Skeletal muscle and plasma concentrations of cefazolin during complex paediatric spinal surgery

BACKGROUND

Surgical site infections (SSIs) can have devastating consequences for children who undergo spinal instrumentation. Prospective evaluations of prophylactic cefazolin in this population are limited. The purpose of this study was to describe the pharmacokinetics and skeletal muscle disposition of prophylactic cefazolin in a paediatric population undergoing complex spinal surgery.

METHODS

This prospective pharmacokinetic study included 17 children with adolescent idiopathic scoliosis undergoing posterior spinal fusion, with a median age of 13.8 [interquartile range (IQR) 13.4-15.4] yr and a median weight of 60.6 (IQR 50.8-66.0) kg. A dosing strategy consistent with published guidelines was used. Serial plasma and skeletal muscle microdialysis samples were obtained during the operative procedure and unbound cefazolin concentrations measured. Non-compartmental pharmacokinetic analyses were performed. The amount of time that the concentration of unbound cefazolin exceeded the minimal inhibitory concentration for bacterial growth for selected SSI pathogens was calculated.

RESULTS

Skeletal muscle concentrations peaked at a median of 37.6 (IQR 26.8-40.0) µg ml(-1) within 30-60 min after the first cefazolin 30 mg kg(-1) dose. For patients who received a second 30 mg kg(-1) dose, the peak concentrations reached a median of 40.5 (IQR 30.8-45.7) µg ml(-1) within 30-60 min. The target cefazolin concentrations for SSI prophylaxis for meticillin-sensitive Staphylococcus aureus (MSSA) and Gram-negative pathogens were exceeded in skeletal muscle 98.9 and 58.3% of the intraoperative time, respectively.

CONCLUSIONS

For children with adolescent idiopathic scoliosis undergoing posterior spinal fusion, the cefazolin dosing strategy used in this study resulted in skeletal muscle concentrations that were likely not to be effective for intraoperative SSI prophylaxis against Gram-negative pathogens.

Pathological fractures in children

Pathological fractures in children can occur as a result of a variety of conditions, ranging from metabolic diseases and infection to tumours. Fractures through benign and malignant bone tumours should be recognised and managed appropriately by the treating orthopaedic surgeon. The most common benign bone tumours that cause pathological fractures in children are unicameral bone cysts, aneurysmal bone cysts, non-ossifying fibromas and fibrous dysplasia. Although pathological fractures through a primary bone malignancy are rare, these should be recognised quickly in order to achieve better outcomes. A thorough history, physical examination and review of plain radiographs are crucial to determine the cause and guide treatment. In most benign cases the fracture will heal and the lesion can be addressed at the time of the fracture, or after the fracture is healed. A step-wise and multidisciplinary approach is necessary in caring for paediatric patients with malignancies. Pathological fractures do not have to be treated by amputation; these fractures can heal and limb salvage can be performed when indicated.

Fractures of the odontoid in children with an open basilar synchondrosis

Fractures of the odontoid in children with an open basilar synchondrosis differ from those which occur in older children and adults. We have reviewed the morphology of these fractures and present a classification system for them.

There were four distinct patterns of fracture (types IA to IC and type II) which were distinguished by the site of the fracture, the degree of displacement and the presence or absence of atlantoaxial dislocation. Children with a closed synchondrosis were classified using the system devised by Anderson and D’Alonzo. Those with an open synchondrosis had a comparatively lower incidence of traumatic brain injury, a higher rate of missed diagnosis and a shorter mean stay in hospital. Certain subtypes (type IA and type II) are likely to be missed on plain radiographs and therefore more advanced imaging is recommended. We suggest staged treatment with initial stabilisation in a Halo body jacket and early fusion for those with unstable injuries, severe displacement or neurological involvement.

Klippel-Feil syndrome: clinical features and current understanding of etiology

Klippel-Feil syndrome occurs in a heterogeneous group of patients unified only by the presence of a congenital defect in the formation or segmentation of the cervical spine. Numerous associated abnormalities of other organ systems may be present. This heterogeneity requires comprehensive evaluation of all patients and treatment regimes that can vary from modification of activities to extensive spinal surgeries. This also has made delineation of diagnostic and prognostic classes difficult and has complicated elucidation of the genetic etiology of the syndrome. Furthermore, it is unclear whether Klippel-Feil syndrome is a discrete entity, or if it is one point on a spectrum of congenital spinal deformities. Pedigree analysis has identified a human genetic locus for the disease. Mouse models suggest members of the PAX gene family and Notch signaling pathway as possible etiologic candidates. Only by identifying the link between the genetic etiology and the phenotypic pathoanatomy of Klippel-Feil syndrome will we be able to rationalize the heterogeneity of the syndrome.

Hereditary multiple exostoses: one center's experience and review of etiology

Hereditary multiple exostosis is a genetic disorder characterized by multiple osteochondromas that can cause pain, deformity, and potential malignant degeneration. Linkage analysis has identified a family of EXT genes which, if mutated, can lose heterozygosity and potentially cause osteochondromas. A database was established of 43 patients with hereditary multiple exostoses treated at a tertiary pediatric healthcare system. Twenty patients had a known family history of the disorder. All patients were diagnosed between birth and 13 years. Symptoms or deformity were observed in the forearms of 29 patients, the knees of 37 patients, and the ankles of 28 patients. Valgus knee deformity related to hereditary multiple exostoses, previously reported to be attributable to proximal tibial changes alone, resulted from proximal tibial or distal femoral valgus deformities in this series. Twenty-seven patients required between one and five surgeries to address their lesions. No patient had malignant degeneration of an osteochondroma; however, three patients had first-degree relatives with transformation of an osteochondroma to chondrosarcoma. This database now may be a resource for additional analysis. By correlating specific genetic mutations with clinical manifestations, it may be possible to stratify patients into subtypes of hereditary multiple exostoses and identify genetic markers associated with malignant degeneration.

Orthopaedics in the developing world: present and future concerns

Half of the world's population lack access to adequate primary health care, and two thirds lack access to orthopaedic care. Globally, the need for health care outstrips the available resources. This problem is compounded in the developing world by a lack of trained medical personnel, a lack of medical facilities, and, in many regions, an inability to access existing facilities. There is little specific epidemiologic data about the exact burden of musculoskeletal disease in these countries, but most agree that it is reasonable to assume that it will increase. In the least developed and developing nations, problems with access are related to fundamental issues such as infrastructure, physical facilities, equipment, and trained personnel. There are a number of ways in which the orthopaedic community can become involved in ameliorating the burden. Education is the most effective method of providing a sustainable solution. The objective of educational organizations should be to train local health-care workers at all levels in their own environment to provide sustainable and appropriate care so that the programs become self-sufficient and ensure a continued supply of competent medical personnel.

Analysis of the cause, classification, and associated injuries of 166 consecutive pediatric pelvic fractures

SUMMARY

Pediatric pelvic fractures are serious injuries. Anatomical differences exist between pediatric and adult populations, leading to different causes and rates of death, fracture patterns, and associated injuries. This study is the largest consecutive series of pediatric pelvic fractures from one institution emphasizing the unique aspects seen in pediatrics. One hundred sixty-six children were included. Plain radiography and computed tomography scans were used to classify pelvic fractures. Multisystem injuries occurred in 60%, and 50% sustained additional skeletal injuries. The death rate was 3.6%. Head and/or visceral injuries were the causes of all deaths. Life-threatening hemorrhage did not occur. Urethral injury was not seen as often as in adults. Anterior ring fractures were the most common type, dominated by pedestrian versus motor vehicle trauma. Anatomical differences and mechanism of injury may play a role in these contrasting findings.

The orthopedists' perspective: bone tumors, scoliosis, and trauma

Although a detailed, comprehensive look at pediatric orthopedists' use of imaging is beyond the scope of this article, we offer an orthopedist's perspective of the role imaging plays in the care of children with tumors, scoliosis, and trauma. Given the growing, dynamic state of a child's skeleton, the long-term consequences of injury must always be considered.

A technique of occipitocervical arthrodesis in children using autologous rib grafts

STUDY DESIGN

Description of an operative technique with an illustrative case report.

OBJECTIVES

The technique is presented to provide an alternative to iliac crest graft procedures for achieving occipitocervical fusion in children. This technique is particularly useful in children with instability after extensive decompression or laminectomy and in children with a large protuberant occiput.

SUMMARY OF BACKGROUND DATA

The majority of techniques previously described for occipitocervical fusion in children rely on corticocancellous iliac crest autograft. Results generally have been promising; however, it can be difficult to harvest enough graft to span large defects after extensive decompression or to contour an iliac crest graft to a protuberant occiput. Structural rib autograft is superior in terms of availability and its unique and modifiable contour. Theoretical benefits of rib graft include superior strength and lower donor site morbidity.

METHODS

The surgical technique is described. A case of a 2-year-old boy with Down's syndrome and myelopathy secondary to cervical instability is reviewed.

RESULTS

The patient underwent occipitocervical arthrodesis using the technique described. The child made a full neurologic recovery, and at the 2-years follow-up evaluation, the graft had incorporated and the spine was stable.

CONCLUSION

A technique of occipitocervical arthrodesis in children is described using autologous rib graft. This procedure was designed to span large defects or to deal with a large protuberant occiput; however, it is also useful for less demanding cases and may offer several advantages compared with procedures relying on iliac crest graft.

Anterior vertebral screw strain with and without solid interspace support

STUDY DESIGN

This in vitro biomechanical study examines segmental anterior vertebral screw strain and solid rod construct stiffness with and without the addition of multilevel, threaded cortical bone dowels in a bovine model.

OBJECTIVE

To determine whether strain at the bone-screw interface is higher at the end levels during physiologic range loading, and whether solid interspace support decreases segmental strain on the implant.

SUMMARY OF BACKGROUND DATA

Anterior instrumentation provides greater correction and preserves distal motion segments. However, nonunion and implant failure are observed more frequently than with posterior segmental instrumentation, and when observed, loss of fixation occurs at the end levels.

METHODS

Eight calf spines underwent mechanical testing in the following sequence: 1) intact condition, 2) anterior release with anterior solid rod and bicortical rib grafts, and 3) anterior release with anterior solid rod and threaded cortical bone dowels (L2-L5). Instrumented vertebral screws were used to assess strain within the vertebral body by the near cortex, whereas an anterior extensometer spanning the instrumented segments was used to measure segmental displacements to calculate construct stiffness. The protocol included axial compression (-400 N), right lateral bending (4 Nm (Newton-meter), away from the implant), and left lateral bending (4 Nm, toward the implant). Statistical analysis included a one-way analysis of variance and a Student-Newman-Keuls post hoc test. A pilot study was performed using four additional specimens loaded for 4000 cycles to investigate macroscopic loosening after fatigue loading.

RESULTS

In lateral bending toward the implant, the strain was higher at both end levels, with no differences between the rib and dowel reconstructions. The stiffness values were greater than the intact values for both groups. In lateral bending away from the implant, the strain also was higher at both end screws, and the dowel group had less strain at these levels than the rib group. Both groups were stiffer than the intact condition, and the dowel group was stiffer than the rib group. Axial compressive strain also was higher at the end levels, but this difference did not reach statistical significance. The rib group did not reach intact stiffness values, whereas the dowel group was stiffer than the intact condition. The fatigue study showed gross loosening at one or both end levels in all cases.

CONCLUSIONS

Higher strain was observed at the bone-screw interface in both end screws of an anterior solid rod construct during lateral bending, which correlates with the clinically observed failure location. This suggests that physiologic range loading may predispose to failure at the end levels. Disc space augmentation with solid implants increased construct stiffness in all three load paths and decreased strain at the end levels in lateral bending away from the implant. Future implant modifications should achieve better fixation at the end screws, and the current model provides a means to compare different strategies to decrease strain at these levels.

Results of brace treatment of scoliosis in Marfan syndrome

STUDY DESIGN

Retrospective review of a defined Marfan population with traditional indications for bracing.

OBJECTIVES

To determine the success rate of brace treatment in keeping curves from progressing by more than 5 degrees or exceeding 45 degrees.

SUMMARY OF BACKGROUND DATA

Few studies exist regarding brace treatment of Marfan syndrome, and they include many patients with curves of more than 45 degrees, as well as some who are near maturity. All of the prior studies risk the possibility of some selection bias.

METHODS

Patients were selected from support groups and several institutions. Inclusion criteria were: Definite diagnosis of Marfan syndrome, curve of 45 degrees or less, Risser sign 2, 1, or 0 at inception of bracing, recommended wear of 18 hours or more per day, and follow-up until maturity or surgery (minimum, 2 years). Success was defined as curve progression of 5 degrees or less and final curve remaining 45 degrees or less. Failure was a final curve of more than 45 degrees. Twenty-four patients met the criteria. There were 15 girls and 9 boys. Twenty-two patients wore a brace as recommended. Two additional patients were unable to tolerate it.

RESULTS

Mean age at inception of bracing was 8.7 years (range, 4-12 years). There were 14 double major, 6 thoracic, and 4 thoracolumbar curves with a mean size of 29 degrees at the beginning of bracing. The stated wearing time averaged 21 hours per day. Five patients had significant pain over bony prominences. Although correction of the curve in brace was good (45%), only 4 of the patients had success, and in 20 of the 24 treatment was considered a failure. Mean progression was 6 degrees +/- 8 degrees per year, for a final mean curve of 49 degrees. Sixteen of the patients had, or were advised to have, surgical correction. The difference in age and degree of curvature were not statistically significant between the success and nonsuccess groups.

CONCLUSIONS

The success rate for brace treatment of Marfan scoliosis is 17%, which is lower than that reported for idiopathic scoliosis. Possible reasons include increased progressive forces, altered transmission of corrective pressure to the spine, and younger age at inception of bracing. Because there was no control group, it is unknown whether bracing slowed curve progression. Physicians should understand that most patients with Marfan syndrome who have a curve of more than 25 degrees and a Risser sign of 2 or less will reach the surgical range, even with brace treatment.

Two primary osteosarcomas in a patient with Rothmund-Thomson syndrome

Rothmund-Thomson syndrome is an autosomal recessive disorder characterized by poikilodermatous skin changes that develop in infancy. Associated manifestations include juvenile cataracts, sparse hair, short stature, skeletal defects, dystrophic nails and teeth, and hypogonadism. An increased incidence of malignancy, including osteosarcoma, has been reported in patients with Rothmund-Thomson syndrome. The molecular basis of the disorder is not known. This report describes a patient with Rothmund-Thomson syndrome in whom two primary osteosarcomas developed 12 years apart. The presentation, diagnosis, and treatment of osteosarcoma in this patient with Rothmund-Thomson syndrome are described. Cytogenetic and molecular analysis of peripheral blood and skin fibroblasts had low level mosaicism for trisomy of chromosomes 2 and 8. Although several patients have been described with mosaic trisomy 8 and i(2q) (mosaic isochromosome for the long arm of chromosome 2), the patient described here is the first to have mosaic trisomy for the entire chromosomes 2 and 8. The cytogenetic findings in this patient are consistent with an underlying defect in chromosomal stability.

Major pediatric hand trauma associated with fireworks

OBJECTIVES

To characterize the injury pattern and economic impact of major pediatric hand trauma secondary to fireworks.

DESIGN

Retrospective.

SETTING

Pediatric Level I trauma center.

INTERVENTION

N/A MAIN OUTCOME MEASUREMENTS: Fractures, amputations, soft tissue defects, length of hospitalization, number and type of procedures performed were obtained from charts, radiographs, and operative reports. Hospital charges were obtained from the billing office.

PATIENTS/PARTICIPANTS

Records of patients with a diagnosis of fireworks-related injuries admitted over a period of ten years were reviewed. Twenty-two patients were identified to have sustained twenty-two hand injuries. The group consisted of nineteen boys and three girls, with an average age of 9.3 years (range, 4 to 17 years).

RESULTS

There were thirty-one fractures, nineteen amputations, and one dislocation. The nineteen amputations occurred in nine hands. Local skin graft or flap coverage was required in six hands acutely, and delayed soft tissue procedures were performed on four hands. Four hands had digital neurovascular injuries; two required microsurgical repairs at the time of injury, and two were irreparable. Resource use included: average hospital stay of 4.3 days (range, 0 to 20), average number of trips to the operating room, 1.2 (range, 0 to 3), and average hospital charges of $11,582 (range, $1,035 to $39,489).

CONCLUSIONS

This study illustrates the severity of pediatric hand injuries associated with fireworks and the significant burden placed on medical resources in treating these injuries. Efforts toward public education and legislative reforms may help to prevent these unnecessary injuries.

Avascular necrosis in children with acute lymphoblastic leukemia

This study describes the prevalence and demographics of avascular necrosis (AVN) in children with acute lymphoblastic leukemia (ALL). With improving survival of ALL patients on modern chemotherapy regimens, an increasing number of children with AVN will be presenting to orthopaedists. From 1991 to 1996, 202 patients were treated for ALL at a major tertiary pediatric cancer referral center. Eight patients (4.0%) subsequently developed AVN at an average of 30.0 months after beginning chemotherapy. A total of 27 documented joints were involved, with an average of 3.4 joints affected per patient diagnosed with AVN. The subset of patients with high-risk ALL who underwent an aggressive chemotherapy protocol was particularly susceptible to developing AVN. Six of 58 high-risk ALL patients (10.3%) developed AVN at an average of 18.5 months. As ALL patients now frequently survive into adulthood, orthopaedists will be increasingly called on to manage AVN affecting multiple joints in children and young adults.

Prevention of positional brachial plexopathy during surgical correction of scoliosis

Continuous intraoperative monitoring of spinal cord function using somatosensory evoked potentials (SSEP) has gained nearly universal acceptance as a reliable and sensitive method for detecting and possibly preventing neurologic injury during surgical correction of spinal deformities. In several reports, spinal cord injury was identified successfully based on changes in SSEP response characteristics, specifically amplitude and latency. Less well documented and used, however, is monitoring of peripheral nerve function with SSEPs to identify and prevent the neurologic sequelae of prolonged prone positioning on a spinal frame. The authors describe a patient who underwent surgical removal of spinal instrumentation but was not monitored. A brachial plexopathy developed in this patient from pressure on the axilla exerted by a Relton-Hall positioning frame during spinal surgery. In addition, data are presented from 15 of 500 consecutive pediatric patients who underwent surgical correction of scoliosis between 1993 and 1997 with whom intermittent monitoring of ulnar nerve SSEPs was used successfully to identify impending brachial plexopathy, a complication of prone positioning. A statistically significant reduction in ulnar nerve SSEP amplitude was observed in 18 limbs of the 500 patients (3.6%) reviewed. Repositioning the arm(s) or shoulders resulted in nearly immediate improvement of SSEP amplitude, and all awoke without signs of brachial plexopathy. This complication can be avoided by monitoring SSEPs to ulnar nerve stimulation for patients placed in the prone position during spinal surgery.

Fracture patterns in children and young adults who fall from significant heights

Trauma is a leading cause of morbidity and mortality for children and young adults. When all causes of trauma are considered, falls are the most common mechanism of injury. To address specifically age-related fracture patterns in children who fall, we identified 125 consecutive patients, 21 years old or younger, who fell from a height of 10 feet or greater. The medical records and radiographs for 110 of these patients were available for review. Patients were divided into three groups based on age: there were 25 infant/toddlers (0-2 years), 55 children (3-10 years), and 30 adolescent/young adults (11-21 years). We found statistically significant differences in fracture distribution between the groups. The adolescent/young adult group sustained a greater number of vertebral fractures (p<0.003) and total fractures per fall (p<0.015). The children, in contrast, had a greater number of long bone fractures (p<0.05). Knowledge of age-related fracture patterns could result in improved diagnosis and treatment of these injuries.

Growth disturbances after distal tibial physeal fractures

Twenty-four patients with distal tibial growth disturbance were reviewed. Disturbances were classified as physeal bar (prior to deformity), angular, linear or combined deformities. Treatment consisted of osteotomy in fourteen, epiphyseodesis in seven, excision of bony bar in two, and observation in one patient. Follow up was an average 36.6 months (range 4-129 months) after treatment of growth disturbance. The age at time of injury was 10.4 years of age average (range 3-15 years). There were 12 SH2, 2 SH3, 7 SH4, and 3 SH5 distal tibial physeal fractures. Thirteen of 15 fractures considered high energy and only 1 of 9 fractures considered low energy resulted in angular deformity. Angular and linear deformities presented an average 46 months (range 12-120 months) and physeal bars at an average 14 months (range 6-25 months) after injury. Patients with a delay in presentation of growth disturbance greater than 24 months had angular deformities in 92% compared with 33% in children presenting less than or at 24 months. Treatment based on type of deformity, age at time of injury, and growth remaining was considered successful in 83%. Patients with angular or linear deformities were more likely to present late, have high energy injuries, be male patients and have Salter-Harris types IV and V. Early diagnosis and treatment of growth disturbance can prevent severe deformity.

Augmentation of an anterior solid rod construct with threaded cortical bone dowels. A biomechanical study

STUDY DESIGN

This static, nondestructive, in vitro biomechanical study examines anterior solid rod construct stiffness following the addition of multilevel, threaded cortical bone dowels in a bovine model. A comparison is made with a clinically relevant posterior construct with and without an anterior release.

OBJECTIVES

To determine if the addition of solid, multilevel disc space implants will increase construct rigidity, while maintaining or enhancing anterior column length.

SUMMARY OF BACKGROUND DATA

Anterior instrumentation for thoracolumbar and lumbar scoliosis has achieved greater correction and preserved distal motion segments; however, kyphosis over the instrumented segments and nonunion have been observed more frequently than with posterior segmental spinal instrumentation.

METHOD

Fifteen calf spines underwent mechanical testing. Group A (n = 7) included anterior constructs: 1) intact, 2) anterior release/rod/rib graft (L2-L5), and 3) anterior release/rod/dowels (L2-L5). Group B (n = 8) included posterior constructs: 1) intact, 2) posterior rod without anterior release (T13-L5), 3) posterior rod (T13-L5)/anterior release/rib graft (L2-L5). The protocol included axial compression (-600 N), axial rotation (+7 Nm), flexion/extension (+7.5 Nm), and lateral bending (+7.5 Nm). An anterior extensometer measured segmental displacements to calculate construct stiffness. Lateral radiographs evaluated alignment for the anterior constructs. Statistical analysis involved a one way analysis of variance (ANOVA) and a Student-Newman-Keuls post hoc test.

RESULTS

All reconstructions restored stiffness to intact values with the exception of the dowels alone in axial rotation. The rod/dowel construct was stiffer than all other groups in axial compression, flexion/extension, and lateral bending, with the exception of the posterior rod without discectomy, which was superior in flexion and statistically similar in extension, lateral bending, and axial rotation. The anterior construct with rib graft was equivalent to the posterior construct with rib graft in all modes of testing. The dowels created greater lordosis than the bicortical rib grafts.

CONCLUSIONS

Disc space augmentation increased stiffness except in axial rotation, in which values were restored to the intact level. Stiffness was superior to a clinically relevant posterior instrumentation comparison group following anterior release, and was equivalent to a posterior construct without anterior release except in anterior flexion. In addition, the implants enhanced lordosis. Increased rigidity should improve rates of arthrodesis, while maintenance of sagittal alignment may prevent pathologic compensatory curves in adjacent spinal segments. Further research is required to determine the optimal method of achieving structural interspace support.

Aggressive fibromatosis from infancy to adolescence

Aggressive fibromatosis is a rare fibroproliferative disorder with a variable biologic potential that is locally morbid but does not metastasize. Eighteen patients with extraabdominal fibromatosis were treated with a multidisciplinary approach over a 27-year period. Our observations, coupled with a review of the literature, suggest that conservative surgery with the goal of a wide margin coupled with adjuvant therapies may result in adequate control of disease from infancy to adolescence. Amputation should be reserved for cases in which the disease or its treatment have resulted in a nonfunctional or chronically painful extremity. Radiation should be used as a last resort in the skeletally immature because of the risk of growth disturbance, contracture, and secondary malignancy. Chemotherapy may have a role in children with inoperable disease, in those who have gross residual tumor after an intralesional procedure, for disease progression or recurrence, and neoadjuvant therapy should be investigated as a means to achieve a wide margin in some cases.

A comparison of various angles of halo pin insertion in an immature skull model

STUDY DESIGN

A basic science biomechanical study involving an animal model.

OBJECTIVES

To evaluate the effect of varying angles of halo pin insertion on the force generated at the pin-bone interface, and thereby the stability of the halo pin-bone interaction during insertion.

BACKGROUND DATA

Because of variations in the shape and size of the pediatric skull, halo pins often are inserted at various angles rather than perpendicular to the skull. Concern exists that the high complication rate associated with pediatric halo use may result in part from less than ideal structural properties at the halo pin-bone interface.

METHODS

The authors used a fetal calf skull model to simulate the thickness and structural properties of the pediatric skull. Halo pins were inserted at angles of 0 degree (perpendicular), 10 degrees, 15 degrees, and 30 degrees into skull segments via a halo ring. Load generated at the pin-bone interface was measured using a modified mechanical testing device. Twenty trials were conducted per angle, with the endpoint being specimen failure, pin penetration, or maximum load.

RESULTS

Mean maximum loads per unit thickness were 82.15 +/- 7.54 N/mm at 0 degree, 68.80 +/- 4.79 N/mm at 10 degrees, 51.49 +/- 5.08 N/mm at 15 degrees, and 42.38 +/- 3.51 N/mm at 30 degrees, There was a significant difference between perpendicular insertion (0 degree) and 15 degrees angles of insertion. There was also a significant difference between the 10 degrees and 30 degrees angles of insertion.

CONCLUSIONS

Perpendicular halo pin insertion in an immature skull model was shown to result in increased load at the pin-bone interface. This improved structural behavior may help to reduce the incidence of complications of halo application in children.

Diagnosing aneurysmal and unicameral bone cysts with magnetic resonance imaging

The differential between aneurysmal bone cysts and unicameral bone cysts usually is clear clinically and radiographically. Occasionally there are cases in which the diagnosis is not clear. Because natural history and treatment are different, the ability to distinguish between these two entities before surgery is important. The authors reviewed, in a blinded fashion, the preoperative magnetic resonance images to investigate criteria that could be used to differentiate between the two lesions. All patients had operative or pathologic confirmation of an aneurysmal bone cyst or unicameral bone cyst. The authors analyzed the preoperative magnetic resonance images of 14 patients with diagnostically difficult bone cysts (eight children with unicameral bone cysts and six children with aneurysmal bone cysts) and correlated these findings with diagnosis after biopsy or cyst aspiration and contrast injection. The presence of a double density fluid level within the lesion strongly indicated that the lesion was an aneurysmal bone cyst, rather than a unicameral bone cyst. Other criteria that suggested the lesion was an aneurysmal bone cyst were the presence of septations within the lesion and signal characteristics of low intensity on T1 images and high intensity on T2 images. The authors identified a way of helping to differentiate between aneurysmal bone cysts and unicameral bone cysts on magnetic resonance images. Double density fluid level, septation, and low signal on T1 images and high signal on T2 images strongly suggest the bone cyst in question is an aneurysmal bone cyst, rather than a unicameral bone cyst. This may be helpful before surgery for the child who has a cystic lesion for which radiographic features do not allow a clear differentiation of unicameral bone cyst from aneurysmal bone cyst.

Fibrous lesion of the distal femur associated with angular deformity

Unilateral femoral angulation is uncommon. We describe two children with unilateral progressive distal femoral varus and limb-length discrepancy. These deformities were associated with a fibrous lesion involving the medial aspect of the distal femoral metaphysis. Both patients were 15 to 16 months old. In both, the deformity was progressive, resulting in excisional biopsy and osteotomy. The gross and microscopic appearance of both lesions was similar, and the histology was dense fibrous connective tissue. The patients' femoral alignment was maintained at follow-up of a minimum of 16-36 months. The etiology of these lesions is unknown; they are associated with progressive deformity and appear to respond well to surgical intervention.

Surgical management of calcaneal unicameral bone cysts

Unicameral bone cysts are not seen commonly in the calcaneus. Little is known about the etiology and natural history of these lesions. Calcaneal cysts often are symptomatic, although some of these lesions are detected as incidental findings. Treatment has been advocated based on the fear of pathologic fracture and collapse. Several published series have been divided in their favor for either open treatment or injection management. These series are small, and the optimal treatment is still in question. The current study compared the efficacy of methylprednisolone acetate injection treatment with curettage and bone grafting in the treatment of unicameral bone cysts of the calcaneus. All patients treated for unicameral bone cysts of the calcaneus during the past 7 years at two institutions were reviewed. Eleven patients met inclusion criteria. All diagnoses were confirmed radiographically or histologically. Demographic information, presenting complaints, diagnostic imaging, treatment modalities, and outcome were analyzed. Long term radiographic and subjective followup was obtained. Eighteen surgical procedures were performed on 11 patients with 12 cysts. Nine injections performed on six patients failed to show healing of the cyst. Nine cysts treated with curettage and bone grafting showed cyst healing. At mean followup of 28 months (range, 12-77 months), all 11 patients had no symptoms; there were no recurrences of the cyst in the nine patients who underwent bone grafting and persistence of the cyst in the two patients who underwent injection therapy. This review reports one of the largest series of cysts in this location. The results indicate that steroid injection treatment, although useful in other locations, may not be the best option for the management of unicameral bone cysts in the calcaneus. Curettage and bone grafting yielded uniformly good results.

Pyomyositis in children and adolescents: report of 12 cases and review of the literature

Pyomyositis initially was observed more commonly in the developing world but now is reported with increasing frequency in the United States. The presentation is nonspecific and the differential diagnoses are many. We found the clinical history, laboratory findings, and response to treatment similar to those observed in different areas of the world. Magnetic resonance imaging (MRI) with gadolinium injection, in addition to helping to make the diagnosis, may help differentiate between early and late stages that help guide treatment. Coexisting bone changes (58%) may represent either the sensitivity of MRI to reactive inflammatory changes or the presence of a coexisting osteomyelitis. All patients responded to antibiotics and drainage if abscesses were present. Although the optimal duration of antibiotic therapy remains unclear, a shorter course should be considered in patients with a good clinical response, even when MRI shows nonspecific bony abnormalities. Percutaneous drainage was successful in five cases and may represent an alternative to the traditional surgical approach.

Pretreatment bone scan in SCFE: a predictor of ischemia and avascular necrosis

Sixty-two consecutive patients with 73 slipped capital femoral epiphyses (SCFEs) underwent pretreatment planar technetium bone scan to identify the presence of ischemia of the femoral head. The relationship of pretreatment ischemia and the development of avascular necrosis (AVN) was evaluated after a minimum follow-up of 12 months. All patients were treated with spica casting or pinning across the physis. No forceful manipulation was performed. None of the 63 stable SCFEs demonstrated ischemia by bone scan, and none developed AVN. Of the 10 unstable SCFEs, six demonstrated ischemia by bone scan, and five of the six developed AVN. None of the four unstable SCFEs without ischemia on bone scan developed AVN. Pretreatment bone scan is a sensitive predictor for development of AVN in unstable SCFEs and may provide a method for evaluating interventional treatments for AVN associated with SCFE.

A comparative evaluation of halo pin designs in an immature skull model

To design an improved halo pin for use in pediatric patients, three commonly used halo pins were evaluated with a mechanical testing apparatus and segments of prepared fetal calf skull. The pins were driven through the bone segments while the load at the bone-pin interface was measured. New pins were designed with respect to pin tip and flange width and similarly compared. Mean maximum loads to penetration, normalized for bone segment thickness, were 55.6 N/mm for the PMT Corporation pin, 61.5 N/mm for the Bremer pin, and 73.6 N/mm for the Ace pin. Four new, short tipped pins were designed and compared with the Ace pin, and there was no significant difference. Finally, four new pins were designed with varying flange widths. Mean maximum loads, normalized for bone segment thickness, were 68.9 N/mm for the 4.2 mm flange, 72.2 N/mm for the 4.7 mm flange, 92.9 N/mm for the 5.2 mm flange, and 96.4 N/mm for the 5.7 mm flange. The findings of this investigation are clinically important because they may help to explain the variability in the complication rates seen with the use of different halo systems in children. The three halo pins currently on the market have different pin designs, including tip lengths and flange distances, which contribute to the difference in load to penetration for each pin. The new, wide flanged, short tipped halo pin design might decrease the complication rate of halo use in children by providing an improved capacity to resist penetration despite increased loads of application.

Orthopaedic manifestations of chronic graft-versus-host disease

Chronic graft-versus-host disease (GVHD) is a well-recognized complication of allogeneic bone marrow transplantation (BMT). Musculoskeletal manifestations include joint contractures, polymyositis, polyserositis, and fasciitis. We present 14 patients with orthopaedic complications of chronic GVHD. Long-term conservative management of joint contractures with physical therapy and orthotics was generally successful in restoring patients' premorbid functional status. Surgical release of joint contractures yielded poor results and rendered the affected joints unresponsive to further conservative treatment. Surgical intervention in the treatment of joint contractures resulting from chronic GVHD does not appear qualitatively to improve functional status in patients affected with this disease process.

Differential diagnosis of pediatric musculoskeletal masses

MR imaging plays a major role in the evaluation of children with soft tissue and bone tumors. While the imaging characteristics of these lesions are often nonspecific, MR imaging provides valuable information on the extent of disease and relationship of tumors to the neurovascular bundle and other vital structures. This article reviews the radiographic and MR imaging appearances and clinical presentations of a wide range of musculoskeletal masses that occur in children.

Cervical spine disorders in infants and children

The evaluation of children with cervical spine disorders requires an understanding of the anatomic and developmental features that are particular to the pediatric spine. In this article, cervical spine developmental anatomy is briefly reviewed, along with common radiographic features of the pediatric cervical spine. The epidemiology, clinical presentation, and management of congenital cervical anomalies are considered. The evaluation and management of pediatric cervical trauma are also reviewed. Other disorders with common cervical spine involvement, such as skeletal dysplasias, connective tissue disorders, inflammatory arthritides, and storage disorders, are discussed.