Involvement of the zygapophyseal joint in ankylosing spondylitis: relation to the bridging syndesmophyte.

OBJECTIVE

To determine the prevalence of zygapophyseal (ZA) joint ankylosis in ankylosing spondylitis (AS) and the relation of this ankylosis to the presence of bridging syndesmophytes.

METHODS

Roentgenograms of the cervical and lumbar spine of 50 patients with AS were scored by a vertebral body score according to Taylor and a newly developed score for ZA joint involvement.

RESULTS

At the cervical level 22% of the ZA joints were ankylosed and 16% of the levels presented bridging syndesmophytes. In the lumbar spine 22% of ZA joints were ankylosed and 16% of the vertebral levels showed ankylosis in both ZA joints. Bridging syndesmophytes were present in 11% of the vertebral levels. Ankylosis of the ZA joints and bridging syndesmophytes were seen simultaneously in 14% of the cervical levels and in 9% of all lumbar levels. Ankylosed ZA joints were present in 21% of the lumbar levels without bridging syndesmophytes and in 8% of the cervical levels without bridging syndesmophytes. Bridging syndesmophytes at a given level without ankylosis of the respective ZA joint were uncommon: 4 of 201 lumbar levels and 4 of 238 cervical levels. Ankylosis of the ZA joint and presence of bridging syndesmophytes is markedly associated, but in a discordant way.

CONCLUSION

The ZA joint is affected in a major way in AS. Involvement of the ZA joint and the presence of syndesmophytes are related. An asymmetric relation suggests that the ZA joint is primarily involved in AS.