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Fractures of the odontoid process of the axis create problems of specific osteosynthesis. The different techniques described so far require an external support and limit the movements of the cranio-cervical joint. These 2 drawbacks are avoided by direct screw fixation of the odontoid process in cases where conditions are favourable to this procedure.
The axis from twenty-two cadavera was removed at autopsy and was sectioned in the sagittal plane to a thickness of one millimeter with use of a surface-stained block-grinding technique. Combined two and three-dimensional analysis included an evaluation of the volume of the trabecular bone, the trabecular interconnection, and the cortical thickness as well as qualitative investigation of the structure of the cancellous bone. The body of the axis, the base of the odontoid process, and the odontoid process were analyzed separately. The base of the odontoid process is a region of least resistance for fractures because of its unique microarchitecture. The mean volume of trabecular bone of the base of the odontoid process is 55 per cent less than that of the axis and the odontoid process. The base also has a markedly poorer trabecular interconnection and a cortical thickness that is one-third that of the odontoid process. In all of the specimens, trabeculae that were disconnected from the trabecular lattice (trabeculae with free ends) were demonstrated in the base of the odontoid process. The formation of microcallus in six (27 per cent) of the specimens supports the hypothesis that microfractures occur as a result of stress peaks, mechanical fatigue, and the relative insufficiency of bone in the static condition. Therefore, the base of the odontoid process can be considered as a site of predilection for fractures.
Fifteen percent of cervical spine fractures involve the odontoid process. Most odontoid fractures can be classified as Types I through III according to the scheme developed by Anderson and D'Alonzo. We report a case of a vertically oriented fracture through the odontoid process that does not fit into any of these categories. Only two such cases have been described in the literature. Our patient is an 18-year-old man who sustained an axial loading injury to his cervical spine. Plain lateral cervical tomography and computed tomography were performed to characterize the fracture and to evaluate the instability. The patient was placed in a rigid orthosis for 12 weeks, and at 6-month follow-up, he had full range of motion and showed no evidence of abnormal movement, as revealed by flexion-extension studies. This case demonstrates the shortcomings of the current classification system for odontoid fractures and value of plain tomography and computed tomography in evaluating odontoid fractures.
Pyogenic osteomyelitis of the odontoid process is a rare condition requiring a high index of suspicion for diagnosis. The three cases presented illustrate that patients with severe neck pain, aggravated by rotation, and persistent fever without apparent source should be studied carefully to exclude infection of the C1-C2 area. The unusual anatomy of the C1-C2 articulation may make routine diagnostic studies difficult to interpret. Computed tomography, magnetic resonance imaging, and 111In-labeled white blood cell scans may improve diagnostic accuracy. Treatment includes rigid immobilization, high dose antibiotics, and surgical stabilization in selected cases.
Six cases of spontaneous fracture of the odontoid process in rheumatoid arthritis are presented. Fifty-one patients with atlantoaxial subluxation in rheumatoid arthritis underwent surgery between 1981 and 1990. This included six patients (in 10%) who had subluxation accompanied by fracture of the odontoid without apparent trauma. The mean patient age was 58 years and all had a long history of rheumatoid arthritis. No trauma was considered to be the cause of the fracture. This is a fracture caused by erosion and osteoporosis of the odontoid process due to rheumatoid synovitis, aging and steroid therapy. In addition, another cause is a dynamic load produced from the instability accompanying atlantoaxial subluxation working on the odontoid in cervical extension. It is important remember that the odontoid process is susceptible to spontaneous fracture.
Fracture of the odontoid process in young children is possibly not as rare as hitherto believed. In this paper, two more patients with this fracture are presented, and an important diagnostic clinical sign is described. Both patients sustained the injury by falling from heights no greater than sixty-one to ninety-one centimeters. In each instance, injury to the cervical spine was suspected but initial roentgenograms failed to reveal any fracture. The patients were quite comfortable when lying supine and when fully erect. Each child strongly resisted any attempt at extension of the neck and cried bitterly when brought to either the erect or the recumbent position unless the head was passively supported. This a valuable clinical sign when injury to the odontoid process is suspected. Subsequent roentgenograms confirmed the diagnosis in each instance.
The origin of transverse arterial branches that contribute to the arterial supply of the odontoid process (dens axis) is not clear. Dissections were performed on 20 injected fetal and adult human cranio-cervical junctions to demonstrate the origin of the arteries that contribute feeding branches to the arteries supplying the neck of the odontoid process. At its termination near the anterior arch of the atlas, the ascending pharyngeal artery gave off transverse branches that anastomosed with the anterior ascending arteries to the odontoid process. It also gave off a branch that traversed the hypoglossal canal and anastomosed with the posterior ascending artery. A small branch linked the posterior ascending artery to the first transverse branch. This investigation complements previous work on the arterial supply to the odontoid process.
A case of an osteoblastoma located in the odontoid process in a 7 year-old boy who presented with torticollis is reported. CT scan and MRI disclosed the lesion, but diagnosis was established by a CT-guided needle biopsy. Surgery through a transoral approach allowed total excision of the tumor. This is, to our knowledge, the first case reported of an osteoblastoma of the odontoid process.
The most common injury to the odontoid process in children under the age of seven years is a fracture through the synchondrosis with or without anterior displacement of the odontoid process, but this is not the only type of fracture of the odontoid process in this age-group. Fractures above and below the synchondrosis and fractures with posterior displacement were described. Typical clinical features of these fractures are: (1) major and blunt trauma, (2) neck pain and resistance to active and passive head movements; and (3) no or only slight neurological deficits. Conservative treatment had excellent results in the majority of cases. Nevertheless, there are a few specific indications for surgery.
The so-called "peridentale aureole" ("crowned odontoid"), a horseshoe-like calcification around the odontoid process, can occasionally be shown on transbuccal views of the occipito-atlantoaxial region, but is commonly only seen on a.p. tomography in patients with osteoarthrosis of the anterior atlantoaxial joint. Tomographic examinations reveal that these irregular horseshoe-like calcifications around the odontoid peg represent mainly the osteophyte formation on the superior border of the anterior arch of the atlas. These calcifications are often surrounding a smaller calcification on the tip of the odontoid process. The peridentale aureole or crowned odontoid process is easily overlooked unless tomography is performed, and misinterpretations are possible if the radiologist is not familiar with this appearance of osteoarthrosis and some other joint diseases of the anterior atlantoaxial joint.
We reviewed eleven patients less than seven years old with fractures of the odontoid process in an effort to establish a more standard form of treatment for the injury and to determine what complications, if any, occur as a result of fractures of the odontoid process in pediatric patients. Our study showed that children with odontoid fractures that are recognized and treated promptly usually do well. The fracture can usually be reduced by passive manipulation or by the "hanging head technique". Support in the reduced position for two to three months in a Minerva jacket or halo cast should be long enough to permit healing. Our study suggests that fractures of the odontoid process in young patients almost always heal.
In the year 1981, J. Böhler completed for the first time a screw fixation for unstable fractures of the odontoid process of the axis. This surgical technique preserves the anatomy and the physiology of the articulation between the atlas and the axis, as a guarantee for a good functional recovery. It is not a very difficult technique when performed by a trained surgeon with a very good X-ray image intensification for the per-operative control. We have treated 32 unstable fractures of the odontoid process without any neurological complication per- or post-operatively. We had a follow-up on only 29 cases. In 19 cases the fracture healed in leading to a good bone union, complete mobility and no residual pain. Seven patients complained of residual pain or a limitation in cervical movement, because of the association with other cervical fractures, an age superior of 70 years, or a major initial instability. In 2 cases the authors noted a non-union and a secondary displacement because of technical faults at the beginning of their experience. These good results determined the authors to prefer the direct screw fixation for the unstable fractures of the odontoid process, to the posterior arthrodesis which leads to functional limitations.
A clinical study of fractures of the odontoid process showed a 62 per cent failure on union. Of many features studied, only displacement and its direction had a definite bearing on non-union of the fracture. Blood supply was considered as a possible etiological factor. The blood supply of the human odontoid was elucidated by means of studying 19 human autopsies by means of microangiography. The dog was found to have a similar blood supply and hence, was used as the experimental model. Two osteotomies were performed; one below the accessory ligaments and one above the accessory ligaments. All osteotomies carried out below the accessory ligament united and all carried out above failed to unite. Microangiographic studies revealed however, that avascular necrosis was not the cause of non-union. Further anatomic studies revealed that different size gaps occurred depending on the level of the osteotomy, with a large gap occurring in the osteotomy of the odontoid which was performed above the accessory ligament. First the result of immobilization and the healing of the odontoid osteotomy was derived, by carrying out an instant occipito-cervical fusion by means of wire loops and methylmethacrylate. In distinction to the free floating apical segment of non-immobolized spines, with a high odontoid osteotomy, the occipito-cervical fusion resulted in a dense fibrous tissue stabilizing the apical fragment but at no time was bony union observed. A final attempt was to secure immobilization and reduce the gap, by carrying out only a partial osteotomy. The osteotomy was performed in such a way that the posterior cortex was left intact. Union occurred in all instances. The fracture gap and movement play a definite role in the pathogenesis of pseudarthrosis of the odontoid process. Where gap and movement were eliminated, union occurred. It is difficult to transpose this experimental situation to the clinical one, for the assessment of gap clinically, is only radiographic. This method is much too imprecise to be of value in this assessment. The fact however, that a high rate of non-union is associated with a high degree of displacement, supports the experimental thesis.
Studies on the morphology of the odontoid process by various methods strongly suggest a functional adaption of this bony element. With regard to the inclination of the dens axis and the varying position of its articular facets, a modified trabecular system can be observed. Photoelastic experiments confirm that these modifications are correlated with two specific kinds of mechanical stress. The straight odontoid process is only subjected to stress due to compression, but the dorsally inclined dens to bending stress. Based on the morphological and experimental findings, flexion and extension between the first and second vertebrae (in addition to rotation as the principle movement) are discussed.
The authors describe a case of direct screw fixation of the odontoid process via an anterolateral retropharyngeal subhyoid pre-sternomastoid approach and discuss the indications for this operation. In this particular case, immobilization by a cervical collar or a halo vest was not chosen because of its constraining character and the risk of secondary displacement and pseudarthrosis. C1-C2 or occipitospinal arthrodesis, whether performed via a posterior, lateral or anterior approach, is difficult to perform and always leads to a functional handicap. The transoral approach does not allow direct screw fixation of the dens. Dens screwing via an anterior pre-sternomastoid subhyoid approach is the most logical and least disabling technique. The subhyoid approach is much simpler than the suprahyoid approach. This technique is used in fractures of the odontoid process with an ablique downward and backward fracture line, with or without arch fracture of C1, and allows screwing perpendicular to the fracture line. Considering the present results and the literature, the double screw fixation does not seem to be justified.
Clinical and roentgenologic studies were performed in 69 children with Down's syndrome, without the separate odontoid process, that could be followed for more than 5 years. At the follow-up examination, the atlanto-odontoid process interval (AOI) in flexion, neutral, and extension of the cervical vertebrae significantly decreased when compared with the one at the initial examination. This was particularly obvious up to 5 years of age. Although 14 of 69 cases (20.3%) had atlanto-axial instability at the initial examination, this decreased to four cases (5.8%) at the follow-up examination. However, there were two cases of atlanto-axial instability who were over 10 years of age. There was no significant difference in the minimum sagittal diameter (MSD) at the atlantal level between each position at both the initial and follow-up examinations. Moreover, there was a tendency for the MSD of the cases of positive instability at the follow-up examination to be smaller than those of the cases of negative instability. The degree of ligament laxity improved with increasing age and there was statistically the negative correlation. Although there was a tendency for the AOI to decrease with improvement of the degree of ligament laxity, the correlation could not be confirmed.
The objective of this study is to analyse the advantages and disadvantages of different surgical technics of odontoid process fracture stabilization. We try to find the best indications for each of them. We won't consider stable odontoid fractures which haven't treated by surgical therapy. A review of ninety acute dens fractures since 1979 has been analysed before 1985, the most of our injured person had a surgical stabilization by posterior approach. The analysis of our results had incited us, since that date, to vary our indications, by taking possibilities of anterior approach into consideration. So, have been realized 55 C1-C2 lacings, 20 of which with bone graft, 12 occipito-cervical arthrodesis, 10 screw fixations of odontoid process, 9 atlanto-axial arthrodesis by screw fixations, 2 posterior fixations by CD pediatric instrumentation, 1 Knodt instrumentation, 1 osteosynthesis by trans-oral exposure. Patients have been seen again, 1 month, 3 month, 6 month, 1 year later. Results have been estimated: Clinically by cervical mobility study in rotation and by local pain (16 excellent results, 24 good results, 27 middle results, and 23 bad results); Radiologically by analysis of specific complications of each technic (8 secondary removing, 6 incomplete deplacement corrections, 4 excessive corrections, 3 pseudarthrosis). We have regrouped global results technic by technic. We propose a therapeutic planning in which each technic can find the best result. The objective is to assure an effective retention by preserving movings of superior cervical spine.
In eighteen patients who had long-standing severe rheumatoid polyarthritis, cranial subluxation of the odontoid process was caused by erosion and collapse of both the occipitocervical and the atlantoaxial facet joints. In five of the patients, the subluxation caused impairment of cranial nerves. One patient was tetraparetic. Six patients had a posterior fusion of the spine; of these, three also had laminectomy of the atlas. Operative treatment seemed to arrest the subluxation, but there was appreciable functional improvement in only four of the six patients. During an average of four years of follow-up, in the twelve conservatively treated patients, the cranial subluxation of the odontoid process progressed, on average, from 8.6 to 10.5 millimeters.