Overall complication rate was 39%, and 26% of the patients were reoperated for mechanical or neurological complications. Risk factors include number of instrumented vertebra, fusion to the sacrum, PSO, and preoperative pelvic tilt of 26° or more. There is a 44% risk of a new operation in the 6-year-period after the primary procedure.

Discectomy for lumbar discal herniation is the most commonly performed spinal surgery. The basic principle of the various techniques is to relieve the nerve root compression induced by the herniation. Initially, the approach was a unilateral posterior 5-cm incision: the multifidus was detached from the vertebra, giving access through an interlaminar space in case of posterolateral herniation; an alternative paraspinal approach was used for extraforaminal herniation. Over the past 30 years, many technical improvements have decreased operative trauma by reducing incision size, thereby reducing postoperative pain and hospital stay and time off work, while improving clinical outcome. Magnification and illumination systems by microscope and endoscope have been introduced to enable minimally invasive techniques. Several comparative studies have analyzed the clinical results of these various techniques. Although the methodology of most of these studies is debatable, all approaches seem to provide clinical outcomes of similar quality. At all events, minimally invasive techniques reduce hospital stay. While technical proficiency is essential, the final result depends on strict compliance with a prerequisite for surgical indication: close correlation between clinical symptoms and radiological findings. It is essential to discuss the risk/benefit ratio and explain the pros and cons of the recommended technique to the patient.

IV - Multicenter retrospective study.

Level IV.

The pelvis may be seen as a single vertebra, between the spine and the femurs. The anatomy of this pelvic vertebra has changed with the evolution of species, notably with the transition to bipedalism, with the consequent appearance of lumbar lordosis. The lumbosacral angle, almost non-existent in other mammals, is at its greatest in humans. Pelvic and spinal radiological parameters reflect the sagittal balance of the spine in bipedal humanity. Applications in the management of spinal imbalance are numerous. Arthrogenic or degenerative kyphosis is the stereotypic example of spinal aging. Postoperative flat back following spine surgery is hard to prevent. Scoliosis surgery in adults should now take greater account of the patient's individual sagittal balance, by analyzing the pelvic and spinal parameters. The extent of arthrodeses performed during adolescence to manage idiopathic scoliosis may also induce problems of balance in adulthood if these elements are not taken into account.