Michael A. Finn

Anterior Fixation of Odontoid Fractures in an elderly Population

OBJECT Fractures of the odontoid process are the most common fractures of the cervical spine in patients over the age of 70 years. The incidence of fracture nonunion in this population has been estimated to be 20-fold greater than that in patients under the age of 50 years if surgical stabilization is not used. Anterior and posterior approaches have both been advocated, with excellent results reported, but surgeons should understand the drawbacks of the various techniques before employing them in clinical practice. METHODS A retrospective review was undertaken to identify patients who had direct fixation of an odontoid fracture at a single institution from 1991 to 2006. Patients were followed up using flexion-extension radiographs, and stability was evaluated as bone union, fibrous union, or nonunion. Patients with bone or fibrous union were classified as stable. In addition, the incidence of procedure- and nonprocedure-related complications was extracted from the medical record. RESULTS Of the 57 patients over age 70 who underwent placement of an odontoid screw, 42 underwent follow-up from 3 to 62 months (mean 15 months). Stability was confirmed in 81% of these patients. In patients with fixation using 2 screws, 96% demonstrated stability on radiographs at final follow-up. Only 56% of patients with fixation using a single screw demonstrated stability on radiographs. In the immediate postoperative period, 25% of patients required a feeding tube and 19% had aspiration pneumonia that required antibiotic treatment. CONCLUSIONS Direct fixation of Type II odontoid fractures showed stability rates > 80% in this challenging population. Significantly higher stabilization rates were achieved when 2 screws were placed. The anterior approach was associated with a relatively high dysphagia rate, and patients must be counseled about this risk before surgery.

Edema is a precursor to central nervous system peritumoral cyst formation.

Despite the common occurrence and frequent clinical effects of peritumoral cysts in the central nervous system (CNS), the mechanism underlying their development and evolution is not understood. Because they commonly produce peritumoral cysts and because serial magnetic resonance imaging (MRI) is obtained in von Hippel–Lindau disease patients, hemangioblastomas provide an opportunity to examine the pathophysiology of CNS peritumoral cyst formation. Serial MRI was correlated with the clinical findings in 16 von Hippel–Lindau disease patients with 22 CNS hemangioblastomas (11 spinal cord; 11 cerebellar) that were associated with the appearance and evolution of peritumoral cysts. Hemangioblastoma‐associated cyst wall histomorphological analysis was performed on postmortem tissues from three von Hippel–Lindau disease patients (not in the clinical series). Comparative proteomic profiling was performed on peritumoral cyst fluid and serum. Vascular endothelial growth factor levels were determined in peritumoral cysts. MRI clearly showed peritumoral edema that developed and slowly and progressively evolved into enlarging hemangioblastoma‐associated cysts in all tumors (mean follow‐up, 130 ± 38 months; mean ± standard deviation). Postcontrast MRI demonstrated convective leakage of gadolinium into cysts. Mean time required for edema to evolve into a cyst was 36 ± 23 months (range, 8–72 months). Thirteen (59%) hemangioblastoma‐cysts became symptomatic (mean time to symptom formation after cyst development, 35 ± 32 months; range, 3–102 months) and required resection. Protein profiles of cyst fluid and serum were similar. Mean cyst fluid vascular endothelial growth factor concentration was 1.5ng/ml (range, 0–5.4ng/ml). Histology of the cyst walls was consistent with reactive gliosis. CNS peritumoral cyst formation is initiated by increased tumor vascular permeability, increased interstitial pressure in the tumor, and plasma extravasation with convective distribution into the surrounding tissue. When the delivery of plasma from the tumor exceeds the capacity of the surrounding tissue to absorb the extravasated fluid, edema (with its associated increased interstitial pressure) and subsequent cyst formation occur. Ann Neurol 2005;58:392–399

Spinal lipomas: clinical spectrum, embryology, and treatment

Spinal lipomas, particularly lipomas of the conus medullaris and terminal filum, are the most common form of occult spinal dysraphism and represent a wide spectrum of disease with regard to anatomy, clinical presentation, and treatment options. These lesions, however, are united by a similar embryology and pathological mechanism by which symptoms arise. Recently, the treatment of these lesions has generated much controversy, with some physicians advocating surgical treatment for all patients regardless of symptoms and others proposing that surgery be withheld until symptoms develop. The authors discuss lumbosacral spinal lipomas, with particular attention to the theories of their origin, anatomical and pathological features, and treatment options, including a review of current controversies.

Atlantoaxial transarticular screw fixation: update on technique and outcomes in 269 patients.

BACKGROUNDTransarticular screw (TAS) fixation is our preferred method for stable internal fixation of the atlantoaxial joint because of its excellent outcomes, versatility, and cost-effectiveness. OBJECTIVEIn this article, we update our series of patients who have undergone TAS fixation, with attention to surgical technique, planning, complication avoidance, and anatomic suitability. METHODSWe retrospectively reviewed 269 patients (150 women, 119 men; average age, 52.9 years; age range, 17–90 years) who underwent placement of at least 1 TAS. In total, 491 TASs were placed for stabilization necessitated by various pathologic conditions. The mean follow-up period was 15.7 months (range, 0–106 months). RESULTSFusion was achieved in 99% of 198 patients monitored until fusion or nonunion requiring revision, or for 2 years. Forty-five patients had a complication, for a rate of 16.7%. Five early patients had vertebral artery injuries, 1 of which was bilateral and fatal. No recent patients had vertebral artery injuries. Other complications did not result in neurologic morbidity. Review of all atlantoaxial fusions by the senior author (R.I.A.) revealed that the TAS fixation technique could be successfully applied in 86.7% of sides considered. The main reasons for inapplicability were anatomic (recognized on preoperative planning) in 77% and abandonment secondary to concern about possible vertebral artery injury on the first side attempted in 13.8%. CONCLUSIONThe placement of TASs is safe and effective for stabilizing the atlantoaxial articulation. Refinements in technique, such as 3-dimensional stereotactic workstation for trajectory planning, have reduced the rate of serious complications. Clinical outcomes are excellent, with nearly 100% of patients achieving stable bony union.BACKGROUND Transarticular screw (TAS) fixation is our preferred method for stable internal fixation of the atlantoaxial joint because of its excellent outcomes, versatility, and cost-effectiveness. OBJECTIVE In this article, we update our series of patients who have undergone TAS fixation, with attention to surgical technique, planning, complication avoidance, and anatomic suitability. METHODS We retrospectively reviewed 269 patients (150 women, 119 men; average age, 52.9 years; age range, 17-90 years) who underwent placement of at least 1 TAS. In total, 491 TASs were placed for stabilization necessitated by various pathologic conditions. The mean follow-up period was 15.7 months (range, 0-106 months). RESULTS Fusion was achieved in 99% of 198 patients monitored until fusion or nonunion requiring revision, or for 2 years. Forty-five patients had a complication, for a rate of 16.7%. Five early patients had vertebral artery injuries, 1 of which was bilateral and fatal. No recent patients had vertebral artery injuries. Other complications did not result in neurologic morbidity. Review of all atlantoaxial fusions by the senior author (R.I.A.) revealed that the TAS fixation technique could be successfully applied in 86.7% of sides considered. The main reasons for inapplicability were anatomic (recognized on preoperative planning) in 77% and abandonment secondary to concern about possible vertebral artery injury on the first side attempted in 13.8%. CONCLUSION The placement of TASs is safe and effective for stabilizing the atlantoaxial articulation. Refinements in technique, such as 3-dimensional stereotactic workstation for trajectory planning, have reduced the rate of serious complications. Clinical outcomes are excellent, with nearly 100% of patients achieving stable bony union.

Surgical treatment of occipitocervical instability

OBJECTIVEInstability of the occipitocervical junction can be a challenging surgical problem because of the unique anatomic and biomechanical characteristics of this region. We review the causes of instability and the development of surgical techniques to stabilize the occipitocervical junction. METHODSOccipitocervical instrumentation has advanced significantly, and modern modular screw-based constructs allow for rigid short-segment fixation of unstable elements while providing the stability needed to achieve successful fusion in nearly 100% of patients. This article reviews the preoperative planning, the variety of instrumentation and surgical strategies, as well as the postoperative care of these patients. RESULTSCurrent constructs use occipital plates that are rigidly fixed to the thick midline keel of the occipital bone, polyaxial screws that can be placed in many different trajectories, and rods that are bent to approximate the acute occipitocervical angle. These modular constructs provide a variety of methods to achieve fixation in the atlantoaxial complex, including transarticular screws or C1 lateral mass screws in combination with C2 pars, C2 pedicle, or C2 translaminar trajectories. CONCLUSIONSurgical techniques for occipitocervical instrumentation and fusion are technically challenging and require meticulous preoperative planning and a thorough understanding of the regional anatomy, instrumentation, and constructs. Modern screw-based techniques for occipitocervical fusion have established clinical success and demonstrated biomechanical stability, with fusion rates approaching 100%.

Spinal radiosurgery for metastatic disease of the spine.

BACKGROUND Metastatic tumor in the spinal column is common, causing symptomatic spinal cord compression in approximately 25,000 patients annually. Although surgical treatment of spinal metastases has become safer, less invasive, and more efficacious in recent years, there remains a subset of patients for whom other treatment modalities are needed. Stereotactic radiosurgery, which has long been used in the treatment of intracranial lesions, has recently been applied to the spine and enables the effective treatment of metastatic lesions. METHODS We review the evolution of stereotactic radiosurgery and its applications in the spine, including a description of two commercially available systems. RESULTS Although a relatively new technique, the use of stereotactic radiosurgery in the spine has advanced rapidly in the past decade. Spinal stereotactic radiosurgery is an effective and safe modality for the treatment of spinal metastatic disease. CONCLUSIONS Future challenges involve the refinement of noninvasive fiducial tracking systems and the discernment of optimal doses needed to treat various lesions. Additionally, dose-tolerance limits of normal structures need to be further developed. Increased experience will likely make stereotactic radiosurgery of the spine an important treatment modality for a variety of metastatic lesions.

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.

The cervical end of an occipitocervical fusion: A biomechanical evaluation of 3 constructs - Laboratory investigation

OBJECT Stabilization with rigid screw/rod fixation is the treatment of choice for craniocervical disorders requiring operative stabilization. The authors compare the relative immediate stiffness for occipital plate fixation in concordance with transarticular screw fixation (TASF), C-1 lateral mass and C-2 pars screw (C1L-C2P), and C-1 lateral mass and C-2 laminar screw (C1L-C2L) constructs, with and without a cross-link. METHODS Ten intact human cadaveric spines (Oc-C4) were prepared and mounted in a 7-axis spine simulator. Each specimen was precycled and then tested in the intact state for flexion/extension, lateral bending, and axial rotation. Motion was tracked using the OptoTRAK 3D tracking system. The specimens were then destabilized and instrumented with an occipital plate and TASF. The spine was tested with and without the addition of a cross-link. The C1L-C2P and C1L-C2L constructs were similarly tested. RESULTS All constructs demonstrated a significant increase in stiffness after instrumentation. The C1L-C2P construct was equivalent to the TASF in all moments. The C1L-C2L was significantly weaker than the C1L-C2P construct in all moments and significantly weaker than the TASF in lateral bending. The addition of a cross-link made no difference in the stiffness of any construct. CONCLUSIONS All constructs provide significant immediate stability in the destabilized occipitocervical junction. Although the C1L-C2P construct performed best overall, the TASF was similar, and either one can be recommended. Decreased stiffness of the C1L-C2L construct might affect the success of clinical fusion. This construct should be reserved for cases in which anatomy precludes the use of the other two.

Somatic mutations in VHL germline deletion kindred correlate with mild phenotype

Generally, von Hippel–Lindau (VHL) disease is caused by a germline mutation of the VHL gene (chromosome 3p), and tumorigenesis is initiated from a “second‐hit” deletion. A subset of VHL patients have a germline deletion of the VHL gene, and the molecular events leading to tumorigenesis are not fully understood. To determine the molecular pathogenesis of tumor formation in this setting, we analyzed five central nervous system hemangioblastomas from three patients of a single VHL germline deletion kindred, all displaying mild clinical phenotype. Rather than loss of heterozygosity (the “second hit” in VHL germline mutation patients), all tumors from this kindred showed “second‐hit” point mutations on the wild‐type allele. Moreover, in two patients who each had two hemangioblastomas resected each tumor contained a unique mutation. The specific germline deletion and the overall genetic makeup of the patient did not predict these random “second‐hit” point mutations. These results suggest that in patients with germline deletion of a tumor suppressor gene there is a unique genetic mechanism underlying tumorigenesis. This unique genetic mechanism correlates with and may help to understand the mild clinical phenotype seen in these patients.

Endovascular balloon angioplasty for treatment of posttraumatic venous sinus thrombosis. Case report.

In severe cases, posttraumatic cerebral sinus thrombosis can result in venous congestion and persistent intracranial hypertension refractory to both conventional medical therapy and surgical decompression. The authors report a unique case of a patient successfully treated with endovascular mechanical thrombolysis using balloon angioplasty for clinically significant posttraumatic venous sinus thrombosis and review the reported treatments for cerebral venous sinus occlusive disease. This 18-year-old man suffered severe closed head injury from a fall while skateboarding. A head CT scan demonstrated basilar skull fractures involving the left jugular foramen. A CT angiogram revealed thrombosis of the left transverse sinus and occlusion of the sigmoid sinus and internal jugular vein. Despite treatment with anticoagulation therapy and decompressive hemi- and suboccipital craniectomies, intracranial hypertension remained refractory. Serial angiography demonstrated progressive sinus occlusion. Endovascular balloon thrombolysis of the left transverse and sigmoid sinuses resulted in immediate reduction of intracranial pressures and improved sinus patency. Intracranial pressure measurements remained low after the procedure. The patient eventually improved neurologically, was able to follow commands and walk, and was discharged to a rehabilitation facility for further recovery. Anticoagulation therapy, surgical decompression, and endovascular thrombolysis have been reported as treatment modalities for clinically significant posttraumatic venous sinus thrombosis. In this case, endovascular mechanical thrombolysis with balloon angioplasty resulted in resolution of thrombus and successful immediate reduction of intracranial pressure. This treatment may be considered in patients with critically elevated intracranial pressure from posttraumatic venous sinus occlusion refractory to other treatment measures.