Development of adjacent segment degeneration (ASD) secondary to fusion

Case 1

MRI cervical spine Sagittal T2w image shows:

E/o C5-6 Post discectomy fusion, which was done to relive cord compression by disc extrusion at this level. No cord compression at C5-6 at present.

But there are advanced degenerative changes at adjacent levels particularly C3-4, C4-5 and C6-7 causing cord compression.

Case 2

MRI cervical spine Sagittal Tw image shows:

C5-6 Congenital fusion, as the intervening C5-6 disc is rudimentary with concavity of combined anterior surfaces of C5 and C6 - 'wasp waist' sign.

Absent normal cervical lordosis.

Marked degenerative changes at adjacent levels particularly C4-5 and C6-7.

In these cases I've tried to focus on the relation between fusion of vertebral bodies let it be post discectomy or congenital and the advancement of degenerative changes at adjacent levels.

Development of adjacent segment degeneration (ASD) secondary to fusion :

1.     The mechanical and shearing motion exerted by the lever moment at adjacent levels.

2.     Increased intra discal pressures at adjacent levels which is proved in vitro during normal load testing.

Combination of these two mechanisms is postulated as being responsible for hypermobility and accelerating degenerative changes in the pathogenesis of adjacent segment degeneration (ASD)