Biomedical subjects

David W Polly

Publications and source records attributed to David W Polly.

44 records · Page 3Linked to original sources

PubMed2002

Economic evaluation of bone morphogenetic protein versus autogenous iliac crest bone graft in single-level anterior lumbar fusion: an evidence-based modeling approach.

STUDY DESIGN: Economic evaluation provides a framework to explicitly measure and compare the value of alternative medical interventions in terms of their clinical, health-related quality-of-life, and economic outcomes. Computerized economic models can help inform the design of future prospective studies by identifying the cost-drivers, the most uncertain parameter estimates, and the parameters with the greatest impact on the results and inferences. OBJECTIVE: An economic analysis of bone morphogenetic protein versus autogenous iliac crest bone graft for single-level anterior lumbar fusion poses several methodologic challenges. This article describes how such an economic evaluation may be framed and designed, while enumerating challenges, offering some solutions, and suggesting an agenda for future research. SUMMARY OF BACKGROUND DATA: An evidence-based modeling approach can incorporate epidemiologic, clinical, and economic data from several sources including randomized clinical trials, peer-reviewed literature, and expert opinion. Sensitivity analyses can be conducted by varying key parameter estimates within a reasonable range to assess the impact on the results and inferences. RESULTS: Preliminary results suggest that from a payer perspective, the upfront price of bone morphogenetic protein is likely to be entirely offset by reductions in the use of other medical resources. That is, bone morphogenetic protein appears to be cost neutral. The cost offsets were attributable largely to prevention of pain and complications associated with autogenous iliac crest bone graft, as well as reduction of the costs associated with fusion failures. CONCLUSIONS: Future research should focus on quantifying the health-related quality-of-life impact of bone morphogenetic protein relative to autogenous iliac crest bone graft, as well as the impact on lost productivity.

Activities of Daily Living↗

PubMed2002

Accuracy of thoracic pedicle screws in patients with and without coronal plane spinal deformities.

STUDY DESIGN: This retrospective observational study evaluated 399 transpedicular thoracic screws using postoperative computed tomography (CT). OBJECTIVES: To examine the in vivo accuracy of transpedicular thoracic screws in patients with and without coronal plane spinal deformities. SUMMARY OF BACKGROUND DATA: There are no comparative studies regarding the safety and accuracy of thoracic pedicle screws in patients with and without coronal plane spinal deformities. METHODS: Curve magnitude and segmental vertebral rotation were determined from preoperative radiographs. Postoperative CT was used to assess the placement accuracy of titanium thoracic pedicle screws. RESULTS: Forty-seven patients underwent instrumented posterior spinal fusion using 399 titanium thoracic pedicle screws. Fully contained screw accuracy in patients with coronal plane spinal deformities was less than in patients without coronal plane spinal deformities at T9-T12 (59% vs. 73%, P = 0.04) and overall (42% vs. 62%, P = 0.001). There was no difference between the overall percentages of acceptably positioned screws (< or = 2 mm of medial or < or = 6 mm of lateral pedicle perforation) in patients with coronal plane spinal deformities (98%) versus patients without coronal plane spinal deformities (99%) (P = 0.69). Penetration of the anterior vertebral cortex was more frequent in patients with coronal plane spinal deformities than in those without coronal plane spinal deformities (8.0% vs. 1.0%, P = 0.008). There was no correlation between the accuracy of screw placement and the degree of segmental rotation, screw proximity to the curve apex, or screw position relative to the curve concavity or convexity (P > 0.12). There were no neurologic or vascular complications. CONCLUSIONS: The overall percentage of acceptably positioned screws was 98% in patients with coronal plane spinal deformities and 99% in patients without coronal plane spinal deformities. In patients with coronal plane spinal deformities, penetration of the pedicle wall and the anterior vertebral cortex was increased at T9-T12 and overall.

Adolescent↗

PubMed2002

Advantage of pedicle screw fixation directed into the apex of the sacral promontory over bicortical fixation: a biomechanical analysis.

STUDY DESIGN: A biomechanical study of human cadaveric sacra using insertional torque and bone mineral density was conducted to determine the optimal sagittal trajectory of S1 pedicle screws. OBJECTIVE: To measure the maximal insertional torque of sacral promontory versus bicortical pedicle screw fixation. SUMMARY OF BACKGROUND DATA: Fixation of instrumentation to the sacrum is commonly accomplished using S1 pedicle screws, with previous studies reporting biomechanical advantages of bicortical over unicortical S1 screws. The biomechanical effect of bicortical screws (paralleling the endplate) versus screws directed into the apex of the sacral promontory is unknown. METHODS: For this study, 10 fresh frozen cadaver sacra were harvested and evaluated with dual-energy radiograph absorptiometry to assess bone mineral density. Matched 7.5-mm monoaxial stainless steel pedicle screws then were randomly assigned by side (left versus right) and placed bicortically or into the apex of the sacral promontory under direct visualization. Maximum insertional torque was recorded for each screw revolution with a digital torque wrench (TQJE1500, Snap-On Tools, Kenosha, WI). RESULTS: Maximum bicortical S1 screw insertional torque averaged 5.22 +/- 0.83 inch-pounds, as compared with the maximum sacral promontory S1 screw insertional torque of 10.34 +/- 1.94 inch-pounds. This resulted in a 99% increase in maximum insertional torque (P = 0.005) using the "tricortical" technique, with the screw directed into the sacral promontory. Mean bone mineral density was 940 +/- 0.25 mg/cm2 (range, 507-1428 mg/cm2). The bone mineral density correlated with maximal insertional torque for the sacral promontory technique (r = 0.806; P = 0.005), but not for the bicortical technique (r = 0.48; P = 0.16). CONCLUSIONS: The screws directed into the apex of the sacral promontory of the S1 pedicle resulted in an average 99% increase in peak insertional torque (P = 0.005), as compared with bicortical S1 pedicle screw fixation. Tricortical pedicle screw fixation correlates directly with bone mineral density.

Absorptiometry, Photon↗

PubMed2002

The use of interbody cage devices for spinal deformity: a biomechanical perspective.

Spinal instrumentation has revolutionized the treatment of spinal deformities and offers a plethora of techniques and designs to surgically treat deformity conditions. The authors address the biomechanical properties afforded by various posterior and anterior spinal instrumentation mechanisms, with and without intervertebral reconstruction, and the principles associated with optimal reconstruction techniques. The integration of multiple strategies can improve anterior and posterior construct stiffness in the treatment of spinal deformities. Structural interbody support probably is the best method to minimize longitudinal rod and screw-bone interface strain. Moreover, anterior load-bearing structural grafts and interbody devices have been shown to increase construct stiffness, decrease the incidence posterior implant failure, permit the use of smaller diameter longitudinal rods, and may enhance the rate of successful spinal arthrodesis. From a biomechanical standpoint, treatment of medium to high-grade spondylolisthesis with stand-alone interbody or transvertebral cages, in the absence of supplemental posterior fixation, is contraindicated. Collectively, the included studies reinforce the principles of load sharing between the anterior and posterior spinal columns and affirm the biomechanical dominance of anterior column support in circumferential spinal arthrodesis.

Biomechanical Phenomena↗

PubMed2002

A giant herniated disc following intradiscal electrothermal therapy.

The introduction of intradiscal electrothermal therapy for the management of discogenic back pain has been met with intense interest over the past few years. During this time there have been several noncontrolled studies published on the procedure, most of which have shown excellent outcomes but few, if any, complications. The authors describe a 29-year-old, 152-kg active duty male soldier who underwent two-level intradiscal electrothermal therapy for L4-L5 and L5-S1 discogenic pain. Before the procedure, the patient had a small L5-S1 contained herniation, with no signs of radiculitis. Postprocedure, the patient developed radicular symptoms and was noted on MRI to have a large L5-S1 disc herniation effacing the left S1 nerve root. Follow-up discography revealed a negative discogram at L4-L5. The patient proceeded to undergo a single-level lumbar fusion, which resulted in nearly complete relief of his radicular and axial low back pain. Two years post-surgery, he is off all narcotic medications and continues to work full-time as a soldier. This case illustrates both the potential benefits and complications that may be associated with intradiscal electrothermal therapy.

Adult↗

PubMedDate not supplied

Disc arthroplasty: lessons learned from total joint arthroplasty.

BACKGROUND CONTEXT: With the rapid emergence of new disc arthroplasty designs and ongoing clinical trials, there is great anticipation among clinicians. Inevitably there will be challenges associated with adoption of this new technology. Potential lessons learned from the extensive experience with extremity arthroplasty may predict some of the perils and pitfalls associated with motion-preserving devices in spinal applications. PURPOSE: To review the extremity total joint literature for lessons that may be transferable to disc arthroplasty and anticipate predictable problems that will occur. STUDY DESIGN/SETTING: A literature review and conjectural analysis of key lessons learned from the experience of extremity total joint arthroplasty and anterior lumbar interbody fusion devices with subsequent application of these lessons to disc arthroplasty in the lumbar spine. METHODS: Limited data are available on disc arthroplasty. RESULTS: Particular areas of controversy and uncertainty exist. The ongoing US Food and Drug Administration Investigational Device Exemption clinical trials may provide additional insight into these questions. CONCLUSIONS: Complications will occur. These will be approach related, device related and patient-selection related. Studying the experience of extremity joint arthroplasty may accelerate the learning curve for lumbar disc arthroplasty.

Arthroplasty, Replacement↗

PubMedDate not supplied

Perioperative blood and blood product management for spinal deformity surgery.

BACKGROUND CONTEXT: Spinal deformity surgery, like many other orthopedic procedures, involves significant operative blood loss. In order to avoid the necessity of bank blood transfusions, many blood management strategies have been devised. PURPOSE: The goal of this review is to analyze the utility of current blood management strategies. STUDY DESIGN/SETTING: Review paper. METHODS: Using Medline reviews, pertinent data on blood management agents and strategies were assembled. RESULTS: Techniques can be organized into preoperative, intraoperative and postoperative categories. Preoperative techniques include autologous blood donation and red cell augmentation. In addition to some established surgical and anesthesia techniques, recent pharmacologic agents have become available to include thrombotic agents and antifibrinolytics, which surgeons may add to their intraoperative armamentarium. A brief mention of postoperative blood salvage drains is also included. CONCLUSIONS: The judicious use of the agents and techniques can significantly reduce the need for blood transfusions in the setting of spinal deformity surgery.

Blood Loss, Surgical↗

PubMedDate not supplied

Anterior thoracic scoliosis constructs: effect of rod diameter and intervertebral cages on multi-segmental construct stability.

BACKGROUND CONTEXT: Many studies have reported on the use of anterior instrumentation for thoracolumbar scoliosis and more recently thoracic scoliosis. However, the optimal construct design remains an issue of debate. PURPOSE: To optimize construct design and enhance implant survival until a successful spinal arthrodesis is achieved. STUDY DESIGN: This study evaluated the effect of rod diameter and intervertebral cages on construct stiffness and rod strain using a long-segment, anterior thoracic scoliosis model with varying levels of intervertebral reconstruction. METHODS: Sixteen fresh-frozen calf spine specimens (T1 to L1) were divided into two groups based on rod diameter reconstruction (4 mm and 5 mm). Testing included axial compression, anterior flexion, extension and lateral bending with variations in the number and level of intervertebral cage reconstructions: apical disc (one), end discs (two), apical and end discs (three), all seven levels (seven). Multisegmental construct stiffness and rod strain were determined and normalized to the intact specimen for analysis. RESULTS: The seven-level intervertebral cage construct showed significantly greater stiffness in axial compression for both the 4-mm (366% increased stiffness) and 5-mm (607% increased stiffness) rod groups (p<.001). The remaining constructs were not significantly different from each other (p>.05). In flexion, similar results were obtained for the 4-mm construct (p<.001) but not the 5-mm construct, because the reconstruction-alone, one-, two- and three-cage constructs were all significantly stiffer than the intact specimen (p<.05). Multisegmental construct stiffness under extension loading, as well as right and left lateral bending, also exhibited significant differences between the seven-level interbody cage reconstructions and the remaining constructs. Apical rod strain for both the 4-mm-rod and 5-mm-rod groups were significantly higher for the two cage constructs (a cage at either end but not the apex where the strain gauges were located) as compared with the other constructs (p<.05). These differences were more pronounced in the 4-mm-rod group. Similar results were obtained in anterior flexion, extension and lateral bending. CONCLUSIONS: Intervertebral cages at every level significantly improved construct stiffness compared with increasing rod diameter alone. Moreover, cages markedly decreased rod strain, and when structural interbody supports were not used, axial compression created the greatest rod strain.

Animals↗