Novel Graft Technique for Lumbopelvic Reconstruction After Sacral Tumor Resection: A Case Report.

CASE: Reconstruction after sacral tumor resection carries a high risk of nonunion and requires a slow return to weight-bearing. A bilateral iliac-crest graft, mobilized on a muscular pedicle, was used to graft and fuse the spine and pelvis after resection of a massive sacral schwannoma. Long-term follow-up and three-dimensional computed tomography imaging demonstrate rapid incorporation and solid fusion, with hypertrophy of the graft struts and excellent return to function. CONCLUSION: This novel graft technique provides structural autograft bone that bridges the iliolumbar resection gap, providing a vascularized autograft that incorporates rapidly and reliably.

Trephine Technique for Iliac Crest Bone Graft Harvest: Long-term Results.

STUDY DESIGN: Report of surgical technique and long-term outcome; review of prospectively gathered data and follow-up survey of patient cohort. OBJECTIVE: The aim of this study was to review surgical technique for a trephine graft harvest technique and assess perioperative complications/pain, long-term outcome, and patient satisfaction after anterior iliac crest bone graft (ICBG) harvest for anterior cervical fusion. SUMMARY OF BACKGROUND DATA: Rates of complications and residual pain after ICBG harvest have reduced its utility as a source of autograft for spinal fusion. Less invasive options reduce morbidity, and trephine harvest is a simple technique, with low morbidity and perioperative and long-term pain. It has not been presented in the peer-reviewed spine literature, and the long-term experience has not been previously reported. METHODS: Sixty-eight patients undergoing anterior cervical discectomy and fusion (ACDF), using allograft spacers, underwent ICBG harvest using a 3.5 mm trephine by a minimally invasive approach. Perioperative complications, pain incidence and Visual Analog Scale (VAS) were analyzed. Thirty consecutive patients were subsequently surveyed for long-term follow-up regarding pain, function, and satisfaction. RESULTS: No perioperative (0-6 weeks) graft-site complications (infection, hematoma, fracture, wound dehiscence) occurred. There were no reoperations, and no treatment required for graft-site complaints. No patient reported clinically significant perioperative pain (>3/10). At long-term follow-up (mean 45 months) no patients reported pain >3/10 at their graft-site, and the mean VAS was 0.20/10. No patient was impaired by graft-site symptoms, and all were satisfied with their graft harvest. CONCLUSION: Trephine graft harvest minimizes soft tissue dissection, periosteal elevation, and cortical disruption. Outcome using this technique eliminated perioperative complications in this study group, and reduced pain in both perioperative and long-term assessments. Compared to historical outcomes, trephine harvest provides sufficient graft with comparable or improved results relative to other minimally invasive approaches, and significantly improved relative to traditional open techniques. LEVEL OF EVIDENCE: 4.

Surgical Site Infections in Posterior Lumbar Surgery: A Controlled-Cohort Study of Epidural Steroid Paste.

STUDY DESIGN: A retrospective, single-center cohort study of consecutive patients undergoing posterior lumbar decompression between 2007 and 2013 was conducted. OBJECTIVE: To compare rates of surgical site infection between matched cohorts of patients undergoing lumbar surgery with and without intraoperative application of epidural steroid pastes. SUMMARY OF BACKGROUND DATA: Epidural steroid agents reduce postoperative pain and inflammation following lumbar surgery, reducing the use of postoperative narcotics and improving McGill pain scores. Preliminary studies have, however, suggested an increase in surgical site infections following the use of these steroid-containing pastes. METHODS: We reviewed 758 patients undergoing decompression performed at a single center by surgeons who either routinely used or never used an analgesic steroid paste. Patients undergoing instrumentation or revision surgery were excluded, and surgical and postoperative protocols were uniform. Two hundred eighty-three patients met specific inclusion and exclusion criteria. Demographic, clinical, and surgical data were assessed and correlated to the incidence of postoperative infections. Multivariate logistic regression controlled for confounding characteristics and identified independent predictors of postoperative surgical-site infections. RESULTS: Patient demographics, comorbidities, and perioperative protocols were similar between groups. There were six acute infections among 103 patients receiving steroid paste (5.83%), and two infections among 180 patients not receiving paste (1.11%), a statistically significant difference which remained after controlling for confounding characteristics (odds ratio 6.74, P = 0.01). All but one infection occurred among patients with identifiable preoperative risk factors for infection. CONCLUSION: The observed increase in infection among patients receiving pain paste is clinically significant, but infection was primarily observed among at-risk patients. The present study confirms suspicions raised in preliminary studies, and we recommend caution when treating patients with identifiable, comorbid risk factors. LEVEL OF EVIDENCE: 3.

Biomechanical evaluation of a simulated T-9 burst fracture of the thoracic spine with an intact rib cage.

OBJECT: Classic biomechanical models have used thoracic spines disarticulated from the rib cage, but the biomechanical influence of the rib cage on fracture biomechanics has not been investigated. The well-accepted construct for stabilizing midthoracic fractures is posterior instrumentation 3 levels above and 2 levels below the injury. Short-segment fixation failure in thoracolumbar burst fractures has led to kyphosis and implant failure when anterior column support is lacking. Whether shorter constructs are viable in the midthoracic spine is a point of controversy. The objective of this study was the biomechanical evaluation of a burst fracture at T-9 with an intact rib cage using different fixation constructs for stabilizing the spine. METHODS: A total of 8 human cadaveric spines (C7-L1) with intact rib cages were used in this study. The range of motion (ROM) between T-8 and T-10 was the outcome measure. A robotic spine testing system was programmed to apply pure moment loads (± 5 Nm) in lateral bending, flexion-extension, and axial rotation to whole thoracic specimens. Intersegmental rotations were measured using an optoelectronic system. Flexibility tests were conducted on intact specimens, then sequentially after surgically induced fracture at T-9, and after each of 4 fixation construct patterns. The 4 construct patterns were sequentially tested in a nondestructive protocol, as follows: 1) 3 above/2 below (3A/2B); 2) 1 above/1 below (1A/1B); 3) 1 above/1 below with vertebral body augmentation (1A/1B w/VA); and 4) vertebral body augmentation with no posterior instrumentation (VA). A repeated-measures ANOVA was used to compare the segmental motion between T-8 and T-10 vertebrae. RESULTS: Mean ROM increased by 86%, 151%, and 31% after fracture in lateral bending, flexion-extension, and axial rotation, respectively. In lateral bending, there was significant reduction compared with intact controls for all 3 instrumented constructs: 3A/2B (-92%, p = 0.0004), 1A/1B (-63%, p = 0.0132), and 1A/1B w/VA (-66%, p = 0.0150). In flexion-extension, only the 3A/2B pattern showed a significant reduction (-90%, p = 0.011). In axial rotation, motion was significantly reduced for the 3 instrumented constructs: 3A/2B (-66%, p = 0.0001), 1A/1B (-53%, p = 0.0001), and 1A/1B w/VA (-51%, p = 0.0002). Between the 4 construct patterns, the 3 instrumented constructs (3A/2B, 1A/1B, and 1A/1B w/VA) showed comparable stability in all 3 motion planes. CONCLUSIONS: This study showed no significant difference in the stability of the 3 instrumented constructs tested when the rib cage is intact. Fractures that might appear more grossly unstable when tested in the disarticulated spine may be bolstered by the ribs. This may affect the extent of segmental spinal instrumentation needed to restore stability in some spine injuries. While these initial findings suggest that shorter constructs may adequately stabilize the spine in this fracture model, further study is needed before these results can be extrapolated to clinical application.

Special note: preliminary findings--epidural steroid paste in posterior lumbar surgery: surgical site complications in a case-controlled cohort.

STUDY DESIGN: Retrospective cohort analysis of consecutive, case-matched patients. OBJECTIVE: To determine the risk of acute postoperative complications in patients receiving epidural steroid paste. SUMMARY OF BACKGROUND DATA: Epidural steroid agents reduce postoperative pain and inflammation after lumbar surgery, reducing postoperative narcotic use and improving McGill pain scores. Small studies have suggested an increase in surgical site infections after use of steroid-containing pain-paste. However, no larger study exists to address this concern. METHODS: A total of 364 patients undergoing lumbar decompression by surgeons routinely or never using an analgesic steroid paste were reviewed. A total of 123 patients met specific inclusion criteria: 61 steroid-paste (StP) group, 62 in no-paste (NoP) group. Surgical procedures were laminectomy/laminotomy at 1 to 2 adjacent levels. Patients undergoing instrumentation or revision surgery were excluded. Surgical and postoperative protocols were uniform. Retrospective review of clinical data assessed the incidence of postoperative surgical site complications. RESULTS: Patient demographics, characteristics, and perioperative protocols were similar. Only in-patient admission differed­75% in the steroid-paste (StP) group versus 45% in the no-paste (NoP) group (P < 0.0001). There were 5 acute infections, 4 in the StP (6.7% [1.8%­15.9%]) and 1 in the NoP groups (1.67% [0.03%­8.7%]), P = 0.21. One additional StP patient had delayed wound healing. All StP group infections/complications occurred in patients with identifiable comorbid risk factors. CONCLUSION: The observed 4-fold increase in wound complications in the StP group is concerning, although the difference in infection rates was not significant. Stratifying patients by identifiable risk factors could account for some of this difference. The benefits of an epidural agent may outweigh the small risk of surgical site complications in most patients, but we recommend caution when treating patients with identifiable risk factors. A larger study is in progress. LEVEL OF EVIDENCE: 3

Prospective randomized controlled trial of The Stabilis Stand Alone Cage (SAC) versus Bagby and Kuslich (BAK) implants for anterior lumbar interbody fusion.

BACKGROUND: Degenerative disc disease is common and debilitating for many patients. If conservative extensive care fails, anterior lumbar interbody fusion has proven to be an alternative form of surgical management. The Stabilis Stand Alone Cage(SAC) was introduced as a method to obtain stability and fusion. The purpose of this study was to determine whether the Stabilis Stand Alone Cage (SAC) is comparable in safety and efficacy to the Bagby and Kuslich (BAK) device. METHODS: As part of a prospective, randomized, controlled FDA trial, 73 patients underwent anterior interbody fusion using either the SAC(56%) or the BAK device (44%). RESULTS: Background characteristics were similar between the two groups. There was no significant difference between the SAC and BAK groups in mean operative time or mean blood loss during surgery. Adverse event rates did not differ between the groups. Assessment of plain radiographs could not confirm solid fusion in 63% of control and 71% of study patients. Functional scores from Owestry and SF-36 improved in both groups by the two-year follow-up. There were no significant differences between the SAC and BAK patients with respect to outcome. CONCLUSIONS: Both the Stabilis Stand Alone Cage and the BAK Cage provided satisfactory improvement in function and pain relief, despite less than expected radiographic fusion rates. The apparent incongruency between fusion rates and functional outcomes suggests that either radiographs underestimate the true incidence of fusion, or that patients are obtaining good pain relief and improved function despite a lower rate of fusion than previously reported. This was a Level III study.

Plate fixation in the cervical spine: traditional paramedian screw configuration compared with unique unilateral configuration.

OBJECT: This study compared the fixing strength and stability achieved by a unilateral plate and screw configuration against a standard cervical fixation plate using a single-level corpectomy and allograft strut graft model. METHODS: Multidirectional in vitro flexibility tests were performed using a robotic spine testing system. Human cadaveric spines were assessed for spinal stability after vertebral corpectomy and anterior instrumentation. Specimens were mounted cranially and caudally on custom jigs that were then attached to load cells on the robotic system's end effector and base pedestal. C2-T1 spine specimens (n = 6) were tested intact; then after C-5 corpectomy (the vertebral body was excised), allograft placement and anterior plate fixation were performed. The surgeons performed a uniform corpectomy and reconstruction of each specimen in a protocol fashion. Two plates were compared: a unilateral 4-hole cervical plate designed to obtain rigid fixation using 4 convergent fixation screws all placed unilateral to the vertebral midline, and a standard cervical plate with bilateral plate screw configuration. The plate testing sequence was selected at random to limit bias. Fixation screws were matched for length and diameter. Pure moments were applied under load control (maximum 1.8 Nm) in flexion, extension, left/right lateral bending, and left/right axial rotation. Vertebral motion was measured using an optoelectronic system. The mean relative range of motion between C-4 and C-6 was compared among groups using repeated-measures ANOVA (significance level of 0.05). RESULTS: In comparing the intact construct and 2 different plates in all planes of motion, only motion in extension (intact vs. unilateral plate, p = 0.003; intact vs. standard plate, p = 0.001) and left axial rotation (intact vs unilateral plate, p = 0.019) were significantly affected. In terms of immediate cervical stability after 1-level corpectomy and placement of an allograft reconstruction, the unilateral plate showed comparable stiffness to the standard plate in all 3 motion planes (flexion [p = 0.993], extension [p = 0.732], left lateral bending [p = 0.683], right lateral bending [p = 0.546], left axial rotation [p = 0.082], and right axial rotation [p = 0.489]). The unilateral plate showed a trend toward improved stiffness in axial rotation. In no direction did the unilateral configuration prove significantly less stiff than the traditional configuration. CONCLUSIONS: The unilateral plate design proposed here requires minimal dissection and retraction beyond the midline of tissues susceptible to scar, postoperative pain, and swelling. The authors' study suggests that a unilateral plate can be configured to provide comparable fixation strength and torsional stiffness compared with traditional, widely accepted plate designs.

Properties of an interspinous fixation device (ISD) in lumbar fusion constructs: a biomechanical study.

BACKGROUND: Segmental fixation improves fusion rates and promotes patient mobility by controlling instability after lumbar surgery. Efforts to obtain stability using less invasive techniques have lead to the advent of new implants and constructs. A new interspinous fixation device (ISD) has been introduced as a minimally invasive method of stabilizing two adjacent interspinous processes by augmenting an interbody cage in transforaminal interbody fusion. The ISD is intended to replace the standard pedicle screw instrumentation used for posterior fixation. PURPOSE: The purpose of this study is to compare the rigidity of these implant systems when supplementing an interbody cage as used in transforaminal lumbar interbody fusion. STUDY DESIGN: An in vitro human cadaveric biomechanical study. METHODS: Seven human cadaver spines (T12 to the sacrum) were mounted in a custom-designed testing apparatus, for biomechanical testing using a multiaxial robotic system. A comparison of segmental stiffness was carried out among five conditions: intact spine control; interbody spacer (IBS), alone; interbody cage with ISD; IBS, ISD, and unilateral pedicle screws (unilat); and IBS, with bilateral pedicle screws (bilat). An industrial robot (KUKA, GmbH, Augsburg, Germany) applied a pure moment (±5 Nm) in flexion-extension (FE), lateral bending (LB), and axial rotation (AR) through an anchor to the T12 vertebral body. The relative vertebral motion was captured using an optoelectronic camera system (Optotrak; Northern Digital, Inc., Waterloo, Ontario, Canada). The load sensor and the camera were synchronized. Maximum rotation was measured at each level and compared with the intact control. Implant constructs were compared with the control and with each other. A statistical analysis was performed using analysis of variance. RESULTS: A comparison between the intact spine and the IBS group showed no significant difference in the range of motion (ROM) in FE, LB, or AR for the operated level, L3-L4. After implantation of the ISD to augment the IBS, there was a significant decrease in the ROM of 74% in FE (p<.001) but no significant change in the ROM in LB and AR. The unilat construct significantly reduced the ROM by 77% compared with FE control (p<.001) and by 55% (p=.002) and 42% (p=.04) in LB and AR, respectively, compared with control. The bilat construct reduced the ROM in FE by 77% (p<.001), LB by 77% (p=.001), and AR by 65% (p=.001) when compared with the control spine. There was no statistically significant difference in the ROM in FE among the stand-alone ISD, unilat, and bilat constructs. However, in both LB and AR, the unilat and the bilat constructs were significantly stiffer (reduction in the ROM) than the ISD and the IBS combination. The ISD stability in LB and AR was not different from the intact control with no instrumentation at all. There was no statistical difference between the stability of the unilat and the bilat constructs in any direction. However, LB and AR in the unilat group produced a mean rotation of 3.83°±3.30° and 2.33°±1.33°, respectively, compared with the bilat construct that limited motion to 1.96°±1.46° and 1.39°±0.73°. There was a trend suggesting that the bilat construct was the most rigid construct. CONCLUSIONS: In FE, the ISD can provide lumbar stability comparable with Bilat instrumentation. It provides minimal rigidity in LB and AR when used alone to stabilize the segment after an IBS placement. The unilat and the more typical bilat screw constructs were shown to provide similar levels of stability in all directions after an IBS placement, though the bilat construct showed a trend toward improved stiffness overall.

Hybrid dynamic stabilization: a biomechanical assessment of adjacent and supraadjacent levels of the lumbar spine.

OBJECT: The object of this study was to evaluate the effect of hybrid dynamic stabilization on adjacent levels of the lumbar spine. METHODS: Seven human spine specimens from T-12 to the sacrum were used. The following conditions were implemented: 1) intact spine; 2) fusion of L4-5 with bilateral pedicle screws and titanium rods; and 3) supplementation of the L4-5 fusion with pedicle screw dynamic stabilization constructs at L3-4, with the purpose of protecting the L3-4 level from excessive range of motion (ROM) and to create a smoother motion transition to the rest of the lumbar spine. An industrial robot was used to apply continuous pure moment (± 2 Nm) in flexion-extension with and without a follower load, lateral bending, and axial rotation. Intersegmental rotations of the fused, dynamically stabilized, and adjacent levels were measured and compared. RESULTS: In flexion-extension only, the rigid instrumentation at L4-5 caused a 78% decrease in the segment's ROM when compared with the intact specimen. To compensate, it caused an increase in motion at adjacent levels L1-2 (45.6%) and L2-3 (23.2%) only. The placement of the dynamic construct at L3-4 decreased the operated level's ROM by 80.4% (similar stability as the fusion at L4-5), when compared with the intact specimen, and caused a significant increase in motion at all tested adjacent levels. In flexion-extension with a follower load, instrumentation at L4-5 affected only a subadjacent level, L5-sacrum (52.0%), while causing a reduction in motion at the operated level (L4-5, -76.4%). The dynamic construct caused a significant increase in motion at the adjacent levels T12-L1 (44.9%), L1-2 (57.3%), and L5-sacrum (83.9%), while motion at the operated level (L3-4) was reduced by 76.7%. In lateral bending, instrumentation at L4-5 increased motion at only T12-L1 (22.8%). The dynamic construct at L3-4 caused an increase in motion at T12-L1 (69.9%), L1-2 (59.4%), L2-3 (44.7%), and L5-sacrum (43.7%). In axial rotation, only the placement of the dynamic construct at L3-4 caused a significant increase in motion of the adjacent levels L2-3 (25.1%) and L5-sacrum (31.4%). CONCLUSIONS: The dynamic stabilization system displayed stability characteristics similar to a solid, all-metal construct. Its addition of the supraadjacent level (L3-4) to the fusion (L4-5) did protect the adjacent level from excessive motion. However, it essentially transformed a 1-level lumbar fusion into a 2-level lumbar fusion, with exponential transfer of motion to the fewer remaining discs.

Pedicle screw insertion angle and pullout strength: comparison of 2 proposed strategies.

OBJECT: Minimally invasive pedicle screws inserted vertically (that is, dorsoventrally) through the pedicle, as opposed to the more common coaxial technique, offer potential advantages by minimizing soft-tissue stripping during screw placement. The screws are designed for insertion through a medial starting point with vertical trajectory through the pedicle and into the vertebral body. As such, no lateral dissection beyond the insertion point is necessary. However, the effects of this insertion technique on the screw biomechanical performance over a short- and long-term are unknown. The authors investigated the pullout strength and stiffness of these screws, with or without fatigue cycling, compared with comparably sized, traditional screws placed by coaxial technique. METHODS: Twenty-one lumbar vertebrae (L-3, L-4, and L-5) were tested. Each pedicle of each vertebra was instrumented with either a traditional, coaxial pedicle screw (Group A), placed through a standard starting point, or a vertically oriented, alternative-design screw (Group B), with a medial starting point and vertical trajectory. The specimens were divided into 2 groups for testing. One group was tested for direct pullout (10 specimens) while the other was subject to pullout after tangential (toggle) cyclic loading (11 specimens). The screws were cycled in displacement control (± 5 mm producing ~ 4-Nm moment) at a rate of 3 Hz for 5000 cycles. Pullout tests were performed at a rate of 1 mm/minute. RESULTS: Two-way ANOVA showed that Group B screws with a medial starting point (2541 ± 1090 N for cycled vs 2135 ± 1323 N for noncycled) had significantly higher pullout loads than Group A screws with a standard entry point (1585 ± 766 N for cycled vs 1417 ± 812 N noncycled) (p = 0.001). There was no significant effect of cycling or screw insertion type on pullout stiffness. Tangential stiffness of the Group B screws was significantly less than that of the Group A screws (p = 0.001). The stiffness of both screws in the toe region was significantly affected by cycling (p = 0.001). CONCLUSIONS: The use of Group B screws inserted through a medial starting point showed greater pullout load than a Group A screw inserted through a standard starting point. The greater pullout strength in Group B screws may be due to screw thread design and increased cortical bone purchase at the medial starting point. Nevertheless, anatomical considerations of the medial starting point, that is, pedicle or lateral vertebral body cortex breach, may limit its application. The medial starting point of the Group B screw was frequently in the facet at the L-3 and L-4 pedicle entry points, which may have clinical importance.

Transpedicular aspiration of osteoprogenitor cells from the vertebral body: progenitor cell concentrations affected by serial aspiration.

BACKGROUND CONTEXT: Spinal fusion is facilitated when the fusion site is augmented with autograft bone. Iliac crest, long the preferred source of autograft material, is the site of frequent complications and pain. Connective tissue progenitor cells (CTPs) aspirated from marrow provide a promising alternative to traditional autograft harvest. The vertebral body represents an even larger potential reservoir of progenitor cells than the ilium. PURPOSE: To test the hypothesis that a suitable concentration of osteoprogenitor cells can be aspirated from different depths of the vertebral body, maintaining progenitor cell concentrations comparable to the "gold standard," the iliac crest, even after sequential aspirations along the same transpedicular axis. STUDY DESIGN: Prospective clinical investigation quantifying CTP concentrations within the vertebral body relative to depth of sequential aspirations. PATIENT SAMPLE: Adult men and women undergoing elective posterior lumbar fusion and pedicle screw instrumentation (six men and seven women, mean age 56 years [range 40-74 years]). OUTCOME MEASURES: Cell count, CTP concentration (CTPs/cc marrow), and CTP prevalence (CTPs/million cells) were calculated for both individual and pooled aspirate samples. METHODS: Thirteen patients were enrolled into an institutional review board-approved protocol studying transpedicular aspiration of marrow progenitor cells. Connective tissue progenitor cells were aspirated from four depths along the transpedicular axis of the vertebral body and quantified according to cell concentration and CTP prevalence. Histochemical analysis of alkaline phosphatase-positive colony-forming units (CFUs) provided the prevalence of vertebral CTPs relative to depth of aspiration, vertebral level, age, and gender. RESULTS: Four 2.0cc aspirations were obtained from each pedicle of lumbar vertebrae selected for pedicle screw fixation (four 2.0cc aspirates from each of four pedicles). Aspirates of vertebral marrow demonstrated comparable or greater concentrations of CFUs compared with standards previously established for the iliac crest. Overall, the 208 aspirations from 26 vertebral bodies provided a mean CTP concentration of 741.5+/-976.2 CTPs per cubic centimeter of marrow, ranging from a mean concentration of 1316+/-1473 CTPs per cubic centimeter of marrow at superficial (30mm) aspirations to 439+/-557 CTPs per cubic centimeter marrow at deepest (45mm) aspiration depths (p<.00002). There were no significant differences relative to vertebral body level, side aspirated, or gender. An age-related decline in cellularity was suggested for vertebral body aspirates. CONCLUSIONS: The vertebral body is a potential marrow reservoir for aspiration of autograft osteogenic CTPs that can be used to augment spinal fusion. The cancellous bone within that portion of the vertebral body routinely cannulated during pedicle screw placement allows serial aspirations with only modest depletion of progenitor cell concentrations or dilution with peripheral blood. Connective tissue progenitor cell concentrations from all depths were comparable to the mean levels previously established for the iliac crest. The ability to simultaneously harvest progenitor cells for graft augmentation while preparing the pilot hole for pedicle screw fixation will expand the potential for cell harvest techniques for fusion augmentation and reduce the need for iliac crest harvest.

The effects of inflammation on glial fibrillary acidic protein expression in satellite cells of the dorsal root ganglion.

STUDY DESIGN: After undergoing L5 hemilaminectomy, chromic gut suture was placed onto the DRG and the animals were sacrificed at various time-points. OBJECTIVE: The purpose of this study was to identify the effects of inflammation on satellite cells (SCs) of the dorsal root ganglion (DRG) by analyzing glial fibrillary acidic protein (GFAP) expression in of the DRG at various time points. SUMMARY OF BACKGROUND DATA: SCs are neuroglial cells that closely interact with nerve cells of the DRG. The role of SC remains unknown GFAP expression increases in response to CNS injury. Loss of GFAP has impaired Schwann cell proliferation and delayed nerve regeneration after injury. METHODS: Sixty rats underwent a left L5 hemilaminectomy. In Group I, a chromic-gut suture was place topically on the DRG (n = 30), Group II was the sham surgery group (n = 30). DRGs were harvested at 6, 24, 48, 72 hours, and 7 days after surgery. In Group III, 6 control rats were killed and their bilateral L5 DRG harvested. The harvested DRG were analyzed using light microscopy for SC immunoreactivity, using GFAP, HIS-36, TNF-alpha, IL-1alpha, IL-1beta, IL-6 monoclonal antibodies. RESULTS: One hundred thirty-two DRGs were harvested for analysis. Naïve controls and neurons did not express GFAP. The SC sheath expressed GFAP as early as 6 hours postchromic gut application. In Group I, GFAP expression steadily increased after chromic-gut application with 100% of SC soma and SC sheaths being GFAP positive at 7 days. The contralateral DRG demonstrated delayed GFAP expression, with 83% of SC soma and SC sheaths were GFAP positive at 7 days. In Group II, 89% of sacs expressed GFAP by 7 compared to 79% in the contralateral undisturbed DRG. CONCLUSION: Under physiologic conditions, the expression of GFAP by SCs is undetectable. As the inflammatory process develops, GFAP expression steadily increases with 100% of SCs being GFAP immunoreactive 7 days after chromic gut application. These data suggest that SCs are the primary source of GFAP in the DRG. We hypothesize that SC play an important role in the response to early inflammatory injury.

Identifying serious causes of back pain: cancer, infection, fracture.

Most patients with back pain have a benign condition, but tumors, infections, and fractures must be considered during an initial evaluation because overlooking them can have serious consequences. This article discusses the presentation and diagnostic strategies of these serious causes of back pain.

Screw design alters the effects of stress relaxation on pullout.

Stress relaxation during pullout of a pedicle screw decreases the peak load and stiffness of the bone-screw interface. However, it is unknown whether this can be generalized to all types of screw designs. This study aimed to show whether screw design altered the effects of stress relaxation on the mechanical performance of the pedicle screw during pullout. Twelve calf vertebrae were obtained: six vertebrae were instrumented with 7.5x40 mm conical pedicle screws and the other six with 5.0x40 mm cylindrical pedicle screws. The screws with two different designs were pulled out using either a standard pullout or a stress relaxation pullout protocol. Both bone-screw interfaces had lower stiffness in the stress relaxation pullout model than in the standard pullout model, but it was significant in only the cylindrical design group (P<0.05). However, the stress relaxation and standard pullout models did not yield any difference in peak loads in either screw type. Although stress relaxation at the bone-screw interface can alter the mechanical performance of the screw, this may be eliminated by modifying the screw design. A better understanding of viscoelastic properties of the bone-screw interface may help improve implant design and thus, clinical outcomes.

Masquerade: nonspinal musculoskeletal disorders that mimic spinal conditions.

Nonspinal musculoskeletal disorders frequently cause neck and back pain and thus can mimic conditions of the spine. Common mimics are rotator cuff tears, bursitis in the hip, peripheral nerve compression, and arthritis in the shoulder and hip. A thorough history and physical examination, imaging studies, and ancillary testing can usually help determine the source of pain.

Cortex of the pedicle of the vertebral arch. Part I: Deformation characteristics during screw insertion.

OBJECT: Elastic deformation has been proposed as a mechanism by which vertebral pedicles can maintain pullout strength when conical screws are backed out from full insertion. The response to the insertion technique may influence both the extent of deformation and the risk of acute fracture during screw placement. The aim of this study was to determine the deformation characteristics of the lumbar pedicle cortex during screw placement. METHODS: Lumbar pedicles with linear strain gauges attached at the lateral and medial cortices were instrumented using 7.5-mm pedicle screws with or without preconditioning by insertion and removal of 6.5-mm screws. The strains and elastic recoveries of the medial and lateral cortices were determined. RESULTS: Mean medial wall strains tended to be lower than mean lateral wall strains when the 6.5-mm and 7.5-mm screw data were pooled (p = 0.07). After the screws had been removed, 71 to 79% of the deformation at the lateral cortex and 70 to 96% of the deformation at the medial cortex recovered. When inserted first, the 7.5-mm screw caused more plastic deformation at the cortex than it did when inserted after the 6.5-mm screw. Occasional idiosyncratic strain patterns were observed. No gross fracture was observed during screw placement. CONCLUSIONS: Screw insertion generated plastic deformation at the pedicle cortex even though the screw did not directly contact the cortex. The lateral and medial cortices responded differently to screw insertion. The technique of screw insertion affected the deformation behavior of the lumbar pedicles. With myriad options for screw selection and placement available, further study is needed before optimal placement parameters can be verified.

Cortex of the pedicle of the vertebral arch. Part II: Microstructure.

OBJECT: Although the gross anatomy of the pedicle in the human spine has been investigated in great detail, knowledge of the microanatomy of trabecular and cortical structures of the pedicle is limited. An understanding of the mechanical properties and structure of the pedicle bone is essential for improving the quality of pedicle screw placement. To enhance this understanding, the authors examined human cadaveric lumbar vertebrae. METHODS: In this study, the authors obtained seven human cadaveric lumbar vertebrae. The lateral and medial cortices of these pedicle specimens were sectioned and embedded in polymethylmethacrylate. Cross-sectional slices of cortex were obtained from each specimen and imaged with the aid of a high-resolution light microscope. Assessments of osteonal orientation, determinations of relative dimensions, and histomorphometric studies were performed. RESULTS: The cortex of the pedicle in each human lumbar vertebra had an osteonal structure with haversian canals laid down mainly in the anteroposterior (longitudinal) direction. The organization of osteons across the transverse cross-section was not homogeneous. The layer of lamellar bone that typically envelops cortical bone structures (such as in long bones) was not observed, and the lateral cortex was significantly thinner than the medial cortex (p < 0.05). CONCLUSIONS: The cortical bone surrounding the pedicle differed from bone in other anatomical regions such as the anterior vertebral body and femur. The osteonal orientation and lack of a lamellar sheath may account for the unique deformation characteristics of the pedicle cortex seen during pedicle screw placement.

Primary pedicle screw augmentation in osteoporotic lumbar vertebrae: biomechanical analysis of pedicle fixation strength.

STUDY DESIGN: Pedicle screw pullout testing in osteoporotic and control human cadaveric vertebrae, comparing augmented and control vertebrae. OBJECTIVE: To compare the pullout strengths of pedicle screws fixed in osteoporotic vertebrae using polymethyl methacrylate delivered by 2 augmentation techniques, a standard transpedicular approach and kyphoplasty type approach. SUMMARY OF BACKGROUND DATA: Pedicle screw instrumentation of the osteoporotic spine carries an increased risk of screw loosening, pullout, and fixation failure. Osteoporosis is often cited as a contraindication for pedicle screw fixation. Augmentation of the vertebral pedicle and body using polymethyl methacrylate may improve fixation strength and construct survival in the osteoporotic vertebrae. While the utility of polymethyl methacrylate has been demonstrated for salvage of screws that have been pulled out, the effect of the cement technique on pullout strength in osteoporotic vertebrae has not been previously studied. METHODS: Thirteen osteoporotic and 9 healthy human lumbar vertebrae were tested. All specimens were instrumented with pedicle screws using a uniform technique. Osteoporotic pedicles were augmented with polymethyl methacrylate using either a kyphoplasty type technique or a transpedicular augmentation technique. Screws were tested in a paired testing array, randomly assigning the augmentation techniques to opposite sides of each vertebra. Pullout to failure was performed either primarily or after a 5000-cycle tangential fatigue conditioning exposure. After testing, following screw removal, specimens were cut in the axial plane through the center of the vertebral body to inspect the cement distribution. RESULTS: Pedicle screws placed in osteoporotic vertebrae had higher pullout loads when augmented with the kyphoplasty technique compared to transpedicular augmentation (1414 +/- 338 versus 756 +/- 300 N, respectively; P < 0.001). An unpaired t test showed that fatigued pedicle screws in osteoporotic vertebrae augmented by kyphoplasty showed higher pullout resistance than those placed in healthy control vertebrae (P = 0.002). Both kyphoplasty type augmentation (P = 0.007) and transpedicular augmentation (P = 0.02) increased pullout loads compared to pedicle screws placed in nonaugmented osteoporotic vertebrae when tested after fatigue cycling. CONCLUSIONS: Pedicle screw augmentation with polymethyl methacrylate improves the initial fixation strength and fatigue strength of instrumentation in osteoporotic vertebrae. Pedicle screws augmented using the kyphoplasty technique had significantly greater pullout strength than those augmented with transpedicular augmentation technique and those placed in healthy control vertebrae with no augmentation.