Transfusion medicine management for reconstructive spinal repair in a patient with von Willebrand's disease and a history of heavy surgical bleeding.

STUDY DESIGN: A case report of a multidisciplinary approach to a second reconstructive back surgery in a patient with von Willebrand's disease, flatback syndrome, and a history of heavy surgical bleeding is presented. OBJECTIVE: To review the perioperative planning and assessment of hemostasis and transfusion medicine management, including administration of Humate P, a Factor VIII preparation with high von Willebrand factor content. SUMMARY OF BACKGROUND DATA: Reconstructive spinal procedures may require significant transfusion support even in patients with normal preoperative hemostasis. In addition to the hemostatic problem caused by von Willebrand's disease, the reported patient requested minimal exposure to allogeneic blood products because of hepatitis C infection acquired from previous transfusions. METHODS: The multidisciplinary team included the patient, hematologist, blood bank medical director, anesthesiologist, and operating surgeon. Preoperative assessment showed a Type 2A von Willebrand's disease variant. A careful planning process included a test infusion of desmopressin and extensive autologous donations of red cells, plasma, and platelets, which were collected before the procedure. RESULTS: Anterior and posterior spine fusions were performed during a 14-hour procedure. Hemostasis and clinical response were excellent. Humate P was administered perioperatively as assessed by the baseline Factor VIII and von Willebrand's disease levels, the plasma volume, the half-life of infused Humate P, and the anticipated risk and tolerance for bleeding. The estimated blood loss was 5 L. Replacement included 9 units of autologous red cells, 6 units of autologous plasma, 2 autologous plateletpheresis collections, a single allogeneic plateletpheresis product, and 17,000 units of Humate P administered over the perioperative period. CONCLUSIONS: Using a careful multidisciplinary approach, excellent hemostasis can be achieved with minimal exposure to untreated allogeneic blood products during aggressive spinal surgery in a patient with a clinically significant congenital coagulopathy.

Hemivertebral excision for congenital scoliosis in very young children.

The present study reports the results of a consecutive series of six very young children who underwent single-anesthetic sequential anterior and posterior hemivertebral excision. The children, all less than 34 months old (mean age 19 months), presented with high magnitude or progressive congenital scoliosis related to an unbalanced hemivertebra. Curve correction required hemivertebral excision, which was accomplished during a single operative event using sequential anterior and posterior procedures. The intraoperative curve correction was maintained with plaster immobilization for 3 months. All patients were followed for at least 24 months. Pre-and postoperative spinal radiographs were analyzed for initial and final curve correction. Excellent correction of preoperative deformity was obtained and maintained throughout the follow-up period. The mean postoperative curve correction (67%; range 52%-84%) compared favorably with the average correction at final follow-up (70%; range 50%-85%). Radiographs revealed a consistently solid arthrodesis with no evidence of curve progression. There were no neurologic or other significant complications. In conclusion, single-anesthetic sequential anterior and posterior hemivertebral excision appears to be a safe and efficacious procedure for the management of congenital scoliosis in very young children.

In vivo accuracy of thoracic pedicle screws.

STUDY DESIGN: A retrospective observational study of 279 transpedicular thoracic screws using postoperative computed tomography (CT). OBJECTIVE: To determine the accuracy of transpedicular thoracic screws. SUMMARY OF BACKGROUND DATA: Previous studies have reported the importance of properly placed transpedicular thoracic screws. To our knowledge, the in vivo accuracy of pedicle screw placement throughout the entire thoracic spine by CT is unknown. METHODS: The accuracy of thoracic screw placement within the pedicle and vertebral body and the resultant transverse screw angle (TSA) were assessed by postoperative CT. Cortical perforations of the pedicle were graded in 2-mm increments. Screws were regionally grouped for analysis. RESULTS: Forty consecutive patients underwent instrumented posterior spinal fusion using 279 titanium thoracic pedicle screws of various diameters (4.5-6.5 mm). The regional distribution of the screws was 39 screws at T1-T4, 77 screws at T5-T8, and 163 screws at T9-T12. Fifty-seven percent of screws were totally confined within the pedicle. Although medial perforation of the pedicle wall occurred in 14% of screws, in <1% there was >2 mm of canal intrusion. Lateral pedicular perforation occurred in 68% of perforating screws and was significantly more common than medial perforation (P < 0.0005). Seventeen screws penetrated the anterior vertebral cortex by an average of 1.7 mm. Screws inserted between T1 and T4 had a decreased incidence of full containment within the pedicle (P < 0.0005) and vertebral body (P = 0.039) compared with T9-T12. The mean TSA for screws localized within the pedicle was 14.6 degrees and was significantly different from screws with either medial (mean 18.0 degrees ) or lateral (mean 11.5 degrees ) pedicle perforation (P < 0.0005). Anterior vertebral penetration was associated with a smaller mean TSA of 10.1 degrees (P = 0.01) and with lateral pedicle perforation (P < 0.0005). There were no neurologic or vascular complications. CONCLUSIONS: Ninety-nine percent of screws were fully contained or were inserted with either < or =2 mm of medial cortical perforation or an acceptable lateral breech using the "in-out-in" technique. Anterior cortical penetration occurred significantly more often with lateral pedicle perforation and with a smaller mean TSA. The incidence of fully contained screws was directly correlated with the region of instrumented thoracic spine.

Incidence, epidemiology, and occupational outcomes of thoracolumbar fractures among U.S. Army aviators.

BACKGROUND: The routine occupational hazards of flying and parachute jumping place U.S. Army aviators at risk for sustaining high-energy traumatic injuries, such as thoracolumbar fractures. METHODS: A longitudinal, prospective, epidemiologic database was used to determine the incidence, injury history, and aeromedical disposition of U.S. Army aviators who sustained thoracolumbar fractures for calendar years 1987 to 1997. RESULTS: The overall incidence rate of thoracolumbar fracture was 12.8 per 100,000 aviators per year. Thirty aviators with thoracolumbar fractures were identified, and the average age at time of injury was 35.9 years (range, 25-59 years). Mean follow-up after injury was 6.5 years (range, 2-12 years). Helicopter crashes and parachuting accidents accounted for 73% of fractures. Neurologic injury occurred in 10% of aviators. Seventy-seven percent of injured aviators recovered sufficiently to return to aviation service. There was no association between type of treatment and eventual termination from aviation duties (relative risk, 1.1; 95% confidence interval, 0.7-1.6). CONCLUSION: Occupational hazards of Army aviators place them at risk for sustaining thoracolumbar fractures. These data are relevant to future decisions for research and resource allocation for aviation safety and policy.

Lumbar sagittal contour after posterior interbody fusion: threaded devices alone versus vertical cages plus posterior instrumentation.

STUDY DESIGN: An observational radiographic study examining lumbar sagittal contour of patients undergoing posterior interbody arthrodesis. OBJECTIVES: To compare operative alterations of lumbar sagittal contour after posterior interbody fusion using threaded interbody devices alone versus vertical cages combined with posterior compression instrumentation. SUMMARY OF BACKGROUND DATA: Technique-related alterations of lumbar sagittal contour during interbody arthrodesis have received little attention in the spinal literature. METHODS: Standing lumbar radiographs were measured for preoperative and postoperative segmental lordosis at levels undergoing posterior interbody arthrodesis using either stand-alone side-by-side threaded devices or vertical cages combined with posterior transpedicular compression instrumentation. Sagittal plane segmental correction (or loss of correction) was calculated and statistically compared. RESULTS: The radiographs of 30 patients (34 spinal segments) undergoing lumbar or lumbosacral arthrodesis were compared. Seventeen patients (18 segments) had undergone interbody fusion using threaded cages,whereas 13 patients (16 segments) underwent fusion using vertically oriented mesh cages combined with posterior compression instrumentation. Preoperative segmental lordosis averaged 8 degrees for both groups. For patients undergoing fusion with threaded cages, there was a mean lordotic loss of 3 degrees/segment. For patients undergoing fusion with vertically oriented mesh cages combined with posterior compression instrumentation,there was a mean lordotic gain of 5 degrees/segment. This difference in segmental sagittal plane contour was highly significant (P = 0.00). CONCLUSION: Threaded fusion devices placed under interbody distraction with the endplates parallel fail to preserve or reestablish segmental lordosis. Vertical cages, however, when combined with posterior compression instrumentation, not only maintain segmental lordosis, but also can correct sagittal plane deformity.

The effects of hook pattern and kyphotic angulation on mechanical strength and apical rod strain in a long-segment posterior construct using a synthetic model.

STUDY DESIGN: Synthetic spine models were used to compare the effects of hook pattern and kyphotic angulation on stiffness and rod strain in long-segment posterior spinal constructs. OBJECTIVES: To examine the biomechanical effects of hook patterns and kyphotic angulation on long-segment posterior spinal constructs. SUMMARY OF BACKGROUND DATA: Kyphotic deformities managed by increasing rod diameter and hence construct stiffness have shown decreased postoperative loss of correction and hardware complications. The biomechanical effects of hook pattern and kyphosis are unknown. METHODS: Spine models of 0 degrees, 27 degrees 54 degrees sagittal contour, composed of polypropylene vertebral blocks and isoprene elastomer intervertebral spacers, representing T3-T12, were used for biomechanical testing of long-segment posterior spinal constructs. Models were instrumented with 6.35-mm titanium rods and one of the following hook configurations: 20-hook compression, 16-hook compression, 16-hook claw apex-empty,16-hook claw apex-full, or 8-hook claw. Construct stiffness and rod strain during axial compression were determined. RESULTS: The compression-hook patterns provided at least a 45% increase in construct stiffness (P = 0.013)and a 22% decrease in rod strain (P < 0.0001) compared with those obtained with the claw-hook pattern with the best biomechanical performance. When analyzing all five hook patterns, there was a 19% decrease in construct stiffness and 27% increase in rod strain when progressing from straight alignment to 27 degrees of sagittal contour (P < 0.0001). Progressing from straight alignment to 54 degrees decreased construct stiffness by 48% and increased rod strain by 55% (P < 0.0001). Construct stiffness was inversely correlated to rod strain in all five hook patterns (R2 = 0.82-0.98, P < 0.001). CONCLUSIONS: Using compressive-hook patterns and decreasing the kyphotic deformity significantly increases construct stiffness and decreases rod strain.

Biomechanics of long segment fixation: hook patterns and rod strain.

This is an in vitro study of the mechanical effects of varying hook attachment patterns in long segment kyphotic deformity. In such cases, the optimal implant bulk, fatigue life, and construct rigidity to reliably achieve fusion are still unquantified. Rod strains were measured for multiple laminar hook patterns in a synthetic thoracic spine test bed. Stresses were calculated from strain data. The model displayed similar flexion bending stiffness to the thoracic spine. None of the hook patterns significantly changed overall construct stiffness. Greatest rod strains were seen when utilizing away-facing apical hooks. This model was too stiff to detect differences in construct stiffness. Nonetheless, rod stress analysis showed that for multisegment thoracic constructs, particularly with fixed kyphosis, minimizing apical hooks will minimize rod strain. If periapical hooks are necessary, orienting the hooks toward the apex will minimize rod strain.

Measurement of thoracic and lumbar fracture kyphosis: evaluation of intraobserver, interobserver, and technique variability.

STUDY DESIGN: Statistical analysis of various measurement techniques for thoracolumbar burst fracture kyphosis on lateral radiograph. OBJECTIVE: To determine the most reliable measurement technique. SUMMARY OF BACKGROUND DATA: The treatment of thoracic and lumbar burst fractures involves many factors, including the degree of resultant kyphosis. Although various methods have been described, no study has directly compared these methods for reliability and reproducibility. METHODS: Fifty lateral radiographs of thoracic and lumbar burst fractures were randomly selected and measured on two separate occasions by three spine surgeons using five different measurement techniques. Radiograph quality, fracture type, and the center beam location were determined. Statistical analysis included analysis of variance for repeated measures and analysis of variance using a generalized linear model. RESULTS: Intraclass correlation coefficients were most consistent for Method 1 (rho = 0.83-0.94) followed by Method 4 (rho = 0.65-0.89) and Method 5 (rho = 0.73-0. 85). Intraobserver agreement (% of repeated measures within 5 degrees of the original measurement) ranged between 72% and 98% for all techniques for all three observers, with Method 1 showing the best agreement (84%-98%). Paired comparisons between observers varied considerably with interobserver reliability correlation coefficients ranging from 0.52 to 0.93. Method 1 showed the highest interobserver reliability coefficient (0.81, range 0.71-0.93) followed by Method 5 (0.71, range 0.68-0.75). Method 1 also had the highest percentage of agreement within categories (90% within 5 degrees ). CONCLUSIONS: Method 1 (measuring from the superior endplate of the vertebral body one level above the injured vertebral body to the inferior endplate of the vertebral body one level below) showed the best intraobserver and interobserver reliability overall.

The effect of kyphosis on the mechanical strength of a long-segment posterior construct using a synthetic model.

STUDY DESIGN: This experimental study used synthetic spine models to compare the effect of the angle of kyphosis, rod diameter, and hook number on the biomechanical stiffness of a long-segment posterior spinal construct. OBJECTIVE: To examine the biomechanical effects of incremental kyphosis on variously instrumented long-segment posterior spinal constructs. SUMMARY OF BACKGROUND DATA: Euler's formula for loading of curved long columns would suggest that kyphosis has a profound impact on the biomechanical behavior of long-segment posterior spinal constructs. The effects of sagittal contour on the mechanical properties of long-segment posterior spinal constructs have not been well documented. METHODS: Kyphotic and straight synthetic spine models were used to test long-segment posterior instrumentation constructs biomechanically while varying rod diameter and the number of hook sites. The synthetic spines, composed of polypropylene vertebral blocks and isoprene elastomer intervertebral spacers, were fabricated with either 0 degrees, 27 degrees, or 53 degrees of sagittal contour. The models were instrumented with 5.5- or 6.35-mm titanium rods, and with either 8 or 12 hooks. The models were loaded from 0 to 300 N in a cyclical ramp fashion using an MTS 858 Bionix testing device testing device. Construct stiffness (force and displacement) during axial compression was determined. RESULTS: Straight model: Changing the hook number from 8 to 12 caused a 32% increase in construct stiffness with the 5.5-mm rod. Changing the rod diameter from 5.5 to 6.35 mm caused a 36% increase in construct stiffness with the 8-hook pattern. Changing both the rods and hooks caused the stiffness to increase 44%. 27 degrees MODEL: Changing the hook number from 8 to 12 caused a 20% increase in construct stiffness with the 6.5-mm rod. Changing the rod diameter from 5.5 to 6.35 mm caused a 29% increase in construct stiffness with the 12-hook pattern. Changing both the rods and hooks caused the construct stiffness to increase 26%. 53 degrees MODEL: Changing the hook number from 8 to 12 caused a 14% increase in construct stiffness with the 6.35-mm rod. Changing the rod diameter from 5.5 to 6.35 mm caused a 17% (P<0.0005) increase in construct stiffness with the 12-hookpattern. Changing both rods and hooks caused the stiffness to increase 21%. Summary data on angular kyphosis: Using the same rod diameter and the same number of hooks, and progressing from a straight alignment to 27 degrees of sagittal contour decreased construct stiffness 32%. Going from straight alignment to 53 degrees decreased the stiffness 59.6%. All reported values were statistically significant (P < 0.0005). CONCLUSIONS: The biomechanical stiffness of the straight spine was sensitive to both an increase in hook fixation sites and an increase in rod diameter. The kyphotic spines, however, were more sensitive to variations in rod diameter. Although with increasing kyphosis, the optimum instrumentation strategy will maximize both rod diameter and the number of hook sites, instrumented kyphotic spines remain biomechanically "disadvantaged" as compared with nonkyphotic instrumented spines.

The biomechanical significance of anterior column support in a simulated single-level spinal fusion.

This study examines the biomechanical effects of interbody cages and variations in posterior rod diameter in a simulated single-level spinal fusion. A single-level spinal fusion model composed of polyethylene cylinders, posterior pedicular instrumentation, and variously positioned single or dual interbody cages was used for biomechanical testing. Constructs were tested under compressive flexural load, with measurement of stiffness, rod strain, cage strain, and intracage pressure. A strong linear correlation emerged between the mean construct stiffness and cage positioning within the sagittal plane that was inversely related to posterior rod strain. Two small titanium mesh cages were equivalent to one large cage. In a single-level spine model, the presence of and sagittal position of interbody cages significantly influences overall construct stiffness. Cage strain increased with more anterior positions and was inversely related to rod strain.

Occult intraspinal anomalies in congenital scoliosis.

Thirty consecutive patients with congenital spinal deformity underwent magnetic resonance imaging (MRI) to determine the incidence of occult intraspinal anomaly. These congenital spinal deformities included 29 cases of congenital scoliosis and one case of congenital kyphosis. Physical examination findings and plain radiographs were reviewed in an attempt to correlate these findings with subsequent intraspinal pathology. Nine patients had intraspinal anomalies identified on MRI consisting of five with tethered cord, four with syringomyelia, three with lipoma, and one with diastematomyelia. One patient required surgery for diastematomyelia; another underwent release of his tethered cord. Only one patient, with diastematomyelia associated with a syrinx and bifocal tethering, had his anomaly suggested by physical examination and plain radiographs. Two other patients had findings on plain radiographs previously associated with high prevalence of occult intraspinal anomalies; one patient with congenital kyphosis had a tethered cord, and one patient with a unilateral hemivertebrae associated with a contralateral bar had a tethered cord. Two of nine patients with occult intraspinal anomalies required surgery for their anomaly. In patients with a congenital spinal deformity, we found nine (30%) of 30 to have an associated anomaly within the spinal canal. Only three of these nine had plain radiographs and physical examination findings suggestive of their subsequent MRI findings. Given the poor correlation between findings on physical examination, plain radiographs, and subsequent occult intraspinal anomalies on MRI, we believe that MRI is helpful in evaluating patients with congenital spinal anomalies.

A modified wake-up test for use in very young children undergoing spinal surgery.

In a consecutive series of five very young children undergoing hemivertebrectomy and fusion, a modified intraoperative wake-up test was used to confirm neurologic integrity. Standard leads attached to a nerve stimulator and positioned over the plantar aspect of each foot were used to apply tetanic electrical stimulation at the time of intraoperative wake-up. Four children responded vigorously with flexion and extension of the knees and ankles after only minimal delay. One neurologically intact child did not respond because of technical issues. This report describes our favorable preliminary experience with this technique.

Reversible ischemic myelopathy during scoliosis surgery: a possible role for intravenous lidocaine.

An unusual and previously unreported case of partially reversible ischemic myelopathy after limited unilateral segmental vessel ligation during scoliosis surgery is described. Intravenous lidocaine, used intraoperatively for its vasoactive properties, induced an immediate and meaningful recovery of neurologic function. The conceptual and pharmacologic basis for this intervention is discussed in view of this exceedingly rare complication of segmental vessel ligation.

Early diagnosis of Hurler's syndrome with the aid of the identification of the characteristic gibbus deformity.

This case study describes the clinical evaluation and diagnosis of Hurler's syndrome in a 7-month-old child who was noted to have a thoracolumbar kyphosis (gibbus deformity), coarse facial features, and possible evidence of gross motor delay. The diagnosis of Hurler's syndrome was aided specifically by the identification of the gibbus deformity. Children with Hurler's syndrome appear nearly normal at birth, and the most common early presenting features are the nonspecific symptoms of rhinitis and inguinal hernia. Most often, the earliest possible diagnosis of Hurler's syndrome is contingent on the recognition of the initial pattern of musculoskeletal abnormalities, which become increasingly pronounced after the 6th month. Because of the characteristic progression of neurological and intellectual deterioration found in children with Hurler's syndrome, early diagnosis and treatment are critical to the preservation of long-term intellectual development. The pathophysiology of Hurler's syndrome and the causes of kyphosis in infancy and childhood are discussed.

Spine fractures in active duty soldiers and their return to duty rate.

To evaluate the outcome of thoracolumbar spine fractures in active duty soldiers, we conducted a retrospective review of 23 soldiers followed at a single institution. Twenty-two charts were available for review. The average age was 31.9 years (range, 19-49 years), and the average follow-up was 3.6 years (range, 2-11 years). There were 20 males and 2 females. All injuries except one occurred between 1990 and 1994, and all were treated by a single surgeon. We attempted to correlate five independent variables with regard to whether the patient returned to his or her previous duty or was required to undergo a medical evaluation board to determine fitness for duty. The variables included military rank, physical job demands, fracture type, initial neurological status, and initial treatment (operative versus nonoperative). Fourteen of the 22 soldiers (64%) underwent medical evaluation boards, whereas 8 (36%) returned to their previous duties. We found a strong correlation between increasing military rank and return to preinjury duties. As expected, physical job demands correlated strongly with eventual disposition, in that soldiers in jobs with low physical demands were more likely to be retained on active duty in their present position. Neurologic status (except motor deficit), type of fracture (except fracture-dislocation), and initial treatment did not correlate well with eventual disposition.

Revision pedicle screws. Bigger, longer shims--what is best?

STUDY DESIGN: To evaluate the effect of change in screw dimensions and hole augmentation in pedicle screw revisions, the insertional torque was determined, and results were compared with those in control specimens in an in vitro study using cadaveric thoracolumbar spines. OBJECTIVES: To determine the best method of salvage for failed pedicle screws, by evaluating the insertional torque after placing a larger diameter or longer screw into a stripped hole. Use of a shim and use of larger and longer screws were also investigated. Finally, the effect on insertional torque of simply removing and replacing a pedicle screw in its original hole was investigated. SUMMARY OF BACKGROUND DATA: The effects of using bigger or longer screws and shims to salvage failed pedicles have been studied. The interaction between how much larger, how much longer, and inserting with or without shims, has not been well studied. Optimizing reinsertional torque through the use of bigger screws risks exceeding the pedicle capacity. Using longer screws risks violation of the anterior vertebral body, thereby placing the great vessels and viscera at risk. By knowing the relative contribution of increase in length and diameter, the surgeon can optimize the risk-benefit ratio. METHODS: Eight cadaveric spines from T10 to S1 were harvested. The specimens underwent radiographic screening and bone densitometry. A modified Latin square randomization was designed to evaluate the screw diameters and lengths. Each pedicle was its own control. A 35- x 6.5-mm screw was used as a control. Test screws were placed after pedicle screw hole failure was achieved and documented by stripping. For the test screws, the diameters were increased by 1 mm and 2 mm, the lengths were increased by 5 mm and 10 mm. Shims were added randomly. The peak insertional torque was measured for each control screw and test screw placement. In addition, during each screw placement, the screw was removed and replaced to determine the effect. RESULTS: Insertional torque, after the pedicle screw is removed and replaced in the same hole, was decreased by 34% (P < 0.000005). Increasing the diameter of the salvage screw by 2 mm caused the insertional torque to be increased by 8.4% of the original. Increasing the length of the screw did not improve the salvage screw insertional torque. There was an interaction effect for the 1-mm increase in diameter and the increase in length. At this diameter, increasing the length had a significant effect (P = 0.009) on the salvage torque. Using a shim created no improvement in salvage insertional torque (P = 0.77). There was a poor linear correlation between torque and bone mineral density (r = 0.18) in these osteoporotic specimens. CONCLUSIONS: Removing and replacing a pedicle screw in its original hole substantially decreases its mechanical fixation. For pedicle salvage, increasing the diameter causes the greatest restoration of strength. Shims had no effect in pedicle salvage in osteoporotic specimens.

Traction versus supine side bending. Which technique best determines curve flexibility?

STUDY DESIGN: A prospective study performed in two institutions where patients scheduled for surgical management of scoliosis were evaluated with traction and supine side bending radiographs to determine curve flexibility. OBJECTIVE: To determine if there is a difference in the flexibility of curves as determined by side bending or traction films. METHODS: Fifty-eight patients scheduled for surgery underwent preoperative radiographic evaluation using supine side bending and traction radiographs. The surgeons were free to use the information as they saw fit in determining levels of fusion. All curves were measured using the method of Cobb. Curves were analyzed in three groups: > 60 degrees, 50-60 degrees, and < 50 degrees. A comparison then was made between the traction and side bend films to determine which method demonstrated greater flexibility. Measurement error was assumed to be +/- 5 degrees. If the measurements were within 5 degrees, then the two methods were considered to be equivalent. RESULTS: In curves > 60 degrees, greater flexibility was seen on traction films. In curves < 50 degrees, side bending showed greater flexibility. In curves between 50 degrees and 60 degrees, side bending showed greater flexibility in the thoracic spine, whereas in the lumbar spine both films showed equivalent flexibility. CONCLUSIONS: Traction shows greater curve flexibility in curves > 50 degrees, whereas in curves < 50 degrees, side bending shows greater flexibility.

The effect of a wrist brace on injury patterns in experimentally produced distal radial fractures in a cadaveric model.

We compared patterns of bony and ligamentous injury with distal radial fractures in braced and unbraced wrists using 20 paired fresh cadaveric upper extremities. A commercially available wrist brace was placed on one wrist in each pair. Specimens were then placed in a fast-loading gravity-driven device and subjected to loads averaging 16 kg from an average height of 78 cm. Postfracture radiographs were obtained, the specimens were dissected, and fracture patterns and ligamentous integrity were assessed. The following fracture types were produced: distal radial fractures (eight unbraced, seven braced) and intraarticular (seven unbraced, four braced). Radiographically, seven unbraced wrists demonstrated carpal bone fracture and one braced wrist demonstrated carpal fractures. Eight unbraced and three braced wrists sustained carpal intrinsic ligament injuries, four unbraced and one braced wrists demonstrated extrinsic ligament injuries. More capsular tears occurred in the unbraced group (N = 8) than in the braced group (N = 1). This model demonstrated a difference in the patterns of injury in unbraced and braced wrists subjected to the same mechanical conditions, which suggests that use of a wrist brace may alter patterns of wrist injury.

The removal of a transdural pedicle screw placed for thoracolumbar spine fracture.

STUDY DESIGN: This report describes the method of removal of a pedicle screw that had been misplaced through the thecal sac and the cauda equina instead of its proper location within the pedicle. OBJECTIVES: A patient who previously had undergone placement of pedicle screws and Roy-Camille plates for fixation of L1 burst fracture presented to the authors with neurologic deficits and a cerebrospinal fluid leak. Computed tomography myelogram and surgical findings demonstrated misplacement of three of the screws, one of which was placed through the dura with resulting impingement of nerve roots within the thecal sac. SUMMARY OF BACKGROUND DATA: Removal of the screws was required for neural decompression and resolution of the cerebrospinal fluid leak. METHODS: The patient underwent laminectomy to expose the screw and primary durotomy to include the entry point of the screw. This technique allowed safe removal under direct vision, with direct protection of the nerve roots. A subsequent anterior fusion procedure was performed. RESULTS: The patient regained full neurologic function, and his cerebrospinal fluid leak ceased. At 2-year follow-up evaluation, he describes only mild, occasional back pain. CONCLUSIONS: Penetration of the dura and injury to the neural elements can occur when pedicle screw instrumentation is used. Removal of the screw under these circumstances may cause additional neurologic injury. Durotomy and direct visualization of the neural elements in this case was a valuable adjunct to safe removal of the screw.

The effect of intraoperative blood loss on serum cefazolin level in patients undergoing instrumented spinal fusion. A prospective, controlled study.

STUDY DESIGN: This study is a prospective, controlled study of the effect of intraoperative and postoperative blood loss during spinal surgery on serum cefazolin level. OBJECTIVES: To determine what effect, if any, intraoperative blood loss has on serum antibiotic levels, and to determine if adjustment of the dose or dose interval is appropriate in operative cases of significant blood loss. SUMMARY OF BACKGROUND DATA: The problem of infection at the operative site after posterior spinal fusion with internal fixation is significant. It commonly has been accepted that blood loss results in a more rapid clearance of antibiotic. METHODS: Nineteen patients scheduled for elective spinal fusion with internal fixation were enrolled in this study. Each patient served as his or her own control. Baseline cefazolin clearance was determined the week before surgery. Cefazolin clearance again was determined intraoperatively. Blood loss was recorded throughout the procedure. RESULTS: The mean blood loss was 650 mL. There was no significant difference between preoperative and intraoperative cefazolin clearance, and there was no correlation between blood loss and cefazolin level. CONCLUSIONS: It is not necessary to give cefazolin at a dosing interval of less than 4 hours with blood losses of up to 1200 mL. This will maintain the antibiotic concentrations well above the minimum inhibitory concentration.