Type 1 lesions are localised to the central subchondralportions of the discovertebral junction and this can occurin both ankylosed and non-a
Type 1 lesions are localised to the central subchondralportions of the discovertebral junction and this can occur
in both ankylosed and non-ankylosed spines.Osteoporosis of vertebrae is marked in ankylosing spondylitis. This results in weakening of the subchondral bone and displacement of the discal contents through the cartilaginous end plate into the vertebral body.Apophyseal joint involvement may lead to instability and recurrent traumatic insult to the disc-bone interface. This eventually produces infarction of cartilaginous endplate allowing the discal material into the vertebral body.Inflammatory changes in subchondral bone itself may lead to osseous weakening and discal displacement .Radiologically the lesions appear as irregularity of central portion of the superior and inferior vertebral margins with surrounding sclerosis.
Type2 -These are peripheral localized lesions occuring in the anterior or posterior part of discovertebral junction. The anterior lesion is attributed to collapse of osteoporotic anterior vertebral margin as occurs in
osteoporotic kyphosis and also alternatively to injury to the anterior fibres of annulus fibrosus leading to invasion and replacement of discal material by vascular fibrous tissue as in senile kyphosis.The mechanism of the
localised posterior lesions though not clear may be due to osteoporotic collapse or cartilagenous nodes. Inflammation of the outer fibres of the annulus fibrosus related to spondylitic process may also play a role.
Radiologically Type 2 lesions are seen as intervertebral disc space narrowing with bony sclerosis, irregularity of discovertebral junction and anterior or posterior discovertebral erosion with intact apophyseal joints.
Type3 Destruction of the whole discovertebraljunction of two adjacent vertebral bodies occurs in patients with advanced ankylosis. There may be a history of trauma and associated fracture through the ankylosed portion. There may be improper healing with callus formation, heamorrhage and minimal inflammatory changes.The adiological appearance of this type is a combination of Type1 and Type 2 lesions.
The radiological features of all types of Andersson lesion including disc space narrowing, destruction of vertebral end plate and sclerosis of adjacent bone mimic infective spondylitis particularly due to tuberculosis