Christopher M.J. Cain

A New Stand-alone Anterior Lumbar Interbody Fusion Device: Biomechanical Comparison with Established Fixation Techniques

Study Design. Established lumbar fixation methods were assessed biomechanically, and a comparison was made with a new stand-alone anterior lumbar interbody cage device incorporating integrated anterior fixation. Objectives. To compare the stability of a new stand-alone anterior implant (Test-device) with established fixation methods to assess its suitability for clinical use. Our hypothesis being that the Test-device would provide stability comparable to that provided by an anterior cage when supplemented with posterior pedicle screw fixation. Summary of Background Data. It is accepted that the use of rigid pedicle screw instrumentation increases the chance of achieving a solid fusion, but its use may be associated with a significant increase in postoperative morbidity caused by disruption of the posterior musculature. It is also evident that this increased fusion rate is generally not associated with increased clinical success. This dilemma has led to a search for a solution and to the development of the Test-device anterior lumbar interbody device. Methods. The kinematic properties of either the L3–L4 or L4–L5 lumbar motion segment of 8 cadaveric lumbar spines have been tested using the following sequence of fixation: intact, Test-device, Test-device and translaminar facet screws (TS), Cage and TS, Cage and Universal Spine System (USS), and Cage and small stature USS. Results. All fixation techniques except the cage and TS decreased (P < 0.05) range of motion (ROM), neutral zone (NZ), and elastic zone (EZ), and increased (P < 0.05) stiffness in comparison to the intact motion segment in all test modes. There was a significant increase (P < 0.01) in the ROM, NZ, and EZ, and decrease in the stiffness of the cage and TS group in comparison to all other stabilizationtechniques in flexion and rotation. There was no significant difference in the ROM, NZ, EZ, and stiffness between the Test-device and cage and USS groups in flexion, extension, and bending. The Test-device resulted in a significantly lower EZ (P < 0.05) and a significantly higher stiffness (P < 0.05) in rotation than all other fixation methods. Conclusions. The Test-device alone provided similar and the Test-device and TS higher stability than the pedicle screw constructs evaluated. These results support progression to clinical trials using the Test-device as a stand-alone implant.

Retrograde Ejaculation After Anterior Lumbar Spine Surgery

Study Design. A retrospective cohort study. Objective. To compare the incidence of retrograde ejaculation (RE) after anterior lumbar spine surgery with disc replacement versus fusion with the use of recombinant human bone morphogenetic protein-2 (BMP). Summary of Background Data. Anterior lumbar interbody fusion (ALIF) has become a popular choice for treating a number of pathologies, largely because it preserves the posterior paravertebral muscles and ligaments. Despite these advantages, the anterior approach is also associated with various complications, one of which is RE. A recent study has questioned whether the risk of RE is increased by the use of BMP in ALIF procedures rather than by the approach alone. Methods. We conducted a retrospective review of all male patients who received ALIF using BMP or artificial disc replacement (ADR) on at least the L5–S1 level between 2004 and 2011. Medical records were evaluated for the occurrence of RE, and patients were contacted via the phone to obtain current information. The incidence of RE was then compared between the 2 anterior lumbar surgery procedures. Results. Of the 95 cases of anterior surgery including L5–S1, 54 patients underwent ALIF with BMP (56.8%) and 41 patients were treated with ADR (43.2%). Postoperative RE occurred in 4 of the 54 ALIF patients (7.4%) and in 4 of the 41 ADR patients (9.8%). The incidence of RE was not significantly different between groups (P = 0.7226). At latest follow-up, 1 ALIF and 1 ADR patient reported resolution of the RE. Conclusion. This study found that RE occurred at a similar rate in patients treated with ADR and ALIF with BMP. The overall rate of RE after retroperitoneal anterior lumbar surgery was higher than expected, which underscores the importance of counseling patients about this risk and specifically questioning patients about the symptoms of RE at postoperative visits.

Bony and Vascular Anatomy of the Normal Cervical Spine in the Sheep

Study Design This study analyzed the vascular and skeletal anatomy of the sheep cervical spine. It discusses the comparative anatomy of the cervical spine of sheep and humans. Objectives To establish the suitability of the sheep model for studying the pathophysiology of traumatic and degenerative conditions of the cervical spine. Summary of Background Data Many studies have attempted to evaluate the pathophysiology of spinal cord trauma, hypoxia, and variations in the local environment of the spinal cord using a variety of animal models. Few of the studies identified in an extensive literature review report or comment on the validity of these models regarding anatomy. Methods Techniques of macro- and micro-dissection and vascular casting with latex and methyl-methacrylate were employed and the anatomy of sheep was compared with that of humans. Results On an anatomical basis, we found the sheep to be a suitable model for studying the pathophysiology of spinal cord trauma and disorders relative to humans. Conclusions To properly assess the effect of various pathological processes on the spinal cord, an anatomically valid model is required. This study established that the sheep is a suitable animal model for studies of this type.

Predictors of spine deformity progression in adolescent idiopathic scoliosis: A systematic review with meta-analysis

AIM To evaluate published data on the predictors of progressive adolescent idiopathic scoliosis (AIS) in order to evaluate their efficacy and level of evidence. METHODS SELECTION CRITERIA (1) study design: randomized controlled clinical trials, prospective cohort studies and case series, retrospective comparative and none comparative studies; (2) participants: adolescents with AIS aged from 10 to 20 years; and (3) treatment: observation, bracing, and other. SEARCH METHOD Ovid MEDLINE, Embase, the Cochrane Library, PubMed and patent data bases. All years through August 2014 were included. Data were collected that showed an association between the studied characteristics and the progression of AIS or the severity of the spine deformity. Odds ratio (OR), sensitivity, specificity, positive and negative predictive values were also collected. A meta-analysis was performed to evaluate the pooled OR and predictive values, if more than 1 study presented a result. The GRADE approach was applied to evaluate the level of evidence. RESULTS The review included 25 studies. All studies showed statistically significant or borderline association between severity or progression of AIS with the following characteristics: (1) An increase of the Cobb angle or axial rotation during brace treatment; (2) decrease of the rib-vertebral angle at the apical level of the convex side during brace treatment; (3) initial Cobb angle severity (> 25(o)); (4) osteopenia; (5) patient age < 13 years at diagnosis; (6) premenarche status; (7) skeletal immaturity; (8) thoracic deformity; (9) brain stem vestibular dysfunction; and (10) multiple indices combining radiographic, demographic, and physiologic characteristics. Single nucleotide polymorphisms of the following genes: (1) calmodulin 1; (2) estrogen receptor 1; (3) tryptophan hydroxylase 1; (3) insulin-like growth factor 1; (5) neurotrophin 3; (6) interleukin-17 receptor C; (7) melatonin receptor 1B, and (8) ScoliScore test. Other predictors included: (1) impairment of melatonin signaling in osteoblasts and peripheral blood mononuclear cells (PBMC); (2) G-protein signaling dysfunction in PBMC; and (3) the level of platelet calmodulin. However, predictive values of all these findings were limited, and the levels of evidence were low. The pooled result of brace treatment outcomes demonstrated that around 27% of patents with AIS experienced exacerbation of the spine deformity during or after brace treatment, and 15% required surgical correction. However, the level of evidence is also low due to the limitations of the included studies. CONCLUSION This review did not reveal any methods for the prediction of progression in AIS that could be recommended for clinical use as diagnostic criteria.

Perioperative and long-term clinical outcomes for bone morphogenetic protein versus iliac crest bone graft for lumbar fusion in degenerative disk disease: systematic review with meta-analysis.

Study Design: Systematic review with meta-analysis. Objectives: To compare the perioperative and long-term postoperative effectiveness of bone morphogenetic protein (BMP) for lumbar arthrodesis in skeletally mature adults with degenerative disk disease (DDD) to that of the current golden standard treatment, iliac crest autologous bone graft (ICBG). Summary of Background Data: The treatment efficacy of lumbar arthrodesis in DDD is a complex clinical and economic issue for patients and health care providers. Methods: Comprehensive electronic literature search was performed using following databases: Ovid MEDLINE; Embase; Cochrane Library; Central Register of Controlled Trials (CENTRAL); Database of Abstracts of Reviews of Effects; Methodology Register; Technology Assessment Database; and Economic Evaluation Database. The full year ranges of each database until May of 2012 were included. Results: Eight randomized controlled clinical trials of 383 citations were selected. The included studies involved 1138 participants. The pooled 2-year postoperative clinical outcomes were equivalent in BMP and ICBG groups, and exceeded minimum clinically important differences for Oswestry Disability Index, SF-36 (physical scale), and numeric rating scale (back pain). ICBG was associated with increased pain and complications at the donor site (P<0.01). The pooled average operative time was 21 minutes less in BMP versus ICBG (P<0.001). The pooled rate of additional surgical treatment was 2 times less in the BMP than in the ICBG groups (P=0.006). The pooled risk of nonunion at 24-month follow-up was 2 times less in the BMP than in the ICBG groups (P=0.037), however, this effect was likely biased. Conclusions: BMP, in particular rhBMP-2, is a good alternative to autogenous bone graft, especially in cases when harvesting of autologous bone is contraindicated or undesirable, operation time is limited, and there are no contraindications for BMP use. However, the current study did not reveal evidence robust enough to develop strong medical recommendations concerning BMP use for lumbar arthrodesis in degenerative disk disease.

Long-term Treatment Effects of Lumbar Arthrodeses in Degenerative Disk Disease: A Systematic Review With Meta-Analysis.

Study Design: Systematic review with meta-analysis. Objective: To (1) evaluate long-term patient-centered clinical outcomes after lumbar arthrodesis with or without decompression for lumbar spondylosis (LS); and (2) compare these outcomes with those of alternative treatments, including nonsurgical and surgical which maintain mobility of the lumbar spine. Summary of Background Data: The effective treatment of LS is a complex clinical and economic concern for patients and health care providers. Methods: Selection criteria: (1) randomized controlled clinical trials (RCTs) comparing treatment effects of lumbar arthrodesis with other interventions; (2) participants: skeletally mature adults with lumbar degenerative disk disease. Search methods: Ovid MEDLINE, Embase, the Cochrane Library, and others. All years through February of 2013 were included. Patient-centered clinical outcomes before treatment, at 12, 24, or >24 months of follow-up, and rate of complications and additional surgical treatment were collected. A meta-analysis was performed to evaluate pooled treatment effects. The GRADE approach was applied to evaluate the level of evidence. Results: The review included 38 studies of 5738 participants. All studies showed strong or at least moderate treatment effects of lumbar arthrodesis at 12, 24, and 48–72 months of follow-up. The level of evidence was moderate at 12 and 24 months, and low at 48–72 months. The pooled long-term treatment effect of lumbar arthrodesis exceeded those of: nonsurgical treatment (P<0.0001) with a moderate level of evidence, and decompression without fusion (P=0.005) with a low level of evidence. The treatment effect of lumbar arthrodesis showed a small inferiority versus arthroplasty at 12 and 24 months of follow-up (P<0.001), but not after 24 months postoperative. Conclusions: This review indicates that surgical stabilization of the lumbar spine is an effective treatment for LS; in particular, for patients with severe chronic low back pain that has been resistant to ≥3 months of conservative therapy.

Strain in Posterior Instrumentation Resulted by Different Combinations of Posterior and Anterior Devices for Long Spine Fusion Constructs

STUDY DESIGN Clinically related experimental study. OBJECTIVE Evaluation of strain in posterior low lumbar and spinopelvic instrumentation for multilevel fusion resulting from the impact of such mechanical factors as physiologic motion, different combinations of posterior and anterior instrumentation, and different techniques of interbody device implantation. Currently different combinations of posterior and anterior instrumentation as well as surgical techniques are used for multilevel lumbar fusion. Their impact on risk of device failure has not been well studied. Strain is a well-known predictor of metal fatigue and breakage measurable in experimental conditions. METHODS Twelve human lumbar spine cadaveric specimens were tested. Following surgical methods of lumbar pedicle screw fixation (L2-S1) with and without spinopelvic fixation by iliac bolt (SFIB) were experimentally modeled: posterior (PLF); transforaminal (TLIF); and a combination of posterior and anterior interbody instrumentation (ALIF+PLF) with and without anterior supplemental fixation by anterior plate or diverging screws through an integrated plate. Strain was defined at the S1 screws, L5-S1 segment of posterior rods, and iliac bolt connectors; measurement was performed during flexion, extension, and axial rotation in physiological range of motion and applied force. RESULTS The highest strain was observed in the S1 screws and iliac bolt connectors specifically during rotation. The S1 screw strain was lower in ALIF+PLF during sagittal motion but not rotation. Supplemental anterior fixation in ALIF+PLF diminished the S1 strain during extension. Strain in the posterior rods was higher after TLIF and PLF and was increased by SFIB; this strain was lowest after ALIF+PLF, as supplemental anterior fixation diminished the strain during extension, in particular, cages with anterior screws more than anterior plate. Strain in the iliac bolt connectors was mainly determined by direction of motion. CONCLUSIONS Different devices modify strain in low posterior instrumentation, which is higher after transforaminal and posterior techniques, specifically with spinopelvic fixation. LEVEL OF EVIDENCE N/A.STUDY DESIGN Clinically related experimental study. OBJECTIVE Evaluation of strain in posterior low lumbar and spinopelvic instrumentation for multilevel fusion resulting from the impact of such mechanical factors as physiologic motion, different combinations of posterior and anterior instrumentation, and different techniques of interbody device implantation. SUMMARY OF BACKGROUND DATA Currently different combinations of posterior and anterior instrumentation as well as surgical techniques are used for multilevel lumbar fusion. Their impact on risk of device failure has not been well studied. Strain is a well-known predictor of metal fatigue and breakage measurable in experimental conditions. METHODS Twelve human lumbar spine cadaveric specimens were tested. Following surgical methods of lumbar pedicle screw fixation (L2-S1) with and without spinopelvic fixation by iliac bolt (SFIB) were experimentally modeled: posterior (PLF); transforaminal (TLIF); and a combination of posterior and anterior interbody instrumentation (ALIF+PLF) with and without anterior supplemental fixation by anterior plate or diverging screws through an integrated plate. Strain was defined at the S1 screws, L5-S1 segment of posterior rods, and iliac bolt connectors; measurement was performed during flexion, extension, and axial rotation in physiological range of motion and applied force. RESULTS The highest strain was observed in the S1 screws and iliac bolt connectors specifically during rotation. The S1 screw strain was lower in ALIF+PLF during sagittal motion but not rotation. Supplemental anterior fixation in ALIF+PLF diminished the S1 strain during extension. Strain in the posterior rods was higher after TLIF and PLF and was increased by SFIB; this strain was lowest after ALIF+PLF, as supplemental anterior fixation diminished the strain during extension, in particular, cages with anterior screws more than anterior plate. Strain in the iliac bolt connectors was mainly determined by direction of motion. CONCLUSIONS Different devices modify strain in low posterior instrumentation, which is higher after transforaminal and posterior techniques, specifically with spinopelvic fixation. LEVEL OF EVIDENCE N/A.

What Is the Clinical Relevance of Radiographic Nonunion After Single-Level Lumbar Interbody Arthrodesis in Degenerative Disc Disease?: A Meta-Analysis of the YODA Project Database.

Study Design. Meta-analysis of 4 randomized controlled clinical trials (RCTs). Objective. The aim of the study was to determine if patients with degenerative disc disease who achieve radiographic fusion after single-level lumbar interbody arthrodesis have better clinical outcomes than patients with radiographic pseudarthrosis at 12 and 24 months postoperative. Summary of Background Data. The clinical relevance of successful fusion after lumbar arthrodesis with recombinant human bone morphogenetic protein-2 or iliac crest bone autograft has recently been questioned in the literature. Methods. Individual patient-level data of 4 RCTs were obtained from the Yale University Open Data Access Project project and analyzed. Clinical outcomes (Oswestry Disability Index [ODI]; Numeric Rating Scales [NRSs] for back and leg pain) were compared between patients with radiographically confirmed fusion and those with radiographic nonunion 1 and 2 years postoperative. The results of each study were first analyzed separately, and then were pooled by meta-analysis. The GRADE approach was applied to evaluate the level of evidence. Results. A total of 496 patients with clinical and radiographic data at 1- and 2-year follow-ups were identified. Of these, 5.5% (95% confidence interval: 3.7; 8.3) had radiographic nonunion which did not require reoperation. Patients with fusion had better improvements in ODI (P < 0.001) and NRS back pain scores (P < 0.001). The overall percentage of fused patients with ODI and NRS back pain scores that exceeded the criteria for minimal clinically important differences was also significantly higher than that of patients with nonunion (ODI, odds ratio [OR] = 2.7, P = 0.019; NRS back pain, OR = 3.5, P = 0.033). The predictive values of fusion for clinical outcomes, however, were poor, with low specificity and low negative predictive values. Conclusion. The presence of radiographic fusion is clinically significant, as patients with fusion had better clinical outcomes at 1 and 2 years postoperative than those with nonunion; however, patient-centered clinical outcomes should also be taken into consideration as independent, complimentary variables when assessing treatment success. Level of Evidence: 1

Patient-Specific Templating of Lumbar Total Disk Replacement to Restore Normal Anatomy and Function

The purpose of this study was to develop a tool to determine optimal placement and size for total disk replacements (TDRs) to improve patient outcomes of pain and function. The authors developed a statistical shape model to determine the anatomical variables that influence the placement, function, and outcome of lumbar TDR. A patient-specific finite element analysis model has been developed that is now used prospectively to identify patients suitable for TDR and to create a surgical template to facilitate implant placement to optimize range of motion and clinical outcomes. Patient factors and surgical techniques that determine success regarding function and pain are discussed in this article.

Pelvic Incidence Changes Between Flexion and Extension

STUDY DESIGN Retrospective single-center. OBJECTIVES To investigate changes in pelvic incidence from flexion to extension. To assess interobserver error in the measurement of pelvic incidence. BACKGROUND Pelvic incidence (PI) has been considered a static parameter since it was originally described. But recent studies have shown that PI can change with age and after spinal procedures. Changes in PI based on position have not been investigated. METHODS Seventy-two patients who had obtained flexion and extension radiographs of the lumbar spine were identified using strict inclusion and exclusion criteria. PI along with pelvic tilt (PT), sacral slope (SS), and lumbar lordosis were measured in both flexion and extension by two independent measurers. Variations in all parameters and interobserver measurement reliability were analyzed for the entire group. RESULTS PI changed significantly from flexion to extension with a general tendency to decrease: mean (-0.94°), p <.044. However, these changes might have had opposite vectors, and exceeded | 6°| (measurement error) in 20% of cases, with a maximum of 12°. Inconsistencies in changes of SS, as opposed to PT from flexion to extension, were found to be the major factor determining changes in PI (p >.001). Obesity significantly contributed to differences in PI between flexion and extension (p = .003). CONCLUSIONS PI is a dynamic parameter that changes between flexion and extension. Changes in SS are the main factor involved in these changes, implicating movement through the sacroiliac joints as the cause. Obese patients have greater changes in PI from flexion to extension. LEVEL OF EVIDENCE Level II.STUDY DESIGN Retrospective single-center. OBJECTIVES To investigate changes in pelvic incidence from flexion to extension. To assess interobserver error in the measurement of pelvic incidence. BACKGROUND Pelvic incidence (PI) has been considered a static parameter since it was originally described. But recent studies have shown that PI can change with age and after spinal procedures. Changes in PI based on position have not been investigated. METHODS Seventy-two patients who had obtained flexion and extension radiographs of the lumbar spine were identified using strict inclusion and exclusion criteria. PI along with pelvic tilt (PT), sacral slope (SS), and lumbar lordosis were measured in both flexion and extension by two independent measurers. Variations in all parameters and interobserver measurement reliability were analyzed for the entire group. RESULTS PI changed significantly from flexion to extension with a general tendency to decrease: mean (-0.94°), p <.044. However, these changes might have had opposite vectors, and exceeded | 6°| (measurement error) in 20% of cases, with a maximum of 12°. Inconsistencies in changes of SS, as opposed to PT from flexion to extension, were found to be the major factor determining changes in PI (p >.001). Obesity significantly contributed to differences in PI between flexion and extension (p = .003). CONCLUSIONS PI is a dynamic parameter that changes between flexion and extension. Changes in SS are the main factor involved in these changes, implicating movement through the sacroiliac joints as the cause. Obese patients have greater changes in PI from flexion to extension. LEVEL OF EVIDENCE Level II.