Stephen Bartol

Complications in the Use of rhBMP-2 in PEEK Cages for Interbody Spinal Fusions

Study Design All patients of spinal interbody fusion using polyetheretherketone (PEEK) cages and recombinant human bone morphogenetic protein (rhBMP)-2 performed over a 16-month period were reviewed. Objective To determine the suitability of PEEK cages when used in conjunction with rhBMP-2 in interbody spinal fusion. Summary of Background Data Bone morphogenetic proteins are increasingly being used in spinal fusion to promote osteogenesis. PEEK is a semicrystalline aromatic polymer that is used as a structural spacer to maintain the disc and foraminal height. Their use has led to increased and predictable rates of fusion. However, not many reports of the adverse effects of their use are available. Methods Fifty-nine consecutive patients of interbody spinal fusion in the cervical or lumbar spine using a PEEK cage and rhBMP-2 were followed for an average of 26 months after surgery. A clinical examination and a record of Oswestry Disability Index, Visual Analog Scale for pain, and a pain diagram were performed preoperatively and at every follow-up visit. All patients had plain radiographs carried out to assess fusion. Ten patients of lumbar spine fusion were additionally evaluated with a computed tomography scan. Results All cases demonstrated an appreciable amount of new bone formation by 6 to 9 months in the cervical spine and by 9 to 12 months in the lumbar spine. End plate resorption was visible radiologically in all cervical spine fusions and majority of lumbar fusions. Cage migration was observed to occur maximally in patients with transforaminal lumbar interbody fusion and posterior lumbar interbody fusion. Disc space subsidence was seen in both cervical and lumbar arthrodesis with the latter showing a lesser incidence, but with a greater degree of collapse. Conclusions PEEK cages and rhBMP-2 when used in spinal fusion give consistently good fusion rates. However, the early role of BMP in the resorptive phase may cause loosening, cage migration, and subsidence.

Lumbar Spine Fusion in Obese and Morbidly Obese Patients

Study Design. Single-center retrospective study. Objective. The aim of the study was to compare the surgical experience, clinical outcomes, and effect on body weight between obese and morbidly obese patients undergoing lumbar spine fusion surgery. Summary of Background Data. Obese and morbidly obese patients undergoing spinal fusion surgery are a challenge to the operating surgeon. Only few reports are available on the perioperative data in this group of patients. Further, it is unknown if the degree of obesity has an effect on the surgical experience and clinical outcomes including body weight. Methods. A retrospective study of 63 patients undergoing lumbar spinal fusion was carried out. The main inclusion criteria were a body mass index (BMI) equal to or greater than 30. Information recorded included surgical set-up time, surgical time, blood loss, American Association of Anesthesiologists score, and surgical complications. At follow-up, the Oswestry Disability Index and visual analog scale for back and leg pain were recorded along with a pain diagram and radiographic evaluation. Results. The obese group had lower American Association of Anesthesiologists scores. The surgical time was dependent on the number of levels fused and was independent of the BMI. Blood loss during surgery was marginally greater in the obese patients. Neither group showed significant change in weight and BMI. Clinical outcomes showed improvement in visual analog scale for back and leg pain with some improvement in Oswestry scores and were independent of the BMI of the patient. The incidence of postoperative complications was significant in 45% of morbidly obese and 44% of obese patients. Conclusion. Obese and morbidly obese patients have multiple comorbidities, and the spinal surgeon should be prepared to encounter perioperative complexities. Operative times are longer in comparison with normal weight patients with a higher incidence of postoperative complications. No weight loss occurs after spinal surgery.

Biomechanical analysis of different techniques in revision spinal instrumentation: larger diameter screws versus cement augmentation.

Study Design. Biomechanical analysis. Objective. To determine the relative strengths of 2 different forms of revision spinal instrumentation using a validated, constant load, cyclic testing mechanism. Summary of Background Data. Spinal fusion with instrumentation procedures are on the rise. As such, so are revision procedures. A few studies have looked at revision instrumentation techniques. Both increased pedicle screw diameter as well as cement augmentation of pedicle screw fixation have been proposed, used clinically and tested biomechanically. To our knowledge, no comparative study exists between these techniques. Methods. Using an instron servohydraulic loading machine, we tested pedicle screws inserted in both the anatomic (angled) and Roy-Camille (straight) insertion technique with both larger diameter (8 mm) pedicle screws, as well as standard diameter (6 mm) pedicle screws augmented with polymethylmethacrylate bone cement. Each of these techniques was subjected to constant load under cyclic conditions for 2000 cycles at 2 Hz. Computerized data collection was used at all time points. Comparisons were made between primary instrumentation data (previously published) and large diameter screws for revision. Further comparisons were made between large diameter screws and cement augmented screws. Results. The larger diameter screws compared with the cement augmented screws showed significant differences in: initial stiffness with straight insertion technique (P < 0.01), stiffness damage with straight insertion technique (P < 0.01), and creep damage with straight insertion technique (P = 0.01). There was also a significant difference between large diameter and primary instrumentation technique all calculated values (P < / = 0.05). Conclusion. The larger diameter screws were equivocal or significantly more resilient than the cement augmented standard diameter screws at the strongest of the insertion angles for all values. Since rigidity of the instrumentation construct is one of the very few factors that is surgeon controlled, this could influence the choice of instrumentation in revision spinal arthrodesis.

Three-dimensional dynamic in vivo motion of the cervical spine: assessment of measurement accuracy and preliminary findings

BACKGROUND CONTEXT Previous research has quantified cervical spine motion with conventional measurement techniques (eg, cadaveric studies, motion capture systems, and fluoroscopy), but these techniques were not designed to accurately measure three-dimensional (3D) dynamic cervical spine motion under in vivo conditions. PURPOSE The purposes of this study were to characterize the accuracy of model-based tracking for measuring 3D dynamic cervical spine kinematics and to demonstrate its in vivo application. STUDY DESIGN Through accuracy assessment and application of technique, in vivo cervical spine motion was measured. METHODS The accuracy of model-based tracking for measuring cervical spine motion was determined in an in vitro experiment. Tantalum beads were implanted into the vertebrae of an ovine specimen, and biplane X-ray images were acquired as the specimens neck was manually moved through neck extension and axial neck rotation. The 3D position and orientation of each cervical vertebra were determined from the biplane X-ray images using model-based tracking. For comparison, the position and orientation of each vertebra were also determined by tracking the position of the implanted beads with dynamic radiostereometric analysis. To demonstrate in vivo application of this technique, biplane X-ray images were acquired as a human subject performed two motion tasks: neck extension and axial neck rotation. The positions and orientations of each cervical vertebra were determined with model-based tracking. Cervical spine motion was reported with standard kinematic descriptions of translation and rotation. RESULTS The in vitro validation demonstrated that model-based tracking is accurate to within +/-0.6 mm and +/-0.6 degrees for measuring cervical spine motion. For the in vivo application, there were significant rotations about all three anatomical axes for both the neck extension and axial neck rotation motion tasks. CONCLUSIONS Model-based tracking is an accurate technique for measuring in vivo, 3D, dynamic cervical spine motion. Preliminary data acquired using this technique are in agreement with previous studies. It is anticipated that this experimental approach will enhance our understanding of cervical spine motion under normal and pathologic conditions.

Radiographic and CT Evaluation of Recombinant Human Bone Morphogenetic Protein-2–Assisted Spinal Interbody Fusion

OBJECTIVE Bone morphogenetic proteins BMPs, when used in spinal fusion, hasten healing and initiate distinct imaging features. We undertook a study to record and analyze the radiographic and CT changes after the use of recombinant human bone morphogenetic protein-2 (rhBMP-2) in spinal fusion surgery. MATERIALS AND METHODS This study included 95 patients who underwent spinal interbody fusion using rhBMP-2. The lumbar spine fusion cohort consisted of 23 patients who underwent anterior lumbar interbody fusion, 36 patients who underwent transforaminal lumbar interbody fusion, and two patients who underwent posterior lumbar interbody fusion. The remaining 34 patients underwent anterior cervical decompression and fusion. RESULTS A polyetheretherketone cage was used as an interbody spacer in 59 patients (82 levels) and an allograft bone was the spacer in 36 patients (55 levels). Patients were evaluated 2 and 6 weeks after the procedure and then 3, 6, 12, and 24 months after the procedure. All patients underwent radiography at every follow-up visit, and CT evaluation was performed in 32 patients. CONCLUSION Features observed on imaging that we attributed to the use of rhBMP-2 included an enhanced fusion rate and an increased incidence of prevertebral soft-tissue swelling in patients who underwent cervical fusion. Endplate resorption was observed in 100% of patients who underwent cervical fusion and in 82% of the lumbar levels. Subsidence of the cage resulting in narrowing of the disk space was seen in more than 50% of cases. Cage migration and heterotopic bone formation in the spinal canal and neural foramen occurred maximally in the lumbar spine of patients in whom a polyetheretherketone cage was placed using a transforaminal approach.

Three-dimensional motion analysis of the cervical spine for comparison of anterior cervical decompression and fusion versus artificial disc replacement in 17 patients: clinical article.

OBJECT Cervical arthroplasty with an artificial disc (AD) has emerged as an alternative to anterior cervical discectomy and fusion (ACDF) for the management of cervical spondylosis. This study aims to provide 3D motion analysis data comparing patients after ACDF and AD replacement. METHODS Ten patients who underwent C5-6 ACDF and 7 who underwent C5-6 AD replacement were enrolled. Using biplanar fluoroscopy and a model-based track technique (accurate up to 0.6 mm and 0.6°), motion analysis of axial rotation and flexion-extension of the neck was performed. Three nonoperative segments (C3-4, C4-5, and C6-7) were assessed for both intervertebral rotation (coronal, sagittal, and axial planes) and facet shear (anteroposterior and mediolateral). RESULTS There was no difference in total neck motion comparing ACDF and AD replacement for neck extension (43.3° ± 10.2° vs 44.3° ± 12.6°, p = 0.866) and rotation (36.0° ± 6.5° vs 38.2° ± 9.3°, p = 0.576). For extension, when measured as a percentage of total neck motion, there was a greater amount of rotation at the nonoperated segments in the ACDF group than in the AD group (p = 0.003). When comparing specific motion segments, greater normalized rotation was seen in the ACDF group at C3-4 (33.2% ± 4.9% vs 26.8% ± 6.6%, p = 0.036) and C6-7 (28.5% ± 6.7% vs 20.5% ± 5.5%, p = 0.009) but not at C4-5 (33.5% ± 6.4% vs 31.8% ± 4.0%, p = 0.562). For neck rotation, greater rotation was observed at the nonoperative segments in the ACDF group than in the AD group (p = 0.024), but the differences between individual segments did not reach significance (p ≥ 0.146). Increased mediolateral facet shear was seen on neck extension with ACDF versus AD replacement (p = 0.008). Comparing each segment, C3-4 (0.9 ± 0.5 mm vs 0.4 ± 0.1 mm, p = 0.039) and C4-5 (1.0 ± 0.4 mm vs 0.5 ± 0.2 mm, p = 0.022) showed increased shear while C6-7 (1.0 ± 0.4 mm vs 1.0 ± 0.5 mm, p = 0.767) did not. CONCLUSIONS This study illustrates increased motion at nonoperative segments in patients who have undergone ACDF compared with those who have undergone AD replacement. Further studies will be required to examine whether these changes contribute to adjacent-segment disease.

Dynamic measurements of cervical neural foramina during neck movements in asymptomatic young volunteers

PurposeNeural foraminal dimensions are considered important in nerve root compression and development of cervical radiculopathy, but baseline data regarding their range during normal motion are not available. An in vivo study of cervical foraminal motion was conducted to characterize normal 3D dynamic foraminal dimensions during physiological neck motion and compare between different tasks and intervertebral segments.MethodsBiplane X-ray imaging and computed tomography-based markerless tracking were used to measure foraminal height (FH) and width (FW) from five asymptomatic subjects during neck axial rotation and extension. FH and FW were quantified as the minimum (SI.Min and AP.Min), range (SI.Range and AP.Range), and median (SI.Med and AP.Med) of superoinferior (SI) and anteroposterior (AP) dimensions for each trial and as the coefficient of variation of these variables from three trials (SI.Med.CV and AP.Med.CV, SI.Range.CV and AP.Range.CV) at C3-4 through C6-7 levels for each subject. Differences were analyzed using mixed model ANOVA.ResultsAP.Range and AP.Med.CV were greater (P < 0.0001) while AP.Min and AP.Range.CV were smaller (P < 0.0006 and P < 0.0005) during neck extension than rotation. SI.Range and SI.Med.CV were greater for extension than rotation at C5-6 (P < 0.002 and P < 0.03), whereas SI.Med.CV was greater for rotation than extension at C3-4 (P < 0.03). AP.Range (P < 0.02), AP.Med.CV (P < 0.05), SI.Range (P < 0.0004), and SI.Med.CV (P < 0.02) were different between cervical levels, the latter two being during extension only.ConclusionsPatterns of FH and FW during normal motion are different between tasks and cervical levels. These findings are expected to provide a basis for future studies of spinal degeneration and surgical efficacy.

Facet Sparing Foraminal Decompression Using the Flexible Shaver Foraminotomy System: Nerve Safety, Pain Relief, and Patient Satisfaction

ABSTRACT Background: A number of surgical options exist for decompressing lumbar foraminal stenosis. Flexible shaver foraminotomy is a recent addition to this armamentarium. While the foraminotomy device has been incorporated into clinical practice, the literature on its safety and efficacy remain limited. We aimed to evaluate nerve safety, pain relief, and patient satisfaction in a series of patients treated with the iO-Flex shaver system (Amendia, Inc., Marietta, Georgia). Methods: Thirty-one consecutive patients with lumbar foraminal stenosis underwent foraminal decompression using the flexible microblade shaver system at 62 neuroforamina. The shavers were inserted into each foramen using an open hemilaminotomy and fluoroscopic guidance. Nerve mapping via mechanomyography (MMG) was used to ensure nerve safety. Perioperative charts were reviewed to find the incidence of neurologic complications and to quantify pain relief. Average office-based follow-up was 5.3 months. A 3-item questionnaire was administered to assess patient satisfaction during late follow-up, which occurred at an average of 21 months. Results: No planned iO-Flex foraminotomies were aborted. Neurologic complications included transient dysesthetic pain in 1 patient (3.2%, n = 31), and transient numbness in 3 patients (9.7%, n = 31). There were no motor deficits. The composite nerve complication rate was 12.7%. Preoperative visual analog scale scores decreased from a mean of 7.1 (n = 31, standard deviation [SD] 2.0) to a mean of 3.5 (n = 30, SD 2.5). If asked to repeat their decision to do surgery, 81% of patients would redo the procedure. The rate of patient dissatisfaction was 19%. Conclusions: Decompression of lumbar foramina using the flexible shaver system and MMG nerve mapping is safe and effective, although the short-term sensory complication with this technique may be higher than previously reported. Patient satisfaction with iO-Flex foraminotomy is comparable to reported satisfaction outcomes for traditional lumbar decompression. Level of Evidence: 4.

Artificial Disc Versus Fusion: Effect on Three-Dimensional Dynamic In Vivo Cervical Spine Motion

Intervertebral disc degeneration in the cervical spine is a common condition that often manifests as cervical disc disease, resulting in pain, motor weakness and sensory deficits. The most common surgical treatment strategy involves removal of the diseased disc and fusion of the adjacent vertebrae. Although fusion typically relieves symptoms at the surgical site, evidence of degeneration in the adjacent disc has been reported in 25–92% of patients [1,2]. It has been hypothesized that the progression of adjacent segment degeneration is a result of increased motion at the segments adjacent to the site of fusion [3]. As a response to this proposed mechanism of degeneration, artificial discs were designed with the goals of preserving motion at the operative site and maintaining normal motion in the adjacent segments. However, the extent to which normal adjacent segment motion is maintained in artificial disc patients compared to fusion patients remains unknown. Thus, the objective of this study was to compare the dynamic, three-dimensional (3D) motion of the cervical spine in fusion patients and artificial disc replacement patients.Copyright

Three-Dimensional In-Vivo Cervical Spine Kinematics: Preliminary Comparison of Fusion Patients and Normal Control Subjects

Degenerative disc disease (DDD) of the cervical spine is a common condition that causes significant pain and disability. Treatment for DDD in 2000 exceeded 110,000 patients in the United States alone [1]. A common treatment option for patients involves removal of the degenerated disc and fusion of the adjacent vertebral bodies. However, previous research has shown that as many as 25–92% of patients treated with fusion have disc degeneration at the adjacent levels within 10 years after surgery [2,3]. It has been hypothesized that this is the result of a change in adjacent vertebral segment motion [4]. However, it is unknown if spinal fusion alters motion at these segments. Thus, the objective of this study was to compare the dynamic, three-dimensional (3D) motion of the cervical spine in normal control subjects and spinal fusion patients.Copyright