Changes in disc height and posteroanterior displacement after fusion in patients with idiopathic scoliosis: a 9-year follow-up study.
BACKGROUND
In scoliosis patients treated with long segment spinal fusion, degenerative changes like retrolisthesis and disc space narrowing below fusion have been observed. However, there is disagreement concerning their incidence and dependency on the location of the lowest instrumented vertebra.


METHODS
To evaluate temporal changes in disc height and posteroanterior displacement (indicating listhesis) below fusion, 40 patients with adolescent idiopathic scoliosis, mainly treated with Cotrel-Dubousset instrumentation, were retrospectively investigated in this longitudinal study with a follow-up of on average 9.2 years (median 9.4 y) after surgery. Disc height and displacement were measured from lateral radiographs by means of distortion-compensated roentgen analysis (DCRA). Additionally, a mathematical model was developed to determine the influence of vertebral tilt in scoliosis on disc height and displacement.


RESULTS
Overall, no significant decrease in disc height was observed during follow-up. Concerning listhesis a small but significant retrolisthesis was found in segments L2/L3 and L3/L4. Compared with normative data, there was no significant listhesis for the L5/S1 segment. Nevertheless, separating the study group into subsamples of identical distal fusion level revealed a significant correlation between the amount of posteroanterior displacement at L5/S1 and the location of the lowest instrumented vertebra. With a reduction of free motion segments, listhesis increased into posterior direction. Taking the tilt correction into account led to considerably increased values of disc height whereas displacement was affected only to a minor degree.


CONCLUSIONS
Long segment spinal fusion in young patients with idiopathic scoliosis did not lead to disc space narrowing during 9.2 years follow-up. However, the observed increase in retrolisthesis potentially indicates the initiation of a degenerative process. These only minimal changes might be referred to the preservation of a physiologic lumbar lordosis. Without correction for vertebral tilt disc space narrowing is overestimated.
Lerner
Thomas
T
Klinik und Poliklinik für Allgemeine Orthopädie, Universitätsklinikum Münster, Albert-Schweitzer-Str 33, D-48149 Münster. lernert@mednet.uni-muenster.de
Frobin
Wolfgang
W
Bullmann
Viola
V
Schulte
Tobias
T
Brinckmann
Paul
P
Liljenqvist
Ulf
U
D000293:Adolescent; D000328:Adult; D002648:Child; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D016268:Internal Fixators / Q000009:adverse effects* / Q000592:standards; D007403:Intervertebral Disc / Q000000981:diagnostic imaging* / Q000473:pathology / Q000503:physiopathology; D007405:Intervertebral Disc Displacement / Q000000981:diagnostic imaging* / Q000209:etiology / Q000503:physiopathology; D008137:Longitudinal Studies; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging* / Q000473:pathology / Q000503:physiopathology; D008297:Male; D008962:Models, Theoretical; D011183:Postoperative Complications / Q000000981:diagnostic imaging* / Q000473:pathology / Q000503:physiopathology; D011859:Radiography; D012189:Retrospective Studies; D012600:Scoliosis / Q000601:surgery*; D013123:Spinal Fusion / Q000009:adverse effects* / Q000295:instrumentation / Q000379:methods; D013168:Spondylolisthesis / Q000000981:diagnostic imaging / Q000209:etiology / Q000503:physiopathology; D013995:Time