The Lumbar Adjacent Segment Stenosis (LASS) Trial

Globally, musculoskeletal disorders are the leading causes of years lived with disability, with spinal disorders contributing to 70% of this burden. The consequences for patients, their families and society are significant.

Lumbar spinal stenosis is a common condition with an increasing prevalence, largely due to an aging population. It is caused by degenerative changes in the supporting structures of the lumbar spine leading to symptoms like low-back pain and radiating pain to the lower extremities as well as numbness and weakness causing walking restrictions. Annually, about 200,000 to 250,000 new cases are diagnosed in the United States alone and this condition is the most frequent indication for spinal surgery in patients older than 65 years of age. Approximately 10% of the population over 50 years suffer from symptomatic lumbar spinal stenosis.

Lumbar surgery may be indicated in patients with various degenerative spinal conditions when non-surgical treatment has failed, and radiological findings are consistent with clinical symptoms. Decompression (removal of stenotic structures to relieve nerve pressure) and spinal fusion (the use of screws, rods, plates, or other devices to assist in achieving fusion between vertebral bodies) remain the cornerstone of operative treatment. The volume of lumbar spine surgery has increased considerably over the past decades, particularly for more complex procedures such as instrumented fusion, and especially among the elderly. In the United States, the hospital costs of lumbar instrumented fusion procedures is reported to be higher than for any other surgical procedure such as percutaneous coronary angioplasty and knee- and hip arthroplasty. In Norway, approximately 700 lumbar spinal fusions are performed every year, with about half of them being reoperations.

Lumbar spinal fusion has the highest complication rates among all spinal surgeries. Complications involving either the segment above or below (=adjacent to) a previously fused segment can arise years after the initial fusion. An annual incidence of 2,5-4% for new subsequent surgery after initial lumbar fusion is reported, 13.6% and 22.2% were re-operated within 5 and 10 years respectively. The majority of reoperations following an initial fusion are due to spinal stenosis adjacent to a previously fused segment (Lumbar Adjacent Segment Stenosis - LASS), and these patients constitute a substantial subgroup within the extensive and growing patient population with spinal stenosis.

At present, there are no guidelines or prospective studies that can advise clinicians on how patients with LASS should be treated, and this issue is emerging as one of the most relevant and debated questions within degenerative spine surgery. According to register data, the most common treatments are either extending the fusion beyond the symptomatic adjacent stenotic segment or just decompression of the stenotic structures, with a tendency of performing just decompression in patients with cranial LASS and decompression with extended fusion in patients with caudal LASS. However, there is large variation in surgical practices both between and even within hospitals. Considering the increasing prevalence of LASS, costs, and risks associated with spinal fusions, there is need for randomized trials to evaluate surgical practice and the relative efficacy of the two most common surgical treatments.