We made a prospective study of 43 consecutive patients treated for intraforaminal (34) or extraforaminal (9) herniations of a lumbar disc by excision through an interlaminar approach, using an operating microscope. The intraforaminal herniations were contained or extruded in 52% and sequestrated in 47%; for extraforaminal herniation the proportions were 66% and 33%, respectively. There was additional posterolateral protrusion or spinal stenosis at the level of the lateral herniation in seven and four cases, respectively. The patients were reviewed at three months and two years after surgery. Radiographs showed three grades of facetectomy: grade I, removal of 50% or less, grade II, excision of 51% to 75%, and grade III, subtotal or total facetectomy.

For intraforaminal herniations the results were excellent or good in 88% of patients when reviewed at three months and in 91% at two years. For extraforaminal herniations, there was an excellent or good outcome in 89% of patients in the short term and in all in the long term. The facetectomy had been grade I in 14 and grade II in 25; it had been grade III in four, but only one had had total facetectomy. No patient had developed vertebral hypermobility as a result of the operation.

An intralaminar approach using an operating microscope can provide adequate access to a lateral protrusion. It has the advantage of allowing the treatment of posterolateral protrusion or posterior annular bulge and of spinal stenosis at the same level.