Single-Level Instrumented Lumbar Interbody Fusion: The Impact of ASCs on Evidence-Based Medicine

Peer Reviewed


Evidence-based medicine is the emerging trend in health care reform focused on making health care safer, less complicated, and more cost-effective. This process requires physicians to capture, trend, and report on costs, treatment outcomes, and patient satisfaction to the Centers for Medicare and Medicaid Services (CMS), payers, and patients. This study was conducted to develop a database for comparison to other sources, including a Medicare database, hospital inpatient and/or outpatient data, and published literature.


An IRB-approved, retrospective chart review was conducted on consecutive patients treated at a single Ambulatory Surgical Center (ASC) for single-level lumbar degenerative disc disease with an interbody fusion and posterior pedicle screw fixation.

Data collected included demographics (age, gender, body mass index [BMI]), health status (tobacco/alcohol use, co-morbidities, medications), pathology (primary diagnosis, spine level, treatment construct), intra-operative data (operative [OR]) time, anesthesia time, fluoroscopy time, complications), and post-operative information (length of stay, re-admission, changes in pain level/medications).

Surgical Technique

  • Anesthesia: All patients were treated under general anesthesia. Patients were premedicated with Valium prior to surgery, and a long-acting anesthetic agent was infiltrated in the soft tissue at the end of surgery.
  • Positioning: Patients were positioned prone on a Wilson frame.
  • Neuromonitoring: Neuromonitoring was performed throughout the entire procedure.
  • Incision: A midline incision was made over the interspinous space of the operated level extending from the center of the superior spinous process to the center of the inferior spinous process.
  • Decompression/discectomy: Once the posterior elements of the adjacent levels were exposed, a specialized retractori was placed to allow visualization of the operative site. Bilateral medial facetectomies were performed, and the interspinous ligament removed. A lamina spreader was placed to afford slight distraction, and the epidural space was entered at the level of the medial facetectomy on one side. A nerve root retractor was placed medially to protect the traversing nerve root, and the disc space entered after an annulectomy was performed. The disc space was emptied, and a PEEK implantii packed with bone graft was placed. This procedure was repeated on the contralateral side. On this side, the disc space was evacuated, bone graft was placed in the middle of the disc space, and another PEEK implant was placed to complete the interbody fusion.
  • Screw insertion: The pars interarticularis of the superior body was identified, and a pedicle screwiii was placed in a superior and lateral direction into the pedicle (Figures 1 and 2). The inferior screw was placed in a posterior-to-anterior direction with a slightly divergent angle into the inferior pedicle (Figures 1 and 2). A short lordotic 4.75mm cobalt chrome rod was used to connect the ipsilateral pedicle screws. These steps were then repeated on the contralateral side (Figures 3 and 4).
  • Closure: Operative site closure was performed with a buried, subcuticular absorbable suture and without a drain. A multi-layered sterile dressing was used which allowed the patient to shower after 48 hours.

Figure 1: AP screw starting points and trajectories.Figure 1: AP screw starting points and trajectories. Image Courtesy of Dwight S. Tyndall, MD, FAAOS. ©

Figure 2: Lateral screw trajectory.Figure 2: Lateral screw trajectory. Image Courtesy of Dwight S. Tyndall, MD, FAAOS. ©

Figure 3: A/P image of final construct.Figure 3: A/P image of final construct. Image Courtesy of Dwight S. Tyndall, MD, FAAOS. ©

Figure 4: Lateral image of final construct.Figure 4: Lateral image of final construct. Image Courtesy of Dwight S. Tyndall, MD, FAAOS. ©


There were seven patients treated at our ASC with a single-level posterior lumbar interbody fusion (PLIF) between November, 2014 and August, 2015. This group consisted of three females and four males; average age was 42 years old (range 31-52), and average BMI was 29.5 (range 23.2 – 36.6). Three patients were smokers, and three patients reported occasional alcohol use. Three patients had private insurance and four patients had Workers’ Compensation. No other significant co-morbidities were present in this group of patients. The primary diagnosis was degenerative disc disease for five patients and spondylolisthesis for two patients. The spine levels treated were L4-L5 (n=3) and L5-S1 (n=4). The implant construct for all patients included PEEK interbody spacers and corticocancellous pedicular fixation system implantsiv.

The intra-operative and outcome metrics measured were: operative time (OR), anesthesia time (Anes), fluoroscopy time (Fluoro), estimated blood loss (EBL), and pain scores (Table 1).
Table 1. Intra-operative and Outcome MetricsIntra-operative and Outcome MetricsThere was one intra-operative complication in which the patient suffered a small dural tear prior to implantation of the interbody device and pedicle screws. The durotomy was too small to require sutures, but as a precaution, the patient stayed at the ASC overnight. All other patients were ambulatory and discharged on the same day they were admitted. There were no other post-operative complications. All patients received Physical and Occupational Therapy instructions prior to discharge and the smokers received cessation advice and handouts.


Instrumented lumbar fusion is a common treatment for lower-lumbar disease that has failed conservative treatment.1 That being said, the conventional surgical application of this treatment is not without drawbacks. Perhaps the greatest drawback is the amount of surgical exposure and tissue disruption necessary to obtain the traditional trajectory and placement of the screws. As a result, there is significant bleeding and soft tissue ablation during the exposure.2,3

The required dissection also has the potential to lead to long surgical times, significant post-surgery pain, and the need for an inpatient hospital stay.4 In the current atmosphere of cost containment, value-based medicine, and the need for patient-centric treatment, these metrics make this surgical approach less desirable.

A new and novel surgical technique for lumbar fusionv may offer benefits over conventional instrumented spinal fusion. This new procedure utilizes a small, midline incision and a divergent screw trajectory that enters the vertebra at a point medial and inferior to the facet. As a result, the required incision is approximately 4cm (Figure 5), and the lateral dissection requirement is limited to the facet joint and the lateral pars, therefore, sparing the neurovascular bundle. The midline exposure also provides exceptional decompressive access. These attributes have the potential to lead to a minimally ablative surgical technique, a short operative time, minimal blood loss, minimal post-surgical pain, and quick recovery.

An additional advantage of a shorter operative time is the potential for direct benefit in the outpatient environment, such as less use of materials (anesthesia supplies, etc.), less staff utilization (faster post-surgery recovery and less need for overnight stay), and better use of OR time resources. It also has the potential to afford the ability to do more cases in the same amount of time.

Despite these significant operational advantages, the most important advantage of this procedure over traditional lumbar instrumented fusion is its impact on the patient’s experience. This small study showed that patients had minimal complications and postsurgical pain and morbidity. This led to minimal post-surgery pain medication usage and allowed them to be mobilized and begin post-surgery rehab more quickly.

Figure 5 Post op WoundFigure 5 Post op Wound. Image Courtesy of Dwight S. Tyndall, MD, FAAOS. ©


While greater study is required, this study cohort demonstrated that with appropriate technique, single-level lumbar fusion in selected patients is a safe and effective surgical procedure for the ambulatory surgery environment.

Surgical techniques such as this one offer potentially significant advantages, including reduced anesthesia/surgery time, reduced blood loss, faster recovery time, and equivalent clinical outcomes to other fusion techniques. Additionally, this technique is ideally suited for the ASC/current healthcare environment with its emphasis on value and cost containment.

Disclosure: Dwight S. Tyndall, MD is a paid consultant and shareholder in Spineology, Inc.

Peer Discussion

Joshua Ammerman, MD
Washington Neurosurgical Associates
Washington, DC

In this small, retrospective chart review, the authors have attempted to examine a surgical technique aligned with the growing role of ambulatory surgery centers (ASCs) in the care of degenerative spine disease. While the broad economic benefits of surgical care based in ASCs are well understood, technique limitations continue to constrain the types of patients and types of procedures that can be successfully transitioned from the hospital setting to an ASC.

The “minimally invasive" surgical movement in spine disease now presents an opportunity to migrate these patients into the outpatient setting. With that in mind, the authors have reviewed their technique and experience with a midline, "less invasive" instrumented laminectomy and interbody fusion procedure utilizing a divergently placed pedicle screw. This divergent screw, a close relative to the well-described cortical pedicle screw, minimizes lateral dissection of the posterior spinal elements, which in turn reduces blood loss and tissue retraction, thereby reducing post-operative pain and sedentary behavior, permitting an outpatient surgical algorithm.

In addition, many surgeons feel that the medial to lateral, inferior to superior trajectory of this group of screw approaches directs the implants away from the neural structures and therefore, reduces the risk of neural injury. Overall, the authors should be commended for their early work in this growing and important clinical area.

Author’s Response

Dwight Tyndall, MD
Orthopaedic Spine Surgeon
Orthopaedic Specialists of Northwest Indiana
Munster, IN

To Dr. Ammerman’s point, this is a small sample of patients and it may be difficult to extrapolate the patients’ results and experiences to a wider population. That said, it is hopeful this paper triggers discussion and an examination of what can be done to deploy this new and novel technique with its potential benefits (eg, cost savings, decreased postoperative pain, ASC-friendly) to a broader patient population.

Updated on: 11/06/19
Continue Reading
Minimally Invasive Transforaminal Lumbar Interbody Fusion (TLIF): Technical Feasibility and Initial Results
Joshua M. Ammerman, MD
Washington Neurosurgical Associates
Washington, DC

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