Strain on intervertebral discs after anterior cervical decompression and fusion.
METHODS
An analysis of the change in strain distribution of intervertebral discs present after anterior cervical decompression and fusion by an original method. The analytical results were compared to occurrence of herniation of the intervertebral disc on magnetic resonance imaging.


OBJECTIVE
To elucidate the influence of anterior cervical decompression and fusion on the unfused segments of the spine.


BACKGROUND
There is no consensus regarding the exact significance of the biomechanical change in the unfused segment present after surgery.


METHODS
Ninety-six patients subjected to anterior cervical decompression and fusion for herniation of intervertebral discs were examined. Shear strain and longitudinal strain of intervertebral discs were analyzed on pre- and postoperative lateral dynamic routine radiography of the cervical spine. Thirty of the 96 patients were examined by magnetic resonance imaging before and after surgery, and the relation between alteration in strains and postsurgical occurrence of disc herniation was examined.


RESULTS
In the cases of double- or triple-level fusion, shear strain of adjacent segments had increased 20% on average 1 year after surgery. Thirteen intervertebral discs that had an abnormally high degree of strain showed an increase in longitudinal strain after surgery. Eleven (85%) of the 13 discs that showed an abnormal increase in longitudinal strain had herniation in the same intervertebral discs with compression of the spinal cord during the follow-up period. Relief of symptoms was significantly poor in the patients with recent herniation.


CONCLUSIONS
Close attention should be paid to long-term biomechanical changes in the unfused segment.
Matsunaga
S
S
Department of Orthopaedic Surgery, Faculty of Medicine, Kagoshima, Japan. shunji@med1.kufm.kagoshima-u.ac.jp
Kabayama
S
S
Yamamoto
T
T
Yone
K
K
Sakou
T
T
Nakanishi
K
K
D000328:Adult; D000368:Aged; D001696:Biomechanical Phenomena; D002574:Cervical Vertebrae / Q000503:physiopathology / Q000601:surgery*; D019299:Decompression, Surgical / Q000009:adverse effects*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007403:Intervertebral Disc / Q000000981:diagnostic imaging / Q000293:injuries* / Q000473:pathology; D007405:Intervertebral Disc Displacement / Q000150:complications / Q000175:diagnosis / Q000601:surgery; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular; D012008:Recurrence; D013117:Spinal Cord Compression / Q000175:diagnosis / Q000209:etiology / Q000601:surgery; D013123:Spinal Fusion / Q000009:adverse effects*; D013180:Sprains and Strains / Q000175:diagnosis / Q000209:etiology* / Q000503:physiopathology; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome