought to be “loose” with a nearly zero peak extraction torque and fibrous encapsulation. Increased osseointegration with HA may result in a decreased incidence of screw loosening and improved outcomes of transpedicular spinal instrumentation in nonfusion procedures.