A plate-rod device for treatment of cervicothoracic disorders: comparison of mechanical testing with established cervical spine in vitro load testing data

Posterior cervical internal fixation has long been accomplished using wires, hooks, and rods. More recently, the cervical lateral mass screw and plate or rod systems have been used effectively in unstable lower cervical spine disorders. Each form of fixation has its advantages and disadvantages. Interspinous wiring and lateral mass screw placement obviate canal penetration in the cervical region but are associated with a potential neurologic risk as a result of canal encroachment. Minor canal intrusion by laminar hooks in the thoracic spine pose a lesser neurologic risk than in the cervical region. To exploit the benefits and safety features of spinal instrumentation, a combination plate rod construct (PRC) has been developed that obviates canal penetration in the cervical region by way of lateral mass and cervical pedicle screw fixation and hooks or wires in the thoracic spine. A biomechanical analysis of the PRC device was performed and compared with the in vivo maximal load data of the cervical spine and established maximal load data of the Roy-Camille posterior cervical fixation system. The PRC has greater strength and resistance to failure than is necessary to sustain maximal in vivo cervical spine loads, and it has also compared favorably with the parameters of the Roy-Camille system. The PRC device, or variations on it, is an excellent option for spinal fixation across the cervicothoracic junction because of its superior biomechanical qualities and versatility in stabilizing a complex anatomic junction of the spine.     

Three-dimensional kinematic stress magnetic resonance image analysis shows promise for detecting altered anatomical relationships of tissues in the cervical spine associated with painful radiculopathy

For some patients with radiculopathy a source of nerve root compression cannot be identified despite positive electromyography (EMG) evidence. This discrepancy hampers the effective clinical management for these individuals. Although it has been well-established that tissues in the cervical spine move in a three-dimensional (3D) manner, the 3D motions of the neural elements and their relationship to the bones surrounding them are largely unknown even for asymptomatic normal subjects. We hypothesize that abnormal mechanical loading of cervical nerve roots during pain-provoking head positioning may be responsible for radicular pain in those cases in which there is no evidence of nerve root compression on conventional cervical magnetic resonance imaging (MRI) with the neck in the neutral position. This biomechanical imaging proof-of-concept study focused on quantitatively defining the architectural relationships between the neural and bony structures in the cervical spine using measurements derived from 3D MR images acquired in neutral and pain-provoking neck positions for subjects: (1) with radicular symptoms and evidence of root compression by conventional MRI and positive EMG, (2) with radicular symptoms and no evidence of root compression by MRI but positive EMG, and (3) asymptomatic age-matched controls. Function and pain scores were measured, along with neck range of motion, for all subjects. MR imaging was performed in both a neutral position and a pain-provoking position. Anatomical architectural data derived from analysis of the 3D MR images were compared between symptomatic and asymptomatic groups, and the symptomatic groups with and without imaging evidence of root compression. Several differences in the architectural relationships between the bone and neural tissues were identified between the asymptomatic and symptomatic groups. In addition, changes in architectural relationships were also detected between the symptomatic groups with and without imaging evidence of nerve root compression. As demonstrated in the data and a case study the 3D stress MR imaging approach provides utility to identify biomechanical relationships between hard and soft tissues that are otherwise undetected by standard clinical imaging methods. This technique offers a promising approach to detect the source of radiculopathy to inform clinical management for this pathology.     

Proposal of a modified, treatment-oriented classification of odontoid fractures.

BACKGROUND CONTEXT: The classification scheme of odontoid fractures described by Anderson and D'Alonzo is the one most commonly used. However, uncertainty exists in the distinction between Type II and "shallow" Type III fractures. Moreover, fractures at the base of the odontoid (Anderson and D'Alonzo Type II) include a spectrum of injury patterns. PURPOSE: To modify the Anderson and D'Alonzo classification of odontoid fractures based on current clinical treatment options. STUDY DESIGN: Proposal of a modified classification system for odontoid fractures. METHODS: A more precise distinction between Type II and III fractures based on the presence/absence of C1-C2 facet involvement is proposed. A modified classification of Type II fractures based on fracture line obliquity, displacement and comminution is then proposed, because these are factors deemed to influence management. To evaluate the reproducibility of this classification, 52 odontoid fractures were reviewed and classified by four attending spine surgeons and three spine fellows. RESULTS: There was substantial agreement (at least five of seven respondents) in 70% of cases. The overall kappa value for the modified classification system was 0.48, indicating moderate agreement, and there were no differences in kappa values between attending spine surgeons and fellows. CONCLUSIONS: The reproducibility of this system was demonstrated by the moderate agreement observed when applied to odontoid fractures at our institution. The proposed utility of this system is its ability to guide clinical decision making in the treatment of odontoid fractures. Prospective application of this modified classification system and suggested treatment options is now required.     

Evaluation of a novel pedicle probe for the placement of thoracic and lumbosacral pedicle screws

BACKGROUND: Pedicle screw instrumentation is common in the lumbar spine and is gaining acceptance in the thoracic spine. The pedicle is generally cannulated with a gearshift probe or curette. SafePath (Mekanika, Boca Raton, FL) is an alternative pedicle probe designed for pedicle cannulation. This is a blunt-tipped, nonaggressive drill that seeks the cancellous portion of the pedicle. OBJECTIVE: The objective of this study was to evaluate the accuracy of this device in comparison with techniques commonly used for pedicle cannulation. METHODS: Four osteoligamentous fresh-frozen thoracic to sacral cadaveric spines were studied. The pedicles of one side of each cadaver were cannulated with the SafePath device. The contralateral pedicles were cannulated with either a gearshift probe or a 3-0 cervical curette. The accuracy of pedicle probe placement was evaluated by radiography, computed tomography (CT) scan, and direct observation via dissection. RESULTS: By direct observation, 51 of 128 pedicles were violated (40%). There were not significant differences between the results obtained with the gearshift probe or curette; there were 2 of 22 lumbosacral violations (9%) and 14 of 45 thoracic violations (33%). With the SafePath device, there were 0 of 22 lumbosacral violations (0%) and 34 of 45 thoracic violations (76%). SafePath performed significantly better in the lumbar spine and significantly worse in the thoracic spine. The accuracy for determining pedicle violation was 88% for radiography and 85% for CT. CONCLUSIONS: The results of this in vitro study suggest that the SafePath device may represent an alternative to traditional pedicle cannulation techniques in the lumbosacral spine. However, the opposite is true in the thoracic spine, where SafePath performed significantly worse than traditional techniques.     

Surgical treatment of thoracic spinal stenosis: a 2- to 9-year follow-up

STUDY DESIGN: A retrospective investigation of the results of operative treatment of patients with symptomatic thoracic spinal stenosis. OBJECTIVES: To establish the effectiveness and define the limitations of surgical treatment for stenosis of the thoracic spinal canal. SUMMARY OF BACKGROUND DATA: In contrast to cervical and lumbar stenosis, symptomatic narrowing of the thoracic spinal canal is rarely encountered. Although the treatment of thoracic stenosis has been described in multiple case reports and in several small series with minimal follow-up evaluation, there are few studies of patients treated surgically for this condition with follow-up evaluation beyond 2 years. METHODS: Twelve patients who underwent operative decompression for symptomatic stenosis of the lower thoracic spine were followed up for an average period of 62.4 months. Surgery was performed on the thoracic spine alone in four cases and on the combined thoracolumbar spine in eight. Factors that were investigated included pain severity, lower extremity motor function, ambulatory status, and postoperative complications. RESULTS: The level of pain after surgery was decreased in eight patients and unchanged in four patients. Of the 10 patients with a motor deficit before surgery, eight had improvement of muscle function. Of the 11 patients with a gait disturbance before surgery, ambulatory status was improved in seven, unchanged in two, and worse in two. One patient lost neural function secondary to surgical intervention. There were five cases in which the early result subsequently deteriorated because of recurrent stenosis, spinal deformity/instability, or both. CONCLUSIONS: Thoracic stenosis can occur in isolation or, more commonly, in association with lumbar stenosis. Ideally, operative treatment should address all stenotic segments and directly decompress the primary anatomic abnormalities causing neural element compression. Although satisfactory short-term results can be expected, deterioration of the early outcome because of the potential for recurrent stenosis and deformity/instability at the thoracolumbar junction can sometimes be seen with longer follow-up evaluation periods.     

Degenerative lumbar stenosis: diagnosis and management.

Degenerative lumbar stenosis is a common cause of disabling back and lower extremity pain among older persons. The process usually begins with degeneration of the intervertebral disks and facet joints, resulting in narrowing of the spinal canal and neural foramina. Associated factors may include a developmentally narrow spinal canal and degenerative spinal instability. Nonoperative management includes restriction of aggravating activities, physical therapy, and anti-inflammatory medications. If nonoperative treatment has failed, surgical treatment may be appropriate. Decompression should be performed so as to address all clinically relevant neural elements while maintaining spinal stability. If instability is present, autogenous intertransverse bone grafting is recommended. There may be an advantage to augmenting some of these procedures with internal fixation. Surgical success rates as high as 85% have been reported, but may be compromised by inadequate decompression, inadequate stabilization, or medical comorbidities. Short-term follow-up data indicate that operative management provides more effective relief than nonoperative treatment, but prospective studies comparing the effects of nonoperative and operative interventions on the long-term natural history of lumbar spinal stenosis are needed.     

Spinal injuries after falls from hunting tree stands.

BACKGROUND CONTEXT: Spinal injuries are common sequelae of falls from hunting tree stands. Significant neurological injury is not uncommon and can result in significant morbidity as well as enormous expenditure of health care dollars. Recent literature on the subject is limited. PURPOSE: The purpose of this study was to identify precipitating causes, characterize the spectrum of spinal injury, and determine potential interventional safety and prevention recommendations. STUDY DESIGN: A retrospective study. METHODS: Medical record review of 22 patients admitted either directly or via referral to a level I spinal cord injury referral center over a 10-year period (1995-2005) after a fall from a hunting tree stand. RESULTS: All patients were men with a mean age of 46 years (range, 27-80 years). Initial acute care hospitalization averaged 10 days (range, 2-28 days). The average height of fall was 18 feet (range, 10-30 feet). Four of 19 falls (21%) occurred during the morning hours, 2 of 19 falls occurred during the afternoon, and 13 of 19 falls (68%) occurred during the evening hours. Time lapse from injury to presentation to an emergency department ranged from 30 minutes to 14 hours. Alcohol use was a factor in 2 of 20 falls (10%). Hypothermia complicated 3 of 21 cases (14%). Associated injuries were present in 12 of 21 patients (57%) and included fractures to the axial and appendicular skeleton, pneumothoraces, a retroperitoneal bleed, and a brachial plexopathy. Eight of 22 patients (37%) sustained injury to the cervical spine. Five of these 8 patients (63%) had neurological deficits (3 complete and 2 incomplete spinal cord injuries). Thirteen of 22 (59%) patients sustained injury to the thoracic or lumbar spine. Ten of these 13 (77%) had neurologic deficits (3 complete and 7 incomplete). Nine of 22 (41%) patients were treated nonoperatively; the remaining 13 (59%) underwent operative intervention. CONCLUSIONS: Falls from hunting tree stands remain a significant cause of spinal injury and subsequent disability. The best intervention for these injuries is prevention. There is a continued need for hunter safety education to reduce the incidence of these injuries with emphasis on safety harness usage, proper installation and annual inspection of tree stands, hunting in groups with periodic contact, the use of communication devices, and abstinence from alcohol consumption while hunting.