Adjacent segment disease

Adjacent segment degeneration and adjacent segment disease are terms referring to degenerative disease known to occur after reconstructive spine surgery, most commonly at an immediately adjacent functional spinal unit. These can include disc degeneration, instability, spinal stenosis, facet degeneration, and deformity….

Previously reported biomechanical studies on the effects of various types of spinal fusion procedures upon the adjacent segment indicate a significant degree of increased stress at that segment.

ASD has been considered a potential long-term complication of spinal arthrodesis. However, the exact mechanisms and risk factors related to ASD are not completely understood.

The true incidence and clinical impact of degenerative changes at the adjacent segment is unclear because there is lack of a universally accepted classification system that rigorously addresses clinical and radiological issues 1).

Seven classification systems of spinal degeneration, including degeneration at the adjacent segment, were identified. None have been evaluated for reliability or validity specific to patients with degeneration at the adjacent segment. The ways in which terms related to adjacent segment “degeneration” or “disease” are defined in the peer-reviewed literature are highly variable.

No formal classification system for either cervical or thoracolumbar adjacent segment disorders currently exists 2).

Degenerative adjacent segment stenosis after lumbar fusion

Adjacent-segment stenosis and spondylosis can be treated with a number of different operative techniques. Lateral interbody fusion provides an attractive alternative with reduced blood loss and complications, as there is no need to re-explore a previous laminectomy site. A minimally invasive lateral approach provided high fusion rates when performed with osteobiological adjuvants 3).

Zhong et al. from the Department of Spinal Surgery, Nanfang Hospital, Southern Medical University, Guangzhou, China. and Department of Orthopaedic Surgery, University of California, San Francisco, CA, USA, retrospectively assessed adult patients who had undergone decompression and instrumented fusion for lumbar spondylolisthesis between January 2006 and December 2012. The incidence of ASD was analyzed. Potential risk factors included the patient-related factors, surgery-related factors, and radiographic variables such as sagittal alignment, preexisting disc degeneration and spinal stenosis at the adjacent segment.

A total of 154 patients (mean age, 58.4 years) were included. Mean duration of follow-up was 28.6 months. Eighteen patients (11.7%) underwent a reoperation for ASD; 15 patients had reoperation at cranial ASD and 3 at caudal ASD. The simultaneous decompression at adjacent segment (p=0.002) and preexisting spinal stenosis at cranial adjacent segment (p=0.01) were identified as risk factors for ASD. The occurrence of ASD was not affected by patient-related factors, the types, grades and levels of spondylolisthesis, surgical approach, fusion procedures, levels of fusion, number of levels fused, types of bone graft, use of bone morphogenetic proteins, sagittal alignment, preexisting adjacent disc degeneration and preexisting spinal stenosis at caudal adjacent segments.

The findings suggest the overall incidence of ASD is 11.7% in adult patients with lumbar spondylolisthesis after decompression and instrumented fusion at a mean follow-up of 28.6 months, the simultaneous decompression at the adjacent segment and preexisting spinal stenosis at cranial adjacent segment are risk factors for ASD 4).

A study presents 18 patients in whom new symptoms developed from the segment adjacent to a fusion after an average symptom-free interval of 8.5 years (1-38 years). The most common pathologic condition at the adjacent segment was hypertrophic degenerative arthritis of the facet joints. Spinal stenosis was found there in eight cases; severe disc degeneration in five; degenerative spondylolisthesis in two; and spondylolysis acquisita in one 5).

1) , 2)
Kraemer P, Fehlings MG, Hashimoto R, Lee MJ, Anderson PA, Chapman JR, Raich A, Norvell DC. A systematic review of definitions and classification systems of adjacent segment pathology. Spine (Phila Pa 1976). 2012 Oct 15;37(22 Suppl):S31-9. doi: 10.1097/BRS.0b013e31826d7dd6. PubMed PMID: 22885835.
Wang MY, Vasudevan R, Mindea SA. Minimally invasive lateral interbody fusion for the treatment of rostral adjacent-segment lumbar degenerative stenosis without supplemental pedicle screw fixation. J Neurosurg Spine. 2014 Dec;21(6):861-6. doi: 10.3171/2014.8.SPINE13841. Epub 2014 Oct 10. PubMed PMID: 25303619.
Zhong ZM, Deviren V, Tay B, Burch S, Berven SH. Adjacent segment disease after instrumented fusion for adult lumbar spondylolisthesis: Incidence and risk factors. Clin Neurol Neurosurg. 2017 May;156:29-34. doi: 10.1016/j.clineuro.2017.02.020. Epub 2017 Feb 27. PubMed PMID: 28288396.
Lee CK. Accelerated degeneration of the segment adjacent to a lumbar fusion. Spine (Phila Pa 1976). 1988 Mar;13(3):375-7. PubMed PMID: 3388124.
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