In vivo Mouse Model of Spinal Implant Infection.

Spine implant infections portend poor outcomes as diagnosis is challenging and surgical eradication is at odds with mechanical spinal stability. The purpose of this method is to describe a novel mouse model of spinal implant infection (SII) that was created to provide an inexpensive, rapid, and accurate in vivo tool to test potential therapeutics and treatment strategies for spinal implant infections. In this method, we present a model of posterior-approach spinal surgery in which a stainless-steel k-wire is transfixed into the L4 spinous process of 12-week old C57BL/6J wild-type mice and inoculated with 1 x 103 CFU of a bioluminescent strain of Staphylococcus aureus Xen36 bacteria. Mice are then longitudinally imaged for bioluminescence in vivo on post-operative days 0, 1, 3, 5, 7, 10, 14, 18, 21, 25, 28, and 35. Bioluminescence imaging (BLI) signals from a standardized field of view are quantified to measure in vivo bacterial burden. To quantify bacteria adhering to implants and peri-implant tissue, mice are euthanized and the implant and surrounding soft tissue are harvested. Bacteria are detached from the implant by sonication, cultured overnight and then colony forming units (CFUs) are counted. The results acquired from this method include longitudinal bacterial counts as measured by in vivo S. aureus bioluminescence (mean maximum flux) and CFU counts following euthanasia. While prior animal models of instrumented spine infection have involved invasive, ex vivo tissue analysis, the mouse model of SII presented in this paper leverages noninvasive, real time in vivo optical imaging of bioluminescent bacteria to replace static tissue study. Applications of the model are broad and may include utilizing alternative bioluminescent bacterial strains, incorporating other types of genetically engineered mice to contemporaneously study host immune response, and evaluating current or investigating new diagnostic and therapeutic modalities such as antibiotics or implant coatings.

Progress not panacea: vancomycin powder efficacy and dose evaluated in an in vivo mouse model of spine implant infection.

BACKGROUND: Intrawound vancomycin powder (VP) has been rapidly adopted in spine surgery with apparent benefit demonstrated in limited, retrospective studies. Randomized trials, basic science, and dose response studies are scarce. PURPOSE: This study aims to test the efficacy and dose effect of VP over an extended time course within a randomized, controlled in vivo animal experiment. STUDY DESIGN/SETTING: Randomized controlled experiment utilizing a mouse model of spine implant infection with treatment groups receiving vancomycin powder following bacterial inoculation. METHODS: Utilizing a mouse model of spine implant infection with bioluminescent Staphylococcus aureus, 24 mice were randomized into 3 groups: 10 infected mice with VP treatment (+VP), 10 infected mice without VP treatment (No-VP), and 4 sterile controls (SC). Four milligrams of VP (mouse equivalent of 1 g in a human) were administered before wound closure. Bioluminescence imaging was performed over 5 weeks to quantify bacterial burden. Electron microscopy (EM), bacterial colonization assays (Live/Dead) staining, and colony forming units (CFU) analyses were completed. A second dosing experiment was completed with 34 mice randomized into 4 groups: control, 2 mg, 4 mg, and 8 mg groups. RESULTS: The (+VP) treatment group exhibited significantly lower bacterial loads compared to the control (No-VP) group, (p<.001). CFU analysis at the conclusion of the experiment revealed 20% of mice in the +VP group and 67% of mice in the No-VP group had persistent infections, and the (+VP) treatment group had significantly less mean number of CFUs (p<.03). EM and Live/Dead staining revealed florid biofilm formation in the No-VP group. Bioluminescence was suppressed in all VP doses tested compared with sterile controls (p<.001). CFU analysis revealed a 40%, 10%, and 20% persistent infection rate in the 2 mg, 4 mg, and 8 mg dose groups, respectively. CFU counts across dosing groups were not statistically different (p=.56). CONCLUSIONS: Vancomycin powder provided an overall infection prevention benefit but failed to eradicate infection in all mice. Furthermore, the dose when halved also demonstrated an overall protective benefit, albeit at a lower rate. CLINICAL SIGNIFICANCE: Vancomycin powder is efficacious but should not be viewed as a panacea for perioperative infection prevention. Dose alterations can be considered, especially in patients with kidney disease or at high risk for seroma.

Management of Terminal Osseous Overgrowth of the Humerus With Simple Resection and Osteocartilaginous Grafts.

BACKGROUND: Osseous overgrowth is a common complication in children after humeral transcortical amputation. Capping tibial overgrowth with the proximal fibula has been shown to be the most effective treatment. However, best treatment practices are not clear for the humerus. We compared patients treated surgically for humeral osseous overgrowth with simple resection or autologous osteocartilaginous graft to determine if this treatment were as effective in the humerus as it has been in the tibia. METHODS: A retrospective review of humeral amputees from 1987 to 2011 at a pediatric hospital was performed. Patients with 2 years follow-up who underwent surgical treatment for established humeral overgrowth were included. Patients initially managed with simple resection were compared with those managed with autologous osteocartilaginous grafts. Descriptive statistics were calculated for demographic and outcome variables. T tests and χ tests were used to compare differences between groups. RESULTS: Eighteen humeri in 16 patients met inclusion criteria. Mean age at surgery was 8.3 (2.6 to 13.6) years and mean follow-up was 6.3 (1.5 to 10.4) years. Thirteen humeri underwent simple resection, with recurrent overgrowth in 9, and revision surgery in 8 at a mean 2.6 years. Five humeri were primarily managed with autologous osteocartilaginous grafts. Two developed non-overgrowth-related complications at 1 and 42 months. Including revision procedures after simple resection, 10 humeri were managed with autologous osteocartilaginous grafts. Thirty percent (3/10) required revision surgery; however, there were no cases of recurrent overgrowth. χ comparison showed lower rates of complications (P=0.004) and reoperation (P=0.012) with capping as compared with simple resection. CONCLUSIONS: Autologous osteocartilaginous capping of the humerus has a significantly lower rate of complications and reoperation compared with simple resection. However, the capping procedure has the potential for other complications related to difficulty with graft fixation. Surgeons should be aware that the outcomes are not as consistent as when the technique is applied to osseous overgrowth of the tibia and anticipate the possibilities of hardware prominence and difficulty with fixation. LEVEL OF EVIDENCE: Level 3-therapeutic-retrospective comparative.

Strength of Thoracic Spine Under Simulated Direct Vertebral Rotation: A Biomechanical Study.

BACKGROUND: Direct vertebral rotation (DVR) has gained increasing popularity for deformity correction surgery. Despite large moments applied intraoperatively during deformity correction and failure reports including screw plow, aortic abutment, and pedicle fracture, to our knowledge, the strength of thoracic spines has been unknown. Moreover, the rotational response of thoracic spines under such large torques has been unknown. PURPOSE: Simulate DVR surgical conditions to measure torsion to failure on thoracic spines and assess surgical forces. STUDY DESIGN: Biomechanical simulation using cadaver spines. METHODS: Fresh-frozen thoracic spines (n = 11) were evaluated using radiographs, magnetic resonance imaging (MRI) and dual-energy x-ray absorptiometry. An apparatus simulating DVR was attached to pedicle screws at T7-T10 and transmitted torsion to the spine. T11-T12 were potted and rigidly attached to the frame. Strain gages measured the simulated surgical forces to rotate spines. Torsional load was increased incrementally till failure at T10-T11. Torsion to failure at T10-T11 and corresponding forces were obtained. RESULTS: The T10-T11 moment at failure was 33.3 ± 12.1 Nm (range = 13.7-54.7 Nm). The mean applied force to produce failure was 151.7 ± 33.1 N (range = 109.6-202.7 N), at a distance of approximately 22 cm where surgeons would typically apply direct vertebral rotation forces. Mean right rotation at T10-T11 was 11.6°±5.6°. The failure moment was significantly correlated with bone mineral density (Pearson coefficient 0.61, p = .047). Failure moment also positively correlated with radiographic degeneration grade (Spearman rho > 0.662, p < .04) and MRI degeneration grade (Spearman rho = 0.742, p = .01). CONCLUSION: The present study indicated that with the advantage of lever arms provided with DVR techniques, relatively small surgical forces, <200 N, can produce large moments that cause irreversible injury. Although further studies are required to establish the safety of surgical deformity correction surgeries, the present study provides a first step in the quantification of thoracic spine strength.

Osteocartilaginous transfer of the proximal part of the fibula for osseous overgrowth in children with congenital or acquired tibial amputation: surgical technique and results.

BACKGROUND: Osseous overgrowth is a common problem in children after tibial transcortical amputation. We present the results of forty-seven children (fifty tibiae) treated for tibial osseous overgrowth with an autologous osteocartilaginous cap from the proximal part of the ipsilateral fibula. METHODS: We reviewed the records of all patients who underwent amputation at a single pediatric hospital from 1990 to 2011. All patients who had been followed for a minimum of two years after undergoing osteocartilaginous capping with the proximal part of the ipsilateral fibula to treat established tibial overgrowth were included. Patients with acquired and congenital amputations were compared. RESULTS: Fifty tibiae in forty-seven patients met our inclusion criteria. There were thirty-one acquired and nineteen congenital amputations. The mean age at surgery was 7.6 years (range, 2.1 to 15.6 years), and the mean duration of follow-up was 7.2 years (range, 2.2 to 15.4 years). Five tibiae (10%) in four patients had recurrence of the overgrowth at a mean of 5.4 years (range, 2.8 to 7.6 years) after the osteocartilaginous transfer. There was no significant difference in the results between children with an acquired amputation and those with a congenital amputation. CONCLUSIONS: At a mean of 7.2 years after autologous osteocartilaginous capping with the proximal part of the fibula, 90% of the limbs had not had recurrent overgrowth. This is a safe and effective treatment of long-bone overgrowth following either congenital or acquired amputation in children.

Outcomes of lower extremity orthopedic surgery in ambulatory children with cerebral palsy with and without gait analysis: results of a randomized controlled trial.

This study examined the impact of gait analysis on surgical outcomes in ambulatory children with cerebral palsy (CP) through a randomized controlled trial. 156 children with CP (94 male; age 10.2 ± 3.7 years) underwent gait analysis and were randomized to two groups: Gait Report group (N = 83), where the referring surgeon received the patient's gait analysis report, and Control group (N = 73), where the surgeon did not receive the gait report. Outcomes were assessed pre- and 1.3 ± 0.5 years post-operatively. An intent-to-treat analysis compared outcomes between the two groups. Outcome measures included the Gillette Functional Activity Questionnaire (FAQ), Gait Deviation Index (GDI), oxygen cost, gross motor function measure, Child Health Questionnaire (CHQ), Pediatric Outcomes Data Collection Instrument (PODCI), and Pediatric Evaluation and Disability Inventory. The outcomes that differed significantly between groups were change in health from the CHQ, which was rated as much better for 56% (46/82) of children in the Gait Report group compared with 38% (28/73) in the Control group (p = 0.04), and upper extremity physical function from the PODCI. Gait outcomes (FAQ and GDI) improved more when over half of the recommendations for a patient were followed or the recommended extent of surgery (none, single, or multi-level) was done (p ≤ 0.04). On average, however, only 42% of the recommendations were followed in the Gait Report group, compared with 35% in the Control group (p = 0.23). This is much less than the >85% reported in previous studies and may account for the lack of differences between groups for some of the outcome measures.

Influence of gait analysis on decision-making for lower extremity orthopaedic surgery: Baseline data from a randomized controlled trial.

Previous studies examining the influence of gait analysis on surgical decision-making have been limited by the lack of a control group. The aim of this study was to use data from a randomized controlled trial to determine the effects of gait analysis on surgical decision-making in children with cerebral palsy (CP). 178 ambulatory children with CP (110 male; age 10.3±3.8 years) being considered for lower extremity orthopaedic surgery underwent gait analysis and were randomized into one of two groups: gait report group (N=90), where the orthopaedic surgeon received the gait analysis report, and control group (N=88), where the surgeon did not receive the gait report. Data regarding specific surgeries were recorded by the treating surgeon before gait analysis, by the gait laboratory surgeon after gait analysis, and after surgery. Agreement between the treatment done and the gait analysis recommendations was compared between groups using the 2-sided Fisher's Exact test. When a procedure was planned initially and also recommended by gait analysis, it was performed more often in the gait report group (91% vs. 70%, p<0.001). When the gait laboratory recommended against a planned procedure, the plan was changed more frequently in the gait report group (48% vs. 27%, p=0.009). When the gait laboratory recommended adding a procedure, it was added more frequently in the gait report group (12% vs. 7%, p=0.037). These results provide a stronger level of evidence demonstrating that gait analysis changes treatment decision-making and also reinforces decision-making when it agrees with the surgeon's original plan.

Efficacy of intraoperative cell salvage systems in pediatric idiopathic scoliosis patients undergoing posterior spinal fusion with segmental spinal instrumentation.

STUDY DESIGN: Retrospective case-control study. OBJECTIVE: Determine whether intraoperative cell salvage system use during pediatric posterior spinal fusion (PSF) with segmental spinal instrumentation for idiopathic scoliosis decreases intraoperative and perioperative (intraoperative plus postoperative) allogeneic blood transfusion. SUMMARY OF BACKGROUND DATA: Intraoperative cell salvage and reinfusion can reduce or obviate perioperative allogeneic blood transfusion. Despite these benefits, their efficacy in pediatric PSF is unclear. Reported complications include transient hematuria, altered hemostasis, and electrolyte imbalance. METHODS: A total of 54 consecutive idiopathic scoliosis patients were studied: 21 non-cell saver and 33 cell saver patients. Data included age, body mass index, Cobb angle, perioperative hemoglobin levels, mean arterial pressure, surgical time, levels fused, perioperative estimated blood loss, and perioperative transfusions. A chi2 and t tests were performed for intraoperative and perioperative allogeneic transfusion between groups. A regression analysis was performed between selected covariates and allogeneic transfusion. Relative risk analysis examined significant covariates regarding allogeneic transfusion rate. RESULTS: Allogeneic transfusion rates were lower in the cell saver group (6% vs. 55% intraoperative and 18% vs. 55% perioperative, P < 0.05). Mean allogeneic transfusion volumes (mL/kg) were also lower (0.4 vs. 9.1 intraoperative and 1.9 vs. 11.1 perioperative, P < 0.05). Multivariate analysis confirmed these differences were independent of perioperative blood loss, and also demonstrated that surgical time and blood loss were significantly related to allogeneic transfusion volume. The allogeneic transfusion relative risk was 2.04 in patients with surgery >6 hours and 5.87 in patients not receiving cell saver blood. All patients with surgeries >6 hours and estimated blood loss >30% of total blood volume received cell saver system blood. CONCLUSION: Cell saver use decreased allogeneic transfusion, particularly in surgeries >6 hours with estimated blood loss >30% of total blood volume. This study confirms the utility of routine cell saver use during PSF with segmental spinal instrumentation for idiopathic scoliosis.

Decreased body mass index and restrictive lung disease in congenital thoracic scoliosis.

BACKGROUND: Pediatric patients with congenital thoracic scoliosis often have restrictive lung disease and low body weight for age. In other patients with respiratory disorders, the work of breathing can increase basal metabolic demands and predispose patients to cachexia. The primary study aim was to determine if severity of restrictive lung disease, as measured by pulmonary spirometry, correlates to decreased body mass index (BMI) in patients with congenital thoracic scoliosis. A secondary study aim was to determine what patient factors and radiographic measures correlate to low BMI. METHODS: Forty-nine consecutive patients with congenital thoracic scoliosis underwent pulmonary function testing, spinal radiographs, and BMI percentile for age calculations. Severity of restrictive lung disease was quantified by the forced vital capacity percentile (FVC%). The BMI percentile for age was also ranked as normal, moderately, or markedly decreased (0, <1, or <2 SDs below normal, respectively). The t tests were performed between BMI rank and FVC% as well as forced expiratory volume in 1 second (FEV1). A stepwise multivariate linear regression analysis was performed between BMI percentile and FVC%, age, sex, type and extent of previous spine fusion, radiographic measures, and pulmonary spirometry measures. RESULTS: The mean BMI percentile for all patients was 43% (range, 2%-98%). Both FVC% and FEV1 percentile were significantly decreased in patients with abnormal BMI (77% vs 51%, P = 2.78 *10(-1) for FVC%; 75% vs 52%, P = 0.00021 for FEV1 percentile). Multivariate analysis showed that FVC% was the only tested variable that significantly correlated to BMI percentile. There was a 13.6 times higher risk of having an abnormal BMI in patients with moderate to severe restrictive lung disease. CONCLUSIONS: Decreased pulmonary function compromise strongly correlates to low BMI in patients with congenital thoracic scoliosis. When considering moderate to severe restrictive lung disease as defined by FVC%, patients are at much higher risk of being significantly underweight. Body mass index is another important sign of thoracic insufficiency syndrome in these patients. LEVEL OF EVIDENCE: Prognostic case-control study, level III.

Does early thoracic fusion exacerbate preexisting restrictive lung disease in congenital scoliosis patients?

BACKGROUND: Congenital thoracic scoliosis is associated with diminished pulmonary function. Early posterior thoracic spinal fusion surgery may additionally impact pulmonary function beyond the natural history of the disease by further inhibiting thoracic growth. The primary study aim is to determine if early thoracic spine fusion patients have diminished pulmonary function versus untreated patients at a similar age. The secondary study aim is to determine how plain radiographic measurements of thoracic deformity change over time and correlate to pulmonary function in these patients. METHODS: Sequential spinal radiographs and one-time pulmonary function tests were performed in 43 consecutive congenital thoracic scoliosis patients with either a history of early posterior thoracic fusion or no surgery. Multiple stepwise t testing compared the patient-related and radiographic variables in the early surgery and no surgery groups. Multiple stepwise linear regression analysis examined the effect of the variables at final follow-up on forced vital capacity and forced expiratory volume. RESULTS: All patients exhibited decreased forced vital capacity, but there was no difference between early surgery and no surgery groups at an average follow-up age of 10.5 years. A mid- (versus low) thoracic apex, decreased space available for the lung, and decreased age-corrected thoracic width correlated with decreased forced vital capacity. Between initial and final radiographic follow-up, the rate of change in thoracic height and width was decreased in the early surgery versus no surgery group. CONCLUSIONS: Early posterior spinal fusion decreases radiographic measures of thoracic growth over time, but pulmonary function was similar to untreated patients at 10.5 years of age. The data suggest pulmonary function and thoracic size as measured on plain radiographs correlate directly. Therefore, pulmonary function testing at the end of growth should be performed to determine the ultimate pulmonary consequences of early surgery.

Transient meralgia paresthetica after pediatric posterior spine fusion.

Meralgia paresthetica (MP) rarely occurs during posterior spine surgery. The study goal was to examine risk factors associated with the incidence of MP. A review of 56 consecutive pediatric patients undergoing posterior spine fusion for scoliosis was performed. Patients with abnormal sensation in the lateral thigh preoperatively and prior spine surgery were excluded. All patients were positioned prone on the Jackson (Orthopaedic Systems, Inc., Union City, CA) spinal table with either (1) the lower leg support table and thigh supports or (2) the lower leg suspension sling. Data on patient weight, diagnosis, surgeon, duration of surgery, presence of MP, symptoms, and symptom duration were collected. A logistic regression analysis was performed between independent variables and presence of MP. There were 10/56 patients with MP (18%). Symptoms were anterolateral thigh numbness without pain or weakness. Symptoms in all cases were resolved, on average, before the 6-week postoperative visit (range 2-24 weeks). Patients with MP more often had idiopathic scoliosis (28% vs 7%; P < 0.05) were positioned with the lower leg sling instead of the flat table support (31% vs 13%; P < 0.05) and trended toward longer surgery times (451 vs 388 minutes; NS). Abnormal body mass index, age at surgery, surgeon, and sex did not correlate to MP. MP can occur after pediatric posterior spine surgery. Symptoms were minor, temporary, and did not require treatment. Shorter surgical times and use of thigh pads in conjunction with the lower leg support table may decrease the incidence of MP.

Perioperative complications of threaded cylindrical lumbar interbody fusion devices: anterior versus posterior approach.

Few data are available to evaluate approach-related differences in perioperative complications with lumbar interbody fusion devices. Complications occurring in the intraoperative and immediate postoperative period were identified and categorized for 31 consecutive posterior lumbar interbody fusions (PLIFs) and 88 consecutive anterior lumbar interbody fusions (ALIFs). In this study, all lumbar interbody fusions were conducted with threaded cylindrical devices as stand-alone internal fixation devices. Multivariate analysis was used to account for potential covariates and identify factors associated with an increased complication risk. Twenty-two percent of the patients had a perioperative complication. The relative risk of having a perioperative complication was 4.75 times higher for the PLIF group. All intraoperative complications occurred in the PLIF group. The relative risk of having a major postoperative complication was 6.8 times higher in the PLIF group than the ALIF group. Anterior approached patients tended to have visceral (ileus, 6%) and vascular (deep venous thrombosis, 2%) complications. In the posterior group, complications were neurologic and dura related (pseudomeningocele, 16%; epidural hematoma, 3%) and occurred most frequently in patients that had had previous posterior lumbar surgery (31% with major complication).