Dennis G. Crandall

Transforaminal Lumbar Interbody Fusion Versus Anterior Lumbar Interbody Fusion as an Adjunct to Posterior Instrumented Correction of Degenerative Lumbar Scoliosis : Three Year Clinical and Radiographic Outcomes

Study Design. Prospective, nonrandomized consecutive single surgeon series. Objective. To compare the clinical and radiographic outcomes in degenerative lumbar scoliosis (DLS) patients treated with posterior instrumented correction and fusion with additional anterior lumbar interbody fusion (ALIF) versus transforaminal lumbar interbody fusion (TLIF) to help define whether anterior surgery should be routinely required in treating DLS. Summary of Background Data. The benefits of interbody support in promoting postoperative stability and arthrodesis are well established. Whether the interbody fusion is better performed from an anterior or posterior approach has not been studied for patients undergoing surgical correction for DLS. Methods. Forty consecutive patients with DLS, stenosis, and olisthesis underwent posterior instrumented reduction/arthrodesis at average 7 levels (range: 4–9 levels). Additional ALIF was performed in 20 patients, TLIF in the other 20. Follow-up averaged 38 months (24–68 months). Oswestry Disability Index (ODI), visual analog pain scores (VAS) were evaluated preoperative, 1 and 2 years postoperative. Radiograph measurements included the scoliosis, T12 to S1 lordosis, coronal and sagittal balance, and pelvic incidence. CT evaluation of the fusion integrity was performed after 1 year. Results. The ALIF group complications included 4 nonunions, 5 adjacent level fractures, 5 adjacent degeneration, 3 infections, and 1 footdrop. Revision surgery was performed in 8 of 20. Medical complications included 2 nonfatal pulmonary embolus, 1 ileus requiring colostomy, and 1 stroke. TLIF group complications included 3 adjacent segment degeneration, 2 adjacent fractures, 2 nonunions, and 1 infection and transient footdrop. Two of 20 required revision surgery. VAS and ODI improvements for both groups showed significant improvement frompreoperative (P < 0.0019) but were not different. Deformity correction was also similar (70%) between ALIF and TLIF groups. Conclusion. With current deformity correction techniques, both ALIF and TLIF are effective in DLS surgery. Anterior surgery is not routinely required to treat all cases of DLS.

Transforaminal lumbar interbody fusion with rhBMP-2 in spinal deformity, spondylolisthesis, and degenerative disease--part 2: BMP dosage-related complications and long-term outcomes in 509 patients.

Study Design. Retrospective review of prospectively collected data. Objective. Without industry funding, the study evaluated short- and long-term complications related to off-label bone morphogenetic protein (BMP) used with transforaminal lumbar interbody fusion (TLIF) from a large consecutive series. Complications and results were analyzed by BMP dose, fusion length, and primary versus revision surgery. Based on the results, surgical technique and BMP dose recommendations were proposed. Summary of Background Data. Off-label use of BMP in TLIF, although common, has only been studied in small series and case reports using various techniques, cage types, and doses of BMP. Several of these studies have reported minimal complications. Others report problems related to BMP, which has led to questions regarding current widespread use of TLIF with BMP. Method. TLIF with rhBMP-2 was performed at 872 discs in 509 consecutive adults who underwent open posterior instrumented fusion and had minimum 2-year follow-up; diagnoses included degenerative disease (179), spondylolisthesis (207), deformity (123). Patient age averaged 61 years: 12% were smokers and 41% had revision surgery. TLIF was performed at 1.7 levels: single level: 229, 2 levels: 201, 3 levels: 74, 4 levels: 5. Local autograft was used for backfill around and behind each rectangular cage. Varying doses of interbody BMP were used at an average 7.3 mg per disc (range: 2–12 mg per disc). Results. At 5 years average follow-up, 8 patients developed pseudoarthrosis at levels of TLIF (8 of 872 discs, 0.92%). Seroma (0.4%) and ectopic bone growth (0.6%) were too infrequent to be associated with a particular BMP dose. Deep infection was 2.6% overall (1.7% of the degenerative group). Symptomatic osteolysis or cage subsidence did not occur. Significant long-term improvement was noted in clinical and functional outcomes compared with preoperation. Conclusion. Five-year follow-up after TLIF with BMP, independent of industry, confirms effective arthrodesis in short and long fusions, both primary and revision. Most complications occurred in deformity patients. BMP-related complications (seroma, ectopic bone) were rare. Level of Evidence: 3

Biomechanical Comparison of Force Levels in Spinal Instrumentation Using Monoaxial versus Multi Degree of Freedom Postloading Pedicle Screws

Study Design. Biomechanical analysis and simulations of correction mechanisms and force levels during scoliosis instrumentation using two types of pedicle screws and primary correction maneuvers. Objectives. To biomechanically analyze implant-vertebra and inter-vertebral forces during scoliosis correction, to address the hypothesis that multi degree of freedom (MDOF) postloading screws with a direct incremental segmental translation (DIST) correction technique significantly reduce the loads as compared with monoaxial (MA) tulip-top design screws with a rod derotation technique (RDT). Summary of Background Data. MA screw is widely used for spinal instrumentation. The MDOF screw was introduced as a refinement of the correction philosophy based on multiaxial screws. The kinematics of the MDOF construct is fundamentally different and offers more degrees of freedom than that of the MA construct; however, a systematic comparison of their biomechanics has not been done so far. Methods. A biomechanical model was developed to simulate the instrumentation of six scoliotic patients, first with the MDOF screws and DIST. Then, the instrumentation with MA screws and RDT was simulated using the same cases. Thirty more simulations were done to study the force-level sensitivity to small implant placement variation. Results. There was a small average difference of 7°, 5°, and 4° between the two simulated systems for the computed main thoracic Cobb angle, kyphosis, and apical axial rotation, respectively. On average, the mean, standard deviation (SD), and maximum values of the implant-vertebra forces for MDOF screws were 56%, 59%, and 59%, respectively, lower than those for the MA screws, while the intervertebral forces for the MDOF screws were 31%, 37%, and 36% lower, respectively. Under the same set of random small implant placement changes, the mean, SD, and maximum values of implant-vertebra force magnitude changes for MDOF screws were 93%, 92%, and 95%, respectively, lower than those for MA screws. Conclusion. With MDOF screws and DIST, it is possible for spinal deformity to be reduced similarly as with the MA screws and RDT, but with lower forces and better load distributions, and the force level is less sensitive to implant placement variation.

Biomechanical comparison of cervical interbody cage versus structural bone graft.

BACKGROUND CONTEXT Clinically, cervical interbody cages provide fusion rates equivalent to structural bone grafting. No published studies have biomechanically compared cages with grafts. PURPOSE We sought to compare the stability offered by threaded interbody cages versus structural bone graft and to evaluate the additional stability provided by adding a one- or two-level anterior plate to both interbody techniques. STUDY DESIGN/SETTING Nondestructive nonconstraining repeated-measures in vitro flexibility tests were performed on surgically instrumented specimens. SUBJECT SAMPLE: Sixteen human cadaveric specimens were separated into two groups (specimens receiving graft and specimens receiving cage) with matched bone mineral density. OUTCOME MEASURES Angular range of motion (ROM), neutral zone (NZ) and elastic zone (EZ) were quantified to assess stability. Students t tests compared outcomes between and within groups. METHODS Quasistatic nonconstraining torques (maximum 1.5 Nm) induced flexion, extension, lateral bending and axial rotation while angular motion was recorded stereophotogrammetrically. Specimens were tested normal, after discectomy, with graft or cage, with two-level plate and with one-level plate. RESULTS Graft alone and cage alone reduced ROM and EZ but not NZ to within normal. In both groups, adding a one- or two-level plate significantly reduced motion in all modes of loading. There were no significant differences in motion parameters between groups whether plated or unplated. A two-level plate provided significantly better stability than a one-level plate. CONCLUSIONS The interbody cage performed equivalently to the structural graft. Substantial increases in stability can be gained for either interbody technique by adding an anterior plate.

Characteristics of immediate and fatigue strength of a dual-threaded pedicle screw in cadaveric spines

BACKGROUND CONTEXT Novel dual-threaded screws are configured with overlapping (doubled) threads only in the proximal shaft to improve proximal cortical fixation. PURPOSE Tests were run to determine whether dual-threaded pedicle screws improve pullout resistance and increase fatigue endurance compared with standard pedicle screws. STUDY DESIGN/SETTING In vitro strength and fatigue tests were performed in human cadaveric vertebrae and in polyurethane foam test blocks. PATIENT SAMPLE Seventeen cadaveric lumbar vertebrae (14 pedicles) and 40 test sites in foam blocks were tested. OUTCOME MEASURES Measures for comparison between standard and dual-threaded screws were bone mineral density (BMD), screw insertion torque, ultimate pullout force, peak load at cyclic failure, and pedicular side of first cyclic failure. METHODS For each vertebral sample, dual-threaded screws were inserted in one pedicle and single-threaded screws were inserted in the opposite pedicle while recording insertion torque. In seven vertebrae, axial pullout tests were performed. In 10 vertebrae, orthogonal loads were cycled at increasing peak values until toggle exceeded threshold for failure. Insertion torque and pullout force were also recorded for screws placed in foam blocks representing healthy or osteoporotic bone porosity. RESULTS In bone, screw insertion torque was 183% greater with dual-threaded than with standard screws (p<.001). Standard screws pulled out at 93% of the force required to pull out dual-threaded screws (p=.42). Of 10 screws, five reached toggle failure first on the standard screw side, two screws failed first on the dual-threaded side, and three screws failed on both sides during the same round of cycling. In the high-porosity foam, screw insertion torque was 60% greater with the dual-threaded screw than with the standard screw (p=.005), but 14% less with the low-porosity foam (p=.07). Pullout force was 19% less with the dual-threaded screw than with the standard screw in the high-porosity foam (p=.115), but 6% greater with the dual-threaded screw in the low-porosity foam (p=.156). CONCLUSIONS Although dual-threaded screws required higher insertion torque than standard screws in bone and low density foam, dual-threaded and standard pedicle screws exhibited equivalent axial pullout and cyclic fatigue endurance. Unlike single-threaded screws, the mechanical performance of dual-threaded screws in bone was relatively independent of BMD. In foam, the mechanical performance of both types of screws was highly dependent on porosity.

Transforaminal lumbar interbody fusion with rhBMP-2 in spinal deformity, spondylolisthesis, and degenerative disease--part 1: Large series diagnosis related outcomes and complications with 2- to 9-year follow-up.

Study Design. Retrospective review of prospectively collected data. Objective. To evaluate long-term clinical outcomes and complications of the transforaminal lumbar interbody fusion (TLIF) procedure from a large consecutive series, without industry funding. Clinical outcomes and complications are analyzed by diagnosis and primary versus revision surgery to assess whether TLIF with bone morphogenic protein (BMP) is appropriate for common use in deformity, spondylolisthesis, and degenerative disease. Summary of Background Data. A common method for achieving spinal arthrodesis includes TLIF with a cage and off-label interbody BMP-2, supported by posterior arthrodesis and a pedicle screw construct. There are no large studies analyzing outcomes and complications after TLIF in different diagnoses, for primary and revision surgery, leading some to question the widespread use of TLIF. Methods. A total of 509 consecutive adults underwent open posterior instrumented fusion, augmented with TLIF at 872 discs using a cage and rhBMP-2, with minimum 2-year follow-up. Cohort diagnoses included 179 degenerative, 207 spondylolisthesis, and 123 deformity patients. Patient age averaged 61 years, 207 had undergone prior decompression or fusion surgery. All patients underwent posterior instrumented fusion and pedicle screw instrumentation at average 3.6 levels (range, 1–16); all patients had TLIF 1.7 levels (range, 1–4 levels) with BMP and autograft, stabilized with an interbody cage. Results. At average 59 months follow-up, 12 patients developed pseudoarthrosis, 8 at TLIF levels (8/872 discs, 0.92%) most commonly at L5–S1 (6/8). Significant clinical improvement was noted in patients with deformity, spondylolisthesis, and degenerative disease undergoing primary and revision surgery. Overall, visual analogue scale preoperative score was 6.6, at 1 year 3.8, at 2 years 3.5 (P < 0.001) and the preoperative ODI was 50.9, at 1 year 36.1, and at 2 years 35.0 (P < 0 0.001). Pain medication requirements also declined. Conclusion. The efficacy of TLIF with BMP is supported in this large series with long-term follow-up, independent of industry. Reliable fusion and improved outcomes can be expected in adults undergoing TLIF for deformity, spondylolisthesis, and degenerative disease. Most complications occurred in patients with deformity. Level of Evidence: 3

Comparative analysis of clinical outcomes and complications in patients with degenerative scoliosis undergoing primary versus revision surgery.

Study Design. Retrospective cohort analysis of prospectively collected data. Objective. To compare clinical outcomes and postoperative complications in patients with lumbar degenerative scoliosis who underwent primary (P) versus revision (R) surgery. Summary of Background Data. Revision surgery for spinal deformity is technically challenging and may be associated with greater risks of complications and inferior clinical outcomes. There is a paucity of data in the literature comparing primary versus revision surgery in patients with degenerative scoliosis with respect to their clinical outcomes and complications. Methods. An analysis of 84 consecutive patients with degenerative scoliosis who underwent primary versus revision surgery between 2002 and 2010 with a minimum 2-year follow-up was performed. Results. There were 53 patients in the primary group and 31 in the revision group. The average number of previously operated levels in the revision group was 3.5 ± 2.6. Mean age at surgery, sex, and body mass index were similar between the 2 groups, as well as comorbidities and postoperative complication rates (P > 0.05). Although a greater preoperative coronal imbalance was noticed in the revision group (P: 2.5 cm vs. R: 4.8 cm, P = 0.022), the final radiographical measures were comparable between the 2 groups. At 2-year follow-up, Oswestry Disability Index and visual analogue scale scores improved significantly in both groups compared with preoperatively (P < 0.001). The improvement in scores of Oswestry Disability Index and visual analogue scale preoperatively to final follow-up was similar between the 2 groups (P > 0.05). Conclusion. Revision patients achieved the same radiographical and clinical outcomes as primary patients. The complication rates were similar between primary and revision patients. Revision patients benefit from surgery just as much as primary patients at 2-year follow-up. Level of Evidence: 3

Does Obesity Affect Surgical Outcomes in Degenerative Scoliosis

Study Design. Retrospective cohort analysis of prospectively collected data. Objective. To determine whether an association exists between body mass and surgical outcomes in patients with degenerative scoliosis after long instrumented spinal arthrodesis (≥ 4 discs). Summary of Background Data. Obesity is thought to be associated with increased surgical complications and inferior clinical outcomes in adults. There are no studies analyzing the effect of obesity on surgical outcomes in patients with degenerative scoliosis after long instrumented spinal arthrodesis. Methods. Eighty-four consecutive patients with degenerative scoliosis (69 females and 15 males; mean age, 68.6 ± 8.0 yr) with a minimum follow-up of 2 years were included in this study. Patients were divided into 3 groups according to body mass index (BMI): obese (BMI ≥ 30 kg/m2, n = 19), overweight (BMI = 25–29.9 kg/m2, n = 35), and normal weight (BMI < 25 kg/m2, n = 30). Radiographical measures, Oswestry Disability Index, visual analogue scale score, as well as comorbidities and complications were reviewed and analyzed for all patients preoperativelyand at 1- and 2-year follow-ups. Results. Compared with the normal weight group, no significant differences in surgical methods, comorbidities, complication rates, curve correction, or radiographical measures were found in the obese and overweight groups, except for a greater preoperative lumbar lordosis in the overweight group (−40.3° ± 13.8° vs. −26.0° ± 18.9°, P < 0.05). At 2-year follow-up, Oswestry Disability Index and visual analogue scalescores improved significantly in all groups compared with preoperatively (P < 0.01). The changes of Oswestry Disability Index and visual analogue scalescores from preoperatively to final follow-up were similar in the 3 groups (P > 0.05). Conclusion. Obesity did not affect the amount of deformity correction and did not increase comorbidities and postoperative complication rates. Overweight patients had a greater lumbar lordosis before surgery than normal weight patients. Obese and overweight patients benefited from surgery just as much as normal weight patients at 2-year follow-up. Level of Evidence: 4

Revision spinal fusion in patients older than 75: is it worth the risks?

Study Design. Retrospective clinical study of a prospective database. Objective. This study aims to determine whether revision spinal fusion surgery is worthwhile in patients older than 75 from a risk-benefit perspective. Summary of Background Data. The benefits of spinal fusion in patients older than 65 is well documented. However, the clinical benefit to patients older than 75 of revision surgery, which often yields worse outcomes with higher complication rates, is uncertain. Methods. Ninety-nine consecutive patients older than 75 with minimum 2-year follow-up underwent spinal fusion as either a primary (n = 58) or revision (n = 41) operation. Diagnoses were spondylolisthesis (n = 43), scoliosis (n = 28), kyphosis (n = 5), and other degenerative spinal disorders (n = 26). Outcomes were obtained prospectively by visual analogue scale (VAS) and Oswestry Disability Index (ODI) at preoperative, 1-year, 2-year, and latest follow-up. Results. Revision patients had significantly worse scores compared with primary patients at all time intervals, for both VAS (preoperative: 6.4 vs. 5.8, 1 yr: 3.6 vs. 2.4, 2 yr: 4.7 vs. 2.5) and ODI (preoperative: 52.2 vs. 44.1, 1 yr: 37.3 vs. 25.6, 2 yr: 47.0 vs. 25.0). Both groups improved significantly at 1 year postoperatively. At 2 years, the results of revision surgery deteriorated (&Dgr;VAS: −1.7, &Dgr;ODI: −5.2), whereas the benefits of primary procedures were maintained (&Dgr;VAS: −3.3, &Dgr;ODI: −19.1). Complications were generally greater in the revision group and included revision surgery (8[19.5%] vs. 7[12.1%]), nonunion (2[4.9%] vs. 3[5.2%]), adjacent level fracture (4[9.8%] vs. 6[10.3%]), infection (6[14.7%] vs. 2[3.4%]), foot drop (0[0.0%] vs. 4[6.9%]), imbalance (4[9.8%] vs. 1[1.7%]), pulmonary failure (1[2.4%] vs. 1[1.7%]), and death (0[0.0%] vs. 1[1.7%]). Conclusion. Despite having worse initial ODI and VAS scores, revision patients older than 75 initially benefit as much as patients older than 75 undergoing primary operations. However, at 2 years, revision patients do not have a sustained benefit despite a higher complication rate. Level of Evidence: 4

Analysis of Segmental Mobility Following a Novel Posterior Apical Short-Segment Correction for Adolescent Idiopathic Scoliosis

Study Design. A prospective, nonrandomized, multicenter study. Objectives. The purpose of this study was to evaluate the amount of motion present at instrumented but unfused segments and at motion segments adjacent to the instrumentation following application of a new posterior apical short-segment correction technique for correcting adolescent idiopathic scoliosis (AIS). Summary of Background Data. High-density pedicle screw instrumentation and posterior arthrodesis of all instrumented levels is the most common surgical treatment for AIS stabilization. The consequence of long fusion is an abnormal load on adjacent levels with an increased risk of future adjacent segment degeneration. Methods. This new system applied translational and derotational forces over a short apical segment. The short apical region was prepared for fusion while maintaining motion of unfused vertebral segments. Radiographic data were collected pre-operatively, at surgery, and at 3, 6, and 12 months after surgery. Results. Twenty-one female patients, mean age of 14.2 years (10.6–16.9 years) with Lenke 1A/1B curves, were enrolled. The range of motion in the unfused instrumented segment was significantly higher than the apical fused segment (11 vs. 0.9, P < 0.001). The range of motion of unfused vertebral levels distal to the construct at one year did not differ significantly from their respective pre-op values. When the analysis was extended to understand the impact of lower instrumented vertebra (LIV) on motion of unfused segments distal to the construct, it appeared that (1) the change in motion from pre-op to 12 months post-op as a function of LIV is not statistically significant; and (2) The motion of the unfused distal vertebral segments at 12 months does not statistically increase with a lower LIV. Conclusion. Through one year, this novel technique achieved and maintained similar AIS correction to current posterior fusion techniques while maintaining the mobility of unfused motion segments with less implant density. Level of Evidence: 4