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Study design Retrospective review. Objective Evaluate radiographic and clinical outcomes for infants and children, who underwent rigid occipito-cervical fixation for traumatic craniocervical dissociation (tCCD). Summary of background data Traumatic craniocervical dissociation is devastating. Children are at high risk but make up a large number of survivors. Non-rigid fixation has traditionally been favored over screw and rod constructs due to inherent challenges involved with instrumenting the pediatric craniocervical junction. Therefore, outcomes for rigid occipito-cervical instrumentation in infants and young children with tCCD remain uncertain. Methods Retrospective review of children who survived tCCD between 2006 and 2016 and underwent rigid occipito-cervical fixation. Results Fifteen children, from 8 months to 8 years old (mean, 3.8 yr), were either a passenger (n = 11) or a pedestrian (n = 4) in a motor vehicle accident. Seven patients had weakness: five with quadriplegia, one with hemiparesis, and one with bilateral upper extremity paresis. Ten patients had concurrent C1-2 instability. At last follow-up, four patients had improved motor function: one with bilateral upper extremity paresis and one with hemiparesis regained full strength, one with quadriplegia regained function on one side while another regained function in bilateral upper extremities. All underwent rigid posterior occipito-cervical fixation, with two patients requiring additional anterior and posterior fixation at non-contiguous levels. Fourteen patients were stable on flexion-extension x-rays at a mean follow-up of 31 months (9-1 yr or longer, 7-2 yr or longer). There were no cases of deformity, growth disturbance, or subaxial instability. Conclusion Children who survive tCCD may regain function after stabilization. Rigid internal rod and screw fixation in infants and young children safely provided long-term stability. We advocate using C2 translaminar screws to exploit the favorable anatomy of pediatric lamina to minimize the risks of occipitocervical (OC) instrumentation. Level of evidence 4.

A retrospective study.This retrospective study assessed whether short same-segment fixation (SSSF) is better than short-segment posterior fixation (SSPF) for reducing thoracolumbar fractures, improving the kyphosis angle, maintaining vertebral height, or reducing the incidence of broken screws.In clinical practice, single-segment thoracolumbar fractures were then more likely to be treated with SSPF that included pedicle fixation at the level of the fracture (short same-segment fixation, or SSSF). Whether SSSF could really achieve vertebral height recovery, improve the kyphosis, reduce postoperative kyphosis loss, and reduce the incidence of internal fixation failure better than SSPF.Patients treated with SSPF or SSSF at our institution during 2006 to 2014 were reviewed. Effects of thoracolumbar fracture reduction, improved kyphosis angle, and maintaining vertebral height were compared between groups. Logistic regression analysis was used to identify factors related to instrumentation breakage and correlation analysis to assess possible relations between loss of correction of the kyphosis angle (LAWAC) and other factors.Altogether, 130 patients were enrolled (53 SSPF, 77 SSSF). SSPF (22F, 31M) group's mean (range) age was 37.7 (16-60) years, and the follow-up was 26.2 (9-120) months. SSSF (27F, 50M) group's mean (range) age was 39.3 (17-61) years, and the follow-up was 23.2 (9-60) months. All patients underwent either internal fixation or screw repair. Immediately postoperatively, restoration after middle vertebral fractures was better in SSSF patients than in SSPF patients (P = 0.003), with no differences in other fracture-related factors (P 0.05). Only LAWAC was significantly associated with instrumentation breakage (P 0.05). Also, immediately postoperatively, the anterior/posterior vertebral heights ratio was negatively related to LAWAC.Pedicle fixation of the fracture did not obtain better recovery of anterior or posterior vertebral heights nor did it improve AWA restoration. There was no significant difference in LAWAC between groups or in the incidence of broken screws. LAWAC may increase the incidence of broken screws.4.

STUDY DESIGN Unilateral facet dislocation was created in human cadaveric cervical spines. Specimens were sequentially instrumented with posterior or anterior screws and plates, and studied biomechanically. OBJECTIVE To determine the biomechanical differences between anterior and posterior fixation for stabilization of a reduced unilateral cervical facet dislocation. SUMMARY OF BACKGROUND DATA Although previous studies have compared anterior to posterior instrumentation, no data exist on the biomechanics of either type of stabilization after this particular injury. METHODS In 6 human cadaveric cervical spine segments, a reproducible unilateral facet dislocation was created and then unlocked (reduced). Nondestructive torques were applied to specimens that were intact, injured-reduced, fixated using posterior nonlocking lateral mass plates, and fixated using a bone graft plus an anterior nonlocking plate. Flexion, extension, lateral bending, and axial rotation were measured stereophotogrammetrically. RESULTS Lateral mass plating was more effective than anterior plating in limiting motion after reduction of a unilateral facet dislocation. Averaged, over all loading directions, lateral mass plates reduced the range of motion to 17% of normal; anterior plates reduced range of motion to 89% of normal. In all loading directions, lateral mass plates performed significantly better than anterior plates (P < 0.05, paired Student t-tests). CONCLUSIONS Anterior and posterior plating effectively stabilized a reduced unilateral facet dislocation. Lateral mass fixation provided better immobilization than anterior graft and plate.

Study Design. Review article. Objective. To review the indications, technical details, and complications of lateral mass and transfacet mass fixation methods. Summary of Background Data. Potential advantages of rigid fixation in subaxial cervical spine have been defined as early mobilization, faster healing and fusion, and increased fusion rates. Lateral mass screw fixation has been the most popular fixation technique for posterior instrumentation. Transfacet screw fixation, on the other hand, is an alternative method less commonly used. Methods. Narrative and review of the literature. Results. Several different techniques aiming for the most safe and secure lateral mass screw fixation have been described by several different authors. Lateral mass screws provide rigid fixation and high fusion rates in patients with healthy bone. Complications are rare when patients' anatomy is well documented and proper technique is used. Transfacet screw fixation is another method less commonly used and with better biomechanical stability. Conclusion. Lateral mass screw provides excellent 3-dimensional fixations from C3 to C7, and currently it is also the most commonly performed posterior fixation method.

Twenty-five of 26 consecutive patients were studied after posterior lumbar interbody fusion using ethylene oxide-sterilized allograft bone for posterior lumbar interbody fusion and autologous bone for posterolateral fusion with posterior fixation using pedicle screws and variable screw placement plates.Patients were studied at 1 year to determine rate of complications, pseudarthrosis, and re-operations.Clinical success was determined by combined five-point analog pain and function scales. Fusion success was determined by plain radiographs.Complications occurred in four of 25 patients (16%). Re-operations were done in nine of 25 patients (36%) with seven re-operations (28%) to treat frank failures of the donor bone. Although some patients subsequently improved with repeat surgery, the result of the donor bone posterior lumbar interbody fusion was excellent in nine patients, good in four, fair in eight, and poor in four. Posterior lumbar interbody fusion success was achieved in 14 of 25 patients (56%). Clinical success was achieved in 15 of 25 patients (60%).Although the mechanical principles of posterior lumbar interbody fusion were affirmed, the adequacy of ethylene oxide-sterilized allograft bone in meeting the mechanical and biologic needs of posterior lumbar interbody fusion was questioned.

Study Design. A biomechanical in vitro study using human cadaveric spine. Objective. To compare the biomechanical stability of pedicle screws versus various established posterior atlantoaxial fixations used to manage atlantoaxial instability. Summary of Background Data. Rigid screw fixation of the atlantoaxial complex provides immediate stability and excellent fusion success though has a high risk of neurovascular complications. Some spine surgeons thus insert shorter C2 pedicle or pars/isthmus screws as alternatives to minimize the latter risks. The biomechanical consequences of short pedicle screw fixation remain unclear, however. Methods. Seven human cadaveric cervical spines with the occiput attached (C0-C3) had neutral zone (NZ) and range of motion (ROM) evaluated in three modes of loading. Specimens were tested in the following sequence: initially (1) the intact specimens were tested, after destabilization of C1-C2, then the specimens underwent (2) C1 lateral mass and C2 short pedicle screw fixation (PS-S), (3) C1 lateral mass and C2 long pedicle screw fixation (PS-L), (4) C1 lateral mass and C2 intralaminar screw fixation (ILS), (5) Sonntag's modified Gallie fixation (MG) and (6) C1-C2 transarticular screw fixation with posterior wiring (TAS + MG). (7) The destabilized spine was also tested. Results. All instrumented groups were significantly stiffer in NZ and ROM than the intact spines, except in lateral bending, which was statistically significantly increased in the TAS + MG group. The MG group's NZ and ROM values were statistically significantly weaker than those of the PS-S, PS-L, and the ROM values of the TAS + MG groups. The ILS group's NZ values were higher than those of the TAS + MG group and for ROM, than that of the PS-S and PS-L groups. In flexion, the NZ and ROM values of the TAS + MG group were significantly less than those of the PS-S, PS-L, ILS, and MG groups. In axial rotation, the NZ and ROM values of the MG group were statistically significantly higher than those of the PS-S, PS-L, ISL and TAS + MG groups. Conclusion. The TAS + MG procedures provided the highest stability. The MG method alone may not be adequate for atlantoaxial arthrodesis, because it does not provide sufficient stability in lateral bending and rotation modes. The C2 pedicle screw and C2 ILS techniques are biomechanically less stable than the TAS + MG. In the C1 lateral mass-C2 pedicle screw fixation, the use of a short pedicle screw may be an alternative when other screw fixation techniques are not feasible.

STUDY DESIGN Case report and review of the literature. OBJECTIVE To present an os odontoideum with bipartite atlas and synovial cyst at the C1-C2 junction in a 13-year-old girl and to review the relevant background literature. SUMMARY OF BACKGROUND DATA Bipartite atlas associated with os odontoideum and synovial cyst at the C1-C2 junction is extremely rare. METHODS The patient's clinical presentation, evolution of physical findings, and sequential radiologic studies. Surgery of the bipartite atlas with os odontoideum and synovial cyst. Posterior fixation between occipital and C 2 without resection of the mass was performed. RESULTS The patient had significant improvement and spontaneous regression of the cyst was identified on the follow-up magnetic resonance imaging (MRI) taken 3 months after posterior fixation. To our knowledge, no case of a bipartite atlas with os odontoideum and synovial cyst with complete recovery of an accompanying quadriparesis after reduction has been previously reported in English medical literature. CONCLUSION We described a rare association of an anterior arch defect, posterior arch aplasia, os odontoideum, and synovial cyst at the C1-C2 junction. This case report supports surgical intervention of synovial cyst with craniovertebral instability using posterior fixation without resection of the cyst.

While odontoid fractures are common injuries, disagreement exists regarding treatment. Some authors claim a high rate of pseudoarthrosis and have therefore recommended early posterior fixation and fusion. This, however, results in decreased cervical rotation. Therefore, it has been recommended that a more direct approach to the fracture be taken. Results on anterior screw fixation in 14 patients are reported. The technique was found to be especially useful in multiple trauma patients, patients who refuse halo treatment, and in some nonunions.

Five different reconstructions of the atlantoaxial complex were biomechanically compared in vitro in a nondestructive test.To determine whether non-bone graft-dependent one-point fixation affords stability levels equivalent to three-point reconstructions.Previous investigations have demonstrated that three-point fixation, using bilateral transarticular screws in combination with posterior wiring, provide the most effective resistance to minimize motion around C1-C2. However, placement of transarticular screws is technically demanding. Posterior wiring techniques affording one-point fixation have failure rates of approximately 15%, with failure considered to be secondary to structural bone graft failures. One-point, non-bone graft-dependent fixations have not been tested.Eight human cervical specimens, C0-C3 were loaded nondestructively. Unconstrained three-dimensional segmental motion was measured. The reconstructions tested were two one-point fixations, one two-point fixation, and two three-point fixations.Under axial rotation two and three-point reconstructions provided better stiffness than the one-point reconstructions (P0.05). During flexion-extension, higher stiffness levels were observed in one- and three-point fixations when compared with the intact spine (P0.05). In lateral bending no significant differences were observed among the six groups, although the trend was that reconstructions including transarticular screws provided greater stability than one-point fixations.The current findings substantiate the use of three-point fixation as the treatment of choice for C1-C2 instability. [l: atlantoaxial fixation, biomechanics, cervical spine, instability, spinal instrumentation, transarticular screws]

Study Design. An in vitro test of calf spine lumbar segments to compare biomechanical stabilization of a rigid versus a dynamic posterior fixation device. Objectives. To compare flexibility of a dynamic pedicle screw fixation device with an equivalent rigid device. Summary of Background Data. Dynamic pedicle screw device studies are not as prevalent in the literature as studies of rigid devices. These devices contain the potential to enhance load sharing and optimize fusion potential while maintaining stability similar to that of rigid systems. Methods. Load-displacement tests were performed on intact and stabilized calf spines for the dynamic and rigid devices. Stability across a destabilized L3–L4 segment was restored by insertion of either a 6 mm × 40 mm dynamic or rigid pedicle screw fixation device across the L2–L4 segment. The screws then were removed, 7 mm × 45 mm pedicle screws of the opposite type were inserted, and the construct then was re-tested. Axial pull-out tests were performed to assess the likely effects of pedicle screw replacement on the load-displacement data. Results. Results indicated a 65% reduction in motion in flexion–extension and a 90% reduction in lateral bending across the destabilized level for both devices, compared with intact spine values. Reduction in axial rotation motion was much smaller than in other modes. Axial pull-out tests showed no weakening of the bone–screw interface. Conclusions. Both devices provided significant stability of similar magnitudes in flexion, extension, and lateral bending. In axial rotation, the devices only could restore stability to levels similar to those in an intact spine. The dynamic device offers a design that may enhance load sharing without sacrificing construct stability.

In vivo study, using cadaveric dog cervical spine, was performed in which the middle segment of the vertebral body was removed producing anterior instability. Eleven various methods of stabilization utilizing polymethylmethacrylate and other fixation devices were employed, and their static strength in hyperextension was tested and compared. A portion of the same dog's cervical spine in each case was used as a control. The results indicate that all fixation methods failed to regain the normal structural strength in extension. Cement with wire or chain methods of fixation were superior to other methods in this study. Fixation rigidity approaching rigidity of the normal spine appeared to be a significant factor determining the strength of the reconstructed cervical spine. Combined anterior and posterior fixation did not provide further strength, although it did increase the rigidity of the fixation.