34 Atlantoaxial Joint Degenerative Arthritis and Craniovertebral Instability

10.1055/b-0034-81411

34 Atlantoaxial Joint Degenerative Arthritis and Craniovertebral Instability

Goel, Atul, Shah, Abhidha, Rajan, Sanjay

The atlantoaxial joints are the most mobile in the body. The lateral masses of the atlas and axis form a pillar of stability and mobility for the neck and head. Like all other joints, they are subject to arthritis. With the general aging of the population, the issue of arthritis is becoming more relevant. Osteoarthritis of the atlantoaxial joint is a well-defined phenomenon that eventually results in atlantoaxial instability. The process of joint degeneration and instability is progressive and extends over several months to years. This instability is probably the result of degeneration of the articular cartilage, reduction of the joint space, and secondary incompetence of the ligaments controlling the movements.1–3

Degenerative arthritis of the atlantoaxial joint is rarely discussed, and most of the literature on the subject is in the form of isolated reports.1,4–9 Difficulty in obtaining good quality images and in direct visual assessment of the joint has probably made the diagnosis and evaluation of arthritis relatively less common. We retrospectively identified 108 patients who were diagnosed as having atlantoaxial instability secondary to degenerative osteo-arthritis of the atlantoaxial joints on the basis of presenting clinical features, radiological imaging, and direct observation of the joint status during surgery that involved opening, manipulation, and fixation of the joints. These patients were treated in our department of neurosurgery between 1990 and 2008.10 The following discussion is based on this experience.

Clinical Features

Pain in the neck on movement often forms the earliest and most prominent symptom. The more classical pattern is of an elderly patient presenting with symptoms of pain in the neck on movement, along with restriction of neck movement and gradually progressive quadriparesis over a few days to several months. The incidence and severity of quadriparesis vary in different reports; this variation reflects the duration of the disease before the diagnosis is clinched. Sensory symptoms are relatively mild and typically include bilateral upper and lower extremity paresthesias and kinesthetic sensation deficits. A history of mild to moderately severe trauma, from a few days to several years prior to diagnosis, may be present in a substantial number of patients. In most of these cases, the symptoms progress from the time of trauma. Palpable crepitus with motion has also been identified as a presenting symptom.4 Carrying of heavy weights over the head has been shown to cause increased incidence of cervical spondylotic changes and basilar invagination.11

Radiological Features

Among the more constant radiological features is reduction of the height of the lateral mass complex due to reduction of the joint space ( Figs. 34.1 and 34.2 ). Erosion of the bones of the lateral masses and body of the atlas and axis is usually observed in more chronic situations.12 Degenerative erosion of the facets of the atlas and axis, the odontoid process, and the body of the axis, as well as periodontoid ligamentous degenerative changes, is also frequent ( Figs. 34.3, 34.4, 34.5, 34.6, 34.7, 34.8, 34.9, 34.10, and 34.11 ). The changes seen in our series of 108 patients are summarized in Table 34.1.

The term basilar invagination in cases of craniovertebral arthritis has been used synonymously with cranial settling and vertical odontoid migration. 11,13–15 In our experience, basilar invagination was only mild to moderate, and in none of the cases did the tip of the odontoid process migrate > 9 mm above the Chamberlain line. This is unlike the basilar invagination observed in rheumatoid arthritis cases in which the superior migration of the odontoid process is significantly greater because of the more severe lateral mass bone collapse. In our series, the alignment of the facets was horizontal and not oblique, as was observed in cases with congenital basilar invagination in our earlier reports.16,17

Atlantoaxial joint arthritis is expected to eventually result in atlantoaxial instability in all cases. However, in those presenting early, this may not be evident.4 In our experience, all patients presented with mobile atlantoaxial dislocation, and more than half showed hypermobility. The dislocation may only be partially reducible due to the presence of nonyielding tissues around the odontoid process. The subtlety of instability may make the diagnosis difficult in soame cases.

**Fig. 34.1a–e Images of a 65-year-old male patient.** a Preoperative computed tomography (CT) scan with the head of the patient in flexion shows the atlantoaxial dislocation and basilar invagination. Erosion of the dens and periodontoid degenerative tissue can be seen. Osteophyte-like ossification in the region of the apical ligament and atlantodental joint can be observed. Degenerative changes in the cervical spine are seen. b Preoperative CT scan with the head in an extended position showing reduction of the dislocation. c Three-dimensional CT scan showing ossification near the apical ligament at the site of its attachment to the clivus. d Postoperative CT scan shows realignment of the craniovertebral junction and fixation. e Postoperative radiograph showing fixation with plate and screws and bone graft.

**Fig. 34.2a–h Images of a 58-year-old female patient.** a Preoperative radiograph with the head in flexion showing marked atlantoaxial dislocation. b Preoperative radiograph with the head in extension showing partial reduction of the dislocation. c Preoperative CT scan showing the dislocation. Erosive changes in the dens and degenerative changes in the cervical spine can be seen. d T1-weighted magnetic resonance imaging (MRI) showing the dislocation. Preodontoid degenerative tissue can be seen. e Postoperative CT scan showing fixation in an incompletely reduced position. f Postoperative CT with the sagittal cut through the lateral masses. A metal spacer is seen in the distracted joint, in addition to fixation with plate and screws. g Coronal cut showing spacers in the atlantoaxial joints and screws in the facets of the atlas and axis. h Postoperative radiograph showing the plate and screw fixation. Metal spacers can be seen.

**Fig. 34.3a, b Images of 57-year-old male patient.** a Preoperative CT scan showing extensive degenerative changes in the periodontoid region and in the facets. b Coronal cut showing degenerative changes in the lateral masses. Reduction of joint space height and osteophyte formation in the facets can be observed.

**Fig. 34.4 Coronal CT scan showing degenerative changes in the atlantoaxial joints of a 68-year-old man.** Degeneration is more marked on one side, where erosive changes are observed in the facets of the atlas and axis.

**Fig. 34.5a, b Images of a 70-year-old male patient.** a CT scan showing degenerative periodontoid changes. Calcification of the anterior occipitoatlantal membrane can be seen. b Coronal image showing degenerative changes in the atlantoaxial joints. Osteophytes can be seen in the facets of the atlas and axis.

**Fig. 34.6a, b Images of a 67-year-old male patient.** a Preoperative CT scan showing extensive periodontoid degenerative changes. Atlantoaxial dislocation and basilar invagination can be seen. b Postoperative scan showing reduction and fixation of the region.

**Fig. 34.7a–d Images of a 68-year-old female patient.** a T2-weighted MRI showing degenerative periodontoid changes. Elevation of the posterior longitudinal ligament/tectorial membrane is clearly visible. b T1-weighted MRI showing the periodontoidal soft tissue and degenerative changes. c CT scan in flexion showing subtle basilar invagination and atlantoaxial dislocation. d Postoperative CT scan showing reduction of the dislocation and of basilar invagination.

**Fig. 34.8 Image of a 49-year-old female patient. Paraodontoid degenerative change is seen.**

**Fig. 34.9a–e Images of 61-year-old male patient.** a T1-weighted MRI showing a retro-odontoid ligamentous degenerative tumorlike mass. The posterior longitudinal ligament/tectorial membrane can be seen elevated posteriorly by the mass. b T2-weighted MRI showing the retro-odontoid hypointense mass. Signal intensity changes in the cord can be seen. c Lateral radiograph in flexion shows subtle atlantoaxial dislocation. d Lateral radiograph in extension showing incomplete reduction of the dislocation. e Postoperative radiograph showing atlantoaxial fixation. The reduction of the dislocation is incomplete.

**Fig. 34.10a–g Images of a 65-year-old male patient.** a Radiograph with the neck in a flexed position shows moderate atlantoaxial dislocation. b Radiograph with the neck in extension showing incomplete reduction of the dislocation. c CT scan showing basilar invagination and atlantoaxial dislocation. Osteophyte-like changes are seen in the region of the apical ligament. d MRI showing periodontoid degenerative soft tissue and atlanto-axial dislocation leading to cord compression. e Postoperative CT scan showing incomplete reduction of the dislocation and of the basilar invagination. f Postoperative CT scan with the sagittal cut traversing through the joint showing plate and screw fixation. g Radiograph with the head in flexion showing the fixation.

Degenerative pannus, also referred to as articular, ganglion, synovial, or juxtafacet cyst, may arise from the degenerating synovial lining of any joint in the body.18–21 Pannus related to atlantoaxial joint arthritis probably represents degenerative ligaments and secondary osteophyte-like tissue formation in the periodontoid region.3,22 Degenerating tissues are typically isointense on T1-weighted magnetic resonance imaging (MRI) and iso- to hypointense on T2-weighted MRI ( Fig. 34.9 ) and do not enhance on contrast administration. In some cases, the retro-odontoid mass may have a tumorlike appearance, resulting in posterior “buckling” of the posterior longitudinal ligament or the tectorial membrane and indentation of the cord substance ( Figs. 34.7 and 34.9 ). Such a retro-odontoid “pseudotumor” is a well-defined entity.23–26 We recently reported a case of rheumatoid arthritis having both atlantoaxial dislocation and basilar invagination. In this case, we identified laxity and buckling of the posterior spinal ligaments as a cause of retro-odontoid pannus formation. This feature was confirmed by the dramatic reduction of the pannus immediately following surgery that involved distraction of the facets of the atlantoaxial joint.27

Retro-odontoid ligamentous hypertrophy appears to be related to laxity of ligaments due to reduced atlantoaxial height and secondary to progressive degenerative changes in the region. The pathogenesis of the degenerative changes simulates to an extent the formation of posterior osteophytes in cases with spinal degeneration. It appears that the presence of retro-odontoid ligamentous degenerative hypertrophy in an elderly person can be diagnostic evidence that suggests atlantoaxial instability, even when such instability is not clearly visualized on radiological imaging. In general, it is observed that retro-odontoid ligamentous degenerative changes are identified and are thicker in cases where the atlantoaxial instability is less marked and the entire degenerative process is more chronic in nature. As opposed to cases of rheumatoid arthritis, where the process is more chronic or long- standing, bone destruction of the facets of the atlas and axis and osteomalacia are not as pronounced in cases of degeneration-related arthritis. Degeneration of the atlantodental joint may be observed in a minority. Cervical spondylotic degenerative disease is likely to be present to varying degrees in the rest of the spine in most cases.

**Fig. 34.11a–i Images of a 78-year-old patient.** a Radiograph with the neck in a flexed position showing atlanto-axial dislocation. b Radiograph with the neck in extension showing incomplete reduction of the dislocation. c CT scan showing basilar invagination and atlantoaxial dislocation. Osteophyte-like changes are seen in the region of the apical ligament. d CT scan with the sagittal section traversing the atlantoaxial joint. It shows arthritis and dislocation of the atlantoaxial joint and chronic arthritic changes in the rest of the spine. e Coronal section of CT showing degenerative changes in the atlantoaxial joint. f T1-weighted MRI showing periodontoid degenerative soft tissue and atlantoaxial dislocation leading to cord compression. g T2-weighted MRI showing periodontoid degenerative soft tissue and atlantoaxial dislocation leading to cord compression. Degenerative changes in the rest of the spine are evident. h Postoperative CT scan showing reduction of the dislocation and of the basilar invagination. i Radiograph with the head in flexion showing the fixation.

**Table 34.1** Radiological findings
Serial No.	Finding	Incidence (%)
1	Reduction of the height of the atlantoaxial lateral mass complex	100
2	Erosion of the bones of the atlas and axis	76
3	Periodontoid degenerative tissue	90
4	Periodontoid osteophyte-like bone formation	28
5	Retro-odontoid tumorlike ligamentous hypertrophy indenting into the cord	13
6	Mobile atlantoaxial dislocation	100
	Subtle mobility	46
	Hypermobility	54
	Completely reducible	59
	Incompletely reducible	41
7	Basilar invagination	68