Daniel R. Fassett

Biologic Solutions for Degenerative Disk Disease

Study Design Literature review. Objective Review the potential use of biologic therapies for the treatment of degenerative disk disease. Summary of Background Data Degeneration of the intervertebral disk is a common occurrence which, although asymptomatic in most instances, may result in axial skeletal pain, radiculopathy, and myelopathy. Significant progress has been made in understanding the pathophysiology of degenerative disk disease and as a result, new biologic therapies, including molecular, gene, and cell-based strategies, are being investigated to halt and reverse disk degeneration. Results Growth factors, inflammatory inhibitors, proteinase inhibitors, and intracellular regulatory proteins are among the molecular therapies that have been studied with encouraging results in both in vitro and in vivo experiments. However, the utility of these therapies in humans may be limited because of the limited therapeutic duration. Gene therapies have the potential to overcome the limited therapeutic duration of molecular treatments by transferring genes to the cells within the disk to encode for therapeutic proteins with potential long-term local production. Gene therapy for disk regeneration has been successful in a number of animal studies, but significant concerns exist with the safety of the many vectors used for gene transfer. Cell-based therapies, including reimplantation of nucleus pulposus cells expanded in culture and stem cell therapies, have also been studied extensively in animal models with good results. The EuroDisc clinical trial is currently underway in Europe exploring the reimplantation of disk cells that are removed at the time of diskectomy and expanded ex vivo. Mesenchymal stem cells, which are readily available without ethical concerns, are being studied extensively for disk regeneration. Mesenchymal stem cells can differentiate into a phenotype similar to native nucleus pulposus cells and have shown the potential for disk regeneration in animal studies. Conclusions Biologic therapies for intervertebral disk regeneration have produced very encouraging results in both in vitro and in vivo studies. Despite successful experimental results, these therapies face a number of hurdles before acceptance for human use including safety concerns, efficacy in high-order animal and human studies, and issues with the role and timing of these treatments.

Use of allograft bone for posterior C1–2 fusion

OBJECT An iliac crest autograft is the gold standard for bone grafting in posterior atlantoaxial arthrodesis but can be associated with significant donor-site morbidity. Conversely, an allograft has historically performed suboptimally for atlantoaxial arthrodesis as an onlay graft. The authors have modified a bone grafting technique to allow placement of a bicortical iliac crest allograft in an interpositional manner, and they evaluated it as an alternative to an autograft in posterior atlantoaxial arthrodesis. METHODS The records of 89 consecutive patients in whom C1-2 arthrodesis was performed between 2001 and 2005 were reviewed. RESULTS Forty-seven patients underwent 48 atlantoaxial arthrodeses with an allograft (mean follow-up 16.1 months, range 0-49 months), and 42 patients underwent autograft bone grafting (mean follow-up 17.6 months, range 0-61.0 months). The operative time was 50 minutes shorter in the allograft (mean 184 minutes, range 106-328 minutes) than in the autograft procedure (mean 234 minutes, range 154-358 minutes), and the estimated blood loss was 50% lower in the allograft group than in the autograft group (mean 103 ml [range 30-200 ml] vs mean 206 ml [range 50-400 ml], respectively). Bone incorporation was initially slower in the allograft than in the autograft group but equalized by 12 months postprocedure. The respective fusion rates after 24 months were 96.7 and 88.9% for autografts and allografts. Complications at the donor site occurred in 16.7% of the autograft patients, including 1 pelvic fracture, 1 retained sponge, 1 infection, 2 hernias requiring repair, 2 hematomas, and persistent pain. CONCLUSIONS The authors describe a technique for interpositional bone grafting between C-1 and C-2 that allows for the use of an allograft with excellent fusion results. This technique reduced the operative time and blood loss and eliminated donor-site morbidity.

Intracranial subarachnoid hemorrhage resulting from cervical spine dural arteriovenous fistulas: literature review and case presentation

Cervical dural arteriovenous fistulas (dAVFs) are a rare cause of intracranial subarachnoid hemorrhage (SAH) but should be considered when other sources are not found. Subarachnoid hemorrhage caused by dAVF is thought to occur as a result of venous hypertension in most cases. The clinical presentation, acute onset of severe headache, is similar to that in patients with other causes of SAH; however, severe neurological deficits (Hunt and Hess Grade IV and V SAH) have not been reported in SAH caused by cervical dAVFs. Patients with this type of SAH commonly report suboccipital headache, neck pain, and nausea, and thus these hemorrhages can be easily dismissed as perimesencephalic SAH. Vigilant evaluation with 4-vessel cerebral angiography, including selective catheterization of both proximal vertebral arteries, should be performed. The practice of unilateral vertebral artery injection with reflux into the contralateral vertebral and posterior inferior cerebellar arteries has the potential to overlook cervical dAVF. Magnetic resonance imaging may be useful to evaluate for other causes of SAH but is probably not sensitive for the identification of a cervical dAVF. Surgical treatment of this lesion has an excellent outcome.

Inflammatory pseudotumor of the cavernous sinus and skull base.

Inflammatory pseudotumor is a non-neoplastic process of unknown etiology characterized by a proliferation of connective tissue with an inflammatory infiltrate. Intracranial inflammatory pseudotumors classically involve the cavernous sinus but can also occur in the supratentorial or infratentorial compartments and spinal canal. Symptoms are dependent on location, and, when present in the cavernous sinus, typically include cranial nerve palsies of those nerves in the cavernous sinus. These lesions are rapidly responsive to steroid therapy. Surgery is typically indicated for biopsy only, but complete resection may be justified for lesions outside the cavernous sinus.

Surgical treatment of nonrheumatoid atlantoaxial degenerative arthritis producing pain and myelopathy.

Study Design. A retrospective review. Objective. The purpose of this study was to evaluate the clinical and pathologic findings and surgical treatment outcomes for atlantoaxial osteoarthritis. Summary of Background Data. Nonrheumatoid atlantoaxial osteoarthritic degeneration can occur at either the atlantodental articulation or lateral mass articulations. This condition may present with neck pain or myelopathy in the setting of a compressive degenerative pannus. There is a paucity of literature on this topic with only case reports and small case series. Methods. A retrospective chart review was performed to identify patients treated for C1–C2 osteoarthritis. Patient demographics, clinical presentation, neurologic examination, visual analog pain scores, radiographic findings, surgical treatment, outcomes, and complications were recorded for each patient. Results. Twenty-six patients (18 with pannus at the atlantodental articulation and 8 primarily with lateral mass articulation arthritis; 10 men, 16 women; mean age 74 years) were surgically treated for atlantoaxial osteoarthritis. Eleven patients presented primarily with complaints related to myelopathy (all with a degenerative pannus) and 15 presented with cervicalgia only. All patients were treated with posterior atlantoaxial arthrodesis, and 13 patients with myelopathy or severe canal compromise from an irreducible subluxation also had transoral odontoidectomy. All myelopathic patients had improvement in neurologic function (10 of 11 improved 1 Ranawat grade). Neck pain improved in 93% of patients with preoperative neck pain complaints (mean visual analog score before surgery = 7.0, follow-up = 1.3). Fusion was demonstrated in all patients with adequate follow-up. Conclusion. Atlantoaxial osteoarthritis can result in neck pain and myelopathy. In the setting of a degenerative pannus and myelopathy, most patients will improve neurologically after transoral decompression and arthrodesis. Patients with pannus and no myelopathy were effectively treated with posterior fusion alone, although 2 with irreducible subluxation required an initial transoral decompression to allow realignment before fusion. Posterior arthrodesis alone provided significant pain relief in most patients.

Combined S-1 and S-2 sacral alar-iliac screws as a salvage technique for pelvic fixation after pseudarthrosis and lumbosacropelvic instability Technical note

Lumbosacropelvic pseudarthrosis after long spinal fusions for treatment of adult degenerative scoliosis remains a challenging condition. Moreover, although pelvic fixation with iliac screws is widely used in deformity surgery to provide a biomechanically strong distal anchor for long thoracolumbar constructs, there are very few options available after failed pelvic fixation with iliac screws. The authors conducted a retrospective review of the surgical charts and imaging findings of patients subjected to revision surgery for lumbosacropelvic pseudarthrosis from August 2011 to August 2012. This review identified 5 patients in whom a salvage technique combining both S-1 and S-2 sacral alar-iliac (SAI) screws had been performed. In this technical note, the authors present a detailed anatomical discussion and an appraisal of the sequential intraoperative steps of this new technique involving a combination of S-1 and S-2 SAI screws. The discussion is illustrated with a surgical case in which this technique was used to treat a patient with pseudarthrosis that had developed after fixation with classic iliac screws. In conclusion, although S-2 SAI screws have previously been reported as an interesting alternative to classic iliac wing screws, this report is the first on the use of combined S-1 and S-2 SAI screws for pelvic fixation as a salvage technique for lumbosacropelvic instability. According to the reported experience, this technique provides a biomechanically robust construct for definitive pelvic fixation during revision surgeries in the challenging scenarios of pseudarthrosis and instability of the lumbosacropelvic region.

Comparison of fusion assessment techniques: computer-assisted versus manual measurements

OBJECT Fusion assessment after cervical arthrodesis can be subjective. Measures such as bridging bone quantification or extent of (limited) motion on dynamic studies are common but difficult to interpret and fraught with biases. We compared manual measurement and computer-assisted techniques in assessing fusion after anterior cervical discectomy and fusion (ACDF). METHODS One hundred patients who underwent ACDF (512 intervertebral levels) were randomly selected for this radiographic review (follow-up 3-36 months). Two assessment techniques were performed by different observers, with each blinded to the results of the other. The manual spinous process displacement measurement technique was used to calculate motion between the spinous processes under magnification on a digital imaging workstation. Computer-assisted measurements of intervertebral angular motion were made using Quantitative Motion Analysis (QMA) software. Fusion criteria were arbitrarily set at 1 mm of motion for the manual technique and 1.5 degrees of angular motion for the QMA technique. RESULTS The manual measurement technique revealed fusion in 61.7% (316 of 512) of the interspaces assessed, and QMA revealed fusion in 64.3% (329 of 512). These two assessment techniques agreed in 87.5% of cases, with a correlation coefficient of 0.68 between the two data sets. In cases in which the two techniques did not agree, QMA revealed fusion and the manual measurement revealed nonfusion in 64% of the disagreements; 98% of the disagreements occurred when motion was < 2 mm or 2 degrees. CONCLUSIONS Although osseous fusion after arthrodesis remains difficult to assess, new computer-assisted techniques may remove the subjectivity generally associated with assessing fusion.

Biomechanical analysis of a new concept: an add-on dynamic extension plate for adjacent-level anterior cervical fusion.

Study Design. A biomechanical study on a pneumatically controlled 7-axis spine simulator using Delron and human cadaveric spine models. Objectives. To compare the biomechanical properties of an anterior cervical extension plate with comparable-length anterior cervical plates. Summary of Background Data. Adjacent-level anterior cervical surgery next to a previously plated fusion can be technically challenging because of scarring from the previous surgery and the extensive exposure potentially required. An extension plate that attaches to an existing cervical plate could make adjacent-level cervical surgery less problematic. Methods. Flexibility and load sharing were tested in 18 delron models and 10 cadaveric spines. An extension plate (E-plate, Aesculap, Tüttlingen, Germany) at C5–C6 was attached to a single-level plate (ABC plate, Aesculap) at C4–C5 and compared with a two-level plate (ABC plate) spanning C4–C6. Segmental motion was monitored with optical tracking, and interbody graft load was measured with a load cell. Statistical analysis was performed with a Student’s t test’. Results. In the delron models, both constructs displayed virtually 100% load sharing for the full interbody graft and subsidence models, and range of motion in flexion-extension or axial rotation was not statistically significantly different. The failure mode for the extension plate was lateral bending. In the cadaveric spines, load sharing, range of motion, and stiffness were not statistically significantly different between constructs. Conclusions. This extension plate appears to be biomechanically equivalent to the ABC cervical plates with which it was compared in this study.

Evidence on magnetic resonance imaging of Brown-Séquard spinal cord injury suffered indirectly from a gunshot wound : Case report

The authors describe a rare case of Brown-Séquard syndrome as a result of indirect, concussive trauma to the spinal cord from a gunshot wound (GSW) and present the magnetic resonance (MR) imaging evidence obtained in this interesting case. The patient was shot in the anterior neck and the bullet passed through the lateral aspect of the C-7 lateral mass and transverse process. Bone fragments from the lateral aspect of C-7 were displaced posteriorly into the soft tissues, but no abnormalities were noted within the spinal canal except for high-intensity signal on T2-weighted MR imaging within the right side of the spinal cord. This is the first reported case to provide MR imaging evidence of a Brown-Séquard spinal cord injury as a result of indirect trauma (concussive injury) from a GSW.