Lumbar disc herniation. Clinical outcome and segmental stability using a new radiological classification and radiostereometry

Sammanfattning: Satisfactory results following conventional lumbar discectomy have been reported in 70-90% of cases. Remaining or recurrent low back pain or sciatica is, however, seen in many patients for reasons not yet fully understood. A relationship has previously been shown between the morphologic characteristics, i.e. shape and direction, of the disc herniation on preoperative films and the clinical results after surgery. Disturbed motion pattern or instability of the operated motion segment has also been presented as possible cause to poor postoperative results. Aims: To analyze 1) the relation between morphological characteristics of LDH on preoperative films analyzed with a new classification and the postoperative results and 2) the effect of the surgical procedure on inducible displacement of motion segments subjected to surgery for LDH, and 3) the relation between this inducible displacement and the portoperative results. Patients and methods: A new morphological classification of lumbar disc herniations was developed based on computed tomography (CT) and magnetic resonance tomography (MRI) images and subsequently applied on a retrospective study population comprising 142 patients. Following a reliability analysis of the classification, the preoperative images of 150 patients in a prospective study were graded according to the proposed classification and compared to 2 years outcome after surgery. Radiostereometric analysis (RSA) was used in 21 patients to prospectively analyze postoperative inducible segmental motion (inducible displacement) of the operated segment between supine and standing position over a 5 year period and results of RSA before discharge were compared to the clinical results 5 years after surgery. Results and conclusions: A high intra- and interrater reliability was found for the proposed classification. Larger sagittal and longitudinal distribution of the disc herniations were found on grading of CT images compared to MRI images. Morphologic characteristics of the herniation such as position in the spinal canal, direction and size were of no importance for the postoperative clinical results. The RSA analysis revealed a stiffening of the lumbo-sacral segments but no increase of inducible displacement 5 years after surgery. The pattern of inducible displacement in the sagittal plane at the two operated levels, which might be explained by grades of degeneration, was associated with a poor clinical outcome.