Biomedical subjects

Neil R Crawford

Publications and source records attributed to Neil R Crawford.

At least 19 recordsLinked to original sources

PubMed2007

Hangman's fracture: a biomechanical comparison of stabilization techniques.

STUDY DESIGN: In vitro biomechanical flexibility experiment studying 5 sequential conditions. OBJECTIVE: To determine the biomechanical differences among 3 fixation techniques after a simulated hangman's fracture. SUMMARY OF BACKGROUND DATA: Type II hangman's fractures are often treated surgically with a C2-C3 anterior cervical discectomy, fusion, and plating. Other techniques include direct fixation with C2 pars interarticularis screws or posterior C2-C3 fixation connecting C2 pars screws to C3 lateral mass screws. METHODS: Seven cadaveric specimens (Oc-C4) were tested intact, after a simulated hangman's fracture, and after each fixation technique. Flexion, extension, lateral bending, and axial rotation were induced using nonconstraining torques while recording angular motions stereophotogrammetrically. RESULTS: Direct screw fixation reduced motion an average of 61% +/- 13% during lateral bending and axial rotation compared to the injured state (P < 0.007). However, instability remained during flexion and extension. Posterior C2-C3 rod fixation provided significantly greater rigidity than anterior plate fixation during lateral bending (P < 0.008) and axial rotation (P < 0.04). CONCLUSIONS: Direct fixation of the pars ineffectively limits flexion and extension after a Type II hangman's fracture. If pars screw fixation can be achieved, posterior C2-C3 fixation more effectively stabilizes a hangman's fracture than anterior cervical plating.

Adult↗

PubMed2006

Biomechanical assessment of anterior lumbar interbody fusion with an anterior lumbosacral fixation screw-plate: comparison to stand-alone anterior lumbar interbody fusion and anterior lumbar interbody fusion with pedicle screws in an unstable human cadaver model.

STUDY DESIGN: Human lumbosacral cadaveric specimens were tested in an in vitro biomechanical flexibility experiment using physiologic loads in 5 sequential conditions. OBJECTIVE: To determine the biomechanical differences between anterior lumbar interbody fusion (ALIF) using cylindrical threaded cages alone or supplemented with an anterior screw-plate or posterior pedicle screws-rods. SUMMARY OF BACKGROUND DATA: Clinically and biomechanically, stand-alone ALIF performs modestly in immobilizing the unstable spine. Pedicle screws improve fixation stiffness significantly, but supplementary anterior instrumentation has not been studied. METHODS: There were 7 specimens tested: (1) intact, (2) after discectomy and facetectomy to induce moderate rotational and translational hypermobility, (3) with 2 parallel ALIF cages, (4) with cages plus a triangular anterior screw-plate, and (5) with cages plus pedicle screws-rods. Pure moments without preload induced flexion, extension, lateral bending, and axial rotation; linear shear forces induced anteroposterior translation. Angular and linear motions were measured stereophotogrammetrically, and range of motion (ROM) and stiffness were quantified. RESULTS: Compared to the destabilized spine, interbody cages alone reduced ROM by 77% during flexion, 53% during extension, 60% during lateral bending, 69% during axial rotation, and 71% during anteroposterior shear (P < 0.001, analysis of variance/Fisher least significant difference). Addition of an anterior plate or pedicle screws-rods, respectively, further reduced ROM by 8% or 13% during flexion (P = 0.21), 21% or 28% during extension (P = 0.15), 5% or 25% during lateral bending (P = 0.04), 11% or 18% during axial rotation (P = 0.13), and 18% or 18% during anteroposterior shear (P = 0.17). Compared to stand-alone ALIF, both the anterior screw-plate and pedicle screw-rod fixation reduced vertebral ROM to less than 1.2 degrees of rotation and less than 0.1 mm of translation. CONCLUSIONS: The anterior screw-plate and pedicle screws-rods both substantially reduced ROM and increased stiffness compared to stand-alone interbody cages. There was no significant difference in the amount by which the supplementary fixation devices limited flexion, extension, axial rotation, or anteroposterior shear; pedicle screws-rods better restricted lateral bending.

Aged↗

PubMed2006

Comparative analysis of anterior petrosectomy and transcavernous approaches to retrosellar and upper clival basilar artery aneurysms.

OBJECTIVE: To compare two techniques, transcavernous approach (TcA) and anterior petrosectomy (AP), used to manage retrosellar and upper clival basilar artery (BA) aneurysms. METHODS: AP and TcA were carried out on nine sides of cadaver heads. With use of a computerized tracking system, the area of surgical exposure in the ventral surface of the brain stem, the superficial area of exposure, and the linear exposure of the BA were evaluated. The angles of approach in the horizontal and vertical axes were measured using a robotic microscope. The caudal extent of exposure was determined by an aneurysm clip applied to proximal BA, and the distance between the clip and the floor of the sella was quantified after performing TcA. RESULTS: TcA (1127.3 +/- 438.4 mm2) provided a greater superficial exposure than AP (697.7 +/- 219.1 mm2) (P = 0.01). There were no statistical differences in the deep working exposure (P = 0.303) between TcA (206.9 +/- 40.7 mm2) and AP (260.2 +/- 137.1 mm2). The linear exposure of the BA was greater for AP (22.7 +/- 6.2 mm2) than for the TcA (12.8 +/- 2.9 mm2) (P = 0.004). The caudal extent of exposure averaged 6.1 mm from the floor of the sella. No differences were found in horizontal angles (P = 0.596); however, vertical angles were significantly greater for the TcA than AP (15.2 +/- 3.4) (P = 0.004). CONCLUSION: From an anatomic standpoint, the TcA offers more advantages than the AP, when approaching retrosellar BA aneurysms, except for those cases in which proximal control is the principal issue and the neck of the aneurysm is located more than 6.0 mm below the floor of the sella.

Analysis of Variance↗

PubMed2006

Quantification and comparison of telovelar and transvermian approaches to the fourth ventricle.

OBJECTIVE: To quantify the exposure to the fourth ventricle obtained with the telovelar and transvermian approaches. METHODS: The telovelar, with and without C1 posterior arch removal, and transvermian approaches were performed on six cadaveric heads. The area of surgical exposure was calculated from triangles formed by defined anatomic points. A robotic microscope was used to determine the "angle of approach" for the same points. RESULTS: The maximal allowable vertical angle of attack to the obex of the fourth ventricle was significantly greater with the telovelar approach than with the transvermian approach (P < 0.002), but there was no difference at the rostral fourth ventricle. The maximal allowable horizontal angle of attack at the level of the obex, Luschka, and rostral fourth ventricle was significantly greater with the telovelar than with the transvermian approach (P < 0.001). Removal of the C1 posterior arch with the telovelar approach significantly increased the vertical angle of approach to the obex (P < 0.001) and rostral aspect of the fourth ventricle (P = 0.005) compared with the telovelar alone. The telovelar approach with C1 arch removal offered a larger working area than the transvermian approach (P < 0.001). CONCLUSION: Except for the vertical angle to the rostral aspect of the fourth ventricle, the telovelar approach provides greater angle of exposure in all planes than the transvermian approach. Removal of the C1 posterior arch obviates this sole advantage of the transvermian approach. The telovelar approach offers a corridor through noneloquent arachnoid planes and a safe and capacious working environment.

Cerebellum↗

PubMed2006

The pterional-transsylvian approach: an analytical study.

OBJECTIVE: Splitting of the sylvian fissure (SF) improves exposure with the pterional (PT) approach. Traditionally, the choice of whether or not to split the SF and how far to open it has depended on the neurosurgeon's experience and preference rather than on quantifiable data. We undertook this study to evaluate the effects of progressive splitting of the SF on surgical exposure with the PT approach. METHODS: A PT craniotomy was performed on nine sides of cadaver heads. Splitting the SF was divided into four steps: 1) dissection of the basal cisterns, 2) dissection of the sphenoidal compartment, 3) dissection of the operculoinsular compartment to the anterior ascendant ramus, and 4) dissection progressing 2.0 cm distal to the anterior ascendant ramus. The degree of the retraction and the relative position of the brain retractors were kept constant. After each step, we used a computerized tracking system to measure the area of surgical exposure of the circle of Willis, the angles of approach to the carotid bifurcation, and the distance between the frontal lobe and skull base. RESULTS: Exposure of the circle of Willis, angles of approach to the carotid bifurcation, and linear distance between the frontal lobe and skull base all increased significantly as splitting of the SF progressed from Steps 1 to 2 and from Steps 2 to 3. There was no significant difference between Steps 3 and 4. CONCLUSION: Exposure of the basal cisterns and circle of Willis by the PT approach is optimized when dissection of the SF reaches the anterior ascendant ramus. Further splitting of the SF provides no additional gain.

Cadaver↗

PubMed2006

Quantitative analysis of the working area and angle of attack for the retrosigmoid, combined petrosal, and transcochlear approaches to the petroclival region.

OBJECT: The authors quantitatively assessed the working areas and angles of attack associated with retrosigmoid (RS), combined petrosal (CP), and transcochlear (TC) craniotomies. METHODS: Four silicone-injected cadaveric heads were bilaterally dissected using three approaches progressing from the least to the most extensive. Working areas were determined using the Optotrak 3020 system on the upper and middle thirds of the petroclivus and brainstem. Angles of attack were studied using the Elekta SurgiScope at the Dorello canal and the origin of the anterior inferior cerebellar artery (AICA). The TC approach provided significantly greater (p < 0.001) working areas at the petroclivus (755.6 +/- 130.1 mm2) and brainstem (399.3 +/- 68.2 mm2) than the CP (354.1 +/- 60.3 and 289.7 +/- 69.9 mm2) and RS approaches (292.4 +/- 59.9, 177.2 +/- 54.2 mm2, respectively). The brainstem working area associated with the CP approach was significantly larger (p < 0.001) than that associated with the RS route. There was no difference in the petroclival working area comparing the CP and RS approaches (p = 0.149). The horizontal and vertical angles of attack achieved using the TC approach were wider than those of the CP and RS at the Dorello canal and the origin of the AICA (p < 0.001). CONCLUSIONS: The CP approach offers a more extensive working area than the RS for lesions involving the anterolateral surface of the brainstem, but not for petroclival lesions. The TC approach provides the widest corridor, improving the working area and angle of attack to both areas, but hearing must be sacrificed and the facial nerve is at risk.

Brain Stem↗

PubMed2006

Anatomical and quantitative description of the transcavernous approach to interpeduncular and prepontine cisterns. Technical note.

OBJECT: The management of wide-necked, giant, or unsuccessfully coil-treated basilar apex aneurysms requires a wide exposure, for both working area and linear visualization of the basilar artery (BA). Cranial-based approaches, such as the transcavernous approach, have been proposed to deal with such aneurysms; whether abbreviated forms of this approach might provide similar exposure remains controversial. The authors examine this issue quantitatively. METHODS: Four alcohol-preserved cadaveric heads injected with pigmented silicone were prepared for bilateral dissection. After completing an orbitozygomatic craniotomy, the surgeons worked in a reverse direction, performing the transcavernous approach in five steps: 1) posterior clinoidectomy; 2) cavernous sinus opening; 3) anterior clinoidectomy; 4) cutting of the distal dural ring; and 5) cutting of the proximal dural ring. Performing the complete transcavernous approach significantly increased the working area and linear exposure of the BA compared with abbreviated forms of the approach (p < 0.05). Opening the roof of the cavernous sinus significantly increased the working area compared with posterior clinoidectomy alone (p = 0.014); however, additional gains in exposure required completing the transcavernous approach. Resection of the anterior clinoid process combined with opening of only the distal dural ring did not significantly increase the working area or linear exposure of the BA. CONCLUSIONS: The complete transcavernous approach significantly increases the working area and linear exposure of the BA compared with the more conservative forms of approach.

Basilar Artery↗

PubMed2006

A biomechanical comparison of three anterior thoracolumbar implants after corpectomy: are two screws better than one?

OBJECT: A flexibility experiment using human cadaveric thoracic spine specimens was performed to determine biomechanical differences among thoracolumbar two-screw plate, single-screw plate, and dual-rod systems. A secondary goal was to investigate differences in the ability of the systems to stabilize the spine after a one- or two-level corpectomy. METHODS: The authors evaluated 21 cadaveric spines implanted with a titanium mesh cage and three types of anterior thoracolumbar supplementary instrumentation after one-level thoracic corpectomies. Pure moments were applied quasistatically while three-dimensional motion was measured optoelectronically. The lax zone, stiff zone, and range of motion (ROM) were measured during flexion, extension, left and right lateral bending, and left and right axial rotation. Corpectomies were expanded to two levels, and testing was repeated with longer hardware. Biomechanical testing showed that the single-bolt plate system was no different from the dual-rod system with two screws in limiting ROM. The single-bolt plate system performed slightly better than the two-screw plate system. Across the same two levels, there was an average of 19% more motion after a two-level corpectomy than after a one-level corpectomy. In general, however, the difference across the different loading modes was insignificant. CONCLUSIONS: Biomechanically, the single-screw plate system is equivalent to a two-screw dual-rod and a two-screw plate system. All three systems performed similarly in stabilizing the spine after one- or two-level corpectomies.

Adult↗

PubMed2006

Biomechanical comparison of two new atlantoaxial fixation techniques with C1-2 transarticular screw-graft fixation.

OBJECT: Two new techniques for atlantoaxial fixation have been recently described. In one technique, C-2 intralaminar screws are connected with C-1 lateral mass screws; in the second, C-1 and C-3 lateral mass screws are interconnected and C-2 is wired sublaminarly. Both techniques include a C1-2 interspinous graft. The authors compared these techniques with the gold-standard, interspinous graft-augmented C1-2 transarticular screw fixation and with a control C1-2 interspinous graft fixation procedure alone. METHODS: In six human cadaveric occiput-C4 specimens, nonconstraining 1.5-Nm pure moments were applied to induce flexion, extension, lateral bending, and axial rotation during which three-dimensional angular motion was measured optoelectronically. Each specimen was tested in the normal state, with graft alone (after odontoidectomy), and then in varying order after applying each construct with a rewired graft. All three constructs allowed significantly less angular motion at the C1-2 junction than the wired interspinous graft alone during lateral bending and axial rotation (p < 0.01, paired Student t-test) but not during flexion or extension. Transarticular screw fixation with an interspinous graft allowed less motion at the atlantoaxial junction than the two new constructs in several conditions. Differences were greater between the transarticular screw construct and the intralaminar screw construct than between the transarticular screw construct and the C1-3 lateral mass screw construct. During lateral bending and axial rotation, the C1-3 construct allowed less motion at the atlantoaxial junction than the intralaminar screw construct. CONCLUSIONS: Biomechanically, the gold-standard C1-2 transarticular screw fixation outperformed the two new techniques during lateral bending and axial rotation. Wiring C-2 to C1-3 rods provided greater stability than C1-2 laminar screws, but it sacrificed C2-3 mobility. It is unknown whether the small differences observed biomechanically would lead to clinically relevant differences in fusion rates.

Aged↗

PubMed2005

Effect of recombinant human bone morphogenetic protein-2 in an experimental model of spinal fusion in a radiated area.

STUDY DESIGN: An animal model of posterolateral intertransverse process spine fusion was used. OBJECTIVES: To investigate whether recombinant human bone morphogenetic protein-2 (rhBMP-2) can overcome the adverse effects of radiation treatment (RT) on spine fusion. SUMMARY OF BACKGROUND DATA: Spinal metastases are common. Some of these patients are candidates for spinal cord decompression and vertebral reconstruction; however, radiation has significant adverse effects on bone healing. METHODS: A posterolateral fusion model was used with rhBMP-2 or iliac crest bone graft (ICBG). Eighty one-year-old rabbits were divided into eight groups: 1) RT 14 days before surgery, rhBMP-2; 2) RT 14 days before surgery, ICBG; 3) RT 2 days after surgery, rhBMP-2; 4) RT 2 days after surgery, ICBG; 5) RT 14 days after surgery, rhBMP-2; 6) RT 14 days after surgery, ICBG; 7) no RT, rhBMP-2; 8) no RT, ICBG. Animals were killed approximately 35 days after surgery. Manual palpation was the definitive test of fusion. Biomechanical and histologic assessments were also performed. RESULTS: All rhBMP-2 groups had significantly greater fusion rates versus respective ICBG control groups: 1 (86%) versus 2 (0%) (P = 0.005), 3 (100%) versus 4 (0%) (P < 0.0001), 5 (100%) versus 6 (0%) (P < 0.0001), and 7 (100%) versus 8 (60%) (P = 0.003). Stiffness and ultimate strength did not differ significantly between the experimental and control groups. Histologic assessment confirmed new bone formation in the fusion masses from rhBMP-2 groups. CONCLUSIONS: Use of rhBMP-2 produced a significantly greater rate of fusion compared with ICBG in a previously radiated area in an animal model, without the morbidity of ICBG harvesting and without the risk of inadvertently using autograft contaminated by micrometastases.

Animals↗

PubMed2005

Biomechanics of stabilization after cervicothoracic compression-flexion injury.

STUDY DESIGN: Biomechanical laboratory research. OBJECTIVE: To determine whether anterior, posterior, or combined instrumentation provides the best stability for treating a cervicothoracic compression-flexion injury. SUMMARY OF BACKGROUND DATA: As the junction between the mobile cervical spine and rigid thoracic spine, the cervicothoracic junction poses unique challenges to the success of any fixation system spanning this region. Although posterior instrumentation is the preferred method of fixation in the unstable cervical spine, it is unknown whether this is the case across the unstable cervicothoracic junction. METHODS: Flexion, extension, lateral bending, and axial rotation of cadaveric specimens were studied during application of nondestructive pure moments in a sequence of conditions: (1) intact, (2) after destabilization, (3) with posterior instrumentation from C6-T1 or T2, and (4) with corpectomy/graft and anterior alone or combined anterior/posterior instrumentation. RESULTS: Compared to anterior instrumentation, posterior instrumentation allowed an 89% smaller range of motion (ROM) during lateral bending (P = 0.01) and 64% smaller ROM during axial rotation (P = 0.04). In most loading modes, combined instrumentation outperformed either anterior or posterior instrumentation alone. Most biomechanical measurements of stability improved when posterior instrumentation was extended from T1 to T2. Small and usually insignificant reductions in ROM averaging 15% were observed with C7 included in the posterior construct versus C7 excluded. CONCLUSIONS: Combined instrumentation provides a significant improvement in stability over either anterior or posterior instrumentation alone. Extension of the posterior instrumentation to include T2 improves stability at T1-T2 as well as rostral levels. Inclusion of C7 in the construct is largely inconsequential biomechanically.

Adult↗

PubMed2005

Biomechanical analysis of a resorbable anterior cervical graft containment plate.

STUDY DESIGN: A series of in vitro experiments were performed in human cadaveric cervical spines in the normal condition, after discectomy and graft, and instrumented with MacroPore resorbable anterior plates (MacroPore, San Diego, CA). Flexibility, graft containment, and load-to-failure were studied. OBJECTIVE: To assess the stability, strength, and resistance to graft extrusion provided by the resorbable plate after discectomy and grafting. SUMMARY OF BACKGROUND DATA: Metallic plates are known to improve stability after discectomy and graft. Resorbable plates have not been evaluated regarding stability offered or ability to contain the graft. METHODS: Specimens were loaded using nonconstraining, nondestructive torques to induce flexion, extension, lateral bending, and axial rotation. One and 2-level specimens were studied: (1) normal, (2) after discectomy and graft, (3) after resorbable plating with 2 screws per vertebra, and (4) after resorbable plating with 3 screws per vertebra. All specimens were loaded to failure after completing nondestructive tests. Additional 1-level specimens with and without resorbable plate were tested for graft containment using anterior shear force directly on the graft. RESULTS: The 1-level resorbable plate did not limit motion significantly better than grafted but unplated specimens. However, 2-level resorbable plates allowed significantly less motion than grafted but unplated specimens during all loading modes (P < 0.05). Specimens with resorbable plates resisted graft extrusion significantly better than unplated specimens. With 1-level resorbable plates, 2 or 3 screws per vertebra provided equivalent stability; in 2-level plates, 3 screws provided significantly better stability. Comparison to previous 1-level metallic plate data revealed a significant difference in motion only during flexion. CONCLUSIONS: The 1-level resorbable plate does not increase stability compared to grafted but unplated specimens and provides less stability than a metal plate, especially during flexion. However, the resorbable plate substantially improves resistance to graft extrusion. The 2-level resorbable plate significantly reduces motion compared to grafted but unplated specimens. When applying a 2-level plate, 3 screws per vertebra are recommended. In a 1-level plate, 2 or 3 screws per vertebra are equivalent.

Biomechanical Phenomena↗

PubMed2005

Biomechanical analysis of rigid stabilization techniques for three-column injury in the lower cervical spine.

STUDY DESIGN: Comparison of nondestructive multidirectional flexibility in groups of specimens receiving two different posterior instrumentation constructs with or without anterior plating. OBJECTIVE: To compare stability after a three-column injury stabilized posteriorly by lateral mass screws-rods at C5-C6 and pedicle screws-rods at C7 ("LLP") or by pedicle screws-rods at C5-C6-C7 ("PPP"), and to compare posterior, anterior, and combined anterior-posterior fixation. SUMMARY OF BACKGROUND DATA: Pedicle screws resist pullout better than lateral mass screws, but little research has compared the stability of pedicle screws to that of lateral mass screws used within constructs. METHODS: Fourteen human cadaveric C4-T1 specimens were tested intact, posteriorly instrumented (7 LLP and 7 PPP), anteriorly instrumented, or with combined (anterior-posterior) instrumentation. Nonconstraining, nondestructive torques induced flexion, extension, lateral bending, and axial rotation while angular motion was recorded optically. RESULTS: Posterior, anterior, and combined instrumentation each significantly improved stability (P < 0.05). Combined fixation provided significantly better stability than either anterior or posterior instrumentation alone. In no loading mode and in no testing condition was any parameter significantly different between LLP and PPP. Posterior instrumentation provided significantly better stability than anterior instrumentation. CONCLUSIONS: Anterior plate and posterior screw-rod fixation alone improve stability in a two-level, three-column cervical injury model. Combined fixation further improves stability. There is little discernible difference in immediate postoperative stability between posterior rod constructs combining lateral mass and pedicle screws and those using only pedicle screws.

Adult↗

PubMed2005

Unilateral cervical facet dislocation: biomechanics of fixation.

STUDY DESIGN: Unilateral facet dislocation was created in human cadaveric cervical spines. Specimens were sequentially instrumented with posterior or anterior screws and plates, and studied biomechanically. OBJECTIVE: To determine the biomechanical differences between anterior and posterior fixation for stabilization of a reduced unilateral cervical facet dislocation. SUMMARY OF BACKGROUND DATA: Although previous studies have compared anterior to posterior instrumentation, no data exist on the biomechanics of either type of stabilization after this particular injury. METHODS: In 6 human cadaveric cervical spine segments, a reproducible unilateral facet dislocation was created and then unlocked (reduced). Nondestructive torques were applied to specimens that were intact, injured-reduced, fixated using posterior nonlocking lateral mass plates, and fixated using a bone graft plus an anterior nonlocking plate. Flexion, extension, lateral bending, and axial rotation were measured stereophotogrammetrically. RESULTS: Lateral mass plating was more effective than anterior plating in limiting motion after reduction of a unilateral facet dislocation. Averaged, over all loading directions, lateral mass plates reduced the range of motion to 17% of normal; anterior plates reduced range of motion to 89% of normal. In all loading directions, lateral mass plates performed significantly better than anterior plates (P < 0.05, paired Student t-tests). CONCLUSIONS: Anterior and posterior plating effectively stabilized a reduced unilateral facet dislocation. Lateral mass fixation provided better immobilization than anterior graft and plate.

Adult↗

PubMed2005

Biomechanical comparison of anterior versus posterior lumbar threaded interbody fusion cages.

STUDY DESIGN: Biomechanical flexibility tests were performed in specimens receiving anterior lumbar interbody fixation or posterior lumbar interbody fixation using dual threaded cages. OBJECTIVES: To determine differences in stability between anterior lumbar interbody fixation and posterior lumbar interbody fixation immediately after surgery and after fatigue. SUMMARY OF BACKGROUND DATA: No direct biomechanical comparison of lumbar fixation with threaded anterior lumbar interbody fixation or posterior lumbar interbody fixation cages has been performed previously. METHODS.: Sixteen anterior lumbar interbody fixation specimens and 16 posterior lumbar interbody fixation specimens underwent nondestructive biomechanical testing. Flexibility was assessed during applied flexion, extension, lateral bending, axial rotation, and anteroposterior shear before and after fixation and fatigue. After testing, specimens were dissected, and the quality of fixation was graded. RESULTS: Variability in angular range of motion after fixation was greater than normal interspecimen variability by 89% after anterior lumbar interbody fixation and by 117% after posterior lumbar interbody fixation. During flexion-extension and lateral bending, posterior lumbar interbody fixation allowed a mean of 60% smaller neutral zones than anterior lumbar interbody fixation (P < 0.05, nonpaired Student t test). During axial rotation, anterior lumbar interbody fixation allowed 15% less range of motion than posterior lumbar interbody fixation unless facets were kept intact with posterior lumbar interbody fixation (6 of 16 specimens), in which case anterior lumbar interbody fixation allowed 41% greater range of motion than posterior lumbar interbody fixation. During anteroposterior shear, both anterior lumbar interbody fixation and posterior lumbar interbody fixation restrained range of motion to within 50% of normal. Anterior lumbar interbody fixation loosened, on average, 130% more with fatigue than posterior lumbar interbody fixation during anteroposterior shear. CONCLUSIONS: Both anterior lumbar interbody fixation and posterior lumbar interbody fixation provided inconsistent stability. Therefore, stand-alone anterior lumbar interbody fixation or posterior lumbar interbody fixation may often be ineffective clinically. During all modes of loading except axial rotation, posterior lumbar interbody fixation performed slightly better than anterior lumbar interbody fixation, perhaps due to deeper hole preparation and destruction of anterior stabilizers necessary for anterior lumbar interbody fixation. Avoiding resection of facets during posterior lumbar interbody fixation led to significantly better performance during axial rotation.

Biomechanical Phenomena↗

PubMed2005

Biomechanics of lumbar arthroplasty.

There are many issues to consider in evaluating the biomechanics of lumbar arthroplasty, which may consist of a nucleus replacement, a total disc replacement, or a mobile posterior device. The goal of spinal arthroplasty is to replicate or augment the function of the normal spinal elements, by taking into consideration both in the quantity and quality of motion that occurs across the replaced joint. This article describes the relevant parameters for studying the biomechanics of lumbar arthroplasty and briefly summarizes the current knowledge with regard to those parameters in some well-known lumbar nucleoplasty, facet replacement, and total disc arthroplasty devices.

Arthroplasty↗

PubMed2005

Quantitative anatomic study of three surgical approaches to the anterior communicating artery complex.

OBJECTIVE: To compare the angles of approach and area of exposure to the anterior communicating artery (AComA) complex associated with pterional (PT), orbitopterional (OPT), and orbitozygomatic (OZ) craniotomies before and after gyrus rectus resection. METHODS: PT, OPT, and OZ craniotomies were performed on both sides of four heads, and the angles of approach and area of exposure to the AComA complex were measured before and after resection of the gyrus rectus. RESULTS: The vertical angle of approach increased significantly among the PT and OPT (P = 0.001), PT and OZ (P = 0.001), and OPT and OZ approaches (P = 0.005). The horizontal angle of approach was significantly larger between the PT to OPT (P = 0.001) and PT to OZ (P = 0.001) approaches but not between the OPT and OZ approaches (P = 0.757). After gyrus rectus resection, the vertical and horizontal angles of approach increased significantly for the PT approach but not for the OPT and OZ approaches. The area of exposure to the AComA complex increased progressively from the PT to OPT to OZ approach but did not reach statistical significance (P = 0.124). Resection of the gyrus rectus resulted in significant relative gains in the area of exposure for the PT (P = 0.01) and OPT (P = 0.04) approaches but not for the OZ approach (P = 0.88). CONCLUSION: The vertical and horizontal angles of approach to the AComA complex are significantly larger for the OPT and OZ approaches compared with the PT approach. Use of the OZ approach may decrease the need for frontal lobe retraction and resection of the gyrus rectus.

Anterior Cerebral Artery↗

PubMed2005

Biomechanical comparison of C1-2 posterior fixation techniques.

OBJECT: In a nondestructive, repeated-measures in vitro flexibility experiment, the authors compared the acute stability of C1-2 after placement of C-1 lateral mass and C-2 pars interarticularis (LC1-PC2) instrumentation with that of C1-2 transarticular screw fixation. METHODS: The effect of C-1 laminectomy and C1-2 interspinous cable/graft fixation on LC1-PC2 stability was studied. Screw pullout strengths were also compared. Seven human cadaveric occiput-C3 specimens were loaded nondestructively with pure moments while measuring nonconstrained atlantoaxial motion. Specimens were tested with graft alone, LC1-PC2 alone, LC1-PC2 combined with C-1 laminectomy, and graft-augmented LC1-PC2. Interspinous cable/graft fixation significantly enhanced LC1-PC2 stability during extension. After C-1 laminectomy, the LC1-PC2 construct allowed increased motion during flexion and extension. There was no significant difference in lax zone or range of motion between LC1-PC2 fixation and transarticular screw fixation, but graft-assisted transarticular screws yielded a significantly smaller stiff zone during extension. The difference in pullout resistance between C-1 lateral mass screws and C-2 pars interarticularis screws was insignificant. The LC1-PC2 region restricted motion to within the normal range during all loading modes. Atlantal laminectomy reduced LC1-PC2 stability during flexion and extension. CONCLUSIONS: The instrumentation-augmented LC1-PC2 construct performed biomechanically similarly to the C1-2 transarticular screw fixation. The LC1-PC2 construct resisted flexion, lateral bending, and axial rotation well. The weakness of the LC1-PC2 fixation in resisting extension can be overcome by adding an interspinous graft to the construct.

Adult↗