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Biomedical subjects

Neil R Crawford

Publications and source records attributed to Neil R Crawford.

At least 37 records · Page 2Linked to original sources
PubMed2005

Biomechanical evaluation of a bioresorbable odontoid screw.

OBJECT: The authors tested the ability of a resorbable cannulated lag screw composed of a polylactide copolymer to repair Type II odontoid fractures. The resorbable screw was evaluated for its ability to restore strength and stiffness to the fractured odontoid process compared with traditional titanium screws. METHODS: Type II odontoid fractures were created in 14 human cadaveric C-2 vertebrae by applying a posterolaterally directed load and piston displacement was measured. Seven of these specimens were repaired using metal screws and seven were repaired using resorbable screws. Specimens were reinjured using the same mechanism as the initial fracture. Values of ultimate strength and stiffness during failure were statistically compared between metal and resorbable screws and between initial fracture and reinjury. CONCLUSIONS: The stiffness and ultimate strength during initial fracture were significantly greater than those during reinjury in specimens repaired using resorbable screws or titanium screws (p < 0.001). The resorbable and titanium screws both restored 31% of the initial ultimate strength of the intact specimen (p = 0.95). The stiffness of the fractured odontoid process was restored to 15 and 23% of its initial value by repair with resorbable and metal screws, respectively (p = 0.07). The mode of failure in resorbable screws was usually breakage or bending, whereas that in metal screws was consistently cutout of the proximal shaft of the screw through the anterior C-2 vertebral body.

Absorbable Implants↗
PubMed2005

Use of dual transarticular screws to fixate simultaneous occipitoatlantal and atlantoaxial dislocations.

Occipitoatlantal dislocation and atlantoaxial vertical distraction are caused by similar mechanisms, and few individuals survive these injuries. It is hypothesized that the injurious vertical force manifests as a traumatic lesion at different levels of the same ligamentous complex. The authors report the cases of two patients who presented with this combined lesion, describe surgical alternatives for stabilization, and introduce a new technique that combines the use of transarticular screws in a "dual" construct, without involving the unaffected spine.

Accidents, Traffic↗
PubMed2005

Biomechanical analysis of a newly designed bioabsorbable anterior cervical plate. Invited submission from the joint section meeting on disorders of the spine and peripheral nerves, March 2005.

OBJECT: The authors present a biomechanical analysis of a newly designed bioabsorbable anterior cervical plate (ACP) for the treatment of one-level cervical degenerative disc disease. They studied anterior cervical discectomy and fusion (ACDF) in a human cadaveric model, comparing the stability of the cervical spine after placement of the bioabsorbable fusion plate, a bioabsorbable mesh, and a more traditional metallic ACP. METHODS: Seven human cadaveric specimens underwent a C6-7 fibular graft-assisted ACDF placement. A one-level resorbable ACP was then placed and secured with bioabsorbable screws. Flexibility testing was performed on both intact and instrumented specimens using a servohydraulic system to create flexion-extension, lateral bending, and axial rotation motions. After data analysis, three parameters were calculated: angular range of motion, lax zone, and stiff zone. The results were compared with those obtained in a previous study of a resorbable fusion mesh and with those acquired using metallic fusion ACPs. For all parameters studied, the resorbable plate consistently conferred greater stability than the resorbable mesh. Moreover, it offered comparable stability with that of metallic fusion ACPs. CONCLUSIONS: Bioabsorbable plates provide better stability than resorbable mesh. Although the results of this study do not necessarily indicate that a resorbable plate confers equivalent stability to a metal plate, the resorbable ACP certainly yielded better results than the resorbable mesh. Bioabsorbable fusion ACPs should therefore be considered as alternatives to metal plates when a graft containment device is required.

Absorbable Implants↗
PubMed2004

The biomechanical effects of cervical multilevel oblique corpectomy.

STUDY DESIGN: A repeated-measures flexibility test was performed in vitro using human cadaveric spines. OBJECTIVES: To compare changes in cervical biomechanics associated with multilevel oblique corpectomy and standard grafted corpectomy with or without plating. SUMMARY OF BACKGROUND DATA: Standard multilevel plated and unplated corpectomies are susceptible to instability in vitro. The authors are unaware of any previous research on the biomechanics of multilevel oblique corpectomy. METHODS.: Six human cadaveric cervical spine specimens (C3-T1) were tested: 1) normal; 2) after 2-level multilevel oblique corpectomy; 3) after expanding multilevel oblique corpectomy to represent standard grafted and plated corpectomy; and 4) after removing the anterior plate. Pure moments were applied to induce flexion, extension, lateral bending, and axial rotation while recording motion stereophotogrammetrically. RESULTS: Compared to normal, the range of motion after multilevel oblique corpectomy increased 15% during flexion, 18% during extension, 11% during lateral bending, and 18% during axial rotation. These increases were about one-third of the increases observed after standard corpectomy without plating. Multilevel oblique corpectomy caused few alterations in locations of axes of rotation and coupling patterns, whereas standard corpectomy with or without plating significantly altered these parameters in several instances. CONCLUSIONS: Multilevel oblique corpectomy (without graft) induced significantly less instability and altered kinematics less than standard unplated corpectomy with graft. Multilevel oblique corpectomy allowed significantly more motion than standard plated corpectomy with graft. However, the goal of standard corpectomy is fusion. Our results indicate that plating significantly limits spinal mobility after 2-level corpectomy, improving the environment for fusion.

Aged↗
PubMed2004

Biomechanical comparison of anterolateral plate, lateral plate, and pedicle screws-rods for enhancing anterolateral lumbar interbody cage stabilization.

STUDY DESIGN: A repeated measures in vitro flexibility experiment was performed in calf spines. OBJECTIVES: To determine the biomechanical differences among three techniques for augmenting stability of an anterolateral lumbar threaded interbody cage. BACKGROUND: Stand-alone interbody cages are known to inadequately stabilize the spine. Surgeons often add supplementary instrumentation for a more stable construct. METHODS: Six L2-L5 calf spines (L3-L4 level instrumented) were tested: 1) intact; 2) with a single anterolateral interbody cage; 3) with cage plus anterolateral plating; 4) with cage plus lateral plating; and 5) with cage plus pedicle screw fixation. Specimens were loaded in each anatomic plane quasistatically (maximum 5.0 Nm). Angular motion was measured stereophotogrammetrically. RESULTS: The stand-alone interbody cage allowed significantly less range of motion than normal during all loading modes except axial rotation. Addition of pedicle screws-rods, anterolateral plate, or lateral plate significantly further reduced range of motion in all planes. Pedicle screws slightly outperformed the anterolateral plate during extension and lateral bending and slightly outperformed the lateral plate during flexion, extension, and left axial rotation (range of motion differences <0.65 degrees, P < 0.05). The anterolateral plate outperformed the lateral plate during flexion and extension, whereas the lateral plate outperformed the anterolateral plate during lateral bending (range of motion difference <0.57 degrees, P < 0.05). CONCLUSION: Anterolateral or lateral lumbar plating increases stability significantly compared to stand-alone interbody cage fixation. These findings support anterolateral or lateral plate fixation as a potential clinical alternative to pedicle screws-rods in this role and may obviate the need for combined anterior and posterior approaches when spinal instability exists.

Animals↗
PubMed2004

New percutaneously inserted spinal fixation system.

STUDY DESIGN: We describe a new percutaneous minimally invasive spinal fixation system based on pedicle screws and inflatable rods. The rods are inserted in a flexible state and harden following deployment. We test this system in terms of biocompatibility, ferromagnetism, magnetic resonance artifact production, bench top mechanical testing, ease of insertion within cadavers, potential thermal damage to paraspinous muscles in pigs, and long-term device tolerability in sheep. OBJECTIVES: To determine the safety and utility of this system before its use in human subjects. SUMMARY OF BACKGROUND DATA: Composite materials and epoxy compounds have been used safely in a variety of implanted medical devices for years with no signs of systemic toxicity or significant device failures. METHODS: Long-term biocompatibility test of system components was conducted according to International Standards Organization 10993 and Food and Drug Administration Blue Book Memorandum #G95-1 standards. Device components were assessed for magnetic deflection and torque and imaged in a 1.5 Tesla magnetic resonance unit. Full constructs of the system were tested for compression strength, torque, and fatigue per American Society for Testing and Materials F1717 standards. The system was deployed using C-arm fluoroscopic guidance in 11 cadavers and 2 live sheep. Further, the inflatable rods were tested for exothermic damage to paraspinous musculature in 2 pigs. RESULTS: All system components were found to be biocompatible, nonferromagnetic, and produce little magnetic resonance artifact. Compression and torque results for the new system were found to be comparable to standard metallic pedicle screw and rod fixation systems. However, the new system displayed a superior modulus of elasticity relative to standard surgical systems. The new system endured 5 million cycles of repetitive compressions without breakage or significant wear. All cadaver and sheep insertions were performed successfully. Sheep suffered no complications, and minimal blood loss occurred during device insertions. One of the animals killed at 6 months demonstrated no internal organ damage. The self-curing version of polymer used to inflate the flexible rods cured to approximately 53% of its final strength in 90 minutes with maximum external rod temperature of 40.5 C. and no adjacent thermal damage within porcine paraspinous musculature. CONCLUSIONS: The new spinal fixation system is biocompatible, uses a nontoxic polymer, is magnetic resonance compatible, displays favorable biomechanical characteristics, can be easily deployed percutaneously using simple fluoroscopic guidance, is well tolerated in living sheep, caused no muscular thermal damage, and could be used in humans within a reasonable operative time frame. The new system demonstrates the feasibility of percutaneously constructing composite structures in situ within the body.

Animals↗
PubMed2004

In vivo evaluation of bioresorbable polylactide implants for cervical graft containment in an ovine spinal fusion model.

OBJECT: An in vivo study was conducted in an ovine model to investigate the biomechanical changes after the animals underwent single-level anterior cervical discectomy followed by fusion in which autologous tricortical graft was used and implantation of cervical plates for which bioresorbable polymer screws and plates were used. The specific aims of the study were to evaluate whether implant failure or screw backout would occur over time and to measure the change in stiffness at the treated level at various postoperative time periods (3, 6, and 12 months). METHODS: A total of 58 x-ray films were evaluated over the 12-month survival period. No screw breakage or displacement was observed in any animal during the temporal radiographic analysis. Radiographically confirmed fusion appeared to be complete at all time periods longer than 6 months. The biomechanical testing demonstrated dramatic reductions in range of motion at the fusion level in the animals allowed to survive for 6 and 12 months, indicating complete fusion after 6 months. CONCLUSIONS: The bioresorbable polymer cervical graft containment system appears to provide a safe and effective alternative for cervical fusion, and warrants further clinical evaluation for its use in single-level anterior cervical discectomy and fusion without postoperative orthosis.

Absorbable Implants↗
PubMed2004

Vertical atlantoaxial distraction injuries: radiological criteria and clinical implications.

OBJECT: The authors sought to establish radiological criteria for the diagnosis of C1-2 vertical distraction injuries. METHODS: Conventional radiography, computerized tomography (CT), and magnetic resonance (MR) imaging findings in five patients with a C1-2 vertical distraction injury were correlated with their clinical history, operative findings, and autopsy findings. The basion-dens interval (BDI) and the C-1 and C-2 lateral mass interval (LMI) were measured in 93 control patients who underwent CT angiography; these measurements were used to define the normal BDI and LMI. The MR imaging results obtained in 30 healthy individuals were used to characterize the normal signal intensity of the C1-2 joint. The MR imaging results were compared with MR images obtained in five patients with distraction injuries. In the 93 patients, the BDI averaged 4.7 mm (standard deviation [SD] 1.7 mm, range 0.6-9 mm) and the LMI averaged 1.7 mm (SD 0.48 mm, range 0.7-3.3 mm). Based on CT scanning in the five patients with distraction injuries, the BDIs (mean 11.9 mm, SD 3.2 mm; p < 0.001) and LMIs (mean 5.5 mm, SD 2 mm; p < 0.0001) were significantly greater than in the control group. Fast-spin echo inversion-recovery MR images obtained in these five patients revealed markedly increased signal distributed throughout the C1-2 lateral mass articulations bilaterally. CONCLUSIONS: In 95% of healthy individuals, the LMI ranged between 0.7 and 2.6 mm. An LMI greater than 2.6 mm indicates the possibility of a distraction injury, which can be confirmed using MR imaging. Patients with a suspected C1-2 distraction injury may be candidates for surgical fusion of C1-2.

Adolescent↗
PubMed2003

Craniovertebral junction fixation with transarticular screws: biomechanical analysis of a novel technique.

OBJECT: The authors compared the biomechanical stability resulting from the use of a new technique for occipitoatlantal motion segment fixation with an established method and assessed the additional stability provided by combining the two techniques. METHODS: Specimens were loaded using nonconstraining pure moments while recording the three-dimensional angular movement at occiput (Oc)-C1 and C1-2. Specimens were tested intact and after destabilization and fixation as follows: 1) Oc-C1 transarticular screws plus C1-2 transarticular screws; 2) occipitocervical transarticular (OCTA) plate in which C1-2 transarticular screws attach to a loop from Oc to C-2; and (3) OCTA plate plus Oc-C1 transarticular screws. Occipitoatlantal transarticular screws reduced motion to well within the normal range. The OCTA loop and transarticular screws allowed a very small neutral zone, elastic zone, and range of motion during lateral bending and axial rotation. The transarticular screws, however, were less effective than the OCTA loop in resisting flexion and extension. CONCLUSIONS: Biomechanically, Oc-C1 transarticular screws performed well enough to be considered as an alternative for Oc-C1 fixation, especially when instability at C1-2 is minimal. Techniques for augmenting these screws posteriorly by using a wired bone graft buttress, as is currently undertaken with C1-2 transarticular screws, may be needed for optimal performance.

Adult↗
PubMed2003

Biomechanical analysis of multilevel cervical corpectomy and plate constructs.

OBJECT: The authors compared the biomechanical stability of two multilevel cervical constructs involving the placement of equal size anterior cervical plates (ACPs) after decompressive surgery: the first is placed after three-level corpectomy with strut graft and the second after two-level corpectomy and aggressive discectomy with strut graft. In addition, both constructs were evaluated with and without the application of a screw attaching the ACP to the strut graft to determine whether the additional screw enhanced stability in any mode of loading. METHODS: Nondestructive repeated-measures in vitro flexibility tests were performed in human cadaveric cervical spines. Nonconstraining pure moments of up to 1.5 Nm were applied while recording three-dimensional angular motion stereophotogrammetrically at each level from C4-5 to C7-T1. Nine specimens underwent the three-level corpectomy/strut graft procedure and eight specimens the two-level corpectomy/discectomy strut graft procedure. Failures during testing eliminated two of the former specimens and three of the latter specimens from analysis. The construct applied after the two-level procedure allowed a significantly smaller normalized neutral zone during flexion-extension than the three-level construct (p = 0.04). Normalized elastic zone and range of motion were consistently smaller in the two- than in the three-level construct, but the differences were not significant. Addition of a screw to the strut graft significantly reduced motion in the three-level procedure-treated specimens during flexion and lateral bending but had no effect on two-level corpectomy-treated specimens. CONCLUSIONS: The construct associated with the two-level corpectomy/discectomy provided better immediate postoperative stability than that associated with the three-level corpectomy. The addition of a screw to the strut graft conferred stability on the three-level construct but not the two-level construct.

Adult↗
PubMed2003

Biomechanical comparison of facet-sparing laminectomy and Christmas tree laminectomy.

OBJECT: The authors compared differences in biomechanical stability between two decompressive laminectomy techniques for treating lumbar stenosis. A Christmas tree laminectomy (CTL), in which bilateral facetectomies and foraminotomies are performed, was compared with facet-sparing laminectomy (FSL), in which the facets are undercut but not resected. Spinal instability was assessed immediately postoperatively and again after discectomy to model long-term degeneration. METHODS: Sixteen motion segments obtained from five human cadaveric lumbar specimens were studied in vitro by conducting nondestructive flexibility tests. Specimens were tested intact, after FSL or CTL, and again after discectomy. Nonconstraining torques (< or = 5 Nm) were applied to induce flexion, extension, axial rotation, and lateral bending; strings and pulleys were used while vertebral angles were measured. Anteroposterior translation in response to shear loading (< or = 100 N) was also measured. Angular motion, shear motion, and sagittal-plane axes of rotation were compared to evaluate stability. Compared with the intact condition, CTL-treated specimens had significantly larger increases in angular motion during flexion, lateral bending, and axial rotation than their FSL-treated counterparts (p < 0.05, nonpaired Student t-tests). Subsequent discectomy caused greater increases in motion in the CTL group. Axes of rotation shifted less from their normal positions after FSL than after CTL. CONCLUSIONS: This study provides objective evidence that the treatment of lumbar stenosis with FSL induces less biomechanical instability and alters kinematics less than FSL. These findings support the use of the FSL in treating lumbar stenosis.

Biomechanical Phenomena↗
PubMed2002

Unilateral cervical facet dislocation: injury mechanism and biomechanical consequences.

STUDY DESIGN: Human cadaveric cervical spines were subjected to nondestructive repeated-measures flexibility tests before, during, and after unilateral facet dislocation. OBJECTIVES: To assess the relative stability and kinematics of the spine in the normal condition, after unilateral facet lock without bony injury and after reducing (unlocking) the facet dislocation. SUMMARY OF BACKGROUND DATA: Experimental unilateral facet dislocation has been studied only when associated with extensive damage to disc, bone, or both. The relative stability of the normal, locked, and unlocked cervical spine has not been studied. METHODS: Unilateral facet dislocation with minimal associated injury was created by slowly applying axial torque while specimens were bent laterally and flexed. Before and after injury, nondestructive torques were applied about each anatomic axis, while three-dimensional specimen motion was recorded stereophotogrammetrically. RESULTS: Unilateral facet dislocation was created with a mean axial torque of 10.2 +/- 2.7 Nm. After locking, range of motion, lax zone, and stiff zone were significantly reduced relative to normal (P < 0.05). After unlocking, the same parameters were significantly increased relative to normal. The position of the axis of rotation shifted when the facet was locked and the centrode elongated after the facet was unlocked. CONCLUSIONS: Unilateral facet dislocation without fracture can be created with moderate loads when axial torque is applied while the facet is distracted. The spine is stable while the articular masses are locked unilaterally; however, the motion segment becomes overtly unstable after the facet dislocation is reduced.

Adult↗
PubMed2002

Feasibility of a resorbable anterior cervical graft containment plate.

In this article the authors review the history of anterior cervical plating for one- and two-level discectomy for degenerative disease and provide background justification for the design and testing of a cervical plate composed of a resorbable material. The design of the plate is discussed with special reference to modifications of its design and tools compared with metallic plates that are necessary because of the different mechanical properties of the less rigid material. The cadaveric and animal in vivo testing methodologies are described, and a novel testing method for reliably quantifying graft containment is also described. Data from a representative sample are presented. Advantages and disadvantages of resorbable plating are discussed.

Absorbable Implants↗
PubMed2002

Feasibility of a resorbable anterior cervical graft containment plate.

In this article we review the background of anterior cervical plating for one- and two-level diskectomy for degenerative disease and provide background justification for the design and testing of a cervical plate composed of a resorbable material. The design of the plate is discussed with special reference to modifications of implant design and implant tools compared with metallic plates that are necessary because of the different mechanical properties of the less rigid material. Our cadaveric and animal in vivo testing methodologies are described and a novel testing method for reliably quantifying graft containment is also described. Data from a representative sample are presented. Advantages and disadvantages of resorbable plating are discussed.

Absorbable Implants↗
PubMed2002

Working area and angle of attack in three cranial base approaches: pterional, orbitozygomatic, and maxillary extension of the orbitozygomatic approach.

OBJECTIVE: This study was designed to quantify the operative exposure obtained in the pterional, orbitozygomatic, and modified orbitozygomatic with maxillary extension surgical approaches. METHODS: The pterional and orbitozygomatic approaches and a variation of the orbitozygomatic osteotomy that included an extra centimeter of bone resection in the inferior direction ("maxillary extension") were performed on cadaveric heads. For each surgical exposure, the working area was determined by using triangles defined with anatomic points. The "angle of attack" of the approaches for the same target point was determined with the use of a robotic microscope. RESULTS: The maximum allowable angle of attack was significantly greater with the orbitozygomatic approach (37.2 +/- 4.7 degrees) than that with the pterional approach (27.1 +/- 4.3 degrees) (P < 0.001). The angle of attack with the maxillary extension (42.0 +/- 4.9 degrees) was significantly greater than that with the orbitozygomatic approach (P < 0.001). The working areas were 281, 343, and 371 mm(2) for the pterional, orbitozygomatic, and maxillary extension approaches, respectively. The orbitozygomatic approach with maxillary extension had a significantly larger working area than the pterional approach (P = 0.011). CONCLUSION: Increments in bony removal open a wider angle in which to work more than they increase the actual amount of working area. Increasing the amount of bone removed by using an orbitozygomatic approach instead of a pterional approach converts a narrow space into a wide portal, allowing surgeons to work closer to the surgical target while decreasing the need for brain retraction. Extending the orbitozygomatic approach into the maxillary region also improves the exposure area and angle, but less significantly.

Cadaver↗
PubMed1999

Biomechanical analysis of cranial settling after transoral odontoidectomy.

The authors conducted a biomechancial study to determine whether C-1 ring integrity is important in maintaining normal occiput-C-2 separation, specifically when the anterior arch is transected to provide access to the dens during an odontoidectomy procedure. Six human cadaveric occiput-C3 specimens were loaded under axial compression, and the bilateral horizontal separation of the C-1 lateral masses and the vertical compression of the occiput relative to C-2 were recorded. Specimens were first studied after odontoidectomy without C-1 ring transection, then after C-1 anterior arch transection, and finally after C-1 lamina transection. With applied compressive load corresponding to three times the weight of the head, the C-1 ring spread horizontally 1.57 +/- 0.30 mm more when the anterior arch of C-1 was transected than when left intact, resulting in 0.74 +/- 0.44 mm collapse in the occiput-C-2 vertical separation. After laminar transection, the C-1 ring spread 6.55 +/- 2.29 mm more than when it was intact. The resultant vertical separation was a 3.37 +/- 1.89-mm collapse in the occiput-C-2. All changes in C-1 spreading and the occiput-C-2 collapse were statistically significant (p < 0.05, paired Student's t-tests). The C-1 ring continuity prevents horizontal spreading caused by the wedging of C-1 between the occiput and C-2 and thus prevents cranial settling. Therefore, to prevent the subsequent development of disease related to cranial settling, the authors recommend that the surgeon resect part of C-1 only if necessary during odontoidectomy.

Journal Article↗