Introduction. The influence of lumbar and lumbosacral fusion on adjacent moving segments has been the subject of a number of studies, which have shown the origin and progress of degenerative changes and instability brought about by alterations of kinematics and elasticity of the fused segment. Back pains which emerge later in the postoperative period may be the consequence of degeneration and instability in the adjacent segment to the said fusion. The fusion shifts the centre of rotation to the level adjacent to the fusion, which increases the pressure and pull on both the disk and joints. It can be supposed that the pull and attendant pains are in direct proportion to the rigidity of the spondylodesis that is more pronounced after anterior intersomatic fusion and less so after posterior. The development of hyperlordosis or kyphosis in the lumbar region is also a risk factor for adjacent segment failure.

Material and methods. The authors performed a retrospective analysis on a group of 91 patients with spondylolisthesis who had undergone PLIF technique with transpedicular fixation surgery and PLF.

A total of 10 (11%) of 91 patients developed symptomatic next segment desease at a previously asymptomatic level. Date were obtained in patients with next – segment failure based on X-rays studies, neurological assessment and sequential follow-up examinations. The aforementioned patients had a mean age of 42.8 years and the mean follow up period was 8.7 years after surgery. 7 cases were isthmic, 2 degenerative and 1 dysplastic spondylolisthesis.

Fusion in every case entailed the use of autologinous bone grafts, and with the PLIF technique cages, in 3 cases, dowels, in 6 cases, and autofibula in 1 case were used. The mean follow-up period between original surgery and next-segment failure was 3.8 years.

Results. In ten cases from the group there was evidence of instability or degeneration, instability in 3 cases (all above fusion) and degeneration in 7 cases (4 above and 3 below fusion) respectively.

All patients with instability in cranial adjacent segment underwent successfully additional surgery by using 360° fusion with instrumentation (ALIF).

Discussion. In X-rays conducted prior to surgery, signs of hypermobility were present in the cranial adjacent segment in one case. This hypermobility affected the rigidity of the fusion in the caudal segment, which accelerated the progress of instability and caused further surgery to be necessary.

The cause of instability could also be overloading of the spine, damage to the stability of ligament and bone structures sustained during the operation, or a combination of the above.