William C. Welch

Radiosurgery for spinal metastases: clinical experience in 500 cases from a single institution.

Study Design. A prospective nonrandomized, longitudinal cohort study. Objective. To evaluate the clinical outcomes of single-fraction radiosurgery as part of the management of metastatic spine tumors. Summary of Background Data. The role of stereotactic radiosurgery for the treatment of spinal lesions has previously been limited by the availability of effective target immobilization and target tracking devices. Large clinical experience with spinal radiosurgery to properly assess clinical experience has previously been limited. Methods. A cohort of 500 cases of spinal metastases underwent radiosurgery. Ages ranged from 18 to 85 years (mean 56). Lesion location included 73 cervical, 212 thoracic, 112 lumbar, and 103 sacral. Results. The maximum intratumoral dose ranged from 12.5 to 25 Gy (mean 20). Tumor volume ranged from 0.20 to 264 mL (mean 46). Long-term pain improvement occurred in 290 of 336 cases (86%). Long-term tumor control was demonstrated in 90% of lesions treated with radiosurgery as a primary treatment modality and in 88% of lesions treated for radiographic tumor progression. Twenty-seven of 32 cases (84%) with a progressive neurologic deficit before treatment experienced at least some clinical improvement. Conclusions. The results indicate the potential of radiosurgery in the treatment of patients with spinal metastases, especially those with solitary sites of spine involvement, to improve long-term palliation.

Combination kyphoplasty and spinal radiosurgery: a new treatment paradigm for pathological fractures

OBJECT Patients with symptomatic pathological compression fractures require spinal stabilization surgery for mechanical back pain control and irradiation for the underlying malignant process. The authors evaluated a treatment paradigm of closed fracture reduction and fixation involving kyphoplasty and subsequent spinal radiosurgery. METHODS Twenty-six patients (six men and 20 women, mean age 72 years) with pathological compression fractures (16 thoracic and 10 lumbar) were prospectively evaluated. Histological diagnoses included 11 lung, nine breast, four renal, one cholangiocarcioma, and one ocular melanoma. Seven lesions had received prior external-beam radiation therapy. All patients underwent kyphoplasty that involved the percutaneous transpedicular technique. Fiducial markers allowing for image guidance during CyberKnife treatment were placed, at time of the kyphoplasty, in the pedicles at adjacent levels. Patients underwent single-fraction radiosurgery (mean time after kyphoplasty 12 days) in an outpatient setting. The tumor dose was maintained at 16 to 20 Gy (mean 18 Gy) to the 80% isodose line. The treated tumor volume ranged from 12.7 to 37.1 cm3. No acute radiation-induced toxicity or new neurological deficit occurred during the follow-up period (range 11-24 months, median 16 months). Axial pain improved in 24 (92%) of 26 patients. CONCLUSIONS The combined kyphoplasty and spinal radiosurgery treatment paradigm was found to be clinically effective in patients with pathological fractures; there was no significant spinal canal compromise. In this technique two minimally invasive surgical procedures are combined to avoid the morbidity associated with open surgery while providing both immediate fracture fixation and administering a single-fraction tumoricidal radiation dose.

Frameless stereotactic guidance for surgery of the upper cervical spine.

OBJECTIVE The goal was to evaluate and describe the use of a frameless, computed tomography-guided, stereotactic technique in complex procedures involving the craniocervical junction. METHODS Eleven procedures, including transoral odontoid resection, posterior atlantoaxial fusion with transarticular C1-C2 screw fixation, and spinal tumor resection, were performed in the preceding 26 months. In each case, frameless stereotaxy was used to plan the incision, to define resection margins, and to determine the appropriate orientation of instrumentation. RESULTS There were no intraoperative complications noted. Each patient underwent adequate resection of the pathological lesion and satisfactory placement of instrumentation. The stereotactic system provided detailed anatomic visualization, which increased the confidence of the surgeon during the procedure. The system limited the need for extensive surgical exposure, reduced fluoroscopy time, and decreased the risk of neurovascular injury. CONCLUSION Frameless stereotaxy provided the surgeon with intraoperative information regarding the extent of bone and soft tissue resection. It provided a multidimensional view of anatomic relationships in the operative field, which significantly increased surgical accuracy and safety.

Spinal Facet Joint Biomechanics and Mechanotransduction in Normal, Injury and Degenerative Conditions

The facet joint is a crucial anatomic region of the spine owing to its biomechanical role in facilitating articulation of the vertebrae of the spinal column. It is a diarthrodial joint with opposing articular cartilage surfaces that provide a low friction environment and a ligamentous capsule that encloses the joint space. Together with the disc, the bilateral facet joints transfer loads and guide and constrain motions in the spine due to their geometry and mechanical function. Although a great deal of research has focused on defining the biomechanics of the spine and the form and function of the disc, the facet joint has only recently become the focus of experimental, computational and clinical studies. This mechanical behavior ensures the normal health and function of the spine during physiologic loading but can also lead to its dysfunction when the tissues of the facet joint are altered either by injury, degeneration or as a result of surgical modification of the spine. The anatomical, biomechanical and physiological characteristics of the facet joints in the cervical and lumbar spines have become the focus of increased attention recently with the advent of surgical procedures of the spine, such as disc repair and replacement, which may impact facet responses. Accordingly, this review summarizes the relevant anatomy and biomechanics of the facet joint and the individual tissues that comprise it. In order to better understand the physiological implications of tissue loading in all conditions, a review of mechanotransduction pathways in the cartilage, ligament and bone is also presented ranging from the tissue-level scale to cellular modifications. With this context, experimental studies are summarized as they relate to the most common modifications that alter the biomechanics and health of the spine-injury and degeneration. In addition, many computational and finite element models have been developed that enable more-detailed and specific investigations of the facet joint and its tissues than are provided by experimental approaches and also that expand their utility for the field of biomechanics. These are also reviewed to provide a more complete summary of the current knowledge of facet joint mechanics. Overall, the goal of this review is to present a comprehensive review of the breadth and depth of knowledge regarding the mechanical and adaptive responses of the facet joint and its tissues across a variety of relevant size scales.

Immediate biomechanical effects of lumbar posterior dynamic stabilization above a circumferential fusion.

Study Design. Biomechanical in vitro human cadaveric lumbar flexibility testing with 6 sequential treatments. Objective. To compare the range of motion (ROM) of dynamic one-level posterior stabilization constructs to one-level rigid rod fixation constructs and to study the effects of extending the posterior construct to the adjacent superior level. Summary of Background Data. Patients experiencing pain and biomechanical instability at one level may also present with radiographic or other indicators of early degeneration at an adjacent level. Clearly, fusion would be warranted at the symptomatic level, but the treatment plan for the adjacent level remains controversial. Additionally, the effects on adjacent motion segments above a fusion level are currently not well understood. Methods. Thirteen fresh frozen human cadaveric lumbar spines (L1–L5) were tested in 6 modes of loading: 3 were randomized to dynamic posterior stabilization constructs and 7 to a rigid rod pedicle screw system. Each group was subjected to 6 treatments. Results. When comparing the instrumented treatments, only Treatment 6, two-level hybrid constructs, exhibited a statistically significant effect in flexion-extension bending at L2–L3 between the posterior dynamic system and rigid rod fixation (P = 0.014). Conclusion. ROM at the superior adjacent level (L2–L3) demonstrated no significant difference between intact, destabilized, one-level posterior fixation, and one-level circumferential fusion at the index level (L3–L4) when comparing posterior dynamic stabilization to rigid rod fixation. However, ROM at the superior adjacent level (L2–L3) was significantly greater for lateral bending and axial rotation when both levels (L2–L3 and L3–L4) were stabilized with a dynamic stabilization system. When thefunctional spinal units were instrumented with a two-level hybrid construct, two-level posterior instrumentation (L2–L3 and L3–L4) with a cage at the index level (L3–L4), all bending modes generated significantly greater ROM for the dynamic stabilization group at L2–L3 compared with rigid rod fixation.

Osteoinductive bone graft substitutes for lumbar fusion: a systematic review

OBJECT Autograft and allograft, the standard approaches for lumbar fusion procedures, have important disadvantages. Bone graft substitutes such as recombinant human bone morphogenetic proteins (rhBMP-2 and rhBMP-7) have emerged as viable alternatives. The authors conducted a systematic review to compare the efficacy and safety of osteoinductive bone graft substitutes using autografts and allografts in lumbar fusion. METHODS A search for prospective controlled trials was conducted on MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials databases. Data were extracted for key outcomes including radiographically demonstrated nonunion, Oswestry Disability Index, operating time, blood loss, and length of hospital stay. The quality of randomized controlled trials was assessed using the Jadad scale. Meta-analyses were performed when feasible, and heterogeneity was assessed using the Q statistic and the I(2) statistic. RESULTS Seventeen of 732 potential studies met the inclusion criteria, with 9 examining rhBMP-2, 3 examining rhBMP-7, 3 examining demineralized bone matrix, and 2 examining autologous growth factor. Recombinant human BMP-2 significantly decreased radiographic nonunion when compared with autologous iliac crest bone graft (AIBG) in a meta-analysis (relative risk 0.27, 95% CI 0.16-0.46). Stratification of meta-analyses by the type of surgical procedure performed yielded similar results. Funnel plots suggested publication bias. Trials of rhBMP-2 suggested reductions in the operating time and surgical blood loss, with less effect on the length of hospital stay. There was no difference in radiographic nonunion with the use of rhBMP-7 when compared with AIBG (relative risk 1.02, 95% CI 0.52-1.98). Neither rhBMP-2 nor rhBMP-7 demonstrated a significant improvement on the Oswestry Disability Index when compared with AIBG. The limited data on demineralized bone matrix and autologous growth factor showed no significant improvement in radiographic outcomes. CONCLUSIONS Recombinant human BMP-2 may be an effective alternative to AIBG in lumbar fusion. Data are limited for other bone graft substitutes.

Frameless Stereotactic Guidance: An Intraoperative Adjunct in the Transoral Approach for Ventral Cervicomedullary Junction Decompression

Methods The application of a video-interactive frameless stereotactic guidance system for the treatment of ventral cervlcomedullary junction compression is described in a patient with basilar invagination, odontoid dysgenesis, and a Chiari malformation who had irreducible impingement on the ventral brainstem by a partially fused mass of bone made up of the malformed odontoid peg, the inferior cilvus, and dorsally rpotruding osteophytes at the odontoid-clival junction. Results This technology permitted instantaneous feedback of the surgoens orientation in all planes, facilitating extensive removal of the dens and clival tip to achieved adequate ventral brainstem decompression. In view of the distortion of the craniovertebral anatomy produced by the patients anomalies, the ability to visualize three dimensionally the location of the vertebral arteries also added an element of safety to the lateral bone removal. Similarly, the ability to localize the rostral limit of the cilvus that needed to be resected and the caudal extent of C2 that neede to be removed to acheieve an adequate decompression helped ensure that the extent of bone removal was appropriately tailored to the patients anatomy. Conclusion The authors belive this technique represents a significant advance over standard radiographic intraoperative localization techniques during transoral approaches to the ventral cervicomedullary junction for patients in whom the odontoid is fixed in position in relation to the clivus. This is based on the speed with which localization can be obtained, the accuracy of the information provided, the ability to obtain localization in multiple planes simultaneously, and the lack of radiation exposure during the procedure.

Surgery Versus Nonsurgical Treatment of Lumbar Spinal Stenosis: A Randomized Trial

Background: Primary care management decisions for patients with symptomatic Lumbar Spinal Stenosis (LSS) remain a challenge and non-surgical guidance is limited by lack of evidence.

Da Vinci Robot-assisted transoral odontoidectomy for basilar invagination.

The transoral approach is an effective way to decompress the craniocervical junction due to basilar invagination. This approach has been described and refined, but significant limitations and technical challenges remain. Specifically, should the transoral route be used for intradural pathology, such as a meningioma, or should an inadvertent durotomy occur during extradural dissection, achieving a watertight closure of the dura in such a deep and narrow working channel is limited with the current microscopic and endoscopic techniques. Even closure of the posterior pharyngeal mucosa can be challenging, and problems with wound dehiscence encountered in some case series may be attributable to this difficulty. These problems, and the corollary aversion to the procedure felt by many neurosurgeons, led our group to investigate an alternative approach.

Persistently electrified pedicle stimulation instruments in spinal instrumentation. Technique and protocol development.

STUDY DESIGN A prospective review was done of a new intraoperative technique developed to detect and prevent neurologic compromise during pedicle screw insertion. OBJECTIVES To describe in sufficient detail the technique of persistently electrified pedicle stimulation instruments, so that this technique will be available generally to all clinical neurophysiologists and spine surgeons; and to demonstrate the use, typical results, interpretation, and protocol of the technique. SUMMARY AND BACKGROUND DATA Fusion techniques that use pedicle instrumentation have the potential to cause nerve root injury. Several authors have proposed imaging and neurophysiologic methods to improve outcome. The present method represents a significant theoretical departure and advance from previously reported methods. METHODS All relevant instruments used during pedicle instrumentation were converted easily, inexpensively, and quickly into monopolar stimulators with appropriate stimulus voltages to identify broaches of pedicle bone via evoked-electromyograms from relevant muscle groups. RESULTS The persistently electrified pedicle stimulation instrument technique provided accurate intraoperative neurophysiologic information concerning pedicle, integrity in the patients studied. The protocol is standardized and adaptable easily, inexpensively, and quickly to most clinical applications. CONCLUSIONS The persistently electrified pedicle stimulation instrument technique described here is useful for monitoring instrumented lumbar fusion procedures. The use of this protocol may help confirm intraosseous placement of pedicle screws and prevent neurologic injury.