Lumbar Fusion for Adjacent Segment Disease: The Role of Minimally Invasive Approach
Adjacent segment disease (ASD) refers to a clinical spectrum of symptomatic degenerative changes in the segments adjacent to a successfully fused spinal segment(s). Adjacent segment pathology (ASP) is a broader spectrum of constellations, symptomatic and asymptomatic, including adjacent segment degeneration, instability, facet hypertrophy, and stenosis.1 ASP has also been simplistically classified as radiographic ASP (RASP) and clinical ASP (CASP).
ASD is multifactorial and whether it is the product of natural progression of disk degeneration versus iatrogenic surgery related versus patient specific is highly debatable.2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24 Although ASD seems to often develop in the first immediate segment,25 an equal incidence of ASD in the first and the second segment has been reported as well.26 Many studies report a wide range of incidence of ASD varying from 5.2% to 100%.27,28 Survival analysis by Sears et al.29 reported a prevalence of 22.2% of further surgery in the adjacent segment after 10 years. Similarly, Ha et al. reported a 72% survival without ASD after 1 year of fusion surgery, 63% after 2 years, and 52% after 4 years.30 Moreover, Ahn et al.31 reported that the supraadjacent disk was more prone (79.5% of cases) to ASD when compared to the infraadjacent disk (18.8%), and both disks simultaneously (1.8%).
The surgical treatment for ASD via traditional open surgery often follows the same previous approach that can be complicated by the following elements:
Prior scarring incisions and scarring increasing the risk of surgical infection
Prior pseudomeningocele and/or dural scarring
Difficulty of achieving a solid fusion for cases of pseudoarthrosis
This chapter demonstrates the minimally invasive options in dealing with ASD that very often take different route and approach anatomically and conceptually.
Lumbar fusion for ASD is indicated in patients who have failed lengthy conservative treatments. Patients with intractable back pain, radicular or neurogenic claudicatory symptoms, and patients with global coronal or sagittal imbalance are reasonable surgical candidates. The advantages of approaching the ASD using a minimally invasive retroperitoneal psoas sparing technique rather than utilizing the open traditional posterior exposure are numerous:
Open surgeries for ASD, similar to any revision spine surgery, carry a higher risk for complications including infection, wound complications, pseudoarthrosis, increased bleeding, nerve injuries, and dural tears.32, 33, 34 The proposed minimally invasive anterior lumbar surgery, on the other hand, targets the affected disk levels retroperitoneally, obviating the need for repeat posterior dissection through preexisting scar tissue and laminectomy defects.
Minimally invasive spine surgery (MISS) (anterior and/or combined anterior-posterior approaches), depending on the pathology at hand and patient factors, allows the operating surgeon to deal with the ASD using either a targeted anterior only (anterior lumbar interbody diskectomy, fusion, and anterior instrumentation) approach, or a combined anterior-posterior technique.
If the posterior approach is deemed necessary, a minimally invasive surgery (MIS) technique can still be adopted using a Wiltse paramedian exposure centered directly over the hardware, allowing for hardware removal and percutaneous pedicle screw reinstrumentation.
Patient positioning, exposure, anterior/posterior instrumentation techniques, and outcomes have been elucidated and described in separate chapters written by the same authors; see chapters 27, 28, and 30. We hereby describe different scenarios demonstrating the flexibility awarded by MISS compared to open surgical techniques.