W.B. Rodgers, MD
Spine Midwest
200 St. Mary’s Medical Plaza, Ste. 301
Jefferson City, MO, USA 65101
brodgers@spinemidwest.com

Introduction

Adjacent segment disease after lumbar fusion has been well characterized in the literature. The incidence of this disease ranges in some studies from 25% to 40% with the radiographic incidence approaching 100% and the symptomatic incidence nearly 25%. Many theories have been proposed for this entity but most researchers believe that the increased biomechanical stress on the motion segment adjacent to the fused area leads to changes in the intradiscal pressure with resultant hypermobility of the adjacent segment. This hypermobility leads to facet joint degeneration and further radiographic and clinical deterioration (_{12345678910111213141516}). It has also been shown in the literature that re-operations for adjacent segment disease through either traditional posterior or anterior approaches are associated with some improvement in neurologic and functional status but are also associated with significant morbidity and are operatively technically demanding (₉₁₀). The risks associated with anterior approaches of the spine, particularly revision anterior approaches of the spine, include injury to the abdominal contents, iliac vasculature, or sympathetic plexus (₁₈). Posterior revision approaches also carry many similar risks but in addition devitalize the paraspinous musculature and carry risks of inadvertent durotomies and traction neurapraxia (₁₉₂₀).

Recently a novel minimally disruptive spine procedure called extreme lateral interbody fusion or XLIF^® (NuVasive^®, Inc., San Diego, CA) has been developed. XLIF is a 90° off midline or true lateral approach that allows for large graft placement, excellent disk height restoration, and indirect decompression at the stenotic motion segment (_{2122232425262728}). Since the introduction of the XLIF technique to North America in late 2003, early studies have shown its safety and efficacy (₂₆₂₇₂₈). The technique has been reported for use in a variety of degenerative conditions including degenerative scoliosis and revision of failed disk arthroplasties (₂₃₂₄).

In this brief report we outline our experience using the XLIF procedure in the treatment of adjacent segment disease.

Materials And Methods

The authors treated a prospective series of 100 patients with adjacent segment degeneration after prior lumbar fusion using the XLIF technique. Of these 100 patients (59 F, 41M; average age 62.2 years; average BMI 31.2), 79 had undergone prior instrumented posterior fusion procedures, 15 had undergone prior uninstrumented posterior fusion procedures, and 6 had undergone anterior lumbar interbody (ALIF) fusion procedures.

Figure 1

Figure 1: Adjacent segment degeneration above and below a prior L4-5 fusion.

In a previous publication (₂₈), we delineated the fundamental tenets of XLIF surgery, which include careful patient positioning, gentle retroperitoneal dissection, meticulous psoas traverse using neurological monitoring, adequate diskectomy and fusion site preparation, and proper interbody implant placement.

The XLIF procedure is performed through two 3-4 cm incisions. Safe passage to the retroperitoneal space is assured by gentle blunt dissection. As the psoas muscle is traversed, the lumbosacral plexus is protected by the use of automated electrophysiology via dynamic discrete evoked EMG thresholding (NeuroVision^®, NuVasive, Inc.). Exposure is achieved with an expandable three-bladed retractor (MaXcess^®, NuVasive, Inc.), which allows for direct illuminated visualization facilitating diskectomy and complete anterior column stabilization using a large load-bearing implant (CoRoent^® XL, NuVasive, Inc.) that rests on the dense ring apophysis bilaterally.

All cases were performed using a graft composite composed of local bone from the vertebral bodies, bone marrow aspirate and demineralized bone matrix with corticocancellous allograft chips (Optecure^® CCC, Exactech^®, Gainesville, FL). All but one case included supplemental fixation (NuVasive, Inc.): unilateral pedicle screw-rod constructs (⁴³), bilateral pedicle screw-rod constructs (₄), trans-facetal screws (₁), and supplemental lateral instrumentation (⁵¹). In our experience, unilateral pedicle screw-rod constructs appear to be as clinically stable as bilateral constructs; biomechanical data suggests that this fixation should be adequate (³⁰).

Results

Figure 2

Figure 2: Postoperative anterior-posterior radiograph showing anterior stabilization with XLIF interbody implants at L3-4 and L4-5 and AxiaLIF at L5-S1 (Trans1, Wilmington, NC).

Procedures were performed without incident in short OR times and with little intraoperative blood loss: average hemoglobin change from pre- to post-op was 1.34g); and recovery was quick: patients stayed in the hospital an average of 1.13 days. Disk heights were increased an average of 3.4mm, which was maintained out to last follow-up at 6 months. Slip in those with spondylolisthesis was reduced by an average 3.4mm, also maintained through the 6 month follow-up. Fusion was assessed by Lenke score (₁₈) with averages of 2.3 at 3 months and 2.0 at 6 months, indicating good progression of fusion at these time points. Clinical outcomes were also very good, with an average improvement in VAS pain scores of 5.8 from pre-op to 6 months.

Figure 3

Table 1: Perioperative results

Figure 4

Figure 3: CT assessment of fusion one year after XLIF. Note solid bridging of bone in the area of XLIF implant aperture.

No patient required blood transfusions and no patient developed a wound infection. There were 9 complications in the entire group:

Figure 5

Figure 4: Lateral X-ray at 2 weeks post-op identifying vertebral body fracture with implant subsidence.

Discussion

Adjacent segment disease has long been a concern of spinal surgeons treating patients with lumbar fusions. The incidence of this entity may be as high as 40% and is thought to be secondary to the transmission of stress across the immobilized segment (_{12345678910111213141516}).

Our experience using XLIF technology in adjacent segment disease has been most encouraging. By avoiding the complications associated with anterior or posterior procedures (₁₈₁₉₂₀), our patients have routinely been discharged in less than two days and none of them has required blood transfusions. The clinical and radiographic indicators have all improved commensurately and the overall outcome is most encouraging. Of particular note is the absence of infectious complications, which has been as high 14% in some reports (₄). Transfusion and length of stay data has not been reported in the previous literature but the minimally invasive results appear encouraging. No procedure is without complications as our results indicate, but the complications are manageable and less common than reported using traditional techniques (_4691516).

Figure 6

Figure 5: Postoperative lateral X-ray showing XLIF reconstruction above prior ALIF.