The thoracic spine is a structurally unique region that renders it uniquely suceptible to thoracic disc herniation. Surgical management strategies are complicated, in part, by the regional anatomical and biomechanical nuances. Surgical approaches include posterior, posterolateral, and anterior routes. Each isassociated with specific indications and contraindications. The biomechanical principles and safe anatomical trajectories must be considered in the surgical decision-making process. These issues are discussed in the pages that follow.
Andrew E. Wakefield, Michael P. Steinmetz and Edward C. Benzel
Michael P. Steinmetz, Anis Mekhail and Edward C. Benzel
The spinal column is the most frequent site of bone metastasis in the body. Spine surgeons are often involved in the care of these patients only after nonoperative management has failed. Because surgery has been viewed as no better than radiotherapy in the treatment of metastasis of the spine, it has only been used as a salvage approach. These views are based on a body of literature in which laminectomy combined with radiotherapy was compared with radiotherapy alone. Anterior approaches to the spine are now popular and familiar to most surgeons. These approaches allow direct access to the metastatic lesion, reconstruction of the anterior vertebral column, and the placement of anterior instrumentation. Outcomes are frequently much better when this combined treatment is used instead of radiotherapy alone. In selected patients, surgery may be desired as first-line therapy before radio- or chemotherapy has been initiated.
The controversy surrounding surgery for metastatic spinal disease is reviewed. Treatment strategies, both operative and nonoperative, are presented. Indications and strategies for surgery are also presented, and the supporting literature is reviewed.
Michael P. Steinmetz, Christopher D. Kager and Edward C. Benzel
Object. Cervical kyphotic deformation may develop after surgery involving either the ventral or dorsal approach. Regardless of the cause, the development of a cervical kyphotic deformity should be avoided, if possible, and corrected if present, when appropriate. The authors describe their experience with a technique for the ventral correction of iatrogenic (postoperative) cervical kyphosis.
Methods. A retrospective review of cases involving correction of postoperative iatrogenic cervical kyphosis via an ventral approach was performed. The authors conducted an ventral approach to kyphosis correction. The procedure required specific head positioning (in extension), convergent distraction pins, and an ventrally placed implant (axially dynamic when appropriate) with multiple points of fixation including at least one point of intermediate fixation. The pre- and postoperative sagittal angle and clinical status were evaluated.
During a nearly 14-month period, 12 patients met the inclusion criteria. Ten patients underwent a minimum of 6 months of follow up. They comprised the study population. Most patients presented with mechanical neck pain as part of their symptom profile. The mean magnitude of deformity correction (pre- to postoperative) was 20° of lordosis. The mean postoperative sagittal angle was 6° of lordosis. The mean change in the sagittal angle during the follow-up period was 2.2° of lordosis.
Conclusions. The ventral approach to correction of cervical deformity led to the achievement of lordosis in all but one patient. This posture was effectively maintained during the follow-up period. All patients exhibited improvement postoperatively; three experienced complete resolution of their preoperative symptoms. When symptoms are related to postsurgical kyphosis, deformity correction should be considered. Such a procedure may be performed effectively via an ventral approach in most circumstances.
Michael P. Steinmetz, Roseanna M. Lechner and James S. Anderson
Atlantooccipital dislocation (AOD) injuries are highly unstable, and usually result in significant neurological injury and death. Recently the postinjury survival period has increased. In a review of the literature the authors found 41 cases in which survival was greater than 48 hours. This is likely due to improved on-scene resuscitation, spinal immobilization, transportation, new diagnostic techniques, and a higher index of suspicion.
Diagnosis is usually made with plain cervical radiographs, but there are shortcomings associated with this modality in the pediatric population. Diagnosis is aided by high-resolution computerized tomography and magnetic resonance imaging. Infants and toddlers may undergo orthotic immobilization alone, whereas older children usually undergo early occipital cervical fusion. Those with incomplete AOD may be managed successfully with orthotic immobilization.
Timothy A. Moore, Michael P. Steinmetz and Paul A. Anderson
Thoracolumbar fracture-dislocations are devastating injuries. They usually require surgical reduction and stabilization. The authors present a novel technique for reducing these injuries that is predictable and reproducible.
Jeffrey P. Mullin, Breanna Perlmutter, Eric Schmidt, Edward Benzel and Michael P. Steinmetz
In 2009, Santoni and colleagues described a novel technique of posterior instrumentation; the cortical bone trajectory (CBT) was described as a caudocephalad and medial-to-lateral trajectory. Reported indications for CBT fixation include patients with osteoporosis, single-level degenerative disease, or adjacent-segment disease (ASD). In cases of revision surgery, it is technically possible and beneficial to place a traditional pedicle screw and a CBT screw at the same spinal level and side. It remains unclear as to the feasibility of placing both a traditional and a CBT screw at all levels of the lumbar spine and with varying trajectories of the preexisting traditional pedicle screws. Therefore, the authors conducted a study to radiographically assess the feasibility of using CBT and traditional pedicle screws at the same level in a large patient population.
Using a 3D Spine Navigation WorkStation, the authors assessed 47 lumbar spine CT scans. These images were obtained from 2 disparate groups of patients: those who had previously undergone traditional pedicle instrumentation (prior surgery group) and those who had not (no prior surgery group). The authors virtually placed traditional pedicle and CBT screws at each lumbar level bilaterally. It was then determined if the dual trajectories were feasible, as defined by the presence or absence of a collision of the screw trajectories based on 3D imaging.
Overall, the authors evaluated 47 patients and were able to successfully plan dual trajectories in 50% of the pedicles. The no prior surgery group, compared with the prior surgery group, had a significantly greater success rate for dual trajectories. This difference was most significant in the lower lumbar levels (L3–5) where the prior instrumented group had success rates lower than 40% compared with the no prior surgery group's success rate, which was greater than 70%. There was a significant difference between each lumbar level in the lower spine.
There is a significant difference in the feasibility of planning CBT screws in patients who have undergone prior pedicle instrumentation compared with placing CBT and traditional pedicle screws simultaneously, but dual trajectory pedicle screws are a feasible option for posterior lumbar spinal instrumentation, especially as a de novo option in osteoporotic patients or in patients with ASD who underwent previous pedicle instrumentation. Ultimately, the practical clinical utility and biomechanical effects on the spine and instrumentation construct would require additional study.
Rakesh D. Patel, Humberto G. Rosas, Michael P. Steinmetz and Paul A. Anderson
The theoretical advantage of pars interarticularis repair over spinal fusion to correct pars defects is that the treatment is a direct osteosynthesis that preserves motion at the involved functional spinal unit. Several techniques and constructs have been used to achieve greater rigidity, but these techniques may risk entry into the spinal canal, and adverse events are common. A pedicle and laminar screw construct placed entirely outside the spinal canal may offer greater stiffness and achieve higher pars defect healing rates. The purpose of this study was to biomechanically assess an intralaminar screw construct in cadaveric lumbar spines in comparison with other types of constructs typically used in pars repair and to quantify the sizes of screws that can be placed safely in both normal and spondylolytic vertebrae.
The L-4 and L-5 laminae in patients with spondylolysis and in controls who underwent CT (n = 41, each group) were measured by analysis of conventional axial CT images and multiplanar reformations constructed on a Vitrea workstation to determine the feasibility of translaminar fixation with a 4.5-mm-diameter screw. Biomechanical tests for torsion and flexion-extension were performed on 8 fresh human cadaveric lumbar spines before and after modeling for bilateral spondylolytic defects. Three pars repair techniques were tested at each level and in the following sequence: pedicle screw–cable, pedicle screw–rod–hook, and pedicle screw–intralaminar screw.
The majority of laminae can accept 4.5 × 25-mm screws. The cable construct allowed the greatest motion and least stability across the defect in all biomechanical tests. The hook and laminar screw constructs performed similarly in all tests and exhibited no significant difference in stiffness.
A surgically placed intralaminar screw construct may be a safe and effective alternative to current pars repair methods.
Michael P. Steinmetz, Meg Verrees, James S. Anderson and Roseanna M. Lechner
✓ Two children who were 13 months and 3 years old and who had suffered traumatic atlantooccipital dislocation were each treated by being placed in a halo orthosis for 10 weeks. Because of a continued loss of reduction due to the poor fit of the halo vest, a dual-strap augmentation was developed. This strap augmentation allowed consistent reduction to be maintained. Both children were therefore successfully treated nonsurgically with a halo vest. One child remained neurologically intact and the other had improvement in motor strength. There were no complications from the use of strap augmentation for halo vest fixation.
Michael P. Steinmetz, Ann Warbel, Melvin Whitfield and William Bingaman
Object. Despite the wide use of anterior cervical instrumentation in the management of multilevel cervical spondylosis, the incidences of pseudarthrosis and instrument-related failure remain high. The use of a dynamic implant may aid in the prevention of these complications. The purpose of this study was to evaluate the DOC dynamic cervical implant in the treatment of multilevel cervical spondylosis.
Methods. The authors evaluated 34 cases in which anterior multilevel cervical decompression and fusion were performed using the DOC Ventral Cervical Stabilization System. Postoperatively, and at each follow-up visit, the sagittal angle and the degree of subsidence that developed were measured. Fusion rates and clinical outcomes were also evaluated.
The mean postoperative sagittal angle was 14° of lordosis. The mean change in the sagittal angle during the follow-up period was 0.4° of lordosis. By 6 months postoperatively some subsidence had occurred in most patients, with no subsidence occurring in only 15%. By 3 months greater than or equal to 2 mm of subsidence was demonstrated in 61% of cases. The overall fusion rate was 91%. In the majority of patients (79%) symptoms were judged to be improved or resolved.
Conclusions. The DOC dynamic cervical implant permitted controlled subsidence and prevented progression of kyphotic deformity. There was one construct failure (related to a motor vehicle accident) and an overall fusion rate of 91%. The DOC implant is a safe and effective cervical construct for multilevel spondylotic disease.
Ali Chahlavi, Michael P. Steinmetz, Thomas J. Masaryk and Peter A. Rasmussen
✓ Cerebral venous sinus thrombosis is often difficult to manage. Treatment options include systemically delivered anticoagulation therapy or chemical thrombolysis. Targeted endovascular delivery of thrombolytic agents is currently a popular option, but it carries an increased risk of hemorrhage. These strategies require significant time to produce thrombolysis, often in a patient with a rapidly deteriorating neurological condition. Rapid mechanical recanalization with thrombectomy is therefore very attractive; this procedure provides rapid recanalization with no increased risk of hemorrhage from use of thrombolytic agents. Nevertheless, the rheolytic catheter is large and stiff and may not be able to navigate tortuous intracranial vascular anatomy. The authors present their experience with direct dural sinus mechanical thrombectomy performed using the rheolytic catheter via a transcranial route.
Two patients with dural sinus thrombosis and rapidly deteriorating levels of consciousness underwent unsuccessful attempts at mechanical thrombolysis via the usual transfemoral route. Through a burr hole over the dural sinus, mechanical thrombectomy was subsequently performed using the thrombectomy catheter. Sinus patency was restored following treatment and both patients demonstrated neurological recovery.
Hemorrhage or a rapidly deteriorating neurological condition may preclude the use of systemic or locally delivered thrombolytic agents for the treatment of cerebral venous sinus thrombosis. Mechanical thrombectomy may be the treatment of choice in these circumstances. In patients with limited transfemoral access, a transcranial approach may be used to access the cerebral dural sinuses and thrombectomy may be safely and effectively performed. Further evaluation of this therapy is warranted.