Cannulated screws for odontoid screw fixation and atlantoaxial transarticular screw fixation. Technical note

Transcervical approach with endoscopic assistance for surgical treatment of patient with irreducible atlantoaxial dislocation: a case report

We demonstrate the case of a surgery in a patient with irreducible atlantoaxial dislocation (IrAAD) after C2 fracture. The challenges of this case were the flexed head in a forced position, impossibility of neck extension, and revision operation after posterior occipito-cervical fixation. The patient underwent the following surgeries: 1. A ventral release of C1-C2 using transcervical endoscopy; 2. Removal of occipito-cervical system and fibrous block resection in the posterior surfaces of the C1-C2; 3. Reducing of AAD and odontoid screw fixation; 4. Posterior C1-C2-C3 screw fixation. Ankylosing of C1-C2 and C2-C3-C4 fusion was verified by computed tomography scan. There was an improvement in patient status as observed by the increase of the SF-36 scale scores. The use of endoscopic transcervical approach is a good alternative to the transoral approach. Comparative studies of these methods should be performed regarding the choice of an optimal method of decompression in cases of IrAAD.

Stabilized Loading of Hyaluronic Acid-Containing Hydrogels into Magnesium-Based Cannulated Screws

Cannulated screws have a structure for inserting a guide wire inside them to effectively correct complicated fractures. Magnesium, an absorbable metal used to manufacture cannulated screws, may decompose in the body after a certain period of implantation. The hydrogel formed by hyaluronic acid (HA) and polygalacturonic acid (PGA) has been used into Mg-based cannulated screws to prevent bone resorption owing to the rapid corrosion of Mg with unfavorable mechanical properties and a high ambient pH. In addition, Ca ions were added to the gel for cross-linking the carboxyl groups to modify the gelation rate and physical properties of the gel. The developed hydrogels were injected into the Mg-based cannulated screws, after which they released HA and Ca. The possibility of the application of this system as a cannulated screw was evaluated based on the corrosion resistance, gel degradation rate, HA release, toxicity toward osteocytes, and experiments involving the implantation of the screws into the femurs of rats. Ca ions first bound to PGA and delayed the gelation time and dissolution rate. However, they interfered with HA binding and increased the elution of HA at the beginning of gel degradation. Ca(NO₃)₂ concentrations higher than 0.01 M and low pH environments inhibited osteoblast differentiation and proliferation, owing to the elution of HA from the hydrogel. On the other hand, when the HA hydrogel with a proper amount of Ca was inserted into a magnesium screw, the degradation of Mg was delayed, and the presence of the gel contributed to new bone formation and osteocyte expansion.

Short-Term Complications of Anterior Fixation of Odontoid Fractures

STUDY DESIGN

Retrospective study.

OBJECTIVE

Anterior fixation of odontoid fracture has been associated with high morbidity and mortality in small, single institution series. Identifying risk factors may improve risk stratification and highlight factors that could be optimized preoperatively. The objective of this study was to determine the 30-day complication rate following anterior fixation of odontoid fractures and to identify associated risk factors among patients in a large national database.

METHODS

Patients who underwent anterior fixation were identified in the American College of Surgeons National Quality Improvement Program database (ACS NSQIP) from 2007 to 2012. Patient demographics, medical comorbidities, perioperative complications, and postoperative complications up to 30 days were analyzed by univariate and multivariate analysis.

RESULTS

Overall, 103 patients met criteria for the study. The average age was 73.9 years and patients were predominantly white (85.4%). Cardiac comorbidity was common (66.0%), as were dependent functional status (14.6%) and bleeding disorders (13.6%). Complications occurred in 37.9% of patients, and mortality was high (6.8%). Age, white race, and history of bleeding disorders were independently predictive of complications in the multivariate analysis. The postoperative hospital stay was >5 days for 45.6% of patients.

CONCLUSION

In a large, multicenter database study, anterior fixation of odontoid fracture was associated with high morbidity and mortality. Although advanced age was associated with increased risk of complications, patients undergoing anterior fixation were older, on average, than in prior studies. Bleeding disorder was a potentially modifiable risk factor for complications that could be optimized prior to surgery.

Anterior single lag screw fixation in Type II Dens fracture – Indian experience

Increased rate of non-union of Type II Odontoid fractures with rigid external orthosis have been reported. Recently technique of direct anterior screw fixation of the odontoid fracture is being advocated. Here we report the results of 13 cases of Type II dens fracture treated by the above method with an age group ranging from 17 to 73 years. An approach identical to the anterior cervical discectomy was used. Guide tube system devised by Synthes®, single image intensifier and Langenberg retractors was used to place a single cannulated screw through the fracture from C2 body into the dens. Among the 13 cases operated, in 11 cases we were successful. In one case while dissecting the fracture site CSF leak occurred and in another case the guide wire broke leading to abandoning to screw placement. There was no other complication due to the surgical procedure. The follow up period ranged between 2 months to 3 1/2 years. There were no neurological complications or screw fracture. In 9 of the 11 cases (82%) either bony union or fibrous unions have occurred. These results indicate that direct anterior single screw fixation has proved to be a very successful treatment.

A Method to Prevent Occipitocervical Joint Violation Using Plain Radiography During Percutaneous Anterior Transarticular Screw Fixation

STUDY DESIGN

A prospective study of anterior transarticular screw (ATS) fixation patients.

OBJECTIVE

To develop a method to determine screw tip position through plain radiography after percutaneous ATS fixation to prevent occipitocervical joint (OCJ) violation.

SUMMARY OF BACKGROUND DATA

No studies using plain radiography to prevent OCJ violation during percutaneous ATS fixation have been performed.

METHODS

In total, 34 subjects (with 68 screws) who had undergone percutaneous ATS fixation were enrolled. To evaluate the screw tip location in relation to the C1 lateral mass (LM), the screw tip positions were graded 1, 2, or 3 on anteroposterior (AP) radiographs, and I, II, or III on lateral radiographs. OCJ violation was analyzed by postoperative computed tomography (CT).

RESULTS

Screws with tips located lower (tip I) in the LM did not result in OCJ violation. Only one tip in the tip 3 position showed OCJ perforation, and this screw was also located in tip III. Screw perforation rates of tip 1-tip II, tip 1-tip III, and tip 2-tip III were the highest (100%), followed by tip 2-tip II (10.5%) and tip3-tip III (10%).

CONCLUSION

This study provides insights into OCJ violation during percutaneous ATS fixation. According to AP radiography, a percutaneous ATS with the screw tip located in the lateral part of the LM resulted in a lower rate of OCJ perforation, whereas screws located in the medial LM resulted in the highest rate of perforation. Percutaneous ATS with the screw tip located in the neutral part of the LM should ensure that the screw tip is below the upper part of the LM, preventing OCJ violation. These findings may help surgeons assess screw positioning both during and after the operation.

LEVEL OF EVIDENCE

3.

Pooled analysis of non-union, re-operation, infection, and approach related complications after anterior odontoid screw fixation

Background

Anterior odontoid screw fixation (AOSF) has been one of the most popular treatments for odontoid fractures. However, the true efficacy of AOSF remains unclear. In this study, we aimed to provide the pooled rates of non-union, reoperation, infection, and approach related complications after AOSF for odontoid fractures.

Methods

We searched studies that discussed complications after AOSF for type II or type III odontoid fractures. A proportion meta-analysis was done and potential sources of heterogeneity were explored by meta-regression analysis.

Results

Of 972 references initially identified, 63 were eligible for inclusion. 54 studies provided data regarding non-union. The pooled non-union rate was 10% (95% CI: 7%–3%). 48 citations provided re-operation information with a pooled proportion of 5% (95% CI: 3%–7%). Infection was described in 20 studies with an overall rate of 0.2% (95% CI: 0%–1.2%). The main approach related complication is postoperative dysphagia with a pooled rate of 10% (95% CI: 4%–17%). Proportions for the other approach related complications such as postoperative hoarseness (1.2%, 95% CI: 0%–3.7%), esophageal/retropharyngeal injury (0%, 95% CI: 0%–1.1%), wound hematomas (0.2%, 95% CI: 0%–1.8%), and spinal cord injury (0%, 95% CI: 0%–0.2%) were very low. Significant heterogeneities were detected when we combined the rates of non-union, re-operation, and dysphagia. Multivariate meta-regression analysis showed that old age was significantly predictive of non-union. Subgroup comparisons showed significant higher non-union rates in age ≥70 than that in age ≤40 and in age 40 to <50. Meta-regression analysis did not reveal any examined variables influencing the re-operation rate. Meta-regression analysis showed age had a significant effect on the dysphagia rate.

Conclusions/Significances

This study summarized the rates of non-union, reoperation, infection, and approach related complications after AOSF for odontoid factures. Elderly patients were more likely to experience non-union and dysphagia.

Preliminary biomechanical proof of concept for a hybrid locking plate/variable pitch screw construct for anterior fixation of type II odontoid fractures

STUDY DESIGN

A human cadaveric biomechanical proof-of-concept study.

OBJECTIVE

To test whether adding a locking plate to the anterior surface of C2 attaching directly to the interfragmentary screw may reduce potential for anterior screw cutout and improve construct strength.

SUMMARY OF BACKGROUND DATA

The most common mode of failure for screw fixation of dens fractures is via cutout at the anterior body of C2.

METHODS

A human, cadaveric model of type II dens fractures was created and fixed using either a headless, fully threaded variable pitch screw (FTVPS) or a screw with an attachable locking plate construct (LPC). Following quasistatic loading to failure, stiffness and load to failure were compared using t tests. Mode of failure was determined from radiographical and gross inspection.

RESULTS

Load to failure was greater for the LPC than for the FTVPS alone (498 N vs. 362 N, P = 0.04). The LPC consistently failed via compression of cancellous bone posterior to the lag screw, whereas the FTVPS constructs failed via cutout of the screw from the anterior C2 body.

CONCLUSION

Locking plate supplementation of anterior screw fixation of type II odontoid fractures improves construct strength and changes the failure mechanism from anterior screw cutout to posterior displacement of the screw. An attachable locking plate/interfragmentary screw construct may improve clinical outcomes for these fractures.

Comparison of the anatomic risk for vertebral artery injury associated with percutaneous atlantoaxial anterior and posterior transarticular screws

BACKGROUND CONTEXT

As a minimally invasive spine surgery, percutaneous atlantoaxial fixation techniques using anterior transarticular screw (ATS) and posterior transarticular screw (PTS) have promising clinical results. However, transarticular screw fixation is technically demanding and carries a potential risk of iatrogenic vertebral artery (VA) injury. There were no available data comparing the anatomic risk of VA injury associated with these screws.

PURPOSE

To evaluate the trajectories of percutaneous atlantoaxial ATS and PTS through three-dimensional (3D) computerized tomography.

STUDY DESIGN

To compare the anatomic risk of VA injury between percutaneous ATS and PTS.

PATIENT SAMPLE

Sixty patients ranged in age from 19 to 75 years (mean, 45.08 years) and included 35 men and 25 women.

OUTCOME MEASURES

Image measurement of C2 isthmus height and C2 isthmus width and the distance between the medial-most superior articular facet to the medial-most edge of the VA groove of the C2 (D).

METHODS

Sixty consecutive patients (in total) with lower cervical lesions were evaluated through 3D images reconstructed by a rapid 3D system. The maximum possible diameters of the percutaneous atlantoaxial ATS and PTS trajectories were compared and examined. Mean, range, and standard deviations for each type of screw, for left and right trajectories, and for men and women were calculated from 120 percutaneous atlantoaxial ATS and PTS measurements through SPSS.

RESULTS

The maximum mean diameter differed significantly between the trajectories of 120 percutaneous atlantoaxial ATS and PTS. For screw trajectories ≤3.5 mm in diameter, 19.2% of the PTS trajectories were judged as risky, whereas all the anterior ones were judged as safe.

CONCLUSIONS

From an anatomic perspective, percutaneous ATS fixation poses less anatomic risk of VA injury than percutaneous PTS fixation. As an alternative surgical therapy for atlantoaxial subluxation, percutaneous ATS fixation may play a more important role in the future.

Guidewire breakage: an unusual complication of anterior odontoid cannulated screw fixation

The preferred treatment of a type II odontoid fracture is anterior odontoid screw fixation to preserve the cervical spine range of movement. This case report describes an unusual complication of guidewire breakage during anterior odontoid cannulated screw fixation for a 52-year-old patient who presented with a type II odontoid fracture after a motor vehicle accident. The distal segment of the guidewire was bent over the tip of the cannulated odontoid screw and broke off during guidewire withdrawal. The three months follow-up computed tomography examination of the cervical spine showed acceptable screw placement, good odontoid process alignment with incomplete fusion, and no migration of the fractured segment of the guidewire. It is recommended that the guidewire be withdrawn once the cannulated screw is passed through the fractured site into the odontoid process and a new guidewire be used in each surgical procedure instead of been reused to avoid metal stress fatigue that can result in easy breakage.

Avoiding pitfalls in anterior screw fixation for Type II odontoid fractures

Anterior screw fixation of Type II odontoid fractures provides immediate stabilization of the cervical spine while preserving C1–2 motion. This technique has a high fusion rate, but can be technically challenging. The authors identify key points that should be taken into account to maximize the chance for a favorable outcome. Keys to success include proper patient and fracture selection, identification of suitable screw entry point and correct screw trajectory, achieving bicortical purchase, and placing 2 screws when feasible and applicable. The authors review the operative technique and present guidance on appropriate patient selection and common pitfalls in anterior screw fixation, with strategies for avoiding complications.

A novel technique of odontoidoplasty and C1 arch reconstruction: anatomical and biomechanical basis

BACKGROUND

Transoral odontoidectomy and resection of the anterior C1 arch destabilize the atlantoaxial joint and risk its stability.

OBJECTIVE

To preserve stability in such cases we devised and evaluated a proof-of-concept study. The arch and dens were dissected and decompression was performed on cadavers. The dens was replaced with an odontoid screw, and the C1 arch was replaced with a rib-graft substitute using miniplates. We assessed the biomechanical strength of the C1 ring and 3D occipitoatlantoaxial flexibility before and after the repair.

METHODS

Five silicon-injected fixed cadaver heads were dissected. The arch of C1 and dens were preserved and reconstructed using odontoid screws and miniplates. Once the feasibility of the technique was established, we biomechanically tested 6 cadaveric occiput-C2 specimens in 3 phases: (1) intact/normal range of motion (ROM), (2) after transection of dens and C1 arch, and (3) with odontoidoplasty using odontoid screws and C1 arch reconstruction.

RESULTS

After odontoidectomy and arch removal, angular ROM increased significantly in all directions of loading. Resection increased flexion-extension at the occiput-C1 and at C1-C2 by 21% and 129%, respectively. Reconstruction slightly increased flexion-extension stability (16% and 107%, respectively) relative to normal.With 70 N applied compression, the C1 ring separation was 1145% greater than normal. After reconstruction, the separation was only 89% greater than normal (statistically significant, P = .002).

CONCLUSION

C1 arch reconstruction with or without odontoidoplasty restores only partial angular stability of the atlantoaxial joint but provides restoration of the ability of the C1 lateral masses to resist splaying, often observed as postodontoidectomy cranial settling.

Decisão no tratamento das fraturas do odontoide

OBJETIVO: avaliação e determinação de critérios que possam nortear o tratamento das fraturas do odontoide. MÉTODOS: foi realizado estudo retrospectivo e comparativo entre o tratamento conservador e o cirúrgico do odontoide em 24 pacientes com fratura decorrente de trauma. Os pacientes foram avaliados por meio de exame clínico e radiológico e o tratamento efetuado foi avaliado por meio de testes descritivos, distribuição de frequências e testes estatísticos comparativos. RESULTADOS: foram observados 17 pacientes do sexo masculino (70,8%) e 7 do sexo feminino (29,2%), com idades entre 12 e 80 anos (média de 39 anos) e seguimento pós-tratamento de 12 a 110 meses. Em relação às fraturas, não foram observadas fraturas do tipo I, 17 casos apresentaram fratura do tipo II (70,8%) e 7 do tipo III (29,2%), classificadas segundo Anderson e D'Alonzo. A decisão pelo tratamento cirúrgico ou conservador ocorreu em função de critérios de redução e instabilidade. Quando se decidia pelo tratamento cirúrgico, era utilizado o acesso de Southwick-Robinson, utilizando-se um parafuso canulado para a fixação da fratura. Nos pacientes tratados conservadoramente, optou-se pelo halo-gesso ou colar cervical tipo Philadelphia. Independentemente do tipo da fratura, a consolidação ocorreu em média em três meses para os pacientes tratados cirurgicamente, enquanto as fraturas tratadas conservadoramente consolidaram em torno de cinco meses. CONCLUSÕES: apesar de haver uma tendência à consolidação mais rápida quando é realizado o tratamento cirúrgico, o tratamento conservador deve ser considerado, tendo em vista os critérios de redução e instabilidade.

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.

Biomechanical comparison of occipitoatlantal screw fixation techniques

Object

The stability provided by 3 occipitoatlantal fixation techniques (occiput [Oc]–C1 transarticular screws, occipital keel screws rigidly interconnected with C-1 lateral mass screws, and suboccipital/sublaminar wired contoured rod) were compared.

Methods

Seven human cadaveric specimens received transarticular screws and 7 received occipital keel–C1 lateral mass screws. All specimens later underwent contoured rod fixation. All conditions were studied with and without placement of a structural graft wired between the skull base and C-1 lamina. Specimens were loaded quasistatically using pure moments to induce flexion, extension, lateral bending, and axial rotation while recording segmental motion optoelectronically. Flexibility was measured immediately postoperatively and after 10,000 cycles of fatigue.

Results

Application of Oc–C1 transarticular screws, with a wired graft, reduced the mean range of motion (ROM) to 3% of normal. Occipital keel–C1 lateral mass screws (also with graft) offered less stability than transarticular screws during extension and lateral bending (p < 0.02), reducing ROM to 17% of normal. The wired contoured rod reduced motion to 31% of normal, providing significantly less stability than either screw fixation technique. Fatigue increased motion in constructs fitted with transarticular screws, keel screws/lateral mass screw constructs, and contoured wired rods, by means of 19, 5, and 26%, respectively. In all constructs, adding a structural graft significantly improved stability, but the extent depended on the loading direction.

Conclusions

Assuming the presence of mild C1–2 instability, Oc–C1 transarticular screws and occipital keel–C1 lateral mass screws are approximately equivalent in performance for occipitoatlantal stabilization in promoting fusion. A posteriorly wired contoured rod is less likely to provide a good fusion environment because of less stabilizing potential and a greater likelihood of loosening with fatigue.

Biomechanical comparison of a fully threaded, variable pitch screw and a partially threaded lag screw for internal fixation of Type II dens fractures

STUDY DESIGN

Stiffness and load to failure were studied in a human cadaver model of Type II odontoid fractures stabilized with either a single partially threaded lag screw and washer or a headless fully threaded variable pitch screw.

OBJECTIVE

To determine whether a headless fully threaded variable pitch screw provides biomechanically superior fixation of Type II odontoid fractures in comparison with a partially threaded, cannulated lag screw and washer.

SUMMARY OF BACKGROUND DATA

Surgical treatment of Anderson and D'Alonzo Type II odontoid fractures is often performed using a partially threaded cannulated screw and washer. Reported clinical failure rates of this construct are as high as 20%. This technique requires perforation of the cortex of the tip of the dens, placing the brainstem and vertebrobasilar circulation at risk. A headless fully threaded variable pitch screw has not been described for this application.

METHODS

A transverse osteotomy was created at the base of the dens in 16 human cadaver C2 specimens and stabilized using either a headless fully threaded variable pitch screw or a partially threaded cannulated lag screw and washer. Specimens were loaded to failure under a static, posteriorly directed force applied to the surface of the dens. Stiffness and load to failure were measured and the mode of failure for each specimen was determined.

RESULTS

Stiffness and load to failure were greater for the headless, fully threaded variable pitch screw compared with the partially threaded lag screw and washer. The mode of failure for all specimens was via anterior screw cut-out at the C2 vertebral body.

CONCLUSION

A headless, fully threaded variable pitch screw was biomechanically favorable in comparison with a partially threaded lag screw and washer in this cadaver model of Type II dens fractures. The mode of failure at the C2 vertebral body may have important implications for further improvements in construct strength.

Management of odontoid fractures with percutaneous anterior odontoid screw fixation

Minimally invasive techniques have revolutionized the management of a variety of spinal disorders. The authors of this study describe a new instrument and a percutaneous technique for anterior odontoid screw fixation, and evaluate its safety and efficacy in the treatment of patients with odontoid fractures. Ten patients (6 males and 4 females) with odontoid fractures were treated by percutaneous anterior odontoid screw fixation under fluoroscopic guidance from March 2000 to May 2002. Their mean age at presentation was 37.2 years (with a range from 21 to 55 years). Six cases were Type II and four were Type III classified by the Anderson and D'Alonzo system. The operation was successfully completed without technical difficulties, and without any soft tissue complications such as esophageal injury. No neurological deterioration occurred. Satisfactory results were achieved in all patients and all of the screws were in good placement. After a mean follow-up of 15.7 months (range 10-25 months), radiographic fusion was documented for 9 of 10 patients (90%). Neither clinical symptoms nor screw loosening or breakage occurred. Our preliminary clinical results suggest that the percutaneous anterior odontoid screw fixation procedure using a new instrument and fluoroscopy is technically feasible, safe, useful, and minimally invasive.

Biomechanical comparison of two new atlantoaxial fixation techniques with C1–2 transarticular screw–graft fixation

Object

Two new techniques for atlantoaxial fixation have been recently described. In one technique, C-2 intra-laminar screws are connected with C-1 lateral mass screws; in the second, C-1 and C-3 lateral mass screws are interconnected and C-2 is wired sublaminarly. Both techniques include a C1–2 interspinous graft. The authors compared these techniques with the gold-standard, interspinous graft–augmented C1–2 transarticular screw fixation and with a control C1–2 interspinous graft fixation procedure alone.

Methods

In six human cadaveric occiput–C4 specimens, nonconstraining 1.5-Nm pure moments were applied to induce flexion, extension, lateral bending, and axial rotation during which three-dimensional angular motion was measured optoelectronically. Each specimen was tested in the normal state, with graft alone (after odontoidectomy), and then in varying order after applying each construct with a rewired graft. All three constructs allowed significantly less angular motion at the C1–2 junction than the wired interspinous graft alone during lateral bending and axial rotation (p < 0.01, paired Student t-test) but not during flexion or extension. Transarticular screw fixation with an interspinous graft allowed less motion at the atlantoaxial junction than the two new constructs in several conditions. Differences were greater between the transarticular screw construct and the intralaminar screw construct than between the transarticular screw construct and the C1–3 lateral mass screw construct. During lateral bending and axial rotation, the C1–3 construct allowed less motion at the atlantoaxial junction than the intralaminar screw construct.

Conclusions

Biomechanically, the gold-standard C1–2 transarticular screw fixation outperformed the two new techniques during lateral bending and axial rotation. Wiring C-2 to C1–3 rods provided greater stability than C1–2 laminar screws, but it sacrificed C2–3 mobility. It is unknown whether the small differences observed biomechanically would lead to clinically relevant differences in fusion rates.

Biomechanical comparison of four C1 to C2 rigid fixative techniques: anterior transarticular, posterior transarticular, C1 to C2 pedicle, and C1 to C2 intralaminar screws

OBJECTIVE

We performed a biomechanical comparison of several C1 to C2 fixation techniques including crossed laminar (intralaminar) screw fixation, anterior C1 to C2 transarticular screw fixation, C1 to 2 pedicle screw fixation, and posterior C1 to C2 transarticular screw fixation.

METHODS

Eight cadaveric cervical spines were tested intact and after dens fracture. Four different C1 to C2 screw fixation techniques were tested. Posterior transarticular and pedicle screw constructs were tested twice, once with supplemental sublaminar cables and once without cables. The specimens were tested in three modes of loading: flexion-extension, lateral bending, and axial rotation. All tests were performed in load and torque control. Pure bending moments of 2 nm were applied in flexion-extension and lateral bending, whereas a 1 nm moment was applied in axial rotation. Linear displacements were recorded from extensometers rigidly affixed to the C1 and C2 vertebrae. Linear displacements were reduced to angular displacements using trigonometry.

RESULTS

Adding cable fixation results in a stiffer construct for posterior transarticular screws. The addition of cables did not affect the stiffness of C1 to C2 pedicle screw constructs. There were no significant differences in stiffness between anterior and posterior transarticular screw techniques, unless cable fixation was added to the posterior construct. All three posterior screw constructs with supplemental cable fixation provide equal stiffness with regard to flexion-extension and axial rotation. C1 lateral mass-C2 intralaminar screw fixation restored resistance to lateral bending but not to the same degree as the other screw fixation techniques.

CONCLUSION

All four screw fixation techniques limit motion at the C1 to 2 articulation. The addition of cable fixation improves resistance to flexion and extension for posterior transarticular screw fixation.

The contemporary treatment of odontoid injuries

STUDY DESIGN

Review article.

OBJECTIVE

To outline current concepts regarding the assessment and treatment of odontoid fractures.

SUMMARY OF BACKGROUND DATA

Odontoid fractures account for 9% to 15% of adult, cervical spine fractures. These injuries usually result from hyperflexion or hyperextension of the cervical spine during low-energy impacts in the elderly or high-energy impacts in the young and middle aged. Neurologic injury associated with these fractures is rare.

METHODS

A review of pertinent literature was conducted. The information gleaned from this review was summarized.

RESULTS

Odontoid fractures should be evaluated with appropriate imaging to assess the fracture itself as well as exclude other contiguous or noncontiguous fractures. The Anderson and D'Alonzo classification system is most commonly used. True type I and III odontoid fractures are generally thought to be relatively stable and are often treated nonoperatively with immobilization. Type II fractures at the base of the odontoid are less stable, and there are differing opinions regarding the precise definition and optimal treatment of these injuries. Nonoperative treatment options for odontoid fractures include external immobilization with a collar or halo. Operative treatment options for odontoid fractures include one of several posterior C1-C2 fusion constructs or anterior odontoid fixation if the fracture pattern is amenable.

CONCLUSIONS

Despite the frequency of odontoid fractures, there is still much debate regarding the optimal treatment of these fractures, especially the type II fractures. This fact may be because of the absence of an ideal solution for this clinical problem. Certainly, prospective controlled clinical studies are needed.

Posterior atlantoaxial three-point fixation: comparison of intraoperative performance between open and percutaneous techniques

INTRODUCTION

Atlantoaxial instabilities, which require surgical fixation follow a variety of clinical disorders. Different surgical procedures are used for stabilization of the atlantoaxial complex, mainly posterior wiring techniques and transarticular screw fixation. Nowadays, often a combination of transarticular screws and a posterior one-point fixation is used to achieve a three-point fixation, with superior biomechanical stability and good clinical results. Different modifications were developed to improve this technique. In 1995, a percutaneous approach for atlantoaxial stabilization was introduced. In clinical studies, the technique showed a tendency towards better outcome. Beside the outcome, the intraoperative performance is of special interest for minimal invasive approaches. We therefore compared the operation time, screw angulation and blood loss, between the open and percutaneous posterior atlantoaxial techniques.

MATERIALS AND METHODS

Two groups, each consisting of 17 patients, with either open (group 1) or percutaneous (group 2) atlantoxial stabilization, were compared. The operation time was retrospectively acquired from the patient's charts. The data for blood loss was provided by our anaesthesiological department, separated for intraoperative, postoperative and total blood loss. Screw angulation was measured on the postoperative x-ray by an orthopaedic surgeon.

RESULTS

The percutaneous group showed an average intraoperative blood loss of 239.7 ml, compared to 929.4 ml for the open group (p< or =0.001). The analogue values for the postoperative blood loss were 142.9 ml and 379.4 ml for group 2 and group 1, respectively (p=0.008). Consecutively, the total blood loss showed also a statistically significant difference (p< or =0.001). The operation time was significantly different (p< or =0.001), with average values of 175.3 min (group 1) and 110.6 min (group 2). Screw angulation showed a trend towards a steeper angulation in the percutaneous group with an average angle of 56.8 degrees , compared to 53.9 degrees (group 1), although this was not statistically significant (p=0.053).

CONCLUSION

The percutaneous technique for atlantoaxial stabilization with a three-point fixation has clear intraoperative benefits, with shorter operation time and reduced blood loss. A trend towards steeper screw angulation was found and shows at least equal feasibility for transarticular screw placement with the percutaneous technique, compared to the standard open approach.

Die rheumatisch bedingte Instabilität der oberen Halswirbelsäule

Rheumatic manifestation at the cervical spine occurs in more than 50% of all cases in the natural course of this disease. The first cervical manifestation takes place in the upper cervical spine. The initial involvement of the C1/C2 segment leads to atlantodental subluxation. Progressive destruction can result in vertical instability, which is characterized by cranial subluxation of the odontoid process with the danger of resulting stenosis and cervical myelopathy. The goal of diagnosis has to be the early recognition of these changes to establish an effective treatment protocol. Persistent pain, neurological deficits, and progressive radiological signs for instability are indications for operative stabilizing procedures. These procedures avoid progressive destruction and improve the prognosis regarding pain decrease, regression of neurological deficits, and life expectancy.

Virtual placement of posterior C1-C2 transarticular screw fixation

We wanted to evaluate how often safe and effective posterior C1-C2 transarticular screw placement is realizable when it is performed according to guidelines given in the literature. In 50 adult patients, computerized tomography scan data from C0 to C3 were transformed into a 3D spine model. Virtually, bilateral screws were placed from the medial third of the C2-C3 facet joint towards the rim of the C1 anterior arc parallel to midline. Three categories of virtual screw position were rated: optimal (virtual screw inside the C2 pars interarticularis, transversing the middle third of the atlantoaxial joint, and sparing the vertebral artery canal), suboptimal (virtual screw violating the C2 pars interarticularis, and/or transversing the lower or upper third of the C1-C2 joint, and sparing vertebral artery canal), and unacceptable (virtual screw breaching the vertebral artery canal). Optimal placement was seen in 74, suboptimal placement in 11, and unacceptable locations in 15 sites. We conclude that due to the variability of the anatomy of the upper cervical spine, optimal transarticular C1-C2 screw placement is not possible in up to 26%, and even hazardous in up to 15%.

Frameless Stereotactic Image-Guided C1-C2 Transarticular Screw Fixation for Atlantoaxial Instability

OBJECTIVE

We retrospectively studied 20 adults who underwent C1-C2 transarticular screw (TAS) fixation utilizing frameless stereotaxy.

METHODS

The study group comprised 13 men and 7 women, with a mean age of 63 years (range 12-87 years). All patients demonstrated clinical and radiographic evidence of C1-C2 instability. The cause of the instability was trauma in 11 patients, rheumatoid arthritis in 6 patients, failed prior surgery in 2 patients, and congenital malformation in 1 patient. All patients underwent stabilization with C1-C2 TASs using image-guided frameless stereotaxy.

RESULTS

There were no new or worsening neurologic symptoms reported at 18-month follow-up. Motor weakness improved in seven of nine patients, myelopathy in seven of seven, and gait in three of six patients in whom these deficits were present preoperatively. Postoperative complications included one surgical site abscess, one cutaneous pressure ulcer, and one iliac crest donor site infection. Of 36 screws placed, 33 (92%) were well positioned. Normal C1-C2 alignment was achieved in 17 of 20 (85%) patients. In 4 of 20 cases, screw implant, which was thought to be anatomically difficult, if not impossible, on the basis of routine magnetic resonance or computed tomography imaging, was actually accomplished successfully using surgical navigation.

CONCLUSIONS

C1-C2 TAS placement is a safe and accurate surgical technique that may improve neurologic function. Use of intraoperative navigation can facilitate achieving difficult surgical trajectories that match the patient's anatomy, thus allowing TAS implant in patients who otherwise would not be candidates for this type of internal fixation.

A safe screw trajectory for atlantoaxial transarticular fixation achieved using an aiming device

STUDY DESIGN

A retrospective evaluation and characterization of the trajectory of atlantoaxial transarticular screws inserted using an aiming device.

OBJECTIVES

To confirm that the screws were inserted through the safest trajectory, which is through the most dorsal and medial part of the isthmus of C2, and to characterize the trajectory on lateral radiograms by comparison with historical controls.

SUMMARY OF BACKGROUND DATA

Posterior atlantoaxial transarticular screw fixation entails the potential risk of vertebral artery (VA) injury, which may be lethal. Although much literature recommends that the screws should be inserted aiming at the anterior arch of C1, the authors considered that the safest screw path is via the most dorsal and medial part of the isthmus regardless of the C1 anterior arch, and have used an original aiming device to achieve this trajectory.

METHODS

Forty-three consecutive patients who submitted to atlantoaxial transarticular screw fixation using the aiming device were evaluated for screw position using computed tomography (CT) and lateral radiogram. The medialization index (the distance between the screw and the cortex of the spinal canal of C2 on axial CT) and the dorsalization index (the thickness of the bone remaining dorsal to the screw at the isthmus of C2 on sagittal reconstruction CT) were measured. Further, three parameters on the lateral radiograms of these patients were compared with those in the literature and those of our previous cases performed without the aiming device.

RESULTS

Neither VA injury nor violation of the spinal canal was encountered, although 12 high-riding VAs were included in this series. The mean medialization index was 0.21 mm, and the indexes of 86.3% of the screws were zero. The mean dorsalization index was 0.36 mm, and the indexes of 76.8% of the screws were zero. These results demonstrated that most of the screws were inserted as aimed, proving the usefulness of the aiming device. The trajectory of these screws on lateral radiograms was characterized by significantly less bone thickness dorsal to the screw at the isthmus compared with the two control groups. As a result, more screws were pointed above the anterior arch of C1.

CONCLUSIONS

The atlantoaxial transarticular screw was inserted safely as aimed by using the aiming device. The trajectory was characterized by less bone thickness dorsal to the screw on lateral radiogram, which should be a new intraoperative landmark for screw insertion, in place of the anterior arch of C1.

An anatomical study comparing standard fluoroscopy and virtual fluoroscopy for the placement of C1–2 transarticular screws

Object. The authors sought to compare radiation exposure, surgical time, and accuracy of screw placement when using either standard fluoroscopy or virtual fluoroscopy for the placement of C1–2 transarticular screws.

Methods. Twenty-two C1–2 transarticular screws were placed in 11 cadavers in a randomized and alternating order by using either standard fluoroscopy or virtual fluoroscopy (fluoronavigation). The radiation time, procedure time, and accuracy of screw placement were recorded and statistically compared. A small but statistically significant reduction in fluoroscopy time was noted with the virtual fluoroscopy technique but the surgical times were similar between the two techniques. The incidence of noncritical and critical breaches (those at risk of causing a neurovascular injury) was not significantly different between the two groups. Careful analysis of the C1–2 anatomy in these specimens underscored the importance of placing the screw path in a maximally dorsal and medial portion of the C-2 isthmus to avoid injury to the vertebral artery and to maximize the bone purchase of the C-1 lateral mass.

Conclusions. Although virtual fluoroscopy may represent a useful tool for transarticular screw placement, it does not supplant traditional surgical techniques and does not appear to lower the incidence of bone breaches that can occur when performing this demanding procedure.

Atlantooccipital transarticular screw fixation for the treatment of traumatic occipitoatlantal dislocation

✓ The authors describe a new technique of internal atlantooccipital screw fixation involving posterior wiring and fusion for the treatment of traumatic atlantooccipital dislocation, which was performed in a 17-year-old male patient involved in a motor vehicle accident and who suffered from atlantooccipital dislocation without neurological injury. At the 6-month follow-up examination, the patient was neurologically intact with a solid occipitocervical fusion and full range of motion of the neck.

Management of acute odontoid fractures with single anterior screw fixation

The use of anterior odontoid screw fixation has grown in popularity for the management of acute, unstable Anderson and d'Alonzo Type II and rostral Type III odontoid fractures. This study critically reviews our clinical experience of 48 patients with single odontoid screw fixation for the treatment of Type II and Type III odontoid fractures between 1997 and 2001. This series had a complication rate of 10% (malposition rate 6% and non-union rate 4%), with a satisfactory overall fusion rate of 96%. Odontoid screw fixation is technically demanding and requires strict patient selection, thorough preoperative planning and careful surgical technique. In our experience, advanced age should not be considered a contraindication to anterior odontoid screw fixation, as satisfactory results can be obtained in some of these patients. This study also emphasises that sagittally oblique type II fractures are associated with a high rate of fusion failure when treated by anterior odontoid screw fixation, and should be treated with other instrumentation methods, such as posterior atlantoaxial arthrodesis.

Posterior transarticular screw fixation for chronic atlanto-axial instability

Treatment for chronic atlanto-axial instability remains problematic despite recent innovations in new surgical techniques and instrumentation. Our team reviewed a series of 23 cases of patients with chronic atlanto-axial instability who underwent posterior transarticular screw fixation operations between May 1998 and September 2002. Etiologies of these patients included failed prior surgery, rheumatoid arthritis, congenital anomalies and old odontoid fractures. The clinical presentations were nuchal pain and cervical myelopathy or radiculopathy, with sensory and/or motor deficits that persisted for more than 3 months. We routinely used external reduction to realign the C1-C2 axis prior to operating, and operated on patients using halo-vest fixation. After surgery, the halo-vest was replaced by a collar. In the post-operative follow-up, 22 of the 23 patients (96%) were found to have achieved solid, bony or fibrous union of the C1-C2 axis. Eleven of the 14 (79%) patients with pre-operative neck pain experienced immediate relief or significant improvement. Thirteen of the 20 patients (65%) with myelo-radiculopathy demonstrated improvement of previous motor deficits. Major morbidity included a vertebral artery (VA) injury and a malpositioned screw. No cases of mortality or neurological complications occurred in this series. Posterior transarticular C1-C2 screw fixation results in a high fusion rate without the additional need for rigid external immobilization. It allows good neurological recovery in cases of chronic atlanto-axial instability. Judicious pre-surgical planning and meticulous operative technique may avoid neurological complications and vertebral artery injury.

Craniovertebral junction fixation with transarticular screws: biomechanical analysis of a novel technique

OBJECT

The authors compared the biomechanical stability resulting from the use of a new technique for occipitoatlantal motion segment fixation with an established method and assessed the additional stability provided by combining the two techniques.

METHODS

Specimens were loaded using nonconstraining pure moments while recording the three-dimensional angular movement at occiput (Oc)-C1 and C1-2. Specimens were tested intact and after destabilization and fixation as follows: 1) Oc-C1 transarticular screws plus C1-2 transarticular screws; 2) occipitocervical transarticular (OCTA) plate in which C1-2 transarticular screws attach to a loop from Oc to C-2; and (3) OCTA plate plus Oc-C1 transarticular screws. Occipitoatlantal transarticular screws reduced motion to well within the normal range. The OCTA loop and transarticular screws allowed a very small neutral zone, elastic zone, and range of motion during lateral bending and axial rotation. The transarticular screws, however, were less effective than the OCTA loop in resisting flexion and extension.

CONCLUSIONS

Biomechanically, Oc-C1 transarticular screws performed well enough to be considered as an alternative for Oc-C1 fixation, especially when instability at C1-2 is minimal. Techniques for augmenting these screws posteriorly by using a wired bone graft buttress, as is currently undertaken with C1-2 transarticular screws, may be needed for optimal performance.

Anatomic study of the axis for surgical planning of transarticular screw fixation

Transarticular screw fixation has shown increased stability compared with other posterior stabilization techniques. However, there have been few reports on vertebral artery injury related to the screw insertion. The current study measured the parameters of the pedicle and vertebral artery groove of the axis and clarified the accuracy and safety of the transarticular screw fixation. Direct measurements were taken from 98 dry axis vertebrae. The width and height of the pedicle were measured. The mediolateral and anteroposterior dimensions of the vertebral artery groove also were measured. Forty-one percent had asymmetry. In 20% of the specimens, the pedicle was smaller than the diameter of the screw (3.5 mm). The pedicle of the axis has large anatomic variability and asymmetry. Some pedicles were not suitable for atlantoaxial transarticular screw fixation. The risks associated with screw fixation should be prevented by preoperative computed tomography with three-dimensional reconstruction. Screw trajectory reconstruction with coronal and sagittal reconstruction is useful to evaluate the pedicle width and height.

Tratamento cirúrgico das fraturas do odontóide tipo II com parafuso anterior: análise de 15 casos

Apresentamos estudo retrospectivo dos resultados de 15 pacientes consecutivos, com fratura do odontóide tipo II P (fratura com traço oblíquo e deslocamento posterior) e II N (fratura com traço horizontal na base do odontóide), segundo a classificação de Roy-Camille , que foram submetidos a fixação anterior direta do odontóide com parafuso. A série é composta por 13 homens e 2 mulheres, com idade variando entre 14 a 74 anos e período de acompanhamento de 6 a 36 meses (média 20 meses). Tivemos apenas uma complicação relacionada com a técnica cirúrgica: um parafuso mal posicionado necessitando de uma reoperação para ser reposicionado. Não houve óbito. Não houve saída nem quebra de parafuso. Obteve-se 94% de fusão óssea. Propomos que seja utilizada a classificação de Roy-Camille na seleção dos casos cirúrgicos de fraturas do odontóide, pois ela fornece uma abordagem cirúrgica específica para cada tipo de fratura.

Posterior atlantoaxial fixation: biomechanical in vitro comparison of six different techniques

STUDY DESIGN

Six different techniques for atlantoaxial fixation were biomechanically compared in vitro by nondestructive testing.

OBJECTIVE

To evaluate the immediate three-dimensional stability of a new atlas claw combined with transarticular screws and alternative techniques for transarticular screw fixation in comparison with established techniques.

SUMMARY OF BACKGROUND DATA

Posterior transarticular screw fixation in combination with wire-bone graft constructs is frequently used for C1-C2 fixation. Sublaminar wire passage carries the potential risk of neurologic complication. Transarticular screw fixation is technically demanding and, for anatomic reasons, not always feasible.

METHODS

Six human cervical specimens were loaded nondestructively with pure moments, and unconstrained motion at C1-C2 was measured. The six specimens were instrumented with each of the following fixation techniques: Gallie fixation, transarticular screws and Gallie fixation, transarticular screws, transarticular screws and a new atlas claw, isthmic screws in the axis and the atlas claw, and lateral mass screws in the atlas and isthmic screws in the axis connected with rods.

RESULTS

The transarticular screws restricted lateral bending and axial rotation best. The three-point fixations (transarticular + Gallie and transarticular + claw) additionally restricted flexion-extension, with lowest values for transarticular screws and the atlas claw. The alternative techniques were not as stable as the three-point fixations, but more stable than the Gallie fixation.

CONCLUSIONS

Biomechanically, the three-point fixation with transarticular screws and the atlas claw provides a rigid internal fixation that is not dependent on bone graft and sublaminar wiring. In cases wherein transarticular screws are not feasible, the isthmic screws and claw or the lateral mass screws and isthmic screws are biomechanical alternatives with less immediate stability.

Anatomic suitability of the C1-C2 complex for pedicle screw fixation

STUDY DESIGN AND OBJECTIVES

A computed tomography (CT) study of 60 consecutive patients (120 sides) was performed to assess suitability for either transarticular or pedicle screw fixation.

SUMMARY OF BACKGROUND DATA

A C1 lateral mass and C2 pedicle screw fixation with a rigid cantilever beam system has been described. The anatomic constraints relevant for this technique have not.

METHODS

Fifty consecutive patients underwent standard CT of the cervical spine. Pedicle and transarticular screw trajectories were plotted, and the maximum safe diameter for screw placement was determined for each trajectory. Also, trajectories were plotted in 10 additional patients with known craniocervical junction abnormalities using three-dimensional (3-D) imaging and computer-aided navigation tools. Screw placement was considered feasible if a 4-mm diameter trajectory could be plotted without impingement on neural or vascular structures.

RESULTS

Four-millimeter diameter pedicle screws could be placed in 91 of 100 C2 pedicles in the CT studies and in 20 of 20 pedicles in the 3-D studies. Four-millimeter diameter C1-C2 transarticular screws could be placed in 94 of 100 sides in the CT study and in 19 of 20 sides in the 3-D study. Four sides could tolerate a C2 pedicle screw and not a transarticular screw; the opposite situation existed in five sides. Placement of screws into C1 was not an issue in any patient. The mean maximum diameter of potential transarticular screws was 6.5 mm, and the mean maximum diameter of the pedicle screws was 5.3 mm (P < 0.01).

CONCLUSIONS

C1-C2 pedicle screw fixation is a technique that appears to be widely applicable and may represent an alternative fixation technique in selected patients.

Isolated fractures of the axis in adults

FRACTURES OF THE ODONTOID:

STANDARDS

There is insufficient evidence to support treatment standards.

GUIDELINES

Type II odontoid fractures in patients 50 years and older should be considered for surgical stabilization and fusion.

OPTIONS

Type I, Type II, and Type III fractures may be managed initially with external cervical immobilization. Type II and Type III odontoid fractures should be considered for surgical fixation in cases of dens displacement of 5 mm or more, comminution of the odontoid fracture (Type IIA), and/or inability to achieve or maintain fracture alignment with external immobilization. TRAUMATIC SPONDYLOLISTHESIS OF THE AXIS (HANGMAN'S FRACTURE):

STANDARDS

There is insufficient evidence to support treatment standards.

GUIDELINES

There is insufficient evidence to support treatment guidelines.

OPTIONS

Traumatic spondylolisthesis of the axis may be managed initially with external immobilization in most cases. Surgical stabilization should be considered in cases of severe angulation of C2 on C3 (Francis Grade II and IV, Effendi Type II), disruption of the C2--C3 disc space (Francis Grade V, Effendi Type III), or inability to establish or maintain alignment with external immobilization. FRACTURES OF THE AXIS BODY (MISCELLANEOUS FRACTURES):

STANDARDS

There is insufficient evidence to support treatment standards.

GUIDELINES

There is insufficient evidence to support treatment guidelines.

OPTIONS

External immobilization is recommended for treatment of isolated fractures of the axis body.

C1-C2 pedicle screw fixation with rigid cantilever beam construct: case report and technical note

OBJECTIVE AND IMPORTANCE

Transarticular screw fixation of the C1-C2 complex provides immediate rigid fixation of the unstable spine. The technique is not feasible in a certain proportion of patients because of the position of the vertebral artery or the patient's body habitus.

CLINICAL PRESENTATION

The authors describe a rigid screw technique for the surgical treatment of a woman who was excluded as a candidate for C1-C2 transarticular screw fixation.

TECHNIQUE

C1-C2 pedicle screw fixation was achieved using a fixed moment arm cantilever beam system. This system provided immediate rigid fixation of the C1-C2 complex in a patient who was not a candidate for transarticular screw fixation.

CONCLUSION

This technique is technically more forgiving than posterior transarticular screw fixation and may be applied to a broader spectrum of patients.

Accuracy of atlantoaxial transarticular screw insertion

STUDY DESIGN

The accuracy and safety of atlantoaxial transarticular screw insertion were evaluated in clinical cases.

OBJECTIVES

To evaluate the accuracy and safety of atlantoaxial transarticular screw insertion under lateral fluoroscopic monitoring without opening the joint.

SUMMARY OF BACKGROUND DATA

Atlantoaxial transarticular screw fixation has been reported to be biomechanically superior to posterior atlantoaxial wiring techniques. Several clinical series have been reported in the literature. In some reports, the risk of screw insertion in this technique has been pointed out.

MATERIALS AND METHODS

Fifty-six consecutive patients with atlantoaxial instability were treated by transarticular screw fixation. One hundred twelve screw insertions in these 56 patients were assessed by surgical record and computed tomographic examination. One screw could not be inserted because of the difficulty of adequate placement during operation; 111 screws were therefore inserted. Adequate position was defined as when the screw perforated the lateral atlantoaxial joint.

RESULTS

In this series, neither vertebral artery injury nor spinal cord injury was experienced clinically. One guide wire was broken during drilling with a cannulated drill. Computed tomographic examination demonstrated that 106 screws perforated the atlantoaxial joint. Therefore, 95.5% of screws were adequately positioned. There were two screws positioned lateral to the joint, two medially, and one anteroinferiorly to the joint.

CONCLUSIONS

Atlantoaxial transarticular screw insertion using image intensifier without opening the lateral joint was performed safely, but not accurately, in all cases.

Management of acute odontoid fractures: operative techniques and complication avoidance

In this article the authors describe the management of Type II odontoid fractures with special attention to operative technique and avoidance of complication. Anterior odontoid screw fixation is a procedure the authors have performed over the last 8 years in cases with acute Type II and rostral Type III odontoid fractures. In cases of Chronic Type II odontoid fractures and in patients with transverse ligament disruption, the authors prefer to undertake posterior transarticular facet screw fixation supplemented by bone graft and interspinous C1–2 wiring.

The technical aspects of these procedures are described with a focus on operative nuances. Selection criteria and techniques that the authors have refined over the years have helped them to optimize success rates and minimize complications.

Evidence-based analysis of odontoid fracture management

Object

The management of odontoid fractures remains controversial. Evidence-based methodology was used to review the published data on odontoid fracture management to determine the state of the current practices reported in the literature.

Methods

The Medline literature (1966–1999) was searched using the keywords “odontoid,” “odontoid fracture,” and “cervical fracture” and graded using a four-tiered system. Those articles meeting selection criteria were divided in an attempt to formulate practice guidelines and standards or options for each fracture type. Evidentiary tables were constructed by treatment type.

Ninety-five articles were reviewed. Five articles for Type I, 16 for Type II, and 14 for Type III odontoid fractures met selection criteria. All studies reviewed contained Class III data (American Medical Association data classification).

Conclusions

There is insufficient evidence to establish a standard or guideline for odontoid fracture management. Given the extent of Class III evidence and outcomes reported on Type I and Type III fractures, a well-designed case-controlled study would appear to provide sufficient evidence to establish a practice guideline, suggesting that cervical immobilization for 6 to 8 weeks is appropriate management. In cases of Type II fracture, analysis of the Class III evidence suggests that both operative and nonoperative management remain treatment options. A randomized trial or serial case-controlled studies will be required to establish either a guideline or treatment standard for this fracture type.

Management of acute odontoid fractures with single-screw anterior fixation

OBJECTIVE

Accepted management strategies for odontoid fractures include external immobilization and surgical stabilization using anterior or posterior approaches. Displaced Type II fractures and rostral Type III fractures are at high risk for nonunion. Anterior fixation of odontoid fractures with a single cortical lag screw is a relatively new technique that combines rigid internal stabilization with preservation of intrinsic C1-C2 motion. We retrospectively reviewed our series of 26 consecutive patients who underwent odontoid screw fixation, to further define the safety and efficacy of the technique.

METHODS

During a 5-year period, 26 patients presented with acute traumatic Type II odontoid fractures. Ten patients were female and 16 were male, with a mean age of 35 years. All patients underwent anterior odontoid screw fixation by the senior surgeon (RWH), within a mean of 3 days after injury. All patients were postoperatively maintained in external orthoses, for a mean of 7.2 weeks, and were monitored with serial clinical and radiographic examinations.

RESULTS

With a mean follow-up period of 30 months, radiographic fusion was documented for 25 of 26 patients (96%). No complications related to the surgical approach were identified, and all patients remained in neurologically stable condition. Two complications (8%) were related to the instrumentation; one patient required external immobilization because of suboptimal screw placement, and one patient required posterior atlantoaxial arthrodesis because of inadequate fracture reduction.

CONCLUSION

Single-screw anterior odontoid fixation was associated with a relatively low complication rate and a high fusion rate in this study. We think that this should be the preferred treatment method for acute Type II odontoid fractures.

Biomechanical comparison of C1-C2 posterior fixations. Cable, graft, and screw combinations

STUDY DESIGN

Four combinations of cable-graft-screw fixation at C1-C2 were compared biomechanically in vitro using nondestructive flexibility testing. Each specimen was instrumented successively using each fixation combination.

OBJECTIVES

To determine the relative amounts of movement at C1-C2 after instrumentation with various combinations of one or two transarticular screws and a posterior cable-secured graft. Also to determine the role of each component of the construct in resisting different types of loading.

SUMMARY OF BACKGROUND DATA

Spinal stiffness increases after instrumentation with two transarticular screws plus a posterior wire-graft compared with a wire-graft alone. Other C1-C2 cable-graft-screw combinations have not been tested.

METHODS

Eight human cadaveric occiput-C3 specimens were loaded nondestructively with pure moments, and nonconstrained motion at C1-C2 was measured. The instrumented states tested were a C1-C2 interposition graft attached with multistranded cable; a cable-graft plus one transarticular screw; two transarticular screws alone; and a cable-graft plus two transarticular screws.

RESULTS

The transarticular screws prevented lateral bending and axial rotation better than the posterior cable-graft. The cable-graft prevented flexion and extension better than the screws. Increasing the number of fixation points often significantly decreased the rotation and translation (paired t test; P < 0.05). Axes of rotation shifted from their normal location toward the hardware.

CONCLUSIONS

It is mechanically advantageous to include as many fixation points as possible when atlantoaxial instability is treated surgically.

Posterior C1-C2 transarticular screw fixation for atlantoaxial arthrodesis

OBJECTIVE

To assess the outcomes associated with C1-C2 transarticular screw fixation.

METHODS

The clinical outcomes of 121 patients treated with posterior C1-C2 transarticular screws and wired posterior C1-C2 autologous bone struts were evaluated prospectively. Atlantoaxial instability was caused by rheumatoid arthritis in 48 patients, C1 or C2 fractures in 45, transverse ligament disruption in 11, os odontoideum in 9, tumors in 6, and infection in 2.

RESULTS

Altogether, 226 screws were placed under lateral fluoroscopic guidance. Bilateral C1-C2 screws were placed in 105 patients; each of 16 patients had only one screw placed because of an anomalous vertebral artery (n = 13) or other pathological abnormality. Postoperatively, each patient underwent radiography and computed tomography to assess the position of the screw and healing. Most screws (221 screws, 98%) were positioned satisfactorily. Five screws were malpositioned (2%), but none were associated with clinical sequelae. Four malpositioned screws were reoperated on (one was repositioned, and three were removed). No patients had neurological complications, strokes, or transient ischemic attacks. Long-term follow-up (mean, 22 mo) of 114 patients demonstrated a 98% fusion rate. Two nonunions (2%) required occipitocervical fixation. In comparison, our C1-C2 fixations with wires and autograft (n = 74) had an 86% union rate.

CONCLUSION

Rigidly fixating C1-C2 instability with transarticular screws was associated with a significantly higher fusion rate than that achieved using wired grafts alone. The risk of screw malpositioning and catastrophic vascular or neural injury is small and can be minimized by assessing the position of the foramen transversaria on preoperative computed tomographic scans and by using intraoperative fluoroscopy and frameless stereotaxy to guide the screw trajectory.

Unilateral posterior atlantoaxial transarticular screw fixation

Bilateral posterior C 1-2 transfacet screw placement with associated posterior bone graft wiring is the accepted treatment for patients with atlantoaxial instability. This technique was modified to treat 19 patients with atlantoaxial instability and unilateral anomalies that prevented placement of a screw across the C1-2 facet. In these cases, a single contralateral transarticular screw was placed in conjunction with interspinous bone graft wiring to avoid neural or vertebral artery injury and to provide C1-2 stability. Postoperatively, all 19 patients were placed in Philadelphia collars (mean immobilization 8 weeks, range 6-12 weeks). Unilateral C1-2 facet screw fixation was needed for the following reasons: a high-riding transverse foramen of the C-2 vertebra present in 13 patients (left side in eight, right side in five), poor screw purchase in two (left side in both), screw malposition in one (left side), severe degenerative arthritis in one (right side), neurofibroma in one (right side), and fracture of the C-1 lateral mass in one (left side). Six weeks postsurgery, one patient presented with a broken screw and required occipitocervical fusion with a Steinmann pin and wire cable from the occiput to C-3 to achieve solid fusion. Solid fusions were achieved in the other 18 patients (mean follow-up period 31 months, range 14-54 months); there was no delayed screw breakage, wire breakage, or spinal instability. There were no operative or postoperative neurological or vascular complications. The authors' experience demonstrates that unilateral C1-2 facet screw fixation with interspinous bone graft wiring is an excellent alternative in the treatment of atlantoaxial instability when bilateral screw fixation is contraindicated.