Biomechanical Effects of an Oblique Lumbar PEEK Cage and Posterior Augmentation.

OBJECTIVE: Lumbar interbody spacers are widely used in lumbar spinal fusion. The goal of this study is to analyze the biomechanics of a lumbar interbody spacer (Clydesdale Spinal System, Medtronic Sofamor Danek, Memphis, Tennessee, USA) inserted via oblique lumbar interbody fusion (OLIF) or direct lateral interbody fusion (DLIF) approaches, with and without posterior cortical screw and rod (CSR) or pedicle screw and rod (PSR) instrumentation. METHODS: Lumbar human cadaveric specimens (L2-L5) underwent nondestructive flexibility testing in intact and instrumented conditions at L3-L4, including OLIF or DLIF, with and without CSR or PSR. RESULTS: OLIF alone significantly reduced range of motion (ROM) in flexion-extension (P = 0.005) but not during lateral bending or axial rotation (P ≥ 0.63). OLIF alone reduced laxity in the lax zone (LZ) during flexion-extension (P < 0.001) but did not affect the LZ during lateral bending or axial rotation (P ≥ 0.14). The stiff zone (SZ) was unaffected in all directions (P ≥ 0.88). OLIF plus posterior instrumentation (cortical, pedicle, or hybrid) reduced the mean ROM in all directions of loading but only significantly so with PSR during lateral bending (P = 0.004), without affecting the compressive stiffness (P > 0.20). The compressive stiffness with the OLIF device without any posterior instrumentation did not differ from that of the intact condition (P = 0.97). In terms of ROM, LZ, or SZ, there were no differences between OLIF and DLIF as standalone devices or OLIF and DLIF with posterior instrumentation (CSR or PSR) (P > 0.5). CONCLUSIONS: OLIF alone significantly reduced mobility during flexion-extension while maintaining axial compressive stiffness compared with the intact condition. Adding posterior instrumentation to the interbody spacer increased the construct stability significantly, regardless of cage insertion trajectory or screw type.

Biomechanical Analysis of an Expandable Lumbar Interbody Spacer.

OBJECTIVE: Recently developed expandable interbody spacers are widely accepted in spinal surgery; however, the resulting biomechanical effects of their use have not yet been fully studied. We analyzed the biomechanical effects of an expandable polyetheretherketone interbody spacer inserted through a bilateral posterior approach with and without different modalities of posterior augmentation. METHODS: Biomechanical nondestructive flexibility testing was performed in 7 human cadaveric lumbar (L2-L5) specimens followed by axial compressive loading. Each specimen was tested under 6 conditions: 1) intact, 2) bilateral L3-L4 cortical screw/rod (CSR) alone, 3) WaveD alone, 4) WaveD + CSR, 5) WaveD + bilateral L3-L4 pedicle screw/rod (PSR), and 6) WaveD + CSR/PSR, where CSR/PSR was a hybrid construct comprising bilateral cortical-level L3 and pedicle-level L4 screws interconnected by rods. RESULTS: The range of motion (ROM) with the interbody spacer alone decreased significantly compared with the intact condition during flexion-extension (P = 0.02) but not during lateral bending or axial rotation (P ≥ 0.19). The addition of CSR or PSR to the interbody spacer alone condition significantly decreased the ROM compared with the interbody spacer alone (P ≤ 0.002); and WaveD + CSR, WaveD + PSR, and WaveD + CSR/PSR (hybrid) (P ≥ 0.29) did not differ. The axial compressive stiffness (resistance to change in foraminal height during compressive loading) with the interbody spacer alone did not differ from the intact condition (P = 0.96), whereas WaveD + posterior instrumentation significantly increased compressive stiffness compared with the intact condition and the interbody spacer alone (P ≤ 0.001). CONCLUSIONS: The WaveD alone significantly reduced ROM during flexion-extension while maintaining the axial compressive stiffness. CSR, PSR, and CSR/PSR hybrid constructs were all effective in augmenting the expandable interbody spacer system and improving its stability.

Lumbar Spinal Fixation with Cortical Bone Trajectory Pedicle Screws in 79 Patients with Degenerative Disease: Perioperative Outcomes and Complications.

OBJECTIVE: Biomechanical studies demonstrate that cortical bone trajectory pedicle screws (CBTPS) have greater pullout strength than traditional pedicle screws with a lateral-medial trajectory. CBTPS start on the pars and angulate in a mediolateral-caudocranial direction. To our knowledge, no large series exists evaluating the perioperative outcomes and safety of CBTPS. METHODS: We retrospectively reviewed all patients who received lumbar CBTPS at our institution. Data were collected regarding patient demographics, use of image guidance, operative blood loss, hospital stay, and postoperative complications. RESULTS: A total of 79 patients undergoing CBTPS fusion for degenerative lumbosacral disease with back pain were included in the analysis (42 female, 37 male; October 2011-January 2015). Twenty patients (25.3%) had previous lumbar spine surgery, 39 (49.4%) had a smoking history, and mean body mass index was 28.7. Mean length of stay was 3.5 days, and mean operative blood loss was 306.3 mL. Image guidance was used in 69 (87.3%) cases. A total of 66 (83.5%) fusions were single level, and 54 (68.4%) fusions were single level without previous surgery. There were 9 complications in 7 (8.9%) patients; these included hardware failure, pseudarthrosis, deep vein thrombosis, pulmonary embolism, epidural hematoma, and wound infection. No complications were caused by misplaced screws. Mean follow-up was 13.2 months. CONCLUSIONS: As CBTPS becomes increasingly popular among spine surgeons performing lumbar fusion, this report provides an important evaluation of technique safety and acceptable perioperative outcomes.

Effects of Anterior Plating on Clinical Outcomes of Anterior Lumbar Interbody Fusion.

STUDY DESIGN: Retrospective review. OBJECTIVE: To compare surgical outcomes of patients who have undergone anterior lumbar interbody fusion (ALIF) with and without plating. SUMMARY OF BACKGROUND DATA: In biomechanical testing, ALIF constructs supplemented with plating (ALIFP) reduce range of motion and increase construct stiffness compared with ALIF alone. However, whether ALIFP constructs translate into improved clinical outcomes over ALIF alone is unknown. METHODS: From 2004 through 2010, 231 patients underwent ALIF with (146) or without (85) plating. Eight patients lost to follow up were excluded from final evaluation. Patients' records were evaluated retrospectively for demographics, complications, and outcomes. RESULTS: At a mean follow-up of 13.7 months (range, 1-108 mo), the mean Economic, Functional, and Total Prolo scores for ALIF patients were 4.23, 3.63, and 7.87, respectively. The mean Oswestry Disability Index (ODI) was 24%. At a mean follow-up of 11.2 months (range, 1-93 mo), the mean Economic, Functional, and Total Prolo scores for ALIFP patients were 4.28, 3.67, and 7.95, respectively. The mean ODI was 22.9%. There was no significant difference between rate of complications or Prolo scores or ODI between the 2 groups (t test). Neither diabetes, hypertension, smoking, sex, nor age older than 55 years was significantly related to whether patients had higher Prolo scores with or without plating. Patients with a normal body mass index and ALIF had significantly better Prolo Economic scores and total scores than patients with a normal body mass index and ALIFP (P=0.04 and 0.02, independent samples t test). Patients were also stratified by surgical indication for surgery, and there was no significant difference in Prolo scores or ODI for patients who underwent ALIF alone versus ALIFP. CONCLUSIONS: Even when stratified by indication for surgery, anterior plating does not seem to improve Prolo scores or ODI, suggesting that not all patients undergoing ALIF require plating.

Biomechanics of a lumbar interspinous anchor with transforaminal lumbar interbody fixation.

OBJECT: To study the stability offered by a clamping lumbar interspinous anchor (ISA) for transforaminal lumbar interbody fusion (TLIF). METHODS: Seven human cadaveric lumbosacral specimens were tested: 1) intact; 2) after placing ISA; 3) after TLIF with ISA; 4) with TLIF, ISA, and unilateral pedicle screws-rod; 5) with TLIF and unilateral pedicle screws-rod (ISA removed); and 6) with TLIF and bilateral pedicle screws-rods. Pure moments (7.5 Nm maximum) were applied in each plane to induce flexion-extension, axial rotation, and lateral bending while recording angular motion optoelectronically. Compression (400 N) was applied while upright foraminal height was measured. RESULTS: All instrumentation reduced angular range of motion (ROM) significantly from normal. The loading modes in which the ISA limited ROM most effectively were flexion and extension, where the ROM allowed was equivalent to that of pedicle screws-rods (P > .08). The ISA was least effective in reducing lateral bending, with this mode reduced to 81% of normal. TLIF with unilateral pedicle screws-rod was the least stable configuration. Addition of the ISA to this construct significantly improved stability during flexion, extension, lateral bending, and axial rotation (P < .008). Constructs that included the ISA increased the foraminal height an average of 0.7 mm more than the other constructs (P < .05). CONCLUSIONS: In cadaveric testing, the ISA limits flexion and extension equivalently to pedicle screws-rods. It also increases foraminal height. When used with TLIF, a construct of ISA or ISA plus unilateral pedicle screws-rod may offer an alternative to bilateral pedicle screws-rods for supplemental posterior fixation.

Biomechanics of a lumbar interspinous anchor with anterior lumbar interbody fusion.

OBJECT: An interspinous anchor (ISA) provides fixation to the lumbar spine to facilitate fusion. The biomechanical stability provided by the Aspen ISA was studied in applications utilizing an anterior lumbar interbody fusion (ALIF) construct. METHODS: Seven human cadaveric L3-S1 specimens were tested in the following states: 1) intact; 2) after placing an ISA at L4-5; 3) after ALIF with an ISA; 4) after ALIF with an ISA and anterior screw/plate fixation system; 5) after removing the ISA (ALIF with plate only); 6) after removing the plate (ALIF only); and 7) after applying bilateral pedicle screws and rods. Pure moments (7.5 Nm maximum) were applied in flexion and extension, lateral bending, and axial rotation while recording angular motion optoelectronically. Changes in angulation as well as foraminal height were also measured. RESULTS: All instrumentation variances except ALIF alone reduced angular range of motion (ROM) significantly from normal in all directions of loading. The ISA was most effective in limiting flexion and extension (25% of normal) and less effective in reducing lateral bending (71% of normal) and axial rotation (71% of normal). Overall, ALIF with an ISA provided stability that was statistically equivalent to ALIF with bilateral pedicle screws and rods. An ISA-augmented ALIF allowed less ROM than plate-augmented ALIF during flexion, extension, and lateral bending. Use of the ISA resulted in flexion at the index level, with a resultant increase in foraminal height. Compensatory extension at the adjacent levels prevented any significant change in overall sagittal balance. CONCLUSIONS: When used with ALIF at L4-5, the ISA provides immediate rigid immobilization of the lumbar spine, allowing equivalent ROM to that of a pedicle screw/rod system, and smaller ROM than an anterior plate. When used with ALIF, the ISA may offer an alternative to anterior plate fixation or bilateral pedicle screw/rod constructs.

Aneurysm clips.

This communication outlines the development of aneurysm clips, from those originally used by Walter Dandy to those in use today. The history is rich, with many contributions from neurosurgical pioneers and innovators. As a result, the modern neurosurgeon has a wide selection of biocompatible aneurysm clips from which to choose, clips that have known closing pressures and various sizes and shapes, as well as a selection of clip applicators that do not obstruct the surgical field.

Optimizing epilepsy surgery with intraoperative MR imaging.

PURPOSE: The surgical treatment of medically intractable temporal lobe epilepsy includes the resection of temporal lobe structures. Although the reported seizure-free outcomes are highly variable, there is growing evidence that the extent of resection of the mesiotemporal lobe directly correlates with seizure control. METHODS: A moveable, high-field intraoperative magnetic resonance (MR) system was used to monitor and optimize the resection of the amygdala and hippocampus in 14 epilepsy patients. Fourteen patients with intractable seizures of temporal lobe origin underwent standard preoperative investigations including MR imaging, EEG telemetry, single-photon emission computed tomography, and neuropsychologic and sodium amytal testing. Anterior temporal lobectomy was performed on 10 patients, whereas four were treated with selective amygdalohippocampectomy. Intraoperative electrocorticography was applied as required. For all procedures, the objective was to resect the amygdala completely, and hippocampus to the posterior margin of the brainstem. RESULTS: Interdissection intraoperative MR imaging taken when optimal resection was thought to have been achieved revealed residual unresected amygdala or hippocampus in seven of 14 patients. An unexpected acute hematoma was found in one patient. At 17 months' follow-up, 13 (93%) of 14 patients are seizure free or have significantly improved seizure control. CONCLUSIONS: The mobile high-field intraoperative MR system provides high-resolution images without restriction on surgical instruments or techniques. The ability to identify and resect residual mesial temporal lobe targets before craniotomy closure is of potentially tremendous value in optimizing seizure control.

Intraoperative assessment of aneurysm clipping using magnetic resonance angiography and diffusion-weighted imaging: technical case report.

OBJECTIVE AND IMPORTANCE: To use intraoperative magnetic resonance imaging, including magnetic resonance angiography and diffusion-weighted imaging, to monitor the surgical treatment of a patient with an intracranial aneurysm. TECHNIQUE: Intraoperative imaging was performed with a ceiling-mounted, mobile, 1.5-T magnet (developed in collaboration with Innovative Magnetic Resonance Imaging Systems, Inc., Winnipeg, MB, Canada) that included high-performance 20-mT/m gradients. Pre- and postclipping, intraoperative, T1-weighted, angiographic and diffusion-weighted magnetic resonance images were obtained from a patient with an incidental, 8-mm, anterior communicating artery aneurysm. RESULTS: T1-weighted images demonstrated brain anatomic features, with visible shifts induced by surgery. Magnetic resonance angiography demonstrated the aneurysm and indicated that, after clipping, the A1 and A2 anterior cerebral artery branches were patent. Diffusion-weighted studies demonstrated no evidence of brain ischemia. CONCLUSION: For the first time, intraoperative magnetic resonance imaging has been used to monitor the surgical treatment of a patient with an intracranial aneurysm.