SpineUniverse Case Study Library

TLIF with Unilateral Pedicle Screws and Aspen™ Spinous Process Fixation System

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A 59-year-old Caucasian female homemaker and avid golfer presents with low back pain and right buttock pain that radiates into the lateral aspect of her shin. Sitting worsens pain and lying down helps to relieve pain.

Past medical history is significant for a major car accident at age 16. She has had no prior spine surgery.


She is 5'2" tall and weighs 112 pounds. Neurologically, she has bilateral extensor hallucis longus weakness of 4+/5. The patient has not undergone bone density study.

Prior Treatment

Non-operative treatment includes selective nerve root blocks, epidural steroid injections and physical therapy.


Plain anteroposterior (Fig. 1A), lateral (Fig. 1B, 1C), flexion/extension x-rays (Figs. 2A, 2B), and sagittal and axial MRIs (Figs. 3A, 3B) reveal a 4 mm slip at L4-L5. In flexion, the slip accentuated to 8 mm. She did not reduce in extension. There is no pars defect.

ap x-ray, thoracolumbarFigure 1A

lateral x-ray, thoracolumbarFigure 1B

lateral x-ray, L3-S1, 4 mm slipFigure 1C

lumbar flexion x-rayFigure 2A

lumbar extension x-rayFigure 2B

thoracolumbar sagittal MRI, 4mm slip at L4-L5Figure 3A

lumbar axial MRIFigure 3B


Right L5 radiculopathy with Grade 1 spondylolisthesis

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Selected Treatment

The patient was pre-authorized for a minimally invasive L4-L5 transforaminal lumbar interbody fusion (TLIF) with unilateral pedicle screws and spinous process plating (Aspen™ Spinous Process Fixation System, LANX®, Broomfield, CO).

The procedure was started with two stab skin incisions about 3.5 cm from the spinous process over the right L4 and L5 pedicles using Jamshidi® needles followed by placement of K-wires. A 22 mm dilation tube system (METRx™ MicroDiscectomy System, Medtronic Sofamor Danek, Memphis, TN) was utilized through which a TLIF was performed. An 8 mm PEEK (polyether ether ketone) graft, packed with autologous bone was placed from lateral to medial. The two stab skin incisions were connected. Cannulated screws were placed and rod was secured under compression. The same skin incision was used to come to the midline. This incision was about 3.5 cm over from the spinous processes. A new fascial incision was made in the midline to expose the spinous process. Because the patient was thin in size, we were able to use the same incision to subperiosteally strip the paraspinal muscles and implant an 8 mm Aspen™ Spinous Process Fixation System packed with autologous bone.

Surgeon's Comment
Biomechanical data in cadaver studies suggest a spinous process plate gives excellent support in flexion and extension but is less robust for lateral bending and rotation. The addition of unilateral pedicle screws provides support in lateral bending and rotation. Placement of bilateral pedicle screws adds greater risk of nerve root injury without supplanting biomechanical stability as does the construct with unilateral pedicle screws and spinous process plate.

Intra-operative fluoroscopy (Figs. 4A, 4B) was used for placement of the pedicle screws, interbody graft, and spinous process fixation system.

intra-operative fluoroscopic view shows pedicle screw placementFigure 4A

intra-operative fluoroscopy (lateral), pedicle screw placement at L4 and L5Figure 4B

A post-operative plain x-ray was taken prior to hospital discharge at day 3. She was discharged without a brace. Medications at discharge included OxyContin (10mg every 12 hours as needed) and Percocet (5mg every 4 to 6 hours as needed).


3 month follow-up: The patient was exercising with pool activities; aquatic walking. She was driving, complained of no leg pain, and tolerated shopping up to 3 hours. A plain x-ray was obtained.

AP post-operative x-rays

AP lumbar x-ray, 3 months post-opFigure 5A. 3 months

lumbar AP x-ray, 5 months post-opFigure 5B. 5 months

lumbar AP x-ray, 9 months post-opFigure 5C. 9 months

Aspen Spine with FillerAspen™ Spinous Process Fixation System by LANX®

Lateral post-operative x-rays

lumbar lateral x-ray, 3 months post-opFigure 6A. 3 months

lumbar lateral x-ray, 5 months post-opFigure 6B. 5 months

lumbar lateral x-ray, 9 months post-opFigure 6C. 9 months

Long-term follow-up: She has progressed to vigorous physical therapy with a personal trainer. Vicodin is taken for occasional pain. Plain x-rays at 5 and 9 months show solid fusion and interbody bony bridging.

The descriptions of the results obtained from use of the Aspen Spinal Fixation System in this promotional piece are based on the physician's actual experience. The results achieved in any particular case using the Aspen device can vary and the results achieved in the case may not be typical. The use of the Aspen device entails certain risks, such as the possibility of implant bending or breakage, loosening, movement or migration of the device, or bone or spinous process fracture. In addition, the Aspen device should be used for only those indications described in the Package Insert for the Aspen device, entitled "Important Information on the Lanx Spinal Fixation System," a copy of which may be obtained by contacting Lanx Customer Service at 1.866.378.4195. Refer to the Package Insert for a more complete description of indications, contraindications, warnings and other information about the product.

*The physician author of this case has been compensated for his illustration by Lanx, Inc.

With innovative solutions uniquely designed by surgeons for surgeons, Lanx specializes in devices and systems for all segments of spinal surgery. Integrating leading technology and state-of-the-art engineering, our products have been created to meet the specific surgical needs of our customers and improve outcomes for their patients.

Lanx, Inc. 390 Interlocken Crescent, Suite 890, Broomfield, Colorado 80021
Ph 303.443.7500 Fax 303.443.7501 www.lanx.com

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Case Discussion

Dr. Shah presents a creative treatment for a common spinal condition treated with decompression and fusion. Degenerative spondylolisthesis with stenosis is one of only a few spinal disorders which have been studied by several randomized controlled trials. In two historic studies, the treatment of spondylolisthesis via decompression and fusion leads to favorable clinical outcomes (Weinstein et al. 2009. JBJS 91:1295-1304; Fischgrund et al. Spine. 1997. 22: 2807-12). Thus the question is how to best perform the decompression and fusion.

As in all surgical strategies, the goal is to achieve adequate decompression and fusion with the least of amount of unnecessary collateral damage. Using the minimally invasive transforaminal lumbar interbody fusion technique (MIS TLIF) achieves several important goals of surgery. First, a thorough bilateral decompression can be achieved through a unilateral approach. Second, a high rate of fusion is likely by utilizing the interbody space for arthrodesis. Third, the paramedian approach preserves the tendon attachment of the multifidus muscle to the L3 spinous process, which serves as a dynamic stabilizer of the adjacent segment. This, combined with decreased blood loss, less post-operative pain, and a lower infection rate, make the MIS TLIF approach a compelling treatment option for this patient.

The majority of clinical studies for MIS TLIF uses bilateral pedicle screw fixation and remains the gold standard. Although a few studies show clinical success using unilateral pedicle screw constructs, biomechanical studies clearly show that unilateral pedicle screw fixation confers much less stability to the fusion construct. Thus, supplemental fixation of unilateral pedicle screws has gained some interest. The method of interspinous plate fixation with an MIS TLIF with unilateral pedicle screws offers a safe and simple option in cases where bilateral pedicle screw fixation is undesirable. For instance, many pedicles at L1, L2 and in some L3 levels can be exceedingly narrow, making percutaneous pedicle screw fixation challenging. Insertion of the interspinous process plate can be performed on the ipsilateral side to the pedicle screws, thus preserving the soft tissue integrity of the entire contralateral side. Furthermore, the tendon attachment of the multifidus muscle to the cephalad spinous process remains intact. While further clinical experience will be necessary to confirm the efficacy of this strategy, the theoretical basis of this strategy is sound. It is intriguing to consider the potential efficacy of using the interspinous plate without any pedicle screws. If viable, this would decrease cost of surgery, avoid potential complications related to percutaneous pedicle screw insertion, and may decrease the incidence of symptomatic hardware. I look forward to future studies that better examines the efficacy of this interesting treatment strategy.

Author's Response

We thank Dr. Kim for his thoughtful comments. He brings up several interesting considerations that may be of value when using the minimally invasive approach along with this construct.

The issue of preservation of adjacent segment muscle complex and perhaps decreasing the incidence of adjacent segment stenosis might be advantages that need to be clearly evaluated in a randomized study. We would like to point out that this construct using the spinous process plating system should be avoided when a pars defect is present. This must be carefully evaluated pre-operatively when a spondylolisthesis is substantial.


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