Tensile failure of C2 pedicles and of subsequent direct repair in a porcine model

Combined anterior C2-C3 fusion and C2 pedicle screw fixation for the treatment of unstable hangman's fracture: a contrast to anterior approach only

STUDY DESIGN

A retrospective clinical study was used to evaluate the effect of a new surgical treatment of the hangman's fractures.

OBJECTIVE

To determine the treatment efficacy of combined anterior C2-C3 reduction and fusion and posterior compressive C2 pedicle screw fixation for the management of unstable hangman's fractures.

SUMMARY OF BACKGROUND DATA

The classification of hangman's fractures as proposed by Levine-Edwards was used to classify and guide the treatment of these injuries. Most of these fractures respond to a variety of conservative therapies, but recently, earlier surgery has been increasingly advocated by authors from several countries for the rapid stabilization of these fractures. If surgery is indicated, an anterior approach using a C2-C3 reduction and fusion is preferred usually. Another well-accepted surgical method is the direct transpedicular osteosynthesis by the dorsal approach. However, there was rare report of the combined use of these 2 techniques.

METHODS

A group of 45 surgical patients were all diagnosed with radiograph, magnetic resonance imaging (MRI), and 3D CT scans. Initial and final radiographs were measured for anterior translation and angulation of the C2-C3 complex. Initial external skull traction with extension was used in all patients after admission to reduce the fracture. Then an anterior C2-C3 discectomy followed by an interbody fusion and locking plate fixation was performed. Intraoperative reduction was confirmed by fluoroscopic control. About 29 patients therefore received anterior surgeries only since satisfactory reduction was achieved during the procedure. For the 16 patients who had persistent large residual gaps after the anterior procedure, additional same stage posterior C2 compressive pedicle screws were placed. Clinical and radiologic comparisons were performed in these 2 groups.

RESULTS

The follow-up ranged from 24 to 54 months, with an average 33.6 months. There was radiographic evidence of continuity of the fracture and the bone graft seen at 4.7 months on average. Neck pain and neurologic deficits resolved in nearly all patients after surgery. The anterior translation of anterior-posterior surgery group decreased more significant compared to anterior surgery group, although with no statistical significance. The fractures were closed with a slight gap no more than 2 mm in anterior-posterior surgery group. The residual kyphosis in anterior-posterior surgery group was still a little larger than it in anterior surgery group. No internal fixation failures or infections were observed.

CONCLUSION

We believe that the need for single stage 360° fusion of hangman's fractures can be somewhat predicted by a combination of high resolution imaging. For hangman's fractures with significant deformity and gapping, it is our experience that immediate single-stage anterior-posterior reduction, instrumentation, and arthrodesis achieve superior postoperative reduction and long-term functional outcomes.

Traumatic spondylolisthesis of the axis: a biomechanical comparison of clinically relevant anterior and posterior fusion techniques

Object

Surgical management of unstable traumatic spondylolisthesis of the axis includes both posterior and anterior fusion methods. The authors performed a biomechanical study to evaluate the relative stability of anterior fixation at C2–3 and posterior fixation of C-1 through C-3 in hangman's fractures.

Methods

Fresh-frozen cadaveric spine specimens (occipital level to T-2) were subjected to stepwise destabilization of the C1–2 complex, replicating a Type II hangman's fracture. Intact specimens, fractured specimens, and fractured specimens with either anterior screw and plate or posterior screw and rod fixation were each tested for stability. Each spine was subjected to separate right and left rotation, bending, flexion, and extension testing.

Results

Anterior fixation restored stiffness in flexion and extension movements to values greater than those for intact specimens. For other movement parameters, the values approximated those for intact specimens. Posterior fixation increased the stiffness to above those values seen for anterior fixation specimens.

Conclusions

In cadaveric spine specimens subjected to a Type II hangman's fracture, both anterior fixation at C2–3 and posterior fixation with C-1 lateral mass screws and C-2 and C-3 pedicle screws resulted in a consistent increase in stiffness, and hence in stability, over intact specimens.

Safety and efficacy of C2 pedicle screws placed with anatomic and lateral C-arm guidance

STUDY DESIGN

This is a retrospective review of 150 C2 pedicle screw placements. Candidates had their C2 pedicle morphology assessed through three-dimensional imaging, including preoperative image guidance. After surgery, the patients were serially CT scanned. Follow-up, with fusion assessment, ranged from 1 to 12 years.

OBJECTIVE

We will show that an open technique combined with lateral C-arm guidance provides rapid placement of C2 pedicle screws.

SUMMARY OF BACKGROUND DATA

C2 pedicle screws can be successful anchors for a variety of cervical problems. Standard intraoperative image guidance, biplane fluoroscopy, or free hand techniques all have their drawbacks.

METHODS

After adequate C2 exposure, the C2 pedicle is palpated. The dissector remains stationary to provide coronal orientation while a lateral C-arm radiograph is obtained for sagittal orientation. The drill trajectory is set, the C2 pedicle cannulated, and a cancellous screw placed.

RESULTS

A total of 71 patients had bilateral screws placed and 8 patients had unilateral screws placed. The overall complication rate was 2.7%.

CONCLUSIONS

In our series, we have found a consistent way to cannulate the C2 pedicle. C2 fixation serves as an integral part of cervical reconstruction. Preoperative planning, anatomic knowledge, and lateral C-arm orientation create a low morbidity method for C2 screw placement.

Verletzungen des kraniozervikalen Übergangs

Injuries to the upper cervical spine (C0-C2) play a major role in surgical treatment of traumatic sequelae in the entire cervical spine. Even though the number of such operations has increased in recent years, there are no clear treatment recommendations for most types of cervical spine injuries. In view of the wide range of injury types and the correspondingly large number of treatment options, this review focuses mainly on the following types of injuries: C0 fractures, occipital condyle fractures (OCF), atlanto-occipital dislocation (AOD), atlas fractures, atlantoaxial dislocation (AAD), and axis fractures. Important aspects of the mechanisms of injury, clinical signs and symptoms, diagnostic procedures, and treatment options are discussed. Special emphasis is placed on comparatively reviewing the different treatment options discussed in the literature. A summary in table form is presented at the end of each chapter for quick reference.

Estimating the compressive strength of the porcine cervical spine: an examination of the utility of DXA

STUDY DESIGN

The failure strength of porcine spinal units was correlated with vertebral size and bone mineralization. The accuracy of the resulting predictive equations was tested with an independent sample of spinal units.

OBJECTIVES

To determine if dual energy x-ray absorptiometry (DXA)-obtained measures of bone mineralization can be used to accurately predict the compressive tolerance of porcine spinal units.

SUMMARY OF BACKGROUND DATA

Porcine spinal units are often used in place of cadaveric tissues, and normalization is used to improve the transferability of model results. In compressive testing, normalization can be performed to the estimated compressive strength. Bone mineralization measures have been shown to be positively correlated with compressive tolerance and have been used to predict the tolerance of human spinal units. However, the accuracy of these predictive equations has not been assessed with an independent sample.

METHODS

Twenty porcine cervical spinal units were scanned (DXA) to obtain measures of bone mineral content (BMC) and bone mineral density (BMD). The units were compressed to failure, and the failure loads were correlated with the measured bone mineralization and endplate area of the spinal unit. The regression equations were used to predict the compressive tolerance of an independent sample of spinal units.

RESULTS

BMC (P = 0.078) and BMD (P = 0.2834) were not significantly correlated to compressive strength. Endplate area was the most highly correlated variable, with an r of 0.5329. The use of a predictive equation including BMC on the second independent sample resulted in errors of estimation of 1.4 +/- 1.2 kN, corresponding to 13% of the average compressive strength. In comparison, the use of an equation employing endplate area alone resulted in estimation errors of 11%.

CONCLUSIONS

Measures of BMC/BMD did not enhance predictions of compressive strength and will not reduce errors in compressive load normalization in a porcine model. The poor correlations found between BMC and compressive strength may be due to the non-load-bearing anterior processes of the porcine cervical spine.