Surgical treatment of acute type II and rostral type III odontoid fractures managed by anterior screw fixation.

Objectives: In the present study, the authors comment on their experience with anterior odontoid screw fixation in the management of odontoid fractures, in an attempt to further assess the safety and the efficacy of this procedure.

Materials and Methods: A retrospective analysis of 50 consecutive patients with reducible type II or rostral type III odontoid fractures, operated at our hospital with anterior odontoid screw fixation. Radiographic bony fusion, complications, and clinical outcome were evaluated.

Results: Solid bony fusion was evident in 38 (90.5%) of the patients. One mechanical instrumentation-related complication occurred, without clinical significance. No other major complications related to the procedure were noted. A satisfactory range of motion in the cervical spine was observed in all patients.

Conclusions: Anterior odontoid screw fixation is a safe and effective procedure for the treatment of type II and rostral type III odontoid fractures. Compliance to the specific indications and contraindications of this operation is crucial for optimal outcome.

Key Words: anterior, fusion, odontoid fracture, screw fixation

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Fractures of the axis involving the dens represent a fairly common entity of spinal injury, accounting for 10 to 18% of all cervical spine fractures. (1-11) Odontoid fractures are divided into three groups, depending on the anatomic location of the fracture, according to a widely accepted classification system proposed by Anderson and D'Alonzo (1) in a key paper in 1974. The classification of odontoid fractures provides a useful guide for prognosis and treatment. It is well recognized that displaced type II and "shallow" type III fractures of the odontoid process are at the highest risk for nonunion, (12) prompting immediate intervention and stabilization to reduce the risk of irreversible compromise of the spinal cord.

Treatment of this highly unstable entity remains a puzzling issue. Conservative management, mainly halo vests and cervical orthoses, have failed to yield a satisfactory rate of union and degree of stabilization of the fracture. A variety of surgical approaches have been used, such as C1-C2 posterior wiring and fusion, C1-C2 transarticular screw stabilization, and posterior clamping techniques. (12) The complex anatomy of the higher cervical region and the distinct biomechanical relations among the components of the craniocervical junction pose high-standard criteria for the selection of the most appropriate surgical technique.

Posterior wiring and fusion, once the most commonly used procedure, has been shown to achieve high rates of bony union. (13-15) This procedure, however, substantially restricts the rotary range of motion at the C1-C2 level. In an attempt to combine a high union rate and immediate stabilization of the spine, with preservation of a satisfactory range of motion, Nakanishi et al (16) and Bohler et al (17) independently introduced an anterior screw fixation technique for the treatment of type II odontoid fractures. Since then, an increasing number of reports have proclaimed the safety and efficacy of this procedure. (11,18-27)

In our retrospective study, we present our experience with 50 patients treated for reducible type II or rostral type III odontoid fractures, using anterior odontoid screw fixation.

Materials and Methods

Our cohort was composed of 50 consecutive patients treated at our hospital from August 1995 to April 2004. Thirty-two of our patients were male and 18 were female, with a mean age of 47.7 (age range, 17 to 81 years). All patients had traumatically acquired reducible type II or rostral type III odontoid fractures. Preoperative evaluation entailed plain cervical spine radiographs (Fig. 1.) as well as CT (Fig. 2.) and MRI of the cervical spine. The MRI study is of paramount importance, since it delineates the condition of the atlantal transverse ligament. In 14 patients, implantation of two screws was performed, whereas the single-screw technique was used in the remaining 36 patients. All patients were placed on a Miami J cervical collar for a 4-week period after the operation.

Follow-up was available in 42 patients (84%); seven patients were lost to follow-up, and one died as a result of causes unrelated to the procedure. Mean follow-up period was 53.4 months (range, 6 to 87 months). Patients were evaluated for bony fusion, using strict radiologic criteria. Dynamic lateral cervical spine radiographs (flexion/extension) at 6 weeks and at 2, 6, 12, and 24 months after surgery were obtained, as well as a CT scan of the upper cervical spine (C1-C3) at 6 months after the operation. Assessment of the patient's symptoms, if any, as well as a thorough neurologic evaluation, was performed at each follow-up visit. Neck flexion, extension, and lateral bending were specifically examined.

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Surgical technique

Anterior odontoid screw fixation was performed under general anesthesia, with the patient in a neutral supine position. Closed reduction of the odontoid process under fluoroscopic guidance was performed when dislocation was evident. The insertion of bite blocks on each side of the endotracheal tube, as well as the use of biplanar fluoroscopy (Figs. 3 and 4), was of paramount importance for the adequate visualization of the anatomic structures. With the help of a 1.2 mm diameter K-wire, one or two cannulated screws (Synthes, Inc., Paoli, PA) were advanced, under fluoroscopic observation, until the tip of the screw(s) passed the cortex of the odontoid tip and the head of the screw rested against the surface of the vertebral body of C2. Immediate walking was recommended after surgery.

Results

Solid bony fusion (presence of bony trabeculation across the fracture line), evident in plain radiographs and CT scans of the cervical spine, was observed in 38 patients (90.5%) (Fig. 5). Fusion was achieved at 6 months after surgery in 9 cases (21.4%), at 12 months after surgery in 18 cases (42.9%), and at 18 months after surgery in 11 cases (26.2%). No solid fusion was noted in 4 patients (9.5%), in all of these cases, a complete 24-month follow-up was available. One of these patients underwent posterior C1-C2 transarticular screw fixation and wiring because of radiographically detected abnormal motion. No surgical intervention was required in the remaining three patients. No significant difference in fusion rates and clinical outcome was noted regarding age, sex, and number of screws implanted. Bony fusion was observed in 8 patients (72.7%) with two screws placed, and in 30 patients (96.8%) with a single screw, a difference that reached statistical significance (P = 0.0263, Z = -2.2220 difference of proportions, two-tailed methodology).

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On clinical evaluation, no symptomatology was encountered at the 6-month postoperative follow-up visit. All patients were free of pain medication and had returned to their premorbid level of daily activities. Range of motion in the cervical spine was well preserved in our series. More specifically, the postoperatively obtained dynamic radiographic studies (Fig. 6) revealed that the flexion ranged between 11 to 33 degrees, with a mean value of 24.2 degrees. The range of extension was 9 to 34 degrees, and the mean was 23.3 degrees. Similarly, the rotatory range of motion was found to be 7 to 40 degrees (mean, 23.9 degrees) to the right, whereas the respective values for left turn were 5 to 39 degrees (mean, 23 degrees).

Instrumentation-related complications were encountered in one patient (2.4%) in whom a screw fracture occurred. Since no clinical symptoms were evident and stable fibrous union had developed, no surgical intervention was considered necessary. Another intraoperative fracture of the implanted K-wire occurred without posing any further problems to the positioning of the screw.

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Medical complications, not related to instrumentation, developed in three patients (7.3%). In two cases, a superficial wound infection was successfully treated with oral antibiotics. In the remaining case, the patient had development of pulmonary atelectasis that resolved uneventfully within 1 week.

Discussion

A variety of therapeutic modalities have been used for the successful and immediate stabilization of acute type II and "shallow" type III odontoid fractures. Conservative treatment with halo vests and external orthotic devices, although useful adjuncts in the management of these cervical injuries, have been documented to lead to unacceptably high rates of nonunion, ranging from 0 to 64%, (8,19,24,28-31) especially in the elderly. The complex pattern of vascular supply to the odontoid process seems to be associated with the high rates of nonunion, especially with fractures occurring at the base of the dens. (32)

Posterior surgical approaches, mainly atlantoaxial wiring and fusion and C1-C2 transarticular screw fixation, have been recruited to achieve higher union rates and greater stabilization of these fractures. Postoperative rates of fusion after use of these techniques have been reported to be excellent in several studies. (13-15) Posterior stabilization procedures have, however, serious disadvantages. Atlantoaxial fusion leads to a substantial restriction of the rotatory range of motion of the C1-C2 complex and an approximately 10% reduction of cervical spine flexion/extension, (24,33) In addition, intraoperative morbidity, sometimes associated with the site of the collection of the autologous graft, is not negligible. On the other hand, C1-C2 transarticular screw stabilization carries the serious risk of damaging the vertebral artery, with disastrous consequences.

The need for establishing a safe therapeutic approach that would provide immediate stabilization of reducible type II and rostral type III odontoid fractures while maintaining adequate mobility of the cervical spine has led to the development of the anterior screw fixation technique. Since its introduction about two decades ago, a large number of clinical trials have been conducted, providing evidence for the safety and efficacy of this technique. (11,18-27)

Anterior odontoid screw fixation has been associated with high rates of fracture union in several studies. (18,21-24,34,35) Subach et al (21) and Verheggen and Jansen (22) reported an overall union rate of 96% and 94.4%, respectively, which is comparable to fusion rates achieved by posterior C1-C2 arthrodesis. (13-15) Our study further confirms the efficacy of anterior screw fixation for the treatment of odontoid fractures.

However, controversy exists in the literature regarding the impact of age on the outcome of patients undergoing this procedure. (19,36-38) Berlemann and Schwarzenbach (36) concluded in their clinical trial that anterior odontoid screw fixation is safe and effective in the elderly. Their results were further supported by Borm et al. (37) who demonstrated in a case-control study that fusion rates were similar between a group of younger (< 70 years) and a group of older (> 70 years) patients. Anderson et al, (38) on the other hand, observed a high risk of complications among the elderly (> 65 years) and recommended posterior C1-C2 fusion as the treatment of choice in this group of patients. In our cohort, no statistically significant difference between age groups was noted.

Age of the fracture has also been implicated as an important prognostic factor. Apfelbaum et al (39) observed a significantly lower rate of fusion in patients with remote fractures (> 18 months after trauma) compared with patients with recent fractures ([less than or equal to] 6 months after trauma). The great difference in bone fusion between the two groups (88% versus 25%) led Apfelbaum et al to the conclusion that anterior odontoid screw fixation is not an appropriate treatment for patients with old odontoid fractures. In the same study, the authors noted that there was no statistically significant difference in bony fusion in regard to patient sex, age, and number of screws used. Analysis of our data provides further evidence in support of these observations. The issue of one-versus two-screw implantation has been addressed by several other authors (24,40,41) without convincing evidence for the superiority of the insertion of two screws over a single screw.

The rate of complications associated with anterior odontoid screw fixation has been reported to be low, (22,25,39,42) comparable to that observed for posterior fusion. (13,43) We noted one case of mechanical instrumentation failure that did not affect the patient's outcome. Aebi et al (34) also reported a case of screw breakage. Apfelbaum et al (39) noted that a screw pulled out of the body of C2 in five of their patients; in all of those however, comminuted C2-body fractures were identified, which is considered to be one of the contraindications for this procedure. It should also be noted that screw misplacement may have fatal consequences. Daentzer et al (44) reported such a case of screw malpositioning that resulted in formation of pseudoaneurysm of the vertebral artery, with subsequent subarachnoid hemorrhage and death 4 days after surgery.

This last observation emphasizes the significance of developing well-established indications and contraindications for performing anterior odontoid screw fixation. Patients older than 7 years, with reducible odontoid type II or rostral type III fractures, acquired no longer than 6 months before the operation, (39) are generally considered to be optimal candidates for this procedure. Contrariwise, disruption of the atlantal transverse ligament, comminuted fractures, irreducible fractures, fractures in patients with a short, thick neck and/or barreled chest, as well as fractures lying in oblique orientation to the frontal plane are well described contraindications for anterior screw technique. (11,12,45)

Conclusion

Our clinical study provides further evidence for the safety and efficacy of anterior odontoid screw fixation for the treatment of reducible type II and rostral type III fractures of the dens. A careful selection of appropriate surgical candidates, together with a meticulous lege artis approach, are of paramount importance for the good functional outcome of the patients.

References

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At the height of laughter, the universe is flung into a kaleidoscope of
new possibilities.
--Jean Houston

Kostas N. Fountas, MD, PHD, Theofilos G. Machinis, MD, Eftychia Z. Kapsalaki, MD, PHD, Vassilios G. Dimopoulos, MD, Carlos H. Feltes, MD, Richard Liipfert, MS, Kim W. Johnston, MD, FACS, Hugh F. Smisson, MD, FACS, and Joe S. Robinson, MD, FACS

From the Departments of Neurosurgery and Neuroradiology, The Medical Center of Central Georgia, Mercer University, School of Medicine, Macon, GA.

None of the participants of this study have financial support or provision of supplies for any material presented. Also, no commercial or proprietary interest in any drug, device, or equipment mentioned in this article has been held by any of the participants of this study.

Reprint requests to Dr. Kostas N. Fountas, 840 Pine Street, Suite 880, Macon, GA 31201. Email: [e-mail]

Accepted May 9, 2005.

RELATED ARTICLE: Key Points

* Anterior odontoid screw fixation is a safe procedure for the treatment of reducible type II and rostral type III odontoid fractures.

* High rates of bony union are associated with this anterior approach, comparable to those accomplished with posterior techniques.

* A satisfactory range of motion in the cervical spine is preserved with the anterior odontoid screw fixation technique, providing a good quality of life for the patient.